Opportunistic Screening With CT: Comparison of Phantomless BMD Calibration Methods

Area of Science:

• Radiology and Imaging
• Osteoporosis Research
• Medical Physics

Background:

• Opportunistic screening for osteoporotic fracture risk utilizes computed tomography (CT) scans not originally intended for osteoporosis assessment.
• Traditional bone mineral density (BMD) quantification requires a calibration phantom, which is often missing in retrospectively analyzed CT scans.
• Phantomless calibration techniques have been developed as an alternative for BMD estimation in CT imaging.

Purpose of the Study:

• To review the principles of four existing phantomless calibration methods for CT-based BMD assessment.
• To compare the performance of these phantomless methods against the gold standard of simultaneous calibration (ΔBMD).
• To evaluate the effectiveness of phantomless calibration with and without precalibration using a reference dataset.

Main Methods:

• Four phantomless calibration methods were applied to two datasets: a standardized CT protocol dataset (DS1, n=350) and a clinical routine dataset (DS2, n=114).
• Three methods required precalibration with a reference dataset containing a calibration phantom, selecting optimal internal reference materials (air, blood, adipose tissue, cortical bone).
• A fifth method, based on average calibration parameters from the reference dataset, was also applied. Performance was assessed using ΔBMD.

Main Results:

• Phantomless methods requiring precalibration demonstrated good performance, with ΔBMD ranging from 0.1 ± 2.7 mg/cm³ to 2.4 ± 3.5 mg/cm³ in DS1.
• These precalibrated methods showed similar means but significantly higher standard deviations in the more variable DS2 dataset.
• The phantomless method without precalibration performed significantly worse, with ΔBMD values of 12.6 ± 13.2 mg/cm³ (DS1) and 0.5 ± 8.8 mg/cm³ (DS2).

Conclusions:

• Phantomless BMD calibration is effective for opportunistic screening when precalibrated with a reference dataset.
• Precalibration significantly improves the accuracy and reliability of phantomless BMD measurements from CT scans.
• These findings support the potential of phantomless calibration for widespread adoption in clinical practice for osteoporosis risk assessment.