SDSU Department of Physics Master’s Thesis Defense: Matthew Randazzo

Speaker: Matthew Randazzo

Title: ” A Rapid CTDI Check Using In-Air Measurements and a Method to Measure the Spatially-Varying HVL in CT Scanners Using a Real-Time Dose Probe”

Time:  12:30-1:30 pm, Thursday, September 11, 2014

Place:  P-245



The simplest and most standardized metric for reporting the estimated dose from a series of computed tomography (CT) scans is the CT dose index (CTDI). Although this quality control (QC) procedure is required on an annual basis by the FDA, performing such measurements more frequently (e.g. monthly or even weekly) would present the opportunity to expose an unexpected drift in CT scanner output from its commissioned settings and allow for an earlier correction to the problem. This would ensure scans are performed with optimal image quality and avoid the possibility of exposing patients to ancillary ionizing radiation. However, correctly aligning CTDI phantoms can be a laborious, time-intensive process. The first part of this study is a proposed method to construct a CTDI ratio look-up to derive values of CTDIw using only in-air measurements. This could serve as a quick monthly or weekly CTDIw QC check with a minimum of three simple in-air measurements without devoting a large amount of time toward CTDI phantom setup.

Although CTDI serves as a useful metric for quantifying CT radiation output to compare different scanning protocols, it does not contain enough information to accurately evaluate dose to a specific patient or organ of interest. For this reason, Monte Carlo (MC) simulations are used to compute patient-specific dose for research purposes.  Accurate calculations largely rely on a researcher’s ability to correctly model the x-ray source fluence and spectra, which are largely defined by an internal bow tie (BT) filter. The second part of this project explores the feasibility of employing an aluminum cylinder half value layer (HVL) measurement technique in conjunction with a real-time dose probe to completely assess the HVL along the BT filter axis in a CT scanner with a minimum of three scans. The data from this method could be used to calculate the angle-dependent fluence and energy spectrum along the BT filter axis, which could be used as beam model input for MC dose computations. This technique is significant not only for its rapid approach, but also that each scan can be completed using routine scan protocols rather than service or localization protocols – eliminating the possible reliance on a service engineer.


Committee Members:

Dr. Mauro Tambasco (Chair)

Dr. Usha Sinha

Dr. Satish Sharma


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