Evaluation of radiation dose in lumbar spine computed tomography in a single Moroccan center

Weight-bearing gantry-free cone-beam CT of the lumbar spine: Image quality analysis and dose efficiency

PURPOSE

The effect of static forces under load limits the prognostic value of lumbar spine CT in a horizontal position. Using a gantry-free scanner architecture, this study was designed to assess the feasibility of weight-bearing cone-beam CT (CBCT) of the lumbar spine and to establish the most dose-effective combination of scan parameters.

METHODS

Eight formalin-fixated cadaveric specimens were examined with a gantry-free CBCT system in upright position with the aid of a dedicated positioning backstop. Cadavers were scanned with eight combinations of tube voltage (102 or 117 kV), detector entrance dose level (high or low), and frame rates (16 or 30 fps). Five radiologists independently analyzed datasets for overall image quality and posterior wall assessability. Additionally, image noise and signal-to-noise ratio (SNR) were compared based on region-of-interest (ROI) measurements in the gluteal muscles.

RESULTS

Radiation dose ranged from 6.8 ± 1.6 (117 kV, dose level low, 16 fps) to 24.3 ± 6.3 mGy (102 kV, dose level high, 30 fps). Both image quality and posterior wall assessability were favored with 30 over 16 fps (all p ≤ 0.008). In contrast, both tube voltage (all p > 0.999) and dose level (all p > 0.096) did not significantly impact reader assessment. Image noise decreased considerably with higher frame rates (all p ≤ 0.040), while SNR ranged from 0.56 ± 0.03 to 1.11 ± 0.30 without a significant difference between scan protocols (all p ≥ 0.060).

CONCLUSIONS

Employing an optimized scan protocol, weight-bearing gantry-free CBCT of the lumbar spine allows for diagnostic imaging at reasonable radiation dose.

Size-Specific Dose Estimates for Thoracic and Abdominal Computed Tomography Examinations at Two Moroccan Hospitals

Size-specific dose estimates (SSDE) are the latest topic of interest in patient radiation-dose studies in computed tomography (CT). The aim of this study is to calculate and evaluate the doses (SSDE) by measuring the effective diameter (ED) of cross-sectional images collected during CT examinations of the chest and abdomen in Moroccan hospitals. Doses (SSDE) were calculated based on cross-sectional images by measuring the effective diameters of 75 patients in both examinations (45 for the thorax and 30 for the abdomen). Specific conversion factors for (ED) were used to convert the registered CTDIvol to SSDE, according to the instruction in the American Association of Physicists (AAPM) Report 204. In thoracic CT, the CTDIvol and SSDE values ranged from 5.8 to 10.7 mGy (mean: 8.08) and 9.55 to 15.37 mGy (mean: 12.13), respectively. For abdominal CT, CTDIvol and SSDE values ranged from 4.8 to 12.2 mGy (mean: 7.95) and 8.01 to 14.15 mGy (mean: 11.31), respectively. The results show that the SSDE is a useful tool and could potentially educate CT operators on its effective use as a way to optimize radiation dose instead of CTDIvol, in particular to establish diagnostic reference levels.