Mahesh H. Mankani, MD Sergei A. Kuznetsov, PhD Nilo A. Avila, MD Albert Kingman, PhD Pamela Gehron Robey, PhD Index terms: Animals Bone marrow, transplantation Bones, CT, 40.12119 Computed tomography (CT), quantitative, 40.12119 Hydroxyapatite Phantoms Published online 10.1148/radiol.2302011529 Radiology 2004; 230:369 –376 Abbreviations: BMD = bone mineral density HA-TCP = hydroxyapatite–tricalcium phosphate ROC = receiver operating characteristic 1 From the Division of Plastic Surgery, Department of Surgery, University of California–San Francisco, San Fran- cisco General Hospital, 1001 Potrero Ave, Ward 3A, San Francisco, CA 94110 (M.H.M.); Craniofacial and Skeletal Diseases Branch (S.A.K., P.G.R.) and Biostatistics Core, Office of the Director (A.K.), National Institute of Dental and Craniofacial Research, Na- tional Institutes of Health, Bethesda, Md; Department of Radiology, Clinical Center, National Institutes of Health, Be- thesda, Md (N.A.A.). Received Septem- ber 14, 2001; revision requested Oc- tober 23; final revision received May 23, 2003; accepted June 18. Address correspondence to M.H.M. (e-mail: mmankani@sfghsurg.ucsf.edu). Author contributions: Guarantor of integrity of entire study, M.H.M.; study concepts and design, M.H.M.; literature research, M.H.M.; clinical and experimental studies, M.H.M., S.A.K.; data acquisition, M.H.M., S.A.K., N.A.A.; data analysis/ interpretation, all authors; statistical analysis, M.H.M., A.K.; manuscript preparation, definition of intellectual content, editing, revision/review, and final version approval, all authors © RSNA, 2004 Bone Formation in Transplants of Human Bone Marrow Stromal Cells and Hydroxyapatite–Tricalcium Phosphate: Prediction with Quantitative CT in Mice 1 PURPOSE: To determine whether quantitative computed tomography (CT) can be used to estimate the extent of new bone formation in hydroxyapatite–tricalcium phosphate (HA-TCP)– based transplants. MATERIALS AND METHODS: Bone-forming transplants were generated by at- taching cultured human bone marrow stromal cells to aliquots of HA-TCP particles and were placed in subcutaneous pockets in immunocompromised mice. After 8 weeks, the transplants were individually imaged; each scan included a phantom. Overall bone mineral density (BMD) of each transplant was obtained. Hematoxylin- eosin–stained sections of the same transplants were then examined histologically, which is the reference standard for assessing bone formation. The extent of bone in each transplant was scored on a semiquantitative scale ranging from 0 to 4 by three independent blinded observers; the bone score for each transplant was calculated by averaging the three observer scores. BMD was compared with the histologically determined bone score for each transplant. Statistical evaluations included (a) calculation of empiric receiver operating characteristic curves to determine opti- mum BMD thresholds and (b) determination of the relationship between BMD and bone score, including derivation of Pearson correlation coefficients. RESULTS: One hundred twenty transplants were evaluated. Average BMD of 600 mg/cm 3 K 2 HPO 4 or more was noted in transplants with appreciable bone formation (bone score  3), while average BMD of less than 600 mg/cm 3 K 2 HPO 4 was seen in transplants with poor bone formation (bone score  3) (P  .001). Among trans- plants with appreciable bone formation, the BMD was proportional to the extent of mineralized matrix present in the new bone. CONCLUSION: Use of quantitative CT offers a practical approach for the nonin- vasive determination of new bone formation in mineralizing bone marrow stromal cells and HA-TCP transplants. © RSNA, 2004 Transplantation of bone graft extenders, which can reduce the amount of bone graft needed to complete a reconstruction, or bone graft replacements, such as osteoconductive matrices, have gained considerable interest during the past few years. In lieu of or in addition to bone autografts or allografts, surgeons have reconstructed bone defects with materials that contain hydroxyapatite–tricalcium phosphate (HA-TCP) (1–12). However, of great concern to reconstructive surgeons is the current lack of a reliable noninvasive modality for the evaluation of new bone formation in the presence of these mineral- containing matrices, since the extent of bone formation and therefore graft success is uncertain (6,13–15). HA-TCP has a high density, comparable to that of cortical bone. On 369 R adiology