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

ABSTRACT: 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.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.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%).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.

SUBMITTER: Yang K

PROVIDER: S-EPMC5543987 | biostudies-literature | 2017 Jan

REPOSITORIES: biostudies-literature

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

Yang Kai K Li Xinhua X George Xu X X Liu Bob B

Medical physics 20170101 1

<h4>Purpose</h4>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.<h4>Methods</h4>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-r ...[more]

PMID: 28102951

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Project description:BackgroundA calibration phantom-based method has been developed for predicting small lung nodule volume measurement bias and precision that is specific to a particular computed tomography (CT) scanner and acquisition protocol.MethodsThe approach involves CT scanning a simple reference object with a specific acquisition protocol, analyzing the scan to estimate the fundamental imaging properties of the CT acquisition system, generating numerous simulated images of a target geometry using the fundamental imaging properties, measuring the simulated images with a standard nodule volume segmentation algorithm, and calculating bias and precision performance statistics from the resulting volume measurements. We evaluated the ability of this approach to predict volume measurement bias and precision of Teflon spheres (diameters =4.76, 6.36, and 7.94 mm) placed within an anthropomorphic chest phantom when using 3M Scotch Magic™ tape as the reference object. CT scanning of the spheres was performed with 0.625, 1.25, and 2.5 mm slice thickness and spacing.ResultsThe study demonstrated good agreement between predicted volumetric performance and observed volume measurement performance for both volumetric measurement bias and precision. The predicted and observed volume mean for all slice thicknesses was found to be 28% and 13% lower on average than the manufactured sphere volume, respectively. When restricted to 0.625 and 1.25 mm slice thickness scans, which are recommended for small lung nodule volume measurement, we found that the difference between predicted and observed volume coefficient of variation was less than 1.0 %. The approach also showed a resilience to varying CT image acquisition protocols, a critical capability when deploying in a real-world clinical setting.ConclusionsThis is the first report of a calibration phantom-based method's ability to predict both small lung nodule volume measurement bias and precision. Volume measurement bias and precision for small lung nodules can be predicted using simple low-cost reference objects to estimate fundamental CT image characteristics and modeling and simulation techniques. The approach demonstrates an improved method for predicting task specific, clinically relevant measurement performance using advanced and fully automated image analysis techniques and low-cost reference objects.

Dataset Information

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

Publications

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

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