Alexander S. Crowell

New Measurement of the {sup 1}S {sub 0} Neutron-Neutron Scattering Length Using the Neutron-Proton Scattering Length as a Standard

The present paper reports high-accuracy cross-section data for the 2 H(n,nnp) reaction in the neutron-proton (np) and neutron-neutron (nn) final-state-interaction (FSI) regions at an incident mean neutron energy of 13.0 MeV. These data were analyzed with rigorous three-nucleon calculations to determine the 1 S0 np and nn scattering lengths, anp and ann. Our results are ann = -18.7±0.6 fm and anp = -23.5 ±0.8 fm. Since our value for anp obtained from neutron-deuteron (nd) breakup agrees with that from free np scattering, we conclude that our investigation of the nn FSI done simultaneously and under identical conditions gives the correct value for ann. Our value for ann is in agreement with that obtained in � − d measurements but disagrees with values obtained from earlier nd breakup studies.

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.

Exploring the transport of plant metabolites using positron emitting radiotracers.

Short‐lived positron‐emitting radiotracer techniques provide time‐dependent data that are critical for developing models of metabolite transport and resource distribution in plants and their microenvironments. Until recently these techniques were applied to measure radiotracer accumulation in coarse regions along transport pathways. The recent application of positron emission tomography (PET) techniques to plant research allows for detailed quantification of real‐time metabolite dynamics on previously unexplored spatial scales. PET provides dynamic information with millimeter‐scale resolution on labeled carbon, nitrogen, and water transport over a small plant‐size field of view. Because details at the millimeter scale may not be required for all regions of interest, hybrid detection systems that combine high‐resolution imaging with other radiotracer counting technologies offer the versatility needed to pursue wide‐ranging plant physiological and ecological research. In this perspective we describe a recently developed hybrid detection system at Duke University that provides researchers with the flexibility required to carry out measurements of the dynamic responses of whole plants to environmental change using short‐lived radiotracers. Following a brief historical development of radiotracer applications to plant research, the role of radiotracers is presented in the context of various applications at the leaf to the whole‐plant level that integrates cellular and subcellular signals and/or controls.

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 of Stable Isotopes

Here we report on the development of a new molecular imaging technique using inelastic scattering of fast neutrons. Earlier studies demonstrated a significant difference in trace element concentrations between benign and malignant tissue for several cancers including breast, lung, and colon. Unfortunately, the measurement techniques were not compatible with living organisms and this discovery did not translate into diagnostic techniques. Recently we have developed a tomographic approach to measuring the trace element concentrations using neutrons to stimulate characteristic gamma emission from atomic nuclei in the body. Spatial projections of the emitted energy spectra allow tomographic image reconstruction of the elemental concentrations. In preliminary experiments, spectra have been acquired using a 7.5MeV neutron beam incident on several multi-element phantoms. These experiments demonstrate our ability to determine the presence of Oxygen, Carbon, Copper, Iron, and Calcium. We describe the experimental technique and present acquired spectra.

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.

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 22Na 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 NSECTs potential as a breast imaging method.

Non-invasive quantification of iron /sup 56/Fe in beef liver using neutron stimulated emission computed tomography

Neutron spectroscopy is being developed as a non-invasive tool to measure element concentration in the body at molecular levels. We are developing a neutron stimulated emission computed tomography (NSECT) system to identify element concentrations in tissue, using inelastic scattering of neutrons by target nuclei. An incident neutron scatters inelastically with an atomic nucleus to emit a gamma photon whose energy is characteristic of the scattering nucleus. This energy is detected by an energy-sensitive gamma detector to identify the target atom. Here we describe an experiment to non-invasively determine the concentration of natural iron (/sup 56/Fe) in beef liver. A 7.5 MeV neutron beam was used to scan a known quantity of solid iron and establish a ratio of iron concentration to gamma counts for the experimental setup. A known quantity of beef liver was then scanned using the same experimental setup, to obtain gamma spectra showing element concentrations in the liver. Counts from gamma peaks corresponding to excited states in iron were compared with counts from the known iron sample, to yield the iron concentration in the liver. A high purity germanium (HPGe) detector was used to measure the emitted gamma energy. Although the results obtained in this experiment are slightly higher than normal iron limits reported in various studies, they demonstrate the techniques ability to non-invasively quantify iron concentration in a biological organ.

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.

Non-Invasive Estimation of Potassium (39K) in Bovine Liver Using Neutron Stimulated Emission Computed Tomography (NSECT)

Neutron stimulated emission computed tomography (NSECT) is being developed as a non-invasive technique to measure element concentration in in-vivo tissue at molecular levels. We have developed a system that performs this task using an incident neutron beam that scatters inelastically with an atomic nucleus causing it to emit a characteristic gamma photon. An energy-sensitive gamma detector is used to detect this energy and identify the target atom. Here we describe an experiment to determine the concentration of natural potassium (39K) in bovine liver without the need for a biopsy. A 5 MeV neutron beam was used to scan a known quantity of bovine liver to obtain a gamma spectrum showing element concentration in the liver. An aqueous KCl solution calibration sample was then scanned to establish a ratio of potassium concentration to gamma counts for the experimental setup. Counts from gamma peaks corresponding to excited states in 39K were summed and compared with counts from the known calibration sample, to give the concentration of 39K in the liver. A high purity germanium (HPGe) clover detector was used to measure the emitted gamma energy. The results were validated through neutron activation analysis (NAA) of the liver sample. The concentration of 39K reported by NSECT was found to be within 13% of the NAA result, clearly demonstrating the ability of NSECT for non-invasive quantification of element concentration in tissue.