The value of local^99mTc (Sn)-MDP bone to soft tissue uptake ratio in osteoporosis, before and during fluoride therapy

Abstract

The reproducibility and diagnostic value of local bone to soft tissue uptake ratio of^99mTc(Sn)-MDP as a bone tracer was examined in a prospective study in 35 patients who were under investigation and/or treatment for postmenopausal osteoporosis. The ratio of tracer uptake in the second lumbar vertebra (L2) and both femoral shafts was calculated from the number of counts in suitable regions of interest. Results obtained with settings and calculations in the routine practice were compared to the results obtained by revision of all raw data in one run by one person. The results were compared to the serum alkaline phosphatase activity (AP) and to local bone mineral mass as determined by dual photon absorptiometry (DPA). In 15 patients serial measurements during fluoride therapy were also compared to serum osteocalcin values and to bone histomorphomatric data. The precision error of the calculation of uptake ratios from raw counts (including selection of region of interest) was 13.9% for the femoral shaft and 14.7% for L2. The mean difference between left and right femoral shaft in individuals was not significant and its variance was smallP > 0.1). There was a weak but significant linear correlation between local uptake ratio in the spine and AP in the total material (r=0.328P < 0.01). However, changes in local uptake ratio during therapy with fluoride in 15 patients were too small to be of any value and did not correlate with changes in alkaline phosphatase or osteocalcin or trabecular surface covered with osteoblasts. We conclude therefore that local uptake ratio of bone seeking isotopes has no value in assessing general metabolic bone activity in osteoportic patients, for diagnostic purposes or in the follow up of their response to therapy, except for the detection of local untoward reactions.