2. Radionuclide
• A nuclide with excess nuclear energy is called radionuclide.
• Excess nuclear energy makes it unstable.
• Excess energy can be used ia one of three ways
• Emitted from the nucleus as gamma radiation
• Transfer to one of electrons to release it as conversion electron
• Or use to create and emit a new particle (α o β etc) from the nucleus
• During these processes, the radionuclide is said to undergo
radioactive decay and the radiation emitted is ionizing radiation.
• A radionuclide is also called radioactive nuclide, radioactive isotope or
radioisotope.
3. Radioisotopes
• An isotope is a member of a family of an element that all have the
same number of protons but different numbers of neutrons.
• The number of protons in the nucleus determine the element’s
atomic number
• An energetically unstable isotope that will achieve a stable or more
stable lower energy state by radioactive decay is called radioisotope.
4. Radiopharmaceutical
• A pharmaceutical is a substance used in the diagnosis, treatment, or
prevention of disease and for restoring, correcting, or modifying
organic functions.
• Radiopharmaceuticals are group of pharmaceutical drug containing
radioactive isotope.
• Also called radiotracers.
Pharmaceutical
e.g. DMSA
Radioisotope
e.g. 99mTc
Radiopharmaceutical
e.g. 99mTc-DMSA
5. Radiopharmaceutical administration
• A radiopharmaceutical is usually administered to the patient by
injecting intravenously
• This follows some physiological pathway to accumulate for short
period of time in some part of the body.
• For a specific part or region of the patient’s body, specific
radiopharmaceutical is used.
• For example, 99mTc-DMSA is used for kidney scan.
7. List of commonly used radiopharmaceuticals
Part of the body Radiopharmaceutical Part of the body Radiopharmaceutical
Thyroid Na99mTcO4
Liver 99mTc-Tin Colloid
Kidneys 99mTc-DMSA
Kidneys 99mTc-DTPA
Bones 99mTc-MDP
Pancreas 75Se-Selenomethionine
Brain 99mTc-Ceretec
Lung (perfusion) 99mTc-MAA
Lung (ventilation) 133Xe gas
8. Nuclear medicine imaging
• After administration of radiopharmaceutical to the patient, a
specified period of time is waited for:
• Better distribution of radiopharmaceutical to the specified organ
• Removal of background activity from the patient body
• Imaging is performed under a machine/device called gamma camera
• Radiation detectors of the gamma camera are set to take static/planar
images of the patient (who acts as a radioactive source) or revolve
around the patient to perform imaging
10. Nuclear medicine imaging purpose
• The main aim is to obtain the physiological functioning of an organ as
opposed to the mainly anatomical information which is obtained
using X-ray imaging systems or MRI etc.
• Radiation detectors scan slowly over a region of patient body in order
to measure the radiation intensity emitted from individual points
within the region.
12. Production of radioisotopes
• Natural
• Abundantly found in environment
• Longer half-life
• Difficult to handle
• Not suitable for human use
• Artificial
• Synthetically produced
• Shorter half life
• Easy to handle
• Suitable for human use
• Used in medical applications
Radioisotopes
Natural
Artificial
13. Radioisotopes for medical applications
• Radioisotope to be used for imaging should have following characteristics
• Keep the dose as low as reasonably achievable
• Short lived (short half-life)
• Emit γ-ray energies only, no α or β particles
• γ-ray energy should not be so low that radiation gets absorbed completely
before imaging from the patient body and not too high that becomes
difficult to detect (roughly suitable energy is between 100 to 200 KeV)
• Needs to be incorporated into some form of radiopharmaceutical
• It should also be capable of being produced in a form which is amenable to
chemical, pharmaceutical and sterile processing.
15. Radioisotope production_Nuclear fission
• During a spontaneous fission process, a heavy nucleus breaks into a
number of fragments.
• Artificially, a heavier nucleus can be induced fission process by
absorbing neutrons.
• As a result, small fragments with atomic numbers between almost 30
and 65.
• Some of these new nuclei are of value to nuclear medicine and can be
separated from other fission fragments using chemical processes.
• The fission process is controlled inside a device called nuclear reactor.
16. Radioisotope production_Nuclear bombardment
• In this method of radioisotope production charged particles are
accelerated up to very high energies and caused to collide into a
target material.
• Examples of such charged particles are protons, alpha particles and
deuterons.
• New nuclei can be formed when these particles collide with nuclei in
the target material.
• Some of these nuclei are of value to nuclear medicine.
17. Radioisotope production_Nuclear bombardment
• An example of this method is the production of 22Na where a target of
24Mg is bombarded with deuterons
• The target is exposed to the deuterons for a period of time and is
subsequently processed chemically in order to separate out the 22Na
nuclei.
• The type of device commonly used for this method of radioisotope
production is called a cyclotron.
18. Radioisotope production_Radioisotope generator
• This method is widely used to produce certain short-lived
radioisotopes in a hospital or clinic.
• It involves obtaining a relatively long-lived radioisotope which decays
into the short-lived isotope of interest.
• An example is 99mTc which has a half-life of 6 hours
• The Nuclear facility supplies the isotope 99Mo which decays into 99mTc
with a half life of about 2.75 days.
• The 99Mo is called the parent isotope and 99mTc is called the daughter
isotope.
19. Radioisotope production_Radioisotope generator
• So the nuclear facility produces the parent isotope which decays
relatively slowly into the daughter isotope and the daughter is
separated chemically from the parent at the hospital/clinic. The
chemical separation device is called, in this example, a 99mTc
Generator:
• It consists of a ceramic column with 99Mo adsorbed onto its top
surface.
• A solution called an eluent is passed through the column, reacts
chemically with any 99mTc and emerges in a chemical form which is
suitable for combining with a pharmaceutical to produce a
radiopharmaceutical.
20. Radioisotope production_Radioisotope generator
• The ceramic column and collection vials need to be surrounded by
lead shielding for radiation protection purposes.
• All components are produced and need to be maintained in a sterile
condition since the collected solution will be administered to
patients.
• An isotope calibrator is needed when a 99mTc generator is used to
determine the radioactivity for preparation of patient doses and to
check whether any 99Mo is present in the collected solution.
