Molybdenum target x‐ray spectra: A semiempirical model

Tucker, Douglas M.; Barnes, Gary T.; Wu, Xizeng

doi:10.1118/1.596686

Cited by 93 publications

(85 citation statements)

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“…1). This software is based on the work of Tucker and Barnes, 18,19 and the inherent filtration, anode angle, and composition values were adapted for the x-ray tube used. Tube potential and filtration were set for each beam qualities to obtain the associated fluence spectra.…”

Section: Iib Psdmentioning

confidence: 99%

Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range

et al. 2012

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Purpose: Photon dosimetry in the kilovolt (kV) energy range represents a major challenge for diagnostic and interventional radiology and superficial therapy. Plastic scintillation detectors (PSDs) are potentially good candidates for this task. This study proposes a simple way to obtain accurate correction factors to compensate for the response of PSDs to photon energies between 80 and 150 kVp. The performance of PSDs is also investigated to determine their potential usefulness in the diagnostic energy range. Methods: A 1-mm-diameter, 10-mm-long PSD was irradiated by a Therapax SXT 150 unit using five different beam qualities made of tube potentials ranging from 80 to 150 kVp and filtration thickness ranging from 0.8 to 0.2 mmAl + 1.0 mmCu. The light emitted by the detector was collected using an 8-m-long optical fiber and a polychromatic photodiode, which converted the scintillation photons to an electrical current. The PSD response was compared with the reference free air dose rate measured with a calibrated Farmer NE2571 ionization chamber. PSD measurements were corrected using spectra-weighted corrections, accounting for mass energy-absorption coefficient differences between the sensitive volumes of the ionization chamber and the PSD, as suggested by large cavity theory (LCT). Beam spectra were obtained from x-ray simulation software and validated experimentally using a CdTe spectrometer. Correction factors were also obtained using Monte Carlo (MC) simulations. Percent depth dose (PDD) measurements were compensated for beam hardening using the LCT correction method. These PDD measurements were compared with uncorrected PSD data, PDD measurements obtained using Gafchromic films, Monte Carlo simulations, and previous data. Results: For each beam quality used, the authors observed an increase of the energy response with effective energy when no correction was applied to the PSD response. Using the LCT correction, the PSD response was almost energy independent, with a residual 2.1% coefficient of variation (COV) over the 80-150-kVp energy range. Monte Carlo corrections reduced the COV to 1.4% over this energy range. All PDD measurements were in good agreement with one another except for the uncorrected PSD data, in which an over-response was observed with depth (13% at 10 cm with a 100 kVp beam), showing that beam hardening had a non-negligible effect on the PSD response. A correction based on LCT compensated very well for this effect, reducing the over-response to 3%. Conclusion: In the diagnostic energy range, PSDs show high-energy dependence, which can be corrected using spectra-weighted mass energy-absorption coefficients, showing no considerable sign of quenching between these energies. Correction factors obtained by Monte Carlo simulations confirm that the approximations made by LCT corrections are valid. Thus, PSDs could be useful for realtime dosimetry in radiology applications.

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Section: Iib Psdmentioning

confidence: 99%

Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range

et al. 2012

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“…To determine the generated energy spectra, Monte Carlo simulations are used since these are more accurate than tabulated semi-empirical data [16,17,18,19,20]. Moreover, the internal structure of the X-ray tube can be taken into account, which is important for contributions such as secondary radiation.…”

Section: Sourcementioning

confidence: 99%

A realistic projection simulator for laboratory based X-ray micro-CT

Dhaene

Pauwels

Schryver

et al. 2015

Nuclear Instruments and Methods in Physics Research Section B:

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In X-ray Computed Tomography (CT) each voxel of the reconstructed image contains a calculated grey value which represents the linear attenuation coefficient for the materials in that voxel. Conventional laboratory based CT scanners use polychromatic X-ray sources and integrating detectors with an energy dependent efficiency. Consequently the reconstructed attenuation coefficients will depend on the spectrum of the source and the spectral sensitivity of the detector. Beam hardening will alter the spectrum significantly as the beam propagates through the sample. Therefore, sample composition and shape will affect the reconstructed attenuation coefficients as well. A polychromatic projection simulator has been developed at the "Centre for X-ray Tomography" of the Ghent University (UGCT) which takes into account the aforementioned variables, allowing for complete and realistic simulations of CT scans for a wide range of geometrical setups. Monte Carlo simulations of the X-ray tubes and detectors were performed to model their spectral behaviour. In this paper, the implementation and features of the program are discussed. Simulated and real CT scans are compared to demonstrate the quantitative correctness of the simulations. Experiments performed at two different UGCT scanners yield a maximum deviation of 3.9% and 6.5% respectively, between the measured and simulated reconstructed attenuation coefficients.

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“…The x-ray spectrum of this beam is computed based on a validated tube spectrum model. 34 The average energy of this spectrum is 19.84 keV. The 2-D checkerboard phase grating was assumed to be a π/2-grating of a 5-µm period for 20 keV x-ray, but its phase shift value varies with the wavelengths in the spectrum.…”

Section: B Visibilities Of Diffraction Orders In Intensity Fringe mentioning

confidence: 99%

A general theory of interference fringes in x-ray phase grating imaging

Yan

Liu

2015

Med. Phys.

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Purpose: The authors note that the concept of the Talbot self-image distance in x-ray phase grating interferometry is indeed not well defined for polychromatic x-rays, because both the grating phase shift and the fractional Talbot distances are all x-ray wavelength-dependent. For x-ray interferometry optimization, there is a need for a quantitative theory that is able to predict if a good intensity modulation is attainable at a given grating-to-detector distance. In this work, the authors set out to meet this need. Methods: In order to apply Fourier analysis directly to the intensity fringe patterns of twodimensional and one-dimensional phase grating interferometers, the authors start their derivation from a general phase space theory of x-ray phase-contrast imaging. Unlike previous Fourier analyses, the authors evolved the Wigner distribution to obtain closed-form expressions of the Fourier coefficients of the intensity fringes for any grating-to-detector distance, even if it is not a fractional Talbot distance. Results: The developed theory determines the visibility of any diffraction order as a function of the grating-to-detector distance, the phase shift of the grating, and the x-ray spectrum. The authors demonstrate that the visibilities of diffraction orders can serve as the indicators of the underlying interference intensity modulation. Applying the theory to the conventional and inverse geometry configurations of single-grating interferometers, the authors demonstrated that the proposed theory provides a quantitative tool for the grating interferometer optimization with or without the Talbotdistance constraints. Conclusions: In this work, the authors developed a novel theory of the interference intensity fringes in phase grating x-ray interferometry. This theory provides a quantitative tool in design optimization of phase grating x-ray interferometers. C 2015 American Association of Physicists in Medicine.

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Molybdenum target x‐ray spectra: A semiempirical model

Cited by 93 publications

References 0 publications

Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range

Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range

A realistic projection simulator for laboratory based X-ray micro-CT

A general theory of interference fringes in x-ray phase grating imaging

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