Direct 31P imaging in human limb and brain

This article describes two methods for direct imaging of the 31P-metabolites phosphocreatine (PCr) and inorganic phosphate (Pi) and their application in human brain and muscle.

All studies were performed on a 1.5 T whole-body GE Signa scanner, using bird cage resonators double-tuned to 31P and 1H. The pulse sequence was based on a multiple slice, multiple echo imaging sequence. Selection of the PCr signal was achieved either by selective excitation or by the extensive chemical shift artifact in read direction. Examinations were done in two diabetic patients, in four patients with cerebral neoplasms, and in several healthy subjects.

In calf muscle, images showed uniform distribution of PCr in normal muscle; deficits corresponded to bony structures and neurovascular bundles. Repeated exercise (dorsiflexion of the foot) led to selective loss of PCr in the anterior muscle compartment. A simultaneous increase in Pi appeared as a spatially distinct map. Diabetic patients showed more severe changes of PCr distribution in the calf muscle at rest and during much milder exercise. Direct imaging in the human brain with chemical shift selective excitation was completed in 5-30 min. In normal cerebral cortex, PCr was uniformly distributed around deficits marking the lateral ventricles. Tumors exhibiting moderate to severe depletion of PCr appeared as well defined deficits in the PCr image.

Direct imaging of PCr and Pi, with or without selective excitation of PCr, was effective in the human brain and limb. The methods described should lead to greatly improved fast phosphorus imaging. Clinical utility in peripheral ischemia and in localized energy deficits in the brain of patients with tumor, stroke, and other pathologies is anticipated.