A Feasibility Study for Photon-Counting Detector-Based DXA-like Bone Density Scans
Abstract
Purpose
Dual-energy X-ray absorptiometry (DXA) is the clinical standard for bone mineral density assessment but is constrained by energy-integrating detectors. This study investigates the feasibility of DXA imaging using a benchtop photon-counting detector (PCD).
Methods
A benchtop photon-counting system was configured to mimic clinical DXA acquisition by translating the object through a fixed source–detector geometry. Projections were acquired at 70 kVp using energy thresholds at 25, 33, 39, 46, 53, and 65 keV. Short-exposure frames were combined using time-delay integration. Experiments were performed using a bone density phantom with calcium-equivalent inserts and pork riblet samples. Image quality was evaluated using SNR and CNR, bone density calibration was assessed using CT number-like normalization, and dose was estimated as free-in-air kerma at isocenter using SpekPy.
Results
Single-frame projections exhibited limited image quality due to low photon statistics in individual energy bins. The total bin provided the highest per-frame image quality (SNR = 9.7, CNR = 4.1), while the low-energy 25–33 keV bin preserved enhanced bone contrast (SNR = 5.3, CNR = 2.4), and the mid-energy 46–53 keV bin showed the poorest performance (SNR = 2.1, CNR = 0.6). Using 250-frame TDI substantially improved image quality across all bins (SNR =27.1, CNR=14.9). Bone density calibration using a chalk phantom demonstrated a strong linear relationship between CT-number-like intensity and calcium-equivalent concentration for both low-energy (25–33 keV) and high-energy (65-120 keV) ranges (R² = 0.96, 0.97, 0.91). The estimated free-in-air kerma using 250-frame TDI was approximately 11 µGy, comparable to clinical DXA dose levels. Applying this calibration to a pork riblet yielded a calcium concentration of approximately 96–115 mg/mL, consistent with reported rib bone mineral density and CT calibration.
Conclusion
Photon-counting detector–based DXA-style projection imaging is feasible at DXA-level dose using time-delay integration with further calibration.