Comparing Fan Beam and Cone Beam CT for Non-Clinical Imaging of Tuberculosis
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Sutphin, Michelle
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Abstract
Objective: To determine the hounsfield unit (HU) range of normal lung tissue and tubercular diseased lung tissue of the same rhesus macaque on repeat scans using two different manufacturers’ scanners, a non-clinical cone beam computerized tomography scanner (CBCT) versus a clinical fan beam computerized tomography scanner (FBCT). Methods: Serial CT scans on two different CT imaging systems was performed on three rhesus macaques (Macaca mulatta) prior to and after infection with Mycobacterium tuberculosis (Mtb). A low-tube-voltage protocol of 80kV, 820uA at 90ms exposure time/projection (Mediso) and a previously optimized high-tube-voltage protocol consisting of 120kV, 5mA (CereTom) were compared. Tissue composition parameters were analyzed in hounsfield units (HU). Differences between protocols on the cone beam CT and the fan beam CT series were documented. Results: Thoracic CT’s of the same three macaques were scanned serially on both machines every two weeks starting 4 weeks post bronchial installation of Mtb. Including a breath hold in the scanning methodology is necessary to prevent liver artifacts and motion which can obscure TB granulomas, as well as, decrease the total lung volume. These artifacts interfere with the assessment of the HU values of the overall lung. The geometry by which each scanner works is disparate, and the HU range obtained on the FBCT appears to show tubercular lesions as denser than the CBCT. The non-clinical CBCT generated smaller voxels which significantly improved spatial resolution as compared to the FBCT. However, the FBCT generated smaller voxels over a wider slice thickness which increased the voxel size to capture more photons which in turn generated images with less noise and more sensitive to HU density changes. Conclusion: FBCT and CBCT scanner identified diseased lung at approximately the same HU density range, starting around -500 HU and decreasing to a negligible value around +200 HU in monitoring the disease of a M. tuberculosis infected rhesus macaque. Keywords: Fan beam CT, cone beam CT, Hounsfield unit, Mycobacterium tuberculosis, rhesus macaque, computed tomography
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Keywords
Fan beam CT, Hounsfield unit, Rhesus macaque, Cone beam CT, Mycobacterium tuberculosis, Computed tomography