Animal Positron Emission Tomography System Research Articles

Molecular imaging of small animals with dedicated PET tomographs.

Biological discovery has moved at an accelerated pace in recent years, with a considerable focus on the transition from in vitro to in vivo models. As a result, there has been a significant increase in the need to adapt clinical imaging methods, as well as for novel imaging technologies for biological research. Positron emission tomography (PET) is a clinical imaging modality that permits the use of positron-labeled molecular imaging probes for non-invasive assays of biochemical processes. The imaging procedure can be repeatedly performed before and after interventions, thereby allowing each animal to be used as its own control. Positron-labeled compounds that target a range of molecular targets have been and continue to be synthesized, with examples of biological processes ranging from receptors and synthesis of transmitters in cell communication, to metabolic processes and gene expression. In animal research, PET has been used extensively in the past for studies of non-human primates and other larger animals. New detector technology has improved spatial resolution, and has made possible PET scanning for the study of the most important modern molecular biology model, the laboratory mouse. This paper presents the challenges facing PET technology as applied to small animal imaging, provides a historical overview of the development of small animal PET systems, and discusses the current state of the art in small animal PET technology.

Detector response models for statistical iterative image reconstruction in high resolution PET

One limitation in a practical implementation of statistical iterative image reconstruction is to compute a transition matrix accurately modeling the relationship between projection and image spaces. Detector response function (DRF) in positron emission tomography (PET) is broad and spatially-variant, leading to large transition matrices taking too much space to store. In this work, the authors investigate the effect of simpler DRF models on image quality in maximum likelihood expectation maximization reconstruction. The authors studied 6 cases of modeling projection/image relationship: tube/pixel geometric overlap with tubes centered on detector face; same as previous with tubes centered on DRF maximum; two different fixed-width Gaussian functions centered on DRF maximum weighing tube/pixel overlap; same as previous with a Gaussian of the same spectral resolution as DRF; analytic DRF based on linear attenuation of /spl gamma/-rays in detector arrays weighing tube/pixel overlap. The authors found that DRF oversimplification may affect visual image quality and image quantification dramatically, including artefact generation. They showed that analytic DRF yielded images of excellent quality for a small animal PET system with long, narrow detectors and generated a transition matrix for 2-D reconstruction that could be easily fitted into the memory of current stand-alone computers.

Normalization of multispectral data in positron emission tomography

Data acquisition using more than one energy window has been proposed principally for scatter correction in positron emission tomography (PET). However, prior to scatter correction, such data must be corrected for various distortions including detector efficiency and spectral nonuniformities. The aim of this work is to describe and validate a normalization technique that can minimize these undesirable effects. As with conventional methods using broad windows, the technique reduces the non-uniformity of data acquired in several narrow windows, while performing an additional task unique to multispectral acquisition, i.e. to restore symmetry in data acquired by mirror window pairs of individual detectors. Non-uniformity and asymmetry reductions have been achieved by averaging each pair of detectors over all detectors and averaging each mirror window pair, respectively. The method has been validated using data with different degrees of spatial and spectral distortion, and has been found to be capable of restoring the greatest spectral asymmetric acquisition possible with our animal PET system. Unlike the broad-window imaging, a match of spectral composition of photon fluence between the calibration and measurements is not a requirement. In conclusion, multispectral data acquisition in PET is possible with fairly non-uniform detector response. The success of the technique, however, depends on detectors with very stable characteristics.