Micro-CT based quantification of Mouse Brain Vasculature: The effects of acquisition technique and contrast material Introduction It is understood that radiotherapy of the brain results in cognitive deficits. The causes of the deficits are not well-known, but reduced vascularity may be a significant component of the source of cognitive decline. Animal models to study these effects may assist with understanding the mechanisms. If mouse brain vasculature can be accurately quantified, the effects of radiation on the vasculature might be studied, along with the effects of radiation modifiers such as radio-protectants. This study investigates µCT based quantification of normal mouse brain vasculature, focusing on the effect of two acquisition techniques and contrast material. Methods Four mice were scanned on a µCT scanner (Siemens Inveon) using the acquisition and reconstruction parameters listed below. The mice were injected with 40 mg of a colloidal gold contrast agent (Mvivo Au, MediLumine) or 100 µl of an alkaline earth metal-based nanoparticulate contrast agent (Exitron 12000, Miltenyi Biotec). Two acquisition techniques were also performed, a single kVp and a dual kVp technique. The single kVp technique scanned the mouse once at 80kVp. The dual kVp technique scanned the mouse twice using 50kVp and 80kVp. The brain was contoured axially and using MatLab the region outside the contour was removed to create just an image of the brain without the high HU skull (Figure 2). For single kVp acquisition, a threshold was applied so the contrast was selectively segmented (Figure 3). For the dual kVp acquistion, the segmentation was based on the ratio of HU between the two kVps. A 3D rendering of the segmented vessels can is displayed (Figure 4). Once a segmented binary image of the vessels was obtained the vasculature fraction was calculated as the number of segmented voxels divided by the total number of voxels brain voxels after removing the skull. this segmentation was based on the ratio of the HU value of the two kVps. Results and Discussion The dual kVp acquisition amplified noise of the resultant image and the dual energy technique was not explored further. A second complication was found to be due to the high-resolution acquisition resulting in imperfect source/detector position calibration producing ring artifacts. For the single kVp acquisition the brain blood volume had an average of 3.5% for Mvivo Au and 4.0% for Exitron 12000. The contrast-noise ratio was significantly better for images acquired with the Mvivo Au nanoparticles (2.0) than for those acquired with the Exitron 12000 contrast (1.4). Conclusion The effects of acquisition technique and contrast material for quantification of mouse brain vasculature showed that Mvivo Au produced more consistent segmentation of brain vasculature than Exitron 12000 contrast. Dual kVp acquisition holds some promise for segmenting the contrast agent excluding the boney anatomy, avoiding the need for manual segmentation of the skull although contrast-to-noise remains an issue. Authors: Camrin Tipton, MS; Zhihua Qi, PhD; Michael Lamba, PhD; Kathleen LaSance, MS *University of Cincinnati, Cincinnati OH, § Precision Radiotherapy, West Chester OH Space for Images Fig 1- Cropped brain image of a mouse injected with Mvivo Au nanoparticles Fig 2- Contoured brain image with the external removed Fig 3- Contoured brain image only showing pixels with a CT number in the range of the contrast injected Fig 4- 3D visualization of the vessels References Arvind P. Pathak, Eugene Kim, Jiangyang Zhang, Melina V. Jones. (2011). Three-Dimensional Imaging of the Mouse Neurovasculature with Magnetic Reonance Microscopy. PLoS ONE, 1-9. Brige P. Chugh, ason P. Lerch, Lisa X. Yu, Martin Pienkowski, Rogert V. Harrison, R. Mark Henkelman, John G. Sled. (2009). Measurement of cerebral blood volume in mouse brain regions using mirco-computed tomography. NeuroImage, 1312-1318. Erich W. Stein, Konstantin Maslov, Lihong V. Wang. (2009). Noninvasive, In vivo Imaging of the mouse brain using photoacoustic microscopy. Journal of Applied Physics, 1-5. Jerrold T. Bushberg, J.Anthony Seibert, Edwin M. Leidholdt, John M. Boone. (2012). The Essential Physics of Medical Imaging. Philadelphia, PA: Lippincott Williams & Wilkins. Khan, F. M. (2010). The Physics of Radiation Therapy. Philadelphia, PA: Lippincott Williams & Wilkins. Sylvie Delanian, Jean-Louis Lefaix, Pierre-Francois Pradat. (2012). Radiation-induced neuropathy in cancer survivors. Radiotherapy and Oncology, 273-282. Acquisition Siemens Inveon Multimodal Imager Inveon Acquisition Workplace v2.0.0.1050 Axial acquisition 80/50 kVp 500 µA 720 projections 1300 ms per projection 17.56 µm slice thickness Reconstruction HU Calibrated Feldkamp algorithm Noise reduction – slight Shepp-Logan filtration Mouse beam hardening correction applied 18 µm 3 voxel size reconstruction 16 bit per voxel ~3 Gb per data set