Anuj J Kapadia
Associate Professor in Radiology
1) Experimental Implementation of NSECT
Neutron spectroscopy techniques are showing significant promise in determining element concentrations in the human body. We have developed a tomographic imaging system capable of generating tomographic images of the element concentration within a body through a single non-invasive in-vivo scan. This system has been implemented using a Van-de-Graaf accelerator fast neutron source and high-purity germanium gamma detectors at the Triangle Universities Nuclear Laboratory. This setup has been used to obtain NSECT scans for several samples such as bovine liver, mouse specimens and human breast tissue. In order to extract maximum information about a target sample with the lowest possible levels of dose, it is essential to maximize the sensitivity of the scanning system. In other words, the signal to noise ratio for the experimental setup must be maximized. This project aims at increasing the sensitivity of the NSECT system by understanding the various sources of noise and implementing techniques to reduce their effect. Noise in the system may originate from several factors such as the radiative background in the scanning room, and neutron scatter off of components of the system other than the target. Some of these effects can be reduced by using Time-of-Flight background reduction, while others can be reduced by acquiring a separate sample-out scan. Post processing background reduction techniques are also being developed for removing detector efficiency dependent noise. At this point we have acquired element information from whole mouse specimens and iron-overloaded liver models made of bovine liver tissue artificially injected with iron. Tomographic images have been generated from a solid iron and copper phantom. Our final goal is to implement a low-dose non-invasive scanning system for diagnosis of iron overload and breast cancer.
2) Monte-Carlo simulations in GEANT4
For each tomographic scan of a sample using NSECT, there are several acquisition parameters that can be varied. These parameters can broadly be classified into three categories: (i) Neutron Beam parameters: neutron flux, energy and beam width, (ii) Detector parameters: detector type, size, efficiency and location; (iii) Scanning Geometry: spatial and angular sampling rates. Due to the enormous number of combinations possible using these parameters, it is not feasible to investigate the effects of each parameter on the reconstructed image using a real neutron beam in the limited beam time available. A feasible alternative to this is to use Monte-Carlo simulations to reproduce the entire experiment in a virtual world. The effect of each individual parameter can then be studied using only computer processing time and resources. We use the high energy physics Monte-Carlo software package GEANT4, developed by CERN, which incorporates numerous tools required for building particle sources and detectors, and tracking particle interactions within them. The simulations built so far include the neutron source, HPGE and BGO gamma detectors, and several target materials such as iron, liver and breast tissue.
Floyd, C. E., et al. “Neutron stimulated emission computed tomography: Background corrections.” Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions With Materials and Atoms, vol. 254, no. 2, Jan. 2007, pp. 329–36. Scopus, doi:10.1016/j.nimb.2006.11.098. Full Text
Floyd, Carey E., et al. “Introduction to neutron stimulated emission computed tomography..” Phys Med Biol, vol. 51, no. 14, July 2006, pp. 3375–90. Pubmed, doi:10.1088/0031-9155/51/14/006. Full Text
Sharma, A., et al. “Rotating slat collimator design for high-energy near-field imaging.” Progress in Biomedical Optics and Imaging Proceedings of Spie, vol. 6142 I, July 2006. Scopus, doi:10.1117/12.653929. Full Text
Floyd, C. E., et al. “Breast cancer diagnosis using neutron stimulated emission computed tomography: Dose and count requirements.” Progress in Biomedical Optics and Imaging Proceedings of Spie, vol. 6142 II, June 2006. Scopus, doi:10.1117/12.656045. Full Text
Bender, J. E., et al. “The effect of detector resolution for quantitative analysis of neutron stimulated emission computed tomography.” Progress in Biomedical Optics and Imaging Proceedings of Spie, vol. 6142 III, June 2006. Scopus, doi:10.1117/12.652812. Full Text
Kapadia, A. J., et al. “Non-invasive estimation of potassium (39K) in Bovine Liver using Neutron Stimulated Emission Computed Tomography (NSECT).” Ieee Nuclear Science Symposium Conference Record, vol. 4, Jan. 2006, pp. 2076–78. Scopus, doi:10.1109/NSSMIC.2006.354322. Full Text
Sharma, A. C., et al. “Design and construction of a prototype rotation modulation collimator for near-field high-energy spectroscopic gamma imaging.” Ieee Nuclear Science Symposium Conference Record, vol. 4, Jan. 2006, pp. 2021–24. Scopus, doi:10.1109/NSSMIC.2006.354310. Full Text
Kapadia, A. J., et al. “Non-invasive quantification of iron56Fe in beef liver using neutron stimulated emission computed tomography.” Ieee Nuclear Science Symposium Conference Record, vol. 4, Dec. 2005, pp. 2232–34. Scopus, doi:10.1109/NSSMIC.2005.1596778. Full Text
Kapadia, A. J., and C. E. Floyd. “An attenuation correction technique to correct for neutron and gamma attenuation in the reconstructed image of a neutron stimulated emission computed tomography (NSECT) system.” Progress in Biomedical Optics and Imaging Proceedings of Spie, vol. 5745, no. II, Aug. 2005, pp. 737–43. Scopus, doi:10.1117/12.596107. Full Text
Floyd, C. E., et al. “Neutron stimulated emission computed tomography of stable isotopes.” Proceedings of Spie the International Society for Optical Engineering, vol. 5368, no. 1, July 2004, pp. 248–54. Scopus, doi:10.1117/12.535350. Full Text