PET/CT scan

General PET/CT Scan

PET stands for positron emission tomography, an imaging technology that studies the body’s biological functions by measuring energy emitted by a radioactive substance ingested prior to the procedure. The position and concentration of the injected material, detectable because radioactive particles called positrons interact with body tissue to produce gamma radiation, provides information about cell biochemistry and metabolism that can help diagnose a variety of diseases and other problems before physical damage has occurred. (This anatomical damage is what x-rays, CT and MRI are intended to detect.)

Whole-body PET scans are useful for determining the progression of cancer and the effectiveness of cancer treatment. Scans of the brain can aid in the diagnosis and treatment planning of memory or seizure disorders and brain tumors, while scans of the heart are commonly performed to measure blood flow, detect signs of coronary artery disease and determine whether damaged heart muscle is permanently scarred or able to be revived with surgery.

The first step is the injection of a radioactive material, called a tracer, into the body – without it, tissue would not release positrons for the scanner to detect. Produced in a machine called a cyclotron, the tracer is specially designed to attach to a specific compound in the body, such as glucose, water or ammonia. After enough time has passed for the tracer to spread throughout the body and settle in appropriate areas, the patient lies down on the PET scan table and is moved into the machine, where an array of ring-shaped detectors measure the positron emission and create an image. These images appear on a computer screen beside the machine, with different colors depicting various concentrations of the tracer. This information helps radiologists determine, for example, that cancer is present in an area with high glucose absorption (indicating rapid cell metabolism). The preliminary administering of the tracer takes half an hour to an hour to be absorbed. Scanning itself lasts 30-45 minutes.

The only discomfort associated with PET scans may come from the injection of the tracer or from having to remain still within the scanning apparatus. Neither the injected material itself nor the scanner cause pain – you won’t even be able to feel them.

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Image Proliferation of DNA using FLT PET/CT imaging

F-18 fluorothymidine (F-18 FLT) is a radiopharmaceutical complex which targets DNA proliferation and is a useful biomarker in improving imaging specificity in detection of viable tumor, particularly in the setting of recent therapeutic interventions such as radiation therapy. Although F-18 FLT is not approved by FDA for human use in USA, New York Radiology Partners in collaboration with various departments in the hospitals affiliated with Contiuum Health Partners have been involved in a research project cleared by FDA and approved by Institution Review Board (IRB). See the case example below.


Figure I		Figure II

This is an example of a patient with stage IIIa lung cancer who was treated with neoadjuvant chemoradiotherapy.

On figure I, there are two rows of images, the first row illustrates F-18 2-fluorodeoxy glucose FDG PET/CT images at the time of staging demonstrating glucose hypermetabolism at the site of primary right lung malignancy as well as in the right hilar adenopathy. The second row of images are from a prospective, IRB-approved and FDA cleared investigational FLT PET/CT study demonstrating treatment response both at the site of primary malignancy as well as right hilar lymphadenopathy. Focal FLT accumulation in the right scapula is suspicious for focal DNA proliferation. Bone window images of the CT scan (figure II) reveal interval development of a mixed focal lesion in the right scapula, suspicious for metastatic disease and therefore potentially precluding the patient from curative surgery. Biopsy of this lesion is being pursued at the time of this writing.