Physics of Medical Imaging

Two-dimensional dynamic fluid bowtie attenuators

[+] Author Affiliations
James R. Hermus

University of Wisconsin–Madison, Department of Biomedical Engineering, 1415 Engineering Drive, Madison, Wisconsin 53706, United States

Timothy P. Szczykutowicz

University of Wisconsin–Madison, Department of Biomedical Engineering, 1415 Engineering Drive, Madison, Wisconsin 53706, United States

University of Wisconsin–Madison, Department of Medical Physics, 1005 WIMR, 1111 Highland Avenue, Madison, Wisconsin 53705, United States

University of Wisconsin–Madison, Department of Radiology, 1005 WIMR, 1111 Highland Avenue, Madison, Wisconsin 53705, United States

J. Med. Imag. 3(1), 013502 (Jan 22, 2016). doi:10.1117/1.JMI.3.1.013502
History: Received June 18, 2015; Accepted December 11, 2015
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Abstract.  Fluence field modulated (FFM) CT allows for improvements in image quality and dose reduction. To date, only one-dimensional modulators have been proposed, as the extension to two-dimensional (2-D) modulation is difficult with solid-metal attenuation-based fluence field modulated designs. This work proposes to use liquid and gas to attenuate the x-ray beam, as unlike solids, these materials can be arranged allowing for 2-D fluence modulation. The thickness of liquid and the pressure for a given path length of gas were determined that provided the same attenuation as 30 cm of soft tissue at 80, 100, 120, and 140 kV. Liquid iodine, zinc chloride, cerium chloride, erbium oxide, iron oxide, and gadolinium chloride were studied. Gaseous xenon, uranium hexafluoride, tungsten hexafluoride, and nickel tetracarbonyl were also studied. Additionally, we performed a proof-of-concept experiment using a 96 cell array in which the liquid thickness in each cell was adjusted manually. Liquid thickness varied as a function of kV and chemical composition, with erbium oxide allowing for the smallest thickness. For the gases, tungsten hexaflouride required the smallest pressure to compensate for 30 cm of soft tissue. The 96 cell iodine attenuator allowed for a reduction in both dynamic range to the detector and scatter-to-primary ratio. For both liquids and gases, when k-edges were located within the diagnostic energy range used for imaging, the mean beam energy exhibited the smallest change with compensation amount. The thickness of liquids and the gas pressure seem logistically implementable within the space constraints of C-arm-based cone beam CT (CBCT) and diagnostic CT systems. The gas pressures also seem logistically implementable within the space and tube loading constraints of CBCT and diagnostic CT systems.

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© 2016 Society of Photo-Optical Instrumentation Engineers

Citation

James R. Hermus and Timothy P. Szczykutowicz
"Two-dimensional dynamic fluid bowtie attenuators", J. Med. Imag. 3(1), 013502 (Jan 22, 2016). ; http://dx.doi.org/10.1117/1.JMI.3.1.013502


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