Hybrid imaging of peripheral skeletal disease by SPECT/high resolution-flat panel CT (HR-CT)

Objectives To evaluate the impact of HR cone beam CT with flat panel detectors on the diagnostic confidence of bone scintigraphy in patients with orthopedic diseases of the peripheral skeleton.

Methods 41 patients were included in this retrospective analysis. Clinical indications were evaluation of arthroplasty respectively arthrodesis (14 patients), suspected osteomyelitis (13 patients) and degenerative joint disease (14 patients). Imaging was performed using a hybrid system, capable of providing isotropic CT voxels of 0.33x0.33x0.33 mm3 (Philips Brightview XCT). HR images were analysed independently by two readers and compared with Low resolution (LR) images obtained by filtering the HR images to a voxel size of 1.3x1.3x10mm3. Diagnostic confidence was rated on a 3-point scale and interobserver agreement was determined by calculating kappa values.

Results All HR-CT scans were of excellent, diagnostic quality. The SPECT/HR-CT images resulted in a higher diagnostic confidence score (1.8+/-0.33 vs. 1.0+/-0.32, p<0.01) and interobserver agreement (κ=0.5 vs. κ=0.02) when compared to SPECT/LR-CT. The diagnosis made on the SPECT/HR-CT images was in agreement with the final clinical diagnosis in 37 of 41 cases (90%) as compared to 25 of 41 cases (59%, p<0.01 for comparison of diagnostic accuracy). This improvement of diagnostic accuracy was due to the detailed morphologic information of the HR-CT images, which revealed subtle areas of osteolysis and sclerosis. HR-CT also visualized linear hypodense areas around arthroplasties indicating loosening and demonstrated minute bridging trabeculations in arthrodeses.

Conclusions This preliminary study presents promising results for hybrid imaging of peripheral skeletal disease using a SPECT/HR-CT system. Combining SPECT with HR-CT imaging appears markedly superior to SPECT/CT using LR-CT solely for attenuation correction and localization of regions of increased tracer uptake