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Nuclear Medicine
By Kristen Hanson
Nuclear Medicine is considered a medical specialty involving the use of radioactive
substances to aid in the diagnosis and treatment of disease. Nuclear Medicine procedures
combine radionuclides to other elements which form chemical compounds, or they are
combined to preexisting pharmaceuticals which form radio pharmaceuticals. When these
radiopharmaceuticals are given to the patient they can be directed to specific organs and cell
receptors. Radiopharmaceuticals help provide images of the extent of disease based on the
cellular function and makeup rather than relying on physical changes in tissue anatomy.
Nuclear medicine is basically “radiology preformed on the inside”, because it measures
radiation emitting from within the body, whereas X-rays generate radiation towards the body.
The idea of Nuclear Medicine dates as far back as the mid 1920 in Germany. When a
scientist named George de Hevesy performed experiments on rats. He was able to establish
the tracer principle. He administered radionuclides which produced metabolic pathways. Later
on, in 1936 John Lawrence known as “the father of nuclear medicine” made the first application
in patients using an artificial radionuclide phosphorus-32 in treatments for leukemia.[1] Marie
Curie discovered radioactive thorium, polonium and coined the term “radioactivity”
Nuclear medicine received public recognition on December 7, 1946, when the
Journal of the American Medical Association published an article of a successful treatment of a
patient with thyroid cancer. The patient, given radioiodine, the cancer metastasized. Though
the radioiodine was used for thyroid cancer therapy it was later used to tract thyroid function
and also used as therapy for Hyperthyroidism. In the early 1950’s Nuclear medicine gained a
widespread clinical use. Knowledge of radionuclides, detection of radioactivity, and
administering certain radionuclides allowed tracing of biochemical processes. The most
important radionuclide that was discovered was Technetium-99m. It was discovered by C.
Perrier and E. Serge which was the artificial element 43 on the periodic table. Today, the use of
Technetium-99m is the most common element in Nuclear medicine.
By the 1970’s almost all of the body’s organs could be seen using nuclear medicine
procedures. In 1971, American Medical Association officially recognized nuclear medicine as a
specialty.[2] in the 1980’s, radiopharmaceuticals were used in the diagnosis of heart disease.
The discovery and development of the single photon emission computed tomography (SPECT)
led to 3D reconstruction of the heart and thus brought about the field of Nuclear Cardiology.
In a typical nuclear medicine study a patient is intravenously given a radionuclide. Most
diagnostic radionuclides emit gamma rays. Therapeutic nuclides produce cell-damaging
properties. Any patient undergoing nuclear medicine is at risk of inducing cancer. Radiation
dosing guidelines say that it is similar to the risk of an X-ray but it is delivered internally rather
from an outlying source such as an x-ray machine and that the dose is significantly higher.
Nuclear medicine imaging is different from most other types of imaging in that
diagnostic tests reveal the physiological function as opposed to the traditional anatomical
imaging like an x-ray or CT scan. Nuclear medicine imaging is usually for tissues and organs
such as the heart, brain and lungs. Diagnostic tests show how the body handles substances
when there is a disease or pathogen present. When the radionuclide is administered to a
patient, their body will begin to metabolize the chemical and acts accordingly, known as a
tracer. Some aspects of the substance will gravitate to specific region and be absorbed or pool
around disease causing what is known as a “hot spot”. Other disease processes exclude the
radionuclide substance causing a “cold spot.”
Radiopharmaceuticals used in nuclear medicine therapy and investigational diagnosis
emit ionizing radiation which travel only a short distance, minimizing un wanted side effects.
More often than not procedures are done on an outpatient basis. Although the risks of
radiation exposure are not fully understood, precautions are taken to not over expose patients.
“ALARP” (As Low as Reasonably Practical) was developed to take into account that a patient is
not given higher doses of radiation then deemed necessary for proper imaging. The main device
used in nuclear medicine imaging is the gamma camera. The gamma camera detects radiation
emitted by the tracer in the body and then displays an image. With computer processing it can
be displayed in several differ planes: axial, coronal and saggital.
Nuclear medicine has come a long way since the early 1900’s with developing
technology and the ability to diagnose disease on an internal level.
References
1. Donner Labortory: The Birthplace of Nuclear Medicine
http://jnm.snmjournals.org/content/40/1/16N.full.pdf
2. http://intractive.snm.org/docs/whatisnucmed.pdf from the Society of
Nuclear Medicine