Direct and fast measurement of CT beam filter profiles with simultaneous geometrical calibration

Purpose: To accurately measure the beam filter profiles from a variety of CT scanner models and to provide reference data for Monte Carlo simulations of CT scanners. Methods: This study proposed a new method to measure CT beam filter profiles using a linear‐array x‐ray detector (X‐Scan 0.8f3‐512; Detection Technology Inc., Espoo, Finland) under gantry rotation mode. A robust geometrical calibration approach was developed to determine key geometrical parameters by considering the x‐ray focal spot location relative to the linear‐array detector and the gantry's angular increment at each acquisition point. CT beam intensity profiles were synthesized from continuously measured data during a 10° gantry rotation range with calibrated detector response and system geometry information. Relative transmission profiles of nineteen sets of beam filters were then derived for nine different CT scanner models from three different manufacturers. Equivalent aluminum thickness profiles of these beam filters were determined by analytical calculation using the Spektr Matlab software package to match the measured transmission profiles. Three experiments were performed to validate the accuracy of the geometrical calibration, detector response modeling, and the derived equivalent aluminum thickness profiles. Results: The beam intensity profiles measured from gantry rotation mode showed very good agreement with those measured with gantry stationary mode, with a maximal difference of 3%. The equivalent aluminum thickness determined by this proposed method agreed well with what was measured by an ion chamber, with a mean difference of 0.4%. The determined HVL profiles matched well with data from a previous study (max difference of 4.7%). Conclusions: An accurate and robust method to directly measure profiles from a broad list of beam filters and CT scanner models was developed, implemented, and validated. Useful reference data was provided for future research on CT system modeling.

[1]  Habib Zaidi,et al.  Development and validation of MCNP4C-based Monte Carlo simulator for fan- and cone-beam x-ray CT. , 2005, Physics in medicine and biology.

[2]  J H Siewerdsen,et al.  Spektr: a computational tool for x-ray spectral analysis and imaging system optimization. , 2004, Medical physics.

[3]  J Anthony Seibert,et al.  Normalized CT dose index of the CT scanners used in the National Lung Screening Trial. , 2010, AJR. American journal of roentgenology.

[4]  J. Boone,et al.  Experimental validation of a method characterizing bow tie filters in CT scanners using a real-time dose probe. , 2011, Medical physics.

[5]  Cynthia H McCollough,et al.  Measurement of half-value layer in x-ray CT: a comparison of two noninvasive techniques. , 2000 .

[6]  John M Boone,et al.  Monte Carlo evaluation of CTD(infinity) in infinitely long cylinders of water, polyethylene and PMMA with diameters from 10 mm to 500 mm. , 2008, Medical physics.

[7]  J. Boone,et al.  An accurate method for computer-generating tungsten anode x-ray spectra from 30 to 140 kV. , 1997, Medical physics.

[8]  Yannick Poirier,et al.  A measurement‐based X‐ray source model characterization for CT dosimetry computations , 2015, Journal of applied clinical medical physics.

[9]  J. Boone,et al.  Real-time dosimeter employed to evaluate the half-value layer in CT , 2014, Physics in medicine and biology.

[10]  David G Politte,et al.  Technical Note: Measurement of bow tie profiles in CT scanners using radiochromic film. , 2015, Medical physics.

[11]  Ehsan Samei,et al.  Patient-specific radiation dose and cancer risk for pediatric chest CT. , 2011, Radiology.

[12]  John M Boone.  Method for evaluating bow tie filter angle-dependent attenuation in CT: theory and simulation results. , 2010, Medical physics.

[13]  Babak Alikhani,et al.  Non-invasive experimental determination of a CT source model. , 2016, Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics.

[14]  David G Politte,et al.  Measurement of bow tie profiles in CT scanners using a real-time dosimeter. , 2014, Medical physics.

[15]  Cynthia H McCollough,et al.  A method to generate equivalent energy spectra and filtration models based on measurement for multidetector CT Monte Carlo dosimetry simulations. , 2009, Medical physics.

[16]  Mauro Tambasco,et al.  A rapid noninvasive characterization of CT x-ray sources. , 2015, Medical physics.

[17]  Atul Padole,et al.  A new technique to characterize CT scanner bow-tie filter attenuation and applications in human cadaver dosimetry simulations. , 2015, Medical physics.

[18]  D. Dance,et al.  Monte Carlo simulations in CT for the study of the surface air kerma and energy imparted to phantoms of varying size and position. , 2004, Physics in medicine and biology.

[19]  M. Tambasco,et al.  Experimental validation of a kilovoltage x-ray source model for computing imaging dose. , 2014, Medical physics.

[20]  Kai Yang,et al.  Scatter radiation intensities around a clinical digital breast tomosynthesis unit and the impact on radiation shielding considerations. , 2016, Medical physics.

[21]  Cynthia H McCollough,et al.  Variability of surface and center position radiation dose in MDCT: Monte Carlo simulations using CTDI and anthropomorphic phantoms. , 2009, Medical physics.