Mesothelioma Diagnosis – Positron Emission Tomography (PET) Scan

5 months ago

Positron Emission Tomography scanning (PET) provides more information than x–rays or CT Scan and MRI scans, detecting biological changes and extremely small cancerous tumors. Able to indicate whether a tumor is benign or malignant, PET scanning also shows the extent to which cancer has spread. This can help detect how far mesothelioma has spread into the patient's body, and whether the human cells are malignant or not. It may be used to determine whether surgery is necessary or if treatment therapies are working. Various studies have shown PET scans to be more successful in diagnosing the presence of malignant mesothelioma when compared to standard mesothelioma diagnostic procedures (e.g. thoracoscopy or surgical biopsy).

Because cancers metabolize sugars at a higher rate than normal tissues or organs, the PET scan shows where there is abnormal activity and can pinpoint the areas of active disease. It differentiates scar tissue from tumor. It also can accurately image and measure the metabolic function of cancer to track the effects of radiation or chemotherapy, supplying doctors with information that can help avoid unnecessary surgery.

What is Positron Emission Tomography (PET) Scan?

Mesothelioma Diagnosis - PET-Scanner

Positron emission tomography (PET) is a nuclear medicine imaging technique which produces a three-dimensional image or picture of functional processes in the body.

The PET scan is a useful diagnostic and prognostic tool because it reveals the location of cancer cells in three dimensions, with more accuracy and finer detail than some of the other tests. PET scans employ the metabolic processes of cells to make highly detailed images of the inside of the body. Prior to a PET scan, the patient receives an intravenous injection of a solution of radioactive glucose. The patient’s body is then scanned with equipment that can detect the presence of the radioactive substance. Because cancer cells use sugar much more quickly than healthy tissues, the cancerous tissue absorbs the radioactive material. A scanner can spot the radioactive deposits, distinguishing cancerous from healthy tissue.

How is PET( Positron Emission Tomography ) Scan work?

PET Scan Procedure

To conduct the scan, a short-lived radioactive tracer isotope is injected into the living subject (usually into blood circulation). The tracer is chemically incorporated into a biologically active molecule. There is a waiting period while the active molecule becomes concentrated in tissues of interest; then the research subject or patient is placed in the imaging scanner. The molecule most commonly used for this purpose is fluorodeoxyglucose (FDG), a sugar, for which the waiting period is typically an hour. During the scan a record of tissue concentration is made as the tracer decays.

As the radioisotope undergoes positron emission decay (also known as positive beta decay), it emits a positron, an antiparticle of the electron with opposite charge. After travelling up to a few millimeters the positron encounters an electron. The encounter annihilates them both, producing a pair of annihilation (gamma) photons moving in opposite directions. These are detected when they reach a scintillator in the scanning device, creating a burst of light which is detected by photomultiplier tubes or silicon avalanche photodiodes (Si APD). The technique depends on simultaneous or coincident detection of the pair of photons moving in approximately opposite direction (it would be exactly opposite in their center of mass frame, but the scanner has no way to know this, and so has a built-in slight direction-error tolerance). Photons that do not arrive in temporal "pairs" (i.e. within a timing-window of few nanoseconds) are ignored.

A PET scan is sometimes performed in tandem with a CT scan, providing even more detailed and useful results. Particularly beneficial during diagnosis of the disease, the combination of a CT Scan and PET scan renders fast, detailed results that accurately reflect the presence and stage of mesothelioma.

Test results for PET scans are commonly available within a few days. As with CT scans, PET scans are interpreted first by a specialist and then forwarded to a patient’s physician, who explains the test results to the patient.

PET Use for Mesothelioma Diagnosis and Staging

PET has helped lung cancer patients avoid chest surgery by finding tumors that an operation would not remove (see PET Scans Detect Lung Cancer Spread, American Cancer Society). Medicare has approved its use in the diagnosis and staging of melanoma, lymphoma, and cancers of the lung, esophagus, colon, rectum, mouth and throat.

Recent studies indicate that PET holds great promise for diagnosing mesothelioma and determining mesothelioma staging, or the extent to which tumors have spread. At the University of Pennsylvania Medical Center, researchers evaluated 28 patients for mesothelioma using the sugar tracer fluoro–2–deoxy–D–glucose (FDG) and PET (Chest. 1998 Sep; 114(3): 713–22). In a comparison of PET imaging with thoracoscopy or surgical biopsies, PET successfully indicated the presence of disease in 24 patients, and of benign conditions in the other four. The uptake of FDG was significantly higher in diseased cells, and PET analysis also showed tumors in the lymph nodes of 9 patients. The lymph nodes appeared normal in CT scans.

Another study at Brigham and Women’s Hospital and Harvard Medical School in Boston traced 15 patients, 11 of whom had mesothelioma and four who were disease–free (J Nucl Med. 2002 Sep; 43(9): 1144–9). PET results were compared with laboratory analysis of biopsied fluids and tissues. PET detected all 11 primary tumors, and confirmed the absence of disease in the other four patients. Out of 28 disease–positive lesions, PET accurately detected 27.

These studies indicate that although CT scans are a standard test for mesothelioma patients, PET also has a role in mesothelioma diagnosis. Whether or not you should have a PET scan is a decision that should be discussed with your doctor. He or she will make a judgment based on your particular case and your other test results.

Source: Mesothelioma Site