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 weightbearing 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 & PLUSMN; 1.6 (117 kV, dose level low, 16 fps) to 24.3 & PLUSMN; 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 & LE; 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 & LE; 0.040), while SNR ranged from 0.56 & PLUSMN; 0.03 to 1.11 & PLUSMN; 0.30 without a significant difference between scan protocols (all p & GE; 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.