A temperature-stable cryo-system for high-temperature superconducting MR in-vivo imaging

Functional quantitative susceptibility mapping (fQSM) of rat brain during flashing light stimulation

Functional magnetic resonance imaging (fMRI) based on the blood oxygenation level-dependent (BOLD) contrast has become an indispensable tool in neuroscience. However, the BOLD signal is nonlocal, lacking quantitative measurement of oxygenation fluctuation. This preclinical study aimed to introduced functional quantitative susceptibility mapping (fQSM) to complement BOLD-fMRI to quantitatively assess the local susceptibility and venous oxygen saturation (SvO₂). Rats were subjected to a 5 Hz flashing light and the different inhaled oxygenation levels (30% and 100%) were used to observe the venous susceptibility to quantify SvO₂. Phase information was extracted to produce QSM, and the activation responses of magnitude (conventional BOLD) and the QSM time-series were analyzed. During light stimulation, the susceptibility change of fQSM was four times larger than the BOLD signal change in both inhalation oxygenation conditions. Moreover, the responses in the fQSM map were more restricted to the visual pathway, such as the lateral geniculate nucleus and superior colliculus, compared with the relatively diffuse distributions in the BOLD map. Also, the calibrated SvO₂ was approximately 84% (88%) when the task was on, 83% (87%) when the task was off during 30% (and during 100%) oxygen inhalation. This is the first fQSM study in a small animal model and increases our understanding of fQSM in the brains of small animals. This study demonstrated the feasibility, sensitivity, and specificity of fQSM using light stimulus, as fQSM provides quantitative clues as well as localized information, complementing the defects of BOLD-fMRI. In addition to neural activity, fQSM also assesses SvO₂ as supplementary information while BOLD-fMRI dose not. Accordingly, the fQSM technique could be a useful quantitative tool for functional studies, such as longitudinal follow up of neurodegenerative diseases, functional recovery after brain surgery, and negative BOLD studies.

Comparisons between the 35 mm quadrature surface resonator at 300 K and the 40 mm high-temperature superconducting surface resonator at 77 K in a 3T MRI imager

This study attempts to compare the signal-to-noise ratio (SNR) of the 40 mm High-Temperature Superconducting (HTS) surface resonator at 77 K and the 35 mm commercial quadrature (QD) surface resonator at 300 K in a 3 Tesla (T) MRI imager. To aquire images for the comparison, we implemented a phantom experiment using the 40 mm diameter Bi₂Sr₂Ca₂Cu₃O_x (Bi-2223) HTS surface resonator, the 35 mm commercial QD surface resonator and the 40 mm professionally-made copper surface resonator. The HTS surface resonator at 77 K provided a 1.43-fold SNR gain over the QD surface resonator at 300 K and provided a 3.84-fold SNR gain over the professionally-made copper surface resonator at 300 K on phantom images. The results agree with the predictions, and the difference between the predicted SNR gains and measured SNR gains is 1%. Although the geometry of the HTS surface resonator is different from the QD surface resonator, its SNR is still higher. The results demonstrate that a higher image quality can be obtained with the HTS surface resonator at 77 K. With the HTS surface resonator, the SNR can be improved, suggesting that the HTS surface resonator is a potentially helpful diagnostic tool for MRI imaging in various applications.