Whole-body PET can detect unsuspected extrathoracic metastases in up to 10% of patients when CT scanning fails to detect them, and may also alter management in up to 40% of cases. PET may be used to evaluate adrenal masses, with sensitivities and specificities of PET reported to be 100% and 80–100% respectively[7].
A PET/CT scan can be more sensitive than other imaging tests and may find cancer sooner than other tests do. Not all tumors take up the radiotracer, but PET/CT is highly accurate in differentiating from the benign and malignant tumors it finds, particularly in some cancers such as lung and musculoskeletal tumors.
Though most cancers are picked up on PET CT, there are a few which do not. The most important of these would be cancer of stomach (signet cell type). In such cases performing this test would be waste. However, there are cancers which are very sensitively detected which include lymphoma, GIST, etc.
The diagnostic accuracy of PET-CT was 93.5%, and the false positive rate was 6.50%.
In cancer cells, there is an overproduction of glucose transporters and, as a result, increased FDG uptake. However, not all PET-positive lesions are cancer, and in many instances, PET findings can be false positive."
FDG is not only a cancer specific imaging agent, false positive results may be observed with benign diseases. False positive results are commonly observed in areas of active inflammation or infection (Gupta et al., 20000), with a reported false positive rate of 13% and false negative rate of 9% (Alavi et al., 2002).
A CT scan (also known as a computed tomography scan, CAT scan, and spiral or helical CT) can help doctors find cancer and show things like a tumor's shape and size. CT scans are most often an outpatient procedure. The scan is painless and takes about 10 to 30 minutes.
The PET scan accurately determined the outcome of 90% patients, while the combination of all the conventional images accurately determined the outcome of only 75% of patients.
As a result, both the overall diagnostic yield and accuracy of PET/CT-guided biopsy were 97.62%. These results compare favorably with those of CT-guided bone biopsy (overall diagnostic yield: 81.82% and accuracy: 76.36%, respectively).
PET scans can show solid tumors in the brain, prostate, thyroid, lungs, and cervix. The scans can also evaluate the occurrence of colorectal, lymphoma, melanoma, and pancreatic tumors. They are also used to assess if treatment is being effective in eliminating cancer.
PET scanning can give false results if chemical balances within the body are not normal. Specifically, test results of diabetic patients or patients who have eaten within a few hours prior to the examination can be adversely affected because of altered blood sugar or blood insulin levels.
Modern clinical PET scanners have a resolution limit of 4 mm, corresponding to the detection of tumors with a volume of 0.2 ml (7 mm diameter) in 5:1 T/B ratio.
Based on the imaging, PSMA PET-CT was 27% more accurate than the standard approach at detecting any metastases (92% versus 65%). Accuracy was determined by combining the scans' sensitivity and specificity, measures that show a test's ability to correctly identify when disease is present and not present.
Not all that lights up on a PET scan can or should be considered malignancy, and clinical context can become even more pertinent. Inflammatory cells, sarcoidosis, and other thoracic etiologies such as silicone-induced granuloma, can cause PET scans to light up, giving false positives [3,4,5].
Discussion: The detection limit of PET is in the magnitude of 10(5) to 10(6) malignant cells.
CT scans are more accurate than PET scans, but PET scans can be used to diagnose cancer at an early stage. Both scans are painless and take about 30 minutes to complete. If you're unsure which scan is right for you, be sure to talk to your doctor about PET and CT protocols.
The major drawback to standard PET is that the images are of substantially lower resolution than, for example, those of CT and MRI, and PET is generally poor at delineating anatomic detail.
It is quite true that a "positive" PET scan should, in most cases, be followed up by a biopsy. Many benign conditions also produce PET images that show significant metabolism of the tracer.
PET/CT-guided biopsies may help in difficult situations, especially when it is important to know which part of the tumor is active or which lesion is active in patients with multiple, widespread lesions.
If a PET scan is not funded by Medicare, patients have to pay between $800 and $1000.
In general, PET scans may be used to evaluate organs and/or tissues for the presence of disease or other conditions. PET may also be used to evaluate the function of organs, such as the heart or brain. The most common use of PET is in the detection of cancer and the evaluation of cancer treatment.
A Computed Tomography, otherwise known as a CT scan, uses computers and rotating X-ray machines to create cross-sectional images of the body. These images provide more detailed information than normal X-ray images.
Weight changes, including unintended loss or gain. Skin changes, such as yellowing, darkening or redness of the skin, sores that won't heal, or changes to existing moles. Changes in bowel or bladder habits. Persistent cough or trouble breathing.
Taking a sample of the tissue called a biopsy. Medical imaging, such as X-ray, CT scan or MRI. Physical examination. Specialized tests such as a mammogram for breast cancer and a Pap smear for cervical cancer.
Do I have to pay for a PET scan? There is no cost for most PET scans if you are a citizen or permanent resident of Australia and covered by Medicare. For a limited number of indications that are not approved by Medicare, there can be a charge to the patient.