We present a novel imaging technique based on the translation of the object through the field of view of one or more stationary multipinhole detectors. This new imaging method is called Translatory SPECT or T-SPECT. The benefits of T-SPECT lie in its simple mechanical design along with the potential for imaging otherwise inaccessible regions. The setup of various T-SPECT systems is described and results of numerous simulation studies are presented demonstrating the imaging capabilities of such systems. Specifically, we study T-SPECT with different detector arrangements and compare the performance of T-SPECT with that of SPECT with rotation (R-SPECT). We validate our simulation findings with results from an experiment in which we image a Jaszczak phantom using both R-SPECT and T-SPECT.
The temporal distribution of decay events recorded by a gamma camera in 'list mode' differs from the Poisson distribution because of dead-time effects. We propose a new model for the dead-time behaviour of a gamma camera. The most important feature of our model is that the loss of events occurs in pairs or higher multiples due to the so-called 'pile-up' effect. We analyse the consequences of pile-up for the temporal distribution of events recorded by a gamma camera. The probability distribution for the time intervals between events recorded by the camera is calculated from first principles. We construct estimators for the parameter of the new distribution. We distinguish between the estimation of the total count rate and the estimation of a certain subset of the total count rate. Computer simulation confirms that our estimators are less influenced by dead-time effects than the standard estimator.
Molecular imaging calls for imaging systems with both high resolution and high sensitivity. In small-animal SPECT high resolution is typically achieved using pinhole collimation. In order to improve the sensitivity of single-pinhole systems we employ a novel collimation approach called multi-pinhole imaging. This imaging technique extends conventional singlepinhole collimation through the addition of pinholes on each collimator. An important feature of multi-pinhole imaging is the overlap of projections on the detector. This overlap results in a more efficient coverage of the detector and thus a considerable increase in sensitivity. In this contribution we report on the performance of two multi-pinhole imaging systems: a dualheaded Siemens ECAM and a triple-headed Trionix TRIAD. The big-headed ECAM being upgraded with two 10-pinhole collimators, while the medium-sized detectors of the TRIAD were equipped with three 7-pinhole apertures. Image reconstruction is performed using a dedicated OSEM algorithm. Both systems are characterized by a series of phantom measurements and tested on numerous animal studies. We will show that both systems yield excellent image quality with a reconstructed resolution of 1.2mm and a sensitivity of up to 1600cps/MBq. In addition to regular semi-quantitative single-isotope studies, we will present data on dual-isotope imaging, absolute tracer quantification and the fusion of the SPECT images with MR data of the same animal.
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