Paraplegics whose range of motion is limited by para-osteo-arthropathy (POA) may have difficulty in becoming independent unless the heterotopic bone mass is removed. The recurrence rate is high if the bony mass is not mature at the time of surgery. Radiography and alkaline phosphatase correlations are not trustworthy. In 3 paraplegics with POA, radiolabeled osteotropic agents demonstrated a steady decrease in the uptake ratio (heterotopic/normal bone) followed by a steady-state plateau, reflecting the most useful index of maturation and allowing surgical removal of bone without recurrence.
. (1971) described the use of the electrocardiogram to control time intervals for the collection of enddiastolic and end-systolic images in the gamma camera during equilibrium of an intravascular radioindicator. The volumes and ejection fraction were then calculated from the area and length of the ventricular images (area-length method). Van Dyke et al. (1972) described the use of a television monitor recording from oscilloscope images of the first passage of a radionuclide through the left heart. They used a single 'region-of-interest' over the ventricular image to determine the relative end diastolic and end-systolic counts. They then used an extraventricular region-of-interest to determine the level of background radiation and subtracted this from the end-diastolic and end-systolic counts be-
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