Paul T. Gurney

Design and analysis of a practical 3D cones trajectory

The 3D Cones k‐space trajectory has many desirable properties for rapid and ultra‐short echo time magnetic resonance imaging. An algorithm is presented that generates the 3D Cones gradient waveforms given a desired field of view and resolution. The algorithm enables a favorable trade‐off between increases in readout time and decreases in the total number of required readouts. The resulting trajectory is very signal‐to‐noise ratio (SNR) efficient and has excellent aliasing properties. A rapid high‐resolution ultra‐short echo time imaging sequence is used to compare the 3D Cones trajectory to 3D projection reconstruction (3DPR) sampling schemes. For equivalent scan times, the 3D Cones trajectory has better SNR performance and fewer aliasing artifacts as compared to the 3DPR trajectory. Magn Reson Med, 2006.

In vivo sodium imaging of human patellar cartilage with a 3D cones sequence at 3 T and 7 T

To compare signal‐to‐noise ratios (SNRs) and T*2 maps at 3 T and 7 T using 3D cones from in vivo sodium images of the human knee.

Designing long-T2 suppression pulses for ultrashort echo time imaging.

Ultrashort echo time (UTE) imaging has shown promise as a technique for imaging tissues with T2 values of a few milliseconds or less. These tissues, such as tendons, menisci, and cortical bone, are normally invisible in conventional magnetic resonance imaging techniques but have signal in UTE imaging. They are difficult to visualize because they are often obscured by tissues with longer T2 values. In this article, new long‐T2 suppression RF pulses that improve the contrast of short‐T2 species are introduced. These pulses are improvements over previous long‐T2 suppression pulses that suffered from poor off‐resonance characteristics or T1 sensitivity. Short‐T2 tissue contrast can also be improved by suppressing fat in some applications. Dual‐band long‐T2 suppression pulses that additionally suppress fat are also introduced. Simulations, along with phantom and in vivo experiments using 2D and 3D UTE imaging, demonstrate the feasibility, improved contrast, and improved sensitivity of these new long‐T2 suppression pulses. The resulting images show predominantly short‐T2 species, while most long‐T2 species are suppressed. Magn Reson Med, 2006.

Anisotropic Field-of-Views in Radial Imaging

Radial imaging techniques, such as projection-reconstruction (PR), are used in magnetic resonance imaging (MRI) for dynamic imaging, angiography, and short- imaging. They are robust to flow and motion, have diffuse aliasing patterns, and support short readouts and echo times. One drawback is that standard implementations do not support anisotropic field-of-view (FOV) shapes, which are used to match the imaging parameters to the object or region-of-interest. A set of fast, simple algorithms for 2-D and 3-D PR, and 3-D cones acquisitions are introduced that match the sampling density in frequency space to the desired FOV shape. Tailoring the acquisitions allows for reduction of aliasing artifacts in undersampled applications or scan time reductions without introducing aliasing in fully-sampled applications. It also makes possible new radial imaging applications that were previously unsuitable, such as imaging elongated regions or thin slabs. 2-D PR longitudinal leg images and thin-slab, single breath-hold 3-D PR abdomen images, both with isotropic resolution, demonstrate these new possibilities. No scan time to volume efficiency is lost by using anisotropic FOVs. The acquisition trajectories can be computed on a scan by scan basis.

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. In this work, a new free‐breathing coronary MR angiography technique that reduces scan time and improves robustness to motion is developed. Data acquisition is accomplished using a three‐dimensional cones non‐Cartesian trajectory, which can reduce the number of readouts 3‐fold or more compared to conventional three‐dimensional Cartesian encoding and provides greater robustness to motion/flow effects. To further enhance robustness to motion, two‐dimensional navigator images are acquired to directly track respiration‐induced displacement of the heart and enable retrospective compensation of all acquired data (none discarded) for image reconstruction. In addition, multiple cardiac phases are imaged to support retrospective selection of the best phase(s) for visualizing each coronary segment. Experimental results demonstrate that whole‐heart coronary angiograms can be obtained rapidly and robustly with this proposed technique. Magn Reson Med 69:1083–1093, 2013.

Manganese‐guided cellular MRI of human embryonic stem cell and human bone marrow stromal cell viability

This study investigated the ability of MnCl2 as a cellular MRI contrast agent to determine the in vitro viability of human embryonic stem cells (hESC) and human bone marrow stromal cells (hBMSC). Basic MRI parameters including T1 and T2 values of MnCl2‐labeled hESC and hBMSC were measured and viability signal of manganese (Mn2+)‐labeled cells was validated. Furthermore, the biological activity of Ca2+‐channels was modulated utilizing both Ca2+‐channel agonist and antagonist to evaluate concomitant signal changes. Metabolic effects of MnCl2‐labeling were also assessed using assays for cell viability, proliferation, and apoptosis. Finally, in vivo Mn2+‐guided MRI of the transplanted hESC was successfully achieved and validated by bioluminescence imaging. Magn Reson Med, 2009.

Free-Breathing Multi-Phase Whole-Heart Coronary MRA Using Image-Based Navigators and 3D 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. In this work, a new free‐breathing coronary MR angiography technique that reduces scan time and improves robustness to motion is developed. Data acquisition is accomplished using a three‐dimensional cones non‐Cartesian trajectory, which can reduce the number of readouts 3‐fold or more compared to conventional three‐dimensional Cartesian encoding and provides greater robustness to motion/flow effects. To further enhance robustness to motion, two‐dimensional navigator images are acquired to directly track respiration‐induced displacement of the heart and enable retrospective compensation of all acquired data (none discarded) for image reconstruction. In addition, multiple cardiac phases are imaged to support retrospective selection of the best phase(s) for visualizing each coronary segment. Experimental results demonstrate that whole‐heart coronary angiograms can be obtained rapidly and robustly with this proposed technique. Magn Reson Med 69:1083–1093, 2013.

Free-breathing multiphase whole-heart coronary MR angiography using image-based navigators and three-dimensional cones imaging: 3D Cones Coronary MRA

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. In this work, a new free‐breathing coronary MR angiography technique that reduces scan time and improves robustness to motion is developed. Data acquisition is accomplished using a three‐dimensional cones non‐Cartesian trajectory, which can reduce the number of readouts 3‐fold or more compared to conventional three‐dimensional Cartesian encoding and provides greater robustness to motion/flow effects. To further enhance robustness to motion, two‐dimensional navigator images are acquired to directly track respiration‐induced displacement of the heart and enable retrospective compensation of all acquired data (none discarded) for image reconstruction. In addition, multiple cardiac phases are imaged to support retrospective selection of the best phase(s) for visualizing each coronary segment. Experimental results demonstrate that whole‐heart coronary angiograms can be obtained rapidly and robustly with this proposed technique. Magn Reson Med 69:1083–1093, 2013.

118 Manganese guided cellular MRI enables evaluation of human stromal cell viability

Methods Human stromal cells (Cognate, Sunnyvale, CA) were trypsinized and labeled with different concentrations of MnCl2 in normal saline and incubated for 0.5–1.0 hour at 37°C and 5% CO2. Biological properties of hSC were monitored by modulating the activity of calcium channels using verapamil (calcium channel antagonist). T1 and T2 mapping was performed at 0.01–3.00 mM of MnCl2 solution with 1.5 T GE Excite whole-body MRI scanner (Signa, GE Medical Systems, Milwaukee, WI) with a 5-inch receive only surface coil. For T1 measurements, spin echo (SE) inversion recovery sequence (FOV 12 cm, matrix size of 128 × 128, TR 3000 ms and TE 50–2200 ms at 300 ms steps) were used. We made T2 measurements using SE sequence (FOV 12 cm, matrix size of 128 × 128, TR 2500 ms and TE 10–80 ms at 10 ms steps). Then the data were analyzed to extract T1 and T2 values through nonlinear least-square fits to the SE inversion recovery and the SE decay curve respectively. In vitro cellular MRI was performed using optimized SE sequence (FOV 12 cm, matrix size of 256 × 256, TR 800 ms and TE 3.4 ms). Modulation of hSC calcium channel activity by verapamil was assessed by measuring changes in signal intensity.

230 Manganese guided cellular MRI of human embryonic stem cell viability

Introduction Human embryonic stem cells (hESC) have demonstrated the ability to restore the injured myocardium. MRI has emerged as one of the predominant imaging modalities using iron-oxide nanoparticles to localize the transplanted stem cells. However, this method does not monitor biological activities of the transplanted cells including cellular viability. Manganese chloride (MnCl2) is transported via calcium-channel into the cellular cytoplasm to shorten cellular T1 and generate positive contrast indicative of cellular viability.