Magnetic resonance imaging device and magnetic resonance imaging method

Abstract

To provide a magnetic resonance imaging device improving measurement accuracy of a T2* value using a UTE imaging method.SOLUTION: A magnetic resonance imaging device includes an imaging condition setting part, a data acquisition part, an additional analysis part, and an imaging condition calculation part. The imaging condition setting part sets an imaging condition including a plurality of TEs by using a UTE imaging method. The data acquisition part acquires first MR signal data at a plurality of TEs. The additional analysis part analyzes to specify a region where acquisition of additional MR signal data is required, based on the first MR signal data. The imaging condition calculation part calculates at least one additional TE for acquiring additional MR signal data delayed by ΔTE from at least one TE in the first MR signal data in the region where acquisition of the additional MR signal data is required. The imaging condition setting part further sets an imaging condition including the at least one additional TE by using the UTE imaging method, and the data acquisition part further acquires additional MR signal data at the at least one additional TE.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The embodiments disclosed in this specification and the drawings relate to a magnetic resonance imaging apparatus and a magnetic resonance imaging method. [Background technology]

[0002] A magnetic resonance imaging apparatus is an imaging device that excites the nuclear spins of a subject placed in a static magnetic field with a radio frequency (RF) signal at the Larmor frequency, and generates an image by reconstructing the magnetic resonance (MR) signals generated from the subject in response to the excitation.

[0003] Generally, in tissues with little water content, such as bones and lungs, the transverse relaxation time (T2 value, or T2 value taking into account magnetic field inhomogeneity) is * The T2 * As an imaging method that enables imaging when the value is very short, a technique called Ultrashort Echo Time (UTE) imaging method is known.

[0004] The UTE imaging method is an imaging method that uses a pulse sequence in which the time from excitation pulse application to data collection, i.e., the echo time (TE), is set to be very short. For example, in clinical practice, the effective transverse relaxation rate (R2 * T2 value) using UTE imaging * Value measurement and R2 * However, in the conventional UTE imaging method, when the transverse relaxation time is very short, the T2 * Value measurement and R2 * The measurement of values ​​may not be accurate enough. [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Axel J. Krafft et al., “Quantitative Ultrashort Echo Time Imaging for Assessment of Massive Iron Overload at 1.5 and 3 Tesla”, Magnetic Resonance in Medicine 78:1839-1851 (2017) [Non-Patent Document 2] Tipirneni-Sajja A et al., “Ultrashort Echo Time Imaging for Quantification of Hepatic Iron Overload: Comparison of Acquisition and Fitting Methods via Simulations, Phantoms, and In vivo Data”,1686551626262_0.fcgi?dbfrom=pubmed&retmode=ref&cmd=prlinks&id=30358001 (2019) Summary of the Invention [Problem to be solved by the invention]

[0006] One of the problems that the embodiments disclosed in this specification and the drawings are intended to solve is the T2 * However, the problems to be solved by the embodiments disclosed in this specification and the drawings are not limited to the above problems. Problems corresponding to the effects of the configurations shown in the embodiments described later can also be positioned as other problems. [Means for solving the problem]

[0007] A magnetic resonance imaging apparatus according to an embodiment includes an imaging condition setting unit, a data acquisition unit, an additional analysis unit, and an imaging condition calculation unit. The imaging condition setting unit sets imaging conditions including a plurality of TEs (Echo Times) using a UTE (Ultrashort Echo Time) imaging method. The data acquisition unit acquires initial MR signal data at the set plurality of TEs. The additional analysis unit performs an analysis to specify a region in which additional MR signal data needs to be acquired based on the acquired initial MR signal data. The imaging condition calculation unit calculates at least one additional TE (Additional Echo Time) for acquiring additional MR signal data delayed by ΔTE from at least one TE in the initial MR signal data in the specified region in which additional MR signal data needs to be acquired. The imaging condition setting unit further sets imaging conditions including at least one additional TE using a UTE imaging method, and the data acquisition unit further acquires additional MR signal data at at least one additional TE. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing an example of the overall configuration of a magnetic resonance imaging apparatus according to an embodiment; [Diagram 2] FIG. 13 is an explanatory diagram of T2* value measurement using the UTE imaging method of the comparative example. [Diagram 3] FIG. 2 is an explanatory diagram of data collection according to the UTE imaging method according to the first embodiment. [Figure 4] FIG. 2 is an explanatory diagram of T2* value measurement according to the UTE imaging method according to the first embodiment. [Diagram 5] 1 is a schematic diagram showing an example of the configuration of a processing circuit of a magnetic resonance imaging apparatus according to a first embodiment. [Figure 6] 4 is a flowchart showing an example of processing performed by the magnetic resonance imaging apparatus according to the first embodiment. [Figure 7] 6 is a flowchart showing an example of a process for analyzing a region for acquiring additional MR signal data according to the first embodiment. [Figure 8] An explanatory diagram of attenuation rate and T2* value measurement. [Figure 9] FIG. 13 is a diagram illustrating a histogram of attenuation rate and T2* value. [Figure 10] 10 is a flowchart showing an example of a process for calculating optimal imaging conditions for additional MR signal data according to the first embodiment. [Figure 11] FIG. 11 is a first explanatory diagram regarding a method for calculating an additional TE. [Figure 12] FIG. 2 is a second explanatory diagram regarding the method of calculating additional TE. [Figure 13] 10 is a flowchart showing an example of processing performed by a magnetic resonance imaging apparatus according to the second embodiment. [Figure 14] 13 is a flowchart showing an example of a process for analyzing intermediate high-density data according to the second embodiment. [Figure 15] FIG. 13 is a diagram illustrating a change in histogram of attenuation rate and T2* value due to acquisition of first additional MR signal data. [Figure 16] FIG. 13 is a diagram illustrating a change in histogram of attenuation rate and T2* value due to acquisition of second additional MR signal data. [Figure 17] FIG. 11 is an explanatory diagram of data collection by a UTE imaging method according to a modified example of the second embodiment. [Figure 18] FIG. 13 is an explanatory diagram of data collection according to the UTE imaging method according to the third embodiment. [Figure 19] FIG. 13 is an explanatory diagram of T2* value measurement according to the UTE imaging method according to the third embodiment. [Figure 20] FIG. 11 is a schematic diagram showing an example of the configuration of a processing circuit of a magnetic resonance imaging apparatus according to a third embodiment. [Figure 21] 11 is a flowchart showing an example of processing performed by a magnetic resonance imaging apparatus according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, embodiments of a magnetic resonance imaging apparatus and a magnetic resonance imaging method will be described in detail with reference to the drawings.

[0010] (Overall configuration of magnetic resonance imaging device) A magnetic resonance imaging (MRI) apparatus 1 according to an embodiment can utilize magnetic resonance imaging technology. Fig. 1 is a schematic diagram showing an example of the overall configuration of the MRI apparatus 1 according to an embodiment. The MRI apparatus 1 includes a magnet stand 100, a control cabinet 300, an image processing device 400 such as a console, and a bed 500.

[0011] The magnet gantry 100 and the bed 500 are arranged, for example, in a shielded room called an examination room. On the other hand, the control cabinet 300 is arranged, for example, in a machine room, and the image processing device 400 is arranged, for example, in an operation room. Note that the image processing device 400 may be connected to the MRI apparatus 1 via a network and installed in a remote location away from the operation room.

[0012] The magnet gantry 100 includes a static magnetic field magnet 10, a gradient magnetic field coil 11, and a WB (Whole Body) coil 12. The static magnetic field magnet 10 of the magnet gantry 100 is broadly classified into a cylindrical type in which the magnet has a cylindrical magnetic structure, and an open type in which a pair of magnets are arranged above and below with an imaging space in between. Here, an MRI device 1 with a cylindrical magnet gantry 100 will be described, but an open type MRI device may also be used. Note that the open type MRI device has the same configuration as the cylindrical type MRI device 1, except that the static magnetic field magnet, gradient magnetic field coil, and WB coil that constitute the magnet gantry are parallel plate-shaped.

[0013] The static magnetic field magnet 10 has a roughly cylindrical shape and generates a static magnetic field in a bore into which the subject P is transported. The bore is the space inside the cylinder of the magnet gantry 100. The static magnetic field magnet 10 is composed of, for example, a housing for holding liquid helium, a refrigerator for cooling the liquid helium to an extremely low temperature, and a superconducting coil inside the housing. The static magnetic field magnet 10 may be composed of a permanent magnet. Below, a case where the static magnetic field magnet 10 has a superconducting coil will be described.

[0014] The static magnetic field magnet 10 has a built-in superconducting coil, which is cooled to an extremely low temperature by liquid helium. In the excitation mode, the static magnetic field magnet 10 generates a static magnetic field by applying a current supplied from a static magnetic field power supply to the superconducting coil. After that, when the mode is switched to the persistent current mode, the static magnetic field power supply is disconnected. Once in the persistent current mode, the static magnetic field magnet 10 continues to generate a static magnetic field for a long time, for example, for more than one year.

[0015] The gradient magnetic field coil 11 has a roughly cylindrical shape like the static magnetic field magnet 10, and is placed inside the static magnetic field magnet 10. The gradient magnetic field coil 11 is composed of three gradient magnetic field coils for the X-axis, Y-axis, and Z-axis. Each gradient magnetic field coil is supplied with a gradient magnetic field current (power) from a gradient magnetic field power supply 31 (31x for the X-axis, 31y for the Y-axis, and 31z for the Z-axis), thereby generating gradient magnetic fields in the X-axis, Y-axis, and Z-axis directions and applying them to the subject P. Here, the Z-axis direction is the direction along the static magnetic field, the Y-axis direction is the vertical direction, and the X-axis direction is the direction perpendicular to the Z-axis and Y-axis.

[0016] The WB coil 12 is also called a whole-body coil, and is disposed inside the gradient magnetic field coil 11 in a generally cylindrical shape so as to surround the subject P. The WB coil 12 functions as a transmitting coil. That is, the WB coil 12 transmits RF pulses to the subject P in accordance with radio frequency (RF) signals transmitted from the RF transmitter 32. Meanwhile, the WB coil 12 may also function as a receiving coil in addition to functioning as a transmitting coil that transmits RF pulses. In that case, the WB coil 12 serves as a receiving coil to receive MR signals emitted from the subject P due to excitation of atomic nuclei.

[0017] The MRI apparatus 1 may include a local coil 20 in addition to the WB coil 12. The local coil 20 is placed close to the body surface of the subject P. The local coil 20 may include a plurality of coil elements. There are several types of local coils 20, such as a head coil, a chest coil, an abdominal coil, a spine coil, and a knee coil. Note that, although FIG. 1 shows a case where the local coil 20 is a chest coil, the present invention is not limited to this case.

[0018] The local coil 20 functions as a receiving coil. That is, the local coil 20 receives the above-mentioned MR signal. The local coil 20 may be a transmitting / receiving coil having a function as a transmitting coil that transmits RF pulses in addition to the function as a receiving coil that receives MR signals. That is, the local coil 20 may be a transmitting-only coil, a receiving-only coil, or a coil for both transmitting and receiving.

[0019] The bed 500 includes a bed body 50 and a tabletop 51. The bed body 50 can move the tabletop 51 in the vertical and horizontal directions, and moves the subject P placed on the tabletop 51 to a predetermined height before imaging. Thereafter, during imaging, the tabletop 51 is moved horizontally to move the subject P into the bore.

[0020] The control cabinet 300 includes gradient magnetic field power supplies 31 (for the X-axis 31x, for the Y-axis 31y, and for the Z-axis 31z), an RF transmitter 32, an RF receiver 33, and a sequence controller .

[0021] The gradient magnetic field power supply 31 includes gradient magnetic field power supplies 31x, 31y, and 31z for each channel that drive coils that generate gradient magnetic fields in the X-axis direction, the Y-axis direction, and the Z-axis direction, respectively. The gradient magnetic field power supplies 31x, 31y, and 31z output required currents independently for each channel in response to a command from a sequence controller 34.

[0022] The RF transmitter 32 generates a high-frequency signal based on an instruction from a sequence controller 34. The RF transmitter 32 transmits the generated high-frequency signal to the WB coil 12 and the local coil 20.

[0023] The MR signals received by the WB coil 12 and the local coil 20 are transmitted to the RF receiver 33. The RF receiver 33 performs analog-to-digital (AD) conversion on the MR signals from the WB coil 12 and the local coil 20 and outputs them to a sequence controller 34. The digitally converted MR signals are sometimes called raw data.

[0024] The sequence controller 34, under the control of the image processing device 400, drives the gradient magnetic field power supply 31, the RF transmitter 32, and the RF receiver 33 to image the subject P. When raw data is received from the RF receiver 33 by imaging, the sequence controller 34 transmits the raw data to the image processing device 400.

[0025] The sequence controller 34 includes a processing circuit (not shown). The processing circuit is configured with hardware such as a processor that executes a predetermined program, a field programmable gate array (FPGA), or an application specific integrated circuit (ASIC).

[0026] Next, a description will be given of the image processing device 400. The image processing device 400 includes a processing circuit 40, a memory circuit 41, a display 42, an input interface 43, and a communication circuit 44.

[0027] The processing circuitry 40 has a dedicated or general-purpose processor, and realizes various functions by software processing by executing a program stored in the storage circuitry 41 or directly built into the processing circuitry 40. The processing circuitry 40 realizes the function of controlling the operation of the sequence controller 34, and performing imaging according to a pulse sequence to generate an MR image. The processing circuitry 40 may be configured with hardware such as an FPGA or an ASIC. Various functions described later can also be realized by such hardware. Moreover, the processing circuitry 40 may realize various functions by combining software processing and hardware processing.

[0028] The storage circuitry 41 includes semiconductor memory elements such as a random access memory (RAM) and a flash memory, a hard disk, an optical disk, etc. The storage circuitry 41 may include a portable medium such as a universal serial bus (USB) memory and a digital video disk (DVD). The storage circuitry 41 stores various processing programs used in the processing circuitry 40, data required for executing the programs, and medical images.

[0029] The display 42 is configured by a general display output device such as a liquid crystal display or an OLED (Organic Light Emitting Diode) display. The display 42 displays various information under the control of the processing circuit 40. The display 42 is a display device, and may also be a GUI (Graphical User Interface) capable of receiving various operations from a user, such as a touch panel.

[0030] The input interface 43 includes an input device that can be operated by a user, and an input circuit that inputs a signal from the input device. The input device can be realized by a trackball, a switch, a mouse, a keyboard, a touchpad, a touchscreen, a non-contact input device using an optical sensor, a voice input device, etc. When the input device is operated by a user, the input circuit generates a signal according to the operation and outputs it to the processing circuit 40.

[0031] The communication circuit 44 includes an interface for performing communication connected to a network in a wired or wireless manner. The communication circuit 44 can exchange various data between the network and the memory circuit 41, for example.

[0032] The image processing device 400 controls the entire MRI apparatus 1 using these components. Specifically, imaging conditions and other various information and instructions are received by a user such as an examiner operating an input interface 43 such as a mouse and a keyboard. The processing circuitry 40 then causes the sequence controller 34 to execute a scan based on the input imaging conditions, while reconstructing an image based on data transmitted from the sequence controller 34. The reconstructed image is displayed on a display 42 or stored in a memory circuitry 41.

[0033] (UTE Imaging) The MRI device 1 enables scanning by the UTE imaging method. The UTE imaging method is an imaging method performed using a pulse sequence in which the time from application of an RF excitation pulse to acquisition of MR signal data, i.e., TE, is set to be very short. The UTE imaging method, for example, uses a gradient echo (GRE) type pulse sequence to fill the K-space radially in 2D and cush-ball-shaped in 3D, thereby achieving a T2 * Although the following description is given using a multi-echo UTE imaging method, the UTE imaging method may be a UTE imaging method in which multiple MR signals with different TEs are acquired using a single-echo pulse sequence.

[0034] Here, FIG. 2 shows a T2 * FIG. 2(A) is an explanatory diagram of the measurement of T2 value by one multi-echo UTE imaging scan. * In the case of low-density data collection, T2 * In tissues that show a short value, i.e., a steep attenuation of MR signals, T2 * There was not enough data available to measure a reliable T2 * It becomes difficult to measure the value.

[0035] In addition, Figure 2(B) shows the T2 * In the case of conventional high-density data acquisition to obtain T2 value measurement data, the number of echoes is set to 8, and high-density data acquisition is performed by six multi-echo UTE scans. In Fig. 2(B), the T2 value measurement data obtained by the first scan is * The measured data is shown in hatching. As shown in FIG. 2(B), in the case of conventional high-density data collection, MR signals are acquired at multiple additional TEs delayed by a preset constant ΔTE. Therefore, T2 * In some cases, the additional TE appropriate for the attenuation of MR signals from tissues, etc. from which value measurement data is to be collected may not be set.

[0036] Also, T2 * In tissues that show a short value, i.e., a steep attenuation of MR signals, T2 * To obtain a sufficient amount of data for measuring the T2 value, the number of scans must be increased, which may result in longer imaging times. * Data with a lot of noise after attenuation of MR signals from tissues with short values ​​is also T2 * This will be used as the measurement data for T2 * The accuracy of the measurement data may be reduced.

[0037] Thus, in conventional UTE imaging, T2 * The measurement precision for the value may not be sufficient. Similarly, R2 * Therefore, in the MRI apparatus 1 according to the embodiment, in the additional scan among the multiple scans by the UTE imaging method, the T2 * The TE is set to improve the measurement precision for the value.

[0038] (First embodiment) Fig. 3 is an explanatory diagram of data collection by the UTE imaging method according to the first embodiment. In Fig. 3, data collection by the UTE imaging method according to the first embodiment is performed by three scans, namely, an initial scan, a first additional scan, and a second additional scan, with the number of multi-echoes in 1TR being 6. Data is collected from the first echo to the sixth echo of the initial scan in TE1 to TE6, respectively. Note that the number of multi-echoes is not limited to 6 and may be any number of echoes.

[0039] In the case of three scans, the initial scan, the first additional scan, and the second additional scan, the multi-echo UTE imaging method may be used for all scans, for example. Also, each scan may be performed by a combination of the multi-echo UTE imaging method and the single-echo UTE imaging method, such that the multi-echo UTE imaging method is used for the initial scan, the single-echo UTE imaging method is used for the first additional scan, and the single-echo UTE imaging method is used for the second additional scan. Also, the number of additional scans is not limited to two, and may be one, or three or more.

[0040] 3, data collection of the first echo in the first additional scan is performed at a first additional TE1 delayed by ΔTE1 from TE1. In this manner, data collection of the first echo to the sixth echo in the first additional scan is performed at a plurality of additional TEs delayed by ΔTE1 from TE1 to TE6 of the first echo to the sixth echo in the initial scan.

[0041] Moreover, data collection of the first echo of the second additional scan is performed at the second additional TE1 delayed by ΔTE2 from TE1. In this manner, data collection of the first echo to the sixth echo of the second additional scan is performed at a plurality of additional TEs delayed by ΔTE2 from TE1 to TE6 of the first echo to the sixth echo of the initial scan.

[0042] In other words, the interval between multiple additional TEs of the UTE imaging method set for acquiring additional MR signal data is the same as the interval between multiple TEs of the UTE imaging method set for acquiring the initial MR signal data.

[0043] FIG. 4 shows a T2 * FIG. 4 is a signal decay curve when the data collection of FIG. 3 is performed, and the data collection of the first scan is shown by hatching. As shown in FIG. 4, T2 * When the additional TE suitable for the attenuation of the MR signal of the tissue from which the measurement data is to be collected is set, that is, when the optimal additional TE according to the measurement target is set, T2 * This improves the measurement accuracy of T2 values. * In order to ensure a sufficient amount of data for measuring the T2 value, the number of scans must be increased to prevent the imaging time from becoming too long. * The setting of additional TE to improve the measurement accuracy regarding the value will be described in detail below.

[0044] Fig. 5 is a schematic diagram showing an example of the configuration of the processing circuitry 40 of the MRI apparatus 1 according to the first embodiment. As shown in Fig. 5, the processing circuitry 40 of the first embodiment realizes each of the functions of an imaging condition setting function F1, a data acquisition function F2, an additional analysis function F3, an imaging condition calculation function F4, a high-density data generation function F5, and a map generation function F6. The configuration and operation of each function of the processing circuitry 40 of the first embodiment will be described with reference to Figs. 6 to 12. First, the subject P is placed on the top board 51 of the bed 500 and accommodated in a static magnetic field.

[0045] In step ST10, the imaging condition setting function F1 sets imaging conditions for the first scan, including multiple TEs, using the UTE imaging method. The imaging conditions are set, for example, by a user's operation via the input interface 43 or by reading out imaging conditions previously stored in the storage circuitry 41. As the imaging conditions, for example, the number of multi-echoes, TE, TR, the number of additions, a matrix size used for resolution setting, a slice thickness, FOV (Field Of View), etc. may be set.

[0046] In step ST20, the data acquisition function F2 acquires MR signal data of the first scan under set imaging conditions including a plurality of TEs.

[0047] In step ST30, the additional analysis function F3 performs an analysis to identify a region where additional MR signal data needs to be acquired based on the acquired MR signal data of the initial scan. Here, Fig. 7 is a flowchart showing an example of a process for analyzing a region where additional MR signal data is acquired in step ST30. As shown in Fig. 7, step ST30 is composed of, for example, steps ST301 to ST303.

[0048] In step ST301, an attenuation rate map of the MR signal data of the acquired first scan is calculated. Here, the attenuation rate and T2 * FIG. 8(A) shows three different attenuation values ​​(i.e., three different T2 * FIG. 8(A) illustrates an attenuation map of MR signal data of a first scan corresponding to a phantom having a T2 value. In FIG. 8(A), the attenuation rates are different in each of the regions A0, A1, A2, and A3. 0% in FIG. 8(A) means no attenuation. Note that within each of the regions A0, A1, A2, and A3, there is a uniform attenuation rate (i.e., a uniform T2 value). * It is assumed that the value of

[0049] In addition, for the sake of convenience, the following description will be given using an example in which the imaging target is a phantom as described above, but the imaging target is not limited to this, and generality is not lost even if the imaging target is a human body.

[0050] In FIG. 8B, the signal decay curves of the regions A1, A2, and A3 are depicted. As shown in FIG. 8B, the decay rate is relatively small, i.e., T2 * In the region A1 where the value is relatively long, the T2 * A sufficient amount of data has been acquired from the initial MR signal data for value measurement.

[0051] On the other hand, the decay rate is large, i.e., T2 * In the areas A2 and A3 where the values ​​are short, the T2 * In other words, the amount of data acquired from the MR signal data of the first scan is not sufficient for the measurement of the T2 * The measurement accuracy of the MR signal measurement is low in the regions A2 and A3, so an analysis is performed to identify regions where additional MR signal data needs to be acquired.

[0052] In step ST302, the decay rate and T2 * A decay rate distribution is generated that shows the decay rate and the T2 * The attenuation rate distribution may be generated for the entire region of the MR signal data of the first scan. Alternatively, the attenuation rate distribution may be generated for a region designated on the attenuation rate map of the first MR signal data by a user operation via the input interface 43.

[0053] Here, using Figure 9, the attenuation rate and T2 * The histogram of the decay rate of the T2 value in FIG. 9 shows the histogram of the T2 value in FIG. * In the regions A2 and A3 where the values ​​are short, the decay rate and T2 *9 is an example of an attenuation rate distribution in which the attenuation rate is expressed as a 3D histogram of the values ​​of the input and output signals. In the histogram in FIG. 9, the attenuation rate is large, for example, from 80% to 100%.

[0054] Also, in the histogram of Fig. 9, the decay rate is different, i.e. T2 * Although the histograms for the two regions A2 and A3 have different values, T2 * There are two types of T2 because the values ​​vary. * It is difficult to confirm the peak in the T2 value. * Because the values ​​vary, T2 * When the peak of the value is difficult to confirm, it is also said that the uniformity of the attenuation rate distribution is low. In step ST303, a region where the attenuation rate is large and the uniformity of the attenuation rate distribution is low is specified as a region where additional MR signal data needs to be acquired.

[0055] 6, in step ST40, the imaging condition calculation function F4 calculates at least one additional TE for acquiring additional MR signal data delayed by ΔTE from at least one TE in the initial MR signal data in the region where the specified additional MR signal data needs to be acquired. Here, ΔTE is, for example, a value smaller than the difference between TE1 of the first echo and TE2 of the second echo of the initial MR signal data.

[0056] That is, the imaging condition calculation function F4 calculates an additional TE used to acquire MR signal data of a first echo, among at least one additional TE for acquiring additional MR signal data, so that the additional TE is included between the first echo and the second echo of the initial MR signal data.

[0057] Fig. 10 is a flowchart showing a process example of calculating optimal imaging conditions for additional MR signal data. Fig. 11 and Fig. 12 are explanatory diagrams of a method of calculating additional TE. Here, as shown in Fig. 10, step ST40 is composed of, for example, steps ST401 to ST405.

[0058] In step ST401, the imaging condition calculation function F4 calculates the T2 of the multiple time constant components based on the initial MR signal data in the region where the specified additional MR signal data needs to be acquired. * Dominant time constant T2 approximated by the damping model * Calculate the value T2 * The damping model is a multiple time constant component with T2S * Includes components related to values. Multiple time constant components T2 * The signal strength equation based on the attenuation model is given, for example, by equation (1).

[0059]

number

[0060] Here, T2S * Value is short T2 * Relaxation time of the component, A21 has a short T2 * Component signal strength, T2L * Value is long T2 * Relaxation time of the component, A22 has a long T2 * The signal intensity of the component, n(TE) represents other components such as noise in TE. Based on the TE and signal intensity of each echo acquired in the initial MR signal data, the T2 * The dominant time constant T2 was determined by using a nonlinear least squares method for the damping model. * value, i.e. T2S * The value is calculated.

[0061] In step ST402, the imaging condition calculation function F4 calculates the dominant time constant T2 * Based on the signal decay curve of the value, the signal strength is estimated and divided into a plurality of threshold intervals, which may be at least four threshold intervals, as shown in the first to fourth threshold intervals in FIG.

[0062] As shown in Fig. 11, the threshold is divided into four threshold sections, namely, first to fourth. Specifically, when the signal intensity in the first echo of the initial MR signal data is set as the upper limit Y0 of the first threshold section, the upper limit Y1 of the second threshold section is set as Y1 = Y0 exp(-1 / 2). Similarly, the upper limit Y2 of the third threshold section is set as Y2 = Y0 exp(-1). Moreover, the upper limit Y3 of the fourth threshold section is set as Y3 = Y0 exp(-2), and the lower limit Y4 of the fourth threshold section is set as Y4 = Y0 exp(-3).

[0063] In step ST403, the imaging condition calculation function F4 calculates an estimated T2 for each TE between the first and second echoes of the initial MR signal data. * Estimated T2 based on density * Generate density distribution. Estimate T2 * Density is the estimated T2 at a particular TE that falls within a given threshold category. * Upper limit of values ​​and estimated T2 * The predetermined threshold division is, for example, at least one of the first to fourth threshold divisions divided in step ST402.

[0064] Here, the signal decay curve shown by the solid line in FIG. 11 is a curve with a dominant time constant T2 * The calculated T2S value * Value (e.g., T2Sa * value) in equation (1) * The signal decay curves shown by the dashed lines in FIG. 11 are the signal decay curves given by the dominant time constant T2 * The calculated T2S value * Multiple T2 values ​​are changed slightly * Value (e.g., T2Sb * value) in equation (1) * The signal decay curves shown by the dashed lines are generated by applying the T2S * The values ​​of the parameters other than the value are the same as those of the signal attenuation curve shown by the solid line, for example.

[0065] In Figure 11, when TE is TEa, the estimated T2 * The upper limit of the value is T2Sb * The value is the estimated T2 * The lower limit of the value is T2Sa * In FIG. 11, the estimated T2 * Density is T2Sb * Value and T2Sa * Similarly, the estimated T2 for each TE is expressed as the difference between the * By calculating the density, the estimated T2 * A density distribution is generated.

[0066] In step ST404, the estimated T2 * Estimated T2 based on density distribution * A probability density distribution is generated. Estimate T2 * The probability density distribution is, for example, as shown in FIG. * The density distribution is generated by analyzing it according to, for example, a gamma distribution model.

[0067] In step ST405, at least one additional TE delayed by ΔTE from at least one TE in the initial MR signal data is calculated. Specifically, the imaging condition calculation function F4, for example, arranges an additional TE used to acquire the MR signal data of the first echo among at least one additional TE for acquiring the additional MR signal data between the first echo and the second echo of the initial MR signal data. The additional TE used to acquire the MR signal data of the first echo is calculated by delaying the estimated T2 by ΔTE in a predetermined threshold section among the divided multiple threshold sections. * Estimate T2 based on probability density distribution * It is calculated so that the probability density is highest.

[0068] 6, in step ST50, the imaging condition setting function F1 further sets imaging conditions including at least one additional TE using the UTE imaging method. As for the other imaging conditions, for example, the imaging conditions set in step ST10 are set.

[0069] In step ST60, the data acquisition function F2 further acquires additional MR signal data under set imaging conditions including at least one additional TE.

[0070] In step ST70, the high density data generating function F5 generates intermediate high density data by combining the initial MR signal data and the additional MR signal data as final high density data.

[0071] In step ST80, the map generation function F6 calculates T2 * Calculate the T2 value. * The map generation function F6 also generates a map based on the final high-density data. * Map plus R2 * You can generate a map or T2 * Maps and R2 * Any of the maps may be generated.

[0072] According to the MRI apparatus 1 according to the first embodiment, T2 * The additional TE suitable for the attenuation of the MR signal of the tissue from which the value measurement data is to be collected is set. By setting the additional TE suitable for the attenuation of the MR signal, the T2 * The measurement accuracy for the value is improved. Similarly, R2 * Furthermore, according to the MRI apparatus 1 according to the first embodiment, in addition to the initial MR signal data, the measurement accuracy of the T2 * Additional MR signal data from tissues with short values ​​are also acquired, so the generated T2 * In the map, a wide dynamic range of, for example, 0.3 to 10 [ms] can be achieved.

[0073] Second embodiment FIG. 13 is a flowchart showing an example of processing of the MRI apparatus 1 according to the second embodiment. As shown in FIG. 13, the second embodiment is different from the first embodiment in that it determines whether or not acquisition of additional MR signal data is necessary, and generates intermediate high-density data by synthesizing the initial MR signal data and the additional MR signal data. Other configurations and operations are not substantially different from those of the first embodiment shown in FIG. 1 and FIG. 5, so that the same configurations are denoted by the same reference numerals and redundant explanations are omitted. The configuration and operation of each function of the processing circuitry 40 of the second embodiment will be described using the flowchart of FIG. 13.

[0074] Steps ST10, ST20, and ST30 in the second embodiment are not substantially different from steps ST10, ST20, and ST30 in the first embodiment, and therefore overlapping descriptions will be omitted. In the second embodiment, step ST30 is followed by step ST31. Here, for ease of understanding, step ST31 after step ST30 is referred to as step ST31A, and step ST31 after step ST66 described later is referred to as step ST31B.

[0075] In step ST31A, the additional analysis function F3 performs an analysis to determine whether or not acquisition of additional MR signal data is necessary. The determination of whether or not acquisition of additional MR signal data is necessary is performed in the region where acquisition of additional MR signal data is necessary, which is identified by the additional analysis function F3 in step ST30. The region where acquisition of additional MR signal data is necessary is a region identified based on the attenuation rate of the initial MR signal data and the attenuation rate distribution representing the relationship between the attenuation rate and the T2* value.

[0076] In step ST31A, the additional analysis function F3 determines that acquisition of additional MR signal data is necessary, for example, when the attenuation rate of the initial MR signal data is steeper than a first predetermined attenuation rate. The first predetermined attenuation rate may be, for example, about 70% or more. If it is determined that acquisition of additional MR signal data is necessary (i.e., YES in step ST31A), the process proceeds to step ST40. Here, for ease of understanding, step ST40 after step ST31A is referred to as step ST40A, and step ST40 after step ST31B described later is referred to as step ST40B.

[0077] Steps ST40A, ST50, and ST60 in the second embodiment are not substantially different from steps ST40, ST50, and ST60 in the first embodiment, and therefore will not be described again. In the second embodiment, after step ST60, the process proceeds to step ST65.

[0078] In step ST65, the high density data generating function F5 generates intermediate high density data by combining the initial MR signal data and the additional MR signal data. Note that the high density data in step ST65 is not the final high density data, unlike step ST70 in the first embodiment. Note that before the additional MR signal data is acquired, the initial MR signal data becomes the intermediate high density data. Then, after step ST65, the process proceeds to step ST66.

[0079] In step ST66, the additional analysis function F3 performs an analysis based on the synthesized intermediate high-density data to determine whether or not additional MR signal data needs to be acquired. Here, Fig. 14 is a flowchart showing an example of a process for analyzing intermediate high-density data according to the second embodiment. As shown in Fig. 14, step ST66 is composed of, for example, step ST661 and step ST662.

[0080] In step ST661, an attenuation rate map of the intermediate high-density data is calculated. Then, in step ST662, the attenuation rate and T2* A decay rate distribution is generated that represents the values ​​as a 2D or 3D histogram.

[0081] 15 and 16 show the attenuation rate and T2 * 15 and 16 are explanatory diagrams of changes in the histogram of the attenuation rate and T2 value in the two regions A2 and A3 in FIG. 8(A) in the same manner as FIG. 9. * 13 is an example of a decay rate distribution shown in a 3D histogram of the values.

[0082] In the histogram of FIG. 15, the attenuation rate is large at about 80%, but compared to the histogram of FIG. 9, the attenuation rate is smaller. * Although two peaks in the value can be confirmed, T2 * The value varies widely. * The value data is unreliable.

[0083] In the histogram of Figure 16, the decay rate becomes smaller and T2 * Two peaks in the T2 * In this manner, the analysis of the intermediate high-density data is performed based on the attenuation rate of the intermediate high-density data and the attenuation rate distribution that indicates the relationship between the attenuation rate and the T2* value.

[0084] 13, after step ST66, the process proceeds to step ST31 (i.e., ST31B). Step ST31B differs from step ST31A in that the data used to determine whether or not it is necessary to acquire additional MR signal data is the initial MR signal data or the intermediate high-density data.

[0085] In step ST31B, the additional analysis function F3 determines whether or not additional MR signal data needs to be acquired. The determination of whether or not additional MR signal data needs to be acquired is performed in the region identified in step ST30 where additional MR signal data needs to be acquired.

[0086] Furthermore, the additional analysis function F3 determines that acquisition of additional MR signal data is necessary, for example, when the attenuation rate of the intermediate high-density data is steeper than a second predetermined attenuation rate. The second predetermined attenuation rate may be, for example, about 40% or more. When it is determined that acquisition of additional MR signal data is necessary (i.e., YES in step ST31B), the process proceeds to step ST40 (i.e., ST40B).

[0087] In step ST40B, the imaging condition calculation function F4 calculates at least one additional TE for acquiring additional MR signal data delayed by ΔTE from at least one TE in the intermediate high density data in the region where the specified additional MR signal data needs to be acquired. That is, step ST40B differs from step ST40A in that at least one additional TE is calculated based on the intermediate high density data.

[0088] In step ST40B, the imaging condition calculation function F4 calculates, for example, the T2 * Dominant time constant T2 approximated by the damping model * Then, calculate the dominant time constant T2 * Based on the signal decay curve of the value, the signal intensity is estimated and divided into a plurality of threshold sections. Furthermore, an additional TE used for acquiring the MR signal data of the first echo among at least one additional TE for acquiring additional MR signal data is disposed between the first echo and the second echo of the initial MR signal data. The additional TE used for acquiring the MR signal data of the first echo is set to an estimated T2 * Estimate T2 based on probability density distribution* Calculate so that the probability density is highest.

[0089] Here, as shown in FIG. 11, the imaging condition calculation function F4 calculates the dominant time constant T2 * The signal intensity may be estimated based on a signal attenuation curve of the value, and the predetermined threshold section may be divided into four threshold sections, 1st to 4th, as follows. For example, in the first step ST40B, the predetermined threshold section is set to the second threshold section having the second highest estimated signal intensity among the area sections in which the first MR signal data does not exist, and an additional TE is calculated, and MR signal data is acquired in the first additional scan. After that, when it is determined that acquisition of additional MR signal data is necessary, the predetermined threshold section is set to the first threshold section having the first highest estimated signal intensity among the area sections in which the already acquired MR signal data does not exist, and an additional TE is calculated, and MR signal data is acquired in the second additional scan.

[0090] Alternatively, in the first additional scan, the additional TE may be calculated using the predetermined threshold section as a third threshold section with the third highest estimated signal strength, and MR signal data may be acquired. Also, in the second additional scan, the additional TE may be calculated using the predetermined threshold section as a second threshold section with the second highest estimated signal strength, and MR signal data may be acquired. Furthermore, in the third additional scan, the additional TE may be calculated using the predetermined threshold section as a first threshold section with the first highest estimated signal strength, or a second threshold section with the second highest estimated signal strength, and MR signal data may be acquired.

[0091] After step ST40B, as described above, the process proceeds to steps ST50, ST60, ST65, and ST66. Note that the acquisition of MR signal data in the first additional scan and the acquisition of MR signal data in the second additional scan are performed by the data acquisition function F2 in step ST60.

[0092] In this way, the predetermined threshold divisions may be selected in an order that requires fewer additional MR signal data among the divided threshold divisions. The threshold divisions are not limited to the above-mentioned four, and may be divided into more than four threshold divisions. The additional MR signal data is not limited to the above-mentioned one additional data or two additional data, i.e., the first and second additional data, but may be acquired more than that, as long as it is determined that acquisition of additional MR signal data is necessary.

[0093] Moreover, if it is determined in steps ST31A and ST31B that acquisition of additional MR signal data is not necessary (ie, NO in steps ST31A and ST31B), the process proceeds to step ST70.

[0094] Steps ST70 and ST80 in the second embodiment are not substantially different from steps ST70 and ST80 in the first embodiment, and therefore overlapping descriptions will be omitted.

[0095] According to the MRI apparatus 1 of the second embodiment, the same effect as that of the first embodiment can be obtained. In the second embodiment, in addition to the initial MR signal data, an analysis is performed to determine whether or not additional MR signal data needs to be acquired using intermediate high-density data. Therefore, T2 * Value measurement and R2 * This improves the measurement accuracy in T2 value measurement and enables the acquisition of sufficient additional MR signal data. * A sufficient amount of data can be secured to measure the value.

[0096] (Modification of the second embodiment) Fig. 17 is an explanatory diagram of data collection by the UTE imaging method according to a modified example of the second embodiment. In Fig. 17, data collection by the first scan is performed with the number of multi-echoes within 1TR being 6. Data collection by the first additional scan and the second additional scan is performed with the number of multi-echoes within 1TR being 2. The same TR is used for each of the three scans, the first additional scan, and the second additional scan.

[0097] That is, the modified example of the second embodiment is different from the second embodiment in that the number of multi-echoes in the UTE imaging method set for acquiring additional MR signal data is smaller than the number of multi-echoes in the UTE imaging method set for acquiring the initial MR signal data. Other configurations and operations are substantially the same as those of the second embodiment, so that redundant explanations will be omitted.

[0098] According to the MRI apparatus 1 according to the modified example of the second embodiment, the same effect as that of the second embodiment can be obtained. In the modified example of the second embodiment, as in the second embodiment, the TRs in the three scans, the initial scan, the first additional scan, and the second additional scan, are the same, so the imaging time does not change. However, unlike the second embodiment, in the modified example of the second embodiment, in the additional scans, T2 * Data with a lot of noise components after attenuation of MR signals from tissues with short values, etc., are processed using T2 * Therefore, the T2 * The accuracy of the value measurement data may be improved.

[0099] (Third embodiment) FIG. 18 is an explanatory diagram of data acquisition by the UTE imaging method according to the third embodiment. FIG. 19 is a diagram of T2 * Fig. 19 is a signal decay curve when the data collection of Fig. 18 is performed, and the data collection of the first scan is indicated by hatching.

[0100] 18 and 19, data collection by the initial scan is performed with the number of multi-echoes within 1TR set to 6. Data collection by the first additional scan and the second additional scan is performed with the number of multi-echoes within 1TR set to 2. The same TR is used for each of the three scans, namely, the initial scan, the first additional scan, and the second additional scan. Note that the TR may be different for each additional scan.

[0101] That is, the third embodiment differs from the modified example of the second embodiment shown in Fig. 17 in that a repetition time (TR) of the UTE imaging method set for acquiring additional MR signal data is shorter than the TR of the UTE imaging method set for acquiring initial MR signal data. Also, the third embodiment differs from the second embodiment in that the number of multi-echoes of the UTE imaging method set for acquiring additional MR signal data is smaller than the number of multi-echoes of the UTE imaging method set for acquiring initial MR signal data.

[0102] Fig. 20 is a schematic diagram showing a configuration example of the processing circuitry 40 of the MRI apparatus 1 according to the third embodiment. As shown in Fig. 20, the processing circuitry 40 of the third embodiment is different from the processing circuitry 40 of the second embodiment in that it further realizes a signal correction function F7 that corrects the signal intensity of additional MR signal data. The configuration and operation of each function of the processing circuitry 40 of the third embodiment will be described with reference to the flowchart of Fig. 21.

[0103] Steps ST10, ST20, and ST30 of the third embodiment are not substantially different from steps ST10, ST20, and ST30 of the second embodiment, so duplicated explanations will be omitted. In the third embodiment, after step ST30, the process proceeds to step ST31. Then, if the answer is YES in step ST31, the process proceeds to step ST40.

[0104] For ease of understanding, step ST31 after step ST30 will be referred to as step ST31A, and step ST40 after step ST31A will be referred to as step ST40A. Moreover, step ST31 after step ST66 (described later) will be referred to as step ST31B, and step ST40 after step ST31B will be referred to as step ST40C.

[0105] Steps ST31A, ST40A, ST50, and ST60 in the third embodiment are not substantially different from steps ST31A, ST40A, ST50, and ST60 in the second embodiment, and therefore will not be described again. In the third embodiment, after step ST60, the process proceeds to step ST61.

[0106] In step ST61, the signal correction function F7 corrects the signal intensity of the additional MR signal data. As described above, in the UTE imaging method, for example, a GRE-based pulse sequence is used. The signal intensity formula Sig in a general spoiled GRE method is given by formula (2) when TR>>T2, with an RF pulse having an initial signal intensity M0 and a flip angle θ°. Note that in the GRE-based pulse sequence, T2 is used instead of T2 due to the influence of magnetic field inhomogeneity, etc. * It becomes.

[0107]

number

[0108] As shown in formula (2), the signal intensity is different between the initial MR signal data and the additional MR signal data, which have different TRs. Therefore, the signal intensity of the additional MR signal data needs to be corrected. The signal correction function F7 calculates a signal correction coefficient that minimizes an error between the change in signal intensity between multiple TEs in the initial MR signal data and the additional MR signal data actually acquired, and the change in signal intensity between multiple TEs calculated from a simulation using a theoretical formula under the imaging conditions of the initial MR signal data and the imaging conditions of the additional MR signal data, and corrects the signal intensity of the additional MR signal data. In the third embodiment, after step ST61, the process proceeds to step ST65.

[0109] Step ST65, step ST66, and step ST31 (i.e., ST31B) after step ST66 in the third embodiment are not substantially different from step ST65 and step ST31B in the second embodiment, so duplicated explanations will be omitted. In the third embodiment, after step ST31, the process proceeds to step ST40 (i.e., ST40C).

[0110] In step ST40C, the imaging condition calculation function F4 sets the TR for acquiring additional MR signal data to be shorter than the TR for acquiring the initial MR signal data, and sets the number of multi-echoes for acquiring the additional MR signal data to be smaller than the number of multi-echoes for acquiring the initial MR signal data.

[0111] The imaging condition calculation function F4 calculates at least one additional TE for acquiring additional MR signal data delayed by ΔTE from at least one TE in the initial MR signal data in the region where the specified additional MR signal data needs to be acquired. Then, after step ST40C, as described above, the process proceeds to steps ST50, ST60, ST61, ST65, and ST66.

[0112] Moreover, if it is determined in steps ST31A and ST31B that acquisition of additional MR signal data is not necessary (ie, NO in steps ST31A and ST31B), the process proceeds to step ST70.

[0113] Steps ST70 and ST80 in the third embodiment are not substantially different from steps ST70 and ST80 in the second embodiment, and therefore overlapping descriptions will be omitted.

[0114] According to the MRI apparatus 1 of the third embodiment, the same effect as that of the modified example of the second embodiment can be obtained. Moreover, in the third embodiment, the number of multi-echoes for acquiring additional MR signal data is smaller than the number of multi-echoes for acquiring initial MR signal data, and the TR for acquiring the additional MR signal data is shorter than the TR for acquiring initial MR signal data, so that the imaging time can be further shortened.

[0115] According to at least one of the magnetic resonance imaging apparatuses according to the above-described embodiments, T2 * The measurement accuracy regarding the value can be improved.

[0116] In the above embodiment, the term "processor" refers to a circuit such as a dedicated or general-purpose CPU (Central Processing Unit), GPU (Graphics Processing Unit) or an Application Specific Integrated Circuit (ASIC), a programmable logic device (e.g., a Simple Programmable Logic Device (SPLD), a Complex Programmable Logic Device (CPLD), and a Field Programmable Gate Array (FPGA)).

[0117] When the processor is, for example, a CPU, the processor realizes various functions by reading and executing a program stored in a memory circuit. When the processor is, for example, an ASIC, instead of storing a program in a memory circuit, a function corresponding to the program is directly built into the circuit of the processor as a logic circuit. In this case, the processor realizes various functions by hardware processing that reads and executes the program built into the circuit. Alternatively, the processor can realize various functions by combining software processing and hardware processing.

[0118] In the above embodiment, an example was shown in which a single processor of the processing circuit realizes each function, but a processing circuit may be configured by combining multiple independent processors, and each processor may realize each function. In addition, when multiple processors are provided, a memory circuit for storing a program may be provided for each processor, or one memory circuit may collectively store programs corresponding to the functions of all the processors.

[0119] It should be noted that the imaging condition setting function F1, data acquisition function F2, additional analysis function F3, imaging condition calculation function F4, high-density data generation function F5, map generation function F6, and signal correction function F7 in the description of the embodiments are examples of the imaging condition setting section, data acquisition section, additional analysis section, imaging condition calculation section, high-density data generation section, map generation section, and signal correction section, respectively, as described in the claims.

[0120] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope of the invention and its equivalents described in the claims, as well as in the scope and spirit of the invention. [Explanation of symbols]

[0121] 1...Magnetic Resonance Imaging (MRI) device F1...Imaging condition setting function F2...Data acquisition function F3...Additional analysis function F4...Imaging condition calculation function F5...High-density data generation function F6...Map generation function F7...Signal correction function

Claims

1. an imaging condition setting unit that sets imaging conditions including a plurality of echo times (TEs) using an Ultrashortened Echo Time (UTE) imaging method; A data acquisition unit that acquires initial MR signal data at a plurality of set TEs; an additional analysis unit that performs an analysis based on the acquired initial MR signal data to identify a region that requires acquisition of additional MR signal data; and an imaging condition calculation unit that calculates at least one additional TE (Additional Echo Time) for acquiring the additional MR signal data delayed by ΔTE from at least one TE in the initial MR signal data in the specified region where acquisition of the additional MR signal data is required, The imaging condition setting unit further sets imaging conditions including the at least one additional TE by using an UTE imaging method, and the data acquisition unit further acquires the additional MR signal data with the at least one additional TE. Magnetic resonance imaging device.

2. The UTE imaging method is a multi-echo UTE imaging method; 2. A magnetic resonance imaging apparatus according to claim 1.

3. The additional analysis unit calculates the decay rate of the initial MR signal data, and the decay rate and T2 ＊ a region in which acquisition of the additional MR signal data is required is identified based on an attenuation rate distribution representing a relationship between the attenuation rate distribution and the value, and an analysis is performed to determine whether acquisition of the additional MR signal data is required.

2. A magnetic resonance imaging apparatus according to claim 1.

4. the additional analysis unit determines that acquisition of the additional MR signal data is necessary when an attenuation rate of the initial MR signal data is steeper than a first predetermined attenuation rate; 4. A magnetic resonance imaging apparatus according to claim 3.

5. the imaging condition calculation unit calculates an additional TE used for acquiring MR signal data of a first echo, among the at least one additional TE for acquiring the additional MR signal data, so that the additional TE is included between a first echo and a second echo of the initial MR signal data; 2. A magnetic resonance imaging apparatus according to claim 1.

6. The imaging condition calculation unit calculates a T2 of a plurality of time constant components based on the initial MR signal data in the specified region where the additional MR signal data needs to be acquired. ＊ Dominant time constant T2 approximated by the damping model ＊ Calculate the value, The dominant time constant T2 ＊ Based on the signal decay curve of the value, the signal strength is estimated and divided into a plurality of threshold intervals; The additional TE used for acquiring the MR signal data of the first echo among the at least one additional TE for acquiring the additional MR signal data is set to an estimated T2 ＊ Based on the probability density distribution, the estimated T ＊ Calculate so that the probability density is highest 2. A magnetic resonance imaging apparatus according to claim 1.

7. The plurality of threshold intervals is at least four threshold intervals.

7. A magnetic resonance imaging apparatus according to claim 6.

8. The imaging condition calculation unit calculates the dominant time constant T2 ＊ Based on the signal decay curve of the value, the signal strength is estimated and divided into four threshold sections; Among at least one additional TE for acquiring the first additional MR signal data, an additional TE used for acquiring the MR signal data of a first echo is set to an estimated T2 between the first echo and the second echo of the initial MR signal data in a second threshold section in which the estimated signal intensity is the second highest or in a third threshold section in which the estimated signal intensity is the third highest among the region sections in which the initial MR signal data does not exist. ＊ Based on the probability density distribution, the estimated T ＊ Calculate so that the probability density is highest, The data acquisition unit acquires first additional MR signal data.

8. A magnetic resonance imaging apparatus according to claim 7.

9. The imaging condition calculation unit further calculates an additional TE used to acquire MR signal data of a first echo, among at least one additional TE for acquiring second or third additional MR signal data, between a first echo and a second echo of the initial MR signal data in a first threshold section in which the estimated signal intensity is the first or a second threshold section in which the estimated signal intensity is the second, among region sections in which no already acquired MR signal data exists, by setting an estimated T2 ＊ Based on the probability density distribution, the estimated T ＊ Calculate so that the probability density is highest, The data acquisition unit further acquires second or third additional MR signal data.

9. A magnetic resonance imaging apparatus according to claim 8.

10. a high density data generating unit that generates intermediate high density data by combining the initial MR signal data and the additional MR signal data as final high density data; Based on the final high density data, T2 ＊ Map and R2 ＊ and a map generator configured to generate at least one of the maps.

2. A magnetic resonance imaging apparatus according to claim 1.

11. a high-density data generating unit that generates intermediate high-density data by combining the initial MR signal data and the additional MR signal data, 2. A magnetic resonance imaging apparatus according to claim 1.

12. The additional analysis unit calculates the attenuation rate of the intermediate high density data and the attenuation rate and T2 ＊ and performing an analysis to determine whether acquisition of the additional MR signal data is necessary based on a decay rate distribution representing a relationship between the decay rate distribution and the value.

12. A magnetic resonance imaging apparatus according to claim 11.

13. the additional analysis unit determines that acquisition of the additional MR signal data is necessary when an attenuation rate of the intermediate high density data is steeper than a second predetermined attenuation rate.

13. A magnetic resonance imaging apparatus according to claim 12.

14. The imaging condition calculation unit calculates the T2 of the multiple time constant components based on the intermediate high density data in the specified region where the additional MR signal data needs to be acquired. ＊ Dominant time constant T2 approximated by the damping model ＊ Calculate The dominant time constant T2 ＊ Based on the signal decay curve of the value, the signal strength is estimated and divided into a plurality of threshold intervals; The additional TE used for acquiring the MR signal data of the first echo among the at least one additional TE for acquiring the additional MR signal data is set to an estimated T2 ＊ Based on the probability density distribution, the estimated T ＊ Calculate so that the probability density is highest.

12. A magnetic resonance imaging apparatus according to claim 11.

15. an interval between the multiple additional TEs of the UTE imaging method set for acquiring the additional MR signal data is the same as an interval between the multiple TEs of the UTE imaging method set for acquiring the initial MR signal data; 2. A magnetic resonance imaging apparatus according to claim 1.

16. a number of multi-echoes of the UTE imaging method set for acquiring the additional MR signal data is smaller than a number of multi-echoes of the UTE imaging method set for acquiring the initial MR signal data; 3. A magnetic resonance imaging apparatus according to claim 2.

17. a repetition time (TR) of the UTE imaging method set for acquiring the additional MR signal data is shorter than a TR of the UTE imaging method set for acquiring the initial MR signal data; 2. A magnetic resonance imaging apparatus according to claim 1.

18. a signal correction unit for correcting a signal intensity of the additional MR signal data; 2. A magnetic resonance imaging apparatus according to claim 1.

19. the signal correction unit calculates a signal correction coefficient that minimizes an error between a change in signal intensity among a plurality of TEs in the acquired initial MR signal data and the additional MR signal data and a change in signal intensity among a plurality of TEs calculated from a simulation using a theoretical formula under imaging conditions for the initial MR signal data and imaging conditions for the additional MR signal data, and corrects the signal intensity of the additional MR signal data.

20. A magnetic resonance imaging apparatus according to claim 18.

20. Using the UTE imaging method, imaging conditions including a plurality of TEs are set; Acquire initial MR signal data under imaging conditions including the set multiple TEs; analyzing the acquired initial MR signal data to identify regions requiring acquisition of additional MR signal data; Calculating at least one additional TE for acquiring the additional MR signal data, which is delayed by ΔTE from at least one TE in the initial MR signal data, in the identified region in which acquisition of the additional MR signal data is required; Using a UTE imaging technique, an imaging condition including the at least one additional TE is set; acquiring the additional MR signal data under an imaging condition including the at least one additional TE; Magnetic resonance imaging methods.

Images