Flexible In-Cavity MRI Receiving Coil for Ultrahigh Resolution Imaging of the Pituitary Gland

Purpose: Preclinical design and construction of a flexible intra-sphenoid coil aiming for submillimeter resolution of the human pituitary gland. Methods: Sphenoid sinus measurements determined coil design constraints for use in > 95% of adult patients. Temperature safety parameters were tested. The prototype 2-cm diameter coil was positioned in the sphenoid sinus of cadaveric human heads utilizing the transnasal endoscopic technique that is used clinically. Signal-to-noise ratio (SNR) was estimated comparing the prototype transnasal coil versus a standard clinical head coil. One cadaver pituitary gland was explanted and histologically examined for correlation to the imaging findings. Results: With the coil positioned directly atop the sella turcica at 0 0 angle of the B 0 static field, the craniocaudal distance (24 ± 4 mm) was the limiting constraint. Phantom experiments showed a negligible change in temperature at two sites over 15 minutes. The flexible coil was placed transnasally in cadaveric specimens using an endoscopic approach. The image quality was subjectively superior at higher spatial resolutions relative to the commercial 20-channel head coil. An average 17-fold increase in SNR was achieved within the pituitary gland. Subtle findings visualized only with the transnasal coil had potential pathological correlation with immunohistochemical analysis. Conclusions: A transnasal radiofrequency coil feasibly provides a 17-fold boost in SNR at 3T, providing, in principle, equivalent imaging to a 51T scanner using a standard head coil. The ability to safely improve the quality of pituitary imaging may be helpful in the identification and subsequent surgical resection of small functional pituitary lesions.