An in situ accelerator-based diagnostic for plasma-material interactions science on magnetic fusion devices.

This paper presents a novel particle accelerator-based diagnostic that nondestructively measures the evolution of material surface compositions inside magnetic fusion devices. The diagnostic's purpose is to contribute to an integrated understanding of plasma-material interactions in magnetic fusion, which is severely hindered by a dearth of in situ material surface diagnosis. The diagnostic aims to remotely generate isotopic concentration maps on a plasma shot-to-shot timescale that cover a large fraction of the plasma-facing surface inside of a magnetic fusion device without the need for vacuum breaks or physical access to the material surfaces. Our instrument uses a compact (~1 m), high-current (~1 milliamp) radio-frequency quadrupole accelerator to inject 0.9 MeV deuterons into the Alcator C-Mod tokamak at MIT. We control the tokamak magnetic fields--in between plasma shots--to steer the deuterons to material surfaces where the deuterons cause high-Q nuclear reactions with low-Z isotopes ~5 µm into the material. The induced neutrons and gamma rays are measured with scintillation detectors; energy spectra analysis provides quantitative reconstruction of surface compositions. An overview of the diagnostic technique, known as accelerator-based in situ materials surveillance (AIMS), and the first AIMS diagnostic on the Alcator C-Mod tokamak is given. Experimental validation is shown to demonstrate that an optimized deuteron beam is injected into the tokamak, that low-Z isotopes such as deuterium and boron can be quantified on the material surfaces, and that magnetic steering provides access to different measurement locations. The first AIMS analysis, which measures the relative change in deuterium at a single surface location at the end of the Alcator C-Mod FY2012 plasma campaign, is also presented.

Optimization of coded aperture radioscintigraphy for sentinel lymph node mapping.

PURPOSE: Radioscintigraphic imaging during sentinel lymph node (SLN) mapping could potentially improve localization; however, parallel-hole collimators have certain limitations. In this study, we explored the use of coded aperture (CA) collimators. PROCEDURES: Equations were derived for the six major dependent variables of CA collimators (i.e., masks) as a function of the ten major independent variables, and an optimized mask was fabricated. After validation, dual-modality CA and near-infrared (NIR) fluorescence SLN mapping were performed in pigs. RESULTS: Mask optimization required the judicious balance of competing dependent variables, resulting in sensitivity of 0.35%, XY resolution of 2.0 mm, and Z resolution of 4.2 mm at an 11.5-cm field of view. The findings in pigs suggested that NIR fluorescence imaging and CA radioscintigraphy could be complementary, but present difficult technical challenges. CONCLUSIONS: This study lays the foundation for using CA collimation for SLN mapping, and also exposes several problems that require further investigation.

Sub-millimeter technetium-99m calibration sources.

PURPOSE: Small animal radioscintigraphic imaging systems aim to achieve sub-millimeter resolution. At the present time, sub-millimeter calibration sources that can be placed at will within an imaged volume are not readily available. We have developed a method for producing technetium-99m (Tc-99m) sources in less than 15 minutes with readily available reagents. PROCEDURES: Tc-99m pertechnetate [TcO(4)](-) was incubated with 45 microm to 106 microm diameter spherical anion exchange beads, washed, and mounted as desired for instrument calibration. RESULTS: The procedure yields spherical sources having between 6.8 microCi to 11.1 microCi of Tc-99m per source. This work shows that dual imaging of these sources using white light and radioscintigraphy permits measurement of system performance with high precision. CONCLUSION: Easily prepared, sub-millimeter Tc-99m spherical calibration sources are described, and it is demonstrated that such sources are useful for measuring the resolution and sensitivity of radioscintigraphic systems, such as those designed for small animal imaging.

Coded aperture nuclear scintigraphy: a novel small animal imaging technique.

We introduce and demonstrate the utility of coded aperture (CA) nuclear scintigraphy for imaging small animals. CA imaging uses multiple pinholes in a carefully designed mask pattern, mounted on a conventional gamma camera. System performance was assessed using point sources and phantoms, while several animal experiments were performed to test the usefulness of the imaging system in vivo, with commonly used radiopharmaceuticals. The sensitivity of the CA system for 99mTc was 4.2 x 10(3) cps/Bq (9400 cpm/microCi), compared to 4.4 x 10(4) cps/Bq (990 cpm/microCi) for a conventional collimator system. The system resolution was 1.7 mm, as compared to 4-6 mm for the conventional imaging system (using a high-sensitivity low-energy collimator). Animal imaging demonstrated artifact-free imaging with superior resolution and image quality compared to conventional collimator images in several mouse and rat models. We conclude that: (a) CA imaging is a useful nuclear imaging technique for small animal imaging. The advantage in signal-to-noise can be traded to achieve higher resolution, decreased dose or reduced imaging time. (b) CA imaging works best for images where activity is concentrated in small volumes; a low count outline may be better demonstrated using conventional collimator imaging. Thus, CA imaging should be viewed as a technique to complement rather than replace traditional nuclear imaging methods. (c) CA hardware and software can be readily adapted to existing gamma cameras, making their implementation a relatively inexpensive retrofit to most systems.