Publications by authors named "Dwight G Nishimura"
Article Synopsis
- The study aims to create a new method for high-resolution coronary magnetic resonance angiography (CMRA) that compensates for respiratory motion during free breathing.
- The method uses a specific imaging technique (variable-density 3D cones trajectory) and incorporates advanced motion correction strategies to improve image quality.
- Initial tests on six subjects show that this approach significantly enhances image sharpness compared to traditional methods, as evaluated by both cardiologists and quantitative metrics.
Purpose: To rapidly reconstruct undersampled 3D non-Cartesian image-based navigators (iNAVs) using an unrolled deep learning (DL) model, enabling nonrigid motion correction in coronary magnetic resonance angiography (CMRA).
Methods: An end-to-end unrolled network is trained to reconstruct beat-to-beat 3D iNAVs acquired during a CMRA sequence. The unrolled model incorporates a nonuniform FFT operator in TensorFlow to perform the data-consistency operation, and the regularization term is learned by a convolutional neural network (CNN) based on the proximal gradient descent algorithm.
Purpose: To develop a modular magnetization preparation sequence for combined T -preparation and multidimensional outer volume suppression (OVS) for coronary artery imaging.
Methods: A combined T -prepared 1D OVS sequence with fat saturation was defined to contain a 90° 180° composite nonselective tip-down pulse, two 180° hard pulses for refocusing, and a -90° spectral-spatial sinc tip-up pulse. For 2D OVS, 2 modules were concatenated, selective in X and then Y.
Purpose: To develop a method for banding-free balanced SSFP cardiac cine imaging in a single breath-hold.
Methods: A frequency modulation scheme was designed for cardiac applications to eliminate the time normally required for steady-state stabilization between multiple phase-cycled acquisitions. Highly undersampled acquisitions were reconstructed using a model-based reconstruction that exploits redundancy both over time and between phase cycles.
Purpose: To enable rapid imaging with a scan time-efficient 3D cones trajectory with a deep-learning off-resonance artifact correction technique.
Methods: A residual convolutional neural network to correct off-resonance artifacts (Off-ResNet) was trained with a prospective study of pediatric MRA exams. Each exam acquired a short readout scan (1.
Article Synopsis
- The study aimed to create a 3D cone imaging sequence for heart scans that is better at reducing issues caused by breathing movements and eddy currents.
- The new method uses a phyllotaxis pattern to collect data more efficiently, leading to improved image quality while accepting a trade-off of needing more heartbeats for acquisition.
- Results show that the phyllotaxis approach significantly enhances image sharpness and reduces motion artifacts in coronary artery imaging compared to traditional methods.
Purpose: To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing.
Methods: A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal.
Purpose: Conventional non-Cartesian compressed sensing requires multiple nonuniform Fourier transforms every iteration, which is computationally expensive. Accordingly, time-consuming reconstructions have slowed the adoption of undersampled 3D non-Cartesian acquisitions into clinical protocols. In this work we investigate several approaches to minimize reconstruction times without sacrificing accuracy.
View Article and Find Full Text PDFPurpose: Reduced field-of-view (rFOV) diffusion-weighted imaging (DWI) using 2D echo-planar radiofrequency (2DRF) excitation has been widely and successfully applied in clinical settings. The purpose of this work is to further improve its clinical utility by overcoming slice coverage limitations without any scan time penalty while providing robust fat suppression.
Theory And Methods: During multislice imaging with 2DRF pulses, periodic sidelobes in the slice direction cause partial saturation, limiting the slice coverage.
Purpose: To create a B map and correct for off-resonance with minimal scan time increase for two-dimensional (2D) or 3D non-Cartesian acquisitions.
Methods: Rewinding trajectories that bring the zeroth gradient moment to zero every repetition time (TR) were used to estimate the off-resonance with a center-out 3D cones trajectory, which required an increase in the minimum TR by 5%. The off-resonance estimation and correction was implemented using an algorithm based on binning and object-domain phase correction.
Purpose: To develop a retrospective nonrigid motion-correction method based on 3D image-based navigators (iNAVs) for free-breathing whole-heart coronary magnetic resonance angiography (MRA).
Methods: The proposed method detects global rigid-body motion and localized nonrigid motion from 3D iNAVs and compensates them with an autofocusing algorithm. To model the global motion, 3D rotation and translation are estimated from the 3D iNAVs.
Purpose: To develop a method for acquiring whole-heart 3D image-based navigators (iNAVs) with isotropic resolution for tracking and correction of localized motion in coronary magnetic resonance angiography (CMRA).
Methods: To monitor motion in all regions of the heart during a free-breathing scan, a variable-density cones trajectory was designed to collect a 3D iNAV every heartbeat in 176 ms with 4.4 mm isotropic spatial resolution.
Purpose: We propose a method to acquire B1 distribution plots by encoding in B1 instead of image space. Using this method, B1 data is acquired in a different way from traditional spatial B1 mapping, and allows for quick measurement of high dynamic range B1 data.
Methods: To encode in B1, we acquire multiple projections of a slice, each along the same direction, but using a different phase sensitivity to B1.
Purpose: To develop a technique for high-resolution diffusion-weighted imaging (DWI) and to compare it with standard DWI methods.
Methods: Multiple in-plane bands of magnetization were simultaneously excited by identically phase modulating each subpulse of a two-dimensional (2D) RF pulse. Several excitations with the same multiband pattern progressively shifted in the phase-encode direction were used to cover the prescribed field of view (FOV).
Purpose: To develop a robust motion estimation method for free-breathing body MRI using dense coil arrays.
Methods: Self-navigating pulse sequences can measure subject motion without using external motion monitoring devices. With dense coil arrays, individual coil elements can provide localized motion estimates.
Purpose: To improve the spatial/temporal resolution of whole-heart coronary MR angiography by developing a variable-density (VD) 3D cones acquisition suitable for image reconstruction with parallel imaging and compressed sensing techniques.
Methods: A VD 3D cones trajectory design incorporates both radial and spiral trajectory undersampling techniques to achieve higher resolution. This design is used to generate a VD 3D cones trajectory with 0.
Purpose: Accurate measurement of the nonuniform transmit radiofrequency field is necessary for magnetic resonance imaging applications. The radiofrequency field excitation amplitude (B1) is often obtained by acquiring a B1 map. We modify the B1 estimation using adiabatic refocusing (BEAR) method to extend its range to lower B1 magnitudes.
View Article and Find Full Text PDFPurpose: To develop a magnetization preparation sequence for simultaneous outer volume suppression (OVS) and T2 weighting in whole-heart coronary magnetic resonance angiography.
Methods: A combined OVS and T2 preparation sequence (OVS-T2 Prep) was designed with a nonselective adiabatic 90° tipdown pulse, two adiabatic 180° refocusing pulses, and a 2D spiral -90° tipup pulse. The OVS-T2 Prep preserves the magnetization inside an elliptic cylinder with T2 weighting, while saturating the magnetization outside the cylinder.
Purpose: To develop a new sequence for non-contrast-enhanced peripheral angiography using a sliding interleaved cylinder (SLINCYL) acquisition.
Methods: A venous saturation pulse was incorporated into a three-dimensional magnetization-prepared balanced steady-state free precession sequence for non-contrast-enhanced peripheral angiography to improve artery-vein contrast. The SLINCYL acquisition, which consists of a series of overlapped thin slabs for volumetric coverage similar to the original sliding interleaved ky (SLINKY) acquisition, was used to evenly distribute the venous-suppression effects over the field of view.
Recent advancements in the field of hyperpolarized (13)C magnetic resonance spectroscopy (MRS) have yielded powerful techniques capable of real-time analysis of metabolic pathways. These non-invasive methods have increasingly shown application in impacting disease diagnosis and have further been employed in mechanistic studies of disease onset and progression. Our goals were to investigate branched-chain aminotransferase (BCAT) activity in prostate cancer with a novel molecular probe, hyperpolarized [1-(13)C]-2-ketoisocaproate ([1-(13)C]-KIC), and explore the potential of branched-chain amino acid (BCAA) metabolism to serve as a biomarker.
View Article and Find Full Text PDFPurpose: To develop a self-gated alternating repetition time balanced steady-state free precession (ATR-SSFP) pulse sequence for fat-suppressed cardiac cine imaging.
Methods: Cardiac gating is computed retrospectively using acquired magnetic resonance self-gating data, enabling cine imaging without the need for electrocardiogram (ECG) gating. Modification of the slice-select rephasing gradients of an ATR-SSFP sequence enables the acquisition of a one-dimensional self-gating readout during the unused short repetition time (TR).
Purpose: Accurate measurement of the nonuniform transmit radiofrequency field is useful for many applications in magnetic resonance imaging, such as calibrating the scanner transmit system, evaluating coil performance, and improving image quality and quantitation. The radiofrequency field excitation amplitude (B(1)) is often obtained by acquiring a B(1) map. In this study, a new B(1) mapping method is proposed.
View Article and Find Full Text PDFPurpose: To improve the clinical utility of diffusion-weighted imaging (DWI) by extending the slice coverage of a high-resolution reduced field-of-view technique.
Theory: Challenges in achieving high spatial resolution restrict the use of DWI in assessment of small structures such as the spinal cord. A reduced field-of-view method with 2D echo-planar radiofrequency (RF) excitation was recently proposed for high-resolution DWI.
Purpose: To develop a rapid single-breath-hold 3D late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) method, and demonstrate its feasibility in cardiac patients.
Materials And Methods: An inversion recovery dual-density 3D stack-of-spirals imaging sequence was developed. The spiral acquisition was 2-fold accelerated by self-consistent parallel imaging reconstruction (SPIRiT), which resulted in a total scan time of 12 heartbeats.
Purpose: The balanced steady-state free precession (bSSFP) pulse sequence has shown to be of great interest due to its high signal-to-noise ratio efficiency. However, bSSFP images often suffer from banding artifacts due to off-resonance effects, which we aim to minimize in this article.
Methods: We present a general and fast two-step algorithm for 1) estimating the unknowns in the bSSFP signal model from multiple phase-cycled acquisitions, and 2) reconstructing band-free images.