Relaxation-based magnetic resonance thermometry using a low-field single-sided MRI scanner

Abstract

A magnetic imaging device is disclosed that includes a housing having a face, the housing having a first axis extending through the face into a field of view, and an array of permanent magnets located within the housing, the array of permanent magnets having a unique gradient magnetic field extending from the array of permanent magnets into the field of view relative to the first axis. The magnetic imaging device further includes a gradient coil set, at least one radio frequency coil, a power circuit, a memory that stores a relaxation model for a tissue type, and a control circuit. The control circuit is configured to acquire a T2 data set associated with a structure disposed within the field of view, generate a T2 weighted image of the structure, and convert the T2 weighted image of the structure into a heat map based on the relaxation model for the tissue type.

Description

[Technical field]

[0001] [Background technology]

[0002] Measuring temperature in vivo can guide thermal ablation of soft tissue, however, in certain instances it is difficult to measure temperature in vivo using existing systems. Summary of the Invention

[0003] In one general aspect, the present disclosure provides a magnetic imaging device comprising a housing with a face, a first axis extending through the face into a field of view. The magnetic imaging device further comprises an array of permanent magnets located within the housing, a unique gradient magnetic field extending from the array of permanent magnets into the field of view relative to the first axis. The magnetic imaging device further comprises a gradient coil set, at least one radio frequency coil, a power circuit, a memory storing a relaxation model for a tissue type, and a control circuit in signal communication with the gradient coil set, the at least one radio frequency coil, the power circuit, and the memory. The control circuit is configured to acquire a T2 data set associated with a structure disposed within the field of view and corresponding to the tissue type. The control circuit is further configured to generate a T2-weighted image of the structure and convert the T2-weighted image of the structure into a heat map based on the relaxation model for the tissue type. In another aspect, the present disclosure provides a single-sided magnetic imaging device comprising a housing comprising an array of permanent magnets, wherein a unique gradient magnetic field extends from the array of permanent magnets relative to a first axis into a field of view, the field of view being adjacent to the housing. The single-sided magnetic imaging device further comprises a radio frequency coil, a power circuit coupled to the radio frequency coil, a memory storing relaxation models for tissue at different temperatures, and a control circuit. The control circuit is in signal communication with the radio frequency coil, the power circuit, and the memory. The control circuit is configured to transmit a waveform sequence to the radio frequency coil to generate an echo train sequence, acquire a T2 data set associated with a structure disposed within the field of view, generate a T2 weighted image of the structure, and convert the T2 weighted image of the structure into a heat map based on the relaxation model stored in the memory.

[0004] In another aspect, the present disclosure provides a method for detecting a temperature in an object of interest comprised of a first tissue type using a magnetic resonance imaging device. The method includes acquiring calibration data including T2 data for different temperatures for different tissue types including the first tissue type, generating a model for the different tissue types from the calibration data, placing the object of interest in a field of view, and transmitting a pulse sequence including swept frequency pulses. The method further includes receiving T2 data corresponding to the object of interest, generating a T2 weighted image of the object of interest, and converting the T2 weighted image of the object of interest into a heat map based on the model for the first tissue type. [Brief description of the drawings]

[0005] The novel features of the various aspects are set forth with particularity in the appended claims, but the described aspects, both as to organization and method of operation, can best be understood by reference to the following description taken in conjunction with the accompanying drawings, in which:

[0006] [Figure 1] FIG. 1 is a perspective view of a magnetic resonance imaging (MRI) scanner according to various aspects of the present disclosure.

[0007] [Diagram 2] FIG. 2 is an exploded perspective view of the MRI scanner of FIG. 1 exposing a permanent magnet assembly and gradient coil set within a housing according to various aspects of the present disclosure.

[0008] [Diagram 3] FIG. 2 is an elevational view of the MRI scanner of FIG. 1 in accordance with various aspects of the present disclosure.

[0009] [Figure 4] FIG. 2 is an elevational view of the MRI scanner of FIG. 1 in accordance with various aspects of the present disclosure.

[0010] [Diagram 5] FIG. 2 is a perspective view of a permanent magnet assembly of the MRI scanner of FIG. 1 according to various aspects of the present disclosure.

[0011] [Figure 6] FIG. 2 is an elevational view of a gradient coil set and permanent magnet assembly of the MRI system shown in FIG. 1 in accordance with various aspects of the present disclosure.

[0012] [Figure 7] FIG. 1 is a control block diagram of a single-sided MRI system according to various aspects of the present disclosure.

[0013] [Figure 8] FIG. 13 is a schematic diagram of a magnetic gradient along the Z axis, according to various aspects of the present disclosure.

[0014] [Figure 9] FIG. 13 is a diagram of a pulse sequence that compensates for variations in field of view in a slice along the Z axis, according to various aspects of the present disclosure.

[0015] [Figure 10] 1 is a representative graph of a swept frequency pulse in accordance with various aspects of the present disclosure.

[0016] [Figure 11] FIG. 1 is a diagram of a pulse sequence for collecting T2 relaxation times of structures within a field of view, according to various embodiments of the present disclosure.

[0017] [Figure 12] FIG. 1 is a flow diagram for collecting calibration data and generating a T2 relaxation time versus temperature model, according to various embodiments of the present disclosure.

[0018] [Figure 13] 1 is a graphical representation of an exemplary relaxation model of T2 relaxation time versus temperature, according to various embodiments of the present disclosure.

[0019] [Figure 14] FIG. 13 is a flow diagram for collecting T2 relaxation data and generating a heat map, according to various aspects of the present disclosure.

[0020] [Figure 15] FIG. 11 is an exemplary heat map generated from T2 relaxation data using a relaxation model, according to various aspects of the present disclosure.

[0021] The accompanying drawings are not intended to be drawn to scale. Corresponding reference characters indicate corresponding parts throughout the several views. For clarity, not every component is labeled in every figure. The illustrations described herein illustrate certain embodiments of the invention in one form and such illustrations should not be construed as limiting the scope of the invention in any manner. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] The following international patent applications are hereby incorporated by reference in their entireties: International Patent Application No. PCT / US2020 / 018352, entitled "SYSTEMS AND METHODS FOR ULTRALOW FIELD RELAXATION DISPERSION", filed on February 14, 2020, corresponding to the current International Publication No. WO2020 / 168233. International Patent Application No. PCT / US2020 / 019530, entitled "SYSTEMS AND METHODS FOR PERFORMING MAGNETIC RESONANCE IMAGING," filed on February 24, 2020, corresponding to current International Publication No. WO2020 / 172673; International Patent Application No. PCT / US2020 / 019524, entitled "PSEUDO-BIRDCAGE COIL WITH VARIABLE TUNING AND APPLICATIONS THEREOF," filed on February 24, 2020, corresponding to the current International Publication No. WO2020 / 172672 International Patent Application No. PCT / US2020 / 024776, entitled "SINGLE-SIDED FAST MRI GRADIENT FIELD COILS AND APPLICATIONS THEREOF," filed on March 25, 2020, corresponding to the current International Publication No. WO2020 / 198395. International Patent Application No. PCT / US2020 / 024778, entitled "SYSTEMS AND METHODS FOR VOLUMETRIC ACQUISITION IN A SINGLE-SIDED MRI SYSTEM", filed on March 25, 2020, which corresponds to the current International Publication No. WO2020 / 198396. International Patent Application No. PCT / US2020 / 039667, entitled "SYSTEMS AND METHODS FOR IMAGE RECONSTRUCTIONS IN MAGNETIC RESONANCE IMAGING", filed on June 25, 2020, corresponding to current International Publication No. WO2020 / 264194. International Patent Application No. PCT / US2021 / 014628, entitled "MRI-GUIDED ROBOTIC SYSTEMS AND METHODS FOR BIOPSY," filed on January 22, 2021; and · International Patent Application No. PCT / US2021 / 018834, filed on February 19, 2021, entitled "RADIO FREQUENCY RECEPTION COIL NETWORKS FOR SINGLE-SIDED MAGNETIC RESONANCE IMAGING" International patent application PCT / US2021 / 021464, entitled "PHASE ENCODING WITH FREQUENCY SWEEP PULSES FOR MAGNETIC RESONANCE IMAGING IN INHOMOGENEOUS MAGNETIC FIELDS," filed on March 9, 2021; and International patent application PCT / US2021 / 021461, entitled "PULSE SEQUENCES AND FREQUENCY SWEEP PULSES FOR SINGLE-SIDED MAGNETIC RESONANCE IMAGING," filed on March 9, 2021

[0023] U.S. Patent Application Publication No. 2018 / 0356480, published December 13, 2018, and entitled "UNILATERAL MAGNETIC RESONANCE IMAGING SYSTEM WITH APERTURE FOR INTERVENTIONS AND METHODOLOGIES FOR OPERATING SAME," is also incorporated by reference in its entirety.

[0024] U.S. Provisional Patent Application No. 63 / 180,013, filed April 26, 2021, and entitled "LOCALIZATION GUIDE AND METHOD FOR MRI GUIDED PELVIC INTERVENTIONS," is also incorporated by reference in its entirety herein.

[0025] Before describing various aspects of the MRI system and method in detail, it should be noted that the exemplary embodiments are not limited in application or use to the details of construction and arrangement of parts illustrated in the accompanying drawings and description. The exemplary embodiments may be implemented or incorporated in other embodiments, variations, and modifications, and may be practiced or carried out in various ways. Moreover, unless otherwise indicated, the terms and expressions used herein have been selected for the purpose of describing the exemplary embodiments for the convenience of the reader, and not for the purpose of limiting the same. It will also be understood that one or more of the embodiments, embodiment expressions, and / or examples described below can be combined with any one or more of the other embodiments, embodiment expressions, and / or examples described below.

[0026] According to various aspects, an MRI system is provided that can include a unique imaging region that can be offset from the face of the magnet. Such offset and single-sided MRI systems are less restrictive than traditional MRI scanners. Furthermore, this form factor can have built-in or unique magnetic field gradients that create a range of magnetic field values ​​throughout the region of interest. In other words, the unique magnetic field can be inhomogeneous. The inhomogeneity of the magnetic field strength in the region of interest of a single-sided MRI system can be greater than 200 parts per million (ppm). For example, the inhomogeneity of the magnetic field strength in the region of interest of a single-sided MRI system can be between 200 ppm and 200,000 ppm. In various aspects of the present disclosure, the inhomogeneity in the region of interest can be greater than 1,000 ppm, and can be greater than 10,000 ppm. In one example, the inhomogeneity in the region of interest can be 81,000 ppm.

[0027] The unique magnetic field gradient can be generated by a permanent magnet in the MRI scanner. The magnetic field strength in the region of interest of the single-sided MRI system can be, for example, less than 1 Tesla (T). For example, the magnetic field strength in the region of interest of the single-sided MRI system can be less than 0.5 T. In other examples, the magnetic field strength can be greater than 1 T, for example, 1.5 T. The system can operate at a lower magnetic field strength compared to a typical MRI system, which relaxes the design constraints of the RX coil and / or allows additional mechanisms, such as robotics, to be used in the MRI scanner. Exemplary MRI-guided robotic systems are further described, for example, in International Application PCT / US2021 / 014628, filed January 22, 2021, entitled "MRI-GUIDED ROBOTIC SYSTEMS AND METHODS FOR BIOPSY."

[0028] 1-6 show an MRI scanner 100 and components of the MRI scanner 100. As shown in FIG. 1 and FIG. 2, the MRI scanner 100 includes a housing 120 including a concave face or front surface 125. In other embodiments, the face of the housing 120 can be flat and planar. The front surface 125 can face an object to be imaged by the MRI scanner. As shown in FIG. 1 and FIG. 2, the housing 120 includes a permanent magnet assembly 130, an RF transmit coil (TX) 140, a gradient coil set 150, an electromagnet 160, and an RF receive coil (RX) 170. In other examples, the housing 120 may not include the electromagnet 160. Furthermore, in certain examples, the RF receive coil 170 and the RF transmit coil 140 may be combined into a Tx / Rx coil array. In various examples, the MRI scanner 100 is a single-sided scanner, where various components, such as the permanent magnet assembly 130, the RF transmit coil (TX) 140, the gradient coil set 150, the electromagnet 160, and the RF receive coil (RX) 170, are located on the same side of the field of view.

[0029] Referring primarily to Figures 3-5, the permanent magnet assembly 130 includes an array of magnets. The array of magnets forming the permanent magnet assembly 130 is configured to cover the front 125 or patient-facing surface of the MRI scanner 100 (see Figure 3) and is shown as a horizontal bar in Figure 4. The permanent magnet assembly 130 includes a plurality of cylindrical permanent magnets arranged in parallel. Referring primarily to Figure 5, the permanent magnet assembly 130 includes a parallel plate 132 held together by a bracket 134. The system is mountable to the housing 120 of the MRI scanner 100 at a bracket 136. The parallel plate 132 may have a plurality of holes 138. For example, the permanent magnet assembly 130 may include any suitable magnetic material, including but not limited to rare earth-based magnetic materials, such as neodymium-based magnetic materials, by way of example.

[0030] The permanent magnet assembly 130 defines an access opening or bore 135 that allows access to the patient through the housing 120 from the opposite side of the housing 120. In other aspects of the disclosure, the array of permanent magnets forming the permanent magnet assembly within the housing 120 may be boreless and may define an uninterrupted or continuous arrangement of permanent magnets with no bore defined therethrough. In yet other examples, the array of permanent magnets within the housing 120 may form more than one bore / access opening therethrough.

[0031] According to various aspects of the disclosure, the permanent magnet assembly 130 provides a magnetic field B0 within the region of interest 190 along the Z-axis shown in FIG. 1. The Z-axis is orthogonal to the permanent magnet assembly 130. In other words, the Z-axis extends from the center of the permanent magnet assembly 130 and defines the direction of the magnetic field B0 away from the face of the permanent magnet assembly 130. The Z-axis can define the direction of the primary magnetic field B0. The primary magnetic field B0 can decrease with a unique gradient along the Z-axis, i.e., further away from the face of the permanent magnet assembly 130, in the direction shown by the arrow in FIG. 1.

[0032] In one embodiment, the non-uniformity of the magnetic field of the permanent magnet assembly 130 in the region of interest 190 may be approximately 81,000 ppm. In another embodiment, the non-uniformity of the magnetic field strength in the region of interest 190 relative to the permanent magnet assembly 130 may be between 200 ppm and 200,000 ppm, and in certain instances may be greater than 1,000 ppm, and in various instances may be greater than 10,000 ppm.

[0033] In one embodiment, the magnetic field strength of the permanent magnet assembly 130 may be less than 1 T. In another embodiment, the magnetic field strength of the permanent magnet assembly 130 may be less than 0.5 T. In other examples, the magnetic field strength of the permanent magnet assembly 130 may be greater than 1 T, such as 1.5 T. Referring primarily to FIG. 1, the Y-axis extends up and down from the Z-axis, and the X-axis extends left and right from the Z-axis. The X-axis, Y-axis, and Z-axis are all orthogonal to one another, and the positive direction of each axis is indicated by a corresponding arrow in FIG. 1.

[0034] The RF transmit coil 140 is configured to transmit an RF waveform and associated electromagnetic field. The RF pulses from the RF transmit coil 140 are configured to rotate the magnetization generated by the permanent magnet 130 by generating an effective magnetic field, referred to as B1, that is orthogonal to the direction of the permanent magnetic field (e.g., in the orthogonal plane).

[0035] Referring primarily to FIG. 3, the gradient coil set 150 includes two gradient coil sets 152, 154. The gradient coil sets 152, 154 are disposed on the face or front surface 125 of the permanent magnet assembly 130 between the permanent magnet assembly 130 and the region of interest 190. Each gradient coil set 152, 154 includes a coil portion on either side of the bore 135. With reference to the axes in FIG. 1, the gradient coil set 154 can be, for example, a gradient coil set corresponding to the X-axis, and the gradient coil set 152 can be, for example, a gradient coil set corresponding to the Y-axis. The gradient coils 152, 154 enable encoding along the X-axis and the Y-axis, as described in further detail herein.

[0036] Referring now to FIG. 7, a control schematic of a single-sided MRI system 300 is shown. The single-sided MRI scanner 100 and / or components of the single-sided MRI scanner 100 (FIGS. 1-6) may be incorporated into the MRI system 300 in various embodiments of the present disclosure. For example, the imaging system 300 includes a permanent magnet assembly 308, which may be similar to the permanent magnet assembly 130 (see FIGS. 2-5) in various examples. The imaging system 300 further includes an RF transmit coil 310, which may be similar to the RF transmit coil 140 (see FIG. 3), for example. The imaging system 300 further includes an RF receive coil 314, which may be similar to the RF receive coil 170 (see FIG. 3), for example. In various embodiments, the RF transmit coil 310 and / or the RF receive coil may also be located within the housing of the MRI scanner, and in certain examples, the RF transmit coil 310 and the RF receive coil 314 may be integrated into a combined Tx / Rx coil. The system 300 further includes a gradient coil 320 configured to generate a gradient field to facilitate imaging of objects within the field of view 312 .

[0037] The single-sided MRI system 300 further includes a computer 302 in signal communication with a spectrometer 304 and is configured to transmit and receive signals between the computer 302 and the spectrometer 304 .

[0038] The main magnetic field B0 generated by the permanent magnet 308 extends in a field of view 312, away from the permanent magnet 308 and away from the RF transmit coil 310. The field of view 312 contains a subject being imaged by the MRI system 300.

[0039] During the imaging process, the main magnetic field B0 extends within the field of view 312. The direction of the effective magnetic field (B1) changes in response to RF pulses and associated electromagnetic fields from the RF transmit coil 310. For example, the RF transmit coil 310 is configured to selectively transmit RF signals or pulses to objects, e.g., tissue, within the field of view. These RF pulses change the effective magnetic field experienced by spins within a sample (e.g., tissue of a patient). When the RF pulse is on, the only effective magnetic field experienced by the resonating spins is the RF pulse, which effectively cancels the static B0 magnetic field. The RF pulse can be, for example, a chirp or frequency sweep pulse, as described in more detail herein.

[0040] Additionally, when an object within the field of view 312 is excited by an RF pulse from the RF transmit coil 310, the precession of the object produces an induced or MR current that is detected by the RF receive coil 314. The RF receive coil 314 can transmit the excitation data to an RF preamplifier 316. The RF preamplifier 316 can boost or amplify the excitation data signals and transmit them to the spectrometer 304. The spectrometer 304 can transmit the excitation data to the computer 302 for storage, analysis, and image construction. The computer 302 can, for example, combine multiple stored excitation data signals to generate an image.

[0041] From the spectrometer 304, the signal can be further relayed via an RF power amplifier 306 to an RF transmit coil 310 and via a gradient power amplifier 318 to a gradient coil 320. The RF power amplifier 306 amplifies the signal and transmits it to the RF transmit coil 310. The gradient power amplifier 318 amplifies the gradient coil signal and transmits it to the gradient coil 320.

[0042] Systems and methods for effectively acquiring nuclear magnetic resonance spectra and magnetic resonance images in inhomogeneous fields, such as using single-plane MRI scanners 100 and systems 300, are described herein.

[0043] Imaging using single-sided or open MRI poses many challenges. Typically, two sets of gradient coils in a single-sided system (see FIG. 6) are placed at the face of the permanent magnet assembly. As a result, the amplitude of the gradient decreases as you move away from the face of the permanent magnet assembly. Thus, for a given array of phase encoding, the field of view changes as you move along the axis of the permanent magnetic field B0. In other words, the pulsed gradient coils in a single-sided scanner have a small component along the direction of the permanent gradient.

[0044] FIG. 8 is a schematic diagram 500 of the magnetic field gradient along the Z-axis of the MRI scanner 100. The permanent magnet 130 provides an inherent gradient along the Z-axis. The strength of the Z-gradient decreases with distance from the permanent magnet 130. It can be seen in the schematic that the Z-gradient curves with distance from the permanent magnet, decreasing the strength of the gradient. The MRI scanner 100 images multiple slices to generate a slab. Each slice is excited for imaging with a different frequency. A lower frequency excites tissue in the slice farther from the permanent magnet and a higher frequency excites tissue in the slice closer to the magnet. In the schematic, the slab or axial image is generated by imaging the Slice 0 From Slice n Each slice consists of multiple slices that run along the f 0 From f n where f 0 f n It is a smaller frequency.

[0045] According to various aspects of the present disclosure, the added phase can be compensated for by applying phase encoding during a frequency sweep or chirp excitation pulse. A frequency sweep pulse can affect spins at different frequencies at different times during the pulse. This means that it is also possible to impart different amounts of phase to different frequencies by applying phase encoding during the excitation pulse. Spins excited at the beginning of the pulse can accumulate more phase than spins excited at the end of the pulse, which can accumulate very little phase.

[0046] According to various aspects, if spins further from the permanent magnet are excited first and phase encoding is applied during the frequency sweep excitation pulse, those farther away spins may accumulate more phase than spins closer to the permanent magnet that may be excited last. This reverses the usual way that spins accumulate phase from the surface gradient coils and counters the usual variations in gradient strength along the Z axis. By precisely tuning the amount of phase accumulated during the frequency sweep excitation and subsequent phase encoding, it is possible to apply a uniform amount of phase across the XY plane along the Z axis of the permanent magnet.

[0047] FIG. 9 shows a pulse sequence 900 configured to compensate for the variation of the field of view in slices along the Z axis generated by surface gradient coils (see, for example, gradient coils 152, 154 in FIG. 6). This compensation is achieved by phase encoding applied during the frequency sweep excitation pulse. In various examples, the frequency sweep pulses described herein are chirped or chirped pulses with a linear frequency sweep. The chirped excitation pulses can define a linear frequency sweep from low to high. Other monotonic increases from low to high frequencies are also possible. Since the low frequency excites tissues further from the permanent magnet assembly (see, for example, permanent magnet assembly 130 in FIG. 2) and the high frequency excites tissues closer to the permanent magnet assembly, by the end of the pulse, slices further from the magnet will have been phase encoded for a longer time, compensating for the weaker gradient. The first pulse 902 in the pulse sequence is a frequency sweep excitation pulse 902, with the chirped frequency sweep direction set to low to high. The gradients in the X and Y directions begin to dephase (918 and 922), respectively, and are refocused by the second pulse 904 of the pulse sequence. The gradient of Z is constant throughout the pulse sequence. The second pulse 904 is a refocusing pulse that refocuses the X and Y gradients. After the second pulse 904, a spectral echo 906 occurs, where the X and Y gradients dephase (920 and 924), respectively. After the spectral echo 906, the signal is read with a chirp echo train 908. The chirp echo train 908 includes a third pulse 910, a spin echo 912, a fourth pulse 914, and a spectral echo 916. In one embodiment, the third pulse 910 can be a second refocusing pulse, and the fourth pulse 914 can be a second excitation pulse.

[0048] In this embodiment, the changing field of view is overcompensated during the excitation pulse and then balanced with the phase encoding. The amount of phase accumulated during the frequency sweep needs to be precisely adjusted to apply a uniform amount of phase to the XY plane of the slice being imaged. In other words, the amount of phase at each slice needs to be precisely adjusted to account for the changing field of view. In other words, the scale of the object at each slice needs to be adjusted so that all slices have the same scale of the object. For example, the adjustment can be done by adjusting the power of the gradient pulse applied during the frequency sweep pulse while collecting 2D images along the XZ or YZ axis. The gradient power can be increased until the size of the object does not change along the Z axis. The slices can then be combined to synthesize a high quality slab image without any blurring due to the combination.

[0049] FIG. 10 shows a representative graph 1000 of a swept frequency pulse or chirp pulse with the sweep direction set from low to high. A chirp excitation pulse with the sweep direction set from low to high is an example of a frequency swept excitation pulse. The frequency of a chirp pulse with the sweep direction set from low to high starts at a low frequency and the frequency increases over time for the duration of the pulse. The pulse starts at the lowest desired frequency and ends when it reaches the maximum desired frequency. The pulse frequency in graph 1000 can be a negative to positive frequency offset relative to the baseband frequency. In other words, the frequency is swept from negative to positive plus the baseband frequency. For example, for a frequency sweep of + / -100KHz, the sweep is from 100KHz below the baseband frequency to 100KHz above the baseband frequency.

[0050] The frequency of the chirp pulses may vary from the minimum (lowest) desired frequency to the maximum (highest) desired frequency. The sweep rate of the pulse is the difference between the highest and lowest frequencies in the pulse divided by the time required to transition between the highest and lowest frequencies. In one embodiment, the frequency range covered by the swept frequency pulses used in the swept frequency pulse sequence 900 may range from -20KHz to 20KHz, i.e., 40KHz, with the center frequency varying from slab to slab. For example, the slabs may be centered at 2.62MHz, 2.75MHz, 2.65MHz, 2.72MHz, 2.79MHz, 2.69MHz, etc. For a slab centered at 2.62MHz, the chirp pulses will sweep a range from 2.60MHz to 2.64MHz, i.e., 40KHz. In other embodiments of the present disclosure, bandwidths as low as 10KHz to as high as 200KHz may be used for the frequency swept pulses. Additionally, the sweep range may be less than 40 KHz in various examples.

[0051] Referring again to FIG. 8, f 0 corresponds to the lowest frequency of the chirp pulse, and f n can correspond to the highest frequency of the chirped pulse. The chirped pulse is first applied to tissue that is farther from the permanent magnet assembly, e.g., a slice. 0 and later, tissue closer to the permanent magnet assembly, e.g., a slice n In other words, the adjacent slices include a proximal slice and a distal slice, where the proximal slice is located closer to the magnetic imaging device than the distal slice, and objects in the distal slice are excited before objects in the proximal slice. The frequency range of the chirp pulses can correspond to the slices of the slab being imaged.

[0052] Referring again to FIG. 9, the first pulse 902 is a chirp excitation pulse with a sweep direction set from low to high. This pulse excites tissue in slices farther from the permanent magnet assembly before exciting tissue in slices closer to the permanent magnet assembly. Phase encoding during chirp excitation accumulates different amounts of phase at different frequencies. Specifically, slices farther from the permanent magnet assembly accumulate more phase than slices closer to the permanent magnet assembly. In other words, objects in slices more distal from the permanent magnet assembly accumulate more phase than objects in slices more proximal to the permanent magnet assembly. Phase encoding during the frequency sweep excitation pulse, along with adjustment of the phase accumulated in each slice, can account for the phase in each slice and prevent echoes from drifting outside the acquisition window. After accounting for changes in the field of view in the slices along the Z axis, the slices can be combined into a slab to generate high quality axial images where the scale of objects in each slice is the same size.

[0053] There are several ways to measure temperature using magnetic resonance. The most common method is to use chemical shift. The chemical shift of water changes with temperature, so by monitoring how the chemical shift changes, the temperature can be monitored. This method only works for voxels with exchanging protons, such as water. Other molecules, such as fat, do not have a chemical shift that changes with temperature. Monitoring the temperature of fat is typically done by measuring the relaxation time of the tissue. As the temperature changes, so does the relaxation rate. A relaxation map can be collected and then converted to a temperature map by performing a calibration for that particular type of tissue.

[0054] In chemical shift-based methods, the frequency change due to chemical shift is small at low magnetic fields. If the main magnetic field is inhomogeneous, the frequency spread due to the inhomogeneity will obscure the chemical shift change due to temperature. This problem makes chemical shift-based methods unsuitable for low-field single-sided MRI systems. A relaxation-based temperature measurement method is required for low-field single-sided systems.

[0055] As mentioned above, measuring frequency shifts due to chemical shifts requires the field to be sufficiently uniform to resolve differences due to chemical shifts, so in an inhomogeneous magnetic field, frequency shifts due to chemical shifts may be undetectable. Temperature changes can alternatively be monitored by using relaxation data, for example, T2 relaxation times. T2 relaxation times change as tissue temperature affects the exchange rate of bonds in the body, changing the overall motion of spins within a voxel. These T2 relaxation times can then be converted to temperature using a model that correlates T2 relaxation to temperature. Models can be constructed by calibrating a particular tissue type by measuring T2 relaxation times at various temperatures. A different model is required for each tissue type. By fitting the T2 relaxation times to a model that incorporates changes in rotational diffusion and changes in exchange times, the temperature of each voxel can be estimated, resulting in a low-field temperature map.

[0056] MRI scanner 100 (FIG. 1) is an example of a single-sided MRI system capable of implementing the above-described methods. The single-sided MRI system includes a housing with a face, with a first axis extending through the face into a field of view. The single-sided MRI system further includes an array of permanent magnets located within the housing, with unique magnetic gradients extending from the array of permanent magnets into the field of view relative to the first axis. The single-sided MRI system further includes a gradient coil set, a radio frequency coil, a power circuit, a memory storing a relaxation model for a tissue type, and a control circuit in signal communication with the gradient coil set, the radio frequency coil, and the memory. The control circuit is configured to acquire a T2 data set from the radio frequency coil associated with a structure located within the field of view and corresponding to the tissue type. For example, the structure comprises tissue of the tissue type. The control circuit is further configured to generate a T2 weighted image of the structure and convert the T2 weighted image of the structure into a heat map based on the relaxation model for the tissue type.

[0057] Single-sided MRI systems offer many advantages for guiding in vivo thermal ablation of soft tissue. For example, the MRI system is open, allowing better access to the patient than standard closed MRI systems. Additionally, single-sided MRI systems can be more cost-effective than closed MRI systems. In various examples, single-sided MRI systems provide better results for thermal ablation due to better access to the patient and the thermal ablation area, and the ability to provide a live temperature map of the thermal ablation area. In comparison, conventional high-field MRI systems are often clinically impractical for thermal therapy due to their high cost, operational complexity, and difficult-to-access form factor.

[0058] Since this method for measuring temperature using magnetic resonance is for a system with a device whose single-sided configuration produces a non-uniform magnetic field, the echo train sequence can be collected with chirps wide enough to efficiently excite and refocus the field. In one embodiment, the pulse sequence can include phase encoding along two axes, but no additional encoding in the echo train. In an alternative embodiment, the pulse sequence can include phase encoding along two axes and additional encoding in the echo train. In another embodiment, one of the imaging axes can be spatiotemporally encoded, while the other is encoded by phase encoding. In yet another embodiment, both the x-axis and the y-axis can be spatiotemporally encoded. The chirp pulses are generated by a radio frequency coil, and the phase encoding is applied by a gradient coil set.

[0059] In an alternative embodiment, the method can be applied with a uniform magnetic field.

[0060] FIG. 11 shows a diagram of a pulse sequence 1100 that can be used to collect T2 relaxation times of structures in the field of view of an MRI system. The pulse sequence can be used with the single-sided open MRI system of FIG. 1 using, for example, a low magnetic field. Similar to pulse sequence 900 (FIG. 9), the first pulse in pulse sequence 1100 is a frequency sweep excitation pulse 1102 with a chirp frequency sweep direction set from low to high. The gradient of Z is constant throughout the pulse sequence. After the second pulse 1104, phase encoding 1112 and 1114 are applied along the X and Y gradients, respectively. Then, multiple swept frequency pulses 1110 can be transmitted by the radio frequency coil. In FIG. 11, swept frequency pulse 1106 is the first pulse of the multiple swept frequency pulses 1110, and swept frequency pulse 1108 is the last pulse in the multiple swept frequency pulses 1110.

[0061] The multiple swept frequency pulses 1110 constitute an echo train sequence that is received by the radio frequency coil. In some aspects, the radio frequency coil can be one unit that both transmits and receives. In other aspects, the radio frequency coil can include a set of at least two coils, at least one coil that transmits and at least one coil that receives. Each swept frequency pulse generates an echo, and the echo time of each echo can be from about 2 milliseconds to about 20 milliseconds. The echo train sequence can include anywhere from about 10 to about 100 echoes. In alternative aspects, there may be more than 100 echoes or less than 10 echoes in the echo train sequence. The bandwidth of the swept frequency pulse can be from about 10 KHz to about 200 KHz.

[0062] T2 data can be calculated from each echo in the echo train sequence. In one embodiment, the T2 data set can be generated based on a plurality of sweep frequency pulses. In another embodiment, the T2 data set can be generated based on a plurality of sweep frequency pulses and phase encoding between the plurality of sweep frequency pulses. The T2 relaxation time can be determined by fitting the echo amplitude versus echo time to a monoexponential decay function.

[0063] The method of measuring temperature in vivo using magnetic resonance involves first collecting a calibration for the type of tissue being measured. Calibration requires measuring the T2 relaxation times of excised tissue or phantoms designed to mimic tissue at various temperatures. The response of the relaxation times to temperature is then fitted to a model. Each tissue type may have a unique model.

[0064] FIG. 12 shows a flow diagram 1200 for collecting calibration data for a particular tissue type. The calibration data can later be used to generate a T2 relaxation time vs. temperature model for the particular tissue type. The T2 relaxation times are measured for the tissue type at various temperatures. For example, the structure having the tissue type can be an excised tissue or a phantom designed to mimic the tissue type. In block 1202, an MRI system, such as MRI scanner 100 (FIG. 1), generates a unique gradient magnetic field that extends into the field of view from one side of the magnetic imaging device relative to the z-axis. In block 1204, the structure is heated or cooled to a desired temperature in a temperature list. The temperature list can include various temperatures that the tissue type can reach. In other words, the temperature list can include multiple temperatures predicted for the tissue type of the structure. In block 1206, the structure is placed in the field of view while the structure is at the desired temperature. In block 1208, the MRI system transmits a pulse sequence, such as pulse sequence 1100 (FIG. 11). In block 1210, the MRI system receives an echo train sequence based on the pulse sequence. In block 1212, the MRI system calculates T2 relaxation data based on the echoes in the echo train sequence. In block 1214, the MRI system checks whether each temperature in the temperature list has a corresponding T2 relaxation time. If there is no T2 relaxation data for each temperature in the temperature list, the system proceeds to block 1204 and the structure is heated or cooled to another temperature in the temperature list. The above data acquisition loop can continue until each temperature in the temperature list has T2 relaxation data. If each temperature has corresponding T2 relaxation data, the system proceeds to block 1216. In block 1216, a model for the temperature of the structure is generated based on the T2 relaxation data at that temperature in the temperature list. Additional models can be obtained for various tissue types.

[0065] In an exemplary calibration method, a phantom made of a bottle filled with honey was used for the structure. A calibration step was performed on the phantom by subjecting it to controlled heating in a water bath to various temperatures. The phantom was then placed in a receive coil surrounded by insulation. Once placed in the insulated receive coil, the MRI machine was used to obtain the bulk T2 relaxation time of the phantom, and the phantom temperature was immediately measured using a FLIR-E6390 thermal camera. After measuring the T2 relaxation time and corresponding temperature, the phantom was removed from the receive coil and heated in a water bath to another desired temperature. The process was repeated to successfully obtain measurements of the T2 relaxation time for each desired temperature. The T2 relaxation times were identified by fitting the echo amplitude versus echo time to a monoexponential decay function.

[0066] The T2 relaxation time and corresponding temperature measurements for an exemplary calibration method are shown in the graphical representation 1300 in FIG. 13, where a phantom (a bottle filled with honey) was used. The y-axis of the graphical representation 1300 is R 2 where R 2 is the reciprocal of the T2 relaxation time. In other words, R 2 is 1 / T2. In one embodiment, R 2 The time was derived by fitting the decay of the signal amplitude in the echo train to a monoexponential function. An exemplary model relating relaxation time to temperature is shown by line 1302 in the graphical representation 1300. Line 1302 is described by the following equation:

number

[0067] In various examples, the relationship of relaxation time versus temperature can correspond to a monoexponential model. For example, in the exemplary calibration method and associated data set shown in FIG. 13, the T2 relaxation time varied monotonically with the temperature of the phantom, increasing with increasing temperature. This is consistent with the decrease in viscosity of honey as it is heated, which can be clearly seen by observing how honey flows more easily at higher temperatures. Furthermore, in various embodiments of the present disclosure, it is assumed that the product of the Larmor frequency and the correlation time is much smaller than 1, R 2 By making x proportional to the rotational correlation time, the model and relationships shown in the above equation can be generated.

[0068] In alternative embodiments of the present disclosure, other equations can be used to fit the T2 relaxation time and temperature data.

[0069] Once the calibration data for the relevant tissue types are complete and models are generated for each tissue type, a temperature map or heat map can be collected for the relevant tissue type. A temperature map can be generated by acquiring a T2 map or T2 weighted image using a 3D echo train sequence as described further herein. A 3D echo train sequence may include phase encoding along two axes, but no additional encoding in the echo train. Such a pulse sequence results in a data set in which each echo is a distinct, separate image of T2 weighting. In various examples, each echo can be reconstructed into a separate image. The series of images can be converted into a T2 map by fitting the pixel intensity to an exponential decay (e.g., a monoexponential function) versus echo time. From this fit, a T2 time is generated by each pixel with a signal. The T2 map obtained by this fit can then be converted into a temperature map by calibration, such as the calibration formula described above for a particular structure. If the tissue type is known, the calibration formula can map the T2 relaxation time to temperature.

[0070] FIG. 14 shows a flow diagram 1400 for using collected T2 relaxation data to generate a heat map based on a T2 relaxation time versus temperature model that can be obtained by a calibration method described further herein. In block 1402, an MRI system (e.g., MRI scanner 100 (FIG. 1)) generates a unique gradient magnetic field that extends from one side of the magnetic imaging device relative to the z-axis into a field of view in which the structure is located. In block 1404, the MRI system transmits a pulse sequence, e.g., pulse sequence 1100 (FIG. 11). In block 1406, the MRI system receives an echo train sequence based on the pulse sequence. In one embodiment, the echo train sequence can be a 3D echo train sequence. In block 1408, the MRI system calculates T2 relaxation data based on echoes in the echo train sequence. In block 1410, the MRI system generates a T2 weighted image based on the T2 relaxation data. In block 1412, the MRI system converts the T2 weighted image into a heat map based on the T2 relaxation time versus temperature model. The tissue type of the structure is the same as the tissue type of the T2 relaxation time versus temperature model. In one aspect, the tissue type of the structure can be manually entered so that the correct model is used. In another aspect, the tissue type of the structure can be automatically calculated based on a predefined tissue type model. For example, the tissue type can be identified by mapping structural information from a predefined model onto an image of the structure.

[0071] To generate the exemplary temperature map 1500 shown in FIG. 15, the structure used for the calibration data was heated again and then placed in an insulated coil for imaging. A 3D single point imaging scan was performed and an echo train was used to collect T2 weighted images or maps. A separate image was generated with each echo and the intensity of each pixel was fitted to a mono-exponential decay function versus echo time. From these fits, a T2 map was generated for the heated structure and then converted to the temperature map 1500 using the exemplary calibration model.

[0072] The T2 maps used to generate the heat map 1500 were collected with a single-sided open MRI system using permanent gradients and low-field MRI. For example, the main magnetic field strength can be operational at 58 mT to 74 mT. An exemplary method for collecting the T2 maps is to use a 3D single point imaging sequence.

[0073] In alternative embodiments, other MRI systems can be used to acquire the T2 maps used to generate the heat maps.

[0074] Temperature maps obtained using the above-described method show significant temperature gradients consistent with thermal camera measurements. Due to the low magnetic field and form factor of low-field single-sided MRI machines, integrating the above-described relaxation-based MR thermometry with thermal ablation devices can provide improved guidance and better treatment outcomes in certain instances.

[0075] example Various aspects of the subject matter described herein are set forth in the following numbered examples.

[0076] Example 1 - A magnetic imaging device comprising a housing with a face, a first axis extending through the face into a field of view. The magnetic imaging device further comprises an array of permanent magnets located within the housing, a unique gradient magnetic field extending from the array of permanent magnets into the field of view relative to the first axis. The magnetic imaging device further comprises a gradient coil set, at least one radio frequency coil, a power circuit, a memory storing a relaxation model for a tissue type, and a control circuit in signal communication with the gradient coil set, the at least one radio frequency coil, the power circuit, and the memory. The control circuit is configured to acquire a T2 data set associated with a structure located within the field of view corresponding to the tissue type. The control circuit is further configured to generate a T2 weighted image of the structure and convert the T2 weighted image of the structure into a heat map based on the relaxation model for the tissue type.

[0077] Example 2 - The magnetic imaging apparatus of example 1, wherein the relaxation model comprises a monoexponential model.

[0078] Example 3 - The magnetic imaging apparatus of example 1 or example 2, wherein the gradient coil and the at least one radio frequency coil are coupled to a power circuit.

[0079] Example 4 - the magnetic imaging device of Example 1, Example 2, or Example 3, wherein the control circuitry is further configured to transmit a pulse sequence including a plurality of swept frequency pulses.

[0080] Example 5 - The magnetic imaging apparatus of example 4, wherein the T2 data set is generated from a plurality of swept frequency pulses.

[0081] Example 6 - The magnetic imaging apparatus of example 4 or example 5, wherein each swept frequency pulse produces an echo having a duration between 2 milliseconds and 20 milliseconds.

[0082] Example 7 - The magnetic imaging device of example 4, example 5, or example 6, wherein the plurality of swept frequency pulses generates between 10 and 100 echoes.

[0083] Example 8 - The magnetic imaging device of example 4, example 5, example 6, or example 7, wherein the bandwidth of each swept frequency pulse is between 10 KHz and 200 KHz.

[0084] Example 9 - The magnetic imaging device of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, or Example 8, wherein the radio frequency coil is configured to transmit pulses having a frequency between 1 megahertz and 21 megahertz.

[0085] Example 10 - A magnetic imaging device according to example 1, example 2, example 3, example 4, example 5, example 6, example 7, example 8, or example 9, wherein the magnetic field strength within the field of view is less than 1 Tesla.

[0086] Example 11 - A magnetic imaging device according to example 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, wherein the magnetic field non-uniformity within the field of view is between 200 ppm and 200,000 ppm.

[0087] Example 12 - A magnetic imaging device as described in Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, or Example 11, wherein the relaxation model is generated from calibration data including multiple T2 relaxation data for different temperatures for a tissue type.

[0088] Example 13 - A magnetic imaging device as described in Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, or Example 12, wherein the magnetic imaging device is a single-sided magnetic imaging device and the housing and the gradient coil set are located on a first side of the field of view.

[0089] Example 14 - The magnetic imaging apparatus of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, or Example 13, further comprising a user input device configured to receive a tissue type of the structure.

[0090] Example 15 - A magnetic imaging device as described in Example 1, Example 2, Example 3, Example 4, Example 5, Example 6, Example 7, Example 8, Example 9, Example 10, Example 11, Example 12, or Example 13, further comprising an automated tissue type recognition module configured to identify a tissue type model corresponding to the structure and record the tissue type model together with the structure.

[0091] Example 16 - A single-sided magnetic imaging device comprising a housing comprising an array of permanent magnets, wherein a unique gradient magnetic field extends from the array of permanent magnets relative to a first axis into a field of view, the field of view being adjacent to the housing. The single-sided magnetic imaging device further comprises a radio frequency coil, a power circuit coupled to the radio frequency coil, a memory storing relaxation models for tissue at different temperatures, and a control circuit. The control circuit is in signal communication with the radio frequency coil, the power circuit, and the memory. The control circuit is configured to: transmit a waveform sequence to the radio frequency coil to generate an echo train sequence; acquire a T2 data set associated with a structure disposed within the field of view; generate a T2 weighted image of the structure; and convert the T2 weighted image of the structure into a heat map based on the relaxation models stored in the memory.

[0092] Example 17 - The single-sided magnetic imaging device of example 16, wherein the relaxation model comprises a mono-exponential model.

[0093] Example 18 - The single-sided magnetic imaging device of example 16 or example 17, wherein the echo train sequence includes phase encoding.

[0094] Example 19 - The single-sided magnetic imaging device of Example 16, Example 17, or Example 18, wherein the T2 data set is generated based on an echo train sequence.

[0095] Example 20 - The single-sided magnetic imaging device of Example 16, Example 17, Example 18, or Example 19, wherein the echo train sequence includes echoes having a duration between 2 milliseconds and 20 milliseconds.

[0096] Example 21 - The single-sided magnetic imaging device of Example 16, Example 17, Example 18, Example 19, or Example 20, wherein the echo train sequence includes 10 to 100 echoes.

[0097] Example 22 - The single-sided magnetic imaging device of example 16, example 17, example 18, example 19, example 20, or example 21, wherein the echo train sequence is generated by a plurality of swept frequency pulses having a bandwidth between 10 KHz and 200 KHz.

[0098] Example 23 - The single-sided magnetic imaging device of Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, or Example 22, wherein the radio frequency coil is configured to transmit pulses having a frequency between 1 megahertz and 21 megahertz.

[0099] Example 24 - A single-sided magnetic imaging device as described in Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, Example 22, or Example 23, wherein the magnetic field strength within the field of view is less than 1 Tesla.

[0100] Example 25 - A single-sided magnetic imaging device according to Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, or Example 24, wherein the magnetic field non-uniformity within the field of view is between 200 ppm and 200,000 ppm.

[0101] Example 26 - A single-sided magnetic imaging device as described in Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, or Example 25, wherein the relaxation model is generated from calibration data including multiple T2 data at different temperatures for different tissue types.

[0102] Example 27 - A single-sided magnetic imaging device as described in Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, or Example 26, further comprising a gradient coil set located within the housing, wherein the gradient coil set, the radio frequency coil, and the housing are located on a first side of the field of view.

[0103] Example 28 - A single-sided magnetic imaging device as described in Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, or Example 27, wherein the radio frequency coil comprises a radio frequency transmitting coil, and the single-sided magnetic imaging device further comprises a radio frequency receiving coil.

[0104] Example 29 - A single-sided magnetic imaging device as described in Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, or Example 28, further comprising a user input device configured to receive a tissue type of the structure corresponding to a tissue type per relaxation model.

[0105] Example 30 - A single-sided magnetic imaging device as described in Example 16, Example 17, Example 18, Example 19, Example 20, Example 21, Example 22, Example 23, Example 24, Example 25, Example 26, Example 27, or Example 28, further comprising an automated tissue type recognition module configured to identify a tissue type model corresponding to the structure and record the tissue type model together with the structure, the tissue type model corresponding to the tissue type for each relaxation model.

[0106] Example 31 - A method of detecting temperature in an object of interest comprised of a first tissue type using a magnetic resonance imaging device. The method includes obtaining calibration data including T2 data for different temperatures for different tissue types including the first tissue type, generating a model for the different tissue types from the calibration data, placing the object of interest within a field of view, and transmitting a pulse sequence including swept frequency pulses. The method further includes receiving T2 data corresponding to the object of interest, generating a T2 weighted image of the object of interest, and converting the T2 weighted image of the object of interest into a heat map based on the model for the first tissue type.

[0107] Example 32 - The method of Example 31, further comprising receiving a first input identifying a first tissue type of the object of interest.

[0108] Example 33 - The method of Example 31 or Example 32, further comprising: the RF coil set transmitting a pulse sequence including swept frequency pulses; and receiving T2 data corresponding to the object of interest.

[0109] Example 34 - The method of Example 31, Example 32, or Example 33, wherein the magnetic resonance imaging device comprises a permanent magnet assembly, and the method further comprises the permanent magnet assembly generating a unique magnetic gradient field within the field of view.

[0110] While several embodiments have been shown and described, it is not the intention of the applicant to restrict or limit the scope of the appended claims to such details. Numerous modifications, variations, permutations, combinations, and equivalents to those embodiments may be realized and will occur to those skilled in the art without departing from the scope of the present disclosure. Moreover, the structure of each element associated with the described embodiments may alternatively be described as a means for providing the function performed by the element. Furthermore, where certain materials are disclosed for a particular component, other materials may be used. It is therefore understood that the above description and the appended claims are intended to cover all such modifications, combinations, and variations as fall within the scope of the disclosed embodiments. The appended claims are intended to cover all such modifications, permutations, permutations, combinations, and equivalents.

[0111] The foregoing detailed description describes various forms of devices and / or processes through the use of block diagrams, flow charts, and / or examples. To the extent that such block diagrams, flow charts, and / or examples include one or more functions and / or operations, it will be understood by those skilled in the art that each function and / or operation in such block diagrams, flow charts, and / or examples can be individually and / or collectively implemented by a wide range of hardware, software, firmware, or substantially any combination thereof. Those skilled in the art will recognize that some aspects of the forms disclosed herein may also be implemented in whole or in part in an integrated circuit, as one or more computer programs running on one or more computers (e.g., as one or more programs running on one or more computer systems), as one or more programs running on one or more processors (e.g., as one or more programs running on one or more microprocessors), as firmware, or substantially any combination thereof, and that designing circuitry and / or writing code for the software and / or firmware is well within the skill of those skilled in the art in light of the present disclosure. In addition, those skilled in the art will appreciate that the mechanisms of the subject matter described herein can be distributed as one or more program products in a variety of forms, and that the illustrative forms of the subject matter described herein apply regardless of the particular type of signal-bearing medium used to actually perform the distribution.

[0112] The instructions used to program the logic to implement the various disclosed aspects may be stored in memory in the system, such as dynamic random access memory (DRAM), cache, flash memory, or other storage. Additionally, the instructions may be distributed over a network or by other computer readable media. Thus, a machine readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer), such as, but not limited to, a floppy disk, an optical disk, a compact disk, a read-only memory (CD-ROM), and a magneto-optical disk, a read-only memory (ROM), a random access memory (RAM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a magnetic or optical card, a flash memory, or any tangible machine readable storage used in transmitting information over the Internet via an electrical, optical, acoustical, or other form of propagated signal (e.g., carrier wave, infrared signal, digital signal, etc.). Accordingly, non-transitory computer-readable media encompasses any type of tangible machine-readable medium suitable for storing or transmitting electronic instructions or information in a form readable by a machine (eg, a computer).

[0113] The term "control circuitry" as used in any embodiment herein may refer to, for example, hardwired circuitry, programmable circuitry (e.g., a computer processor including one or more individual instruction processing cores, a processing unit, a processor, a microcontroller, a microcontroller unit, a controller, a digital signal processor (DSP), a programmable logic device (PLD), a programmable logic array (PLA), or a field programmable gate array (FPGA)), a state machine circuit, firmware that stores instructions executed by the programmable circuit, and any combination thereof. The control circuitry may be embodied collectively or individually as circuits that form part of a larger system, such as, for example, an integrated circuit (IC), an application specific integrated circuit (ASIC), a system on a chip (SoC), a desktop computer, a laptop computer, a tablet computer, a server, a smartphone, etc. Thus, as used herein, "control circuitry" includes, but is not limited to, electrical circuitry including at least one discrete electrical circuit, electrical circuitry including at least one integrated circuit, electrical circuitry including at least one application specific integrated circuit, electrical circuitry forming a general purpose computing device configured with a computer program (e.g., a general purpose computer configured with a computer program that at least partially implements the processes and / or devices described herein, or a microprocessor configured with a computer program that at least partially implements the processes and / or devices described herein), electrical circuitry forming a memory device (e.g., a form of random access memory), and / or electrical circuitry forming a communication device (e.g., a modem, a communication switch, or an optoelectronic device).Those skilled in the art will recognize that the subject matter described herein may be implemented in analog or digital fashion or any combination thereof.

[0114] As used in any aspect herein, the term "logic" may refer to apps, software, firmware, and / or circuitry configured to perform any of the aforementioned operations. Software may be embodied as a software package, code, instructions, instruction sets, and / or data recorded on a non-transitory computer-readable storage medium. Firmware may be embodied as hard-coded (e.g., non-volatile) code, instructions, or instruction sets, and / or data in a memory device.

[0115] As used in any aspect herein, the terms "component," "system," "module," and the like may refer to a computer-related entity that is either hardware, a combination of hardware and software, software, or software in execution.

[0116] As used in any aspect herein, an "algorithm" refers to a self-consistent sequence of steps leading to a desired result, where the "steps" refer to manipulations of physical quantities and / or logical states, which may, but do not necessarily, take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It is common usage to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. These and similar terms can be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities and / or states.

[0117] The network may include a packet-switched network. The communication devices may be capable of communicating with each other using a selected packet-switched network communication protocol. One exemplary communication protocol may include an Ethernet communication protocol that may be capable of permitting communication using Transmission Control Protocol / Internet Protocol (TCP / IP). The Ethernet protocol may comply with or conform to the Ethernet standard published by the Institute of Electrical and Electronics Engineers (IEEE) entitled "IEEE 802.3 Standard" published in December 2008 and / or subsequent versions of this standard. Alternatively or additionally, the communication devices may be capable of communicating with each other using an X.25 communication protocol. The X.25 communication protocol may comply with or conform to standards published by the International Telecommunication Union-Telecommunication Standardization Sector (ITU-T). Alternatively or additionally, the communication devices may be capable of communicating with each other using a Frame Relay communication protocol. The Frame Relay communication protocol may comply with or conform to standards published by the Consultative Committee for International Telegraph and Telephone (CCITT) and / or the American National Standards Institute (ANSI). Alternatively, or in addition, the transceivers may be capable of communicating with each other using an Asynchronous Transfer Mode (ATM) communications protocol that may conform to or be compatible with the ATM standard published by the ATM Forum entitled "ATM-MPLS Network Interworking 2.0," published in August 2001, and / or any subsequent versions of this standard. Of course, different and / or later connection-oriented network communications protocols are also contemplated herein.

[0118] As is apparent from the above disclosure, unless expressly stated otherwise, descriptions throughout the above disclosure using terms such as "processing," "operating," "calculating," "determining," "displaying," and the like are understood to represent actions and processes of a computer system or similar electronic computing device that manipulates and transforms data represented as physical (electronic) quantities in the computer system's registers and memory into other data that is similarly represented as physical quantities in the computer system's memory or registers or other such information storage, transmission or display device.

[0119] One or more components may be referred to herein as being "configured to," "configurable to," "operable to," "adapted to," "capable of," "adaptable to," etc. Those skilled in the art will recognize that "configured to" may generally encompass active and / or inactive and / or standby components, unless the context requires otherwise.

[0120] The terms "proximal" and "distal" are used herein with reference to the magnetic imaging device. The term "proximal" refers to a direction toward the magnetic imaging device and "distal" refers to a direction away from the magnetic imaging device. It is further understood that for convenience and clarity, spatial terms such as "vertical," "horizontal," "up," and "down" may be used herein with reference to the drawings. However, these terms are not intended to be limiting and / or absolute.

[0121] Those skilled in the art will recognize that the terms used herein generally, and in the appended claims (e.g., the body of the appended claims) in particular, are generally intended to be "open" terms (e.g., the term "comprising" should be interpreted as "including but not limited to," the term "comprising" should be interpreted as "including at least," the term "comprising" should be interpreted as "including but not limited to," etc.). Where a specific number of claim elements being modified is intended, such intent will be explicitly set forth in the claim, and it will be further understood by those skilled in the art that in the absence of such a statement, no such intent exists. For example, as an aid to understanding, the following appended claims may include the use of the modifiers "at least one" and "one or more" to modify claim elements. However, the use of such expressions should not be construed as meaning that the modification of a claim element with an expression corresponding to the English indefinite article "a" or "an" limits any particular claim containing the claim element so modified to a claim containing only one such element, even when the same claim also contains the modifying expressions "one or more" or "at least one" and, for example, an expression corresponding to the English indefinite article "a" or "an" (for example, an expression corresponding to the English indefinite article "a" and / or "an" should typically be construed to mean "at least one" or "one or more"). The same applies to the use of definite articles used to modify claim elements.

[0122] In addition, even when a specific number of modified claim elements is explicitly recited, one of skill in the art will recognize that this should be interpreted to mean that such elements are typically present in at least the recited number (e.g., the bare element "two elements" without other modifiers typically means at least two elements or more than two elements). Furthermore, in instances where a convention similar to "at least one of A, B, and C, etc." is used, such configuration is intended generally based on how one of skill in the art would understand the convention (e.g., "a system including at least one of A, B, and C" includes, but is not limited to, systems including only A, only B, only C, a combination of A and B, a combination of A and C, a combination of B and C, and / or a combination of A, B, and C, etc.). In instances where a convention similar to "at least one of A, B, or C, etc." is used, such configuration is intended generally based on how one of ordinary skill in the art would understand the convention (e.g., "a system including at least one of A, B, or C" includes, but is not limited to, systems including only A, only B, only C, a combination of A and B, a combination of A and C, a combination of B and C, and / or a combination of A, B and C, etc.). Typically, it will be further understood by those of ordinary skill in the art that disjunctive phrases and / or phrases presenting two or more alternative terms, whether contained in the description, claims, or drawings, should be understood to contemplate the possibility of including one of the terms, either of the terms, or both of the terms, unless the context dictates otherwise. For example, the phrase "A or B" is typically understood to include the possibilities of "A" or "B" or "A and B."

[0123] In light of the appended claims, those skilled in the art will appreciate that the operations described therein may generally be performed in any order. Additionally, while various operational flow diagrams are presented in a certain order, it should be understood that various operations may be performed in other orders than those shown, or may be performed simultaneously. Examples of such alternative orders may include overlapping, alternating, interrupted, reordered, incremental, preliminary, complementary, simultaneous, reversed, or other variant orders, unless the context dictates otherwise. Additionally, terms such as "according to," "related to," or other past tense adjectives are generally not intended to exclude such variants, unless the context dictates otherwise.

[0124] It is important to note that all references to "one embodiment," "embodiment," "exemplary," "one example," etc. mean that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the use of the phrases "in one embodiment," "in an embodiment," "in an example," and "in one example" in various places throughout this specification do not necessarily all refer to the same embodiment. Furthermore, particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

[0125] Any patent application, patent, non-patent publication, or other disclosure referenced herein and / or listed in any application data sheet is incorporated herein by reference to the extent that the incorporated content is not inconsistent with the present specification. Thus, and to the extent necessary, the disclosure expressly set forth herein takes precedence over any inconsistent content incorporated herein by reference. Any document, or portion thereof, that is referred to as being incorporated herein by reference but that is inconsistent with an existing definition, description, or other disclosure content set forth herein is incorporated only to the extent that no inconsistency occurs between the incorporated document and the existing disclosure content.

[0126] In summary, many advantages resulting from the use of the concepts described herein have been described. The above description of one or more embodiments has been presented for purposes of illustration and description. It is not intended to be exhaustive or to be limited to the precise form disclosed. Modifications or variations are possible in light of the above teachings. One or more embodiments have been selected and described to illustrate the principles and practical application, thereby enabling those skilled in the art to use the various embodiments, and with various modifications suited to the particular use envisioned. It is intended that the claims submitted herewith define the full scope.

Claims

1. a housing having a face, a first axis extending through the face into a field of view; an array of permanent magnets located within the housing, wherein a unique gradient magnetic field extends from the array of permanent magnets into the field of view relative to the first axis; a gradient coil set; at least one radio frequency coil; A power circuit; a memory that stores a relaxation model for a tissue type; a control circuit in signal communication with the gradient coil set, the at least one radio frequency coil, the power circuit, and the memory, the control circuit comprising: acquiring a T2 data set associated with a structure corresponding to the tissue type located within the field of view; generating a T2 weighted image of the structure; converting the T2 weighted image of the structure into a heat map based on the relaxation model for the tissue type; a control circuit configured to perform the A magnetic imaging device comprising:

2. The magnetic imaging device of claim 1 , wherein the relaxation model comprises a monoexponential model.

3. The magnetic imaging device of claim 1 , wherein the gradient coil and the at least one radio frequency coil are coupled to the power circuit.

4. The magnetic imaging device of claim 1 , wherein the control circuitry is further configured to transmit a pulse sequence including a plurality of swept frequency pulses.

5. 5. The magnetic imaging device of claim 4, wherein the T2 data set is generated from the plurality of swept frequency pulses.

6. 5. The magnetic imaging device of claim 4, wherein each sweep frequency pulse produces an echo having a duration of 2 to 20 milliseconds, and further wherein each sweep frequency pulse has a bandwidth of 10 to 200 KHz, and wherein the plurality of sweep frequency pulses produces 10 to 100 of the echoes.

7. 10. The magnetic imaging device of claim 1, wherein the radio frequency coil is configured to transmit pulses having a frequency between 1 megahertz and 21 megahertz.

8. 2. The magnetic imaging device of claim 1, wherein the magnetic field strength within the field of view is less than 1 Tesla and the magnetic field non-uniformity within the field of view is between 200 ppm and 200,000 ppm.

9. The magnetic imaging device of claim 1 , wherein the relaxation model is generated from calibration data including a plurality of T2 relaxation data for the tissue type at different temperatures.

10. 2. The magnetic imaging device of claim 1, wherein the magnetic imaging device is a single-sided magnetic imaging device, and the housing and the gradient coil set are located on a first side of the field of view.

11. The magnetic imaging apparatus of claim 1 , further comprising a user input device configured to receive the tissue type of the structure.

12. 2. The magnetic imaging device according to claim 1, identifying a tissue type model corresponding to the structure; recording the tissue type model with the structure; The apparatus further comprises an automated tissue type recognition module configured to perform:

13. a housing comprising an array of permanent magnets, wherein a unique gradient magnetic field extends from the array of permanent magnets about one axis into a field of view, the field of view being adjacent to the housing; a radio frequency coil; a power circuit coupled to the radio frequency coil; a memory for storing relaxation models for tissue at different temperatures; a control circuit in signal communication with the radio frequency coil, the power circuit, and the memory, the control circuit comprising: transmitting a waveform sequence to the radio frequency coil to generate an echo train sequence; acquiring a T2 data set associated with a structure located within the field of view; generating a T2 weighted image of the structure; converting the T2-weighted image of the structure into a heat map based on the relaxation model stored in the memory; a control circuit configured to perform the A single-sided magnetic imaging device comprising:

14. 14. The single-sided magnetic imaging device of claim 13, wherein the echo train sequence includes phase encoding.

15. The single-sided magnetic imaging device of claim 13 , wherein the T2 data set is generated based on the echo train sequence.

16. A single-sided magnetic imaging device as described in claim 13, wherein the echo train sequence includes echoes having a duration of 2 milliseconds to 20 milliseconds, and the echo train sequence includes 10 to 100 echoes, and the echo train sequence is generated by a plurality of sweep frequency pulses having a bandwidth of 10 KHz to 200 KHz.

17. 14. The single-sided magnetic imaging device of claim 13, wherein the radio frequency coil is configured to transmit pulses having a frequency between 1 megahertz and 21 megahertz.

18. 14. The single-sided magnetic imaging device of claim 13, wherein the magnetic field strength within the field of view is less than 1 Tesla and the magnetic field non-uniformity within the field of view is between 200 ppm and 200,000 ppm.

19. 14. The single-sided magnetic imaging device of claim 13, wherein the radio frequency coil comprises a radio frequency transmit coil, and the single-sided magnetic imaging device further comprises a radio frequency receive coil.

20. The single-sided magnetic imaging apparatus of claim 13 , further comprising a user input device configured to receive a tissue type of the structure corresponding to a tissue type for each of the relaxation models.

21. 14. The single-sided magnetic imaging device according to claim 13, identifying a tissue type model corresponding to the structure; recording the tissue type models together with the structures, each corresponding to a tissue type for each relaxation model; The apparatus further comprises an automated tissue type recognition module configured to perform:

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