What is “Nuclear Medicine”?

Nuclear Medicine is a medical specialty that utilizes small amounts of radioactive materials or radiopharmaceuticals, to diagnose and treat diseases. Radiopharmaceuticals are substances targeting to specific organs, bones, or tissues and emit special radioactive rays, which are detected by specialized equipment. Nuclear medicine imaging procedures can often identify abnormalities much earlier in the progression of the disease than with other diagnostic tests.

Is Nuclear Medicine a new specialty?

Nuclear Medicine is an old specialty. Improvements in technology within the last two decades have helped to flourish the practice of Nuclear Medicine.

How often are Nuclear Medicine tests performed?

Approximately 80 different nuclear imaging procedures are available, uniquely providing information about both the function and structure of every major organ system in the body. The major tests, which are performed at our center, are listed. According to one data, approximately 12 million Nuclear Medicine procedures are performed in USA alone annually.

Is an appointment necessary?

Yes, appointments are necessary for this category of examination. Appointments can be made by calling the clinic where you intend to go for the examination.

What documents need I bring along?

Please bring along the letter or request form from a physician requesting for the particular examination.

Also, for easy identification, bring along your identity card or passport. This will also assist to expedite the registration process.

For follow-up cases, it is necessary to have previous x-ray films in order for the radiologist to compare and report on the progress of the condition.

How should I prepare for the nuclear medicine examination?

Generally no special preparation is required for most of the tests. In a heart scan, you may be required to discontinue certain medications for a limited time prior to the test. In a case of renal (kidney) scan, you must drink more water before the test. Generally, drinking more fluids after the procedures will help to eliminate the radiopharmaceutical quickly from the body.

At the clinic, you may be asked to change into an x-ray gown and remove jewellery or ornaments which may obscure the region of interest.

For female patients, they will be asked to certify that they are not pregnant. If there is any possibility of pregnancy, this should be brought to the attention of the physician or radiographer or nurse attending to you.

How is the procedure performed?

In most cases, the radiopharmaceutical is injected or inhaled. Images of the patient are taken using a radiation-sensitive camera, known as a gamma camera. The gamma camera detects gamma rays being emitted by the radiopharmaceutiical in the body. In certain cases, there is a delay between the injection and time of the scan, which can vary from a few hours to a few days. This is to allow the target area of the body to absorb the radiopharmaceutical.

Is the examination painful?

The examination is not painful. As in photograph taking, any movement during the procedure will render the image unclear.

How long will the procedure take?

After the injection of the radiopharmaceutical the patient may take a walk and return about 2-3 hours later for the imaging portion of the examination. The imaging will take about a half hour.

Please prepare to be at the clinic for a total of about 3 hours.

Nuclear Medicine uses gamma rays. How do they differ from other types of rays or radiation?

The four common types of radiation are alpha, beta, gamma, and x-rays.

Alpha ray:

A particle ray consisting of two protons and two neutrons (namely, a nucleus of helium). Alpha rays are produced following spontaneous decay of certain radioactive atoms, such as radium, plutonium, uranium, and radon. Because of its large mass and positive charge, an alpha ray can usually pass only a short distance - less than 1 mm - in water. A single piece of paper can stop an alpha ray effectively.

Beta ray:

A particle ray consisting of a fast electron whose mass is nearly 1/2000 of the mass of a proton or neutron. Beta rays are produced following spontaneous decay of certain radioactive materials, such as tritium (an isotope of hydrogen), carbon-14, phosphorus-32, and strontium-90. Depending on its energy (ie, speed), a beta ray can traverse different distances in water--less than 1 mm for tritium to nearly 1 cm for phosphorus-32.

Gamma ray:

An electromagnetic wave, a gamma ray is similar to ordinary visible light but differs in energy or wavelength. Sunlight consists of a mixture of electromagnetic rays of various wavelengths, from the longest, infrared, through red, orange, yellow, green, blue, indigo, and violet, to the shortest in wavelength, ultraviolet. A gamma ray's wavelength is far shorter than ultraviolet (ie, it is far higher in energy). Since Gamma rays can pass through body they are used in Nuclear Medicine for imaging the body.


X-rays have the same characteristics as gamma rays, although they are produced differently. When high-speed electrons hit metals, electrons are stopped and release energy in the form of an electromagnetic wave. Wilhelm Roentgen first observed this in 1895, who considered it a mysterious ray, and thus called it an X-ray. X-rays consist of a mixture of different wavelengths, whereas gamma-ray energy has a fixed value (or two) characteristic to the radioactive material.


Neutron particles are released following nuclear fission (splitting of an atomic nucleus producing large amounts of energy) of uranium or plutonium. In fact, it is neutrons that trigger the nuclear chain reaction to explode an atomic bomb. Neutrons hardly damage cells because they do not carry any electrical charge. However, the human body contains a large amount of hydrogen (a constituent of water molecules that occupy 70% of the human body), and when neutrons hit the nucleus of hydrogen, ie, a proton that is positively charged, the proton causes ionizations in the body, leading to various types of damage.

We hear a lot about the side effects of Nuclear Radiation. How safe is the use of radiation in the diagnosis of diseases?

We are exposed to various types of naturally occurring radiation from cosmic rays, from radioactive substances in the earth, and from naturally occurring radiation in our bodies. This is commonly referred to as background radiation. The combined annual dose from these sources is thought to range from 0.001 to 0.002 sievert (or from 1 to 2 millisievert [mSv]).

The radiation dose delivered by most of the medical procedures is low. Such low level of radiation is accepted medically, as they help to diagnose and treat different diseases and does not pose any health hazards. However, there is a hazard to foetus if radiation is administered to a pregnant woman when the foetus is between 8 and 15 weeks old.

The table below shows the average annual radiation doses received per capita in the United States 1,2 from naturally occurring and man-made sources of radioactivity.

Natural background, Radon 2.0 mSv
Natural background, other 1.0 mSv
Consumer products 0.1 mSv
Medical diagnostics x-rays 0.39 m
Nuclear Medicine 0.14 mSv
Airline Travel 0.06 mSv
Total background: 3.69 mSv

(1 - US National Council on Radiation Protection and Measurements, NCRP Report No. 93, pp 53-55, 1987. Bethesda, Maryland, USA, NCRP. 2 - Cameron JR. The BERT: a radiation unit for the public. Physics Society 1991:20:2)

Because radioactive substances are injected into the patient, does the patient pose any threat to others?

Most of the diagnostic Nuclear Medicine procedures utilize minute quantity of radioactive material, which is eliminated from the body quickly. Therefore, the patient can resume normal activities immediately. There is no additional requirement of safety, as the patient is not a threat to family and friends.

I have previously undergone ultrasound, x-ray, and CT scan. Why has my doctor referred me for a Nuclear Medicine test?

Nuclear Medicine imaging is unique in that it documents organ function (physiology) and structure, as compared to diagnostic radiology, which is based upon structural appearance (anatomy). The physiological information coupled with anatomical findings, help better management of the disease. All these diagnostic procedures are complementary and do not substitute each other.

I am allergic to penicillin. Does the injection used in the Nuclear medicine procedure induce allergy too?

If you are allergic to other drugs, like penicillin, it does not mean that you will be allergic to radiopharmaceuticals used in Nuclear Medicine procedures. Allergy/hypersensitivity reactions are extremely rare (less than 10 / year world-wide) in Nuclear Medicine tests. The test will not cause any adverse reaction, nausea, dizziness or blurred vision.

How soon after my test can I return to my daily activities?

You can resume your daily activities immediately after the test is over.

I am currently on prescription drugs. Can the radioactive substances counter-act with my medication resulting in an adverse-effect or other side-effects?

There is normally no need to stop your medication except for myocardial perfusion test. In which cases your referring physician will inform you. There are no side effects and you will not feel any abnormal feeling during the test.

What are the common Nuclear Medicine procedures. Can children also undergo these tests too?

Common nuclear medicine applications include diagnosis of thyroid disease, bone scans for cancer patients and orthopaedic injuries, renal scan to assess kidney function/scar, lung scans for blood clots, and liver and gall bladder procedures to diagnose abnormal function or blockages, and cardiac perfusion stress tests to analyze heart function, Children commonly undergo nuclear medicine procedures to evaluate bone pain, injuries, infection and kidney function.

When will the results be ready?

After the films have been processed, the radiologist will report on his/her findings. For urgent work, the results will be ready for collection in two hour's time at the clinic. For routine cases, the results will be despatched to the referring physician's clinic before your next appointment day.


What is PET?

Positron emission tomography, also called PET or a PET scan, is a diagnostic nuclear medicine technique.

All cells need energy to sustain life. PET imaging is unique, which enables us to view and assess the human body from a functional and biochemical perspective, comparing normal and abnormal tissue metabolism, rather than morphological changes as seen by X-ray, CT and MRI.

These images are based upon subatomic particles, emitted from a radioactive substance administered to the patient.

How does PET work?

The most widely used radiotracer in PET imaging is fluorodeoxyglucose (FDG), labelled with F-18.

FDG is glucose analogue. Most of the diseased tissues have a higher rate of glucose utilisation, leading to higher FDG accumulation than healthier tissue. PET exploits this basic principle.

After absorption of these compounds, a scanner records the signals emitted by these tracers. A computer translates these signals into actual images - representing biological causes of normal organ function and failure of organ systems in disease. Affected areas stand out on the images, as regions of increased glucose (FDG) concentration (hot-spots).

How should I prepare for the PET scan?
  • PET is usually done on an outpatient basis.
  • At the time of scheduling please inform the staff about current medication you are taking and if you have diabetes, are pregnant/nursing or claustrophic.
  • Bring along all your previous x-rays, ultrasound, CT or MRI films and any blood test reports.
  • Wear comfortable clothing.
  • Leave jewellery at home.
  • Do not eat any caloric food for at least six hours before your scan. You are encouraged to drink more water. Please avoid all drinks with caffeine and sugar.
  • Try not to smoke on the day of the scan.
  • There should be no change in your medication.
  • Diabetic patients need to regulate their blood glucose level to normal and must expect longer stay in the department.
  • You can expect to be at the department for two to three hours. The actual scan itself takes far less time.
  • Please be punctual. If you need to reschedule, notification must be given 48 hours in advance. This is because the radioactive tracer is expensive and is produced according to the number of scheduled patients.

What happens on the day of the examination?
  • You will need to fill in a questionnaire on your medical history.
  • An intravenous line will be set-up.
  • You may be given a relaxant if necessary. Please bring along a companion with you.
  • You will be given a bowel relaxant orally.
  • Your blood glucose level will be checked.
  • You will be given a small amount of the tracer - labelled glucose (FDG) via an intravenous administration into a peripheral vein.
  • After that, you must wait for 45 to 90 minutes, while your body metabolises the FDG. You will be resting comfortably during this time.
  • You will be asked to lie down on a table that slowly passes through the PET scanner. The scanner resembles a CT scanner. This scan time is approximately 20 minutes. In certain cases, the physician may need an additional scan two hours later. The second scan will not require any additional preparation.
  • Some patients, specifically those with heart disease, may undergo a stress test prior to PET scan, using a pharmaceutical to alter the blood flow to the heart.

The most commonly used radiopharmaceutical FDG is radiolabelled glucose (sugar). Glucose is a common substance that every cell in your body needs in order to function. The radiation exposure associated with PET is similar to that associated with a conventional CT scan. There is no danger to you from a PET study.

What happens after the examination?

You should feel fine. There are no side effects from the injected radiopharmaceutical. You may resume your normal diet following the procedure. You should drink additional fluids for several hours after the scan. There are no physical restrictions after the procedure. The scan results will then be sent to your doctor.