Accessible MRI scanner for prostrate

Abstract

Disclosed are prostate MRI systems in the form of an armchair, configured for imaging a subject's prostate and methods of using thereof. The systems include customized hardware geometries that provide one or more of maximum radiofrequency homogeneity and sensitivity along an area of interest containing the prostate; tuning of radiofrequency such that no further extensive tuning or calibration is needed per subject; and / or radiofrequency pulses sequences incorporated to enhance prostate MRI imaging. The systems include customized radiofrequency coils involving both volume coils and / or array designs that complement the geometry of the spin physics and anatomical positioning. The radiofrequency volume coils are mainly built into the seat, arms, and back of the armchair, for example as a cross-pair loop providing excellent uniformity over the prostate, while an array encircling the pelvis from below allows for proximity, optimal orientation for sensitivity, and low g-factor acceleration in the phase encode direction.

Description

[0001] ACCESSIBLE MRI SCANNER FOR PROSTRATE

[0002] CROSS REFERENCE TO RELATED APPLICATION

[0003] This application claims priority to U.S. provisional application No. 63 / 777,492, filed March 25, 2025, the disclosure of which is incorporated herein by reference.

[0004] FIELD OF THE INVENTION

[0005] The invention is in the field of diagnostic imaging, particularly magnetic resonance imaging (MRI) systems and methods for prostrate imaging.

[0006] BACKGROUND OF THE INVENTION

[0007] The lifetime risk of being diagnosed with prostate cancer is 1 / 8.

[0025] Prostate cancer is the second leading cause of cancer death among men, killing ~35k in the US every year.

[0026] At the same time, overtreatment of prostate cancer remains a major concern, as therapy (or even biopsy) can cause serious morbidity, including urinary and sexual. [27-31] Because of these statistics, it has been challenging to identify a diagnostic pathway that detects all potentially lethal disease without incurring heavy burdens in overtreatment.

[0008] In recent years, prostate magnetic resonance imaging (MRI) has emerged as a tool for identifying most clinically significant prostate cancers while mitigating overdiagnosis. The negative predictive value of MRI is unparalleled, and studies have shown that its use can result in a 50-60% increase in the detection of clinically significant cancers and also decrease the need for biopsies.[l-10] Some of these MRI procedures involve image-guided biopsies using MRI or MRLultrasound fusion technology. In fact, recent findings suggest that many “false positives” of MRI are not due to failures of MRI but rather to the unreliability of standard biopsy techniques. In one study, half the clinically significant lesions identified on MRI but not on biopsy were later found to be clinically significant on repeat biopsy. With whole gland histology, an astounding 80% of MRI “false positives” were ultimately found to harbor significant disease. [11, 12] Thus, prostate MRI utilization for biopsy naive men, has become increasingly common prior to biopsy[8, 32], Nevertheless, due largely to high cost and lack of capacity and availability, prostate MRI, is currently often reserved for those with relatively high risk of clinically significant disease (e.g., prostate-specific antigen (PSA)>4).[13, 14],

[0009] In a four-year trial of screening for prostate cancer with PSA and MRI, omitting biopsy in patients with negative MRI results eliminated more than half of diagnoses of clinically insignificant prostate cancer, and the associated risk of having incurable cancer diagnosed at screening or as interval cancer was very low (Hugosson .TH, et al. N Engl J Med

[0010] 1

[0011] 45838501.12024;391:1083-95). (Screening men 55-69 with PSA>3 is considered to provide an acceptable incremental cost effectiveness ratio (-$53,736 per QALY). [15-17] However, analysis suggests that the optimal diagnostic pathway would image more than half of males over 65, rather than the -10% who meet the current cutoff.

[0033] More specifically, analysis of the IP 1 -PROSTAGRAM study found that providing MRI to all men with PSA>1 would increase sensitivity for clinically significant prostate cancer with no increase in unproductive biopsies. However, this PSA cutoff is lower than the median PSA of men over 65 and there is insufficient MRI capacity to screen such a large cohort.

[0034] It should be noted that targeting biopsies using MRI guidance can, at the same time, decrease the overall number of biopsies. The number of potentially lethal cancers missed due to lack of access to prostate MRI will only increase as the field validates additional metrics available from these images.

[0012] The current rationing of MRI for prostate cancer diagnosis is directly related to the high cost of purchasing, maintaining, and staffing scanners. Installation of an MRI scanner costs several million dollars, while maintenance and cryogens add operational costs running well into the hundreds of thousands of US dollars. Highly trained MR technicians are needed to safely guide subjects through scan preparation, as well as to tailor appropriate technical parameters for each patient and imaging pulse sequence. Furthermore, despite recent impressive reductions in scan time, examination throughput on these expensive machines is limited by elaborate subject setup procedures necessitated by the scanner geometry. Subjects must be isolated in narrow tunnels, must be positioned on a table with appropriate support, provided ear protection, and supplied with headsets for communication.

[0045] Together, problems create significant barriers, and limit access, to prostate MRI.

[0013] Accordingly, an unmet need exists to provide prostate MRI systems and techniques that overcome one or more of the limitations of conventional MRI. A need also remains to address two of the biggest obstacles for more widespread adoption of MRI-based screening for prostate cancer.

[0014] Therefore, it is an object of the invention to provide prostate MRI systems that dramatically decrease cost and thus increase availability.

[0015] It is also an object of the invention to provide prostate MRI systems that alleviate one or more of the limitations described above, in the form of a chair, in which one or more magnets, one or more radiofrequency coils, and / or gradient coils are in positions such as its armrests, sitting surface, and / or back rest.

[0016] It is another object of the invention to provide prostate MRI systems that alleviate one or more of the limitations described above, in the form of an armchair, in which a primary

[0017] 2

[0018] 45838501.1magnet is located in sitting surface, back, and / or the armrests of the armchair, and one or more radiofrequency coils are located in the sitting surface, back, and / or armrests of the chair.

[0019] It is also an object of the invention to provide prostate MRI systems with primary magnets, gradient coils, and / or radiofrequency coils that are customizable and / or customized to imaging a patient’s prostate when the patient is in a seated position.

[0020] SUMMARY OF THE INVENTION

[0021] Disclosed are prostate MRI systems configured for imaging a subject’s prostate and methods of using the prostate MRI system. The MRI system includes customized hardware geometry that provides one or more of maximum radiofrequency homogeneity and sensitivity along an area of interest containing the prostate; tuning of radiofrequency such that no further extensive tuning or calibration is needed per subject; and / or incorporating radiofrequency pulse sequences to enhance prostate MRI imaging. In some forms, these are dedicated prostate MRI systems for imaging the prostate of a subject in a seated position.

[0022] Accordingly, in some forms, the prostate MRI system is in the form of a chair, e.g., an MRI chair. The proposed MRI chair involves aspects of an open, field-cycling magnet; gradients; radiofrequencies; and / or pulse sequences, each carefully configured to develop an improved high-quality accessible prostate MRI system. Gradients along each axis are designed specifically for their role (acquisition vs phase encode), while radiofrequency geometry and tuning are designed to target the field of view while maintaining patient comfort. Pulse sequences are carefully designed and implemented to complement the hardware, yielding high resolution and strong contrast for the needed images.

[0023] The open, field-cycling magnet (NuBO) is incorporated into one or more structures of the chair (e.g., armchair). In some forms, the open, field-cycling magnet is approximately U-shaped, included in the armrest(s) and / or seat portion of the chair, with the main field oriented left-right (LR). The open part of the U can be approximately the width of an economy airplane seat (40 cm) and allows seated prostate imaging. The low position of the prostate places it in a strong region of the polarizing field, providing high signal.

[0024] Furthermore, the prostate is located approximately centrally in a LR direction and an anterior-posterior (AP) direction in a field of view, where the main magnetic field and gradients have well-behaved orientation. Thus, the open, field-cycling magnet provides the Bo field of the MRI chair.

[0025] When a strong LR readout gradient is installed during the data acquisition phase, wire loops in the armrests, seat, and / or back rest of the MRI chair can directly add or subtract field

[0026] 3

[0027] 45838501.1of appropriate (LR) orientation with high efficiency. The disclosed design exploits this efficiency by incorporating a strong readout gradient. This provides access to high-resolution imaging through high bandwidth, reaching the edges of k-space before relaxation and inhomogeneity degrade signal. In some forms, a strong readout gradient can be implemented as part of the Bo design, which can simplify mass production. For example, controlling the two halves of the NuBO system separately, the polarizing and acquisition fields can have comparable strength and be spatially matched without additional hardware.

[0028] Also disclosed are customized radiofrequency coils involving both volume coils and / or array designs that complement the geometry of the spin physics and anatomical positioning. The radiofrequency volume coils are mainly built into the seat, arms, and back rest of the armchair, with a cross-pair loop providing excellent uniformity over the prostate, while an array configured to partially encircle the pelvis from a superior position and / or posterior position allows for proximity, optimal orientation for sensitivity, and low g-factor acceleration in the phase encode direction (e.g., the anterior-posterior direction). The volume coil contains a coil portion detachable from the volume coil and a second coil portion forming the remainder of the volume coil. In use, the detachable portion is anterior to the subject and above the subject’s lap. The volume coil is configured such that in use, a prostate being imaged is located centrally or substantially centrally in a left-right direction and in an anterior-posterior direction. The volume coil can be further configured such that in use, the prostate is located below the detachable coil portion. In some forms, the volume coil contains two intersecting loops of coils, intersecting at an angle of about 120 °C in the arms of the seat. The volume coil can be operated in quadrature transmit and / or quadrature receive mode. If needed, to complement the RF volume coils, the system includes a receiver array that partially encircles the pelvis from below and is perpendicular to the plane of precession. An array of loops, e.g., about 20cm loops, built into the chair seat and back provide good penetration and are complemented by a triangular flex coil placed in the lap. This array also provides excellent geometry for acceleration in the (fixed) phase encode direction, i.e., anterior-posterior direction.

[0029] In some forms, the prostate MRI system (i) can be configured to produce high amplitude gradients in a left-right readout direction (e.g., ~70mT / m), (ii) can be configured to produce phase encoding gradients in an anterior- posterior direction (e.g., ~25mT / m) over a targeted region of interest, such as from 8-18 cm above the surface of the seat on which a subject sits, and / or (iii) preferably contains volume coils and / or a receive array that improve proximity to the prostate while being orthogonal to Bo from three sides. Preferably, the

[0030] 4

[0031] 45838501.1volume coils and receive array are built into the MRI seat for patient comfort.

[0032] Radiofrequency coils are configured in the MRI chair so that in the sitting position the prostate is within a volume which can be fully imaged with T2-weighted (T2w) imaging; T2-weighted-turbo spin echo imaging; T2-weighted and slant slice imaging; or diffusion-weighted imaging (DWI) preferably in <20 minutes. Advantageously, the disclosed prostate MRI systems can provide push-button scanning with negligible patient positioning and no slice planning, such that highly trained and increasingly scarce MR technicians are not needed.

[0033] This change in acquisition workflow can be implemented alongside artificial intelligence (Al) reading of prostate MRI. Images are immediately triaged following acquisition, and the fixed imaging volume, geometry, and contrast of images over many subjects in turn facilitate better algorithms. The MRI system can also provide recommendations for further management options to the patient in real-time. The strategies implemented in the disclosed MRI systems expedite diagnosis and improve care while reducing hardware and personnel costs, making prostate MRI widely accessible.

[0034] BRIEF DESCRIPTION OF THE DRAWINGS FIGs. 1A and IB are non-limiting illustrations of a dedicated prostate MRI system containing an MRI chair. NuBO features an open region similar to an economy airplane seat. Radiofrequency hardware and gradients are built into the armrests and back, with one bar of radiofrequency coil clicked in place after seating. With no slice planning and minimal setup, push button scanning can be performed by personnel of moderate training. The positions of the coils are shown as visible to illustrate the positions of the coils in the MRI chair.

[0035] FIGs.2A-2E show non-limiting features of a NuBO magnet. (a,b) The BO-field direction is primarily left-right and drops with distance from the seat. Current in coils is adjusted to yield high BO field to polarize the spins (maximizing signal), and a low field (24mT) during acquisition (minimizing non-uniform BO effects), (c) One coil of the electromagnet during construction is shown, (d) Echo train data shows that signal acquisition is possible over a second, due to long T2. (e) The high polarization field improves SNR approximately 8x over a static 24mT field. Panels show sequence, echo trains, and signal vs polarization field.

[0036] FIG. 3 is a line graph showing a closer view of echoes acquired with a volume coil at z~10cm and excellent SNR.

[0037] FIGs.4A-4D are line graphs showing: a) Field is strong out to 20cm depth, b) While Bo contains a strong gradient (useful for diffusion encoding), the inhomogeneity is

[0038] 5

[0039] 45838501.1manageable at the 24mT (1MHz) imaging level. Transitions from polarization to consecutive slices requires minimal settling time (~lms). FIGs.4C and 4D show the high performance of the magnet with sharp ramping, short settling time, and high stability.

[0040] FIG. 5 shows generation of a gradient in the left-right direction is accomplished efficiently with planar arrays positioned like ami rests in the geometry of seated prostate imaging. Fields over ROI are shown.

[0041] FIGs. 6A-6D show: (a,b) Manifolds permit distributed water inlets; (c) Custom designed formers, such as those previously engineered can be mounted on a rotating table coupled to a high torque motor; (d) Cover fits tongue and groove for an airtight space appropriate for epoxy under vacuum.

[0042] FIGs. 7A-7C show: (a) Our custom-built field mapping apparatus is a modified 3D printer equipped with a suspended arm whose location in xyz is controlled with Python code. The arm can hold a 3-axis Hall monitor such as the Metrolab THM 1176-MF or the 1176- HF (with 5kHz readout), (a) Experimental field map is shown, (b) a scaled BO field map (20cm x 20cm). (c) For Bl mapping, the arm can also hold a custom 3-axis sniffing probe.

[0043] FIG. 8 shows that with weak readout, inhomogeneity induces some blur (red line). Slant-slice imaging (green) restores sharpness to that seen with double the bandwidth (blue), which matches the reference profile (black).

[0044] FIG. 9 shows an AP gradient made longer in the AP direction to improve gradient efficiency while maintaining patient comfort.

[0045] FIGs. 10A-10D show geometry and Bl simulation of a proposed RF coils. (a,b) Geometry and B1+ simulation of the Tx / Rx cross pair (d,e) Geometry and Bl- simulation of the 4-ch Rx array coil.

[0046] FIGs. 11A and 11B show: a) In the presence of a Gzlike inhomogeneity, slanted isocontours (Gz+Greadout) during readout cause blurring. This is greatly mitigated when exciting a slanted slice with slice gradient (Gz-Greadout) b) The slant slice pulse sequence simply adds a negative readout gradient during each slice selection pulse.

[0047] FIG. 12 shows that a strong diffusion encoding applied after the polarization period can be used to generate diffusion contrast. Very high b-values can be obtained with the intrinsic B0 field.

[0048] DETAILED DESCRIPTION OF THE INVENTION

[0049] I. Definitions

[0050] The phrase “left-right” refers to a direction starting from a subject’s left and progressing to the subject’s right, or starting from a subject’s right and progressing to the

[0051] 6

[0052] 45838501.1subject’s left. Likewise, “anterior-posterior” refers to a direction starting from a subject’s anterior and progressing to the subject’s posterior, or starting from a subject’s posterior and progressing to the subject’s anterior. “Superior-inferior” refers to a direction starting from a superior position of a subject and progressing to an inferior position of the subject, or starting from the inferior and progressing to the superior.

[0053] “Nonuniform,” as relates to a magnetic field, refers to a magnetic a field with more than about 100 ppm variation with respect to changes in spatial location in an imaging region. The field gradient of a nonuniform field could be linear or nonlinear. The orientation of the magnetic field vector can also vary considerably with respect to spatial location in an imaging region.

[0054] “Operably linked” refers to the connection of at least two components in an MRI system via technology including, but not limited to, integrated circuits, electrical cables, ethemet, internet, intranet, Bluetooth, near field communication, WiFi, or a combination thereof.

[0055] “Open,” as relates to the geometry of a magnet, refers to a magnet that does not completely surround an imaging region. As an example, the magnet surrounds the prostate by at most 270°.

[0056] “Pelvic area” refers to an anatomical section of a subject located between the subject’s navel and thighs. More specifically, the pelvic area is located in the lower part of the subject’s abdomen, between the subject’s hip bones and thighs.

[0057] “Substantially,” as relates to a geometric feature, means that the geometric feature is largely, but not wholly in the specified geometry. For example, “substantially planar” means that the structure is largely, but not wholly in a two-dimensional plane.

[0058] IL Magnetic Resonance Imaging Systems and Methods

[0059] Disclosed herein are prostate MRI systems containing hardware components configured for enhanced imaging of a subject’s prostate, and / or software capable of producing pulse sequences to enhance imaging of a subject' s prostate. A dedicated prostate MRI system for imaging in seated position (an “MRI chair” vs the “tunnel”) increases access by solving many issues in siting, maintenance, throughput, and personnel costs. The patient simply sits and a single button triggers acquisition of T2-weighted imaging (T2w), or T2w and diffusion-weighted imaging (DWI) over fixed volume. Preferably, little patient preparation and no scan planning are required, such that the need for costly, highly trained, and increasingly scarce magnetic imaging resonance technicians can be obviated. Preferably under supervision, artificial intelligence (Al) that factors relevant clinical data

[0060] 7

[0061] 45838501.1instantaneously interprets and reports results, optionally with appropriate management options (e,g., biopsy, additional imaging, etc.) [18, 19] An optionally “push button” implementation procedure expedites care and / or limit costs.

[0062] The prostate MRI system includes customized hardware geometry that provides one or more of maximum radiofrequency homogeneity and sensitivity along an area of interest containing the prostate: and / or radiofrequency pulse sequences (e.g., T2-weighted; T2-weighted-turbo spin echo; T2- weighted and slant slice; diffusion- weighted, etc.,) incorporated to enhance prostate MRI imaging. The prostate MRI system can also include customized radiofrequency tuning. In low field imaging, a large bandwidth necessitates a low Q (=®o / A®), which lowers SNR. [21, 50] However, prostates are relatively small (~4cm) and, based on the inventors’ experience in prostate imaging, reliably located at about the center in the lateral (i.e., readout) direction. Thus, sensitivity over this organ requires a much narrower bandwidth than the full abdominal dimensions. Noting this, zoomed imaging over a prostate field of vision (FOV) can be achieved by tuning the coil to high Q, which simultaneously improves SNR. In addition, as the radiofrequency field (Bl) is insensitive to coil load at low field, no further tuning or calibration is needed per patient. Preferably, the system is suitable for imaging in mix-used rooms, such as multi-purpose spaces not necessarily dedicated for MRI imaging.

[0063] The prostate MRI system contains a first component comprising an open, fieldcycling magnet configured to produce a spin-polarizing non-uniform Bo magnetic field and an acquisition non-uniform Bo magnetic field. The prostate MRI system can also contain a second component operably linked to the first component and including one or more coils containing one or more receive coils, one or more volume coils, and / or one or more surface coils (e.g., one or more surface array coils). The one or more coils contain one or more segments configured to occupy a left portion, a right portion, and a posterior portion of a subject’s pelvic area. In some forms, the one or more coils are configured to partially encircle a subject’s pelvic area at the sides, front, back, and below. The prostate MRI system can also further contain a third component operably linked to the first component and containing gradient coils. The acquisition non-uniform Bo magnetic field can have a field strength different from that of the spin polarization non-uniform Bo magnetic field.

[0064] Preferably, the one or more coils of the second component contain one or more receive coils, one or more volume coils, and / or one or more surface coils (e.g., one or more surface array coils). The one or more receive coils, one or more volume coils, and / or one or more surface coils can include one or more wire loops configured to transmit and / or receive

[0065] 8

[0066] 45838501.1radiofrequency. In some forms, the one or more receive coils, one or more volume coils, and / or one or more surface coils contain a coil portion detachable from these one or more coils to allow positioning (e.g., seating) a subject within these one or more coils.

[0067] The one or more coils (e.g., the one or more volume coils) and / or mode of operation place a region of maximum sensitivity and homogeneity centered or substantially centered over the prostate in both anterior-posterior and superior-inferior directions. Lastly, magnetic field gradients generated by sub-components of the third component are from direct currents. Therefore, in some forms, magnetic field variations in an anterior-posterior direction and / or in a left-right direction are direct current fields.

[0068] The field cycling magnet provides for spin polarization at high field (thereby generating strong signal) and image acquisition at low field (thereby minimizing the effect of the inhomogeneous field). However, in some instances, where high resolution image acquisition can be achieved with a strong readout field (e.g., greater than 30 mT / m, such as about 70 mT / m), despite some B0 inhomogeneity, the readout field can have magnetic field strengths similar to that of the spin-polarizing non-uniform Bo magnetic field. A strong LR spatial frequency encoding gradient provides several advantages to the disclosed prostate MRI system. However, implementation of a strong phase encoding gradient can be challenging. Therefore, the system can also be configured to apply weaker spatial encoding gradients (e.g., weaker spatial phase encoding gradient) for the anterior-posterior direction. Further, considering the low duty cycle of a phase encoding gradient channel, this component can be air cooled, simplifying manufacture and providing better space efficiency within the prostate MRI system.

[0069] In some forms, the open, field-cycling magnet is U-shaped composed of two vertical or substantially vertical portions connected to one horizontal or substantially horizontal portion, and contains Bo coils in the vertical or substantially vertical portions of the U-shape. Preferably, in these forms, the Bo coils are planar or substantially planar in the vertical or substantially vertical portions of the U-shape. In some forms, the open, field-cycling magnet is configured to produce a magnetic field gradient in the first direction, preferably wherein the first direction is a left-right direction. A left-right direction is illustrated in FIG. IB.

[0070] There are multiple innovative aspects of the disclosed prostate MRI systems and / or prostate MRI imaging devices. These aspects include, but are not limited to, hardware, customized gradients, radiofrequency transmitters and / or receivers, pulse sequences to enhance prostate imaging, and / or how the data is ultimately used (Al assisted radiology). These developments are briefly described in the following paragraphs.

[0071] 9

[0072] 45838501.1A. Hardware

[0073] Magnetic resonance imaging (MRI) is having major impact on prostate cancer (PC) detection and management because of its excellent sensitivity, specificity, and actionability. Prebiopsy MRI can reduce unnecessary biopsies by 30-40% and increase positive biopsy rates by 50-60%, with scan times <9 minutes. [1-10] Moreover, recent findings suggest the true positive predictive value is even higher, as 50-80% of the “false positive” lesions on MRI are later found to be clinically significant. [11, 12]

[0074] Evidence indicates MRI would positively affect management without increasing oveitreatment if it were cheaper and more available. Analyses of IP 1 -PROSTAGRAM found maximum sensitivity with no increase in biopsies would be achieved if -60% of men over 65 (men with PSA>1) received an MRI. Unfortunately, “current MRI capacity is lacking”, and less than 10% of these men receive MRI. [13, 14] The gap is driven not by balance of diagnosis / overdiagnosis, but by high cost and low availability of reliable MR scanners. [15-17]

[0075] Unlike a superconducting magnet, which requires a large footprint, the disclosed system is suitable for point-of-care sites. While many compact MRI designs have been proposed in recent years, those systems costing less than $500k have several common features. They use arrays of permanent magnets arranged around a cylindrical former to generate a relatively homogeneous B0 field in the center. [49-51] This approach cannot easily exceed ~65mT, and that field is achievable only over small cylinders (e.g., brain or knee, not torso). Most of these systems also use conventional image encoding strategies, namely switchable gradients for slice, frequency, and phase encoding. Although a single-sided low-resolution MRI for biopsy guidance has been developed for prostate, image quality is only suitable for whole organ registration with a prior image, not lesion detection.

[0052] And, there are currently no scanners being developed for widely accessible MRI screening of prostate cancer.

[0076] i. Nonuniform B0 Magnet

[0077] Polarization

[0078] The open, field-cycling magnet system embraces nonuniformity in the B0 field as a design feature, which eliminates many of the design constraints reported in conventional, and even more recently proposed, MR scanners. This opens potential for a high degree of purpose-specific customization. In conventional MR imaging, magnets with significant B0 inhomogeneities cannot be used. The disclosed approach allows high resolution imaging with a highly nonuniform B0 magnet because it incorporates a technique called field cycling.

[0079] 10

[0080] 45838501.1Field cycling allows polarization of spins at high field (thereby generating strong signal) and, when needed, image acquisition at low field (thereby minimizing the effect of the inhomogeneous field). Following ramp down, residual inhomogeneity is treated as a (nonplanar) slice select gradient.

[0081] This open, field-cycling magnet has been integrated into a dedicated prostate MRI system in which additional features are engineered to exploit the preferred primary-purpose nature of the system, maximizing patient comfort, image quality, and simplicity of use. Nonlimiting illustrations of a dedicated prostate MRI system containing an MRI chair are shown in FIGs. 1A and IB. For example, the geometry facilitates strong left-right (LR) acquisition fields (e.g., strong spatial frequency encoding fields), efficiently and comfortably built into the “armrests” of an MRI chair, improving resolution. Meanwhile, phase encode gradients (e.g., in the anterior-posterior direction) can be weaker and managed with air cooling, due to their low duty cycle. Preferably, radiofrequency (RF) coils are mainly built into the seat, with a cross-pair loop, preferably in the armrest section, providing excellent uniformity over the prostate, while an array encircling the pelvis from below and behind allows for proximity, optimal orientation for sensitivity, and low g-factor acceleration in the phase encode direction. High-Q improves sensitivity and naturally zooms FOV left-right. MRI typically requires a homogeneous background field because field inhomogeneities dephase the signal before it can be acquired. The open, field-cycling magnet uses an inhomogeneous electromagnet to provide a high field for polarization and a low field for imaging. Using high field for polarization improves signal, while reducing the BO field after spin polarization provides three advantages: (1) it reduces the impact of field inhomogeneities; (2) it reduces the RF power needed to manipulate spins, and hence the specific absorption rate (SAR, which goes as ®2), and (3) it yields longer T2s (still dependent on tissue type) making very long echo trains feasible, which is ideal for efficient T2w imaging, a key sequence in prostate imaging.

[0061]

[0082] FIGs. 2A and 2B depict a non- limiting open, field-cycling magnet described herein (the white, U-shaped magnet in panels 2A and 2B). This one-sided imaging system generates a nonuniform main magnetic field BO created by a resistive coil with two elements. The coil loops are curved to enhance the field at depth (FIG. 2C). Each coil element is composed of hollow copper wires (with deionized water for efficient cooling) with a maximum current of 275 Amps. The magnet can be designed such that it turns off when not in use, and the 5 Gauss field line is <2m radius, compatible with community settings.

[0083] 11

[0084] 45838501.1FIG. 2D shows that strong signals are obtained, with echoes recorded for up to 1 second after an excitation pulse. The low field readout allows short 180 RF pulses and yields very long T2, enabling very long echo trains. In this figure, 800 echo peaks are shown, collected over nearly a second of acquisition time. It has also been experimentally verified that the enhanced B0 field present during the polarization period dramatically increases SNR (FIG.2E). Using the pulse sequence shown there, SNR increases approximately an order of magnitude over that which would be obtained with a static 24mT field. FIG. 3 shows the high SNR obtainable at ~10 cm distance using a volume coil.

[0085] As described herein, the open, field-cycling magnet can be included in a system for prostate imaging, such as in a seated position (considering the hardware in FIGs. 2A and 2B as the seat and armrests of FIGs. 1A-1C). Open and seated imaging can improve patient accessibility as well as scan throughput. Furthermore, the geometry is conducive to improve encoding and signal acquisition, as well as imaging without slice planning. Therefore, the open-field-cycling (e.g., rampable) Bo electromagnet can be incorporated into the disclosed prostate MR1 system, with a seat-like opening between 30 cm and 50 cm wide, (e.g., 40 cm wide), similar to an economy airplane seat. [20-23] At full current it provides a strong field for high polarization and signal. This field can be inhomogeneous for imaging, but the current and, where needed, field can be ramped down for acquisition, greatly reducing inhomogeneity. The localized switchable field also simplifies sitting and safety concerns.

[0086] FIGs.4A-4C show the main polarizing field as a function of distance from a seat. At full power, as used for polarization, the inhomogeneity in this magnet (FIG. 4A) would make spatial encoding difficult. However, ramping down the magnetic field proportionally ramps down the inhomogeneity. During acquisition, the magnet can be ramped down to a current that places the desired plane at about 1 MHz, followed by excitation at that frequency. Doing so can reduce through-plane bandwidth over 3mm to less than 10kHz, making field inhomogeneities highly manageable (FIG.4B). The inhomogeneous field can also act as a slice select gradient without additional hardware. FIGs.4C and 4D show the high performance of the magnet with sharp ramping, short settling time, and high stability. Thus, while the imaging volume has an inhomogeneous field, each selected (nonplanar) slice is at a single resonance frequency that is defined by having a uniform field (by definition, as the slice is selected using a specific resonance frequency, -1MHz) and bandwidth dependent upon the desired slice thickness. The slices in this smoothly varying nonuniform field can be somewhat nonplanar, but their shape can be known ahead of time through field mapping

[0087] 12

[0088] 45838501.1(noting that field mapping can be required once when the system is installed - not necessarily each time a subject is scanned).

[0089] Readout gradient for left-right (LR) encoding

[0090] In the proposed MRI systems, Bo (e.g., a spin-polarizing non-uniform Bo magnetic field and / or an acquisition non-uniform Bo magnetic field) is oriented in a first direction, such as the left-right (LR) direction. A left-right direction is illustrated in FIG. IB. Thus, a third component of the MRI systems includes gradient coils. The third component is operably linked to the first component. The gradient coils can be built into two vertical or substantially vertical portions connected to one horizontal or substantially horizontal portion. In one aspect, the gradient coils include a subcomponent in the LR “arm-rests” of the polarizing magnet to very efficiently modulate Bo, providing strong frequency spatial encoding. Therefore, in some forms, a subcomponent of the gradient coils is configured to produce a magnetic field gradient in a first direction, preferably wherein the first direction is a left-right direction. In some forms, these gradient coils are planar or substantially planar coils. Many lower field scanners accept relatively weak gradients, which can be air-cooled and driven by extremely low-cost amplifiers. However, having a single strong gradient, e.g., in the read direction, provides numerous advantages, particularly for the disclosed system. It should be noted that Bo is still ramped down, but that ramping down simply gives a signal from the slice. An additional field, whose magnitude varies in the LR direction, preferably is utilized to encode LR position of the spins. Due to the high efficiency of the gradient geometry and the tolerance for nonlinearity, very strong gradient fields (e.g., such as about 70 mT / m) can be achieved using a 50A amplifier. In some forms, the spatial frequency encoding gradient can be between 30 mT / m and 200 mT / m.

[0091] Design of the gradients can be performed using a CoilGen software package[71 J. Non-limiting examples of windings are shown in FIG. 5. In this non-limiting example, fields can be based on a 4-mm square hollow wire (Luvata) wound onto two 40x40cm planes. Preferably, this height is below the sternum of most men, so arms can rest comfortably. The final gradient can have from 20 to 50 windings and / or 1 to 10 layers. In some forms, the final gradient can have 32 windings (12 shown for illustration) and 4 layers. In some forms, the windings can be designed to provide gradients from 30 mT / m to 200mT / m, or 30 mT / m to lOOmT / m over a targeted field of view. In some forms, the targeted field of view is preferably from 8 cm to 18 cm from the horizontal or substantially horizontal portion that preferably forms a portion of the seat.

[0092] 13

[0093] 45838501.1The Bo magnet can be cooled using water and these gradients can tap into that same system.

[0094] An amplifier (AE Techron 7224) can be controlled directly by the TecMag pulse sequence controller. If needed, it can also be controlled by an in-house waveform generator. Rise times below 300us can be encountered during operation. CST studio (Dassault Systems Deutschland GmbH), can be used to model potential eddy currents in the magnet and gradient shields, and overlapped cuts can be placed accordingly. [72, 73]

[0095] Electrical and thermal properties of the gradient can be tested via bench measurements. Note that electromagnetic force from ramping this gradient can be minimal as it can be subject to a background field of only 24mT. Initial field mapping can be performed with an in-house automated mapping equipment, shown in FIGs. 7A-7C. The automated mapping equipment is composed of a magnetometer connected to a 3D printer and has previously been used to map magnetic fields within the NuBO field of view. This can be assessed at various current amplitudes to assess linearity of magnetic field with prescribed input cunent. Spatial linearity is not required.

[0096] Eddy current correction of these gradients can be performed by conventional means, such as via exponential approximation by measuring the gradient impulse response function (GIRF) of the system. For example, the GIRF can be characterized using short gradient pulses, measuring various location with a high temporal resolution magnetometer (Metrolab Q12755). The inventors have previously characterized the GIRF of nonlinear gradients and used it to successfully pre-emphasize waveforms.

[0060] In addition, it is notable that while higher gradient strength is desirable, the goal of up to 70mT / m is not a strict limit. For example, the gradient can be between 30 mT / m and A strong acquisition field allows for high resolution imaging in axial slice orientations, which is preferable for its concordance with current clinical practice. Thus, a minimum acceptance criterion for readout gradients can be 60mT / m. However, with slant slice imaging, even 30mT / m achieves 1mm resolution in the presence of residual field inhomogeneities (FIG. 8, simulating a 3-mm slice). In any case, due to the high cooling efficiency of the disclosed gradient design, amplifiers can be run in series to improve maximum current or minimum rise time.

[0097] Anterior-posterior (AP) coils and gradients for AP encoding As discussed above, a third component of the MRI systems includes gradient coils, preferably being operably linked to the first component. The gradient coils can be built into two vertical or substantially vertical portions connected to one horizontal or substantially horizontal portion. Therefore, in some forms, the gradient coils include a subcomponent in

[0098] 14

[0099] 45838501.1the “arm-rests” of the polarizing magnet to very efficiently modulate Bo, providing spatial phase encoding gradients. In some forms, these gradient coils are planar or substantially planar coils. Preferably, a magnetic field gradient produced by this set of coils is an anterior-posterior direction. An anterior-posterior direction is illustrated in FIG. IB.

[0100] Creating a gradient in the AP direction on a planar former requires smaller loops, which can reduce their efficiency. However, simulations show that this design can readily achieve 25mT / m with a 25 A amplifier. The design for this gradient also takes advantage of the single purpose nature of the disclosed prostate MRI system device. Preferably, the gradient in the AP direction is used only for phase encoding, such that it has far lower duty cycle and can be air cooled despite relatively high winding density.

[0101] Preferably, the gradient generated in the AP direction is a planar gradient. When a planar gradient is desired, the AP planar gradient can be built from a 1.5-mm copper wire with >lmm spacing, 50 turns and two layers. These can be built onto a 40x60cm former, made wider in the AP direction to allow for larger loops that improve gradient efficiency, while respecting patient comfort. Calculations as well as in-house tests show that realistic operation generates approximately <1 °C temperature rise per TR (3-5s), can be manageable with air-cooling.

[0102] Bench measurements, as well as spatial and temporal characterization, can be performed following the procedures outlined above for the LR gradient. As above, self-same and Bo eddy currents can be assessed from a series of experiments exciting and detecting individual isocontours of the gradient. Self-eddy currents can be compensated through waveform modulation. Additional compensatory waveform modifications on other channels can be implemented to manage cross terms as needed. These can be internally set through time / amplitude coefficients on the console, or they can be programmed into an external waveform controller. [60, 75-78]

[0103] If heating over a full volume imaging session is found to exceed the food and drug administration (FDA) accepted limit for gradient temperature (42°C). Further, AP gradients can be modified to provide forced air cooling or water cooling, as needed. The additional planar elements can reduce seat width. If needed, the widths of the prostate MRI systems can be adjusted accordingly.

[0104] Lastly, the magnetic field generated by the third component is preferably a direct cunent field.

[0105] 15

[0106] 45838501.1ii. Radiofrequency coils

[0107] Close-fitting coils in the AP- superior -inferior (SI) plane for prostate imaging While signal is greatly improved by the high field polarization available in the disclosed open, field-cycling magnet, maximizing SNR can still be important. To do this, hardware, e.g., one or more coils can be built that surround the prostate with close proximity. Therefore, in some forms, the prostate MRI system contains a second component containing one or more coils. The one or more coils contain one or more segments configured to occupy a left portion, a right portion, and a posterior portion of a subject’s pelvic area. In some forms, the one or more coils are configured to partially encircle a subject’s pelvic area at the sides, front, back, and below. Preferably, the one or more coils of the second component contain one or more receive coils, one or more volume coils, and / or one or more surface coils. The one or more one or more receive coils, one or more volume coils, and / or one or more surface coils can include one or more wire loops configured to transmit and / or receive radiofrequency. In some forms, the one or more receive coils, one or more volume coils, and / or one or more surface coils contain a coil portion detachable from these one or more coils to allow positioning (e.g., seating) a subject within these one or more coils. The one or more coils (e.g., one or more volume coils) and / or mode of operation place a region of maximum sensitivity and homogeneity centered or substantially centered over the prostate in both anterior-posterior and superior-inferior directions.

[0108] In some forms, the one or more volume coils contain a coil portion detachable from the one or more volume coils and a second coil portion forming the remainder of the one or more volume coils. Preferably, the one or more volume coils are configured such that in use, an organ or tissue being imaged is located centrally or substantially centrally in a left-right direction and in an anterior-posterior direction. The volume coil can be further configured such that in use, an organ or tissue being imaged is located below the detachable coil portion. In some forms, the volume coil contains two intersecting loops of coils, intersecting at an angle between 100 °C and 150 °C, such as about 120 °C. Preferably, the volume coil is capable of being operated in quadrature transmit and / or quadrature receive mode. In some forms, the coil portion detachable from the volume coil is configured to transmit and / or receive radiofrequency. In some forms, the second coil portion forming the remainder of the volume coil is configured to receive radiofrequency.

[0109] Considering the geometry and Bo orientation in the disclosed prostate MRI system, a non-limiting example of such a coil includes a volume coil having a large cross-pair loop and operated in quadrature mode (FIG. 10A-10D).[79, 80] This design puts the region of

[0110] 16

[0111] 45838501.1maximum sensitivity and homogeneity, where the loops intersect, centered over the prostate in both anterior-posterior and superior-inferior directions. A superior-inferior direction is illustrated in FIG. IB. Setting the intersection angle of the coils between 100 °C and 150 °C, such as about 120 °C, facilitates decoupling between the pair, and thus allows the quadrature mode transmission / reception (Tx / Rx) to be used to further increase the pair's Tx efficiency as well as the Rx sensitivity. In some forms, the increase in sensitivity can be 1.414. Note one bar of this coil (on top of the subject’s laps leg) can be removed and re-attached (e.g., by clicking back) into place, similar to the cross-bar of a fair ride.

[0112] While this volume coil can serve as both transmit and receive, the prostate MRI system can also include a multi-channel receiver array, which can be useful for both SNR and / or parallel imaging. Preferably, the multi-channel receiver array of wire loops is operably linked to the first component. In some forms, the multi-channel receiver array of wire loops forms a four-channel receiver array containing four sets of coils. In use, at least one set of coils of the four-channel receiver array is superior to another set of coils, and the at least one set of coils is anterior to another set of coils.

[0113] The geometry of the prostate MRI system is such that spins rotating in the AP-SI plane can be detected with coils parallel to this plane and encircling the pelvis from four directions. Preferably, the multi-channel receiver array of wire loops includes an array of three coils (e.g., 20 cm coils) built into a horizontal or substantially horizontal portion of the prostate MRI system, and at least one vertical or substantially vertical portion of the prostate MRI system. Preferably, the horizontal or substantially horizontal portion and the at least one vertical or substantially vertical portion form the seat and back of the MRI chair, respectively. Further, the array of three coils can be complemented by at least one set of coils (e.g., coils forming or contained in a triangular element). In use, the at least one set of coils is placed over the lower abdomen (FIG. 10C) These locations allow coils large enough for good penetration depth with an array that encircles the pelvis over 180 degrees. This geometry also supports parallel imaging in the anterior-posterior direction, the phase encode direction of this system. Receive coils can be tuned to the lowest bandwidth that captures spins in the center (e.g., about 12 cm) of the readout gradient (~35kHz).

[0114] In the non- limiting illustration of FIGs. 10A-10D, the Tx cross-pair loops and the rear Rx 3-loop elements can be built into a non-magnetic subject chair. Preferably, radiofrequency (RF) coils are mainly built into the seat, with a cross-pair loop providing excellent uniformity over the prostate, while an array encircling the pelvis from below allows for proximity, optimal orientation for sensitivity, and low g-factor acceleration in the phase encode

[0115] 17

[0116] 45838501.1direction. High-Q improves sensitivity and naturally zooms field of view left-right. Each cross-pair loop can be made with copper tubing (41cm A / P x 40cm L / R for good quality factor at -1MHz as well as subject comfort. A 90-degree hybrid coupler can be utilized to drive the coil in quadrature mode. Standard 50 Ohm Roemer matching network can be used for the cross-pair, and a customized-ordered isolation preamplifier can be used after the coil T / R switch.

[0081] With this approach, the cross-pair loops have sufficient decoupling to acquire clean signals as part of the multielement array.

[0117] The 3-loop elements in the rear (e.g., 10-cm diameter) as well as the triangular element can be made with AWG 12 copper wire to ensure good quality factor at -1MHz. A 50 Ohm Roemer matching network and customized-ordered isolation preamplifier can be used to ensure sufficient decoupling.

[0118] Bench tests include SI 1 measurement using the vector network analyzer can be used to determine the coil’s matching and tuning conditions. S21 measurement with two pickup probes can be used to determine the decoupling performance of each coil element. A field mapping system (shown in FIGs. 7A-7C) can be used to map the B l+ / _field of the array coil on both bench and in place to measure the homogeneity, efficiency, and coil coupling. Then, imaging can be acquired on NuBO magnet demonstrating these coils’ performance, both for coupling, homogeneity, and SNR. 20dB isolation and homogeneity <5% RSD on Tx are contemplated.

[0119] Following validation with imaging experiments, acceleration in the AP direction can also be tested. Due to the favorable coil geometry, R=2 can be achieved with very low g-factor, i.e., tolerable noise amplification even in a lower SNR setting. Since averaging can occur, an R=2 could be traded for a doubling of averages, increasing SNR by 40%. Thus, this strategy can be adopted assuming SNR drop is <40%.

[0120] In some forms, a single Tx / Rx large loop (half of the cross-pair) can be used in the prostate MRI system. Flex coils on the abdomen can be used, with little deterioration from breathing motion. Accordingly, the triangular element disclosed above can be placed on the subject’s lower abdomen. If needed, motion correction methods, such as navigators, can be implemented to further improve image quality. An alternative can be to affix the triangle to an angled post coming off the “fair-ride” bar of the volume coil. This post can have adjustable length and angle to accommodate subjects of different sizes. Also contemplated, is the inclusion of multiple RF coils suitable (removable chairs, etc.,) for subjects of different sizes.

[0121] 18

[0122] 45838501.1iii. MRI imaging device

[0123] Also disclosed is an MRI imaging device containing one or more aspects of the prostate MRI system disclosed herein. In some forms, the MRI imaging device contains a horizontal or substantially horizontal portion and two vertical or substantially vertical portions. The horizontal or substantially horizontal portion is located between, and physically connected to, the two vertical or substantially vertical portions. The two vertical or substantially vertical portions contain a first component containing an open, field-cycling magnet configured to produce a spin-polarizing non-uniform Bo magnetic field and an acquisition non-uniform Bo magnetic field in a first direction, optionally wherein the acquisition non-uniform Bo magnetic readout field has a field strength different from that of the spin-polarizing non-uniform Bo magnetic field.

[0124] The MRI imaging device also contains a second component containing a one or more coils containing one or more receive coils, one or more volume coils, and / or one or more surface coils (e.g., one or more surface array coils). One or more segments of the one or more coils are located in the two vertical or substantially vertical portions of the MRI imaging device. Further, in some forms, at least one segment of the one or more volume coils is located in the horizontal or substantially horizontal portion of the MRI imaging device. The one or more coils contain one or more receive coils, one or more volume coils, and / or one or more surface coils. Preferably, the one or more receive coils, one or more volume coils, and / or one or more surface coils contain one or more wire loops. The one or more coils contain one or more segments configured to occupy a left portion, a right portion, and a posterior portion of a subject’s pelvic area. In some forms, the one or more coils are configured to partially encircle a subject’s pelvic area at the sides, front, back, and below. In some forms, the one or more coils contain a coil portion detachable from the one or more coils.

[0125] In some forms, the horizontal or substantially horizontal portion forms a seat portion or part thereof, and the two vertical or substantially vertical portions form two arm rest portions or parts thereof.

[0126] In some forms, the MRI imaging device further contains a third vertical or substantially vertical portion. The third vertical or substantially vertical portion contains one or more segments of the one or more coils.

[0127] B. Pulse sequences

[0128] Also developed are pulse sequences preferably tailored for prostate imaging. Long spin echo trains can be acquired for robust T2w contrast. High resolution can be achieved

[0129] 19

[0130] 45838501.1with the strong readout described above, despite residual Bo inhomogeneity. If needed, to further improve resolution, slant-slice imaging can be utilized, which is an elegant strategy to convert through-slice gradient (the main Bo inhomogeneity) into in-plane spatial encoding.

[0024] Finally, the system can also be employed for DWI, because inhomogeneous Bo at full current doubles as an ultra-strong diffusion encoding gradient. This provides high b-value DWI at short echo times (TE) and high SNR. Preferably, these pulse sequences are generated using the one or more of the three component described above.

[0131] The prostate MRI system can be configured to generate a T2-weighted (T2w) pulse sequence. In some forms, the prostate MRI system is configured to generate a T2-weighted-turbo spin echo (TSE) pulse sequence. In some forms, the prostate MRI system is configured to generate T2w pulse sequence with a strong acquisition gradient (e.g., between 30 mT / m and 200 mT / m) or with both a strong read gradient and slant slice pulse sequence.

[0132] Preferably, the slant slice pulse sequence adds a negative readout gradient during a slice selection pulse. In some forms, the prostate MRI system is configured to generate a diffusion-weighted imaging (DWI) pulse sequence (e.g., single-shot spin-echo echo-planar imaging (EPI) or turbo spin echo (TSE) pulse sequence). Preferably, for DWI, the field cycling B0 magnet can be ramped as an ultra-strong diffusion weighting gradient, providing high b-value with short TE.

[0133] i. Strong readout gradient

[0134] T2w imaging can be utilized for both structural imaging and cancer detection in prostate. The disclosed prostate MRI system is well-suited to T2w imaging because long echo trains can be acquired. Stronger readout gradients and higher bandwidth alone can significantly decrease effects from the inhomogeneous magnetic field. A target resolution can be a slice thickness of 3mm and in-plane resolution of 1mm2.

[0135] The existing T2w-TSE sequence can be the first method applied on phantoms with each new hardware setup. This can be used to measure SNR across echo trains and slices, both with and without spatial encoding. Following a polarization period of 3 seconds, it is contemplated that all slices can be encoded with 8 averages in about 5 minutes (ETL>=32, 10 slices per polarization, TE= 100ms). It should be that for human scanning, localizers would not be necessary, as the imaging volume can be designed to fully contain the ~4cm prostate, with anatomical positioning accomplished by the act of sitting.

[0082]

[0136] ii. Slant-slice encoding

[0137] To further enhance resolution, an acquisition strategy, such as slant-slice encoding can be implemented that minimizes residual blur from inhomogeneity in the B0 magnet.

[0138] 20

[0139] 45838501.1Slant-slice encoding as an imaging strategy is an approach that reduces dephasing from inhomogeneity that is perpendicular to the imaging plane. This is suited for the disclosed prostate MRI system, as the dominant inhomogeneity in the BO field is the residual approximately linear variation in the slice direction. Furthermore, slant-slice encoding as an imaging strategy performs best in conjunction with a strong readout gradient, which can be incorporated into the design disclosed herein.

[0140] Strong readout gradient (i.e. high bandwidth acquisition) should be sufficient to overcome background field inhomogeneities and achieve 1mm image encoding. However, given the mainly linear variation presented by the NuBO magnet, simulations show that alternative pulse sequences can accomplish this even with modest gradient strength. Slant slice imaging is a strategy to harness the background inhomogeneity as part of the in-plane encoding process, leveraging near-orthogonality of (background +readout) vs (background -readout) to minimize contributions from through-plane dephasing. FIG. 11A shows the through-plane voxel definitions during a LR readout gradient in addition to a through-plane residual inhomogeneity. The slant of the voxels through-plane contributes image blur, which is greatly mitigated when imaging a slant slice. While analysis is most straightforward in the case of linear inhomogeneity and readout field, the general principle extends to nonlinear cases as well.

[0024] Its performance at each voxel depends on the relative strength of perpendicular components of background and readout fields at that location.

[0141] Slant-slice encoding can be implemented, adding a negative readout gradient during slice selection, with appropriate rephaser / preread gradients after initial excitation. The pulse sequence is shown in FIG. 11B. Imaging can be performed using both 100% and 50% of the available readout gradients. It is contemplated that slant slice resolution can be most helpful in improving resolution of the low bandwidth acquisitions, which can be utilized to develop hardware with more moderate readout gradient requirements.

[0142] iii. Diffusion- weighted imaging

[0143] The open, field-cycling magnet is well-suited for diffusion weighted imaging because the polarizing field can be blipped to provide strong diffusion weighting. While DWI of prostate is routinely acquired with echo-planar imaging (EPI), diffusion weighted imaging can also be performed with turbo spin echo (TSE) k-space acquisition.

[0083] Both sequences can achieve similar echo times, resolution, and conspicuity, and TSE provides superior insensitivity to inhomogeneity.

[0084] The longer readout of TSE reduces the number of slices possible in a fixed TR, and so has slightly lower scan efficiency. However, for the thicker slices typical of DWI and the small extent of the prostate, these considerations are minor. As

[0144] 21

[0145] 45838501.1in conventional MRI, lower resolution in DWI (2mm voxels, slices matched to T2w to facilitate simultaneous reading) can be employed in the disclosed prostate MRI system. Using a HASTE readout that traverses central k-space at early TE, the full volume at low and high b-value can be acquired in -6 minutes.

[0146] A pulse sequence developed herein and illustrated in FIG.12 shows an innovative approach to use the strong BO gradient to provide a diffusion weighting preparation module. Preparation echoes can encode diffusion with gradient amplitudes greater than 100 mT / m, such as between 100 mT / m and 800 mT / m. The pulse sequence encodes b~6000s / mm2with one pair of 7ms pulses, providing very strong diffusion weighting while maintaining short TE for maximum signal. Diffusion weighting can also be increased by applying serial shorter diffusion encodings (i.e., N>1 in FIG. 12). Because the same gradient provides slice encoding, b- values can be uniform across the slice. However, deviations can be handled. [58, 59, 77] Note that higher b-values have been shown to improve lesion conspicuity. [85-87] The systems can target a maximum b-value of 1000s / mm2to align with typical clinical diffusion weight. Slice encoding and acceleration strategy can be jointly optimized for different hardware capabilities (e.g., as a function of available acquisition field strength).

[0147] As DWI is widely regarded as a low SNR sequence, potential to perform it at low field may be of concern. In reality, DWI in a low field single sided magnet using spin echo train acquisition was demonstrated in brain nearly 20 years ago, and image quality was found to be similar to that found at 1.5T.

[0089] More recent work notes that for anatomy requiring a modest number of slices and for which multidirectional diffusion encoding is not important, the scan time and diagnostic quality are adequate on low field scanners.

[0050] The prostate is a small organ, and clinically relevant ADC reductions in cancer are approximately isotropic (related to decreased luminal fraction). [90-92] Thus, prostate cancer detection is especially well suited to DWI acquisition using the disclosed prostate MRI system. If necessary, larger voxels or additional averages can also be implemented.

[0148] In some forms, the pulse sequences can be ported from a console (such as the TecMag console) to an alternative low-cost console. The software for the user interface can also be developed and its development is envisioned on a device (e.g., a hand-held device such as a tablet (e.g., iPad), mobile phone (e.g., a smart phone) or other hand-held devices). The user interface can have only very limited control - allowing the user to start and stop a study or scan, and to select which pulse sequence to run from a fixed order menu. In addition to prompting for each scan it can include prompts to begin contrast injection, if appropriate. Preferably, none of the pulse sequence parameters will be available for modification by the

[0149] 22

[0150] 45838501.1users unlike on conventional magnets. This ensures that the proper protocol is always applied, and data consistency is maintained to facilitate machine learning and / or deep learning Al assisted radiology.

[0151] Preferably, scans with the disclosed MRI system or MRI imaging device can use EDITER as well as other methods developed for correction of electromagnetic interference. [62, 63] Deep learning based methods can also be implemented to eliminate and / or reduce electromagnetic interference elimination, and / or to boost image quality.

[0064] Preferably, the Bo magnet is water cooled, shielded, and powered by a high performance amplifier. The Bo magnet, read and phase encode gradients can all be fully controlled within the pulse sequence. The shape and dynamics of the existing NuBO magnet have been characterized. [20-23]

[0152] Preferably, the methods involve imaging volumes of 12x20x12cm (LR / AP / HF), centered LR and AP, beginning 8cm from the seat of the scanner. These estimates have been implemented in tests, where many subjects have been scanned paying close attention to the position of the prostate in the spatially varying gradient field. The lateral and ventral position of the prostate are highly reproducible even in men of different sizes, with less than 5cm variability in the superior direction. However, the extent and location of the targeted volume can be easily modified, if these estimates require revision. Note some foldover artifact is acceptable in the AP direction, and the disclosed RF geometry supports acceleration in this direction with very low g-factor, i.e. negligible noise amplification.

[0153] Image reconstraction can be performed on physics-informed reconstruction of nonFourier encoded data. [65-70] Both classical minimization techniques and deep learning methods can be implemented and compared for optimal performance. In addition to the image metrics described herein, diagnostic quality of all images can be regularly reviewed.

[0154] III. Methods of using

[0155] Also disclosed are methods of using the prostate MRI systems and MRI imaging device described herein to image a subject’s prostate in need of imaging. The methods involve exposing the subject to a magnetic field generated using the prostate MRI systems or the MRI imaging device disclosed herein. In use, the subject’s prostate is located within one or more coils containing one or more receive coils, one or more volume coils, and / or one or more surface coils. Preferably, the subject’s prostate is located with an RF volume coil and / or RF coil array. Preferably, during imaging, the subject is in a seated position on a horizontal or substantially horizontal surface, and the subject’s prostate is preferably between 5 cm to 20 cm above the horizontal or substantially horizontal surface. Preferably, the coil

[0156] 23

[0157] 45838501.1portion detachable from the volume coil is present, is anterior to the subject, and is across the subject’s laps. In some forms, the method further involves applying preparation echoes encoding diffusion with gradient amplitudes greater than 500 mT / m, 600 mT / m after spin polarization. Other modes of using the inhomogeneity of Bo to encode diffusion include, but are not limited to, susceptibility-induced gradients, oscillating field gradients from Bo variations, linearly varying Bo fields, stimulated echoes with Bo inhomogeneity, etc.

[0158] References

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[0272] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.

[0273] 30

[0274] 45838501.1

Claims

We claim:

1. A prostate magnetic resonance imaging (MRI) system, the prostate MRI system comprising:a first component comprising an open, field-cycling magnet configured to produce a spin-polarizing non-uniform Bo magnetic field and an acquisition non-uniform Bo magnetic field,a second component operably linked to the first component and comprising one or more coils comprising one or more receive coils, one or more volume coils, and / or one or more surface coils comprising:(i) one or more wire loops configured to transmit and / or receive radiofrequency; and(ii) optionally a coil portion detachable from the one or more coils to allow positioning (e.g., seating) a subject within the one or more coils: and a third component operably linked to the first component and comprising gradient coils,wherein the one or more coils comprise one or more segments configured to occupy a left portion, a right portion, and a posterior portion of a subject's pelvic area.

2. The MRI system of claim 1 , comprising the coil portion detachable from the one or more coils, wherein the coil portion detachable from the one or more coils is configured to occupy an anterior portion of a subject’s pelvic area.

3. The MRI system of claim 1 or 2, wherein the open, field-cycling magnet is U-shaped consisting of two vertical or substantially vertical portions connected to one horizontal or substantially horizontal portion, and comprising Bo coils that are, preferably planar or substantially planar, in the vertical portions of the U-shape.

4. The MRI system of any one of claims 1 to 3, wherein the gradient coils comprise a first set of coils configured to produce a magnetic field gradient (e.g., a spatial frequency encoding gradient) in a first direction, preferably wherein the first direction is a left-right direction with respect to the subject.

5. The MRI system of any one of claims 1 to 4, wherein the gradient coils comprise a second set of coils configured to produce a magnetic field gradient (e.g., a spatial phase encoding gradient) in a second direction, preferably wherein the second direction is an anterior-posterior direction with respect to the subject.3145838501.

16. The MRI system of any one of claims 1 to 5, wherein the one or more receive coils, the one or more volume coils, and / or the one or more surface coils independently form one or more arrays of coils.

7. The MRI system of any one of claims 1 to 6, wherein the one or more receive coils, one or more volume coils, and / or one or more surface coils are located in a seat-like structure allowing for sitting in the MRI system.

8. The MRI system of any one of claims 1 to 7, wherein the one or more coils are configured such that in use, an organ or tissue being imaged is located centrally or substantially centrally in a left-right direction and anterior-posterior direction with respect to the subject.

9. The MRI system of any one of claims 1 to 8, wherein the one or more coils (e.g., the one or more volume coils) are capable of being operated in quadrature transmit mode and / or quadrature receive mode.

10. The MRI system of any one of claims 1 to 9, wherein one or more segments of the one or more coils (e.g., the one or more volume coils) are configured to receive radiofrequency.

11. The MRI system of any one of claims 1 to 10, wherein the gradient coils comprise two pairs of wire loops, wherein a first pair of wire loops is across from a second pair of wire loops.

12. The MRI system of claim 11, wherein the two pairs of wire loops are configured to add and / or subtract a magnetic field to the spin-polarizing non-uniform Bo magnetic field.

13. The MRI system of any one of claims 1 to 12, wherein magnetic field gradients produced by the gradient coils induce magnetic field variation in an anterior-posterior direction and / or left-right direction with respect to a subject.

14. The MRI system of any one of claims 13, wherein the magnetic field variation in the anterior-posterior direction and / or in the left-right direction are direct current fields.

15. The MRI system of any one of claims 1 to 14, further comprising a multi-channel receiver array of wire loops operably linked to the first component.

16. An MRI imaging device comprising a horizontal or substantially horizontal portion and two vertical or substantially vertical portions, and the MRI system of any one of claims 1 to 15, wherein:the first component is located in the two vertical or substantially vertical portions, one or more segments of the second component are located in the two vertical or substantially vertical portions and the horizontal or substantially horizontal portion, and3245838501.1one or more segments of the third component are located in the two vertical or substantially vertical portions.

17. The MRI imaging device of claim 16, wherein the horizontal or substantially horizontal portion comprises a scat portion and the two vertical or substantially vertical portions comprise two arm rest portions.

18. The MRI imaging device of claim 16 or 17, further comprising a third vertical or substantially vertical portion, wherein the third vertical or substantially vertical portion comprises one or more segments of the second component.

19. The MRI imaging device of claim 18, wherein the coil portion detachable from the one or more coils operably links the two vertical or substantially vertical portions and is anterior to the third vertical or substantially vertical portion.

20. A method of imaging a subject’s prostate in need thereof, the method comprising:exposing the subject to a magnetic field generated using the MRI system of any one of claims 1 to 15 or the MRI imaging device of any one of claims 16 to 19, wherein the prostate is located within the one or more coils of the second component.

21. The method of claim 20, wherein the subject is in a seated position on a horizontal or substantially horizontal surface.

22. The method of claim 20 or 21, wherein the prostate is between 4 cm to 20 cm above the horizontal or substantially horizontal surface.3345838501.1

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