Nuclear Medicine and Radiation Physics Vocabulary

Vocabulary flashcards covering diagnostic and therapeutic medical radioisotopes, decay modes, half-life principles, PET imaging mechanics, and radiation dosage metrics.

Technetium-99m ($\text{Tc-99}$)

The most widely used diagnostic medical radioisotope, involved in about $30\%$ of nuclear medicine procedures, emitting low-energy gamma radiation detectable by a gamma camera and having a $6\,\text{hr}$ half-life.

Molybdenum-99 ($\text{Mo-99}$)

The parent nuclide of $\text{Tc-99}$ with a half-life of $66\,\text{hours}$ that progressively decays into $\text{Tc-99}$, enabling practical transport and supply to hospitals.

Fluorine-18 ($\text{F-18}$)

A positron-emitting radionuclide with a half-life of under $2\,\text{hours}$ that undergoes $\beta^+$ decay and serves as an accurate indicator of cell metabolism in PET imaging.

Positron Emission Tomography (PET)

A diagnostic imaging technique utilizing positron-emitting radionuclides like $\text{F-18}$ to detect pair-annihilation gamma rays traveling in opposite directions.

Annihilation

The event in PET imaging where an emitted positron meets an electron in patient tissue, resulting in their mutual destruction and the simultaneous release of two gamma rays in opposite directions.

Alpha Decay

A nuclear decay process where an unstable nucleus emits an alpha particle ($^{4}_{2}\text{He}$), causing the atomic mass number $A$ to decrease by $4$ and atomic number $Z$ to decrease by $2$.

Beta-Minus Decay

A nuclear decay process where a neutron turns into a proton, emitting an electron ($^{0}_{-1}e$ or $^{0}_{-1}\beta$) and an antineutrino; mass number $A$ remains unchanged while atomic number $Z$ increases by $1$.

Beta-Plus Decay

A nuclear decay process where a proton turns into a neutron, emitting a positron ($^{0}_{+1}e$ or $^{0}_{+1}\beta$) and a neutrino; mass number $A$ remains unchanged while atomic number $Z$ decreases by $1$.

Gamma Decay

A decay process in which an excited nucleus releases energy by emitting a high-energy photon without changing its atomic mass number $A$ or atomic number $Z$.

Half-Life

The time taken for the number of undecayed radioactive nuclei in a sample to decrease to half of its previous value, represented in calculations using $N = N_0 \left(\frac{1}{2}\right)^n$.

Targeted Alpha Therapy (TAT)

A treatment method using alpha-emitting radionuclides (such as $\text{Ac-225}$) characterized by high ionizing ability and short tissue range to concentrate energy deposition in diseased cells while sparing healthy tissue.

Beta Emitters in Therapy

Therapeutic radionuclides such as $\text{Lu-177}$ and $\text{Y-90}$ that emit beta particles to deposit energy into tissue, suitable for treating larger tumor regions due to greater penetration range.

Radiopharmaceutical

A radioactive substance administered to a patient that becomes distributed across specific organs or tissues according to biological activity.

Gamma Camera

An external detection device used in nuclear medicine to detect gamma radiation escaping from a patient's body and map tracer accumulation.

Cold Spots

Areas on a diagnostic radiation image that demonstrate little to no accumulation of an administered radiopharmaceutical.

Absorbed Dose ($D$)

The radiation energy deposited per unit mass of absorbing material, defined as $D = \frac{E}{m}$ and measured in Grays ($1\,\text{Gy} = 1\,\text{J/kg}$).

Dose Equivalent ($H$)

A measure of biological harm taking into account radiation type, calculated as $H = DQ$ where $D$ is absorbed dose and $Q$ is the quality factor, measured in Sieverts ($\text{Sv}$).

Spontaneous Transmutation

The natural conversion of one chemical element into another that occurs automatically when an unstable nucleus undergoes radioactive decay.

Artificial Transmutation

The conversion of one element into another caused deliberately by bombarding a target nucleus with nuclear particles or radiation.

Internal Radionuclide Therapy

A therapeutic strategy of delivering radioisotopes directly to tumor sites to maximize local energy deposition while minimizing exposure of healthy surrounding tissues.