Regional 1H transverse magnetization studies in perfused rabbit kidney

A Carr-Purcell-Meiboom-Gill imaging sequence consisting of 128 echoes is used to extract transverse magnetization decay curves (TDCs) at 1.9 T from 1.7 x 1.7 x 5-mm3 voxels within the cortex, outer medulla, and inner medulla of perfused rabbit kidneys. The spatially localized TDCs within each tissue type are found to be better approximated by biexponential, as opposed to monoexponential, functions. The biexponential parameters characterizing the TDCs demonstrate an improved degree of tissue specificity over that available from monoexponential analyses. The fraction of the quickly relaxing TDC component and the relaxation rate of this component are observed to decrease from cortex to inner medulla. A two-site exchange analysis is used to convert biexponential TDC parameters into water volume fractions and exchange rates. The exchange rates between the fast and slowly relaxing pools increased from cortex to inner medulla. All exchange rates were less than 1.5 Hz, indicating a relatively slow water exchange process. The imaging methods and subsequent analyses offer the potential to generate unconventional MR images with tissue contrast dependent upon water compartmentation and exchange.