The effects of x-ray beam hardening on detective quantum efficiency and radiation dose

Wong, Molly D.; Wu, Xizeng; Liu, Hong

doi:10.3233/xst-2011-0310

Cited by 11 publications

(9 citation statements)

References 40 publications

(57 reference statements)

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“…It is worth mentioning that the removal of beam hardening errors changes the performance of the spatial resolution of the FP method. 38 However, the presented results show that the improvement ratio of MTF between the LB and FP methods matches well with that of the wire experiments with and without OFR. As such, we argue that the influence of beam hardening effect on MTF is much smaller than that of OFR in the FP method.…”

Section: Conclusion and Discussionsupporting

confidence: 82%

“…The difference between the raw projection signals and the estimated primary signals is considered to include all the errors, which are mostly removed after scatter correction. It is worth mentioning that the removal of beam hardening errors changes the performance of the spatial resolution of the FP method . However, the presented results show that the improvement ratio of MTF between the LB and FP methods matches well with that of the wire experiments with and without OFR.…”

Section: Conclusion and Discussionsupporting

confidence: 67%

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The role of off‐focus radiation in scatter correction for dedicated cone beam breast CT

et al. 2017

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Purpose: Dedicated cone beam breast CT (CBBCT) suffers from x-ray scatter contamination. We aim to identify the source of the significant difference between the scatter distributions estimated by two recent methods proposed by our group and to investigate its effect on CBBCT image quality. Method: We recently proposed two novel methods of scatter correction for CBBCT, using a library based (LB) technique and a forward projection (FP) model. Despite similar enhancement on CBBCT image qualities, these two methods obtain very different scatter distributions. We hypothesize that the off-focus radiation (OFR) is the contributor and results in nontrivial signals in x-ray projections, which is ignored in the scatter estimation via the LB method. Experiments using a thin wire test tool are designed to study the effect of OFR on CBBCT spatial resolution by measuring the point spread function (PSF) and the modulation transfer function (MTF). A narrow collimator setting is used to suppress the OFR-induced signals. In addition, "PSFs" and "MTFs" are measured on clinical CBBCT images obtained by the LB and FP methods using small calcifications as point sources. The improvement of spatial resolution achieved by suppressing OFR in the wire experiment as well as in the clinical study is quantified by the improvement ratios of PSFs and spatial frequencies at different MTF values. Our hypothesis that OFR causes the imaging difference between the FP and LB methods is verified if these ratios obtained from experimental and clinical data are consistent. Results: In the wire experiment, the results show that suppression of OFR increases the maximum signal of the PSF by about 14% and reduces the full-width-at-half-maximum (FWHM) by about 12.0%. Similar improvement on spatial resolution is achieved by the FP method compared with the LB method in the patient study. The improvement ratios of spatial frequencies at different MTF values without OFR match very well in both studies at a level of around 16%, with an average rootmean-square difference of 0.47%. Conclusion:The results of the wire experiment and the clinical study indicate that the main difference between the LB and FP methods is whether the OFR-induced signals are included after scatter correction. Our study further shows that OFR significantly affects the image spatial resolution of CBBCT, indicating that the visualization of micro-calcifications is susceptible to OFR contamination. Our finding is therefore important in further improvement of diagnostic performance of CBBCT.

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Section: Conclusion and Discussionsupporting

confidence: 82%

Section: Conclusion and Discussionsupporting

confidence: 67%

The role of off‐focus radiation in scatter correction for dedicated cone beam breast CT

et al. 2017

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“…The focal spot size of the x-ray tube varies from 5 μm to 30 μm depending on its output power while the focal spot to the output window distance is 6.8 mm. An inherent filtration of 100 μm of aluminum (Al) and 60 μm of copper (Cu) is used for beam hardening [19]. The x-ray detector is a 130 × 130 mm 2 amorphous silicon flat panel with a 127 μm pixel pitch and 14 bit digital output.…”

Section: Methodsmentioning

confidence: 99%

Investigation of spatial resolution characteristics of an in vivo microcomputed tomography system

Ghani

Zhou

Ren

et al. 2016

Nuclear Instruments and Methods in Physics Research Section A:

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The spatial resolution characteristics of an in vivo micro computed tomography (CT) system was investigated in the in-plane (x-y), cross plane (z) and projection imaging modes. The micro CT system utilized in this study employs a flat panel detector with a 127 μm pixel pitch, a micro focus x-ray tube with a focal spot size ranging from 5-30 μm, and accommodates three geometric magnifications (M) of 1.72, 2.54 and 5.10. The in-plane modulation transfer function (MTF) curves were measured as a function of the number of projections, geometric magnification (M), detector binning and reconstruction magnification (MRecon). The in plane cutoff frequency (10% MTF) ranged from 2.31 lp/mm (M=1.72, 2×2 binning) to 12.56 lp/mm (M=5.10, 1×1 binning) and a bar pattern phantom validated those measurements. A slight degradation in the spatial resolution was observed when comparing the image reconstruction with 511 and 918 projections, whose effect was visible at the lower frequencies. Small value of MRecon has little or no impact on the in-plane spatial resolution owning to a stable system. Large value of MRecon has implications on the spatial resolution and it was evident when comparing the bar pattern images reconstructed with MRecon=1.25 and 2.5. The cross plane MTF curves showed that the spatial resolution increased as the slice thickness decreased. The cutoff frequencies in the projection imaging mode yielded slightly higher values as compared to the in-plane and cross plane modes at all the geometric magnifications (M). At M=5.10, the cutoff resolution of the projection and cross plane on an ultra-high contrast resolution bar chip phantom were 14.9 lp/mm and 13-13.5 lp/mm. Due to the finite focal spot size of the x-ray tube, the detector blur and the reconstruction kernel functions, the system's spatial resolution does not reach the limiting spatial resolution as defined by the Nyquist's detector criteria with an ideal point source. The geometric magnification employed in the micro CTs provide a tradeoff between field of view and spatial resolution for a wide range of applications.

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“…The data show that imaging the spine in PA projection instead of AP can lower the overall OD. The reason for this is related to the lower energy X-rays being absorbed by the superficial organs in close proximity to primary beam entry point; as the beam progresses through the body it hardens thereby reducing the number of lower energy X-rays available for absorption 17 . This makes PA projection preferred for imaging scoliosis in females as it reduces breast dose and consequently reduces the risk of developing radiation-induced cancer 18 .…”

Section: Discussionmentioning

confidence: 99%

Scoliosis imaging: An analysis of radiation risk in the CT scan projection radiograph and a comparison with projection radiography and EOS

et al. 2019

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The effects of x-ray beam hardening on detective quantum efficiency and radiation dose

Cited by 11 publications

References 40 publications

The role of off‐focus radiation in scatter correction for dedicated cone beam breast CT

The role of off‐focus radiation in scatter correction for dedicated cone beam breast CT

Investigation of spatial resolution characteristics of an in vivo microcomputed tomography system

Scoliosis imaging: An analysis of radiation risk in the CT scan projection radiograph and a comparison with projection radiography and EOS

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