What Is the Role of Physics in Nuclear Medicine?

T. Carrier

In the broadest terms, physics studies focus on physical objects, their compositional matter and their interactions and movement through space and time. Physics is used as a means to explain events and situations that occur in the natural world, and physics theories therefore are a strong component of several scientific disciplines, including astronomy, biology and nuclear studies. The use of physics in nuclear medicine involves applying physics principles and theories such as radioactive decay and fusion or fission to generating medical technology. Studying matter at the most basic particle cell levels is the cornerstone of physics in nuclear medicine. Principles in nuclear physics are most often used medically in image testing and pharmaceutical creation.

Electrically charged particle interactions are used to create MRI images.
Electrically charged particle interactions are used to create MRI images.

Nuclear medicine is a form of applied physics. Applications of physics in nuclear medicine make use of physics theories and subdisciplines to design and create working objects or new methods for performing tasks. They use rigorously tested scientific methods and attempt to apply stable and unchanging scientific laws. Quantum mechanics, for example, is a physics subfield that addresses how particles such as those generated in radioactive decay also have wavelike properties and how these particles interact both with each other and with energy forces.

A gamma camera may be used to detect radioactive energy in a person's body.
A gamma camera may be used to detect radioactive energy in a person's body.

Nuclear physics is the foundation of nuclear technology, including nuclear medicine. This broad field is focused on the nuclei found in atoms, particularly their structure and interactions. Scientists can manipulate the inner portions of these cells and create powerful reactions, which usually produce radiation — a basic physics principle of energy moving through space. Nuclear research activities that can generate energy include speeding up, heating up, transferring, decaying, splitting and fusing. The latter activities are especially prominent in nuclear medicine.

Fission and fusion are nuclear reactions that can be used to generate energy for physics in nuclear medicine. The former event involves splitting atomic particles, whereas the latter involves combining atomic material together. Physicists induce these reactions in devices called nuclear reactors. In the medical field, research reactors are often used for analysis, for testing and for producing radioisotopes, or the nuclear material of atoms.

A main component of nuclear physics in medicine relates to diagnostic imaging. These processes — also called nuclide imaging — take place when the physician injects nuclide particles into the body. As these particles decay, they generate radioactive forms of energy called gamma rays. Specific equipment such as gamma cameras then detect differences in radioactivity. Variations often give insight into the functional capacities of different body regions and parts.

In radioactive decay such as that found in imaging practices, the particle activities are known in physics as weak interactions because they do not create a strong and binding effect. Other types of basic interaction types in physics include electromagnetism and gravity. Physicians use the electrically charged particle interactions in electromagneticism to create magnetic resonance imaging (MRI) machines.

Another application of physics in nuclear medicine occurs when nuclide materials are used for medical treatments. For example, when radionuclide material is combined with certain types of drugs, the result of this interaction is radiopharmaceuticals. These treatments are used most often for specific types of conditions, such as cancer. Direct energy radiation sources also can be used in cancer radiation therapy treatments, in which beams of radiation rays are directed at target areas in the body in hopes that they will destroy harmful substances.

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