Spectroscopy with pixelated CdZnTe gamma detectors – experiment versus theory

BackgroundPositron emission tomography (PET) images are being applied for defining radiotherapy targets. However, a recognized method for defining radiotherapy targets is lacking. We investigate the threshold to outline the radiotherapy target of a tumor on PET images and its influencing factors, and then expressed it by formula.MethodsPET imaging for spherical tumors with a different tumor diameter (D), under different system resolutions [full width at half maximum (FWHM)], in different backgrounds with different pixel sizes, was simulated. PET images were analyzed to determine the relationship between the threshold and the factors mentioned above. Finally, the simulation results were verified by phantom experiments.ResultsThe threshold decreased sharply with D for D < 2 FWHM, reached the minimum of 31% at D = 2 FWHM and then increased slowly, and it tended to constant for D > 8 FWHM. The threshold decreased with FWHM for FWHM < D/2, reached a minimum at FWHM = D/2, and then increased. The threshold increased with pixel size for D ≤ FWHM and decreased for D > FWHM. The threshold was independent of the background. The relationship between the threshold and its influencing factors was expressed as a formula. The results of the phantom verification indicated that the error of the target volume delineation that was calculated by the formula was less than 9%.ConclusionsThe threshold changes with tumor size, resolution of the PET system and pixel size according to certain rules. The formula to calculate the threshold could provide a method to estimate threshold to outline the radiotherapy target (tumor).

Raman spectroscopic analysis was performed on columbite-(Mn) samples from a variety of previously studied rare-element pegmatites in Xinjiang, China, including the Jing'erquan No. 1 spodumene-subtype, Dakalasu No. 1 beryl–columbite-subtype and Kalu'an spodumene-subtype pegmatites, to quantify the relationship between the degree of metamictisation of columbite and Raman spectra. For all of the analysed columbites-(Mn), the position (p) and the full width at half maximum (FWHM) of the strongest band, A1g vibration mode related to the Nb/Ta–O bond, in the Raman spectra have a negative correlation. Combined with previously determined U–Pb isotopic data and major–minor-element data for the columbites-(Mn), the degree of metamictisation was quantified using the alpha-decay dose (D) and displacement per atom (dpa), both of which were corrected for effects caused by annealing. The results demonstrate that the columbite-(Mn) from Jing'erquan and Kalu'an are very crystalline, whereas those from Dakalasu are transitional between crystalline and amorphous stages. The main factor influencing the key parameters, i.e. band position and FWHM, of the strongest Raman band of columbite-(Mn) is metamictisation caused by radiation damage, whereas composition and crystal orientation have limited influence. A set of equations are established to quantify the degree of metamictisation of columbite using the band position and the full width at half maximum: FWHM = 8.309 × ln(aD) + 30.11 (R2 = 0.9861); p = –5.187 × ln(aD) + 867.09 (R2 = 0.966); FWHM = 8.1453 × ln(adpa) + 48.425 (R2 = 0.9822); and p = –5.078 × ln(adpa) + 855.67 (R2 = 0.9594).

Technological aspects of development of pixel and strip detectors based on CdTe and CdZnTe

High-resolution pixel detectors for second generation digital mammography

CdZnTe (CZT) detectors are promising detectors, which have many good characteristics such as room temperature operation, reasonable energy resolution, high-detection efficiency to gamma rays, etc. However, energy resolution of CZT is governed by poor mobilities of charge carriers. Many researchers have tried to solve this problem. Among them, a clustering method has been recently proposed which is based on a digital signal processing of preamplifier output waveforms. In this method, we can classify signals according to their shapes and independently treat different shapes. In this paper, we report a new clustering algorithm with adaptive shaping time. The obtained energy resolution for /sup 137/Cs was improved to 5.4-keV full width at half maximum (FWHM) by applying this method.

Characteristics comparison between GaN epilayers grown on patterned and unpatterned sapphire substrate (0 0 0 1)

PurposeThis study proposes an objective method of quantifying the vortex flow in pulmonary arteries to compare the duration of its presence before and after balloon pulmonary angioplasty (BPA) in patients with chronic thromboembolic pulmonary hypertension (CTEPH). MethodsThoracic 4D-flow magnetic resonance imaging was performed in 28 CTEPH patients before and after BPA. Planes were set in pulmonary arteries to evaluate volume flow rate (VFR), the duration, and area of backward flow in the pulmonary trunk, which is a component of the vortex flow. The full width at half maximum (FWHM) of the peak of the time course of VFR of backward flow was assessed to quantify the duration of the vortical flow. ResultsAlthough overall flow patterns after BPA appeared to be the same as the one before BPA, significant decreases in the FWHM, area, and VFR of the backward flow after BPA were found (FWHM: before, 1.88 × 10−1 ± 1.51 × 10−2 [cardiac cycle] vs. after, 1.65 × 10−1 ± 1.86 × 10−2 [cardiac cycle]; area ratio: before, 2.67 × 10−1 ± 1.30 × 10−2 vs. after, 2.38 × 10−1 ± 1.31 × 10−2; VFR: before, 13.6 ± 2.21 [mL/s] vs. after, 11.3 ± 2.36 [mL/s]). ConclusionBPA promoted significant decreases in the FWHM, area, and VFR of backward flow in the pulmonary trunk, thereby facilitating efficient blood transport. The tendencies for these changes were to be larger for cases where BPA more greatly decreased the pressure. The results suggest that the FWHM, area, and VFR are useful indicators for the noninvasive evaluation of the therapeutic effects of BPA.

This paper presents a study of possible models to describe the relation between the scintillation light point-of-origin and the measured photo detector pixel signals in monolithic scintillation crystals. From these models the X, Y and depth of interaction (DOI) coordinates can be estimated simultaneously by nonlinear least-square fitting. The method depends only on the information embedded in the signals of individual events, and therefore does not need any prior position training or calibration. Three possible distributions of the light sources were evaluated: an exact solid-angle-based distribution, an approximate solid-angle distribution and an extended approximate solid-angle-based distribution which includes internal reflection at side and bottom surfaces. The performance of the general model using these three distributions was studied using Monte Carlo simulated data of a 20 × 20 × 10 mm lutetium oxyorthosilicate (Lu2SiO5 or LSO) block read out by 2 Hamamatsu S8550 avalanche photo diode arrays. The approximate solid-angle-based model had the best compromise between resolution and simplicity. This model was also evaluated using experimental data by positioning a narrow 1.2 mm full width at half maximum (FWHM) beam of 511 keV photons at known positions on the 20 × 20 × 10 mm LSO block. An average intrinsic resolution in the X-direction of 1.4 mm FWHM was obtained for positions covering the complete block. The intrinsic DOI resolution was estimated at 2.6 mm FWHM.

Epitaxial thin GaN films (∼60 nm) have been grown on a-plane sapphire substrates at different growth temperatures (500–700 °C) using laser molecular beam epitaxy (LMBE). The effect of growth temperatures on the structural and optical properties of GaN layers grown on low temperature (LT) GaN buffer on prenitridated a-sapphire have been studied systematically. The in situ reflection high energy electron diffraction pattern revealed the three-dimensional epitaxial growth of GaN films on a-sapphire under the adopted growth conditions. The full width at half maximum (FWHM) value of x-ray rocking curves (XRCs) along GaN (0002) and (10-12) planes decreases with increasing growth temperature. The FWHM values of (0002) and (10-12) XRC for the 700 °C grown GaN film are 1.09° and 1.08°, respectively. Atomic force microscopy characterization showed that the grain size of GaN increases from 30–60 to 70–125 nm with the increase in growth temperature as GaN coalescence time is shorter at high temperature. The refractive index value for the dense GaN film grown at 600 °C is obtained to be ∼2.19 at the wavelength of 632 nm as deduced by spectroscopic ellipsometry. Photoluminescence spectroscopy confirmed that the epitaxial GaN layers grown on a-sapphire at 600–700 °C possess near band edge emission at ∼3.39 eV, close to bulk GaN. The GaN growth at 700 °C without a buffer still produced films with better crystalline and optical properties, but their surface morphology and coverage were inferior to those of the films grown with LT buffer. The results show that the growth temperature strongly influences the structural and optical quality of LMBE grown epitaxial GaN thin films on a-plane sapphire, and a growth temperature of &amp;gt;600 °C is necessary to achieve good quality GaN films.

In this paper, characterization of the fiber Bragg grating (FBG) based on grating profile and apodization type has done. The FBG parameters considered here are grating length, grating profile and apodization type. The characteristics of FBG include reflectivity, full width at half maximum (FWHM) and side lobe power. The FBGs having high reflectivity, low FWHM and side lobe power are required for the sensing applications. A GratingMOD simulation tool based on a coupled mode theory and a transfer matrix method is used for the characterization of FBG. The effect of FBG parameters, grating length, grating profile and apodization on the characteristics of FBG is studied. The FBG parameters, grating length, grating profile and apodization type are optimized for the sensing applications. The FBG having grating length, 5 mm, sinusoidal profile and apodization type is optimized.In this paper, characterization of the fiber Bragg grating (FBG) based on grating profile and apodization type has done. The FBG parameters considered here are grating length, grating profile and apodization type. The characteristics of FBG include reflectivity, full width at half maximum (FWHM) and side lobe power. The FBGs having high reflectivity, low FWHM and side lobe power are required for the sensing applications. A GratingMOD simulation tool based on a coupled mode theory and a transfer matrix method is used for the characterization of FBG. The effect of FBG parameters, grating length, grating profile and apodization on the characteristics of FBG is studied. The FBG parameters, grating length, grating profile and apodization type are optimized for the sensing applications. The FBG having grating length, 5 mm, sinusoidal profile and apodization type is optimized.

An experimental study on chemical shifts and X-ray intensity ratios

Introduction: In yttrium-90 imaging, image quality is highly dependent on the selection of energy window and collimator design becausetheY-90 bremsstrahlung photons have a continuous and broad energy distribution. The current study aimed to optimize the bremsstrahlung energy window setting and collimator for the improvement of both resolution and sensitivity. Material and Methods: In the present study, simulation of medical imaging nuclear detectors (SIMIND) Monte Carlo program was used to simulate Siemens Medical System Symbia. The SIMIND was utilized to generate the Y-90 bremsstrahlung single-photon emission computed tomography (SPECT) projection of the point source. Six energy windows settings and two collimators denoting medium energy and high energy were used in order to assess the effect of the energy window on the resolution. Results: The experimental measurements and simulation results showed a similar pattern in the point spread functions with the energy window. The simulation data indicated that the geometric component reached 73%for the energy window within the range of51-120keVusingthe high-energy (HE) collimator. In addition, the obtained results showed that the full width at half maximum (FWHM) and full width at tenth maximum (FWTM)(FWHM=7mm and FWTM=35mm)were higher in this window in comparison to those reported for other windows. Conclusion: According to the obtained results of the present study, the optimal energy window for Y-90 bremsstrahlung SPECT imaging was within the range of 51-120 keV. The obtained optimal energy window and optimal HE collimator had the potential to improve the image resolution and sensitivity of Y-90 SPECT images

This paper experimentally shows how the center wavelength and spectral power distribution (SPD) of displayed color is related to chromostereopsis. Chromostereopsis - a visual illusion whereby the impression of depth is conveyed in two-dimensional color images - can be applied to glassless binocular stereopsis by controlling color saturation even when a commercial liquid crystal display (LCD) is used to display a two-dimensional image. We conducted evaluations of stereoscopic visual effects among monochrome images using an LCD panel and three monochrome backlights whose SPD had a single peak. The center wavelength and full width at half maximum (FWHM) of the SPD for the backlight were varied. The experimental results show that chromostereopsis does not occur strongly when the FWHM of a backlight is larger than 100 nm. We also suggest that the impression of the depth for monochrome images depends on the center wavelength and FWHM of the color, which indicates chromostereopsis can be expressed by the chromatic aberration.

Neutron stimulated emission computed tomography (NSECT) uses photons emitted from inelastic scattering of neutrons with biological objects to quantify the elemental composition of the object and reconstruct an image. Previously, NSECT has been used to detect liver and breast disease in vivo. In this study, we investigated the capability of imaging brain tumors using NSECT. A GEANT4 simulation was developed to model the brain, skull, and a spherical lesion. Images corresponding to phosphorus, sulfur, and iron (both individually and as combinations) were generated from a simulated NSECT scan. Signal-to-noise ratio (SNR) and full width at half maximum (FWHM) in the tumor region were calculated to assess image accuracy (FWHM ≤ 5% error) and detectability (SNR > 2.5). The scan with the least amount of absorbed dose required to achieve these criteria was defined as the optimal acquisition. The lowest dose value was found to be 0.0837 cGy for a 2 cm brain tumor imaged using a single germanium detector, 6 equally spaced angles from 0 to 180 degrees, 20 projections per angle and 0.5 million neutrons per projection. The SNR for the combination of phosphorus, sulfur, and iron with the given condition was 9.288 and FWHM for the iron was 15 mm with the given condition. In conclusion, NSECT is capable of imaging a 2 cm brain tumor using the elemental composition of phosphorus, sulfur, and iron with reasonable SNR, FWHM and radiation dose.

Multileaf-collimator (MLC) defined small fields in radiotherapy are used in high dose, ultra-conformal techniques such as stereotactic radiotherapy and stereotactic radiosurgery. Proximity to critical structures and irreversible damage arising from inaccurate delivery mean that correct positioning of the MLC system is of the utmost importance. Some of the existing techniques for MLC positioning quality assurance make use of electronic portal imaging device (EPID) images. However, conventional collimation verification algorithms based on the full width at half maximum (FWHM) fail when applied to small field images acquired by an EPID due to overlapping aperture penumbrae, lateral electron disequilibrium and radiation source occlusion. The objective of this study was to investigate sub-pixel edge detection and other techniques with the aim of developing an automatic and autonomous EPID-based method suitable for MLC positional verification of small static fields with arbitrary shapes. Methods investigated included derivative interpolation, Laplacian of Gaussian (LoG) and an algorithm based on the partial area effect hypothesis. None of these methods were found to be suitable for MLC positioning verification in small field conditions. A method is proposed which uses a manufacturer-specific empirically modified FWHM algorithm which shows improvement over the conventional techniques in the small field size range. With a measured mean absolute difference from planned position for Varian linacs of 0.01 ± 0.26mm, compared with the erroneous FWHM value of 0.70 ± 0.51mm. For Elekta linacs the proposed algorithm returned 0.26 ± 0.25mm, in contrast to the FWHM result of 1.79 ± 1.07mm.