MAGNETIC-RESONANCE MICROSCOPY - CHALLENGES IN BIOLOGICAL IMAGING USING A 500 MHZ NMR MICROSCOPE

Proton magnetic resonance microscopy of biological systems at a field strength 11.7T (500 MHz resonance frequency) is examined from the poin t of view of signal-to-noise and resolution. Results from three imagin g schemes are discussed. These are: (1) spin warp spin echo (SW-SE); ( 2) projection reconstruction using free induction signals (PR-FID); an d (3) constant time with free induction decay signals (CT-FID). The po int spread functions for the various factors that contribute to resolu tion in each scheme are examined. The SW-SE method meets most of the c hallenges in biological imaging and provides T-2 contrast. CT-FID is a useful method for imaging of biological solids with short T-2 but lo ng data collection times limits its usefulness for in vivo imaging. In comparison, PR-FID is shown to be capable of fast imaging using small gradients. Consequently, diffusion effects can be reduced. Using imag es of the head of a mouse lemur we conclude that a signal-to-noise rat io of 5 is adequate to extract useful neuro-anatomical details in T-2- weighted images. We emphasize the importance of isotropically resolved three-dimensional imaging for examination of anatomical structures, d eveloping cellular patterns, and connectivity relationships in biologi cal systems.