Comparison between visual assessment and quantitative measurement of radioactivity on the bone scintigram in Paget's disease of bone.

Two methods of evaluating bone scintigrams in Paget's disease of bone were compared. Bone scintigraphy was performed after IV injection of 20 mCi 99mTc-Sn-EHDP. Qualitative evaluation was carried out by visual assessment of the photographs of the oscilloscope of the gamma camera, using a scale of six well-defined scores. Quantitative evaluation of uptake of radionuclide was obtained by calculating the ratio of the number of counts per pixel in pagetoid bone with that in comparable normal bone; measurements were performed by a computer interfaced to the gamma camera, after marking the regions of interest with a light-pen. In 42 patients with untreated Paget's disease there was a linear relationship between the visually assessed score and the logarithm of the computer-measured ratio. In 27 patients treated with APD a decrease in uptake was measured in all lesions and was usually also detected visually; however, in 14% of these lesions the changes (ranging from 9% to 70%) were not visible to the eye. Here too, visual estimation of the changes corresponded to the logarithm of the measured changes. In conclusion, there is a semilogarithmic relationship between the visual and the physical methods.