Izvorni znanstveni članak
https://doi.org/10.55378/rv.49.2.1
Validation of Gray Scale on the C-arm in Correlation with Hounsfield Units on CT
Branko Kovalisko
orcid.org/0009-0008-1144-4340
; “Dr. Juraj Njavro” National Memorial Hospital, Vukovar, Croatia
*
Damir Štimac
; Josip Juraj Strossmayer University of Osijek – Faculty of Medicine
Frane Mihanović
; University of Split, Faculty of Health Sciences
* Dopisni autor.
Sažetak
Introduction: Hounsfield Units (HU) on CT represent a quantitative measure of X-ray attenuation in tissue – 0 HU is defined for water, and −1000 HU for air. On a 3D C-arm (cone-beam flat-panel detector imaging), the degree of attenuation is displayed by shades of Gray Scale Values (GSV) in the device’s DICOM image. If a correlation between HU and GSV could be proven, the in vivo or in situ application of mobile radiological devices could be expanded outside hospital settings (e.g., in field forensic investigations), while enabling quantitative image analysis.Aim: To investigate the relationship between the GSV on a mobile 3D C-arm and the HU on a standard CT scanner when imaging the same object (a phantom). Correlation between the mean values of GSV and HU was tested, as well as the difference in the measured GSV and HU values in regard to the DICOM viewer used.Methods: A standard CT calibration quality control phantom was used in this experimental study. The phantom was scanned using a 64-slice medical CT scanner (Siemens Somatom Perspective, 512×512 matrix, 12-bit scale) and a mobile 3D C-arm (Ziehm Vision RFD, 320×320 matrix, 16-bit scale). Scans were performed at 80 kV and 110 kV on the CT and 80 kV and 115 kV on the C-arm. DICOM images were stored and analysed on two independent DICOM software viewers (Onis 2.5 and RadiAnt) to obtain numerical GSV and HU values. Measurements were taken at eight defined ROI areas (P1 – P8) within the phantom (approx. 1 cm2 each), identically located on the CT and C-arm images. For each ROI, the mean GSV (C-arm) and HU (CT) along with the corresponding min, max, and standard deviation were determined. The obtained data were compared and statistically analysed using the Pearson correlation coefficient (with a significance level of p < 0.05).Results: The analysis shows a positive correlation between GSV and HU, but with varying intensity depending on the device voltage. At the same tube voltage on the CT and C-arm (80 kV), a weak positive correlation was found (r = 0.450; p > 0.05). A similarly weak, but consistent, correlation (r = 0.434; p > 0.05) was found between the CT at 110 kV and the C-arm at 80 kV. In contrast, at higher voltages (CT 110 kV and C-arm 115 kV), the correlation was very low, non-significant positive (r = 0.185; p > 0.05). No significant difference was observed in the measurement results between the two different DICOM viewers, suggesting that the choice of software did not affect the obtained values. However, none of the correlations found were statistically significant.Conclusion: The results suggest that a relationship exists between the shades of gray scale on the 3D C-arm and HU on the CT, but the correlation is of weak intensity. The observed correlation is insufficient for reliable quantitative calibration of the C-arm gray scale to the CT HU scale. Therefore, the hypothesis (of no correlation) cannot be confidently rejected. Further research is needed with different phantoms and improved standardization to determine whether mobile CBCT/C-arm systems with appropriate calibration can provide quantitative information comparable to CT. If a strong correlation or the possibility of converting GSV into pseudo-HU is confirmed, it would open up wider applications for 3D C-arms in clinical practice (e.g., implant planning, bone density determination) and field forensic analysis.
Ključne riječi
C-arm; CT phantom; Hounsfield units; gray scale; quantitative analysis
Hrčak ID:
337280
URI
Datum izdavanja:
4.11.2025.
Posjeta: 35 *