Browsing by Subject "Anthropomorphic phantoms"
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Item Open Access Radiation Dose Estimation for Pediatric Patients Undergoing Cardiac Catheterization(2015) Wang, ChuPatients undergoing cardiac catheterization are potentially at risk of radiation-induced health effects from the interventional fluoroscopic X-ray imaging used throughout the clinical procedure. The amount of radiation exposure is highly dependent on the complexity of the procedure and the level of optimization in imaging parameters applied by the clinician. For cardiac catheterization, patient radiation dosimetry, for key organs as well as whole-body effective, is challenging due to the lack of fixed imaging protocols, unlike other common X-ray based imaging modalities.
Pediatric patients are at a greater risk compared to adults due to their greater cellular radio-sensitivities as well as longer remaining life-expectancy following the radiation exposure. In terms of radiation dosimetry, they are often more challenging due to greater variation in body size, which often triggers a wider range of imaging parameters in modern imaging systems with automatic dose rate modulation.
The overall objective of this dissertation was to develop a comprehensive method of radiation dose estimation for pediatric patients undergoing cardiac catheterization. In this dissertation, the research is divided into two main parts: the Physics Component and the Clinical Component. A proof-of-principle study focused on two patient age groups (Newborn and Five-year-old), one popular biplane imaging system, and the clinical practice of two pediatric cardiologists at one large academic medical center.
The Physics Component includes experiments relevant to the physical measurement of patient organ dose using high-sensitivity MOSFET dosimeters placed in anthropomorphic pediatric phantoms.
First, the three-dimensional angular dependence of MOSFET detectors in scatter medium under fluoroscopic irradiation was characterized. A custom-made spherical scatter phantom was used to measure response variations in three-dimensional angular orientations. The results were to be used as angular dependence correction factors for the MOSFET organ dose measurements in the following studies. Minor angular dependence (< ±20% at all angles tested, < ±10% at clinically relevant angles in cardiac catheterization) was observed.
Second, the cardiac dose for common fluoroscopic imaging techniques for pediatric patients in the two age groups was measured. Imaging technique settings with variations of individual key imaging parameters were tested to observe the quantitative effect of imaging optimization or lack thereof. Along with each measurement, the two standard system output indices, the Air Kerma (AK) and Dose-Area Product (DAP), were also recorded and compared to the measured cardiac and skin doses – the lack of correlation between the indices and the organ doses shed light to the substantial limitation of the indices in representing patient radiation dose, at least within the scope of this dissertation.
Third, the effective dose (ED) for Posterior-Anterior and Lateral fluoroscopic imaging techniques for pediatric patients in the two age groups was determined. In addition, the dosimetric effect of removing the anti-scatter grid was studied, for which a factor-of-two ED rate reduction was observed for the imaging techniques.
The Clinical Component involved analytical research to develop a validated retrospective cardiac dose reconstruction formulation and to propose the new Optimization Index which evaluates the level of optimization of the clinician’s imaging usage during a procedure; and small sample group of actual procedures were used to demonstrate applicability of these formulations.
In its entirety, the research represents a first-of-its-kind comprehensive approach in radiation dosimetry for pediatric cardiac catheterization; and separately, it is also modular enough that each individual section can serve as study templates for small-scale dosimetric studies of similar purposes. The data collected and algorithmic formulations developed can be of use in areas of personalized patient dosimetry, clinician training, image quality studies and radiation-associated health effect research.
Item Open Access Task-based assessment of digital breast tomosynthesis: Effect of anatomy from multiple anthropomorphic 3D printed phantoms(2017) Cowart, CharlesPhysical phantoms are an important tool in clinical system evaluation. There exists a lack of suitable anthropomorphic physical phantoms that vary as much as a typical patient population. The lack in diversity in anthropomorphic physical phantoms makes generalizing results found using these phantoms difficult. In order to address this issue, a diverse selection of breast phantoms were 3D printed on a Stratasys Objet350 Connex printer using tissue-approximate photopolymers. These cases were then evaluated on a clinical Hologic Selenia Dimensions Digital Breast Tomosynthesis system. The evaluation consisted of a 4-alternative-forced-choice task printed on a contrast insert with silver-doped ink of concentration 200 mg/mL. The disks ranged in size from 350um-770um and a range of signal intensities was achieved by repeatedly overprinting, layering the ink. Each ink pass corresponded to an increase in signal of 1.4%. The contrast insert was imaged in 8 different orientations, at a fixed kVp of 36, and varied mAs for indicated AGD of 1.4, 2.8, and 4.2 mGy. A channelized-Hotelling observer with Gabor channels was used for evaluation and a percent correct was determined. Detection performance increased as dose increased for all cases. The most dense breast case had the worst detection performance as is had the most overlapping structures to obscure the signal. The approximately average density breast and the fatty, thinner breast performed similarly, however this may be due to the beam filtering used to avoid overexposing the detector with the high kVp and mAs used for this experiment. These results indicate that system performance is dependent on the anatomy being imaged. Further investigations with more phantom cases is needed to better evaluate the anatomical dependence of the system performance.