Improved localizers and anatomical images to enable phosphorus magnetic resonance spectroscopy of liver metastasis at 7T

Abstract

ABSTRACTPhosphorus spectroscopy (31P) at 7T (300 MHz) enables clinically-relevant spatial resolutions and time scales with high potential for monitoring response to cancer treatment. However, at 7T collecting a radiological-grade anatomical image of the liver—which is required for performing localized 31P spectroscopy—presents a challenge. Unlike lower field-strength scanners, there is no body coil in the bore of the 7T and despite inadequate penetration depth (<10 cm), surface coils are the current state-of-the-art for acquiring anatomical (1H) images. Therefore, thus far, high field 31P spectroscopy has been limited to diffuse liver disease. However, the use of antennas enable improved penetration depths at 300 MHz, and when combined with parallel transmit, can enable body imaging at 7T. We have developed a protocol for imaging liver metastases of patients using parallel transmit and 31P spectroscopy at 7T. We used a custom-made liver coil consisting of eight 30-cm dipole antennas tuned to the proton (300 MHz) frequency, and two partially overlapping 20-cm-diameter loops tuned for 31P (120 MHz). The field of view afforded by the two antennas underneath the 31P loops is not sufficient to image the complete boundaries of the liver for chemical shift imaging (CSI) planning and region-of-interest-based B0 shimming. The liver and full axial slice of the abdomen was imaged with eight transmit/receive antennas using parallel transmit B1-shimming to overcome image voids. Through the use of antennas we overcome the challenges for multi-parametric body imaging, and can begin to explore the possibility of monitoring the response of patients with liver metastasis to cancer treatments.ABBREVIATIONS(PDE)Phosphodiester(GPE)Glycerophosphoethanolamine(GPC)Glycerophosphocholine(PME)Phosphomonoesther(PC)Phosphocholine(PE)Phosphoethanalomine(PI)Inorganic Phosphate(PCR)Phosphocreatine(PTC)Phophotidylcholine(CSI)Chemical Shift Imaging(GE)Gradient Echo(L)Left(R)Right(H)Head(F)Foot(A)Anterior(P)Posterior(TR)Repetition Time(TE)Echo Time