Application of high-density 2D receiver coil arrays for improved SNR in prostate MRI.

Purpose: To study if adaptive image receive (AIR) receiver coil elements can be configured into a 2D array with high (>45% by diameter) element-to-element overlap, allowing improved SNR at depth (0.7-1.5× element diameter) versus conventional (20%) overlap.

Comparison of model-based versus deep learning-based image reconstruction for thin-slice T2-weighted spin-echo prostate MRI.

Purpose: To compare a previous model-based image reconstruction (MBIR) with a newly developed deep learning (DL)-based image reconstruction for providing improved signal-to-noise ratio (SNR) in high through-plane resolution (1 mm) T2-weighted spin-echo (T2SE) prostate MRI.

Methods: Large-area contrast and high-contrast spatial resolution of the reconstruction methods were assessed quantitatively in experimental phantom studies. The methods were next evaluated radiologically in 17 subjects at 3.

Model-based image reconstruction with wavelet sparsity regularization for through-plane resolution restoration in T -weighted spin-echo prostate MRI.

Purpose: The purpose is to develop a model-based image-reconstruction method using wavelet sparsity regularization for maintaining restoration of through-plane resolution but with improved retention of SNR versus linear reconstruction using Tikhonov (TK) regularization in high through-plane resolution (1 mm) T -weighted spin-echo (T2SE) images of the prostate.

Methods: A wavelet sparsity (WS)-regularized image reconstruction was developed that takes as input a set of ≈80 overlapped 3-mm-thick slices acquired using a T2SE multislice scan and typically 30 coil elements. After testing in contrast and resolution phantoms and calibration in 6 subjects, the WS reconstruction was evaluated in 16 consecutive prostate T2SE MRI exams.

Cross correlation-based misregistration correction for super resolution T -weighted spin-echo images: application to prostate.

Purpose: The purpose is to develop a retrospective correction for subtle slice-to-slice positional inconsistencies that can occur when overlapped slices are acquired for super resolution in T -weighted spin-echo multislice imaging.

Methods: Spin-echo acquisition of overlapped slices is typically done using multiple passes. After the passes are assembled into the final slice set, consecutive slices are correlated due to their overlap.

Modified acquisition strategy for reduced motion artifact in super resolution FSE multislice MRI: Application to prostate.

Purpose: To reduce slice-to-slice motion effects in multislice -weighted fast-spin-echo ( FSE) imaging, manifest as "scalloping" in reformats, by modification of the acquisition strategy and to show applicability in prostate MRI.

Methods: FSE images of contiguous or overlapping slices are typically acquired using multiple passes in which each pass is comprised of multiple slices with slice-to-slice gaps. Combination of slices from all passes provides the desired sampling.

Use of k -space for high through-plane resolution in multislice MRI: Application to prostate.

Purpose: The goal of this work is to demonstrate 1 mm through-plane resolution in multislice T2SE MRI using k -space processing of overlapping slices and show applicability in prostate MRI.

Methods: Multiple overlapped slices are acquired and Fourier transformed in the slice-select direction. The slice profile is incorporated into a Tikhonov-regularized reconstruction.

Robust and efficient pharmacokinetic parameter non-linear least squares estimation for dynamic contrast enhanced MRI of the prostate.

Purpose: To describe an efficient numerical optimization technique using non-linear least squares to estimate perfusion parameters for the Tofts and extended Tofts models from dynamic contrast enhanced (DCE) MRI data and apply the technique to prostate cancer.

Methods: Parameters were estimated by fitting the two Tofts-based perfusion models to the acquired data via non-linear least squares. We apply Variable Projection (VP) to convert the fitting problem from a multi-dimensional to a one-dimensional line search to improve computational efficiency and robustness.

Conventional vs. reduced field of view diffusion weighted imaging of the prostate: Comparison of image quality, correlation with histology, and inter-reader agreement.

Purpose: To evaluate if Field of view Optimized and Constrained Undistorted Single shot (FOCUS) (GE Healthcare, Waukesha, WI) diffusion weighted images (DWI) provide more reliable imaging than conventional DWI, with non-inferior quantitative apparent diffusion coefficient (ADC) results.

Material And Methods: IRB approval was obtained for this study of 43 patients (44 exams, one patient with two visits) that underwent multiparametric prostate MRI with two DWI sequences and subsequent radical prostatectomy with histology as the gold standard. Randomized DWI sequence images were graded independently by two blinded experienced prostate MRI radiologists with a period of memory extinction between the two separate reading sessions.

Technical Aspects of Contrast-enhanced MR Angiography: Current Status and New Applications.

This article is based on a presentation at the meeting of the Japanese Society of Magnetic Resonance in Medicine in September 2016. The purpose is to review the technical developments which have contributed to the current status of contrast-enhanced magnetic resonance angiography (CE-MRA) and to indicate related emerging areas of study. Technical developments include MRI physics-based innovations as well as improvements in MRI engineering.

Dual echo Dixon imaging with a constrained phase signal model and graph cuts reconstruction.

Purpose: The purpose of this work is to derive and demonstrate constrained-phase dual-echo Dixon imaging within a maximum likelihood framework solved with a regularized graph-cuts-guided optimization.

Theory And Methods: Dual-echo Dixon reconstruction is fundamentally underdetermined; however, adopting a constrained-phase signal model reduces the number of unknowns and the nonlinear problem can be solved under a maximum likelihood framework. Period shifts in the field map (manifesting as fat/water signal swaps) must also be corrected.

Improved performance of prostate DCE-MRI using a 32-coil vs. 12-coil receiver array.

Purpose: To assess whether acquisition with 32 receiver coils rather than the vendor-recommended 12 coils provides significantly improved performance in 3D dynamic contrast-enhanced MRI (DCE-MRI) of the prostate.

Materials: The study was approved by the institutional review board and was compliant with HIPAA. 50 consecutive male patients in whom prostate MRI was clinically indicated were prospectively imaged in March 2015 with an accelerated DCE-MRI sequence in which image reconstruction was performed using 12 and 32 coil elements.

Improved receiver arrays and optimized parallel imaging accelerations applied to time-resolved 3D fluoroscopically tracked peripheral runoff CE-MRA.

Objectives: Three-station stepping-table time-resolved 3D contrast-enhanced magnetic resonance angiography has conflicting demands in the need to limit acquisition time in proximal stations to match the speed of the advancing contrast bolus and in the distal-most station to avoid venous contamination while still providing clinically useful spatial resolution. This work describes improved receiver coil arrays which address this issue by allowing increased acceleration factors, providing increased spatial resolution per unit time.

Materials And Methods: Receiver coil arrays were constructed for each station (pelvis, thigh, calf) and then integrated into a 48-element array for three-station peripheral CE-MRA.

Recent advances in 3D time-resolved contrast-enhanced MR angiography.

Contrast-enhanced magnetic resonance angiography (CE-MRA) was first introduced for clinical studies approximately 20 years ago. Early work provided 3-4 mm spatial resolution with acquisition times in the 30-second range. Since that time there has been continuing effort to provide improved spatial resolution with reduced acquisition time, allowing high resolution 3D time-resolved studies.

Pretreatment imaging of peripheral vascular malformations.

Peripheral vascular malformations (VMs) are complex and diverse vascular lesions which require individualized pretreatment planning. Pretreatment imaging using various modalities, especially magnetic resonance imaging and time-resolved magnetic resonance angiography, is a valuable tool for classifying peripheral VMs to allow proper diagnosis, demonstrate complete extent, identify the nidus, and distinguish between low-flow and high-flow dynamics that determines the treatment approach. We discuss pretreatment imaging findings in four patients with peripheral VMs and how diagnostic imaging helped guide management.

A prospective randomized controlled study of erythromycin on gastric and small intestinal distention: implications for MR enterography.

Objectives: To assess if erythromycin increases gastric emptying and hence improves small intestinal distention during MR enterography.

Methods: Gastric, small intestinal, and large intestinal volumes were assessed with MR after neutral oral contrast (1350ml in 45min) and balanced randomization to erythromycin (200mg i.v.

Selection and evaluation of optimal two-dimensional CAIPIRINHA kernels applied to time-resolved three-dimensional CE-MRA.

Purpose: To develop and validate a method for choosing the optimal two-dimensional CAIPIRINHA kernel for subtraction contrast-enhanced MR angiography (CE-MRA) and estimate the degree of image quality improvement versus that of some reference acceleration parameter set at R ≥ 8.

Methods: A metric based on patient-specific coil calibration information was defined for evaluating optimality of CAIPIRINHA kernels as applied to subtraction CE-MRA. Evaluation in retrospective studies using archived coil calibration data from abdomen, calf, foot, and hand CE-MRA exams was accomplished with an evaluation metric comparing the geometry factor (g-factor) histograms.

Dixon-type and subtraction-type contrast-enhanced magnetic resonance angiography: A theoretical and experimental comparison of SNR and CNR.

Purpose: The purpose of this work is to compare the behavior of the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) in contrast-enhanced MR angiography with background suppression performed by either a Dixon-type or subtraction-type method.

Theory And Methods: Theoretical expressions for the SNR and CNR for both background suppression techniques were derived. The theoretical Dixon:subtraction SNR and CNR ratios were compared to empirical ratios measured from phantom and in vivo studies for Dixon techniques utilizing one, two, and three echoes.

Comparison of manual and semiautomated techniques for analyzing gastric volumes with MRI in humans.

Gastric emptying, accommodation, and motility can be quantified with magnetic resonance imaging (MRI). The first step in image analysis entails segmenting the stomach from surrounding structures, usually by a time-consuming manual process. We have developed a semiautomated process to segment and measure gastric volumes with MRI.

Vascular masking for improved unfolding in 2D SENSE-accelerated 3D contrast-enhanced MR angiography.

Purpose: To describe and evaluate the method we refer to as "vascular masking" for improving signal-to-noise ratio (SNR) retention in sensitivity encoding (SENSE)-accelerated contrast-enhanced magnetic resonance angiography (CE-MRA).

Materials And Methods: Vascular masking is a technique that restricts the SENSE unfolding of an accelerated subtraction angiogram to the voxels within the field of view known to have enhancing signal. This is a more restricted voxel set than that identified with conventional masking, which excludes only voxels in the air around the object.

Acceleration apportionment: a method of improved 2D SENSE acceleration applied to 3D contrast-enhanced MR angiography.

Purpose: In 2D SENSE-accelerated 3D Cartesian acquisition, the net acceleration factor R is the product of the two individual accelerations, R = RY × RZ. Acceleration Apportionment tailors acceleration parameters (RY, RZ) to improve parallel imaging performance on a patient- and coil-specific basis and is demonstrated in contrast-enhanced MR angiography.

Methods: A performance metric is defined based on coil sensitivity information which identifies the (RY, RZ) pair that optimally trades off image quality with scan time reduction on a patient-specific basis.

Prospective comparison of cartesian acquisition with projection-like reconstruction magnetic resonance angiography with computed tomography angiography for evaluation of below-the-knee runoff.

Purpose: To compare prospectively the assessment of stenosis and radiologist confidence in the evaluation of below-the-knee lower extremity runoff vessels between computed tomography (CT) angiography and contrast-enhanced magnetic resonance (MR) angiography in a cohort of 19 clinical patients.

Materials And Methods: The study was compliant with the Health Insurance Portability and Accountability Act of 1996 and approved by the institutional review board. Imaging was performed in 19 consecutive patients with known or suspected peripheral arterial disease; both CT angiography and a more recently developed MR angiography technique were performed within 24 hours of each other and before any therapeutic intervention.