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Ideal Broad-Beam Geometry/attenuation, Effective Energy, and Its Impact in CT Dosimetry

N Ruiz Gonzalez*, G Clarke , UT Health Sciences Center, San Antonio, TX


(Wednesday, 7/17/2019) 10:30 AM - 11:00 AM

Room: Exhibit Hall | Forum 9

Purpose: Published studies suggests that as photon transmission measurements approach ideal broad-beam (BB) geometry and ideal BB attenuation conditions the effective attenuation coefficient (AC) approaches, or is equal to, the energy-absorption coefficient (EAC). A novel device (MuCTâ„¢), a cylindrical step-wedge (CSW), designed to measure the transmission of a rotating x-ray beam as a function of attenuator thickness, was used to investigate whether the apparatus design, combined with a symmetrical x-ray irradiation, approaches ideal BB geometry/attenuation conditions, and allows for experimentally measuring the EAC.

Methods: Measurements were performed in a GE LightSpeedâ„¢ RT 16 (GE, Milwaukee, WI), using an axial scan, one x-ray tube rotation per second, one image per slice, and then repeated for multiple tube potentials, bow-tie filters and slice thicknesses. The BB HVL was calculated using the transmission measurements and log-linear and Lambert W interpolations. An effective AC was calculated from the BB HVL. Using the effective AC and fitted equations to the NIST X-Ray Mass Attenuation Coefficient and Mass Energy-Absorption Coefficient tables for aluminum, the effective energy was interpolated which was then used to interpolate the effective total AC. Finally the interpolated effective total AC was used to estimate the narrow-beam HVL and compared to the manufacturer HVL values.

Results: The experimental estimate of the narrow-beam HVL, when compared to the manufacturer HVL values resulted in a relative difference range of (0.06-1.50%) for the minimum, (2.01-4.23%) for the maximum, (0.87-2.92%) for the average, and (0.77-1.84%) for the standard deviation.

Conclusion: Preliminary data suggests that symmetrical x-ray irradiation and measuring conditions within the MuCTâ„¢ device are close to ideal BB geometry/attenuation conditions. Similarly, the MuCTâ„¢ device seems to be capable of measuring the EAC experimentally, which can then be used to estimate the photon effective energy and the narrow-beam HVL; all important parameters in radiation dosimetry.

Funding Support, Disclosures, and Conflict of Interest: The apparatus designed (the MuCT device) has a U.S. Patent Pending No. 62/654016 and commercialization is forthcoming.


CT, Dosimetry, Quality Assurance


IM- CT: Radiation dosimetry & risk

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