Magnetic Resonance in Medicine

Journal: Magnetic Resonance in Medicine

Abbreviation

Magn Reson Med

Publisher

Wiley

ISSN

0740-3194
1522-2594

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Publications1 - 10 of 69

In vivo MRI of hyperpolarized silicon-29 nanoparticles
Kwiatkowski, Grzegorz; von Witte, Gevin Christoph; Däpp, Alexander; et al. (2024)
Magnetic Resonance in Medicine
Purpose The objective of the present work was to test the feasibility of in vivo imaging of hyperpolarized 50-nm silicon-29 (29Si) nanoparticles. Methods Commercially available, crystalline 50-nm nanoparticles were hyperpolarized using dynamic polarization transfer via the endogenous silicon oxide–silicon defects without the addition of exogenous radicals. Phantom experiments were used to quantify the effect of sample dissolution and various surface coating on T1 and T2 relaxation. The in vivo feasibility of detecting hyperpolarized silicon-29 was tested following intraperitoneal, intragastric, or intratumoral injection in mice and compared with the results obtained with previously reported, large, micrometer-size particles. The tissue clearance of SiNPs was quantified in various organs using inductively coupled plasma optical emission spectroscopy. Results In vivo images obtained after intragastric, intraperitoneal, and intratumoral injection compare favorably between small and large SiNPs. Improved distribution of small SiNPs was observed after intraperitoneal and intragastric injection as compared with micrometer-size SiNPs. Sufficient clearance of nanometer-size SiNPs using ex vivo tissue sample analysis was observed after 14 days following injection, indicating their safe use. Conclusion In vivo MRI of hyperpolarized small 50-nm SiNPs is feasible with polarization levels and room-temperature relaxation times comparable to large micrometer-size particles.
Self-gated cine phase-contrast balanced SSFP flow quantification at 0.55 T
McGrath, Charles; Bieri, Oliver; Kozerke, Sebastian; et al. (2024)
Magnetic Resonance in Medicine
Purpose:To implement cine phase-contrast balanced SSFP (PC-bSSFP) for low-field 0.55T cardiac MRI by exploiting the intrinsic flow sensitivity of the bSSFP slice-select gradient and the in-plane phase-cancelation properties of radial trajectories, enabling self-gated and referenceless PC-bSSFP flow quantification at 0.55 T. Methods: A free-running, tiny golden-angle radial PC-bSSFP approach was implemented on 0.55T and 1.5T systems. Cardiac and respiratory self-gating was incorporated to enable electrocardiogram-free scanning during breath-hold and free-breathing. By exploiting the intrinsic in-plane phase-cancelation properties of radial acquisitions and background phase fitting, referenceless single-point PC-bSSFP was realized. In vivo data were acquired in the ascending aorta of healthy subjects at 0.55 T and 1.5 T during breath-hold and free-breathing. Flow data, SNR, and velocity-to-noise ratio were compared relative to data obtained with phase-contrast spoiled gradient-echo variants. Results: Velocities acquired with PC-bSSFP compared well with data from phase-contrast spoiled gradient-echo (RMSEv = 5.8 cm/s). PC-bSSFP at 0.55 T resulted in high-quality cine magnitude images and phase maps with sufficient SNR and velocity-to-noise ratio. Breath-hold and free-breathing PC-bSSFP performed very similarly, with comparable flow quantification (RMSEv = 5.7 cm/s). Referenceless single-point PC-bSSFP results agreed well with two-point PC-bSSFP (−1.8 ± 5.2 cm/s) while reducing scan times 2-fold. Conclusion: PC-bSSFP is feasible on low-field 0.55T systems, producing high-quality cine images while permitting simultaneous aortic flow measurements during breath-hold and free-breathing and without the need for electrocardiogram gating.
Production of highly polarized [1‐^13C]acetate by rapid decarboxylation of [2‐^13C]pyruvate – application to hyperpolarized cardiac spectroscopy and imaging
Steinhauser, Jonas; Wespi, Patrick; Kwiatkowski, Grzegorz; et al. (2019)
Magnetic Resonance in Medicine
A virtually 1H-free birdcage coil for zero echo time MRI without background signal
Weiger, Markus; Brunner, David O.; Schmid, Thomas; et al. (2017)
Magnetic Resonance in Medicine
Echo‐planar imaging of the human head with 100 mT/m gradients and high‐order modeling of eddy current fields
Hennel, Franciszek; Wilm, Bertram; Roesler, Manuela B.; et al. (2020)
Magnetic Resonance in Medicine
A unipolar head gradient for high-field MRI without encoding ambiguity
Weiger Senften, Markus; Overweg, Johan; Hennel, Franciszek; et al. (2026)
Magnetic Resonance in Medicine
Purpose MRI gradients with a conventional, bipolar design generally face a trade-off among performance, encoding ambiguity, and radiofrequency selectivity used to circumvent said ambiguity. This problem is particularly limiting in cutting-edge brain imaging performed at field strengths ≥ 7 T and using high-performance head gradients. Methods To address this issue, the present work proposes to fundamentally eliminate the encoding ambiguity in head gradients by using a unipolar z-gradient design that takes advantage of the signal-free range on one side of the imaging volume. This concept is demonstrated by implementation of a unipolar head gradient for operation at 7 T. Results Imaging in phantoms and in vivo demonstrates elimination of backfolding due to encoding ambiguity. At the same time, the unipolar design achieves efficiency on par with conventional bipolar design, resulting in high amplitude and slew-rate performance. Conclusion The prospect of gradient systems based on a unipolar design holds promise for all advanced neuroimaging that demands high gradient performance. It will make the greatest difference at 7 T and beyond, where the absence of ambiguity removes a key concern and constraint in terms of radiofrequency behavior and instrumentation.
Motion-compensated diffusion encoding in multi-shot human brain acquisitions: Insights using high-performance gradients
Michael, Eric Seth; Hennel, Franciszek; Pruessmann, Klaas Paul (2024)
Magnetic Resonance in Medicine
Purpose: To evaluate the utility of up to second-order motion-compensated diffusion encoding in multi-shot human brain acquisitions. Methods: Experiments were performed with high-performance gradients using three forms of diffusion encoding motion-compensated through different orders: conventional zeroth-order–compensated pulsed gradients (PG), first-order–compensated gradients (MC1), and second-order–compensated gradients (MC2). Single-shot acquisitions were conducted to correlate the order of motion compensation with resultant phase variability. Then, multi-shot acquisitions were performed at varying interleaving factors. Multi-shot images were reconstructed using three levels of shot-to-shot phase correction: no correction, channel-wise phase correction based on FID navigation, and correction based on explicit phase mapping (MUSE). Results: In single-shot acquisitions, MC2 diffusion encoding most effectively suppressed phase variability and sensitivity to brain pulsation, yielding residual variations of about 10° and of low spatial order. Consequently, multi-shot MC2 images were largely satisfactory without phase correction and consistently improved with the navigator correction, which yielded repeatable high-quality images; contrarily, PG and MC1 images were inadequately corrected using the navigator approach. With respect to MUSE reconstructions, the MC2 navigator-corrected images were in close agreement for a standard interleaving factor and considerably more reliable for higher interleaving factors, for which MUSE images were corrupted. Finally, owing to the advanced gradient hardware, the relative SNR penalty of motion-compensated diffusion sensitization was substantially more tolerable than that faced previously. Conclusion: Second-order motion-compensated diffusion encoding mitigates and simplifies shot-to-shot phase variability in the human brain, rendering the multi-shot acquisition strategy an effective means to circumvent limitations of retrospective phase correction methods.
Stealth RF energy harvesting in MRI using selective shielding
Bjorkqvist, Oskar; Pruessmann, Klaas P. (2024)
Magnetic Resonance in Medicine
Purpose: To utilize the transmit radiofrequency (RF) field in MRI as a power source, near or within the field of view but without affecting image quality or safety. Methods: Power harvesting is performed by RF induction in a resonant coil. Resulting RF field distortion in the subject is canceled by a selective shield that couples to the harvester while being transparent to the RF transmitter. Such shielding is designed with the help of electromagnetic simulation. A shielded harvester of 3 cm diameter is implemented, assessed on the bench, and tested in a 3T MRI system, recording power yield during typical scans. Results: The concept of selective shielding is confirmed by simulation. Bench tests show effective power harvesting in the presence of the shield. In the MRI system, it is confirmed that selective shielding virtually eliminates RF perturbation. In scans with the harvester immediately adjacent to a phantom, up to 100 mW of average power are harvested without affecting image quality. Conclusion: Selective shielding enables stealthy RF harvesting which can be used to supply wireless power to on-body devices during MRI.
On the limitations of echo planar 4D flow MRI
Dillinger, Hannes; Walheim, Jonas; Kozerke, Sebastian (2020)
Magnetic Resonance in Medicine
Referenceless 4D flow MRI using radial balanced SSFP at 0.6 T
McGrath, Charles; Dirix, Pietro; Vousten, Vincent; et al. (2025)
Magnetic Resonance in Medicine
Purpose To implement four-dimensional-flow MRI using phase-contrast balanced steady-state free precession (bSSFP) at 0.6 T using a free-running three-dimensional (3D) radial trajectory and referenceless background phase correction. Methods A free-running, wobbling Archimedean spiral approach including bipolar velocity-encoding gradients (3D PC-bSSFP) was implemented on a 0.6T prototype scanner. Bipolar rewinder gradients were added to ensure first-moment nulling per repetition time. Velocity encoding was performed using a three-point encoding scheme (i.e., omitting a reference measurement). Advanced computer simulations were carried out to validate the approach. Image reconstruction was performed using a locally low-rank approach. Results for anatomical visualization and flow quantification were reconstructed separately with different regularization factors. Background phase correction was achieved using phase estimation on time-averaged reconstructions. In vivo data were acquired in 6 healthy subjects during free breathing. Additional two-dimensional (2D) phase-contrast spoiled gradient-echo (2D PC-GRE) breath-hold data were obtained for reference to compare flow values in the ascending aorta, descending aorta, and pulmonary trunk. Results Velocity data acquired with 3D PC-bSSFP compared well with 2D PC-GRE (root mean square error = 3.96 cm/s), with minor underestimation of velocities (−0.52 cm/s). Cardiac phase-dependent signal-to-noise ratios normalized for differences in scan time and resolution between 3D PC-bSSFP and 2D PC-GRE demonstrate relatively steady values for 3D PC-bSSFP when compared to 2D PC-bSSFP with some reduction during phases of high flow. Conclusion Free-running, referenceless, four-dimensional-flow MRI using radial 3D PC-bSSFP is feasible on a lower-field 0.6T system, producing adequate flow quantification while yielding simultaneously reasonable cine images for concurrent flow and functional assessment of the heart and great vessels.

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