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.

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

PURPOSE: 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. MATERIALS AND METHODS: Sodium concentration has been shown to correlate with glycosaminoglycan content of cartilage and is a possible biomarker of osteoarthritis. Using a 3D cones trajectory, 17 subjects were scanned at 3 T and 12 at 7 T using custom-made sodium-only and dual-tuned sodium/proton surface coils, at a standard resolution (1.3 x 1.3 x 4.0 mm(3)) and a high resolution (1.0 x 1.0 x 2.0 mm(3)). We measured the SNR of the images and the T*(2) of cartilage at both 3 T and 7 T. RESULTS: The average normalized SNR values of standard-resolution images were 27.1 and 11.3 at 7 T and 3 T. At high resolution, these average SNR values were 16.5 and 7.3. Image quality was sufficient to show spatial variations of sodium content. The average T*(2) of cartilage was measured as 13.2 +/- 1.5 msec at 7 T and 15.5 +/- 1.3 msec at 3 T. CONCLUSION: We acquired sodium images of patellar cartilage at 3 T and 7 T in under 26 minutes using 3D cones with high resolution and acceptable SNR. The SNR improvement at 7 T over 3 T was within the expected range based on the increase in field strength. The measured T*(2) values were also consistent with previously published values.

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

This study investigated the ability of MnCl(2) 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 T(1) and T(2) values of MnCl(2)-labeled hESC and hBMSC were measured and viability signal of manganese (Mn(2+))-labeled cells was validated. Furthermore, the biological activity of Ca(2+)-channels was modulated utilizing both Ca(2+)-channel agonist and antagonist to evaluate concomitant signal changes. Metabolic effects of MnCl(2)-labeling were also assessed using assays for cell viability, proliferation, and apoptosis. Finally, in vivo Mn(2+)-guided MRI of the transplanted hESC was successfully achieved and validated by bioluminescence imaging.

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.

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.