Cadmium zinc telluride (CdZnTe, or CZT) is a room-temperature semiconductor radiation detector that has been
developed in recent years for a variety of applications. CZT has been investigated for many potential uses in medical
imaging, especially in the field of single photon emission computed tomography (SPECT). CZT can also be used in
positron emission tomography (PET) as well as photon-counting and integration-mode x-ray radiography and computed
tomography (CT). The principal advantages of CZT are 1) direct conversion of x-ray or gamma-ray energy into
electron-hole pairs; 2) energy resolution; 3) high spatial resolution and hence high space-bandwidth product; 4) room
temperature operation, stable performance, high density, and small volume; 5) depth-of-interaction (DOI) available
through signal processing. These advantages will be described in detail with examples from our own CZT systems. The
ability to operate at room temperature, combined with DOI and very small pixels, make the use of multiple, stationary
CZT "mini-gamma cameras" a realistic alternative to today's large Anger-type cameras that require motion to obtain
tomographic sampling. The compatibility of CZT with Magnetic Resonance Imaging (MRI)-fields is demonstrated for
a new type of multi-modality medical imaging, namely SPECT/MRI. For pre-clinical (i.e., laboratory animal) imaging,
the advantages of CZT lie in spatial and energy resolution, small volume, automated quality control, and the potential for
DOI for parallax removal in pinhole imaging. For clinical imaging, the imaging of radiographically dense breasts with
CZT enables scatter rejection and hence improved contrast. Examples of clinical breast images with a dual-head CZT
system are shown.
Cardiac function is an important physiological parameter in preclinical studies. Nuclear cardiac scans are a standard of care for patients with suspected coronary artery occlusions and can assess perfusion and other physiological functions via the injection of radiotracers. In addition, correlated acquisition of nuclear images with electrocardiogram (ECG) signals can provide myocardial dynamics, which can be used to assess the wall motion of the heart. We have implemented this nuclear cardiology technique into a microSPECT/CT system, which provides sub-millimeter resolution in SPECT and co-registered high resolution CT anatomical maps. Radionuclide detection is synchronized with the R-wave of the cardiac cycle and separated into 16 time bins using an ECG monitor and triggering device for gating. Images were acquired with a 12.5 x 12.5 cm2 small field of view pixilated NaI(Tl) detector, using a pinhole collimator. In this pilot study, rats (N = 5) were injected with 99mTc-Sestamibi, a tracer of myocardium, and anesthetized for imaging. Reconstructed 4-D images (3D plus timing) were computed using an Ordered Subset Expectation Maximization (OSEM) algorithm. The measured perfusion, wall motion, and ejection fractions for the rats matched well with results reported by other researchers using alternative methods. This capability will provide a new and powerful tool to preclinical researchers for assessing cardiac function.
We present an abundance analysis of six main sequence turnoff, subgiant, and giant branch stars toward the Galactic bulge that were observed with Keck/HIRES during microlensing events. This is an early look at the first detailed chemical analysis of main sequence stars in the Galactic bulge. Lensing events allow the effective aperture of Keck to be increased beyond its current dimensions; although, some events still stretched its spectroscopic capabilities. Future large telescopes with high resolution and high throughput spectrometers will allow the study of abundances in distant stellar populations and in less evolved stars with greater ease.
The MACHO experiment is searching for dark matter in the halo of the Galaxy by monitoring more than 50 million stars in the LMC, SMC, and Galactic bulge for gravitational microlensing events. The hardware consists of a 50 inch telescope, a two-color 32 megapixel ccd camera and a network of computers. On clear nights the system generates up to 8 GB of raw data and 1 GB of reduced data. The computer system is responsible for all realtime control tasks, for data reduction, and for storing all data associated with each observation in a database. The subject of this paper is the software system that handles these functions. It is an integrated system controlled by Petri nets that consists of multiple processes communicating via mailboxes and a bulletin board. The system is highly automated, readily extensive, and incorporates flexible error recovery capabilities. It is implemented with C++ in a Unix environment.