Neutron Stimulated Emission Computed Tomography Research Articles

A comparative study of neutron stimulated emission computed tomography based on D-D/D-T neutron source

In this paper, we investigated the applications of D-D and D-T neutron sources in Neutron Stimulated Emission Computed Tomography (NSECT). Four NSECT models were established, including the TiT/TiD targets to generate neutron sources and the presence/absence of iron balls in water phantom to mimic tumors. NSECT system was simulated by using MCNP software, in which the D-D and D-T neutron sources were generated, collimated, transported, and recorded. We studied flux distributions and typical spectrum of both outgoing neutrons and the characteristic gamma-rays for D-D and D-T NSECT. Results show that the optimized NSECT gamma-ray detector locations will be in the direction from 43.6° to 50.9° along the neutron beam propagation direction. The best NSECT gamma-ray detector locations for D-D and D-T NSECT are slightly different, but in both cases the detectors should be aligned in the direction from 43.6° to 50.9°. We found the characteristic peaks of 56Fe and 16O from the energy spectrum of characteristic gamma-ray. This demonstrates that NSECT has the ability to identify elements, which would be very useful in tracking the treatment process and in studying the molecular process of living body (including human-beings). This study gives a comprehensive understanding on the selection of neutron sources and the placement of gamma-ray detectors in NSECT applications.

MCNP simulation study of neutron stimulated emission computed tomography system based on D-T neutron source

In this paper, Neutron Stimulated Emission Computed Tomography (NSECT) system was simulated using MCNP software, including the selection of Neutron source, the design of collimating shielding system, the setting of shielding wall and target body, and the arrangement of detector. The 14 MeV D-T Neutron source created by the Neutron generator located at Lanzhou University, was delivered, collimated and hit a cylindrical water phantom. We recorded and won the flux distribution and typical spectrum of characteristic gamma-ray and outgoing Neutron. This study has a guiding role for the detector layout during NSECT imaging experiment. From the flux distribution and typical spectrum of characteristic gamma-ray and outgoing Neutron, it is clearly shown that the position of NSECT imaging detector should be placed from 43.6° to 50.9° along the Neutron beam propagation direction. The optimized direction would be in 48.5°. From the characteristic gamma-ray spectrum, we found the characteristic peaks of 16O. This result suggests that NSECT has the ability to identify elements and to determine the element concentrations. This work also proved that NSECT could be applied for the early diagnosis of cancer and the checking of hiding explosives and drugs.

SU‐G‐IeP4‐04: DD‐Neutron Source Collimation for Neutron Stimulated Emission Computed Tomography: A Monte Carlo Simulation Study

Purpose:To optimize collimation and shielding for a deuterium‐deuterium (DD) neutron generator for an inexpensive and compact clinical neutron imaging system. The envisioned application is cancer diagnosis through Neutron Stimulated Emission Computed Tomography (NSECT).Methods:Collimator designs were tested with an isotropic 2.5 MeV neutron source through GEANT4 simulations. The collimator is a 52×52×52 cm3 polyethylene block coupled with a 1 cm lead sheet in sequence. Composite opening was modeled into the collimator to permit passage of neutrons. The opening varied in shape (cylindrical vs. tapered), size (1–5 cm source‐side and target‐side openings) and aperture placements (13–39 cm from source‐side). Spatial and energy distribution of neutrons and gammas were tracked from each collimator design. Parameters analyzed were primary beam width (FWHM), divergence, and efficiency (percent transmission) for different configurations of the collimator. Select resultant outputs were then used for simulated NSECT imaging of a virtual breast phantom containing a 2.5 cm diameter tumor to assess the effect of the collimator on spatial resolution, noise, and scan time. Finally, composite shielding enclosure made of polyethylene and lead was designed and evaluated to block 99.99% of neutron and gamma radiation generated in the system.Results:Analysis of primary beam indicated the beam‐width is linear to the aperture size. Increasing source‐side opening allowed at least 20% more neutron throughput for all designs relative to the cylindrical openings. Maximum throughput for all designs was 364% relative to cylindrical openings.Conclusion:The work indicates potential for collimating and shielding a DD neutron generator for use in a clinical NSECT system. The proposed collimator designs produced a well‐defined collimated neutron beam that can be used to image samples of interest with millimeter resolution. Balance in output efficiency, noise reduction, and scan time should be considered to determine the optimal design for specific NSECT applications.

TH-AB-204-06: Using Associated Particle Imaging and Time-Of-Flight Spectroscopy for Eliminating Tomographic Imaging for NSECT: A Simulation Study

Purpose: To evaluate feasibility of associated particle time-of-flight (AP-TOF) neutron imaging with a fan beam source using simulations in GEANT4 and determine its effect on improving scan time in Neutron Stimulated Emission Computed Tomography (NSECT). Previous NSECT experiments have used a pencil-beam, raster-scanned through the entire volume of interest with long scan durations. A fan beam could reduce the scan duration substantially, improving the clinical feasibility of the technique. Methods: A simulation of fast-neutron AP-TOF NSECT was developed in GEANT4. Fast neutrons that undergo inelastic scattering with elemental nuclei in the phantom lead to prompt gamma emission with energy specific to the emitting element used to identify the emitting elements. In the simulation, a 2-degree wide fan beam of 5 MeV neutrons was swept across a prone water breast phantom containing a cancerous lesion. For each neutron emitted, an alpha particle was coincidently emitted in the opposite direction and was used to determine the neutron's flight path. The neutron's time of flight was used to determine the depth of interaction along the flight path. Images were reconstructed for each element in the breast phantom to assess location accuracy with AP-TOF imaging. Results: Images reconstructed from H and Fe showed strong agreement with the locations and geometry of the breast (H-2224 keV) and lesion (Fe-847 keV), with <3% error between the measured and actual locations. Uncertainties in the lateral and axial (i.e., along the beam) directions were determined to arise from uncertainty in the source aperture opening when determining alpha particle location (lateral: 1–2cm) and gamma detection time (axial: 1–2ns). Conclusion: AP-TOF neutron imaging with a pseudo-fan beam is capable of generating clinically relevant images of biological objects without the need for tomographic rotation. With appropriate detection hardware, the ability to eliminate tomographic rotation could reduce NSECT acquisition time by a factor of 8–10.

Geant4 distributed computing for compact clusters

A new technique for distribution of Geant4 processes is introduced to simplify running a simulation in a parallel environment such as a tightly coupled computer cluster. Using a new C++ class derived from the Geant4 toolkit, multiple runs forming a single simulation are managed across a local network of computers with a simple inter-node communication protocol. The class is integrated with the Geant4 toolkit and is designed to scale from a single symmetric multiprocessing (SMP) machine to compact clusters ranging in size from tens to thousands of nodes. User designed ‘work tickets’ are distributed to clients using a client–server work flow model to specify the parameters for each individual run of the simulation.The new g4DistributedRunManager class was developed and well tested in the course of our Neutron Stimulated Emission Computed Tomography (NSECT) experiments. It will be useful for anyone running Geant4 for large discrete data sets such as covering a range of angles in computed tomography, calculating dose delivery with multiple fractions or simply speeding the through-put of a single model.

3D element imaging using NSECT for the detection of renal cancer: a simulation study in MCNP

This work describes a simulation study investigating the application of neutron stimulated emission computed tomography (NSECT) for noninvasive 3D imaging of renal cancer in vivo. Using MCNP5 simulations, we describe a method of diagnosing renal cancer in the body by mapping the 3D distribution of elements present in tumors using the NSECT technique. A human phantom containing the kidneys and other major organs was modeled in MCNP5. The element composition of each organ was based on values reported in literature. The two kidneys were modeled to contain elements reported in renal cell carcinoma (RCC) and healthy kidney tissue. Simulated NSECT scans were executed to determine the 3D element distribution of the phantom body. Elements specific to RCC and healthy kidney tissue were then analyzed to identify the locations of the diseased and healthy kidneys and generate tomographic images of the tumor. The extent of the RCC lesion inside the kidney was determined using 3D volume rendering. A similar procedure was used to generate images of each individual organ in the body. Six isotopes were studied in this work—32S, 12C, 23Na, 14N, 31P and 39K. The results demonstrated that through a single NSECT scan performed in vivo, it is possible to identify the location of the kidneys and other organs within the body, determine the extent of the tumor within the organ, and to quantify the differences between cancer and healthy tissue-related isotopes with p ≤ 0.05. All of the images demonstrated appropriate concentration changes between the organs, with some discrepancy observed in 31P, 39K and 23Na. The discrepancies were likely due to the low concentration of the elements in the tissue that were below the current detection sensitivity of the NSECT technique.

Quantitative Assessment of Lesion Detection Accuracy, Resolution, and Reconstruction Algorithms in Neutron Stimulated Emission Computed Tomography

We present a quantitative analysis of the image quality obtained using filtered back-projection (FBP) with Ram-Lak filtering and maximum likelihood-expectation maximization (ML-EM)-with no post-reconstruction filtering in either case-in neutron stimulated emission computed tomography (NSECT) imaging using Monte Carlo simulations in the context of clinically relevant models of liver iron overload. The ratios of pixel intensities for several regions of interest and lesion shape detection using an active-contours segmentation algorithm are assessed for accuracy across different scanning configurations and reconstruction algorithms. The modulation transfer functions (MTFs) are also computed for the cases under study and are applied to determine a minimum detectable lesion spacing as a form of sensitivity analysis. The accuracy of NSECT imaging in measuring relative tissue concentration is presented for simulated clinical liver cases. When using the 15th iteration, ML-EM provides at least 25% better resolution than FBP and proves to be highly robust under low-signal high-noise conditions prevalent in NSECT. However, FBP gives more accurate lesion pixel intensity ratios and size estimates in some cases; due to advantages provided by both reconstruction algorithms, it is worth exploring the development of an algorithm that is a hybrid of the two. We also show that NSECT imaging can be used to accurately detect 3-cm lesions in backgrounds that are a significant fraction (one-quarter) of the concentration of the lesion, down to a 4-cm spacing between lesions.

Sensitivity analysis for liver iron measurement through neutron stimulated emission computed tomography: a Monte Carlo study in GEANT4

Neutron stimulated emission computed tomography (NSECT) is being developed as a non-invasive imaging modality to detect and quantify iron overload in the human liver. NSECT uses gamma photons emitted by the inelastic interaction between monochromatic fast neutrons and iron nuclei in the body to detect and quantify the disease. Previous simulated and physical experiments with phantoms have shown that NSECT has the potential to accurately diagnose iron overload with reasonable levels of radiation dose. In this work, we describe the results of a simulation study conducted to determine the sensitivity of the NSECT system for hepatic iron quantification in patients of different sizes. A GEANT4 simulation of the NSECT system was developed with a human liver and two torso sizes corresponding to small and large patients. The iron concentration in the liver ranged between 0.5 and 20 mg g−1, corresponding to clinically reported iron levels in iron-overloaded patients. High-purity germanium gamma detectors were simulated to detect the emitted gamma spectra, which were background corrected using suitable water phantoms and analyzed to determine the minimum detectable level (MDL) of iron and the sensitivity of the NSECT system. These analyses indicate that for a small patient (torso major axis = 30 cm) the MDL is 0.5 mg g−1 and sensitivity is ∼13 ± 2 Fe counts/mg/mSv and for a large patient (torso major axis = 40 cm) the values are 1 mg g−1 and ∼5 ± 1 Fe counts/mg/mSv, respectively. The results demonstrate that the MDL for both patient sizes lies within the clinically significant range for human iron overload.

Near-field high-energy spectroscopic gamma imaging using a rotation modulation collimator

Certain trace elements are vital to the body and elemental imbalances can be indicators of certain diseases including cancer and liver diseases. Neutron Stimulated Emission Computed Tomography (NSECT) is being developed as a spectroscopic imaging technique to non-invasively and non-destructively measure and image elemental concentrations within the body. A region of interest is illuminated via a high-energy beam of neutrons that scatter inelastically with elemental nuclei within the body. The excited nuclei then relax by emitting characteristic gamma rays. Acquiring the gamma spectrum in a tomographic manner allows not only the identification of elements, but also the formation of images representing spatial distributions of specific elements. We are developing a high-energy position-sensitive gamma camera that allows full illumination of the entire region of interest. Because current scintillation crystal based position-sensitive gamma cameras operate in too low of an energy range, we are adapting high-energy gamma imaging techniques used in space-based imaging. A high purity germanium (HPGe) detector provides high-resolution energy spectra while a rotating modulation collimator (RMC) placed in front of the detector modulates the incoming signal to provide spatial information. The purpose of this manuscript is to describe the near-field RMC geometry, which varies greatly from the infinite-focus space-based applications and how it modulates the incident gamma flux. A simple geometric model is presented and then used to reconstruct two-dimensional planar images of both simulated point sources and extended sources.

Experimental detection of iron overload in liver through neutron stimulated emission spectroscopy

Iron overload disorders have been the focus of several quantification studies involving non-invasive imaging modalities. Neutron spectroscopic techniques have demonstrated great potential in detecting iron concentrations within biological tissue. We are developing a neutron spectroscopic technique called neutron stimulated emission computed tomography (NSECT), which has the potential to diagnose iron overload in the liver at clinically acceptable patient dose levels through a non-invasive scan. The technique uses inelastic scatter interactions between atomic nuclei in the sample and incoming fast neutrons to non-invasively determine the concentration of elements in the sample. This paper discusses a non-tomographic application of NSECT investigating the feasibility of detecting elevated iron concentrations in the liver. A model of iron overload in the human body was created using bovine liver tissue housed inside a human torso phantom and was scanned with a 5 MeV pulsed beam using single-position spectroscopy. Spectra were reconstructed and analyzed with algorithms designed specifically for NSECT. Results from spectroscopic quantification indicate that NSECT can currently detect liver iron concentrations of 6 mg g−1 or higher and has the potential to detect lower concentrations by optimizing the acquisition geometry to scan a larger volume of tissue. The experiment described in this paper has two important outcomes: (i) it demonstrates that NSECT has the potential to detect clinically relevant concentrations of iron in the human body through a non-invasive scan and (ii) it provides a comparative standard to guide the design of iron overload phantoms for future NSECT liver iron quantification studies.

Neutron-stimulated emission computed tomography of a multi-element phantom

This paper describes the implementation of neutron-stimulated emission computed tomography (NSECT) for non-invasive imaging and reconstruction of a multi-element phantom. The experimental apparatus and process for acquisition of multi-spectral projection data are described along with the reconstruction algorithm and images of the two elements in the phantom. Independent tomographic reconstruction of each element of the multi-element phantom was performed successfully. This reconstruction result is the first of its kind and provides encouraging proof of concept for proposed subsequent spectroscopic tomography of biological samples using NSECT.

Neutron Stimulated Emission Computed Tomography for Diagnosis of Breast Cancer

Neutron stimulated emission computed tomography (NSECT) is being developed as a non-invasive spectroscopic imaging technique to determine element concentrations in the human body. NSECT uses a beam of fast neutrons that scatter inelastically from atomic nuclei in tissue, causing them to emit characteristic gamma photons that are detected and identified using an energy-sensitive gamma detector. By measuring the energy and number of emitted gamma photons, the system can determine the elemental composition of the target tissue. Such determination is useful in detecting several disorders in the human body that are characterized by changes in element concentration, such as breast cancer. In this paper we describe our experimental implementation of a prototype NSECT system for the diagnosis of breast cancer and present experimental results from sensitivity studies using this prototype. Results are shown from three sets of samples: (a) excised breast tissue samples with unknown element concentrations, (b) a multi-element calibration sample used for sensitivity studies, and (c) a small-animal specimen, to demonstrate detection ability from in-vivo tissue. Preliminary results show that NSECT has the potential to detect elements in breast tissue. Several elements were identified common to both benign and malignant samples, which were confirmed through neutron activation analysis (NAA). Statistically significant differences were seen for peaks at energies corresponding to 37Cl, 56Fe, 58Ni, 59Co, 79Br and 87Rb. The spectrum from the small animal specimen showed the presence of 12C from tissue, from bone, and elements 39K, 27Al, 37Cl, 56Fe, 68Zn and 25Mg. Threshold sensitivity for the four elements analyzed was found to range from 0.3 grams to 1 gram, which is higher than the microgram sensitivity required for cancer detection. Patient dose levels from NSECT were found to be comparable to those of screening mammography.

Neutron stimulated emission computed tomography: a Monte Carlo simulation approach

A Monte Carlo simulation has been developed for neutron stimulated emission computed tomography (NSECT) using the GEANT4 toolkit. NSECT is a new approach to biomedical imaging that allows spectral analysis of the elements present within the sample. In NSECT, a beam of high-energy neutrons interrogates a sample and the nuclei in the sample are stimulated to an excited state by inelastic scattering of the neutrons. The characteristic gammas emitted by the excited nuclei are captured in a spectrometer to form multi-energy spectra. Currently, a tomographic image is formed using a collimated neutron beam to define the line integral paths for the tomographic projections. These projection data are reconstructed to form a representation of the distribution of individual elements in the sample. To facilitate the development of this technique, a Monte Carlo simulation model has been constructed from the GEANT4 toolkit. This simulation includes modeling of the neutron beam source and collimation, the samples, the neutron interactions within the samples, the emission of characteristic gammas, and the detection of these gammas in a Germanium crystal. In addition, the model allows the absorbed radiation dose to be calculated for internal components of the sample. NSECT presents challenges not typically addressed in Monte Carlo modeling of high-energy physics applications. In order to address issues critical to the clinical development of NSECT, this paper will describe the GEANT4 simulation environment and three separate simulations performed to accomplish three specific aims. First, comparison of a simulation to a tomographic experiment will verify the accuracy of both the gamma energy spectra produced and the positioning of the beam relative to the sample. Second, parametric analysis of simulations performed with different user-defined variables will determine the best way to effectively model low energy neutrons in tissue, which is a concern with the high hydrogen content in biological tissue. Third, determination of the energy absorbed in tissue during neutron interrogation in order to estimate the dose. Results from these three simulation experiments demonstrate that GEANT4 is an effective simulation platform that can be used to facilitate the future development and optimization of NSECT.

Design and Development of a High-Energy Gamma Camera for Use With NSECT Imaging: Feasibility for Breast Imaging

A new spectroscopic imaging technique, neutron stimulated emission computed tomography (NSECT), is currently being developed to non-invasively and non-destructively measure and image elemental concentrations within the body. NSECT has potential for use in breast imaging as several studies have shown a link between elemental concentration and tumor status. In NSECT, a region of interest is illuminated with a high-energy (3-5 MeV) beam of neutrons that scatter inelastically with elemental nuclei within the body. The characteristic gamma rays that are emitted as the excited nuclei relax allow the identification of elements and the formation of elemental composition images. This imaging technique requires high-resolution and high-energy gamma spectroscopy; thereby eliminating current scintillation crystal based position sensitive gamma cameras. Instead, we propose to adapt high-energy gamma imaging techniques used in space-based imaging. A high purity germanium (HPGe) detector provides high-resolution energy spectra while a rotating modulation collimator (RMC) placed in front of the detector modulates the incoming signal to provide spatial information. Counting the number of gamma events at each collimator rotation angle allows for reconstruction of images. Herein we report on the design and testing of a prototype RMC, a Monte Carlo simulation of this camera, and the use of this simulation tool to access the feasibility of imaging a breast with such a camera. The prototype RMC was tested with a <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">22</sup> Na point source and verified that the RMC modulates the gamma rays in a predictable manner. The Monte Carlo simulation accurately modeled this behavior. Other simulations were used to accurately reconstruct images of a point source located within a 10 cm cube, suggesting NSECT's potential as a breast imaging method.

Breast cancer detection using neutron stimulated emission computed tomography: Prominent elements and dose requirements

Neutron stimulated emission computed tomography (NSECT) is being developed to noninvasively determine concentrations of trace elements in biological tissue. Studies have shown prominent differences in the trace element concentration of normal and malignant breast tissue. NSECT has the potential to detect these differences and diagnose malignancy with high accuracy with dose comparable to that of a single mammogram. In this study, NSECT imaging was simulated for normal and malignant human breast tissue samples to determine the significance of individual elements in determining malignancy. The normal and malignant models were designed with different elemental compositions, and each was scanned spectroscopically using a simulated 2.5 MeV neutron beam. The number of incident neutrons was varied from 0.5 million to 10 million neutrons. The resulting gamma spectra were evaluated through receiver operating characteristic (ROC) analysis to determine which trace elements were prominent enough to be considered markers for breast cancer detection. Four elemental isotopes (133Cs, 81Br, 79Br, and 87Rb) at five energy levels were shown to be promising features for breast cancer detection with an area under the ROC curve (A(Z)) above 0.85. One of these elements--87Rb at 1338 keV--achieved perfect classification at 10 million incident neutrons and could be detected with as low as 3 million incident neutrons. Patient dose was calculated for each gamma spectrum obtained and was found to range from between 0.05 and 0.112 mSv depending on the number of neutrons. This simulation demonstrates that NSECT has the potential to noninvasively detect breast cancer through five prominent trace element energy levels, at dose levels comparable to other breast cancer screening techniques.

Possible use of a BGO array for neutron stimulated emission computed tomography by summing adjacent signals

Neutron stimulated emission computed tomography (NSECT) is a new approach for biological spectroscopy and imaging. Since the gamma-ray photons emitted from stimulated element have energies from 100 keV to about 6 MeV, previous reports have proposed that the projection path can be defined by the neutron beam. In this paper, another possible method has been applied and the performance presented through simulations. When using signals from a single BGO crystal it is impossible to achieve good energy resolution for such high-energy photons. When summing additional signals from adjacent crystals, the energy spectrum becomes much better. Using an energy window with energy resolution of 90 keV, an average intrinsic spatial resolution of 3.938 mm FWHM is obtained.

Neutron stimulated emission computed tomography: Background corrections

Neutron stimulated emission computed tomography (NSECT) is an imaging technique that provides an in-vivo tomographic spectroscopic image of the distribution of elements in a body. To achieve this, a neutron beam illuminates the body. Nuclei in the body along the path of the beam are stimulated by inelastic scattering of the neutrons in the beam and emit characteristic gamma photons whose unique energy identifies the element. The emitted gammas are collected in a spectrometer and form a projection intensity for each spectral line at the projection orientation of the neutron beam. Rotating and translating either the body or the beam will allow a tomographic projection set to be acquired. Images are reconstructed to represent the spatial distribution of elements in the body. Critical to this process is the appropriate removal of background gamma events from the spectrum. Here we demonstrate the equivalence of two background correction techniques and discuss the appropriate application of each.

Introduction to neutron stimulated emission computed tomography

Neutron stimulated emission computed tomography (NSECT) is presented as a new technique for in vivo tomographic spectroscopic imaging. A full implementation of NSECT is intended to provide an elemental spectrum of the body or part of the body being interrogated at each voxel of a three-dimensional computed tomographic image. An external neutron beam illuminates the sample and some of these neutrons scatter inelastically, producing characteristic gamma emission from the scattering nuclei. These characteristic gamma rays are acquired by a gamma spectrometer and the emitting nucleus is identified by the emitted gamma energy. The neutron beam is scanned over the body in a geometry that allows for tomographic reconstruction. Tomographic images of each element in the spectrum can be reconstructed to represent the spatial distribution of elements within the sample. Here we offer proof of concept for the NSECT method, present the first single projection spectra acquired from multi-element phantoms, and discuss potential biomedical applications.