Acta Orthopaedica 2012; 83 (1): 22–25 Figure 1. F-PET scan of a resurfaced hip. Low tracer uptake by prosthetic components, cement, and bone. The dotted red line indi- cates area of low uptake (< 0.65 SUV), which appears black. 11 patients (8 males), with a mean age of 45 (32–67) years at the time of surgery, were analyzed using plain radiography, clinical examination, and repeated F-PET scans. The mean follow-up time was 4.5 (3–6.5) years. 5 of the 11 cases were analyzed twice in this study, and 6 once, after their earlier scans (Table). PET analysis We used a Siemens/CTI Exact HR+ scanner (Siemens/CTI, Knoxville, TN) for the PET measurements. Patients were placed in the supine position on the camera bed. The legs were stabilized by using a vacuum cushion. A venous catheter was inserted in an antecubital or dorsal hand vein for injection of tracer. 40 min after intravenous injection of 150 MBq [18F]- fluoride, a 15-cm section of the body covering the acetabulum and intertrochanteric region was scanned in 2D whole-body mode for 15 min. A 10-min transmission scan for attenua- tion correction was performed after completing the emission acquisition. The CT image from the former study was co-reg- istered and fused with the HR+ PET images to indicate exact anatomical locations in the analysis. The quantitative emission scans were corrected for attenua- tion, scatter, and decay and reconstructed by a process of itera- tive reconstruction. Also, non-attenuation corrected emission scans were reconstructed. Standardized uptake values (SUVs) were calculated by the formula: SUV of tissue = activity in tissue (Bq/mL) × body weight (g) / total injected dose (Bq). Setting average body density to 1 g/mL, this expression gives a unit less value of the regional tissue activity in proportion to the average activity per mL for the entire body. The non-attenuation corrected images were evaluated quali- tatively to rule out uptake artifacts related to motion. Quantitative 18F uptake in the 14 contralateral healthy femo- ral heads, analyzed in coronal projection, of the patients in our earlier report (Ullmark et al. 2009) was mean 1.8 (0.80–3.41) SUV 1 year after surgery. In order to analyze the size of the region without normal metabolism in the femoral heads, we 23 PET 3 13.9 (54) 25.9 (38) 13.1 (36) 12.7 (36) 9.6 (52) 17.2 (79) 14.5 (42) 8.7 (41) 10.2 (45) 8.5 (77) 7.2 (69) 1 2 3 4 5 6 7 8 9 10 11 35 39 58 67 43 47 56 40 51 32 32 PET 1 8.9 (14) 9.7 (12) 17.6 (12) 9.3 (12) 10.2 (34) PET 2 11.3 (29) 12.4 (22) 10.3 (24) 14.0 (24) 9.5 (34) 10.2 (57) 14.8 (27) 8.8 (27) 14.3 (30) 8.6 (63) 7.1 (55) Area of low uptake (< 0.65 SUV), given in cm2, in 11 hip joints con- taining prosthetic components, cement, and bone without tracer uptake. Values in parenthesis denote time (in months) after surgery Case Age at surgery measured the area with an uptake of less than 0.65 SUV in the coronal projection of the hips, in the middle of the femo- ral component. The low-uptake area included the prosthesis, cement, and low-uptake bone. We also performed a visual inspection of the scans. It was not possible to analyze the low- uptake region as volume due to disturbance from the partial volume effect. Results The clinical results were good; they were unchanged in all patients compared to the previous reports (Ullmark et al. 2009, 2011). None of the patients suffered from hip pain. Radiographic results All implants were assessed to be stable, and unchanged from the plain radiographs taken postoperatively. PET results All PET images clearly showed the fluoride uptake in the hip and upper femur, including the low-uptake areas. The area of low uptake corresponded to the acetabular and femoral pros- thetic components, the bone cement, and most of the bone tissue region inside the femoral component (Figure 1). From the first PET scan to last one, the mean area of low uptake for all 11 cases had increased from 10.8 to 12.9 cm2 (Table and Figure 2). Discussion One of the main concerns after reintroduction of hip resurfac- ing arthroplasties during recent years has been the viability of the femoral head. Until recently, it has not been possible to study bone metabolism under the metal femoral component of a resurfacing THA—but F-PET, in contrast to radiographic