Off-axis Spectra Research Articles

Technical Note: SpekPy v2.0—a software toolkit for modeling x‐ray tube spectra

SpekPy is a free toolkit for modeling x-ray tube spectra with the Python programming language. In this article, the advances in version 2.0 (v2) of the software are described, including additional target materials and more accurate modeling of the heel effect. Use of the toolkit is also demonstrated. The predictions of SpekPy are illustrated in comparison to experimentally determined spectra: three radiation quality reference (RQR) series tungsten spectra and one mammography spectrum with a molybdenum target. The capability of the software to correctly model changes in tube output with tube potential is also assessed, using the example of a GE RevolutionTM CT scanner (GE Healthcare, Waukesha, WI, USA) and specifications in the system's Technical Reference Manual. Furthermore, we note that there are several physics models available in SpekPy. These are compared on and off the central axis, to illustrate the differences. SpekPy agrees closely with the experimental spectra over a wide range of tube potentials, both visually and in terms of first and second half-value layers (HVLs) (within 2% here). The CT scanner spectrum output (normalized to 120kV tube potential) agreed within 4% over the range of 70 to 140kV. The default physics model (casim) is adequate in most situations. The advanced option (kqp) should be used if high accuracy is desired for modeling the anode heel effect, as it fully includes the effects of bremsstrahlung anisotropy. SpekPy v2 can reliably predict on- and off-axis spectra for tungsten and molybdenum targets. SpekPy's open-source MIT license allows users the freedom to incorporate this powerful toolkit into their own projects.

A model for the energy and angular distribution of x rays emitted from an x-ray tube. Part II. Validation of x-ray spectra from 20 to 300kV.

To present and validate a complete x-ray emission model (bremsstrahlung and characteristic x-ray emission) for the energy range 20-300kV. An analytical x-ray spectrum model that combines the bremsstrahlung emission model developed in Part I with a previously developed characteristic x-ray emission model is validated by comparison with Monte Carlo calculations, published measured spectra, and models developed by other authors. Furthermore, the assumptions and limitations of previous spectrum models are summarized, and their predictions are compared with results obtained by Monte Carlo simulations of x rays emitted from tungsten and molybdenum targets. The model is able to reproduce narrow-beam Monte Carlo calculations to within 0.5% in terms of the first and second aluminum half-value layer thickness (HVL). Compared with measured spectra, the difference in HVL is < 2% for typical diagnostic and therapeutic beam qualities available at primary standard laboratories. Compared with previous spectrum models, the present model performs especially well for low kilovoltage x-ray beams (below 50kV), and is reliable for a wider range of take-off angles, that is, the angle between the target surface and the direction of emission. The difference in model and Monte Carlo predictions of the energy-fluence weighted air kerma (i.e., the photon energy absorption in air) is < 0.5% using the present model, while previous spectrum models can differ by more than 10%. The x-ray emission model developed in this work has been validated against Monte Carlo calculations and measured results. The model provides an efficient alternative to comprehensive Monte Carlo simulations and is an improvement over previous models. The model can be used to predict both central- and off-axis spectra, as well as off-axis effects such as the (anode) heel effect.

Spectra shifts of a chirped Gaussian pulsed beam propagating in slant atmosphere path

Based on the extended Huygens-Fresnel principle, the cross-spectral density function of a chirped Gaussian pulsed beam propagating in slant atmosphere path was derived, and the spectra shift properties of chirped Gaussian pulsed beam in slant atmosphere path were studied. The results show that the on-axis spectral shifts may be red shift comparing to the spectra at the source plane L = 0, while the off-axis spectra shifts is blue shift. The results also show that the red shift or the blue shift of chirped Gaussian pulsed beam in slant atmosphere path will increase as the parameters C0 and α of slant atmosphere increase.

Effect of Target Angle and Thickness on the Heel Effect and X-ray Intensity Characteristics for 70 kV X-ray Tube Target

To investigate the optimum x-ray tube design for the dental radiology, factors affecting x-ray beam characteristics such as tungsten target thickness and anode angle were evaluated. Another goal of the study was to addresses the anode heel effect and off-axis spectra for different target angles. MCN...

SU-D-BRCD-03: Spectroscopic Characterization of a 6 MV Linear Accelerator Field Using Compton Spectrometry Measurements and Monte Carlo Techniques.

Effective treatment planning for radiotherapy is dependent on accurate spectra determination; however, direct measurements of spectra arecomplicated by fluence rates that exceed detection system limitations. This work demonstrates the potential to use a Compton scattering technique to measure the spectrum of a 6MV linac. These spectra are further characterized using Monte Carlo (MC) simulations. A high-purity germanium detector was used to measure the photon spectrum scattered at35 degrees from the central axis of 3cmx3cm and lOcmxlOcm 6MV fields from a Varian linac. Photons were scattered using aluminum rods positioned at isocenter, and were admitted to the detector through a 30cm-long collimating aperture. The measured Compton-scattered spectra were corrected for background. An MC model of the linac was developed in MCNP5 to calculate central- and off-axis spectra. The model geometry was verified by comparisons with percentage depth-dose and profilemeasurements. The spectroscopic effect of the mean energy, radius, and divergence of the electron beam incident on the target was tested for twofield sizes. The count rate of the scattered beam increased with field size and scattering rod diameter. Preliminary measurements indicate that the spectrum was shifted to lower energies using this technique; however, the signal-to-noise ratio was poor due to leakage and room scatter. MC simulations demonstrate that the central- and off-axis spectra were sensitive to changes in mean electron energy; however, changes in beam diameter and angular divergence did not substantially affect either the central- or off-axis spectra. This work demonstrates that the spectrum from a 6MV linac can be measured using Compton spectrometry. Further work is required to increase the signal-to-noise ratio and correct fordetector response. MC simulations indicate that the spectra were sensitive to variations in the parameters used to define the primary electron beam incident on the target.

Host galaxies of luminous quasars: population synthesis of optical off-axis spectra

There is increasing evidence of a connection between AGN activity and galaxy evolution. To obtain further insight into this potentially important evolutionary phase, we analyse the properties of quasar host galaxies. In this paper, we present a population synthesis modeling technique for off-axis spectra, the results of which constrain host colour and the stellar ages of luminous quasars (M_V(nuc)<-23). Our technique is similar to well established quiescent-galaxy models, modified to accommodate scattered nuclear light (a combination of atmospheric, instrumental and host galaxy scattered light) observed off axis. In our model, subtraction of residual scattered quasar light is performed, while simultaneously modeling the constituent stellar populations of the host galaxy. The reliability of this technique is tested via a Monte-Carlo routine in which the correspondence between synthetic spectra with known parameters and the model output is determined. Application of this model to a preliminary sample of 10 objects is presented and compared to previous studies. Spectroscopic data was obtained via long-slit and integral-field unit observations on the Keck and WIYN telescopes. We confirm that elliptical quasar hosts are distinguishable (bluer) from inactive ellipticals in rest frame B-V colour. Additionally, we note a trend for radio luminous (L_5GHz > 10^40 erg s^-1) quasars to be located in redder host galaxies in comparison to their less luminous radio counterparts. While the host colour and age of our radio luminous sample is in close proximity to the green valley, our radio faint sample is consistent with quiescent star-forming galaxies. However, further observations are needed to confirm these results. Finally, we discuss future applications for our technique on a larger sample of objects being obtained via SALT and WIYN telescope observing campaigns.

Estimation of turbulence spectra parameters from log-amplitude fluctuations spectra of an optical wave

From the general formula for the temporal frequency log-amplitude fluctuations spectra the asymptotic expressions are found, valid for the geometric and wave approximations. A comparison of the plane and spherical wave formulas with those valid for the beam wave is made in all frequency regions. The difference between the on-axis and off-axis beam spectra is presented. The possibility of estimating from the log-amplitude scintillations the inner and outer scales of turbulence together with the exponent of turbulence spectra in the subrange is briefly discussed.

Sound radiation patterns in the frequency domain of cries from a vespertilionid bat

Ultrasonic cries from an immobilized vespertilionid batMyotis daubentoni, were recorded simultaneously in front of the bat (on-axis), and at various off-axis angles. The differences between the on-axis and off-axis spectra were computed and related to the theory of directional emission from a baffled rigid-piston radiator. This theory implies zero radiation at a specific frequency for a given piston diameter and off-axis angle (Fig. 1). The bat's difference spectra showed notches of ca. 25 dB with properties as the zeros of the piston theory (Fig. 7). The structure of off-axis cries was found to be qualitatively predictable from the on-axis cries, using the piston theory (Fig. 4). The difference spectra had a complex, oscillatory fine-structure that could not be accounted for by the basic piston theory.