Comparison of 85Sr, 87mSr, 18F, and 99mTc-labeled phosphates for bone scanning

The observation by Subramanian and his co-workers that a 99mTc-labeled polyphosphate had excellent affinity for bone has led to widespread use of 99mTc-labeled phosphates as bone scanning agents. Initially, only polyphosphate was employed, but because of somewhat inconstant results and difficulty in preparation of this product, other phosphate compounds were sought. We soon discovered that an inorganic compound, pyrophosphate, appeared to have certain advantages over polyphosphate. Other workers formulated diphosphonates (organic phosphates) which also demonstrated advantages over polyphosphates. Comparison studies in rabbits utilizing 85Sr, 87mSr, 18F, and several phosphates (inorganic and organic) proved the 99mTc-labeled phosphates to be clearly superior in delineating normal skeletal anatomy. Studies in humans confirmed that excellent visualization of bone was obtained with 99mTc-labeled phosphates using either a gamma camera or a rectilinear scanner. What was not known, however, was just how reliable this class of agents would prove to be in detecting bone disease when compared to bone-seeking radiopharmaceuticals such as 85Sr, 87mSr, and 18F. Further comparative analyses have clearly demonstrated that both inorganic and organic 99mTc phosphate complexes are extremely sensitive in revealing more bone disease than the older bone scanning agents.