xSPECT Bone^® (xB) is a new reconstruction algorithm developed by Siemens^® in bone hybrid imaging (SPECT/CT). A CT-based tissue segmentation is incorporated into SPECT reconstruction to provide SPECT images with bone anatomy appearance. The objectives of this unique study were, in a context of daily practice, to compare inter-observer agreement (IOA) and diagnostic accuracy between two Siemens^® reconstructions (a new one xB/CT and the commonly used Flash 3D ^® (F3D)/CT).

Two hundred thirteen consecutive patients referred to the Brest nuclear medicine department for non-oncological bone diseases were evaluated retrospectively. Each SPECT/CT was performed on a Symbia Intevo T6 gamma camera (Siemens^®). Two hundred seven SPECT/CT were included (7 patients were excluded and 2 SPECT/CT were performed for the same patient). All SPECT/CT were independently interpreted by two nuclear physicians (one junior and one senior expert) with xB/CT then with F3D/CT three months later. The diagnoses were classified into 5 categories (Normal scintigraphy; Arthritis; Abarticular disease; Fracture or tumour pathology; Complex Regional Pain Syndrome). IOA and diagnostic accuracy were determined using a McNemar test, an unweighted Kappa coefficient and using the clinical and paraclinical follow-up of more than 18 months.

No statistically significant difference between IOA xB and IOA F3D were found (P=0.532). Agreement for xB after categorical classification of the diagnoses was high (κ xB=0.89 [95% CI 0.84–0.93]) but without statistically significant difference with that of F3D (κ F3D = 0.90 [95% CI 0.86–0.94]). Thirty-one (14.9%) inter-reconstruction diagnostic discrepancies were observed whose 21 (10.1%) were classified as major. The follow-up confirmed the diagnosis of F3D in 10 cases, xB in 6 cases and was non-contributory in 5 cases.

xB reconstruction algorithm was found reliable, providing high inter-observer agreement with similar performances to F3D reconstruction in a context of daily practice. Nevertheless, we believe it provides a strong added value to the SPECT/CT images thanks to a striking aesthetic aspect, with the condition of a strict spatial agreement between the SPECT and the CT acquisitions to obtain interpretable xB images.