Evaluation of CT Image Quality of a Cone Beam Micro-CT system with Electron Multiplying CCD

A small animal imaging Micro-CT system was built using an EMCCD detector. EMCCD detectors have a pre-digitization amplification technology, high-resolution, high-sensitivity, low noise at low exposures. The performances of a detector are evaluated by analyzing noise and signal characteristics of the detector. The noise in CBCT reconstructed images when using pre-digitization amplification behaves differently than commonly used detectors and warrants a detailed investigation. In this thesis report, noise characteristics and contrast sensitivity of the newly built EMCCD based Micro-CT scanner was analyzed. Noise analysis was performed based on IEC (International Electrochemical Commission) noise standard by scanning a water phantom. Tube parameters were lowered to minimum delivered by the tube (20kVp and 10W) and detector gain was varied. All the acquired projection images were reconstructed using standard Feld Kamp reconstruction algorithm with a voxel size of 20microm and various mathematical filters were used during reconstruction. Contrast sensitivity was analyzed by imaging a phantom containing different iodine contrast solutions (20% to 70%) filled in six different tubes. First, the phantom was scanned using various x-ray exposures at 40kVp while adjusting the gain by maintaining the background air value of the projection images constant. Next, the exposure was varied while the detector gain was maintained constant. The projection images were reconstructed with a voxel size 20microm using FDK algorithm.;Noise analysis was made by plotting noise power plots. Radial NPS plots showed that noise power level increased with increase in gain. The noise power plots for different reconstruction filters show that different filters have different effect on noise response during reconstruction. Contrast sensitivity was analyzed by calculating ratio of signal-to-noise ratios (SNR) for increased gain with those of low constant gain at each exposure and each iodine concentration. The SNR value at low constant gain was always lower than SNR of high detector gain at all x-ray settings and iodine contrast. The largest increase of SNR approached 1.3 for a low contrast feature of 20% iodine concentration. Despite an increase in noise level as detector gain increases, the SNR improvement shows that signal level also increases. The SNR improvement enhanced the quality of the image and made it a better system for small animal imaging.;In addition to above thesis project, femur, spine, skull and whole body samples of mice were imaged using EMCCD based Micro-CT system. The images were reconstructed and bone analysis was carried out. The bone analysis was carried out using software. This analysis could give details about bone growth, bone volume, structure of the bone and also the amount of calcium content in the bone. Bone analysis using reconstructed images of a bone is one of the most important application of Micro-CT scanners.