Abstract
Nuclear magnetic resonance (NMR) microimaging experiments performed on small samples such as single cells typically require long data acquisition times and are usually carried out on highโfield systems with limited access time. When using small probe coils on millimetre (or smaller) size scale to study single cells, it is desirable to take advantage of the comparatively large volume of homogeneous static magnetic field within the magnet to increase the efficiency of NMR data acquisition. Here we describe the development of a fourโchannel probehead that consists of four individual solenoid coils (length 2.8 mm, outer diameter 2 mm) stacked along the z axis. The probehead was designed for a 17.6 Tesla (750 MHz) wideโbore magnet, and operates within a 40 mm inner diameter gradient set with maximum strength 1 Tesla per metre. We performed simulations to estimate the impact of shielding between the coils on the B~1~ field distribution. Results showed that for coilโshield separations on the order of a coil radius, no significant change in B~1~ homogeneity is expected, and therefore coils were spaced accordingly. Coil isolation of greater than 35 dB was achieved for all coils, and the Q values were โผ160 unloaded and โผ60 loaded with 100 mM NaCl solution. Practical use of the probehead was demonstrated by obtaining simultaneously four threeโdimensional T~1~ maps of chemically fixed Xenopus laevis oocytes at a spatial resolution of 30 ร 60 ร 60 ฮผm. The T~1~ values for the nucleus were โผ2.7 seconds, and the animal pole โผ1.2 seconds. ยฉ 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part B (Magn Reson Engineering) 22B: 7โ14, 2004.