Comparison of reprojected 'pseudoplanar' bone SPECT/CT and planar bone scintigraphy for the detection and localization of foot and ankle osteoarthritis.

Purpose: To compare the performance of pseudoplanar (PP) images reprojected from bone single photon emission computed tomography/computed tomography (SPECT/CT) against 'real' planar bone scintigraphy for the assessment of localization and grading of radiotracer uptake of active osteoarthritic joints in the foot and ankle. Noninferiority of PP images would shorten the protocol substantially.

Methods: Late-phase real planar (RP) and SPECT/CT reconstructed PP images of 96 feet in 48 patients (22 women, 26 men, median age: 49 years, interquartile range: 34-67 years) with foot and ankle osteoarthritis were independently evaluated by three different readers. Presence, localization, and uptake grade (grade 1: mild, 2: moderate, and 3: high uptake of the radiotracer) of the active osteoarthritic joints were assessed. SPECT/CT served as a reference standard, and maximum standardized uptake value (SUVmax) was measured for all active foot and ankle joints.

Results: Overall, 123 of 3168 joints in 48 patients had active osteoarthritis (OA) on SPECT/CT. The most frequently affected joints were the tarsometatarsal (n = 29), upper ankle (27), lower ankle (23), and talonavicular (15) joints. The mean SUVmax of all active joints was 11.9 ± 7.5. The rate of correct detection and localization of active joints for the three readers was 77/82/85% for RP and 80/81/81% for PP, without significant difference. There was substantial agreement between RP and PP images among all the readers (R1 : 0.70, R2 : 0.76, R3 : 0.74). There was a significant correlation for visual uptake grading among all the readers for RP and PP images (P = 0.001).

Conclusion: Planar images can be replaced by reconstructed PP images, leading to a substantially time-saving foot and ankle bone SPECT/CT protocol, as PP images are noninferior to planar images for the detection, localization, and grading of osteoarthritis. We expect that further technical advances coupled with artificial intelligence will improve the performance of hybrid imaging in nononcologic indications.