A 3D CdZnTe detector can provide 3D position information as well as energy information of each individual interaction when a gamma ray is scattered or absorbed in the detector. This unique feature provides the 3D CdZnTe detector the capability to do Compton imaging with a single detector. After detector calibration, real-time data acquisition and imaging are implemented with a single detector system. Because the detector has a finite size and any point in the detector can be the first scattering position, 3D gamma-ray imaging in near field is possible. In this work we will show the result of the 4pi Compton imaging with a single 15mm x 15mm x 10mm CdZnTe detector. Different algorithms for sequence and imaging reconstruction will be addressed and compared. The angular uncertainty is estimated and the most recent results from measurements are presented.

A 3D CdZnTe detector can provide 3D position information as well as energy information of each individual interaction when a gamma ray is scattered or absorbed in the detector. This unique feature provides the 3D CdZnTe detector the capability to do Compton imaging with a single detector. After detector calibration, real-time data acquisition and imaging are implemented with a single detector system. Because the detector has a finite size and any point in the detector can be the first scattering position, 3D gamma-ray imaging in near field is possible. In this work we will show the result of the 4π Compton imaging with a single 15mm × 15mm × 10mm CdZnTe detector. Different algorithms for sequence and imaging reconstruction will be addressed and compared. The angular uncertainty is estimated and the most recent results from measurements are presented.

In this work we describe a 4/spl pi/ Compton imager composed of a single 15 mm /spl times/ 15 mm /spl times/ 10 mm CdZnTe detector. The anode is pixellated into an 11 /spl times/ 11 array to provide position sensitivity in two dimensions. The third coordinate is determined from the observed timing of signals in the detector. The position resolution is approximately 1.2 mm in each dimension. The energy resolution is about 2% for two-pixel events at 662 keV. Images are reconstructed via list-mode maximum likelihood (ML). A new weighting method for ML reconstruction is proposed in which the contributions of small-uncertainty sequences are enhanced relative to sequences with large uncertainties. The new reconstruction method is compared with traditional ML techniques for measured imaging data.

For Compton imaging it is necessary to determine the sequence of gamma-ray interactions in a single detector or array of detectors. This can be done by time-of-flight measurements if the interactions are sufficiently far apart. However, in small detectors the time between interactions can be too small to measure, and other means of gamma-ray sequencing must be used. In this work, several popular sequencing algorithms are reviewed for sequences with two observed events and three or more observed events in the detector. These algorithms can result in poor imaging resolution and introduce artifacts in the backprojection images. The effects of gamma-ray tracking algorithms on Compton imaging are explored in the context of the 4 pi Compton imager built by the University of Michigan.

The spatial information obtained using 3-D position-sensitive detectors can be used to improve the performance of gamma-ray spectroscopy systems. With the energy and position information available for each interaction in the detector signatures of multiple interactions can be recognized and used to reconstruct initial gamma-ray energies or eliminate partial-energy tracks. Unlike a traditional spectrometer, 3-D position sensitive spectrometers make it possible to reject single interactions, suppress Compton continua, identify and reconstruct gamma-ray energies in sequences that begin with pair production, and reconstruct gamma-ray energies in sequences of three or more events that do not include pair production. We have previously presented simulation results of two algorithms that demonstrate the capabilities of intelligent spectroscopy at high energies (>1 MeV). In the current work, we add medium energy techniques and present spectroscopy results from both simulations and measurements using a 2.25-cm(3) CdZnTe detector.

The performance of gamma-ray spectrometers at high energies (several MeV) can be greatly improved through intelligent spectroscopic analysis if spatial information is obtained for each energy deposition. In position-sensitive detectors, the energy and three-dimensional (3-D) position of each interaction in the detector are determined. Recognizing the signatures of multiple interactions in the detector can help to reconstruct the energies of the initial gamma-rays even when the full energies are not deposited. Experimental work by our research group has demonstrated the feasibility of carrying out spatially resolved measurements of individual gamma-ray interactions throughout the volume of a CdZnTe spectrometer. We present the results of a simulation study for gamma-rays incident upon a 6-cm/sup 3/ CdZnTe detector using two reconstruction methods: high-efficiency intelligent spectroscopy (HEIS) in which the peak-to-total ratio is greatly improved relative to traditional spectroscopy while maintaining almost the same intrinsic peak efficiency; and peak-only intelligent spectroscopy (POIS) in which the peak-to-total ratio can approach 0.9, assuming realistic values for energy resolution. Although POIS reduces the intrinsic peak efficiency, it will significantly improve the signal-to-noise ratio for many measurements. The predicted performance is unprecedented for a detector of such small volume and illustrates the gains that can be expected by exploiting 3-D information.

This paper demonstrates the capability of compact gamma‐ray imaging devices using 3‐dimensional position sensitive CdZnTe semiconductor gamma‐ray spectrometers, developed at the University of Michigan. A prototype imager was constructed and tested using two 1 cm cube 3‐dimensional position sensitive CdZnTe detectors. Energy resolutions of 1.5% FWHM for single pixel events at 662 keV gamma‐ray energy were obtained on both detectors, and an angular resolution of about 5° FWHM was demonstrated. The capabilities of proposed devices, which can cover a wider energy range up to 2.6 MeV, are discussed.

We present position sensitivity measurements obtained with one of the 32-fold segmented HPGe detectors from Michigan State University. These measurements were performed with a collimated beam of /sup 137/Cs gamma rays scattered by 90 degrees. This deposits 374 keV at a given location inside the crystal. A position resolution can be determined over many events by examining the digitally recorded pulse shapes on the 32 electrical contacts. If position resolution is adequate, gamma ray Compton camera imaging may be possible.