Resolution recovery in planar bone scans: diagnostic value in metastatic disease

Recovery of spatial resolution lost through increasing lesion-to-detector distance can improve the spatial resolution of planar images. We compare two commercial solutions, HiScan (http://www.scivis.de) and Xact.bone (http://www.ultraspect.com), with unprocessed planar whole-body bone scans. Thirty-five patients with suspected bone metastases were scanned 3 h after injection of 600 MBq (99m)Tc-HMDP at 12 cm/min. Two patients with more than 20 lesions were used for reporter training and were excluded from the analysis. Two blinded reporters categorized each scan as benign, indeterminate or malignant and assigned individual lesions to those same categories. Image quality was first graded on a 1 (worst) to 10 (best) scale for each individual scan, and then all three scans of each patient were ranked according to image quality. Reporter A detected 65, 90 and 83 malignant lesions with the unprocessed scan, HiScan and Xact.bone and 23, 24 and 17 indeterminate lesions, respectively. Reporter B detected 60, 80 and 75 malignant lesions with the unprocessed scan, HiScan and Xact.bone and 17, 16 and 14 indeterminate lesions, respectively. To summarize, reporters A/B detected 38/33% and 28/25% more malignant lesions with HiScan and Xact.bone than with the unprocessed scan, respectively (Friedman's test, P<0.05). The number of indeterminate lesions did not increase, but the percentage of unclear lesions decreased. Mean image quality for the unprocessed scan, HiScan and Xact.bone was 6.5, 9.1 and 7.9 for reporter A and 5.6, 7.5 and 6.7 for reporter B, respectively (P<0.0001). HiScan was ranked best for image quality in 82% of patients and Xact.bone in 18%. Resolution recovery in planar whole-body bone scans significantly increases the absolute number of detectable malignant lesions, decreases the percentage of indeterminate lesions, significantly increases image quality and is an easy-to-implement addition to routine clinical practice.