MRI contrast using solid-state, B1-distorting, microelectromechanical systems (MEMS) microresonant devices (MRDs).

Presently, signal generation in MRI depends on the concentration and relaxivity of protons or other MR-active nuclei, and contrast depends on local differences in signal. In this proof-of-principle study, we explore the use of nonchemical, solid-state devices for generating detectable signal and/or contrast in vitro and in vivo. We introduce the concept of microresonant devices (MRDs), which are micron-sized resonators fabricated using microelectromechanical systems (MEMS) technology.

Sodium MRI of the human kidney at 3 Tesla.

The sodium concentration gradient in the kidney (from the cortex to the medulla) serves to regulate fluid homeostasis and is tightly coupled to renal function. It was previously shown that renal function and pathophysiology can be characterized in rat kidneys by measuring the sodium gradient with (23)Na MRI. This study demonstrates for the first time the ability of (23)Na MRI to map the distribution of sodium in the human kidney and to quantify the corticomedullary sodium gradient.