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Imaging

Nuclear Medicine

Introduction Nuclear medicine involves the injection of radioactive elements into the body to diagnose heart problems. This imaging technique relies on the emission of gamma rays from radioactive material. Radioactive substances provide a contrast to the soft tissue.

A radioactive tracer is pumped into the bloodstream of a patient. The substance releases radiation, which is picked up by a gamma ray camera. One nuclear medicine test is called the thallium stress test. The patient is injected with thallium or another radioactive tracer. The patient then exercises and is imaged by the gamma ray camera. The patient is also imaged without exercise. Computers create the images from multiple views. The information learned from the images is important for comparing blood flow to the heart at rest and at work.

X-ray machines generate a stream of x-rays that penetrate the body. Depending on the densities of the body parts, the remaining x-rays will strike a film. Black parts of the film have little density. The gray parts of the film are somewhat dense. The white parts of the film are what the x-rays had a hard time penetrating and are extremely dense.

This is called myocardial perfusion scanning. Myocardial perfusion scanning is the most common cardiac scanning associated with nuclear medicine.

The nuclear medicine tests are vital for information about the blood flow. Nuclear medicine testing allows blood flow throughout the heart to be diagnosed to make sure certain parts of the heart are getting enough oxygen.

Nuclear medicine tests let doctors assess the damage from a heart attack and how a heart attack is affecting the oxygen uptake in different parts of the heart.



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In the lab...

Types: Many different types of radioactive substances are used. Two radioactive materials that are commonly used are thallium and technetium. Each material has advantages. Thallium is less expensive and can detect lack of oxygen to an organ while a patient is at rest. Technetium produces clearer images and is faster.

Safety Precautions: A patient should avoid caffeine, abstain from alcohol and smoking a day before the imaging. No food should be eaten three hours before the test.

Orientation of Patient: The patient should lie down while the intravenous (IV) infusion is started. The radioactive tracer is injected into the bloodstream of the patient. Then, the patient is told to exercise on a treadmill or on a stationary bike. After the test, the patient lies down in order to let the gamma ray camera to detect the radioactivity. Images of the heart are obtained after the IV administration of the tracer, during the resting condition and again after the exercise. These images are then compared to assess if there is adequate perfusion of the heart during exercise.

Length of Scan: The entire examination (exercise, imaging, etc.) can take three hours. The gamma ray camera scans for approximately 20 minutes. Top

History Timeline

1896: Henri Becquerel was the first scientist to discover radiation.

Early 1900s: Georg von Hevesy used radioactive tracers to study the uptake of radioactive lead by plants. Georg also studied the movement of phosphorous in the human body by using radioactive tracers.

1929: Ernest Lawrence invented the cyclotron. The cyclotron was the first particle accelerator. With this invention, radioactive substances could be produced easily. These substances could be used as radioactive tracers for medical purposes.

1938: Glenn Seaborg along with Emilio Segre, discovered technetium-99. Technetium-99 is a common radioactive tracer used in nuclear medicine. Because of all the upcoming research at the time, a new organization was created. Marshall Brucer headed the Society of Nuclear Medicine.

1943: Georg won the Nobel Prize for the development of the radioactive tracer.

1958: Hal Anger invented the gamma camera. The gamma camera absorbs gamma radiation with a crystal. The absorption produces a flash of light, which is picked up by a computer that constructs an image from these flashes.

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Pathologies Detected by EKG

Nuclear medicine is used to identify blood flow. Nuclear medicine can also detect how an organ is functioning. The following pathologies can be detected by nuclear medicine.

Angina Pectoris – Doctors can detect which muscles are not getting oxygen by examining the blood flow through images.

Coronary Heart Disease – Nuclear medicine allows the doctor to visualize the blood flow and detect any blockages. The stress test is used to detect coronary heart disease. Around 85% of patients who have coronary heart disease will be detected by this test. Around 10% will get a false positive, meaning that the tests suggest the patient has the disease but the patient does not actually have the disease. Nuclear medicine can also follow-up on a patient’s therapy for coronary heart disease.

Silent Ischemia – Since blockages affect the arterial blood supply to the heart, the abnormalities will show up on a stress test.

Drawbacks Nuclear medicine tests require physical effort. The patient must be able to exercise by running on a treadmill or riding a stationary bike. If a patient cannot run due to physical problems, discomfort, or any other reason the patient might then be given a medication (such as dipyridamole) that increases blood flow to the heart. The gamma ray camera scans the patient’s body for 30 to 45 minutes, which might be a long time for some patients to stay still.

The radioactive tracer might pose problems to some patients. The radioactive tracer could be secreted into breast milk. Also, any pregnant woman should be careful about tests that involve radiation because of the potential harm to the fetus. Patients might have an allergic reaction to the tracer, but this is extremely rare.

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