Abdominal MR elastography with multiple driver arrays: performance and repeatability.

Purpose: To evaluate the performance and repeatability assessing liver, spleen, and kidney stiffness with magnetic resonance elastography (MRE), using arrays of pneumatic passive drivers.

Methods: An array of four flexible, pneumatically activated passive drivers for abdominal MRE were developed and tested in this study. Multiple MRE acquisitions were performed prospectively in a series of eleven volunteers, with activation of all combinations of the four drivers, individually and simultaneously.

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.

Reliable Assessment of Swine Renal Fibrosis Using Quantitative Magnetization Transfer Imaging.

Objectives: Quantitative magnetization transfer (qMT) is useful for measurement of murine renal fibrosis at high and ultrahigh field strengths. However, its utility at clinical field strengths and in human-like kidneys remains unknown. We tested the hypothesis that qMT would successfully detect fibrosis in swine kidneys with unilateral renal artery stenosis (RAS) at 3.

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.

Assessment of advanced hepatic MR elastography methods for susceptibility artifact suppression in clinical patients.

Purpose: To assess the success rate, image quality, and the ability to stage liver fibrosis of a standard 2D gradient-recalled echo (GRE) and four different spin-echo (SE) magnetic resonance elastography (MRE) sequences in patients with different liver iron concentrations.

Materials And Methods: A total of 332 patients who underwent 3T MRE examinations that included liver fat and iron quantification were enrolled, including 136 patients with all five MRE techniques. Thirty-four patients had biopsy results for fibrosis staging.

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.

Magnetic resonance elastography: evaluation of new inversion algorithm and quantitative analysis method.

Purpose: To assess mean shear hepatic stiffness calculations using various region of interest (ROI) techniques, a new inversion algorithm, and a confidence threshold mask.

Methods: Seventy-three patients (49 with abnormal liver function tests/known chronic liver disease and 24 healthy liver transplant donors) underwent liver biopsy and magnetic resonance elastography (MRE). MRE data processed with the current inversion algorithm [multiscale direct inversion (MSDI)] was assessed using 2 ROI methods (single vs.

High temporal and spatial resolution 3D time-resolved contrast-enhanced magnetic resonance angiography of the hands and feet.

Methods are described for generating 3D time-resolved contrast-enhanced magnetic resonance (MR) angiograms of the hands and feet. Given targeted spatial resolution and frame times, it is shown that acceleration of about one order of magnitude or more is necessary. This is obtained by a combination of 2D sensitivity encoding (SENSE) and homodyne (HD) acceleration methods.

Feasibility of in vivo MR elastographic splenic stiffness measurements in the assessment of portal hypertension.

Objective: Liver stiffness is associated with portal hypertension in patients with chronic liver disease. However, the relation between spleen stiffness and clinically significant portal hypertension remains unknown. The purposes of this study were to determine the feasibility of measuring spleen stiffness with MR elastography and to prospectively test the technique in healthy volunteers and in patients with compensated liver disease.

Assessment of hepatic fibrosis with magnetic resonance elastography.

Background & Aims: Accurate detection of hepatic fibrosis is crucial for assessing prognosis and candidacy for treatment in patients with chronic liver disease. Magnetic resonance (MR) elastography, a technique for quantitatively assessing the mechanical properties of soft tissues, has been shown previously to have potential for noninvasively detecting liver fibrosis. The goal of this work was to obtain preliminary estimates of the sensitivity and specificity of the technique in diagnosing liver fibrosis, and to assess its potential for identifying patients who potentially can avoid a biopsy procedure.

A modified projection reconstruction trajectory for reduction of undersampling artifacts.

Purpose: To reduce undersampling artifacts for a given number of repetitions of the projection reconstruction (PR) sequence by modifying its k-space trajectory to sample more mid-frequencies while reducing the sampling coverage of the peripheral spatial frequencies.

Materials And Methods: The single k-space spoke measured per repetition in the standard PR was modified so that one complete and two partial spokes were measured per repetition but with decreased k-space extent. The point spread functions (PSFs) and undersampling artifacts of the modified PR were compared with those of the standard PR for various numbers of projections.

Interscan registration using navigator echoes.

A common problem in clinical MRI is anatomic misalignment of imaging slices across successive examinations. This unnecessarily complicates the radiologic assessment of anatomic change over time on serial MRI studies. To address this problem, spherical navigator echoes, which can detect rigid body motion in all six degrees of freedom, were used to guide spatial location and orientation adjustments to an exam prescription to match the reference frame of images acquired in an earlier exam.

On the feasibility of elastic wave visualization within polymeric solids using magnetic resonance elastography.

In this paper, the feasibility of extending previously described magnetic resonance elastography (MRE) dynamic displacement (and associated elasticity) measurement techniques, currently used successfully in tissue, to solid materials which have much higher shear rigidity and much lower nuclear spin densities, is considered. Based on these considerations, the MRE technique is modified in a straightforward manner and used to directly visualize shear wave displacements within two polymeric materials, one of which is relatively stiff.

Continuously moving table data acquisition method for long FOV contrast-enhanced MRA and whole-body MRI.

A method is presented in which an extended longitudinal field of view (FOV), as required for whole-body MRI or MRA peripheral runoff studies, is acquired in one seamless image. Previous methods typically either acquired 3D data at multiple static "stations" which covered the extended FOV or as a series of 2D axial sections. The method presented here maintains the benefits of 3D acquisition while removing the discrete nature of the multistation method by continuous acquisition of MR data as the patient table moves through the desired FOV.

Spherical navigator echoes for full 3D rigid body motion measurement in MRI.

We developed a 3D spherical navigator (SNAV) echo technique that can measure rigid body motion in all six degrees of freedom simultaneously by sampling a spherical shell in k-space. 3D rotations of an imaged object simply rotate the data on this shell and can be detected by registration of k-space magnitude values. 3D translations add phase shifts to the data on the shell and can be detected with a weighted least-squares fit to the phase differences at corresponding points.