Gamma-ray Imaging Techniques Research Articles

Simulation of a gamma-ray imaging technique using detector response patterns

We introduce a novel gamma-ray imaging technique that uses detector response patterns. This method employs multiple shielding cubes randomly positioned in a three-dimensional configuration. Within the volume defined by these cubes, a unique gamma-ray flux pattern is formed based on the incidence direction of the gamma rays. This pattern can be measured using the responses of several scintillator cubes. By pre-measuring the detector response pattern and incidence direction of the gamma rays, the incidence direction can be estimated using an unfolding technique. Simulations were performed using a 137Cs point source. Our results show that a 10 MBq 137Cs source, located 3 m away from the imager, can be imaged with an angular resolution close to 10°. These findings suggest that our new method is comparable to existing gamma-ray imaging techniques. Potential applications of this imaging method include nuclear power plant decommissioning, nuclear medicine, security, and astronomy.

Novel applications of state-of-the-art gamma-ray imaging technique: from nuclear decommissioning and radioprotection to radiological characterization and safeguards

Novel applications of state-of-the-art gamma-ray imaging technique: from nuclear decommissioning and radioprotection to radiological characterization and safeguards

Production and synthesis of a novel 191Pt-labeled platinum complex and evaluation of its biodistribution in healthy mice

We previously reported that our sugar-conjugated platinum complex (cis-dichloro [(2-fluoro-α-d-glucopylanosidyl) propane-1,3-diamine] platinum: FGC-Pt) has low toxicity and tumor growth inhibitory effect comparable to that of cisplatin. We focused on radioactive Pt isotopes in order to analyze the kinetics of FGC-Pt using gamma-ray imaging techniques, assuming that FGC-Pt could be used for chemotherapy in the future. Therefore, in this study, we aimed to develop a non-invasive method to analyze the biodistribution of FGC-Pt using 191Pt-labeled FGC-Pt ([191Pt]FGC-Pt).191Pt was produced via the (n,2n) reaction induced by accelerator neutrons. [191Pt]FGC-Pt was prepared using two different methods. In the first method, [191Pt]FGC-Pt (method A) was obtained through the accelerator neutron irradiation of FGC-Pt. In the second method, [191Pt]FGC-Pt (method B) was synthesized using [191Pt]K2PtCl4, which was obtained by the accelerator neutron irradiation of K2PtCl4. Highly purified [191Pt]FGC-Pt was obtained using the latter method, which suggests that the synthetic method using a 191Pt-labeled platinum reagent is suitable for the radioactivation of platinum complexes.We also aimed to investigate whether a significant correlation existed between the biodistribution of FGC-Pt and [191Pt]FGC-Pt in healthy mice 24 h after tail vein administration. FGC-Pt and [191Pt]FGC-Pt were similarly distributed in healthy mice, with a higher accumulation in the liver and kidney 24 h post injection. In addition, a significant correlation (p < 0.05, r = 0.92) between the 191Pt radioactivity concentration (%ID/g (gamma counter)) and platinum concentration (%ID/g (ICP-MS)) was observed in 13 organs. These results suggest that 191Pt-labeled compounds, synthesized using radioactive platinum reagents, can be used to confirm the biodistribution of platinum compounds. Our study on the biodistribution of [191Pt]FGC-Pt is expected to contribute to the development of novel platinum-based drugs in the future.

Compton imaging for enhanced sensitivity (n,γ) cross section TOF experiments: Status and prospects

Radiative neutron-capture cross sections are of pivotal importance in many fields such as nucle-osynthesis studies or innovative reactor technologies. A large number of isotopes have been measured with high accuracy, but there are still a large number of relevant isotopes whose cross sections could not be experimentally determined yet, at least with sufficient accuracy and completeness, owing to limitations in detection techniques, sample production methods or in the facilities themselves. In the context of the HYMNS (High-sensitivitY Measurements of key stellar Nucleo-Synthesis reactions) project over the last six years we have developed a novel detection technique aimed at background suppression in radiative neutron-capture time-of-flight measurements. This new technique utilizes a complex detection set-up based on position-sensitive radiation-detectors deployed in a Compton-camera array configuration. The latter enables to implement gamma-ray imaging techniques, which help to disentangle true capture events arising from the sample under study and contaminant background events from the surroundings. A summary on the main developments is given in this contribution together with an update on recent experiments at CERN n_TOF and an outlook on future steps.

First in-beam tests on simultaneous PET and Compton imaging aimed at quasi-real-time range verification in hadron therapy

Hadron therapy with protons has advantages with respect to conventional radiotherapy because of the maximization of the dose at the Bragg peak. As a drawback, and because of different systematic uncertainty sources, a quasi-real time monitoring for the proton range verification is required to reduce safety margins. In this respect, two gamma-ray imaging techniques are pursued: prompt gamma-ray monitoring and positron-annihilation tomography (PET). The promising prompt gamma-ray monitoring requires detection systems with large detection efficiency, high time resolution, compactness, fast response, low sensitivity to neutron-induced backgrounds and powerful image reconstruction capabilities. On the other hand, in-beam PET surveys require additionally good γ-ray position reconstruction resolution. In this contribution we show that, to a large extent, both approaches can be simultaneously accomplished by using an array of Compton cameras conveniently arranged around the target volume. Here we demonstrate experimentally the suitability of such an array, named i-TED, for PG monitoring in ion-range monitoring during Hadron Therapy, in-beam PET survey and β+ production yield measurements capability. Furthermore, with the use of GPUs, a quasi-real time PG monitoring and in-beam PET can be achieved.

Design and Implementation of a Portable High-Performance Gamma-Ray Camera

With the growing number of facilities applying nuclear technology in China, a high-performance portable gamma-ray camera that uses well-developed gamma-ray imaging techniques is increasingly required. To fulfill this requirement, we have designed a camera using a self-supported mask, a CsI(Na) array coupled to a silicon photomultiplier (SiPM) rather than the traditional position-sensitive photomultiplier tube (PSPMT) and a highly integrated readout circuit. In addition, with the elimination of multi-Compton events in the crystal array based on a row/column readout circuit incorporated into the data processing method, the peak-to-valley ratio of the flood source map and the image quality quantified by the contrast-to-noise ratio index of <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">137</sup> Cs were improved significantly by 25.8% from 9.8 to 12.3 and 14.8% from 38.7 to 45.0, respectively.

A new contrast-to-noise ratio for image quality characterization of a coded-aperture γ camera

The gamma-ray imaging technique was developed and is widely used in several nuclear engineering fields. Specifically, compared with the traditional point-by-point radiation detector, the coded-aperture gamma camera has advantages of a wide field of view, high angular resolution, and high efficiency. Several methods for characterizing image quality, including the figure of merit (FOM) method and the contrast-to-noise ratio (CNR) method, were assessed and developed. These methods have their respective drawbacks depending on the circumstances. The FOM lacks reliability in exhibiting the impact of background noise fluctuation on the purity of a real image. The CNR characterizes image quality with inconsistent sensitivity while the source moves along the X and Y directions. Therefore, a new CNR method was proposed to achieve better performance and greater consistency in real imaging. With our coded-aperture imaging system developed in the laboratory, we performed simulations within the MATLAB and Geant4 platforms and real imaging experiments to analyze and compare images and the results of these three characterization methods. The results show that the new CNR method is reliable and practical in regard to real imaging performance.

Single pixel compressive gamma-ray imaging with randomly encoded masks

We report on the development and demonstration of a single pixel spectroscopic gamma-ray imaging concept based on the principles of compressed sensing. Compressive gamma-ray images were obtained for both point sources and complex extended sources. The reconstruction of images at different photon energies allowed the spatial mapping of different radionuclides. When compared to traditional aperture based gamma-ray imaging techniques, the point source images were generated with ten times fewer measurements. More complex extended source images were generated with up to three times fewer measurements. Gamma-ray imaging techniques designed around the principles of compressed sensing have the potential to exploit the sparsity typically found in gamma-ray images, leading to a new class of fast and low cost imaging systems.

Quantitative analysis of prompt gamma ray imaging during proton boron fusion therapy according to boron concentration

The purpose of this study is to evaluate the prompt gamma ray imaging technique according to the clinical boron concentration range during proton boron fusion therapy (PBFT). To acquire a prompt gamma ray image from 32 projections, we simulated four head single photon emission computed tomography and a proton beam nozzle using a Monte Carlo simulation. We used modified ordered subset expectation maximization reconstruction algorithm with a graphic processing unit for fast image acquisition. Boron concentration was set as 20 to 100 μg at intervals of 20 μg. For quantitative analysis of the prompt gamma ray image, we acquired an image profile drawn through two boron uptake regions (BURs) and calculated the contrast value, signal-to-noise ratio (SNR), and difference between the physical target volume and volume of the prompt gamma ray image. The relative counts of prompt gamma rays were noticeably increased with increasing boron concentration. Although the intensities on the image profiles showed a similar tendency according to the boron concentration, the SNR and contrast value were improved with increasing boron concentration. This study suggests that a tumor monitoring technique using prompt gamma ray detection can be clinically applicable even if the boron concentration is relatively low.

A Filtered Back-Projection Algorithm for 4π Compton Camera Data

Compton imaging is a gamma-ray imaging technique useful for photons with energies in the range of a hundred keV to several MeV. Measuring gamma rays with a Compton camera results in cone data that needs to be mathematically inverted to determine the incident flux distribution. In the past, filtered back-projection solutions for Compton telescope data required sums of spherical harmonics or stereographically mapping the back-projection, which can result in imaging artifacts. We present a solution to this inversion problem that removes these complexities by embedding the 2-D directional image on the surface of a sphere ${S^2}$ into ${R^3}$ where it is easily solvable. In this manner we relate 2-D Compton $4\pi $ imaging to the 3-D Radon transform, which has known solutions. To accomplish this, the cone data is converted to planar data. Additionally we show how the planar geometry can be used to produce a computationally efficient implementation. This reconstruction is demonstrated with a two-plane, double-sided strip, HPGe Compton camera.

Performance evaluation of a small CZT pixelated semiconductor gamma camera system with a newly designed stack-up parallel-hole collimator

Gamma ray imaging techniques that use a cadmium zinc telluride (CZT) or cadmium telluride (CdTe) pixelated semiconductor detectors have rapidly gained popularity as a key tool for nuclear medicine research. By using a pinhole collimator with a pixelated semiconductor gamma camera system, better spatial resolution can be achieved. However, this improvement in spatial resolution is accomplished with a decrease in the sensitivity due to the small collimator hole diameter. Furthermore, few studies have been conducted for novel parallel-hole collimator geometric designs with pixelated semiconductor gamma camera systems. A gamma camera system which combines a CZT pixelated semiconductor detector with a newly designed stack-up parallel-hole collimator was developed and evaluated. The eValuator-2500 CZT pixelated semiconductor detector (eV product, Saxonburg, PA) was selected for the gamma camera system. This detector consisted of a row of four CZT crystals of 12.8mm in length with 3mm in thickness. The proposed parallel-hole collimator consists of two layers. The upper layer results in a fourfold increase in hole size compared to a matched square hole parallel-hole collimator with an equal hole and pixel size, while the lower layer also consisted of fourfold holes size and pretty acts as a matched square hole parallel-hole collimator. The overlap ratios of these collimators were 1:1, 1:2, 2:1, 1:5, and 5:1. These collimators were mounted on the eValuator-2500 CZT pixelated semiconductor detector. The basic performance of the imaging system was measured for a 57Co gamma source (122keV). The measured averages of sensitivity and spatial resolution varied depending on the overlap ratios of the proposed parallel-hole collimator and source-to-collimator distances. One advantage of our system is the use of stacked collimators that can select the best combination of system sensitivity and spatial resolution. With low counts, we can select a high sensitivity collimator with a 1:5 or 5:1 overlap ratio. For high counts, a 1:1 overlap ratio collimator combination is the best selection at this time. In addition, if a higher system spatial resolution is needed, we can increase the spatial resolution by stacking additional thin collimators. These results demonstrate that the developed small pixelated semiconductor gamma camera system has high potential as an effective instrument for low energy gamma ray imaging.

Three-Dimensional Compton Imaging Using List-Mode Maximum Likelihood Expectation Maximization

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Compton imaging is a gamma ray imaging technique that has many possible applications including homeland security and medical imaging. Using the Compton scattering formula the origin of a scattered <formula formulatype="inline"> <tex Notation="TeX">$\gamma$</tex></formula>-ray can be localized to a point on the surface of a cone using a minimum of two position and energy measurements. List-mode Maximum likelihood expectation maximization (MLEM) is an iterative statistical algorithm that makes successive approximations to the most probable source distribution that would have led to the observed data. Conventional MLEM is often performed in two dimensions, which still requires knowledge of the source-to-detector distance. We propose iteration over all three spatial dimensions in order to maximize the probability in three-dimensional space. This paper reports on the development of a three-dimensional MLEM (3DMLEM) algorithm to reconstruct images from a Compton imager in three dimensions for single, multiple and line sources. Several techniques for reducing convergence times are also discussed. </para>

Photon-induced positron annihilation radiation (PIPAR) — A novel gamma-ray imaging technique for radiographically dense materials

A discussion is presented of some fundamental limitations of the Compton back-scattering technique for imaging radiographically dense materials. These include the low probability of Compton back-scattering for high energy (> 1 MeV) photons, the low energy (and hence high attenuation) of the scattered radiation (≤ 225 keV) at large angles of scattering and the invariable presence of a large multiple scattering background superimposed on the single scattering component. A novel radiographic technique—photon-induced positron annihilation radiation (PIPAR)—is described and is shown to avoid the above limitations. It thus extends significantly the depth range of materials which may be investigated with gamma rays in the reflection geometry. Preliminary experimental results showing the feasibility of PIPAR imaging are presented here for the first time. These were obtained with megavoltage radiation from a linear accelerator exciting positrons in elemental samples through the pair production effect. The 511 keV annihilation line was extracted from the back-scattered radiation using a plastic scintillator detector and a difference filter technique. The experimental arrangement is described and potential applications are briefly discussed.

A new approach to position sensitive gamma-ray spectrometry

A new type of gamma-ray imaging technique which employs digital focusing optics is proposed. This involves producing a real and diminished image of an interaction, from a small fraction of the scintillation photons, by means of a converging lens and an image intensifier/optical detector assembly. The remaining photons, which form the majority, are 'channelled' by total inertial reflection on the crystal surfaces. They are then collected by light pipes and photomultiplier tubes coupled to the edge of the crystal. Thus pulse height and positional information are both retrieved. Our calculations in the energy range 100-700 keV indicate that with a small degradation in energy resolution (5-10%), a spatial resolution of 1-1.5 mm is well within the capabilities of such an approach. A feasibility study using 28 keV X-rays and a 2 mm thick NaI(Tl) crystal ascertain the role of a lens system in the improvement of image resolution.

Specific [formula omitted] binding of 77Br- [formula omitted]-bromospiroperidol in rat brain: A potential tool for gamma ray imaging

The binding of the gamma labeled neuroleptic, 77Br- p -bromosprioperidol, in the rat brain was examined in vivo . This binding parallels the binding of 3H-spiroperidol, in that binding is especially high in dopaminergically innervated areas, is saturable, and is displaced by high doses of unlabeled spiroperidol (1–5). Thus, 77Br- p -bromospiroperidol is a suitable ligand for use in gamma ray imaging techniques for in vivo monitoring of receptor binding.