RESUMO
Phantom-based initial performance assessment of a prototype three-dimensional (3-D) x-ray system and comparison of 3-D tomography with computed tomography (CT) were proposed. A 3-D image quality phantom was scanned with a prototype version of 3-D cone-beam CT imaging implemented on a twin robotic x-ray system using three trajectories (163 deg = table, 188 deg = upright, and 200 deg = side), six tube voltages (60, 70, 81, 90, 100, and 121 kV), and four detector doses (0.348, 0.696, 1.740, and [Formula: see text]). CT was obtained with a clinical protocol. Spatial resolution (line pairs/cm) and soft-tissue-contrast resolution were assessed by two independent readers. Radiation dose was assessed. Descriptive and analysis of variance (ANOVA) ([Formula: see text]) were performed. With 3-D tomography, a maximum of 16 lp/cm was visible and best soft-tissue-contrast resolution was 2 mm at 30 Hounsfield units (HU) for 160 projections. With CT, 10 lp/cm was visible and soft-tissue-contrast resolution was 4 mm at 20 HU. The upright trajectory yielded significantly better spatial resolution and soft tissue contrast, and the side trajectory yielded significantly higher soft tissue contrast than the table trajectory ([Formula: see text]). Radiation dose was higher in 3-D tomography (45 to 704 mGycm) than CT (44 mGycm). Three-dimensional tomography renders overall equal or higher spatial resolution and comparable soft tissue contrast to CT for medium- and high-dose protocols in the side and upright trajectories, but with higher radiation doses.
RESUMO
OBJECTIVES: The aims of this study were to assess feasibility, image quality, and radiation dose and to estimate the optimal dose protocol for the lumbar spine of cadaveric specimens with different body mass indices (BMIs) in the upright position using a prototype 3-dimensional cone-beam computed tomography (CT) software implemented on a robotic x-ray system and compare with CT. MATERIALS AND METHODS: The lumbar spine of 5 formalin-fixed human cadaveric specimens (BMI, 22-35 kg/m) was prospectively assessed in the upright position using prototype software for 3-dimensional tomography implemented on a robotic x-ray system. Specimens were scanned with varying kilovolt values (70, 81, 90, 100, 109, 121 kV) and thereafter with 80 kV (BMI ≤30 kg/m) and 121 kV (BMI >30 kg/m) and varying dose levels (DLs; 0.278, 0.435, 0.548, 0.696, 0.87, 1.09). Computed tomography data were acquired with a standard clinical protocol. Two independent readers rated visibility of the cortex, endplates, facet joints, trabeculae, neuroforamina, posterior alignment, and spinal canal as well as nerve roots. Radiation dose was measured with a cylindrical CTDI phantom. Descriptive statistics and analysis of variance were used (P < 0.05). RESULTS: Average intraclass correlation was excellent (0.94). The lowest technically possible kilovolt and the highest technically possible DL yielded the best image quality. In specimens with a BMI of 30 kg/m or less, depiction of all structures was good and comparable to CT, except for nerve roots. For specimens with a BMI greater than 30 kg/m, image quality was limited. CONCLUSIONS: Three-dimensional cone-beam CT of the lumbar spine in cadaveric specimens in the upright position is feasible. An optimal dose protocol was estimated. Depiction of osseous structures is comparable to CT in specimens with BMI of 30 kg/m or less. Image quality is limited for soft tissue structures and specimens with BMI greater than 30 kg/m.