The diagnostic value of triple head single photon emission computed tomography (3H-SPECT) in avascular necrosis of the femoral head.

Bone scans, triple head single photon emission computed tomography (3H-SPECT) and MRI scans were compared for their ability to detect avascular necrosis of the femoral head (AVN). 3H-SPECT was undertaken 5 hours after injection of 20 mCi of Tc-99m MDP for 20 minutes using a 3 detector rotating gamma camera (TRIAD, Trionix) equipped with ultra-high resolution collimators. The bone scan and 3H-SPECT were diagnosed as positive for AVN when a photopenic defect in the femoral head could be identified. The final diagnosis of AVN was established in 32 patients in 52 hips by MRI and/or histological findings. Unilateral disease was present in 11 patients, while 21 had bilateral disease. Of 32 patients and 52 hips, the bone scan, 3H-SPECT and MRI detected 37, 46 and 52 positive hips respectively. The sensitivity of 3H-SPECT (88.5%) was higher than that of the bone scans (71.5%), and was also higher than that previously reported using a single head SPECT. In AVN, the 3H-SPECT image was much clearer, and permitted more accurate localization of lesions than was possible by a bone scan. Studies including patients with diseases other than AVN and correlation with other methods of imaging is needed to define the role of 3H-SPECT in the diagnosis of AVN more precisely.