Room: AAPM ePoster Library
Purpose: CT (CBCT) installed on modern pre-clinical small-animal radiation research platforms are important to provide a volumetric image for image guidance and treatment planning. It was found that the CBCT system available at our institution could be further improved by performing calibrations to remove artifacts. This study performs a comprehensive calibration and evaluation study to reduce detector lag, veiling glare and beam hardening effects.
Methods: studies were performed on the CBCT of a small animal radiation therapy platform (SmART+, Precision). Rising-edge step-response function in 1 minute was measured and the data was used to fit a lag-response curve that was employed to correct lag artifacts. Veiling glare correction was performed based on deconvolution of the point-spread function estimated from the edge-spread function measured in the projection image of a steel ruler. Correction of beam harden effect was performed using a water-based method to correct water-equivalent projection length. To evaluate the results, we acquired a CBCT scan of a micro-CT test phantom with 600 projections over a full 360° rotation and reconstructed the images using the Feldkamp-Davis-Kress algorithm with Parker weighting. The image quality was evaluated quantitatively by the modular transfer function (MTF) and the CT number accuracy.
Results: correction, artifacts induced by lag, glare and beam hardening were visually reduced. Glare correction increased the MTF of reconstructed images in both the radial and the longitudinal directions. CT number accuracy was improved, as demonstrated by a better correlation with the x-ray attenuation coefficients of insert materials.
Conclusion: comprehensive calibration process reduced artifacts and improved image quality and CT number accuracy of the CBCT to better support preclinical small animal radiation experiments.