Chronological observation on the energy metabolism of skin flaps by 31P-MRS: a novel approach to evaluate the state of a flap.

Although much has been reported on the energy metabolism of various flaps, at present there is no practical noninvasive and nondestructive method to demonstrate chronologically the changes in phosphate compounds in the same subject during the healing process. A skin island flap was obtained from the dorsal side of the posterior extremities in each of 18 Wistar female rats, and a skin arterial island flap (vein included in the pedicle was ligated and divided) also was obtained from the same area in each of 15 Wistar female rats. Chronological changes of ATP, phosphocreatine, and inorganic phosphate were observed by 31P-MRS (magnetic resonance spectroscopy) using surface coils at various intervals ranging from 2 hours to 1 week after the operation. And pH was calculated based on the chemical shift values. The results showed that the PCr/Pi ratio recovered at 4 to 8 hours postoperatively in the survival group, whereas the PCr/Pi ratio lasted at the low level after the operations in the necrosis group. Magnetic resonance spectroscopy is used extensively in studies of brain, heart, and muscle, but we have found only a few papers dealing with magnetic resonance spectroscopy and none with in vivo study in the field of plastic and reconstructive surgery. Since nuclear magnetic resonance imaging is becoming a "bedside" test in the general hospitals, we consider that the PCr/Pi ratio obtained from 31P-MRS can be an effective, noninvasive, and simple method for clinical use in predicting and observing the viability of flaps at an early stage.