Associated particle neutron elemental imaging in vivo: A feasibility study

Abstract

APNEI of certain elements in vivo appears feasible given several timing, sensitivity, and resolution caveats. However, further study is required to determine what the detection limit of iron would be and what image resolution would be in an experimental setup as the present model contains idealized assumptions which overestimate the signal attributable to iron inelastic scatter gamma rays.

Monte Carlo simulations of elemental imaging using the neutron‐associated particle technique

“…Dose, though, would become limiting. While there is a strong, developing foundation in simulation, 9,11,35,36 there are knowledge gaps in APNEI theory that require the development of a prototype APNEI system. For example, beam spot diameter and high count rate HPGe limitations must be explored in the laboratory.…”

“…20,21 The 1 cm dimensions of each voxel were chosen as an estimate of spatial resolution which would be valuable for in vivo applications. 11,22 The 9-voxel target array was suspended in air such that the leading edge of the center voxel was exactly 8 cm from the neutron source spot. The source spotthat from which the 2.45 MeV DD neutrons were emittedwas defined as a circular surface source with negligible depth, 2 mm diameter, and a Gaussian-distributed and isotropic emission profile.…”

“…Additionally, while it is expected that the inclusion of such materials would decrease elemental sensitivity, the time-of-flight collimation technique would allow for the significant exclusion of competing signals, thereby providing for differentiation of target elemental signals from the region of interest. 6,11 It follows then that because the element targeted for imaging in this study was iron, the only iron-bearing cells in the imaging model were those in the 9-voxel target array. Not only is iron (Fe-56) known to be a distinguishing marker in several disease signatures, but it is a logical target element in AP fast neutron analysis studies because of its relatively high inelastic scatter cross-section to DD neutrons (approximately 1 barn).…”

“…Not only is iron (Fe-56) known to be a distinguishing marker in several disease signatures, but it is a logical target element in AP fast neutron analysis studies because of its relatively high inelastic scatter cross-section to DD neutrons (approximately 1 barn). 11 For the purpose of using the neutron AP technique to image iron, the desired nuclear collision and subsequent de-excitation is Fe-56 + n Fe-56* + n' c. The noniron component of each voxel was defined as water, a material which would be relevant to in vivo application (soft tissue approximation) as well as potentially to eventual phantom construction.…”

“…The associated particle technique has been explored as a means of elemental imaging as well as background signal reduction in applications ranging from well logging and homeland security to in vivo medical diagnostics . A comprehensive explanation of the AP technique as well as a schematic of APNEI is provided in the authors’ previous work, which explores the application of APNEI to in vivo medical diagnostics for diseases with elemental signatures . Building upon those preliminary studies regarding elemental response and the technological variables associated with maximizing in vivo imaging resolution, this paper will focus predominantly on small‐scale image simulations using MCNP — with target voxel volumes and a general APNEI system layout which would be relevant in clinical applications.…”