Magnetic resonance imaging (MRI) using an ultra-high magnetic field (7 Tesla) enables detailed and non-invasive studies of the function and anatomy of the human visual cortex, which is the brain region responsible for visual signal processing. However, 7T human MRI often suffers from image shading in the occipital region due to the radiofrequency (RF) wave propagation effect. Dedicated visual cortex coils, on the other hand, often lack the capability to visualize the whole brain which is necessary for image registration. We propose a novel RF coil structure in which a 2-channel transmit and receive (TRx) coil is grafted onto the frontal part of a multi-channel transmit-only/receive-only (TORO, 4Tx/14Rx) visual cortex coil. This coil was tested for high-resolution functional MRI with an in-plane resolution of 0.5 mm. The results showed that the proposed coil achieved a higher (×2.5) temporal signal-to-noise ratio (tSNR) in functional imaging of the visual cortex area than that of a commercial 7T whole-head coil. The added 2-channel TRx elements allowed whole-brain edge images to be acquired, enabling successful brain segmentation and atlas registration without the need for a second scan using a whole-head coil. The proposed coil structure can be useful for high-resolution visual functional MRI at very high magnetic fields due to its sensitivity, open geometry, and compatibility with the standard image processing workflow.
In this study, we propose a novel, multiturn histology coil for microscopic magnetic resonance (MR) imaging of histological tissue slices with substantially higher signal-to-noise-ratio (SNR) outcomes compared with previously developed coils. We performed electromagnetic simulations of the proposed coils and acquired MR images from a gelatin phantom and a rat brain slice with the implemented coils. The performances of the coils were evaluated by comparing the measured and simulated radio-frequency transmission (B1 + ) fields in a flip-angle map form, and with low flip-angle gradient echo images to calculate the SNR increase as a function of the number of turns (n) of the coils. This study was performed on a 3 T MR imaging system. The proposed coil with n = 7 achieved SNR greater than 3.5 times that of a single-turn coil while preserving the highly uniform B1 + field across the imaging region. The proposed method provides new possibilities for high-resolution MR imaging of microscopic tissue samples for biomedical applications.INDEX TERMS magnetic resonance imaging (MRI), microscopy, signal-to-noise ratio (SNR), radiofrequency (RF), Multiturn planar inductor (MTPI)
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