Quantitative solid-state NMR imaging of synthetic calcium phosphate implants

It is shown that solid-state phosphorus-31 nuclear magnetic resonance imagi ng can be used to measure quantitatively the mass of hydroxyapatite (HA), a synthetic calcium phosphate used as an orthopedic implant material, in the presence of bone. A three-dimensional projection reconstruction technique was used to produce solid-state images from 998 free induction decays sampl ed in the presence of a fixed amplitude field gradient whose direction was varied uniformly over the unit sphere. Chemical selection is achieved using T-1 contrast, as the synthetic calcium phosphate has a shorter T-1 (1.8 se c at 4.7 T) compared with the bone (approximately 15 sec at 4.7 T in vivo, 42 sec ex vivo). Experimental results demonstrating the linear relationship between image intensity and HA density in phantoms containing HA and silic on (IV) oxide, and HA and bone are shown. Chemically pure images of bone mi neral and synthetic HA have been computed from images of New Zealand White rabbits acquired in vivo at two different recycle times. The technique can be used to follow noninvasively the resorption and remodeling of calcium ph osphate implants in vivo. (C) 1999 Wiley-Liss, Inc.