PhytoBeta imager: a positron imager for plant biology.

Several positron emitting radioisotopes such as (11)C and (13)N can be used in plant biology research. The (11)CO(2) tracer is used to facilitate plant biology research toward optimization of plant productivity, biofuel development and carbon sequestration in biomass. Positron emission tomography (PET) imaging has been used to study carbon transport in live plants using (11)CO(2). Because plants typically have very thin leaves, little medium is present for the emitted positrons to undergo an annihilation event. The emitted positrons from (11)C (maximum energy 960 keV) could require up to approximately 4 mm of water equivalent material for positron annihilation. Thus many of the positrons do not annihilate inside the leaf, resulting in limited sensitivity for PET imaging. To address this problem we have developed a compact beta-positive, beta-minus particle imager (PhytoBeta imager) for (11)CO(2) leaf imaging. The detector is based on a Hamamatsu H8500 position sensitive photomultiplier tube optically coupled via optical grease to a 0.5 mm thick Eljen EJ-212 plastic scintillator. The detector is equipped with a flexible arm to allow its placement and orientation over or under the leaf to be studied while maintaining the leaf's original orientation. To test the utility of the system the detector was used to measure carbon translocation in a leaf of the spicebush (Lindera benzoin) under two transient light conditions.

A feasibility study using radiochromic films for fast neutron 2D passive dosimetry.

The objective of this paper is threefold: (1) to establish sensitivity of XRQA and EBT radiochromic films to fast neutron exposure; (2) to develop a film response to radiation dose calibration curve and (3) to investigate a two-dimensional (2D) film dosimetry technique for use in establishing an experimental setup for a radiobiological irradiation of mice and to assess the dose to the mice in this setup. The films were exposed to a 10 MeV neutron beam via the (2)H(d,n)(3)He reaction. The XRQA film response was a factor of 1.39 greater than EBT film response to the 10 MeV neutron beam when exposed to a neutron dose of 165 cGy. A film response-to-soft tissue dose calibration function was established over a range of 0-10 Gy and had a goodness of fit of 0.9926 with the calibration data. The 2D film dosimetry technique estimated the neutron dose to the mice by measuring the dose using a mouse phantom and by placing a piece of film on the exterior of the experimental mouse setup. The film results were benchmarked using Monte Carlo and aluminum (Al) foil activation measurements. The radiochromic film, Monte Carlo and Al foil dose measurements were strongly correlated, and the film within the mouse phantom agreed to better than 7% of the externally mounted films. These results demonstrated the potential application of radiochromic films for passive 2D neutron dosimetry.

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.

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 andor controls.