Roy C. Chaney

Phoenix mars mission—The thermal evolved gas analyzer

The Phoenix spacecraft that was launched to Mars in August 2007 landed safely on the Martian northern arctic region on May 25, 2008. It carried six experiments to study the history of water on the planet and search for organic molecules in the icy subsurface Martian soil. The spacecraft is a lander with an arm and scoop designed to dig a trench though the top soil to reach an expected ice layer near the surface. One of the instruments on board is the thermal evolved gas analyzer (TEGA), which consists of two components, a set of eight very small ovens that will heat samples of the ice soil mixtures from the trench to release imbedded gases and mineral decomposition products, and a mass spectrometer that serves as the analysis tool for the evolved gases, and also for measurements of the composition and isotopic ratios of the gases that comprise the atmosphere of Mars. The mass spectrometer is a miniature magnetic sector instrument controlled by microprocessor-driven power supplies. One feature is the gas enrichment cell that will increase the partial pressures of the noble gases in an atmosphere sample by removing all the active gases, carbon dioxide, and nitrogen, to improve the accuracy of their isotopic ratio measurements.

New approaches in medical imaging using plastic scintillating detectors

Abstract A small animal imaging camera was built in our laboratory, using-fast plastic scintillating detectors ( τ = 2–4 ns) and position sensitive photomultipliers (Hamamatsu) digitized using flash ADCs. Pinhole collimators were used for 125 I imaging to achieve submillimeter resolution with scintillating plates of 28 mm radius and 1.5 mm thickness. A high resolution PET module was constructed with arrays of 1.0 mm diameter plastic scintillating fibers. The feasibility of high resolution imaging was demonstrated by the study of brain blood flow in a rat using 125 I IMP in single photon detection mode and with 64 Cu PTSM by using PET mode. Construction of single photon and positron emission tomographic imaging systems for small animals and subsequently for human imaging is in progress.

Method for reducing background artifacts from images in single-photon emission computed tomography with a uniformly redundant array coded aperture

Uniformly redundant array coded apertures have proven to be useful in the design of collimators for x-ray astronomy. They were initially expected to be equally successful in single-photon emission computed tomography (SPECT). Unfortunately, the SPECT images produced by this collimator contain artifacts, which mask the true picture and can lead to false diagnosis. Monte Carlo simulation has shown that the formation of a composite image will significantly reduce these artifacts. A simulation of a tumor in a compressed breast phantom has produced a composite image, which clearly indicates the presence of a 5 mm x 5 mm x 5 mm tumor with a 6:1 intensity ratio relative to the background tissue.

Imaging of folate receptors with I-125 labeled folate using small animal imaging system built with plastic scintillating optical fibers

A small animal whole body imaging device was built with plastic scintillating fibers and application of this system to image folate receptors in mice is described. The prototype imaging device consisted of two layers of 1 mm BCF-10 fibers laid on 6.98 cm acrylic core, one layer with a right handed pitch and the other with a left handed pitch. The fiber readout was performed with a position sensitive photomultiplier and a specialized flash ADC. A coaxial brass mesh collimator (1 mm thick) was used to increase spatial resolution. Histamine- folate conjugate was labeled with I-125 and was found to have receptor binding properties similar to 3H labeled compound. Imaging studies were performed in mice bearing folate receptor +ve (IGROV) tumor and receptor -ve (Meth-A) tumor. In situ imaging of animals sacrificed at 30 min post injection of the tracer showed the localization of the tumor in animals with the folate receptor +ve tumors and the results were negative in animals with receptor -ve tumor. The biodistribution studies confirmed these observations. Our initial studies demonstrate the prospects for development of agents for imaging folate receptors that may have application in drug development and the application of the small animal imaging device built with plastic scintillating detectors in imaging with low energy photons (25 - 35 keV).

Constructing a small laboratory animal imaging device based on scintillating fibers

Scintillating optical fibers have been used to build small detectors for whole-body imaging of small rodents by nuclear medicine techniques. Cylindrical detectors with entrance apertures of 6.8 cm and active lengths of 11.3 cm were constructed using both 3 mm and 1 mm BCF-10 fibers. Fiber readout was performed using position sensitive photomultipliers and a specialized flash ADC system. The efficiencies of these detectors were determined as a function of energy, their resolution was studied, and their potential use for SPECT (single photon emission computed tomography) was explored.

Development of a high resolution scintillating fiber gamma ray telescope

The authors report on further development and testing of a Compton telescope composed of scintillating fibers and position-sensitive photomultipliers. Initial tests of the telescope showed a better than 1-mm (RMS) position resolution and a 17.5-mrad (RMS) angular resolution for 1.2-MeV photons from a collimated /sup 60/Co gamma source. This type of device can be used for constructing large-area telescopes for gamma-ray astronomy. It was shown that this gamma ray telescope worked successfully. >

Testing of the spatial resolution and efficiency of scintillating fiber PET modules

Two experimental PET (positron emission tomography) camera modules were constructed using (1) two 5-cm*5-cm*2.5-cm detector stacks made of parallel 0.5- and 1.0-mm-diameter scintillating fibers and (2) two 5-cm*5-cm*5-cm detector stacks made of alternating x and y layers of 0.5- and 1.0-mm-diameter scintillating fibers. Each stack was viewed by Hamamatsu R2486 position-sensitive photomultipliers. The time resolution of the coincidence system was 10 ns. The spatial resolution and efficiency of the PET modules were tested using an approximately 1 mu Ci. 0. 5-mm-diameter Na-22 source. The best results were achieved with the 1.0-mm parallel fiber stacks: 2.0-mm spatial resolution (full width at half maximum) and 2.3% efficiency. The possibilities of improving the characteristics of this arrangement and particularly the alternating x and y layer stacks are discussed.<<ETX>>

High resolution gamma ray telescope using scintillating fibers and position sensitive photomultipliers

Abstract Recently high photon yielding and long attenuation length step index scintillating plastic fibers have been developed. Scintillating fibers of 1 mm diameter made of polystyrene doped with butyl-PBD and POPOP ( λ = 420 nm), and clad with PMMA (poly-methylmetacrylate) have resulted attenuation lengths over 2 meters. Scintillating fibers stacked up into scintillating fiber planes U, V and W that are rotated by 60° angle relative to each other and coupled to position sensitive photomultipliers can be used as high resolution imaging gamma-ray detectors. We are presenting the design of a large area gamma-ray telescope with high angular and energy resolution for space based experiments, using scintillating fibers and recently developed position sensitive photomultiplier tubes.

Folate receptor imaging with 125I labeled folic acid with a whole body small animal imaging device built with plastic scintillating optical fibers

Abstract A small animal whole body imaging cylindrical device was built with plastic scintillating fibers and position sensitive photomultipliers (Hamamatsu) and digitized using flash ADCs. A co-axial brass mesh collimator (septum thickness 1 mm) was used in combination with an electronic collimation scheme to enhance spatial resolution. Imaging studies with 125 I labeled folic acid were performed in mice bearing folate receptor +ve (IGROV) tumor and receptor −ve (Meth-A) tumor. In-situ imaging of animals sacrificed at 15–30 min post injection of the tracer showed the localization of the tumor in animals with the folate receptor +ve tumors. Our initial studies demonstrate the utility of a device built with plastic scintillating fibers in small animal imaging studies with low energy photons (25–35 keV).

A HIGH RESOLUTION SCINTILLATING FIBER GAMMA-RAY TELESCOPE*

Scintillating fibers coupled to position sensitive photomultipliers have good angular precision and good energy resolution in detecting gamma-rays. Recently high photon yielding and long attenuation length step index scintillating plastic fibers have been developed. Scintillating fibers of 1 mm diameter made of polystyrene doped with butyl-PBD (λ = 420 nm) and clad with PMMA (poly mptAylmetacrylate), have resulted attenuation lengths over 2 meters. Scintillating fibers stacked up into scintillating fiber planes U, V and W that are rotated by 60° angle relative to each other and coupled to position sensitive photomultipliers can be used as high resolution imaging gamma-ray detectors. With this arrangement the Compton electron or pair production point can be determined by the scintillation photons reaching the photomultipliers. A 3-dimensional conversion point accuracy is expected to be 6 rms~1 mm. A large variety of Compton and/or pair production gamma-ray telescopes using scintillator blocks coupled to vacuum photomultipUer tubes has been built earlier for space based experiments. In these cases the scintillator block dimensions were large thus limiting the angular accuracies and resolutions. Here we are presenting the design of a large area gamma-ray detector with high angular and energy resolution for space based experiments, using scintillating fibers and recently developed position sensitive photomultiplier tubes. This detector is under development at the UCLA/UTD laboratories.