What is Nuclear Medicine?
Nuclear Medicine is a clinical speciality where radiopharmaceuticals are administered to the patients for various diagnostic and therapeutic applications.
Radiopharmaceuticals are radioactive drugs and consists of two components, one which is radioactive and other, non-radioactive. The non-radioactive component has unique properties of localising in the organ/tissues of interest. The radioactive component tagged to the non-radioactive component helps to form an image of the distribution of the radiopharmaceutical in the body.
Nuclear Medicine is generally classified into “Diagnostic Nuclear Medicine” and “Therapeutic Nuclear Medicine”.
How is Nuclear Medicine useful?
Nuclear Medicine is unique as it provides the functional information of an organ or tissues of interest in the body, unlike other radiological investigations like X-Ray, Computed Tomography (CT) scan and conventional Magnetic Resonance Imaging (MRI) which provides only structural information.
Nuclear Medicine imaging detects changes or abnormalities in the body tissues at an early stage of the disease and often much before it can be identified by conventional diagnostic procedures. Early detection of disease makes it possible to treat disease sooner in its course and thereby permitting a favourable outcome.
What is Diagnostic Nuclear Medicine?
In Diagnostic Nuclear Medicine, small or trace amounts of radiopharmaceutical is administered to the patient for diagnosing abnormalities in the organ or tissues of the body.
The gamma radiation emitting 99mTc (Technetium-99m), having a half-life of 6 hours is the most commonly used radioisotope for routine Planar and Single Photon Emission Computed Tomography (SPECT) imaging. Also,18F (Fluorine-18) having a half-life of 110 minutes is the most often used radioisotope in Positron Emission Tomography (PET) imaging.
Depending on the type of nuclear medicine investigation, the route of administration of the radiopharmaceutical would also vary. It may be administered either intravenously, orally or through inhalation as aerosols or gases.
The radiotracer localised in the tissues emits energy in the form of gamma radiations, which are detected using special imaging equipments such as a Gamma Camera or a PET scanner. With the help of a computer and certain algorithms, images are created of the tissue or the organ, giving details of its structure and function. A nuclear medicine physician interprets the image and provides the diagnosis.
What is Therapeutic Nuclear Medicine?
In Therapeutic Nuclear Medicine, radiopharmaceuticals are administered either for curing the disease (e.g. hyperthyroidism and differentiated thyroid cancer treatment where 131I – sodium iodide is used) or for palliative treatment (e.g. to relieve pain from spread of cancer to bones where 32P-orthophosphate, 89Sr-chloride are used).
What is Molecular Imaging?
Molecular Imaging is a discipline which enables the visualization, characterization and quantitation of biological processes taking place at cellular level in living tissues without affecting them. Nuclear Medicine studies like PET and SPECT scans, functional MRI and Optical imaging are examples of molecular imaging.
What is PET scan?
Positron Emission Tomography (PET) scan, world over, is recognized as one of the emerging nuclear medicine molecular imaging techniques. It is being used as an important non-invasive tool for many applications in oncology, neurology, cardiology, infection and inflammation imaging procedures. It provides the clinician with three-dimensional images and information about how organs and tissues inside the body are functioning at the molecular and cellular level.
How is a PET scan different from CT or MRI scan?
PET scans provide information on metabolic changes at cellular level which cannot be obtained by other imaging tests like CT scan or MRI. Since disease process often begin with functional changes at the cellular level, a PET scan can often detect the disease in early stages and much before they become evident on CT or MRI scan.
What is a PET-CT scan?
When a CT scan is performed along with a PET scan as a part of the same diagnostic work up, it is termed as PET-CT scan. It uniquely combines the functional information provided by the PET scan with the structural information obtained from the CT scan. This increases the ability to detect disease more accurately as compared to PET and CT alone.
How does a PET-CT scan help my doctor?
A PET-CT scan helps your doctor in the following ways :
To detect disease in its early stages, often before the patient becomes symptomatic especially when other diagnostic tests are likely to give negative results.Assessment of the extent and severity of the disease. To tailor the therapy on an individual basis based on the findings of PET-CT scan report.
Evaluate the effectiveness of a treatment regimen.
Modify treatment plans in response to altered biological behaviour of the tissue.
Assess disease progression.
Identify recurrence of disease and help manage ongoing care.
Which radiotracers are used for PET imaging?
The most widely used PET tracers in India are 18F–Fluorodeoxyglucose (18 F-FDG) & 18F- Sodium Fluoride (18F-NaF).
18F-Fluorodeoxyglucose (18F-FDG) is similar to glucose in structure with subtle differences. The FDG (unlike glucose) gets trapped in abnormal cells due to these differences. This ‘metabolic trapping’ of 18F-FDG forms the basis of 18F-FDG PET-CT scan.
18F-Sodium Fluoride (18F-NaF) is used for imaging of skeletal system (Bone Scanning). It gives sharper and more informative images as compared to 99mTc-Methy-lene-Di-Phosphonate (MDP) bone scan done on Gamma Camera.
Is hospital admission required for a PET-CT scan?
No! Hospital admission is not required for a PET-CT scan. The procedure takes approximately 4 hours from the time of arrival till the end of study.
How should I prepare myself, if I am scheduled for an 18F-FDG PET-CT scan?
You should not eat and drink for at least 6 hours before your scheduled time of appointment. You are, however, permitted to drink plain water only.
You should not undertake any intense and strenuous physical activity or exercise for 24 hours before the scan appointment.
On the day of scan:
You should carry all your relevant medical records, reports, film and/or CD of X-rays, CT, MRI, PET-CT or any other investigation done till date on the day of the study. These are important in the interpretation of your scheduled PET-CT scan by the doctor.
• You should take along an adult attendant.
• You should avoid children and pregnant women accompanying you.
• You should wear loose and comfortable clothing.
• You should not wear any metallic objects, jewellery or valuables .
• You may be required to remain at the Centre for at least 4 hours from the scheduled time of appointment for the PET-CT scan.
For Female Patients Only :
Please inform the staff at the time of
• You are pregnant.
• You think you may be pregnant or
• You are breast-feeding.
For Diabetic Patients Only (in addition to the earlier instructions):
You should not have any anti-diabetic medicines (tablets/ insulin injections) on the day of study.
Your fasting blood sugar level must be below 150 mg/dl at the scheduled time of your appointment.
You may consult your physician to determine the safest way possible to manage your blood sugar level before your scan.
How should I prepare myself, if I am scheduled for an 18F-Fluoride Bone scan?
You need not be fasting at the time of the study.
Diabetic patients can have breakfast and their anti-diabetic medicines.
High blood sugar does not interfere with the results of the scan.
Rest of the instructions to be followed are the same as those of 18F-FDG PET-CT scan (mentioned in the previous section).
What would be the procedures undertaken when I am at the Centre for a PET-CT scan?
A detailed history pertaining to your illness and information relevant to scan would be noted by the doctor and all your previous medical records and reports would also be reviewed.
You would be then directed to a room where a small dosage of radioactive medicine will be injected in your vein.
After injection, you would be asked to quietly relax and rest in a separate room at our Centre for about an hour before you are taken up for the scan.
During this resting period, unless recommended by the staff, no attendants or relatives would be permitted to stay with you in this separate waiting room.
You are advised to stay calm, restrict physical movements and avoid talking to others while present in the room.
You would be required to drink plenty of water after the injection and till you are in the resting room.
You may be given oral contrast to drink. This helps to get a better image quality.
You will be asked to void (pass urine) before starting the scanning procedure.
You would be asked to lie down flat on your back on the bed of the PET-CT scanner and are expected to remain still during the entire scanning period of 15-20 minutes.
After the completion of the scanning, your PET-CT scan would be reviewed and if needed it may be repeated.
Are PET-CT procedures safe?
Yes! PET-CT procedures are safe, painless, non-invasive and cost-effective modality for imaging and treating the disease.
Does one experience any discomfort during the PET-CT procedure?
PET-CT scan procedures are rarely associated with any significant discomfort or side effects. You may feel a slight pin prick when a needle is secured for the injection procedure. You may get a cold sensation moving up your arm when the radiotracer is pushed through the needle. For the scanning you may be asked to raise your arms above your head which may cause slight discomfort but is tolerated well by majority of the patients. When contrast injection is given at the time of scanning, you may get a warm sensation moving up your arm.
Overall, there are no major discomforts experienced.
Is the amount of radiation received from a PET-CT scan very high?
A PET-CT scan has two components: a PET scan and a CT scan, which are done together. The effective dose received from a typical PET scan is 7 milliSievert (mSv). The effective dose received from a CT scan has a very wide range (8-30 mSv) depending on the type of the test, the area of the body scanned and the purpose of the test. The small quantity of radioactive medicine injected for the scan, will lose its radioactivity over time due to its short half-life of 110 minutes. It also passes out of your body through your urine or stool during the first few hours after injection. Hence the amount of radiation exposure which you receive is very small, almost the same as that you receive from natural environment in 3 years.
Does PET-CT scan cause any allergic reactions?
The radiotracers used for PET scan are absolutely safe and have no reported allergic reactions. The CT scan done as a part of PET-CT procedure may be performed with or without injection of a contrast agent. Contrast agents are usually given to extract more information from the study which may not be possible to obtain from a plain CT scan. These contrast agents are known to cause allergic reactions in few patients as seen with any other contrast enhanced CT procedure. The routinely used non-ionic contrast media are safe. However, in very few cases some side effects may be noticed, like :
Minor Reactions: Itching, rashes and stomach upset are common. They are self-limiting and require no treatment.
Moderate reactions: They include shortness of breath, irregular heart beat, and high blood pressure. The chance of such reactions is 1 in 1,000 i.e. 0.1%.
Severe Reactions: They occur rarely and include convulsions, low blood pressure, and unconsiousness. One in 1,00,000 studies (i.e. 0.01% ) can lead to death.
No! Generally, there are no special restrictions. You may resume your routine activities immediately after your scan is over. However, it is advisable to avoid prolonged contact with infants, small children and pregnant women for at least 6 hrs after the scan.
Can a breast-feeding mother undergo a PET-CT scan?
Yes! However, it is recommended that you do not breast-feed your baby for 6-8 hours after the injection has been performed as small amounts of the administered radiotracer might be excreted in breast milk. It is advisable to collect milk before the injection, so that this can be used to provide a feed.
How long does it take to get a PET-CT scan report?
A PET-CT scan report is usually available within 2 days.