Simultaneous NMR microimaging of multiple single-cell samples

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 high-field 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 four-channel 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) wide-bore 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 B₁ field distribution. Results showed that for coil-shield 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 ∼160 unloaded and ∼60 loaded with 100 mM NaCl solution. Practical use of the probehead was demonstrated by obtaining simultaneously four three-dimensional T₁ maps of chemically fixed Xenopus laevis oocytes at a spatial resolution of 30 X 60 X 60 μm. The T ₁ values for the nucleus were ∼2.7 seconds, and the animal pole ∼1.2 seconds.