Douglas J. Rowland

Quantitative imaging of bromine-76 and yttrium-86 with PET: a method for the removal of spurious activity introduced by cascade gamma rays.

Positron Emission Tomography of bromine-76 and yttrium-86 results in the detection of coincident events that are not strictly associated with annihilation photon pairs. Instead, these coincidences occur because prompt gamma rays emitted by these nuclides result in cascades of photons that are emitted within the timing window of the PET scanner. Pairs of detected photons from these cascades are not angularly correlated and therefore contain little information regarding the location of their source. Furthermore, these coincidences are not removed by correction procedures (e.g., randoms, scatter) routinely applied to PET data. If left uncorrected, the cascade coincidences will result in spurious apparent activity within the PET images. A correction, applied within projection space, that removes the cascade coincidence signal from septa-in (i.e., two-dimensional) datasets is proposed and tested on phantom data.

MicroPET imaging with non-conventional isotopes

The utilization of new positron emitting isotopes for position emission tomography (PET) imaging raises several questions about their ability to provide images of good quality and to perform accurate quantification. This issue is even more pertinent when using high-resolution scanners designed for the imaging of small animals. At Washington University, we are currently producing a whole array of positron emitters; some of them, like Ga-66 and Br-76, emit high-energy positrons and prompt gamma rays that affect spatial resolution and increase the random coincidence contribution. We have now started to evaluate these isotopes in terms of their ability to perform high-quality imaging. Spatial resolution measurements were evaluated using the Concorde MicroSystem Inc. microPET-R4 camera. Electron transport calculations have been performed and compared with experimental data. They revealed that for this camera, the detector size is still the limiting factor on resolution for isotopes emitting low-energy positrons like F-18 and Cu-64. The transaxial resolution was measured to be around 2 mm at the center of the field of view (FOV) for these isotopes. The dominant factor becomes the positron range for other isotopes like Cu-60 and Tc-94 m, with transaxial resolution of 3.5 and 4.3 mm, respectively. Due to the long tail of the positron range distribution; a strong contrast reduction is observed. In this paper, experimental data on spatial resolution will be presented for a number of nonconventional PET isotopes, and consequences on image quality will be discussed.

Molecular imaging: the application of small animal positron emission tomography.

The extraordinary advances in genomic technologies over the last decade have led to the establishment of new animal models of disease. The use of molecular imaging techniques to examine these models, preferably with non‐destructive imaging procedures, such as those offered by positron emission tomography (PET), are especially valuable for the timely advancement of research. With the use of small animal PET imaging it is possible to follow individual subjects of a sample population over an extended time period by using highly specific molecular probes and radiopharmaceuticals. In this Prospect small animal PET imaging will be described, specifically focusing on the current technologies, its applications in molecular imaging and the logistics of performing small animal PET. J. Cell. Biochem. Suppl. 39: 110–115, 2002.