What is nuclear medicine?
Specialists in the field of nuclear medicine use safe, pain free and cost-effective methods to image the body and treat disease. Providing doctors with information about both structure and function makes nuclear medicine imaging unique. The technique enables doctors to gather medical information that would otherwise be unattainable, call for surgery, or require more expensive diagnostic tests. Processes within nuclear medicine imaging typically identify abnormalities early in the progress of a disease, often before numerous medical problems are noticeable with other diagnostic tests.
Radioactive materials (radiopharmaceuticals) are used in very small amounts by nuclear medicine. In imaging, the radiopharmaceuticals are detected by advanced cameras that collaborate with computers to yield precise pictures about the area of the body being imaged. In treatment, the radiopharmaceuticals go directly into the organ being treated. The amount of radiation in the average nuclear imaging procedure can be compared to the amount of radiation during a diagnostic x-ray, and the amount received in the average treatment procedure is kept well within safe limits.
Nuclear medicine provides procedures that are essential in many of today’s medical specialties. New and inventive nuclear medicine treatments target molecular levels within the body and revolutionize our comprehension and approach to a variety of diseases and conditions.
Scans are used to diagnose many medical conditions and diseases. Some of the more common tests include the following:
- renal scans - used to examine the kidneys and to detect any abnormalities, such as tumors or obstruction of the renal blood flow.
- thyroid scans - used to evaluate thyroid function.
- bone scans - used to evaluate any degenerative and/or arthritic changes in the joints, to detect bone diseases and tumors, and/or to determine the cause of bone pain or inflammation.
- gallium scans - used to diagnose active infectious and/or inflammatory diseases, tumors, and abscesses.
- heart scans - used to identify abnormal blood flow to the heart, to determine the extent of the damage of the heart muscle after a heart attack, and/or to measure heart function.
- brain scans - used to investigate problems within the brain and/or in the blood circulation to the brain.
- breast scans - often used with mammograms to locate cancerous tissue in the breast.
How are nuclear medicine scans done?
As stated above, nuclear medicine scans may be performed on many organs and tissues of the body. Each type of scan employs certain technology, radiopharmaceuticals, and procedures.
A nuclear medicine scan consists of three phases: tracer (radiopharmaceutical) administration, taking images, and image interpretation. The amount of time between administration of the tracer and the taking of the images may range from a few moments to a few days, depending on the body tissue being examined and the tracer being used. The time required to obtain the images may also vary from minutes to hours.
One of the most commonly performed nuclear medicine examinations is a heart scan. Myocardial perfusion scans and radionuclide angiography scans are the two primary heart scans. In order to give an example of how nuclear medicine scans are done, the process for a heart scan is presented below.
Although each hospital may have specific protocols in place, generally a heart scan may follow this process:
- The patient will be asked to undress from the waist up and put on a gown.
- The patient is connected to an EKG monitor that records the electrical activity of the heart and monitors the heart during the procedure using small, adhesive, electrode patches.
- The patient will lie on a table in the procedure room.
- An intravenous (IV) line is started in the hand or arm.
- During the procedure, the patient will need to lie as still as possible, as any movement can adversely affect the quality of the scan. The gamma camera (a device to scan patients who have been injected with small amounts of radioactive materials) will be positioned over the patient as he/she lies on the table.
- A radioactive tracer will be injected into the IV to "tag" the blood cells so their progress through the patient's heart can be traced with a scanner.
- The gamma camera obtains images of the heart by measuring the amount of the radioactive substance that has been absorbed by the heart tissue as the patient continues to lie on the table.
- The patient may be asked to change positions during the test; however, once the patient has changed position, he/she will need to lie very still.
- If the physician wishes to evaluate the heart's function under stress, the patient may exercise on a treadmill or a bicycle for a period of time. Additional images will be obtained after the exercise period.
- Once all the heart images have been obtained, the IV will be removed, and the patient will be allowed to leave, unless the physician instructs differently.
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What is Positron Emission Tomography (PET)?
Positron Emission Tomography (PET) is a significant diagnostic imaging modality used most commonly in determining the presence and seriousness of cancers, neurological conditions, and cardiovascular disease. PET is the most effective way to check for cancer recurrences and it offers noteworthy advantages over other types of imaging such as CT or MRI scans in detecting disease in many patients.
The images yielded by PET show the chemistry of organs and other tissues like tumors. A radiopharmaceutical, like FDG (fluorodeoxyglucose), including both sugar (glucose) and a radionuclide (a radioactive element) that gives off signals, is injected into the patient, and its emissions are gauged by a PET scanner.
This scanner is made up of an array of detectors that surround the patient. Using the gamma ray signals emitted by the injected radionuclide, PET measures the metabolic activity at a particular site in the body and a computer reassembles the signals into images. Since cancer cells have higher metabolic rates than normal cells, they appear as a denser area on a PET scan. PET is helpful in diagnosing cardiovascular and neurological disease because it highlights areas with increased, diminished or no metabolic activity, thereby locating problems.
Cancer and PET
PET is effective in identifying whether cancer is present, if it has spread, responded to treatment, and if the cancer was eliminated after treatment. PET is considered effective for lung, head and neck, colorectal, esophageal, lymphoma, melanoma, breast, thyroid, cervical, pancreatic, and brain in addition to less-frequently occurring cancers.
- Early Detection: PET images biochemical activity, therefore it can characterize a tumor as benign or malignant, avoiding surgical biopsy when the PET scan yields a negative result. Because PET scans image the entire body, confirmation of distant metastasis can affect treatment plans in some cases from surgical intervention to chemotherapy.
- Staging of Cancer: PET is effective in determining the full extent of disease, particularly in lymphoma, malignant melanoma, breast, lung, colon and cervical cancers.
- Checking for recurrences: PET is the most accurate diagnostic tool used to differentiate tumor recurrences from radiation necrosis or post-surgical changes. This allows for the development of a more rational treatment plan for the patient.
- Assessing the Effectiveness of Chemotherapy: The level of tumor metabolism is contrasted on PET scans taken before and after a cycle of chemotherapy. A successful response seen on a PET scan often precedes alterations in anatomy and is subsequently an earlier indicator of tumor response than seen with other diagnostic modalities.
PET and CT or MRI
PET can be superior to MRI or CT, particularly in distinguishing tumor from benign lesions and in differentiating malignant from non-malignant masses, because it measures metabolism as opposed to “seeing” structure. PET is frequently used in conjunction with MRI or CT through “fusion” to give a full three-dimensional view of an organ and the cancer’s location within the organ. The newest PET scanners are a combination of PET and CT devices, providing important metabolic information from PET superimposed on the high-quality anatomic information from CT.
Neurological Disease
The fact that PET can measure metabolism also has implications in diagnosing Alzheimer’s disease, Parkinson’s disease, epilepsy and other neurological conditions. This is because PET can vividly illustrate areas where brain activity is abnormal.
Alzheimer’s Diagnosis: Until recently, autopsy has been considered the only definitive test for Alzheimer’s disease (AD). Recent studies show that PET can provide crucial diagnostic information and confirm an AD diagnosis. When comparing a normal brain to an AD-affected brain on a PET scan, a distinct mass appears in the area of the AD-affected brain. This pattern is also seen very early in the Alzheimer’s disease course. Conventionally, the confirmation of AD is a long process of elimination that is typically between two and three years of both diagnostic and cognitive tests. Early diagnosis can provide the patient access to therapies, which are more effective earlier in the disease.
- PET is useful in differentiating AD from other dementia disorders such as vascular dementia, Parkinson’s disease, Huntington’s disease, etc.
- PET is one of the most accurate available methods to localize areas of the brain causing epileptic seizures and to determine if surgery is an option for treatment.
Cardiovascular Disease
With the measurement of both blood flow (perfusion) and metabolic rate within the heart, PET scans can locate areas of decreased blood flow, such as areas with blockages, and differentiate living muscle from damaged muscle, which has inadequate blood flow (myocardial viability). This information is significant in those who have previously had myocardial infarction (heart attack) and who are currently being considered for a procedure such as angioplasty or coronary artery bypass surgery.
Information source for Web content includes: the Society for Nuclear Medicine (SNM)
