Bone mineral density radiopaque templates for cone beam computed tomography and multidetector computed tomography

Background: Cone beam computed tomography (CBCT) applied for diagnostics and planning various manipulations in the maxillofacial region, e.g. dental implantation. The advantages of this method are high spatial resolution, low radiation exposure, low cost. However, it has a significant drawback: the inability to determine the density of the jaw bone in Hounsfield Units (HU). Aims: To develop radiopaque templates with sets of X-ray density based on potassium hydrophosphate (PHP) and beta-tricalcium phosphate (betta-TCP), to study templates on various CBCT and multidetector computed tomography (MDCT) devices and to determine a cross-calibration algorithm for assessing the bone mineral density (BMD) of the jaw in HU. Materials and methods: BMD template consists microtubes (0.25 ml), PHP concentrations were set: 49.96; 99.98; 174.99; 349.99; 549.98 mg/ml, as well as a suspension of betta-TCP with an equivalent concentration of PHP 1506 mg/ml: simulate the types of bone density according to C.Mish. The study was carried out on 2 MDCT and 4 CBCT. Cross-calibration was referred on the "standard" MDCT1 mode 120 kV, 200 mA. Results: There was a significant scatter of the X-ray values (HU for MDCT and GV for CBCT) vs BMD; the slopes, bias and the shapes of the curves was differing. After cross-calibration, good comparability corresponding to the MDCT1 mode was shown. The median of the differences before cross-calibration was 160 relative units (HU, GV); after decreased by 10 times and amounted to 16 rel. units (p=0.000). The mean difference for CBCT was significantly higher (30 rel. units) than for MDCT (8 rel. units), p=0.024 Mann-Whitney test. Conclusions: The developed radiopaque template makes it possible to standardize densitometric indicators for CBCT and various MSCT modes, on average, the spread after cross-calibration is reduced by 10 times, which makes it possible to classify bone tissue in HU according to C. Mish.