Insertable inductively coupled volumetric coils for MR microscopy in a human 7T MR system

PURPOSE: To demonstrate the capability of insertable inductively coupled volumetric coils for MR microscopy in a human 7T MR system. METHODS: Insertable inductively coupled volume coils with diameters of 26 and 64 mm (D26 and D64 coils) targeted for monkey and mouse brain specimen sizes were designed and fabricated. These coils were placed inside the imaging volume of a transmit/receive knee coil without wired connections to the main system. Signal‐to‐noise ratio (SNR) evaluations were conducted with and without the insertable coils, and the g‐factor maps of parallel imaging (PI) were also calculated for the D64 coil. Brain specimens were imaged using 3D [Formula: see text] ‐weighted images with spatial resolution of isotropic 50 and 160 μm using D26 and D64 coils, respectively. RESULTS: Relative average (SD) SNRs compared with knee coil alone were 12.54 (0.30) and 2.37 (0.05) at the center for the D26 and D64 coils, respectively. The mean g‐factors of PI with the D64 coil for the factor of 2 were less than 1.1 in the left‐right and anterior‐posterior directions, and around 1.5 in the superior‐inferior direction or when the PI factor of 3 was used. Acceleration in two directions showed lower g‐factors but suffered from intrinsic low SNR. Representative [Formula: see text] ‐weighted images of the specimen showed structural details. CONCLUSION: Inductively coupled small diameter coils insertable to the knee coil demonstrated high SNR and modest PI capability. The concept was successfully used to visualize fine structures of the brain specimen. The insertable coils are easy to handle and enable MR microscopy in a human whole‐body 7T MRI system.