PET-CT

PET-CT has revolutionized many fields of medical diagnosis, by adding precision of anatomic localization to functional imaging, which was previously lacking from pure PET imaging. For example, in oncology, surgical planning, radiation therapy and cancer staging have been changing rapidly under the influence of PET-CT availability, to the extent that many diagnostic imaging procedures and centers have been gradually abandoning conventional PET devices and substituting them by PET-CTs. Although the combined device is considerably more expensive, it has the advantage of providing both functions as stand-alone examinations, being, in fact, two devices in one.

The only other obstacle to a wider dissemination of PET-CT is the difficulty and cost of producing and transporting the radiopharmaceuticals used for PET imaging, which are usually extremely short-lived (for instance, the half life of radioactive fluor₁₈ used to trace glucose metabolism (using fluorodeoxyglucose, FDG) is two hours only. Its production requires a very expensive cyclotron as well as a production line for the radiopharmaceuticals.

Procedure for FDG imaging

A whole body scan, which usually is made from mid-thighs to the top of the head, takes from 5 minutes to 40 minutes depending on the acquisition protocol and technology of the equipment used. FDG imaging protocols acquires slices with a thickness of 2 to 3 mm. Hypermetabolic lesions are shown as false color-coded pixels or voxels onto the gray-value coded CT images. Standardized Uptake Values are calculated by the software for each hypermetabolic region detected in the image. It provides a quantification of size of the lesion, since functional imaging does not provide a precise anatomical estimate of its extent. The CT can be used for that, when the lesion is also visualized in its images (this is not always the case when hypermetabolic lesions are not accompanied by anatomical changes).

FDG doses in quantities sufficient to carry out 4-5 examinations are delivered daily, twice or more times per day, by the provider to the diagnostic imaging center.

For uses in stereotactic radiation therapy of cancer, special fiducial marks are placed in the patient's body before acquiring the PET-CT images. The slices thus acquired may be transferred digitally to a linear accelerator which is used to perform precise bombardment of the target areas using high energy photons (radiosurgery).

See also

External links

Category:Medical imaging Category:Nuclear medicine Category:Radiology Category:Medical tests Category:Neuroimaging Category:Medical physics Category:Oncology