Three-dimensional triple quantum-filtered 23Na imaging of rabbit kidney with weighted signal averaging.

Low signal-to-noise ratio (SNR) has been the main obstacle to multiple quantum-filtered 23Na imaging becoming an important technique for biologic and clinical applications. Through computer simulations and phantom experiments, we show that the SNR in 23Na imaging can be substantially improved by weighted signal averaging. Three-dimensional single quantum and triple quantum (TQ)-filtered 23Na images of an externalized rabbit kidney were collected with this technique. The TQ-filtered image did not show any signal when the animal was alive. However, upon sacrificing the animal, the renal cortex became clearly visible without any significant increase in signal from the medullary region. This increase in TQ-filtered signal in the renal cortex may be caused by an increased concentration of intracellular Na+ in the large intracellular space present herein, compared with the medulla. To our knowledge, this study represents the first example of three-dimensional TQ-filtered 23Na image of a biological sample.