UCLA

Magnetic resonance imaging (MRI) can serve as an efficient tool to examine the internal structure of the human body, especially for soft tissues. The pituitary gland – which regulates hormones in the body – is one example of soft tissue that can be investigated by MRI [1]. One area of particular interest in the study of the pituitary gland is the search for miniature tumors, also called microadenomas. Microadenomas in the pituitary gland are important because they can cause Cushing’s disease, which can cause death if untreated [2]. However, although 60-80% of the pituitary adenomas are microadenomas [3], current 3 T MRI techniques cannot detect up to 50% of the microadenomas [4]. The present work aims to increase detection accuracy by placing miniaturized MRI coils inside the sphenoid sinus (a hollow space or cavity near the pituitary gland), as close as possible to the region of interest (ROI), namely the pituitary gland [5]. By placing MRI surface coils close to the target region, the SNR can be increased, which allows for improved detection accuracy of microadenomas that are too small for current scanning techniques. Previous studies using single-loop surface coils achieved high-SNR images, but in some cases, coils need to be rotated so that they can fit into the cavity near the pituitary gland. In the case of large rotation angles, single-loop surface coils are limited by the intrinsic “dead spot”, especially when rotated 90 degrees [4]. In contrast, figure 8-shaped surface coils are less effected by the signal loss due to coil plane rotations [6]. In this study, we developed a custom-designed surface coil specifically for pituitary gland imaging. Parameters of the coil are optimized based on simulations, including the distance between the two semicircle-shaped components and the coil radius. A linear relationship between the optimal coil radius and target depth is established. The compensation between rotation angle of the coil plane and the horizontal shift of the target is also studied, proving that rotations have a reduced detrimental effect on coil performance as compared to single-loop coils, especially when the target is placed near the coil boundary.