Quantitative Analysis of Three-Dimensional Cone-Beam Computed Tomography Using Image Quality Phantoms

In the clinical setting, weight-bearing static 2D radiographic imaging and supine 3D radiographic imaging modalities are used to evaluate radiographic changes such as, joint space narrowing, subchondral sclerosis, and osteophyte formation. These respective imaging modalities cannot distinguish between tissues with similar densities (2D imaging), and do not accurately represent functional joint loading (supine 3D imaging). Recent advances in cone-beam CT (CBCT) have allowed for scanner designs that can obtain weight-bearing 3D volumetric scans. The purpose of this thesis was to analyze, design, and implement advanced imaging techniques to quantify image quality parameters of reconstructed image volumes generated by a commercially-available CBCT scanner, and a novel ceiling-mounted CBCT scanner. In addition, imperfections during rotation of the novel ceiling-mounted CBCT scanner were characterized using a 3D printed calibration object with a modification to the single marker bead method, and prospective geometric calibration matrices

Image quality and dose of an accelerator-integrated kV CBCT systems

The ability of an imaging modality to precisely determine patient anatomy and provide reliable information about tumor position is critical in the radiotherapy process. As image-guided radiotherapy (IGRT) becomes more popular in radiation treatment, its overall quality and performance, such as the image quality and amount of dose delivered, need to be assessed. The research described in this dissertation was focused on investigation of the image quality of the planar and cone-beam computed tomography (CBCT) images of two imaging systems commonly used in radiotherapy: Varian On-Board Imager (OBI) and Elekta X-ray Volumetric Imager (XVI). Several imaging quality tests were performed using current clinical imaging protocols provided with both systems and various types of image quality phantoms. CBCT imaging dose of each system was also estimated using standard CT dose index (CTDI) phantoms and several imaging protocols. Overall, the image quality between the OBI and XVI was fairly consistent with each other with the exception of high contrast resolution and Hounsfield Unit (HU) accuracy. CTDI of OBI was higher than that of XVI which was related to the different designs and imaging protocols between the two systems.Master of Science in Physic

Proof-of-Concept For Converging Beam Small Animal Irradiator

The Monte Carlo particle simulator TOPAS, the multiphysics solver COMSOL., and several analytical radiation transport methods were employed to perform an in-depth proof-ofconcept for a high dose rate, high precision converging beam small animal irradiation platform. In the first aim of this work, a novel carbon nanotube-based compact X-ray tube optimized for high output and high directionality was designed and characterized. In the second aim, an optimization algorithm was developed to customize a collimator geometry for this unique Xray source to simultaneously maximize the irradiator’s intensity and precision. Then, a full converging beam irradiator apparatus was fit with a multitude of these X-ray tubes in a spherical array and designed to deliver converged dose spots to any location within a small animal model. This aim also included dose leakage calculations for estimation of appropriate external shielding. The result of this research will be the blueprints for a full preclinical radiation platform that pushes the boundaries of dose localization in small animal trials

An evaluation of the stability of image quality parameters of Elekta X-ray volume imager and iViewGT imaging systems

INTRODUCTION: A robust image quality assurance and analysis methodology for image-guided localization systems is crucial to ensure the accurate localization and visualization of target tumors. In this study, the long-term stability of selected image parameters was assessed and evaluated for the cone-beam computed tomography (CBCT) mode, planar radiographic kV mode, and the radiographic MV mode of an Elekta VersaHD. MATERIALS AND METHODS: The CATPHAN, QckV-1, and QC-3 phantoms were used to evaluate the image quality parameters. The planar radiographic images were analyzed in PIPSpro™ with spatial resolution (f30, f40, f50), contrast to noise ratio (CNR) and noise being recorded. For XVI CBCT, Head and Neck Small20 (S20) and Pelvis Medium20 (M20) standard acquisition modes were evaluated for uniformity, noise, spatial resolution, and HU constancy. Dose and kVp for the XVI were recorded using the Unfors RaySafe Xi system with the R/F low detector for the kV planar radiographic mode. For each metric, values were normalized to the mean and the standard deviations were recorded. RESULTS: A total of 30 measurements were performed on a single Elekta VersaHD linear accelerator over an 18-month period without significant adjustment or recalibration to the XVI or iViewGT systems during the evaluated time frame. For the planar radiographic spatial resolution, the normalized standard deviation values of the f30, f40, and f50 were 0.004, 0.003, and 0.003 and 0.015, 0.009, and 0.017 for kV and MV, respectively. The average recorded dose for kV was 67.96 μGy. The standard deviations of the evaluated metrics for the S20 acquisition were 0.083(f30), 0.058(f40), 0.056(f50), 0.021(Water/poly-HU constancy), 0.029(uniformity) and 0.028(noise). The standard deviations for the M20 acquisition were 0.093(f30), 0.043(f40), 0.037(f50), 0.016(Water/poly-HU constancy), 0.010(uniformity) and 0.011(Noise). CONCLUSION: A study was performed to assess the stability of the basic image quality parameters recommended by TG-142 for the Elekta XVI and iViewGT imaging systems. The two systems show consistent imaging and dosimetric properties over the evaluated time frame

Doctor of Philosophy

dissertationSingle Photon Emission Computed Tomography (SPECT) myocardial perfusion imaging (MPI), a noninvasive and effective method for diagnosing coronary artery disease (CAD), is the most commonly performed SPECT procedure. Hence, it is not surprising that there is a tremendous market need for dedicated cardiac SPECT scanners. In this dissertation, a novel dedicated stationary cardiac SPECT system that using a segmented-parallel-hole collimator is investigated in detail. This stationary SPECT system can acquire true dynamic SPECT images and is inexpensive to build. A segmented-parallel-hole collimator was designed to fit the existing general-purpose SPECT cameras without any mechanical modifications of the scanner while providing higher detection sensitivity. With a segmented-parallel-hole collimator, each detector was segmented to seven sub-detector regions, providing seven projections simultaneously. Fourteen view-angles over 180 degree were obtained in total with two detectors positioned at 90 degree apart. The whole system was able to provide an approximate 34-fold gain in sensitivity over the conventional single-head SPECT system. The potential drawbacks of the stationary cardiac SPECT system are data truncation from small field of view (FOV) and limited number of view angles. A tailored maximum-likelihood expectation-maximization (ML-EM) algorithm was derived for reconstruction of truncated projections with few view angles. The artifacts caused by truncation and insufficient number of views were suppressed by reducing the image updating step sizes of the pixels outside the FOV. The performance of the tailored ML-EM algorithm was verified by computer simulations and phantom experiments. Compared with the conventional ML-EM algorithm, the tailored ML-EM algorithm successfully suppresses the streak artifacts outside the FOV and reduces the distortion inside the FOV. At 10 views, the tailored ML-EM algorithm has a much lower mean squared error (MSE) and higher relative contrast. In addition, special attention was given to handle the zero-valued projections in the image reconstruction. There are two categories of zero values in the projection data: one is outside the boundary of the object and the other is inside the object region, which is caused by count starvation. A positive weighting factor c was introduced to the ML-EM algorithm. By setting c>1 for zero values outside the projection, the boundary in the image is well preserved even at extremely low iterations. The black lines, caused by the zero values inside the object region, are completely removed by setting 0< c<1. Finally, the segmented-parallel-hole collimator was fabricated and calibrated using a point source. Closed-form explicit expressions for the slant angles and rotation radius were derived from the proposed system geometry. The geometric parameters were estimated independently or jointly. Monte Carlo simulations and real emission data were used to evaluate the proposed calibration method and the stationary cardiac system. The simulation results show that the difference between the estimated and the actual value is less than 0.1 degree for the slant angles and the 5 mm for the rotation radius, which is well below the detector's intrinsic resolution

Stereotactic localization and targeting accuracy for experimental proton radiosurgery

The purpose of this study was to improve an existing experimental proton radiosurgery system at Loma Linda University Medical Center to reach sub-millimeter accuracy before proton radiosurgery with narrow beams can be used in a clinical trial. Protons, different from photons (i.e., x-rays or gamma rays), are charged with particles that slow down in matter and release a burst of energy near the end of their range (maximum depth of penetration), which is called the Bragg peak, named after the physicist William Henry Bragg who discovered it in 1903. Photon beams deliver most doses over a large area near the surface while a less dose is delivered to deep tissue

Evaluation of cone beam computed tomography with respect to effective radiation dose and diagnostic properties

Cone beam computed tomography (CBCT) is an x-ray modality providing three-dimensional x-ray images. CBCT devices have high resolution compared to traditional medical CT, making them suitable for examination of fine details. However, CBCT devices are worse at showing contrast differences, making them less suitable for examinations of soft tissue such as the brain and many other internal organs. An x-ray modality suitable for imaging of small details and hard tissue fits dental and maxillofacial radiology well. After the introduction of dentomaxillofacial CBCT in 1998, CBCT examinations have spread to become a common and important diagnostic tool in odontology. Today, CBCT examinations complement or replace examinations previously performed by other methods. When choosing an x-ray imaging modality and examination parameters, concern must be taken for the diagnostic value and the radiation dose. The examination should be chosen to provide as low radiation dose as possible while not sacrificing the diagnostic value. In order to provide guidelines on the use of CBCT, scientific knowledge on CBCT and alternative examinations are needed. What is the radiation dose for different examinations and how does the examination affect diagnosis and treatment? This thesis aims to provide additional information in this field, to provide reference data when considering the choice of examination and the establishment of guidelines. In the first paper, examinations of the temporomandibular joint, using CBCT and traditional medical multi-detector CT (MDCT), were compared to determine if CBCT examinations would result in lower radiation dose. The examinations were optimized to find the lowest suitable dose levels, and at these optimized dose levels no significant difference was found between CBCT and MDCT. The second paper investigated the radiation dose from multiple different x-ray examinations of possible resorption impacted maxillary canines in children. CBCT examinations were compared to two-dimensional examinations using intraoral radiographs, and in some cases panoramic radiographs. CBCT examinations ranged from 15 to 140 times higher radiation dose, depending on x-ray device. The third paper investigated the possibility of reducing the image size, and therefore the x-ray dose, in panoramic radiographs. A full-size panoramic radiograph was required in 20% of adult patient cases. The introduction of two different image sizes for adult patients would reduce the collective radiation dose from panoramic examinations by about 40% in our university clinic. The fourth paper investigated radiation doses from different examinations and settings using the Newtom 5G CBCT device. This CBCT model use automatic exposure control and does not allow manual adjustment of exposure parameters. The resulting effective doses should be applicable to examinations of adult patients using this CBCT model

Comparative linear accuracy and reliability of cone beam CT derived 2-dimensional and 3-dimensional images constructed using an orthodontic volumetric rendering program.

The purpose of this project was to compare the accuracy and reliability of linear measurements made on 2D projections and 3D reconstructions using Dolphin 3D software (Chatsworth, CA) as compared to direct measurements made on human skulls. The linear dimensions between 6 bilateral and 8 mid-sagittal anatomical landmarks on 23 dentate dry human skulls were measured three times by multiple observers using a digital caliper to provide twenty orthodontic linear measurements. The skulls were stabilized and imaged via PSP digital cephalometry as well as CBCT. The PSP cephalograms were imported into Dolphin (Chatsworth, CA, USA) and the 3D volumetric data set was imported into Dolphin 3D (Version 2.3, Chatsworth, CA, USA). Using Dolphin 3D, planar cephalograms as well as 3D volumetric surface reconstructions were (3D CBCT) generated. The linear measurements between landmarks of each three modalities were then computed by a single observer three times. For 2D measurements, a one way ANOVA for each measurement dimension was calculated as well as a post hoc Scheffe multiple comparison test with the anatomic distance as the control group. 3D measurements were compared to anatomic truth using Student\u27s t test (PiÜ50.05). The intraclass correlation coefficient (ICC) and absolute linear and percentage error were determined as indices of intraobserver reliability. Our results show that for 2D mid sagittal measurements that Simulated LC images are accurate and similar to those from PSP images (except for Ba-Na), and for bilateral measurements simulated LC measurements were similar to PSP but less accurate, underestimating dimensions by between 4.7% to 17%.For 3D volumetric renderings, 2/3 rd of CBCT measurements are statistically different from actual measurements, however this possibly is not clinically relevant