Multi-institutional MicroCT image comparison of image-guided small animal irradiators

Abstract

To recommend imaging protocols and establish tolerance levels for microCT image quality assurance (QA) performed on conformal image-guided small animal irradiators. A fully automated QA software SAPA (small animal phantom analyzer) for image analysis of the commercial Shelley micro-CT MCTP 610 phantom was developed, in which quantitative analyses of CT number linearity, signal-to-noise ratio (SNR), uniformity and noise, geometric accuracy, spatial resolution by means of modulation transfer function (MTF), and CT contrast were performed. Phantom microCT scans from eleven institutions acquired with four image-guided small animal irradiator units (including the commercial PXi X-RAD SmART and Xstrahl SARRP systems) with varying parameters used for routine small animal imaging were analyzed. Multi-institutional data sets were compared using SAPA, based on which tolerance levels for each QA test were established and imaging protocols for QA were recommended. By analyzing microCT data from 11 institutions, we established image QA tolerance levels for all image quality tests. CT number linearity set to R2 > 0.990 was acceptable in microCT data acquired at all but three institutions. Acceptable SNR > 36 and noise levels <55 HU were obtained at five of the eleven institutions, where failing scans were acquired with current-exposure time of less than 120 mAs. Acceptable spatial resolution (>1.5 lp mm−1 for MTF = 0.2) was obtained at all but four institutions due to their large image voxel size used (>0.275 mm). Ten of the eleven institutions passed the set QA tolerance for geometric accuracy (<1.5%) and nine of the eleven institutions passed the QA tolerance for contrast (>2000 HU for 30 mgI ml−1). We recommend performing imaging QA with 70 kVp, 1.5 mA, 120 s imaging time, 0.20 mm voxel size, and a frame rate of 5 fps for the PXi X-RAD SmART. For the Xstrahl SARRP, we recommend using 60 kVp, 1.0 mA, 240 s imaging time, 0.20 mm voxel size, and 6 fps. These imaging protocols should result in high quality images that pass the set tolerance levels on all systems. Average SAPA computation time for complete QA analysis for a 0.20 mm voxel, 400 slice Shelley phantom microCT data set was less than 20 s. We present image quality assurance recommendations for image-guided small animal radiotherapy systems that can aid researchers in maintaining high image quality, allowing for spatially precise conformal dose delivery to small animals.

A 3D printed modular phantom for quality assurance of image‐guided small animal irradiators: Design, imaging experiments, and Monte Carlo simulations

“…A number of imaging tests did not pass the set criteria suggested by Johnstone et al . In agreement with their study, the longitudinal spatial resolution of 1.5 lp/mm was only achieved for the phantom in vertical orientation (i.e., in standard imaging geometry) and for images reconstructed with 200‐μm voxels.…”

“…The passing criteria for image noise (<55 HU), MTF (>1.5 lp/mm @ 0.2 MTF) and geometric accuracy (<200 lm) were chosen based on a multi-institutional image quality study of conformal small animal irradiators performed with the Shelley phantom. 7 To maintain uniformity, the maximum deviation between the five ROIs of the uniform section was allowed to be 55 HU, similar to the noise criteria, which ensures dose calculation accuracy of 5%. CT number consistency was set in a similar fashion by allowing a maximum deviation in CT number of 55 HU.…”

“…Commercial microCT QA phantoms such as the Shelley Model MCTP 610 (Shelley Medical Imaging Technologies, London, ON, Canada) developed by Du et al . or the CIRS Model 090 (Computerized Imaging Reference Systems Inc, Norfolk, VA, USA) have been used for microCT imaging QA on small animal irradiators . Johnstone et al .…”

“…or the CIRS Model 090 (Computerized Imaging Reference Systems Inc, Norfolk, VA, USA) have been used for microCT imaging QA on small animal irradiators . Johnstone et al . in their multi‐institutional image‐guided irradiator imaging study noticed that the Shelley phantom with its 7‐cm diameter was too large to accurately represent a mouse's body.…”

“…Commercial microCT QA phantoms such as the Shelley Model MCTP 610 (Shelley Medical Imaging Technologies, London, ON, Canada) developed by Du et al 5 or the CIRS Model 090 (Computerized Imaging Reference Systems Inc, Norfolk, VA, USA) have been used for microCT imaging QA on small animal irradiators. 6,7 Johnstone et al 7 in their multi-institutional image-guided irradiator imaging study noticed that the Shelley phantom with its 7-cm diameter was too large to accurately represent a mouse's body. As a result, the image quality observed using the phantom did not necessarily correspond to image quality observed in scanning of mouse-sized animals.…”