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

Purpose: 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 i s that abdominal imaging at 8 T should be possible and should demonstrate u nique information. To our knowledge, this is the first description of imagi ng characteristics of the abdomen at such field strengths using a human MR scanner. Method: An 8 T, 80 cm magnet housed in our department since 1998 w as 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. Results: Our initial results show excellent signal-to-noise ratio and good RF penetration. Structures in the center of the abdomen were well visualiz ed. Homogeneous signal was noted throughout each image without dielectric r esonance artifact. Magnetic susceptibility artifacts were most severe on th e GRE sequences. On the GRE sequences, the images appeared relatively T2 we ighted. Signal voids were seen due to gas in the lung and bowel and suscept ibility artifact at subcutaneous rat-muscle boundaries. The liver and splee n showed similar signal intensity, hypointense to subcutaneous muscle at lo w TE values. There was little internal anatomy of the liver or spleen visib le except for the vessels. The kidney, in contrast, demonstrated very good internal structure with visualization of the cortex and medulla. Linear sig nal voids were depicted in the expected location of normal renal vascular a natomy on the GRE sequences. On the RARE sequences, the images also appeare d 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 slightl y hypointense to muscle. The kidney and pancreas were of higher signal inte nsity than liver and subcutaneous muscle. The gallbladder wall demonstrated a striated pattern of two layers, with an inner hypointense and an outer h yperintense layer on the RARE sequence. The gastric wall demonstrated a str iated pattern of five layers on the RARE sequence. Conclusion: Images of th e dog abdomen with the world's first ultra high field 8 T magnet show robus t image quality and excellent spatial resolution. linage contrast is greate st on the RARE sequence, and susceptibility artifact is strongest on the GR E sequence.