WO2018187338A1

WO2018187338A1 - System and method for robust mr imaging with prepared contrast using cartesian acquisition with spiral reordering (caspr)

Info

Publication number: WO2018187338A1
Application number: PCT/US2018/025896
Authority: WO
Inventors: Ananth J. Madhuranthakam; Joshua S. GREER; Xinzeng WANG; Ivan PEDROSA
Original assignee: Board Of Regents, The University Of Texas System
Priority date: 2017-04-03
Filing date: 2018-04-03
Publication date: 2018-10-11

Abstract

The present invention includes a system and method of three dimensional (3D) magnetic resonance imaging, the method comprising: preparing a contrast in a volume of a subject for magnetic resonance imaging, acquiring a plurality of 3D turbo spin echo (TSE) or 3D Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging data sets of the subject with the prepared contrast with a magnetic resonance scanner, wherein the plurality of 3D TSE of GraSE images are acquired by Cartesian acquisition with spiral reordering, and reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images with the prepared contrast.

Description

SYSTEM AND METHOD FOR ROBUST MR IMAGING WITH PREPARED CONTRAST USING CARTESIAN ACQUISITION WITH SPIRAL REORDERING (CASPR)

TECHNICAL FIELD OF THE INVENTION

The present invention relates in general to the field of magnetic resonance (MR) imaging, and more particularly, to a novel system and method for robust MR imaging with prepared contrast using Cartesian acquisition with spiral reordering (CASPR).

BACKGROUND OF THE INVENTION

Without limiting the scope of the invention, its background is described in connection with magnetic resonance (MR) imaging.

One such system is taught in U.S. Patent No. 7,821,265, issued to Busse, and entitled "Method and apparatus for acquiring MRI data for pulse sequences with multiple phase encode directions and periodic signal modulation." Briefly, this patent is said to teach a method for acquiring magnetic resonance (MR) data for a pulse sequence with periodic signal modulation and a set of views having at least two phase encode directions includes selecting a direction of modulation. While this inventor teaches a radial-like view ordering, the method does not efficiently sample the center of k-space at the beginning of each repetition, thus requiring longer acquisition times.

Another such system is taught in U.S. Patent No. 5,912,557, issued to Wilman, et al., and entitled "Centric phase encoding order for 3D NMR data acquisition." Briefly, these inventors teach a 3DFT NMR scan that is performed by stepping two phase encoding gradients through a sequence of values to sample all locations in k-space, which gradients are stepped such that k-space is covered by sampling closer to the origin of k-space first. Two methods for ordering the k-space sample points are disclosed. These inventors teach a commonly used acquisition strategy for gradient echo imaging based on an elliptical centric view ordering. However, this approach is limited to a gradient echo based acquisition and is particularly sensitive to BO inhomogeneities.

Finally, U.S. Patent Application Publication No. 2015/0327783, filed by Wang, et al., and entitled "Noninvasive 4-D Time-Resolved Dynamic Magnetic Resonance Angiography", is said to teach a method for non-contrast enhanced 4D time resolved dynamic magnetic resonance angiography (dMRA) using arterial spin labeling of blood water as an endogenous tracer and a multiphase balanced steady state free precession readout is presented. Imaging can be accelerated with dynamic golden angle radial acquisitions and k-space weighted imaging contrast (KWIC) image reconstruction and it can be used with parallel imaging techniques. Quantitative tracer kinetic models can be formed allowing cerebral blood volume, cerebral blood flow and mean transit time to be estimated. Vascular compliance can also be assessed using 4D dMRA by synchronizing dMRA acquisitions with the systolic and diastolic phases of the cardiac cycle. These inventors use gradient echo imaging, which provides reduced signal-to-noise ratio (SNR) during acquisition. Thus, this methodology is particularly sensitive to BO inhomogeneities and has been shown to have difficulties imaging brain patients with craniotomy and extending to applications in body imaging such as kidneys due to increased field of view.

SUMMARY OF THE INVENTION

In one embodiment, the present invention includes a method of three dimensional (3D) magnetic resonance imaging, the method comprising: preparing a contrast in a volume of a subject for magnetic resonance imaging; acquiring a plurality of 3D turbo spin echo (TSE) or 3D Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging data sets of the subject with the prepared contrast with a magnetic resonance scanner, wherein the plurality of 3D TSE of GraSE images are acquired by Cartesian acquisition with spiral reordering, by; sorting a plurality of ky-kz views of the plurality of 3D TSE acquisition in their increasing spatial frequency order; sorting the plurality of ky-kz views of the plurality of 3D TSE acquisition based on their angle with respect to at least one of a ky axis or a kz-axis; arranging the plurality of ky-kz views such that innermost views are acquired as the first data point for each of the plurality of 3D TSE acquisition; arranging the remaining ky-kz views such that they are increasingly acquired based on their spatial frequency; acquiring in a spiral-out trajectory each of the plurality of 3D TSE acquisition, while still maintaining Cartesian acquisition based on their angles; and reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images with the prepared contrast. In one aspect, the step of sorting a plurality of ky-kz views of the plurality of 3D TSE acquisition in their increasing spatial frequency order further comprises adding an offset to the true origin to sort all the views. In another aspect, each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE echo train by sampling a center of a k-space and traversing the k-space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid. In another aspect, the 3D magnetic resonance images are obtained without increasing sensitivity to BO inhomogeneities. In another aspect, the prepared contrast can be labeling water in blood for arterial spin labeling (ASL); saturating tissue for chemical exchange saturation transfer (CEST); saturating tissue for magnetization transfer (MT); or a diffusion-weighted preparation. In another aspect, the prepared ASL contrast can be a volume of blood magnetized with a radiofrequency (RF) pulse that inverts or saturates water protons in flowing blood supplying a region or organ to be imaged. In another aspect, the magnetic resonance imaging data sets are acquired with inherent contrast and without providing the subject an exogenous MRI contrast agent. In another aspect, the view ordering with the magnetic resonance scanner uses a standard Fourier transformation reconstruction of the data set acquired on a Cartesian grid. In another aspect, the method further comprises the step of combining the 3D magnetic resonance images with parallel imaging and accelerated acquisitions including compressed sensing (CS). In another aspect, a region imaged is a brain that may include at least one of a craniotomy or external metallic hardware, kidneys, lungs, heart, or for body imaging. In another aspect, the Cartesian acquisition with spiral reordering acquires longer echo trains to minimize motion artifacts and shortens the overall scan time when compared to spiral acquisitions alone. In another aspect, the subject is not provided an exogenous MRI contrast agent. In another embodiment, the present invention includes a method of processing three dimensional (3D) magnetic resonance images, the method comprising: labeling water in a volume of blood of a test subject for magnetic resonance imaging without providing the subject an MRI contrast agent; acquiring a plurality of turbo spin echo (TSE) sequence or Gradient and Spin Echo (GraSE) magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner, wherein the TSE images are acquired by Cartesian acquisition with spiral reordering; and reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO inhomogeneities. In one aspect, each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE echo train by sampling a center of a k-space and traversing the k-space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid. In another aspect, the water is labeled for arterial spin labeling (ASL); saturating tissue for chemical exchange saturation transfer (CEST); saturating tissue for magnetization transfer (MT); or diffusion-weighted preparation. In another aspect, the volume of blood is magnetized with a radiofrequency (RF) pulse that inverts or saturates water protons in flowing blood supplying a region or organ to be imaged. In another aspect, the view ordering with the magnetic resonance scanner uses a standard Fourier transformation reconstruction of the data set acquired on a Cartesian grid. In another aspect, the method further comprises the step of combining the 3D magnetic resonance images with parallel imaging and accelerated acquisitions including compressed sensing (CS). In another aspect, a region imaged is a brain that may include at least one of a craniotomy or external metallic hardware, kidneys, lungs, heart, or for body imaging. In another aspect, Cartesian acquisition with spiral reordering acquires longer echo trains to minimize motion artifacts and shortens the overall scan time when compared to spiral acquisitions alone.

In yet another embodiment, the present invention also includes a method of three dimensional (3D) dynamic magnetic resonance imaging of an imaging space comprising: placing a subject into a substantially homogeneous magnetic field in the imaging space of a magnetic resonance imager; labeling water in a volume of blood of a test subject for magnetic resonance imaging without providing the subject an MRI contrast agent; acquiring a plurality of turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner with a turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence, wherein the TSE images are acquired by Cartesian acquisition with spiral reordering; and reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO inhomogeneities. In one aspect, each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE of GraSE echo train by sampling a center of a k-space and traversing the k-space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid. In one aspect, each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE or GraSE echo train by sampling a center of a k-space and traversing the k-space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid.

In yet another embodiment, the present invention also includes a computerized method of three dimensional (3D) dynamic magnetic resonance imaging, the method comprising: acquiring a plurality of 3D turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging image data sets of the subject with the prepared contrast with a magnetic resonance scanner, wherein the plurality of 3D TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering, and using a processor; sorting a plurality of ky-kz views of the plurality of 3D TSE or GraSE images in their increasing spatial frequency order; sorting the plurality of ky-kz views of the plurality of 3D TSE or GraSE images based on their angle with respect to at least one of a ky axis or a kz-axis; arranging the plurality of ky-kz views such that innermost views are acquired as the first data point for each of the plurality of 3D TSE or GraSE images acquired; arranging the remaining ky-kz views such that they are increasingly acquired based on their spatial frequency; acquiring in a spiral-out trajectory each of the plurality of 3D TSE or GraSE images, while still maintaining Cartesian acquisition based on their angles; reconstructing the magnetic resonance images from the acquired data sets using the processor to provide a set of 3D magnetic resonance images with the prepared contrast; and storing or displaying at least one of the 3D magnetic resonance images. In one aspect, the method further comprises acquiring the plurality of TSE or GraSE sequence magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner, wherein the TSE or GraSe images are acquired by Cartesian acquisition with spiral reordering with the processor; and reconstructing the magnetic resonance images from the acquired TSE or GraSe sequence magnetic resonance imaging data sets using the processor to provide a set of 3D magnetic resonance images without increasing sensitivity to BO inhomogeneities.

In yet another embodiment, the present invention includes a system for three dimensional (3D) dynamic magnetic resonance imaging, the system comprising: a magnetic resonance imager capable of generating a substantially homogeneous magnetic field in an imaging space and capable of detecting a volume of water in blood of a subject for magnetic resonance imaging without providing the subject an MRI contrast agent; a processor comprising a non-transitory computer readable medium comprising instructions stored thereon for: acquiring a plurality of 3D turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging image data sets of the subject with the prepared contrast with a magnetic resonance scanner, wherein the plurality of 3D TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering, and using the processor; sorting a plurality of ky-kz views of the plurality of 3D TSE or GraSE images in their increasing spatial frequency order; sorting the plurality of ky-kz views of the plurality of 3D TSE or GraSE images based on their angle with respect to at least one of a ky axis or a kz-axis; arranging the plurality of ky-kz views such that innermost views are acquired as the first data point for each of the plurality of 3D TSE images acquired; arranging the remaining ky-kz views such that they are increasingly acquired based on their spatial frequency; acquiring in a spiral-out trajectory each of the plurality of 3D TSE or GraSE images, while still maintaining Cartesian acquisition based on their angles; reconstructing the magnetic resonance images from the acquired data sets using the processor to provide a set of 3D magnetic resonance images with the prepared contrast; and storing or displaying at least one of the 3D magnetic resonance images; wherein the processor reconstructs the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images with a processor, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO mhomogeneities; and storing on the computer or in the one or more databases or displaying on a communications interface the 3D magnetic resonance images. In one aspect, the system further comprises: acquiring the plurality of TSE or GraSE sequence magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner, wherein the TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering with the processor; and reconstructing the magnetic resonance images from the acquired TSE or GraSE sequence magnetic resonance imaging data sets using the processor to provide a set of 3D magnetic resonance images without increasing sensitivity to BO inhomogeneities.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the features and advantages of the present invention, reference is now made to the detailed description of the invention along with the accompanying figures and in which:

FIGS. 1A and IB show two sampling patterns of a 3D TSE acquisition using linear (FIG. 1A) and the current invention, Cartesian Acquisition with SPiral Reordering (CASPR) (FIG. IB) view ordering shown in ky-kz plane, where each point represents an echo. The echoes sampled at the beginning of the echo train are shown in blue transitioning to red at the end of each echo train. The CASPR acquisition traverses out in a spiral trajectory but maintaining sampling on a Cartesian grid.

FIGS 2A to 2D show brain perfusion images of the same slice acquired using (FIG. 2A) 30 repetitions of brain perfusion images using an echo planar imaging (EPI) readout and 2D pseudo- continuous arterial spin labeling (pCASL), (FIG. 2B) Average EPI image from 30 repetitions of FIG. 2 A, (FIG. 2C) 3D TSE with linear View Ordering, and (FIG. 2D) 3D TSE with CASPR View Ordering, both using pCASL. The 3D TSE images are axial reformats from a sagittal acquisition (see FIGS. 3A and 3B).

FIGS. 3A and 3B show multiple slices showing complete coverage of the brain using 3D TSE pCASL with (FIG. 3A) linear and (FIG. 3B) the proposed 3D CASPR trajectory.

FIGS. 4A and 4B show 3D pCASL with CASPR view ordering provided robust images of the whole brain (FIG. 4B) compared to multi-slice 2D pCASL with EPI readout (FIG. 4A) across all volunteers. Due to the robustness of CASPR acquisition to B0 inhomogeneities, perfusion signal is preserved at the increased B0 sensitive areas such as frontal lobe and around orbits with 3D CASPR acquisition (FIG. 4B). FIGS. 5A to 5D show multiple slices showing complete coverage of the kidneys using 3D TSE pCASL with (FIG. 5A) linear and (FIG. 5B) the proposed 3D CASPR trajectory. The reformats in different orientations are shown from linear (FIG. 5C) and 3D CASPR (FIG. 5D) trajectories, showing robust images with 3D CASPR.

FIG. 6A is a flowchart that shows the basic steps of the present invention.

FIG. 6B shows another flow chart that describes an example of actual sorting and acquisition of the 3D CASPR view ordering.

FIG. 7 shows an undersampled 3D CASPR trajectory with a compressed sensing (CS) reduction factor of 3, and 5% of fully sampled center of k-space. For each shot, the echo train starts sampling from the center of the k-space and traverses out in a spiral-out trajectory, allowing for completely sampled central k-space for CS reconstruction. Earlier echoes are shown in blue, while the later echoes are shown in red.

FIG. 8 shows the results of 3D Sparse-BLIP reconstruction applied to a fully sampled proton density weighted brain image using the 3D CASPR trajectory. ZP represents the zero filled image using the retrospective undersampling, which was able to be reconstructed using the Sparse-BLIP reconstruction showing minimal error compared to the fully sampled image, due to the fully sampled central k-space that makes the acquisition more robust to the prepared ASL contrast.

FIG. 9 is a 3D ASL image acquired using a fully sampled 3D CASPR trajectory, that were retrospectively undersampled with CS factors of 2 (left column), 2.5 (middle column) and 3 (right column). 3D Sparse- BLIP reconstruction was able to restore the structural details with minimal loss compared to fully sampled image.

FIGS. 10A to IOC show fully sampled (FIG. 10A) and undersampled ASL images with a CS factor of 3, reconstructed using zero- filling (FIG. 10B) and 3D Sparse-BLIP reconstruction (FIG. IOC). The scan time for the fully sampled acquisition was 6 minutes compared to 2 minutes with undersampling.

FIGS. 11A and 11B show multiple slices from the axial reformats of zero-filled (FIG. 11 A) and 3D Sparse-BLIP reconstructed (FIG. 11B) perfusion images.

FIGS. 12A shows the Relative dispersion (RD), measured as the ratio of standard deviation to the mean, shows robust perfusion measurements in different parts of the brain with the current art (CASPR) compared to the prior art (EPF).

FIG. 12B shows the average values measured with both techniques agree with each other. The values shown are average across 5 volunteers.

DETAILED DESCRIPTION OF THE INVENTION

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

To facilitate the understanding of this invention, a number of terms are defined below. Terms defined herein have meanings as commonly understood by a person of ordinary skill in the areas relevant to the present invention. Terms such as "a", "an" and "the" are not intended to refer to only a singular entity, but include the general class of which a specific example may be used for illustration. The terminology herein is used to describe specific embodiments of the invention, but their usage does not limit the invention, except as outlined in the claims.

Magnetic Resonance (MR) imaging has a unique capability of generating images with various inherent contrasts without the administration of exogenous contrast agents. While the majority of these different contrasts can be generated by varying the imaging parameters (e.g. repetition time (TR) and/or echo time (TE)), more interesting contrasts are generated as a preparation (e.g., arterial spin labeling (ASL), diffusion-weighted imaging (DWI), chemical exchange saturation transfer (CEST), magnetization transfer (MT) etc.) before the imaging sequence. A challenge in imaging this prepared contrast is to acquire the signal immediately before the contrast dissipates. The prior art has proposed various imaging methods to acquire these prepared contrasts using either echo planar imaging (EPI) or turbo spin echo (TSE) sequences.

The present inventors have now recognized that an advantage of these prior art sequences is the use of a 90-degree excitation pulse that samples the entire prepared contrast with high efficiency. Specifically, with the turbo spin echo (TSE) sequence, the acquisitions can be extended to three dimensions (3D) for whole volumetric coverage that are challenging with EPI acquisitions. With 3D TSE acquisition, the data are often acquired in multiple shots using various view orderings including linear, radial (1) and/or spiral (2). Specifically, 3D spiral view orderings have shown considerable promise due to the repeated sampling of the center of k-space and has been recommended as a choice of imaging sequence for brain ASL by the expert panel at International Society for Magnetic Resonance in Medicine (ISMRM) (3). However, there are several challenges in applying spiral acquisitions to image brain patients with craniotomy (i.e. external metallic hardware) as well as in extending to body imaging due to increased sensitivity of spiral acquisitions to BO inhomogeneities. In this disclosure, the inventors present a novel system and a method for robust MR imaging with prepared contrast using a novel 3D TSE acquisition using Cartesian Acquisition with SPiral Reordering (CASPR) and show robust ASL prepared non-contrast perfusion images in, e.g., brain and kidneys.

The present invention provides the following distinct advantages over the prior art: (1) Use of a spiral view ordering, yet retaining the Cartesian acquisition strategy, which increases robustness to BO inhomogeneities. (2) Application of CASPR view ordering (4) with a segmented 3D TSE acquisition that can be readily implemented to acquire prepared contrast including but not limited to ASL, CEST and MT. (3) The view ordering can be readily implemented on commercial MR scanners and use the standard Fourier transformation reconstruction since the data are acquired on a Cartesian grid. (4) The CASPR view ordering is readily amenable to combine with parallel imaging and accelerated acquisitions such as compressed sensing (CS).

EXAMPLE 1. Robust 3D pCASL perfusion imaging using a Cartesian Acquisition with Spiral Reordering (CASPR).

Arterial spin labeling can non-invasively measure perfusion, but offers low SNR compared to contrast-enhanced perfusion techniques. The present invention includes a novel 3D TSE with a Cartesian Acquisition with SPiral Reordering (CASPR) that was implemented and combined with pCASL in the brain and kidneys. This sampling technique samples the center of k-space early in each echo train, and was shown to provide significantly improved 3D perfusion images compared to 3D linear acquisitions, and more extensive coverage than 2D acquisitions in a similar scan time.

Arterial spin labeling (ASL) is a perfusion imaging technique with significant clinical potential due to its ability to provide perfusion maps without the administration of exogenous contrast agents. ASL has been well established for brain perfusion, and is being used increasingly to measure renal perfusion. These images are generally acquired using multiple signal averages to account for the low SNR and the characteristic significant variations among the multiple dynamic acquisitions. To overcome these challenges, 3D imaging using spiral acquisitions was recommended on a consensus paper by the ISMRM's ASL expert panel, since the spiral acquisitions sample the center of k-space repeatedly. However, there are several challenges in extending spiral acquisitions outside neuro imaging, particularly to body imaging with areas of increased BO inhomogeneities. A novel 3D TSE acquisition using Cartesian Acquisition with SPiral Reordering (CASPR), was implemented that can be used to image, e.g., brain and kidney perfusion.

The 3D CASPR view ordering is shown in FIG. IB. With this approach, each shot of the 3D TSE echo train begins by sampling the center of k-space and traversing the k-space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid. Since the CASPR trajectory samples the center of k-space at the beginning of each echo train (compared to linear view ordering (FIG. 1A)), this approach maximizes the prepared ASL signal allowing for longer echo trains to shorten the overall scan time, and minimize motion artifacts.

The 3D CASPR view ordering (FIG. IB) was implemented for a pCASL acquisition with background suppression and inflow saturation on a 3T Ingenia scanner (Philips Healthcare, The Netherlands). Brain perfusion images were acquired using 3D CASPR and compared against 3D TSE using a linear sampling scheme (FIG. 1A), as well as multi-slice 2D gradient echo EPI in 3 volunteers. Similarly, kidney perfusion images were acquired in 3 volunteers with 3D CASPR and compared against 3D TSE with linear sampling and 2D SShTSE. The label duration and post-label delay were 1.8s for the brain and 1.5s for the kidneys.

Imaging parameters for brain perfusion were: 2D EPI: scan time = 4:20, axial acquisition, 16 slices and 30 signal averages, 3x3x5 mm resolution, SENSE P reduction = 2.3.

3D Linear: scan time = 4:23, sagittal acquisition, 3x3x3 mm resolution, 56 slices, half-scan factor = 0.6 along Ky, echo train length (ETL) = 86.

3D CASPR: scan time = 5:34, sagittal acquisition, 3x3x3 mm resolution, 52 slices, ETL = 100.

Imaging parameters for coronal kidney perfusion images were:

2D SShTSE: scan time 3:41, 3x3 mm resolution, 10mm slice thickness, 16 signal averages, half- scan factor = 0.6.

3D Linear: scan time: 4:20, 3x3x3 mm resolution, 28 slices, halfscan factor = 0.7 along Ky, ETL = 90.

3D CASPR: scan time: 4:20, 3x3x3 mm resolution, 28 slices, ETL = 120.

FIGS. 2A to 2D show brain perfusion images using multiple repetitions of 2D EPI pCASL (FIG. 2A) and the average of these repetitions (FIG. 2B), compared with 3D TSE acquisition using linear (FIG. 2C) and 3D CASPR (FIG. 2D) trajectories in the same slice. The 2D EPI shows significant variations from repetition to repetition and 3D CASPR shows improved image quality with higher SNR compared to 3D TSE with linear sampling. FIGS. 3A and 3B show multiple slices across the brain acquired using 3D TSE with linear (FIG. 3A) and CASPR (FIG. 3B) view ordering, showing improved SNR with 3D CASPR.

3D pCASL with CASPR view ordering provided robust images of the whole brain (FIG. 4B) compared to multi-slice 2D pCASL with EPI readout (FIG. 4A) across all volunteers. Due to repeated sampling of the center of k-space in each shot, 3D CASPR trajectory provided robust images compared to 3D TSE with linear view ordering.

Similar patterns are observed in kidney perfusion (5A to 5D) showing improved image quality and SNR with 3D CASPR trajectory compared against linear sampling.

The present inventors found that, with ASL acquisitions, it is critical to sample the labeled signal consistently for improved image quality and signal-to-noise -ratio (SNR). The spiral sampling strategy of the present invention provides this capability by repeatedly sampling the center of k-space for each repetition. The example 3D CASPR trajectory provides similar capabilities, while still maintaining the sampling on a Cartesian grid and provides a more robust acquisition for 3D perfusion imaging than the linear acquisition. The 3D CASPR trajectory of the present invention also offers more complete coverage than that of 2D acquisitions in similar scan times due to improved SNR and extended echo trains. Due to the Cartesian sampling, the CASPR trajectory was also found to provide accelerated imaging such as parallel imaging and/or compressed sensing to further reduce the scan times.

FIG. 6A shows a flowchart of the CASPR methodology 10 of the present invention. In first step 12, the water in a volume of blood is labeled for magnetic resonance imaging. Next, in step 14, the user acquires a plurality of turbo spin echo (TSE) sequence magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner, wherein the TSE images are acquired by Cartesian acquisition with spiral reordering. Finally, in step 16, the method reconstructs the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images. Each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE echo train by sampling a center of a k- space and traversing the k-space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid. The methodology 10 can be used in a method of three dimensional (3D) magnetic resonance imaging of an imaging space comprising: placing a subject into a substantially homogeneous magnetic field in the imaging space of a magnetic resonance imager; labeling water in a volume of blood of a test subject for magnetic resonance imaging without providing the subject an MRI contrast agent; acquiring a plurality of turbo spin echo (TSE) sequence magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner with a turbo spin echo (TSE) sequence, wherein the TSE images are acquired by Cartesian acquisition with spiral reordering; and reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO inhomogeneities.

FIG. 6B shows a flow chart 20 that describes an example of actual sorting and acquisition of the 3D

CASPR view ordering. In step 22, a sort the ky-kz views of 3D TSE is conducted in their increasing spatial frequency order. It is also possible to add an offset to the true origin to sort all views. Next, in step 24, it is also possible to sort the ky-kz views of 3D TSE based on their angle with respect to the ky and/or kz-axis. In step 26, the views are arranged such that innermost views are acquired as the first data point for each shot. In step 28, remaining views are arranged such that they are increasingly (based on their spatial frequency) acquired in each shot. Finally, in step 30, within each shot, the views are acquired in a spiral-out trajectory, while still maintaining Cartesian acqusition based on their angles to generate the final images.

EXAMPLE 2 - Accelerated 3D Arterial Spin Labeling using Cartesian Acquisition with Spiral Reordering and Compressed Sensing.

Arterial spin labeling (ASL) is a non-contrast perfusion imaging method for MRI. However, 2D ASL suffers from low signal to noise ratio. 3D ASL is favorable to overcome the limitation of 2D ASL, but 3D acquisition is time-consuming, so acceleration of 3D ASL is highly desired. The new compressed sensing (CS) theory allows perfect reconstruction, far below Nyquist rate. A novel 3D TSE acquisition was implemented using Cartesian Acquisition with SPiral Reordering (CASPR), which can be undersampled and combined with CS. Preliminary results show improved image quality using 3D Sparse-BLIP reconstruction that is comparable to fully sampled acquisition.

Arterial spin labeling (ASL) is a quantitative non-contrast perfusion imaging method that can be performed on standard MRI equipment [1]. However, as discussed hereinabove, 2D ASL suffers from low signal-to-noise-ratio (SNR) and requires multiple signal averages. The higher SNR and increased volume coverage afforded by 3D acquisitions can overcome certain limitations of 2D acquisitions. Hence, the consensus paper on brain perfusion suggested using TSE/GraSE acquisition with 3D spiral trajectories. However, these acquisitions are still long (e.g. 5~7 minutes) for whole brain coverage and can benefit from shortened acquisitions. The sparse signal of the ASL images renders it to be readily applicable with emerging compressed sensing (CS) theory [2-5]. However, the extension of CS algorithms to non-Cartesian acquisitions is non- trivial [6]. In this work, a novel 3D TSE acquisition using Cartesian Acquisition with SPiral Reordering (CASPR) was implemented, which can be readily undersampled and combined with CS reconstruction.

Acquisition: The 3D CASPR view ordering that can be performed with a pseudo-random undersampling was implemented on a 3T Philips Ingenia scanner. Each shot of the 3D TSE echo train begins from the center of the k-space and traverses spirally outwards, yet sampling on the Cartesian ky-kz grid. The k-space was downsampled with a pseudo random undersampling and segmented into multiple spiral interleaves in ky- kz plane (FIG. 7). By sampling the center of k-space at the beginning of each echo train, this approach increases the efficiency of capturing the ASL prepared signal. The fully sampled central part of the k- space can be used for sensitivity estimation. Due to the sampling on the Cartesian grid, this sampling approach can be readily reconstructed using fast Fourier transformations and combined with CS. CS reconstruction was first evaluated on a brain proton density weighted image acquired using the fully sampled k-space with CASPR trajectory. Subsequently, ASL images were acquired using pseudo- continuous labeling and acquired with a fully sampled CASPR trajectory. In both cases, CS reconstruction was evaluated by retrospectively undersampling the k-space. Finally, 3D pCASL images of the brain were acquired using an undersampled CASPR trajectory with a reduction factor R=3, as shown in FIG. 7. Imaging parameters were: TR/TE=6000/12 ms, FOV=200x200xl60 mm3, matrix=80x80 with 52 slices of 6 mm slices, reconstructed to 3 mm slices. Total acquisition time was 6 minutes for fully sampled acquisition and 2 minutes for R=3 undersampled acquisition.

Reconstruction: Sparse-BLIP [7] provides a framework for image reconstruction without knowledge of coil sensitivities. We extended the original 2D Sparse-BLIP method to 3D, where 3D sparsity was considered and sparse constraint was calculated in the x-y-z domain. The objective equation was defined as:

- d, HI + ίϊίΐΨθΟΐ_! + j§ EJiSJ

where / is the desired 3D images and Si is coil sensitivity map from the /-th coil, F is the undersampling Fourier operator, is the undersampled 3D k-space data from the /-th coil, Ψ(·) is the 3D sparse transform operator, such as the 3D total variation (TV) operator or 3D wavelet operator, and 3D TV was selected considering the running efficiency, H^'^¹ is the LI- norm to constraint the sparsity of images,

II "Hi is the L2-norm to constraint the smooth property of the sensitivity, a and β are regularization parameters.

FIG. 8 shows the feasibility of 3D Sparse-BLIP reconstruction as applied to a fully sampled proton density weighted brain image, which was retrospectively undersampled by a factor of 3 using 3D CASPR trajectory. FIG. 9 shows the 3D pCASL images acquired with a fully sampled CASPR trajectory that was undersampled retrospectively with factors of 2, 2.5 and 3. The zero-filled images show more blurring, which were successfully reconstructed using 3D Sparse-BLIP to increase spatial resolution. Compared to fully sampled images, there was minimal error with some loss of details. FIGS. 10A to IOC compare a fully sampled image (6 min acquisition) with an undersampled image using a factor of 3 (2 min acquisition) using zero-filled reconstruction and using 3D Sparse-BLIP reconstruction. FIGS. 11A and 11B show multiple slices of the axial reformats from the undersampled ASL image using zero-filling (FIG. 11 A) and 3D Sparse-BLIP reconstruction (FIG. 11B), which was acquired in 2 minutes.

FIGS. 12A shows the Relative dispersion (RD), measured as the ratio of standard deviation to the mean, shows robust perfusion measurements in different parts of the brain with the current art (CASPR) compared to the prior art (EPI). FIG. 12B shows the average values measured with both techniques agree with each other. The values shown are average across 5 volunteers.

The present inventors implemented an efficient 3D Cartesian Acquisition using SPiral Reordering (CASPR) method for ASL perfusion that can be readily undersampled and combined with CS. Preliminary results show improved image quality using 3D Sparse-BLIP based CS reconstruction that is comparable to fully sampled acquisition. Future optimization will include different undersampling patterns, such as Poisson-disk, for improved image quality. This method, once optimized, can provide whole brain perfusion images in 2 minutes. Thus, the present invention can reduce total acquisition time by 80, 70, 60, 50, 40, 30, 33% or lower percent when compared to current acquisition methods that have a higher signal to noise ratio.

It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method, kit, reagent, or composition of the invention, and vice versa. Furthermore, compositions of the invention can be used to achieve methods of the invention.

It will be understood that particular embodiments described herein are shown by way of illustration and not as limitations of the invention. The principal features of this invention can be employed in various embodiments without departing from the scope of the invention. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures described herein. Such equivalents are considered to be within the scope of this invention and are covered by the claims.

All publications and patent applications mentioned in the specification are indicative of the level of skill of those skilled in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

The use of the word "a" or "an" when used in conjunction with the term "comprising" in the claims and/or the specification may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." The use of the term "or" in the claims is used to mean "and/or" unless explicitly indicated to refer to alternatives only or the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and "and/or." Throughout this application, the term "about" is used to indicate that a value includes the inherent variation of error for the device, the method being employed to determine the value, or the variation that exists among the study subjects.

As used in this specification and claim(s), the words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. In embodiments of any of the compositions and methods provided herein, "comprising" may be replaced with "consisting essentially of or "consisting of. As used herein, the phrase "consisting essentially of requires the specified integer(s) or steps as well as those that do not materially affect the character or function of the claimed invention. As used herein, the term "consisting" is used to indicate the presence of the recited integer (e.g., a feature, an element, a characteristic, a property, a method/process step or a limitation) or group of integers (e.g., feature(s), element(s), characteristic(s), property(ies), method/process steps or limitation(s)) only.

The term "or combinations thereof as used herein refers to all permutations and combinations of the listed items preceding the term. For example, "A, B, C, or combinations thereof is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

As used herein, words of approximation such as, without limitation, "about", "substantial" or

"substantially" refers to a condition that when so modified is understood to not necessarily be absolute or perfect but would be considered close enough to those of ordinary skill in the art to warrant designating the condition as being present. The extent to which the description may vary will depend on how great a change can be instituted and still have one of ordinary skilled in the art recognize the modified feature as still having the required characteristics and capabilities of the unmodified feature. In general, but subject to the preceding discussion, a numerical value herein that is modified by a word of approximation such as "about" may vary from the stated value by at least ±1, 2, 3, 4, 5, 6, 7, 10, 12 or 15%.

All of the compositions and/or methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

REFERENCES - EXAMPLE 1

Alsop, David C, et al. "Recommended implementation of arterial spin—labeled perfusion MRI for clinical applications: A consensus of the ISMRM perfusion study group and the European consortium for ASL in dementia." Magnetic resonance in medicine 73.1 (2015): 102-116.

Robson, Philip M., et al. "Volumetric Arterial Spin-labeled Perfusion Imaging of the Kidneys with a Three-dimensional Fast Spin Echo Acquisition." Academic radiology 23.2 (2016): 144-154.

Usman, Muhammad, et. al. "Highly-efficient free breathing whole heart CINE MRI with self gated 3D CASPR-TIGER trajectory" Proceedings 24th Scientific Meeting, International Society for Magnetic Resonance in Medicine, Singapore (2016).

REFERENCES - EXAMPLE 2

[1] Detre JA, et al. MRM 1992;23:37-45.

[2] Candes EJ, et al. IEEE TIT 2006;52:489-509.

[3] Donoho DL. IEEE TIT 2006;52: 1289-1306.

[4] Lustig M, et al. MRM 2007;58: 1182-1195.

[5] Zhou Y, et al. ISMRM 2013;pp.605.

[6] Zhao L, et al. Neuroimage. 2015;121:205-16.

[7] She H, et al. MRM 2014;71:645-660.

Claims

WHAT IS CLAIMED IS:

1. A method of three dimensional (3D) magnetic resonance imaging, the method comprising: preparing a contrast in a volume of a subject for magnetic resonance imaging;

acquiring a plurality of 3D turbo spin echo (TSE) or 3D Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging data sets of the subject with the prepared contrast with a magnetic resonance scanner, wherein the plurality of 3D TSE of GraSE images are acquired by Cartesian acquisition with spiral reordering, by;

sorting a plurality of ky-kz views of the plurality of 3D TSE acquisition in their increasing spatial frequency order;

sorting the plurality of ky-kz views of the plurality of 3D TSE acquisition based on their angle with respect to at least one of a ky axis or a kz-axis;

arranging the plurality of ky-kz views such that innermost views are acquired as the first data point for each of the plurality of 3D TSE acquisition;

arranging the remaining ky-kz views such that they are increasingly acquired based on their spatial frequency;

acquiring in a spiral-out trajectory each of the plurality of 3D TSE acquisition, while still maintaining Cartesian acquisition based on their angles; and

reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images with the prepared contrast.

2. The method of claim 1, wherein the step of sorting a plurality of ky-kz views of the plurality of 3D TSE acquisition in their increasing spatial frequency order further comprises adding an offset to the true origin to sort all the views.

3. The method of claim 1, wherein each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE echo train by sampling a center of a k-space and traversing the k- space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid.

4. The method of claim 1, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO inhomogeneuies.

5. The method of claim 1, wherein the prepared contrast can be labeling water in blood for arterial spin labeling (ASL); saturating tissue for chemical exchange saturation transfer (CEST); saturating tissue for magnetization transfer (MT); or a diffusion-weighted preparation.

6. The method of claim 1, wherein the prepared ASL contrast can be a volume of blood magnetized with a radiofrequency (RF) pulse that inverts or saturates water protons in flowing blood supplying a region or organ to be imaged.

7. The method of claim 1, wherein the magnetic resonance imaging data sets are acquired with inherent contrast and without providing the subject an exogenous MRI contrast agent.

8. The method of claim 1, wherein the view ordering with the magnetic resonance scanner uses a standard Fourier transformation reconstruction of the data set acquired on a Cartesian grid.

9. The method of claim 1, further comprising the step of combining the 3D magnetic resonance images with parallel imaging and accelerated acquisitions including compressed sensing (CS).

10. The method of claim 1, wherein a region imaged is a brain that may include at least one of a craniotomy or external metallic hardware, kidneys, lungs, heart, or for body imaging.

11. The method of claim 1 , wherein the Cartesian acquisition with spiral reordering acquires longer echo trains to minimize motion artifacts and shortens the overall scan time when compared to spiral acquisitions alone.

12. The method of claim 1, wherein the subject is not provided an exogenous MRI contrast agent.

13. A method of processing three dimensional (3D) magnetic resonance images, the method comprising:

labeling water in a volume of blood of a test subject for magnetic resonance imaging without providing the subject an MRI contrast agent;

acquiring a plurality of turbo spin echo (TSE) sequence or Gradient and Spin Echo (GraSE) magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner, wherein the TSE images are acquired by Cartesian acquisition with spiral reordering; and

reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO inhoinogeneities.

14. The method of claim 13, wherein each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE echo train by sampling a center of a k-space and traversing the k- space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid.

15. The method of claim 13, wherein the water is labeled for arterial spin labeling (ASL); saturating tissue for chemical exchange saturation transfer (CEST); saturating tissue for magnetization transfer

(MT); or diffusion-weighted preparation.

16. The method of claim 13, wherein the volume of blood is magnetized with a radiofrequency (RF) pulse that inverts or saturates water protons in flowing blood supplying a region or organ to be imaged.

17. The method of claim 13, wherein the view ordering with the magnetic resonance scanner uses a standard Fourier transformation reconstruction of the data set acquired on a Cartesian grid.

18. The method of claim 13, further comprising the step of combining the 3D magnetic resonance images with parallel imaging and accelerated acquisitions including compressed sensing (CS).

19. The method of claim 13, wherein a region imaged is a brain that may include at least one of a craniotomy or external metallic hardware, kidneys, lungs, heart, or for body imaging.

20. The method of claim 13, wherein the Cartesian acquisition with spiral reordering acquires longer echo trains to minimize motion artifacts and shortens the overall scan time when compared to spiral acquisitions alone.

21. A method of three dimensional (3D) dynamic magnetic resonance imaging of an imaging space comprising:

placing a subject into a substantially homogeneous magnetic field in the imaging space of a magnetic resonance imager;

acquiring a plurality of magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner with a turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence, wherein the TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering; and

reconstructing the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO irihornogerteiiies.

22. The method of claim 21, wherein each image of the plurality of magnetic resonance images acquired is processed from a 3D TSE or GraSE echo train by sampling a center of a k-space and traversing the k-space in a spiral-out trajectory, while maintaining the sampling on a Cartesian ky-kz grid.

23. A computerized method of three dimensional (3D) dynamic magnetic resonance imaging, the method comprising:

acquiring a plurality of 3D turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging image data sets of the subject with the prepared contrast with a magnetic resonance scanner, wherein the plurality of 3D TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering, and using a processor;

sorting a plurality of ky-kz views of the plurality of 3D TSE or GraSE images in their increasing spatial frequency order;

sorting the plurality of ky-kz views of the plurality of 3D TSE or GraSE images based on their angle with respect to at least one of a ky axis or a kz-axis;

arranging the plurality of ky-kz views such that innermost views are acquired as the first data point for each of the plurality of 3D TSE or GraSE images acquired;

acquiring in a spiral-out trajectory each of the plurality of 3D TSE or GraSE images, while still maintaining Cartesian acquisition based on their angles;

reconstructing the magnetic resonance images from the acquired data sets using the processor to provide a set of 3D magnetic resonance images with the prepared contrast; and storing or displaying at least one of the 3D magnetic resonance images.

24. The method of claim 23, further comprising:

acquiring the plurality of turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner, wherein the TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering with the processor; and reconstructing the magnetic resonance images from the acquired TSE or GraSE sequence magnetic resonance imaging data sets using the processor to provide a set of 3D magnetic resonance images without increasing sensitivity to BO inhomogeneities.

25. A system for three dimensional (3D) dynamic magnetic resonance imaging, the system comprising:

a magnetic resonance imager capable of generating a substantially homogeneous magnetic field in an imaging space and capable of detecting a volume of water in blood of a subject for magnetic resonance imaging without providing the subject an MRI contrast agent;

a processor comprising a non-transitory computer readable medium comprising instructions stored thereon for:

acquiring a plurality of 3D turbo spin echo (TSE) or Gradient and Spin Echo (GraSE) sequence magnetic resonance imaging image data sets of the subject with the prepared contrast with a magnetic resonance scanner, wherein the plurality of 3D TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering, and using the processor;

arranging the plurality of ky-kz views such that innermost views are acquired as the first data point for each of the plurality of 3D TSE images acquired;

reconstructing the magnetic resonance images from the acquired data sets using the processor to provide a set of 3D magnetic resonance images with the prepared contrast; and

storing or displaying at least one of the 3D magnetic resonance images;

wherein the processor reconstructs the magnetic resonance images from the acquired data sets to provide a set of 3D magnetic resonance images with a processor, wherein the 3D magnetic resonance images are obtained without increasing sensitivity to BO inbomogeneities; and

storing on the computer or in the one or more databases or displaying on a communications interface the 3D magnetic resonance images.

26. The system of claim 25, further comprising:

acquiring the plurality of TSE or GraSE sequence magnetic resonance imaging data sets of the test subject with a magnetic resonance scanner, wherein the TSE or GraSE images are acquired by Cartesian acquisition with spiral reordering with the processor; and

reconstructing the magnetic resonance images from the acquired TSE or GraSE sequence magnetic resonance imaging data sets using the processor to provide a set of 3D magnetic resonance images without increasing sensitivity to BO mhomogeneities.