Radioisotope techniques involve the spontaneous disintegration of atomic nuclei through processes like alpha, beta, and gamma decay. Radioactivity is measured in units like curie and becquerel. There are different types of radioactive decay including alpha, beta, gamma, positron, electron capture, and isomeric transition. Radiopharmaceuticals are chemical substances containing radioactive atoms used as tracers in nuclear medicine for diagnosis and therapy. The most commonly used radiopharmaceutical is technetium-99m, which is used in over 80% of nuclear medicine procedures. Other radiopharmaceuticals employ radioisotopes of iodine, indium, fluorine and other elements.

1. Radioisotope Techniques
Radioactivity is spontaneous disintegration of atomic nuclei. The nucleus emits α particles, β particles,
or electromagnetic rays during this process. Approximately 3000 nuclides have been discovered so far
that are unstable. They undergo spontaneous fission to achieve stability. During this process, the
parent nuclide transforms into an atom of a different type, called the daughter nuclide.
Units of Radioactivity
Radioactivity is measured in curie. It is disintegration rate of 1 g radium that is 3.7 × 1010
disintegrations per second. SI unit for radioactivity is Becquerel (Bq), which is defined as one
disintegration per second.
1 Curie (Ci) = 3.7 × 1010 disintegrations per second (dps)
= 2.22 × 1012 disintegrations per minute (dpm)
1 millicurie (mCi) = 3.7 × 107 dps
1 microcurie (μCi) = 3.7 × 104 dps
1 Becquerel (Bq) = 1dps = 2.7 × 10-11 Ci
1 Kilobecquerel (KBq) = 103 dps = 2.7 × 10-8 Ci

2. Radiation dosimetry is calculation of the absorbed dose in matter and tissue resulting from exposure to the
ionizing radiation directly, or indirectly. Three units are related with the dosimetry.
Roentgen (R) for exposure
Rad (radiation absorbed dose) for absorbed dose
Rem (roentgen equivalent man) for dose equivalent.
Types of Radioactive Decay
Alpha (α) Decay
It is a type radioactive decay, in which atomic number of the parent nuclide is reduced to 2 and the mass number by 4 as
the parent nuclei emits an alpha particle. Heavy nuclei such as uranium, neptunium, and radon undergo decay by
emission of α-particle. For example,
Beta (β-) Decay
Beta decay is a radioactive process in which an electron is emitted from the nucleus of a radioactive atom. When a
nucleus is neutron rich i.e., it has higher N/Z ratio compared to the stable nucleus), it decays with β- particle and
antineutrino (ν-
). An antineutrino (ν-
), is a small entity without mass or charge that is needed to conserve energy in
radioactive decay process.

3. Gamma (γ) Decay
Gamma decay is a type of radioactive decay in which atomic nucleus (parent) emit gamma rays without change
in its atomic mass or number. Gamma rays are also known as gamma radiation. Gamma rays are the
electromagnetic radiation of high frequency. Gamma rays do not have charge or mass. It is a form of ionizing
radiation. For example,
Positron (β-) Decay
Proton rich or neutron deficient nuclei (which has N/Z ratio less than that of the stable nuclei) decay by
emitting positron and neutrino. The daughter nuclide has an atomic number 1 less than the parent nuclide.
Positron decay only occurs when the difference in energy is larger than 1.02MeV between a parent and a
daughter nuclide
Electron Capture (EC)
Electron capture is a process of decay for an atom that has too many electrons (nucleus with smaller N/Z ratio
as compared to stable nucleus) and insufficient energy to emit a positron. It is also known as inverse beta
decay. Gian-Carlo Wick gave the theory of EC in 1934, which was later developed by Hideki Yukawa and other
scientists. EC occurs (usually but not necessarily), when the difference in energy is less than 1.02MeV between
a parent and a daughter nuclide

4. Isomeric Transition (IT)
A nucleus can remain at several excited energy states above the ground state. All these excited states are called
isomeric states, which decays to ground state. Time taken for these isomeric states of nuclei to reach ground
stable state varies from picoseconds to several years. The long-lived isomeric state is called metastable state.
Metastable state is denoted by “m”. For example, metastable state of technetium is denoted as 99mTc.
Internal Conversion (IC)
Internal conversion is a type of radioactive decay process in which electrons in one of the lower atomic orbital
interact with an excited nucleus causing emission of the electron from an atom. A high-energy electron is
emitted from the radioactive atom without beta decay. So, the high-speed electrons emitted by internal
conversion are not beta particles. It is an alternative to gamma emission.

5. Radionuclide
• Radionuclide is an atom with unstable nuclei, which undergoes radioactive decay emitting radiation.
• The radionuclides occur naturally, but they can also be produced artificially. The radionuclides are also known as
radioisotopes or radioactive isotopes.
• Henry Bequerel discovered the natural radioactivity in potassium uranyl sulfate. Later Pierre and Madam Currie, E.
Rutheterford, and Soody discovered other radioactive elements.
• More than 3000 artificially produced radionuclides are used currently.
• Radionuclides used in Nuclear Medicine are radioisotopes of iodine, gallium, thallium, technetium, molybdenum,
carbon, and fluorine.
• Physical characteristics of each isotope are different and the selection of radionuclide is done according to its use in
diagnosis or therapy.
• They are categorized into the diagnostic and the therapeutic imaging agents.
• Radionuclide production involves conversion of one nucleus to another involving alteration of number of protons
and/or neutrons in a nucleus.
• It is possible to produce a specific radionuclide by selecting the target nucleus, the bombarding particle, and its energy.

6. Radiopharmaceuticals
• Radiopharmaceuticals (RP) are chemical substances that contain radioactive atoms within their
structure.
• They are used as tracer in nuclear medicine as they are suitable for for diagnostic and therapeutic
purposes in humans.
• Radiopharmaceutical is a combination of a radionuclide (α, β, or γ emitter) and a ligand (proteins,
peptides, drug or an antibiotic).
• More than 95% radiopharmaceuticals are used for diagnostic purpose.
• Characteristics of ideal radiopharmaceuticals include primary photon energy between 50-
500KeV, suitable physical half-life, low toxicity, and suitable chemical form and reactivity.
• Among various available radionuclides, I-131, In-111, and Tc-99m are most promising due to
suitable physiochemical properties, emission characteristics, easy availability, short half-life,
preferential localization into desired organs, and cost effectiveness.
• Nearly 80% of all radiopharmaceutical used in nuclear medicine are 99mTc labeled compounds.
• Quality control tests for radiopharmaceuticals include physicochemical and biological tests. These
tests are unique to radiopharmaceuticals; they are not applicable to conventional drugs.

7. 99mTechnetium (99mTc) labeled Radiopharmaceuticals
Technetium-99m is the most widely used radioisotope (for RP preparation) in diagnostic nuclear
medicine. It is being estimated that over 80% of the 25 million diagnostic nuclear medicine
studies are carried out annually by the use of Technetium-99m. For example, 99mTc-INH and
99mTc-EMB is used for the diagnosis of one of the deadly disease, TB
Radioiodinated Radiopharmaceuticals
Among the radioisotopes of iodine, 123I, 125I, and 131I have physical characteristics that are useful
for the development of radiopharmaceuticals. Radiopharmaceuticals developed can also be
used for SPECT and PET imaging. 123I has been most widely used for receptor binding studies in
SPECT.
111Indium Labeled Radiopharmaceuticals
111In-Diethylene Triamine Pentaacetic Acid (DTPA) and 111In-labeled platelets are
commonly used radiopharmaceuticals for the diagnostic purposes.
18Fluorodeoxyglucose (18FDG)
It is most commonly used radiopharmaceuticals in medical imaging modality i.e. positron
emission tomography

8. Radiolabeled Peptides
111In-labeled Pentetreotide (OctreoScan) is useful for the detection of primary and metastatic neuroendocrine
tumors for example carcinoids, gastrinoma, neuroblastomas, pituitary adenomas, and medullary thyroid
carcinomas. 99mTc-MAG3, a peptide is used for renal imaging. Radiolabeled RGD peptides are used for imaging
hypersensitive reactions.
Radiolabeled Nanocolloids
Nanocolloids are colloids of human serum albumin (HSA) less than 50nm in size, which gets localized at sites of
inflammatory foci through increased capillary permeability. They are radiolabled with 99mTc and are most
commonly used for marrow and lymphatic imaging and for the patients with musculoskeletal infection.
Miscellaneous Radiopharmaceuticals used in Medical Science
11C
11C was first applied to determine photosynthesis in plants and was the first radiotracer used to investigate
fixation of CO in human blood cells. 11C-PIB (Pittsburg compound B) is used for imaging amyloid plaques that
develop in Alzheimer’s disease.
13N-Ammonia
13N is a cyclotron-produced positron emitting radionuclide with half-life of 10 minutes used for the detection of
myocardial ischemia and infarct.

9. 32Phosphorus
32P is used for the treatment of polycythemia vera, leukemia, and neoplastic hematologis disorders, and for the
diagnosis of ocular tumors.
82Rb-Rubidum Chloride
It is a positron emitter produced from 82Sr-82Rb generators and is used in PET imaging of heart.
22Sodium and 24Sodium
22Na is a positron and a gamma emitter while 24Na is a beta and a gamma emitter. Both radionuclides are used
to study electrolytes.
89Strontium Chloride (Metastron)
89Strontium has a half-life of 50.6 days. It is a reactor-produced beta emitter radionuclide. 89Strontium Chloride
is used to help relieve the bone pain that may occur due to cancer. It is also used to study bone metastasis.
201Thallium Chloride
This is used for imaging studies done by gamma camera or SPECT for the detection of brain, breast, and bone
tumors. It is also used for non-specific tumor imaging, myocardial perfusion imaging, and hyperparathyroidism.

10. 133Xenon
133Xenon is chemically inert noble gas. It is used for the ventilation studies of lungs and assessment of cerebral
blood flow.
90Yttrium
90Yttrium is a beta emitter. 90Yttrium-silicate is used to study arthritis conditions as well as some malignant
disease.
The use of radiopharmaceuticals in various imaging studies provides information of functional morphology of
organs in a non-invasive manner. It also provides quick, reliable, specific diagnosis of diseases associated with
the malfunctioning of organs in body, and detection of certain types of cancers
Radioisotopes are used in
Agriculture
Industries
Scientific Research
Medicine