Preclinical time of flight imaging

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ABSTRACT:A preclinical positron emission tomography (PET) imaging method includes acquiring time-of-flight localized PET imaging data from one or more non-human animal subjects and reconstructing the acquired data to form an image. In an illustrative PET scanner includes: radiation detectors (12) viewing an examination region; a subject support assembly (14) supporting a plurality of preclinical studies subjects in the examination region for simultaneous PET imaging; coincidence electronics (20) acquiring time-of-flight localized PET imaging data from the preclinical subjects using the radiation detectors; and reconstruction electronics (22) that (i) perform a filtering operation based at least in part on the time-of flight information, the filtering operation including at least one of discarding non-probative time-of-flight localized PET imaging data and associating time-of-flight localized PET imaging data with individual preclinical subjects and (ii) reconstruct the filtered data to form images of the preclinical subjects.

DESCRIPTION:This application claims the benefit of U.S. provisional application Ser. No. 60/974,585 filed Sep. 24, 2007, which is incorporated herein by reference.

The following relates to the medical arts, and more particularly to preclinical imaging using positron emission tomography (PET), and is described with particular reference thereto. However, the following will find further application in other tasks such as PET imaging for veterinary diagnosis.

In conventional PET imaging, a radiopharmaceutical is administered to a subject so as to distribute through the subject or to aggregate in portions of the subject that are of interest, such as anatomical tissue of interest. The radiopharmaceutical exhibits positron-electron annihilation events that generate oppositely directed gamma rays each having energy of 511 keV. Radiation detectors arranged around the subject detect substantially simultaneous gamma ray detections, i.e. within a selected coincidence time window, and the substantially simultaneous gamma ray detections are assumed to be sourced by the same positron-electron annihilation event lying at some point along the line-of-response connecting the two substantially simultaneous or coincident gamma ray detection events. A data set of such lines-of-response is generated, and is reconstructed using filtered backprojection, iterative backprojection, or another technique to obtain an image of the radiopharmaceutical distribution in the subject.

Time of flight PET imaging is similar, but makes use of the finite time difference between the substantially coincident gamma ray detection events to localize the positron-electron annihilation event along the line-of-response. A gamma ray travels at the speed of light (c), i.e. about 3 centimeters every 100 picoseconds. The spatial localization (Δx) is given by Δx˜c·Δt/2, so for a radiation detector having, as a typical example, a temporal resolution of about 600 picoseconds it follows that the time-of-flight localization provides a spatial resolution along the line-of-response of about 9 centimeters. In practice, this localization may be represented, for example, by a Gaussian distribution having a FWHM of about 9 centimeters. Spatial localization on the order of Δx=9 centimeters is advantageous for imaging a typical human subject having a size substantially larger than this spatial localization.

On the other hand, a mouse, rat, guinea pig, or other small animal of the type typically used in preclinical research is of a size smaller than or comparable with the spatial localization Δx provided by time-of-flight information. Accordingly, time-of-flight localization does not provide additional useful information as to the location of the positron-electron annihilation event within the animal. This recognition, coupled with the substantial additional expense of including high-speed radiation detectors and high-speed and high-capacity time-of-flight localization processing, has heretofore motivated against including time-of-flight capability in preclinical PET scanners.

Moreover, existing preclinical studies have typically used preclinical PET imaging to assess large-scale anatomical features of tumors or other large-scale growths resulting from cancer or other pathologies under study. For example, a study may quantify the effect of a therapy by the reduction in average tumor size (if any) in a statistically significant number of test animals. Such assessments are readily performed using PET imaging since the tumors of interest are substantially larger than the spatial resolution of a typical PET scanner. If the therapy successfully reduces the tumor size below the resolution of the conventional preclinical PET scanner, it is generally assumed that the therapy is indeed effective. This approach is convenient and provides readily comprehended metrics such as tumor size. However, the measured large-scale anatomical features may, or may not, be probative of outcome determinating aspects of the cancer such as the extent of metastasis, that is, the extent to which cancerous tissue has spread away from the primary tumor. It is known that most cancer patients succumb to the effects of metastatic cancer.

The following provides new and improved apparatuses and methods which overcome the above-referenced problems and others.