Canine abdominal MRI at 8 Tesla: initial experience with conventional gradient-recalled echo and rapid acquisition with relaxation enhancement (RARE) techniques.

Abstract

In this manuscript, we present our initial experience with MRI of the abdomen at 8 T of canine subjects both alive and dead. Our hypothesis is that abdominal imaging at 8 T should be possible and should demonstrate unique information. To our knowledge, this is the first description of imaging characteristics of the abdomen at such field strengths using a human MR scanner. An 8 T, 80 cm magnet housed in our department since 1998 was used for our study. GRE and rapid acquisition by relaxation enhancement (RARE) pulse sequences were selected to give reasonable slice profiles with relatively low power. Three dogs were imaged alive and after being killed. Our initial results show excellent signal-to-noise ratio and good RF penetration. Structures in the center of the abdomen were well visualized. Homogeneous signal was noted throughout each image without dielectric resonance artifact. Magnetic susceptibility artifacts were most severe on the GRE sequences. On the GRE sequences, the images appeared relatively T2 weighted. Signal voids were seen due to gas in the lung and bowel and susceptibility artifact at subcutaneous fat-muscle boundaries. The liver and spleen showed similar signal intensity, hypointense to subcutaneous muscle at low TE values. There was little internal anatomy of the liver or spleen visible except for the vessels. The kidney, in contrast, demonstrated very good internal structure with visualization of the cortex and medulla. Linear signal voids were depicted in the expected location of normal renal vascular anatomy on the GRE sequences. On the RARE sequences, the images also appeared T2 weighted. Magnetic susceptibility artifacts at subcutaneous fat-muscle boundaries were absent. Signal voids were noted in vessels with blood flow and gas. The liver and spleen were of similar signal intensity and slightly hypointense to muscle. The kidney and pancreas were of higher signal intensity than liver and subcutaneous muscle. The gallbladder wall demonstrated a striated pattern of two layers, with an inner hypointense and an outer hyperintense layer on the RARE sequence. The gastric wall demonstrated a striated pattern of five layers on the RARE sequence. Images of the dog abdomen with the world's first ultra high field 8 T magnet show robust image quality and excellent spatial resolution. Image contrast is greatest on the RARE sequence, and susceptibility artifact is strongest on the GRE sequence.