Diagnostic X-ray Spectra Research Articles

Validation and study of different parameters in the simulation of diagnostic X-ray spectra using the MCNPX code

In radiology, knowing the X-ray spectrum characteristics makes it possible to estimate the absorbed dose in the patient and to improve image quality. In this study, an X-ray generator was proposed using the MCNPX code and to validate it, the simulated spectrum was compared to the data provided from AAPM Task Group 195, which resulted in a percentage difference of 8.7%. Furthermore, several X-ray spectra were generated and compared to the spectra obtained from commercially available softwares as xpecgen and SpekCalc. The percentage differences were of the order of 13% in comparison with SpekCalc and 8% with xpecgen. The major differences obtained between those spectra were concentrated in the region of characteristic peaks, independently if variations in electron beam energy, target angle or filtration thickness were performed.

Technical note: Water-equivalent thickness of Superflab bolus material at diagnostic x-ray energies.

The purpose of this work was to determine the water-equivalent thickness of Superflab bolus material for narrow and broad field-of-view (FOV) x-ray geometries at diagnostic x-ray energies. Transmission measurements were performed for incremental thicknesses of Superflab bolus material and water in narrow and broad FOV x-ray geometries. The transmission data was fit to a non-linear model for x-ray transmission - the Archer model. Water-equivalent thickness of Superflab was calculated based upon fitting parameters to transmission curves for 75, 95, and 115kV x-ray tube voltages. Measured x-ray transmission factors for water and Superflab were used to determine the water equivalence of Superflab. For all x-ray tube voltages and geometries, the water equivalence of Superflab was greater than one, indicating that Superflab is more attenuating than water. This effect was stronger for broad FOV geometries. At 95kV, 30cm of Superflab corresponded to 32.0cm of water in the narrow FOV geometry, and 34.3cm of water in the broad FOV geometry. The Archer model fitting parameters and Superflab water equivalence are reported for all x-ray beam conditions explored in this work. Superflab bolus material is more attenuating than water at diagnostic x-ray energies. The Archer model and its respective fitting parameters reported in this work may be used to estimate the water-equivalent thickness of Superflab for diagnostic x-ray spectra.

Recent diagnostic developments at the 100 kJ-level laser facility in China

A 100 kJ-level laser facility has been designed to study inertial confinement fusion physics in China. This facility incorporates various diagnostic techniques, including optical, x-ray imaging, x-ray spectrum, and fusion product diagnostics, as well as general diagnostics assistance systems and central control and data acquisition systems. This paper describes recent developments in diagnostics at the facility.

Diagnostic X-ray Spectra Detection by Monte Carlo Simulation

Most diagnostic devices in the medical field use X-ray sources, which emit energy spectra. In radiological diagnosis, the quantitative and qualitative analyses of X-rays are essential for maintaining the image quality and minimizing the radiation dose to patients. This work aims to obtain the X-ray energy spectra used in diagnostic imaging by Monte Carlo simulation. Various X-ray spectra are simulated using a Monte Carlo simulation tool. These spectra are then compared to the reference data obtained with a tungsten anode spectral model using the interpolating polynomial (TASMIP) code. The X-ray tube voltages used are 50, 60, 80, 100, and 110 kV, respectively. CdTe and a-Se detector are used as the detectors for obtaining the X-ray spectra. Simulation results demonstrate that the various X-ray spectra are well matched with the reference data. Based on the simulation results, an appropriate X-ray spectrum, in accordance with the tube voltage, can be selected when generating an image for diagnostic imaging. The dose to be delivered to the patient can be predicted prior to examination in the diagnostic field.

Measured X-ray Spectra and Absorbed Dose Conversion Factors in a Water Equivalent Phantom Irradiated with Diagnostic X-rays

The diagnostic X-ray spectra in a water equivalent phantom have been measured. From these measured spectra, the absorbed dose conversion factors of water were derived. The primary X-ray spectra were also measured and the scattered X-ray spectra were calculated by subtraction. The measurements were made at the depths of 0, 5, 10, 15, and 20 cm in a 20 cm-thick phantom and at the X-ray tube voltages 60, 90, and 120 kV by using a small silicon diode detector. The radiation field size was 30×30 cm2 at the phantom surface. In the obtained spectra, the fraction of the scattered photon number is increased with the depth. The X-ray qualities of the spectra in the phantom were near the qualities of primary X-rays when the depth is 0 cm, and became near the qualities of scattered X-rays as the depth increases. The changes of the X-ray qualities due to the depth change were small; photon mean-energy changes were within 4.6 keV. The changes in the absorbed dose conversion factors were also small (within 0.68%). These conversion factors were 0.4-2.3% larger than those obtained from the effective energy of incident X-rays and only -0.3 to 0.5% larger than those obtained from the X-ray spectra calculated from the aluminum half value layer and the tube voltage of incident X-rays. This study shows experimentally that the absorbed dose in a water-like phantom can be calculated with good accuracy by using the absorbed dose conversion factor obtained from the incident X-rays.

Abstract ID: 189 Uncertainty estimation of MC simulated mammography spectra

Novel breast dosimetry applications require the knowledge of incident X-ray spectra, in mammography energy range [1] . Furthermore, the knowledge of the spectra transmitted through breast tissue is important in the phantom development context. A vast number of MC codes are used as models to generate diagnostic X-ray spectra; however, comparisons of those to experimentally measured X-ray spectra (validations) must be done to assure modelled spectra are representative of real X-ray beams. For these comparisons to be reliable, accurate uncertainty estimation of the counts in the spectra channels is required. This work’s objective was to accurately assess the uncertainties associated to the counts of incident and transmitted mammography MC modelled spectra. In this work, the PENELOPE MC code was used to simulate a CdTe spectrometer’s detection of mammography X-ray spectra, and the attenuation of these spectra after transmission through commercial breast phantoms. Four anode-filter combinations, three commercial breast phantoms and several attenuation thicknesses were used. Altogether, 108 spectra were simulated. The measured spectra emitted by each X-ray generators were used as the MC simulations input spectra, after escape and efficiency distortion effects were corrected by the stripping method. The uncertainty of the modelled spectra’s channels was estimated through MC uncertainty propagation method. For each condition, 25 simulations were performed, varying the input parameters (input spectra and phantom composition) according to their probability density functions. The simulated spectra validation was done through the assessment of the mean weighted squared residuals (MWSR). Except for model’s inaccuracies, good estimation of the uncertainties yields a MWSR equal to 1, which is this quantity’s expected value. The mean of the 108 calculated MWSRs yielded 3.76(03) when only Poisson’s uncertainty was used. Therefore, we conclude Poisson’s uncertainty underestimates the uncertainty of the spectra channels’ counts. The estimation we performed demonstrated better accuracy, it yielded a mean MWSR of 1.17(01).

A method of measuring gold nanoparticle concentrations by x‐ray fluorescence for biomedical applications

This paper reports a technique that enables the quantitative determination of the concentration of gold nanoparticles (GNPs) through the accurate detection of their fluorescence radiation in the diagnostic x-ray spectrum. Experimentally, x-ray fluorescence spectra of 1.9 and 15 nm GNP solutions are measured using an x-ray spectrometer, individually and within chicken breast tissue samples. An optimal combination of excitation and emission filters is determined to segregate the fluorescence spectra at 66.99 and 68.80 keV from the background scattering. A roadmap method is developed that subtracts the scattered radiation (acquired before the insertion of GNP solutions) from the signal radiation acquired after the GNP solutions are inserted. The methods effectively minimize the background scattering in the spectrum measurements, showing linear relationships between GNP solutions from 0.1% to 10% weight concentration and from 0.1% to 1.0% weight concentration inside a chicken breast tissue sample. The investigation demonstrated the potential of imaging gold nanoparticles quantitatively in vivo for in-tissue studies, but future studies will be needed to investigate the ability to apply this method to clinical applications.

Performance of a digital CdTe X-ray spectrometer in low and high counting rate environment

The high performances of CdTe detectors for X-ray and gamma ray spectroscopy are already well known. Among the traditional semiconductor spectrometers, CdTe detectors show high detection efficiency and good room temperature performance and are well suited for the development of compact detection systems. In this work, we investigated the performance of a CdTe detector coupled with a custom digital pulse processing (DPP) system for X-ray spectroscopy. The DPP method, implemented on a PC platform, performs a pile-up inspection and a pulse height analysis of the preamplifier output pulses, digitized by a 14-bit, 100MHz ADC. The spectroscopic results point out the excellent performance of the digital spectrometer both at low (150cps) and at high photon counting rate (up to 370kcps), confirming the high potentialities of CdTe detectors coupled with DPP systems. The detector and the DPP system were developed by our collaboration as a spectrometer prototype for direct measurement of diagnostic X-ray spectra in the 1–40keV energy range.

Quantifying the effect of anode surface roughness on diagnostic x‐ray spectra using Monte Carlo simulation

The accurate prediction of x-ray spectra under typical conditions encountered in clinical x-ray examination procedures and the assessment of factors influencing them has been a longstanding goal of the diagnostic radiology and medical physics communities. In this work, the influence of anode surface roughness on diagnostic x-ray spectra is evaluated using MCNP4C-based Monte Carlo simulations. An image-based modeling method was used to create realistic models from surface-cracked anodes. An in-house computer program was written to model the geometric pattern of cracks and irregularities from digital images of focal track surface in order to define the modeled anodes into MCNP input file. To consider average roughness and mean crack depth into the models, the surface of anodes was characterized by scanning electron microscopy and surface profilometry. It was found that the average roughness (Ra) in the most aged tube studied is about 50 pm. The correctness of MCNP4C in simulating diagnostic x-ray spectra was thoroughly verified by calling its Gaussian energy broadening card and comparing the simulated spectra with experimentally measured ones. The assessment of anode roughness involved the comparison of simulated spectra in deteriorated anodes with those simulated in perfectly plain anodes considered as reference. From these comparisons, the variations in output intensity, half value layer (HVL), heel effect, and patient dose were studied. An intensity loss of 4.5% and 16.8% was predicted for anodes aged by 5 and 50 microm deep cracks (50 kVp, 6 degrees target angle, and 2.5 mm A1 total filtration). The variations in HVL were not significant as the spectra were not hardened by more than 2.5%; however, the trend for this variation was to increase with roughness. By deploying several point detector tallies along the anode-cathode direction and averaging exposure over them, it was found that for a 6 degrees anode, roughened by 50 microm deep cracks, the reduction in exposure is 14.9% and 13.1% for 70 and 120 kVp tube voltages, respectively. For the evaluation of patient dose, entrance skin radiation dose was calculated for typical chest x-ray examinations. It was shown that as anode roughness increases, patient entrance skin dose decreases averagely by a factor of 15%. It was concluded that the anode surface roughness can have a non-negligible effect on output spectra in aged x-ray imaging tubes and its impact should be carefully considered in diagnostic x-ray imaging modalities.

Synthesis, characterization, and computed tomography imaging of a tantalum oxide nanoparticle imaging agent

Water-soluble ≤6 nm tantalum oxide nanoparticles have been synthesized and characterized in solution using HPLC-ICP, DLS, and multinuclear NMR. Nanoparticle formulation permitted intravenous injection, in vivo imaging, and subsequent renal clearance. A clinical CT scanner provided excellent resolution following agent injection, and distribution to the arterial system was visualized. In vitro CT imaging studies indicated that at equal molar concentration of tantalum and iodine, tantalum produced greater image contrast than iodine across the diagnostic X-ray spectrum with contrast benefit increasing with peak X-ray energy.

DXRaySMCS: a user-friendly interface developed for prediction of diagnostic radiology X-ray spectra produced by Monte Carlo (MCNP-4C) simulation

In this work, the general purpose Monte Carlo N-particle radiation transport computer code (MCNP-4C) was used for the simulation of X-ray spectra in diagnostic radiology. The electron's path in the target was followed until its energy was reduced to 10 keV. A user-friendly interface named 'diagnostic X-ray spectra by Monte Carlo simulation (DXRaySMCS)' was developed to facilitate the application of MCNP-4C code for diagnostic radiology spectrum prediction. The program provides a user-friendly interface for: (i) modifying the MCNP input file, (ii) launching the MCNP program to simulate electron and photon transport and (iii) processing the MCNP output file to yield a summary of the results (relative photon number per energy bin). In this article, the development and characteristics of DXRaySMCS are outlined. As part of the validation process, output spectra for 46 diagnostic radiology system settings produced by DXRaySMCS were compared with the corresponding IPEM78. Generally, there is a good agreement between the two sets of spectra. No statistically significant differences have been observed between IPEM78 reported spectra and the simulated spectra generated in this study.

MO-E-332-01: DXS a Diagnostic X-Ray Spectra Generator

Purpose: To numerically generate radiographic x‐ray spectra that can be conveniently employed in radiation transport simulations or other radiation detection applications. Method and Materials: Based initially on the Tucker, et al model, we developed and evaluated a new code, DXS (Diagnostic X‐Ray Spectra), to numerically generate spectra for tungsten‐target x‐ray tubes spanning the radiographic energy range. The model parameters in our code were adjusted by comparison with corresponding MCNP5 simulated spectra; we modified the semi‐analytical formulation for the characteristic x‐ray production, a caveat of Tucker's model, by incorporating a factor that better accounts for the dependence of the K‐peaks on the tube potential. Parametric fitting functions are used to model the self‐attenuation in the target and attenuation due to inherent and added filtration (aluminum,beryllium,copper,tantalum are the options implemented in the code), as well as for the tungsten mass stopping power and the Thomson‐Whiddington constant. Comparison with Monte Carlo simulated and published measured spectra were used to validate the new code. Results: Normalized to unit area DXS code‐generated spectra for several tube potentials from 50 to 140 kVp agree well, less than 2% relative difference in nearly all energy bins (2 keV), with corresponding MCNP5 simulated spectra for similar tube parameters. Few exceptions are noted and may be attributed to either poorer statistics in the low and high energy tails of the spectrum, or to insufficient accuracy of the numerical computations for the steepest part of the spectra at high accelerating potentials. Good agreement is seen between the DXS and Bhat et al measured spectra. Conclusion: The DXS code generates the spectra, according to user specified input parameters (tube potential, anode angle, filtratation) and energy intervals, and augments them into any discretized energy group structure. Hence, the code can be of great benefit in radiation transport simulations.

X-ray spectroscopy and dosimetry with a portable CdTe device

X-ray spectra and dosimetry information are very important for quality assurance (QA) and quality control (QC) in medical diagnostic X-ray systems. An accurate knowledge of the diagnostic X-ray spectra would improve the patient dose optimization, without compromising image information. In this work, we performed direct diagnostic X-ray spectra measurements with a portable device, based on a CdTe solid-state detector. The portable device is able to directly measure X-ray spectra at high photon fluence rates, as typical of clinical radiography. We investigated on the spectral performances of the system in the mammographic energy range (up to ∼40 keV). Good system response to monoenergetic photons was measured (energy resolution of 5% FWHM at 22.1 keV). We measured the molybdenum X-ray spectra produced by a mammographic X-ray unit (GE Senographe DMR) at 28 kV and 30 kV under clinical conditions. The results showed the good reproducibility of the system and low pile-up distortions. Preliminary dosimetric measurements have been regarded as exposure and half value layer (HVL) values obtained from direct measurements and from measured X-ray spectral data, and a good agreement between exposure attenuation curves and the HVL values was obtained. The results indicated that the portable device is suitable for mammographic X-ray spectroscopy under clinical conditions.

An analytic model for the response of a CZT detector in diagnostic energy dispersive x‐ray spectroscopy

A CdZnTe detector (CZTD) can be very useful for measuring diagnostic x-ray spectra. The semiconductor detector does, however, exhibit poor hole transport properties and fluorescence generation upon atomic de-excitations. This article describes an analytic model to characterize these two phenomena that occur when a CZTD is exposed to diagnostic x rays. The analytical detector response functions compare well with those obtained via Monte Carlo calculations. The response functions were applied to 50, 80, and 110 kV x-ray spectra. Two 50 kV spectra were measured; one with no filtration and the other with 1.35 mm Al filtration. The unfiltered spectrum was numerically filtered with 1.35 mm of Al in order to see whether the recovered spectrum resembled the filtered spectrum actually measured. A deviation curve was obtained by subtracting one curve from the other on an energy bin by bin basis. The deviation pattern fluctuated around the zero line when corrections were applied to both spectra. Significant deviations from zero towards the lower energies were observed when the uncorrected spectra were used. Beside visual observations, the exposure obtained using the numerically attenuated unfiltered beam was compared to the exposure calculated with the actual filtered beam. The percent differences were 0.8% when corrections were applied and 25% for no corrections. The model can be used to correct diagnostic x-ray spectra measured with a CdZnTe detector.

Compton‐scattering measurement of diagnostic x‐ray spectrum using high‐resolution Schottky CdTe detector

The analysis of x-ray spectra is important for quality assurance (QA) and quality control (QC) of radiographic systems. The aim of this study is to measure the diagnostic x-ray spectra under clinical conditions using a high-resolution Schottky CdTe detector. Under clinical conditions, the direct measurement of a diagnostic spectrum is difficult because of the high photon fluence rates that cause significant detector photon pile-up. An alternative way of measuring the output spectra from a tube is first to measure the 90 deg Compton scattered photons from a given sample. With this set-up detector, pile-up is not a problem. From the scattered spectrum one can then use an energy correction and the Klein-Nishina function to reconstruct the actual spectrum incident upon the scattering sample. The verification of whether our spectra measured by the Compton method are accurate was accomplished by comparing exposure rates calculated from the reconstructed spectra to those measured with an ionization chamber. We used aluminum (Al) filtration ranging in thickness from 0 to 6 mm. The half value layers (HVLs) obtained for a 70 kV beam were 2.78 mm via the ionization chamber measurements and 2.93 mm via the spectral measurements. For a 100 kV beam we obtained 3.98 and 4.32 mm. The small differences in HVLs obtained by both techniques suggest that Compton scatter spectroscopy with a Schottky CdTe detector is suitable for measuring the diagnostic x-ray spectra and useful for QA and QC of clinical x-ray equipment.

Mammographic x-ray spectra measured by Compton spectroscopy using a high resolution Schottky CdTe detector.

Analysis of x-ray spectra is important for quality assurance (QA) and quality control (QC) of radiographic systems. This is especially true for mammographic x-ray imaging systems which require low-contrast detectability. Under clinical conditions, the measurement of diagnostic x-ray spectra is difficult because of pulse pile-up due to the high fluence rate of incident x-ray photons. However, it is difficult to set a long source-to-detector distance to reduce the number of photons detected per unit time for mammographic x-ray units. Compton spectroscopy is a suitable tool to deal with this problem. Detection of 90-degrees scattered photons only, energy correction and reconstruction are easy using the Klein-Nishina formula. However, x-ray spectra measured by this method have lower energy resolution, because of the geometrical irradiation angle or electron movement in the scatterer. Moreover, spectra measured with a compound semiconductor detector, such as a high resolution Schottky CdTe detector like we used, are distorted by the detector response, which is based on detecting x-ray photon interactions and charge carrier trapping in the semiconductor crystal. While the distortion of spectra caused by the response can be easily corrected by applying a stripping procedure, it is very difficult to reconstruct the broad spectra measured by Compton spectroscopy as sharp spectra such as obtained when directly measured. Some complicated reconstruction algorithms have been reported to fit the shape of spectra obtained by the Compton spectroscopy to sharp standard spectra. However, for QA / QC of the radiographic system, it is not necessary to correct the spectra sharply if the spectral broadening is at a tolerable level and the properties of the broad spectra acquired by the Compton spectroscopy agree with those of the sharp spectra measured directly; i.e. evaluations are necessary only for estimation of spectral shape. In this paper, we compared attenuation curves calculated using Hubbell's attenuation coefficients to estimate the coincidence or difference of spectra measured by the Compton spectroscopy and directly measured in the primary beam. Our results showed that the attenuation curves acquired from the reconstructed spectra measured by the Compton spectroscopy agreed with that acquired from corrected spectra that were directly measured. Moreover, the attenuation curves acquired from the spectra actually measured by adding aluminum attenuators agreed with theoretically calculated curves.

Simulation of the effect of anode surface roughness on diagnostic x-ray spectra

To simulate the effect of the condition of the anode surface on x-ray output the surface roughness of anode fragments of replaced clinical x-ray tubes was determined. A mean roughness of 1.32–5.22 µm giving effective tungsten absorption layers of up to 18 µm thickness in the direction of the x-ray beam was determined. X-ray spectra were then simulated using the measured surface profiles. The most prominent effect was the reduction of the kerma output of the tube with increasing roughness (−33% at 50 kV tube voltage and 5 µm roughness). The effects of beam hardening are less pronounced. The corresponding changes in the spectral parameters are generally small but largest for tube voltages up to 70 kV. For higher voltages the increased photon attenuation above the K-edge of tungsten reduces the effects of roughness on spectral parameters. The maximum shifts in mean photon energy of about 1 keV and in HVL of about 0.2 mm Al were obtained for an anode roughness of 5 µm.

Diagnostic x-ray dosimetry using Monte Carlo simulation

An Electron Gamma Shower version 4 (EGS4) based user code was developed to simulate the absorbed dose in humans during routine diagnostic radiological procedures. Measurements of absorbed dose using thermoluminescent dosimeters (TLDs) were compared directly with EGS4 simulations of absorbed dose in homogeneous, heterogeneous and anthropomorphic phantoms. Realistic voxel-based models characterizing the geometry of the phantoms were used as input to the EGS4 code. The voxel geometry of the anthropomorphic Rando phantom was derived from a CT scan of Rando. The 100 kVp diagnostic energy x-ray spectra of the apparatus used to irradiate the phantoms were measured, and provided as input to the EGS4 code. The TLDs were placed at evenly spaced points symmetrically about the central beam axis, which was perpendicular to the cathode–anode x-ray axis at a number of depths. The TLD measurements in the homogeneous and heterogenous phantoms were on average within 7% of the values calculated by EGS4. Estimates of effective dose with errors less than 10% required fewer numbers of photon histories (1 × 107) than required for the calculation of dose profiles (1 × 109). The EGS4 code was able to satisfactorily predict and thereby provide an instrument for reducing patient and staff effective dose imparted during radiological investigations.

X-ray image intensifier performance and patient doses for combinationsof supplemental beam filters and vascular contrast agents

We present an investigation of the fluoroscopic imaging and dosimetricperformances of iodine- and gadolinium-based vascular contrast agents incombination with K-absorption edge filters of atomic numbers between 50 (tin)and 82 (lead). These combinations were studied using a theoretical model for arange of diagnostic x-ray spectra (55 to 100 kVp) and for water phantomsrepresentative of thin and thick anatomies. Performance was characterized byradiographic contrast, a derived image quality index, the patient integral andentrance skin doses, and the x-ray tube load. For a given thickness of anatomy,an optimum combination of spectrum kVp, contrast agent and supplemental filterwas defined by maximum imaging performance for a minimum or tolerable x-raytube load and patient dose. It was possible to both improve imagingperformance and reduce dose by the use of an appropriate combination ofspectrum kVp and filter. For gadolinium-based contrast, performance wasoptimized with tungsten filtration at 90 kVp for both thin and thickanatomies. It was not possible, however, to optimize the iodinated contrastperformance with a single combination of supplemental filter and spectrum kVp.The optimal performance for iodinated contrast was achieved with gadoliniumfiltration at 60 kVp for thin anatomy and with ytterbium filtration at 80 kVpfor thick anatomy. The best performance for thin anatomy was that of thecombination of iodinated contrast/gadolinium filter at 60 kVp and the bestperformance for thick anatomy was that of the combination of gadolinium-basedcontrast/tungsten filter at 90 kVp.

The calculation of diagnostic X-ray spectra and other data using the Spectrum Processor

The calculation of diagnostic X-ray spectra and other data using the Spectrum Processor