Combined T -preparation and multidimensional outer volume suppression for coronary artery imaging with 3D cones trajectories.

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.

Nonrigid Motion Correction With 3D Image-Based Navigators for Coronary MR Angiography.

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.

3D image-based navigators for coronary MR angiography.

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.

High-resolution variable-density 3D cones coronary MRA.

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.

Combined outer volume suppression and T2 preparation sequence for coronary angiography.

Purpose: 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.

Non-contrast-enhanced peripheral angiography using a sliding interleaved cylinder acquisition.

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.

Self-gated fat-suppressed cardiac cine MRI.

Purpose: 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).

Rapid single-breath-hold 3D late gadolinium enhancement cardiac MRI using a stack-of-spirals acquisition.

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.

Nonrigid autofocus motion correction for coronary MR angiography with a 3D cones trajectory.

Purpose: To implement a nonrigid autofocus motion correction technique to improve respiratory motion correction of free-breathing whole-heart coronary magnetic resonance angiography acquisitions using an image-navigated 3D cones sequence.

Methods: 2D image navigators acquired every heartbeat are used to measure superior-inferior, anterior-posterior, and right-left translation of the heart during a free-breathing coronary magnetic resonance angiography scan using a 3D cones readout trajectory. Various tidal respiratory motion patterns are modeled by independently scaling the three measured displacement trajectories.

Off-resonance-robust velocity-selective magnetization preparation for non-contrast-enhanced peripheral MR angiography.

Purpose: To develop a new velocity-selective (VS) excitation pulse sequence which is robust to field inhomogeneity, and demonstrate its application to non-contrast-enhanced peripheral MR angiography (MRA).

Methods: The off-resonance-robust VS saturation pulse is designed by incorporating 180° refocusing pulses into the k-space-based reference design and tailoring sequence parameters in a velocity region of interest. The VS saturation pulse is used as magnetization preparation for non-contrast-enhanced peripheral MRA to suppress background tissues but not arterial blood based on their velocities.

Non-contrast-enhanced renal and abdominal MR angiography using velocity-selective inversion preparation.

Non-contrast-enhanced MR angiography is a promising alternative to the established contrast-enhanced approach as it reduces patient discomfort and examination costs and avoids the risk of nephrogenic systemic fibrosis. Inflow-sensitive slab-selective inversion recovery imaging has been used with great promise, particularly for abdominal applications, but has limited craniocaudal coverage due to inflow time constraints. In this work, a new non-contrast-enhanced MR angiography method using velocity-selective inversion preparation is developed and applied to renal and abdominal angiography.

Free-breathing multiphase whole-heart coronary MR angiography using image-based navigators and three-dimensional cones imaging.

Noninvasive visualization of the coronary arteries in vivo is one of the most important goals in cardiovascular imaging. Compared to other paradigms for coronary MR angiography, a free-breathing three-dimensional whole-heart iso-resolution approach simplifies prescription effort, requires less patient cooperation, reduces overall exam time, and supports retrospective reformats at arbitrary planes. However, this approach requires a long continuous acquisition and must account for respiratory and cardiac motion throughout the scan.

Three-dimensional first-pass myocardial perfusion MRI using a stack-of-spirals acquisition.

Three-dimensional cardiac magnetic resonance perfusion imaging is promising for the precise sizing of defects and for providing high perfusion contrast, but remains an experimental approach primarily due to the need for large-dimensional encoding, which, for traditional 3DFT imaging, requires either impractical acceleration factors or sacrifices in spatial resolution. We demonstrated the feasibility of rapid three-dimensional cardiac magnetic resonance perfusion imaging using a stack-of-spirals acquisition accelerated by non-Cartesian k-t SENSE, which enables entire myocardial coverage with an in-plane resolution of 2.4 mm.

Reducing artifacts in one-dimensional Fourier velocity encoding for fast and pulsatile flow.

When evaluating the severity of valvular stenosis, the peak velocity of the blood flow is routinely used to estimate the transvalvular pressure gradient. One-dimensional Fourier velocity encoding effectively detects the peak velocity with an ungated time series of spatially resolved velocity spectra in real time. However, measurement accuracy can be degraded by the pulsatile and turbulent nature of stenotic flow and the existence of spatially varying off-resonance.

Methods for registration of magnetic resonance images of ex vivo prostate specimens with histology.

Purpose: To evaluate two methods of scanning and tissue processing to achieve accurate magnetic resonance (MR)-histologic correlation in human prostate specimens.

Materials And Methods: Two prostates had acrylic paint markers injected to define the plane of imaging and serve as internal fiducials. Each was placed on a polycarbonate plane-finder device (PFD), which was adjusted to align the imaging and cutting planes.

Three-dimensional fluid-suppressed T2-prep flow-independent peripheral angiography using balanced SSFP.

Accurate depiction of the vessels of the lower leg, foot or hand benefits from suppression of bright MR signal from lipid (such as bone marrow) and long-T1 fluid (such as synovial fluid and edema). Signal independence of blood flow velocities, good arterial/muscle contrast and arterial/venous separation are also desirable. The high SNR, short scan times and flow properties of balanced steady-state free precession (SSFP) make it an excellent candidate for flow-independent angiography.

Magnetization-prepared IDEAL bSSFP: a flow-independent technique for noncontrast-enhanced peripheral angiography.

Purpose: To propose a new noncontrast-enhanced flow-independent angiography sequence based on balanced steady-state free precession (bSSFP) that produces reliable vessel contrast despite the reduced blood flow in the extremities.

Materials And Methods: The proposed technique addresses a variety of factors that can compromise the exam success including insufficient background suppression, field inhomogeneity, and large volumetric coverage requirements. A bSSFP sequence yields reduced signal from venous blood when long repetition times are used.

In vivo high-resolution magnetic resonance skin imaging at 1.5 T and 3 T.

As a noninvasive modality, MR is attractive for in vivo skin imaging. Its unique soft tissue contrast makes it an ideal imaging modality to study the skin water content and to resolve the different skin layers. In this work, the challenges of in vivo high-resolution skin imaging are addressed.

Wideband SSFP: alternating repetition time balanced steady state free precession with increased band spacing.

Balanced steady-state free precession (SSFP) imaging is limited by off-resonance banding artifacts, which occur with periodicity 1/TR in the frequency spectrum. A novel balanced SSFP technique for widening the band spacing in the frequency response is described. This method, called wideband SSFP, utilizes two alternating repetition times with alternating RF phase, and maintains high SNR and T(2)/T(1) contrast.

Real-time color-flow CMR in adults with congenital heart disease.

CMR is valuable in the evaluation of congenital heart disease (CHD). Traditional flow imaging sequences involve cardiac and respiratory gating, increasing scan time and susceptibility to arrhythmias. We studied a real-time color-flow CMR system for the detection of flow abnormalities in 13 adults with CHD.

Rapid cardiac-output measurement with ungated spiral phase contrast.

An ungated spiral phase-contrast (USPC) method was used to measure cardiac output (CO) rapidly and conveniently. The USPC method, which was originally designed for small peripheral vessels, was modified to assess CO by measuring flow in the ascending aorta (AA). The modified USPC used a 12-interleaf spiral trajectory to acquire full-image data every 283 ms with 2-mm spatial resolution.

Single breath-hold whole-heart MRA using variable-density spirals at 3T.

Multislice breath-held coronary imaging techniques conventionally lack the coverage of free-breathing 3D acquisitions but use a considerably shorter acquisition window during the cardiac cycle. This produces images with significantly less motion artifact but a lower signal-to-noise ratio (SNR). By using the extra SNR available at 3 T and undersampling k-space without introducing significant aliasing artifacts, we were able to acquire high-resolution fat-suppressed images of the whole heart in 17 heartbeats (a single breath-hold).