Feasibility of opportunistic peripheral bone mineral density and structural quantification using an ultra-low dose multi-detector CT

Quantitative computed tomography (QCT) enables accurate assessment of volumetric bone mineral density (vBMD) and bone structure. Peripheral quantitative computed tomography (pQCT) and high-resolution peripheral quantitative computed tomography (HR-pQCT) have been proposed as lower-dose alternatives to conventional QCT; however, their limited availability restricts widespread clinical and research use. To investigate the feasibility of using ultra-low-dose multi-detector computed tomography (MDCT) with a hybrid iterative reconstruction (HIR) algorithm for quantifying tibial vBMD, using synchronous liquid and solid calibration phantoms. Fifty healthy volunteers (28 women and 22 men; age range: 30-60 yr; Tscore > -1) were scanned using a Philips-Brilliance MDCT scanner. To minimize radiation exposure, vBMD was quantified at the 38% distal tibial site using either a liquid calibration phantom (50, 100, and 200 mg/cm3 dipotassium hydrogen phosphate [K2HPO4]) or a solid calibration phantom (50, 100, and 250 mg/cm3 calcium hydroxyapatite [CHA]). A cross-calibration equation was applied to derive equivalent vBMD values between phantom types. Cortical bone structure was evaluated using a semi-automated segmentation approach. Following cross-calibration, BMDK2HPO4 = 1.34 BMDCHA + 13.43, mean cortical vBMD values were 1188.07 ± 29.38 mg/cm3 (CHA) and 1600.92 ± 39.51 mg/cm3 (K2HPO4). The CHA-based cortical vBMD values were consistent with solid-based pCT measurements reported in the literature. Mean cortical thickness was approximately 5 mm. The estimated effective radiation dose is approximately 10µSv, corresponding to daily background radiation levels. This preliminary study demonstrates the feasibility of using HIR-based ultra-low-dose MDCT for peripheral tibial vBMD and structural assessment at the 38% distal site. This approach offers a promising opportunistic alternative in clinical and research settings where pQCT or HR-pQCT systems are unavailable.