NUCLEAR MEDICINE

September 14, 2024
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 TOPIC: NUCLEAR MEDICINE

🌟 IMPORTANT POINTS TO REMEMBER

🔹Radionuclide: Unstable nuclei, having excess or a deficit neutron, are radioactive and transform spontaneously (or decay) until they become stable nuclei, by emitting alpha, beta and gamma radiations in any combination.

🔹Production Of Radionuclide: It is done in the following ways: nuclear reactor, neutron deficit, cyclotron, nuclear decay processes and fission products.

🔹Nuclides With A Neutron Excess B-decay: Such nuclides lose energy and become stable by a neutron changing into a proton and an electron.

🔹IT: In the case of some radionuclides, the gamma rays are not emitted until an appreciable time elapses after the emission of the beta particle.

🔹Nuclides With A Neutron Deficit: Such nuclides may lose energy and become stable by a proton within the nucleus changing into a neutron and a positive electron.

🔹K-EC: Alternatively the nucleus may increase its number of neutrons relative to the number of protons by capturing an extra nuclear electron from the nearest (K) shell.

🔹Gamma Rays: The gamma rays emitted during the radioactive decay of a given radionuclide have specific energies (forming a line spectrum), which are characteristic of the nuclide which emits them. For example, 131I emits mostly 360 keV gamma rays.

🔹Beta Rays: The beta rays are emitted with a continuous spectrum of energies up to a maximum level Emax that is characteristic of the radionuclide.

🔹Positron Emitters: Positive electrons. When a positive beta particle comes to the end of its range, it combines with a nearby negative electron.

🔹Radioactive Decay: A radioactive nucleus does not make its presence known until it decays and emits a beta or a gamma ray, or both. The activity of a radioactive sample is the rate of disintegration: the number of nuclei disintegrating per second.

🔹Physical Half-life: The half-life (t1/2) of a radionuclide is the time taken for its activity to decay to half of its original value.

🔹Exponential Decay: However, long the time is, the activity of a radioactive sample never falls to zero. This is shown by the shape – an exponential curve – of the graph of activity versus time, both being plotted on linear scales.

🔹Effective Half-life: When a radionuclide is used in imaging, it usually forms a part of a salt or an organic compound, the metabolic properties of which ensure that it concentrates in the tissues or organ of interest.

🔹Radiopharmaceuticals: Radiopharmaceuticals can be defined as a radioactive material in the form suitable for administrating in a human for the purposes of therapy or diagnostic investigation.

🔹Ideal Properties For Radionuclide: Detection, high energy, more energetic emission, half-life and easy availability.

🔹Radioisotopes Used In Conventional Nuclear Medicine: Technetium (99mTc) – salivary glands, thyroid bone, blood, liver, lung and heart; gallium (67Ga) – It is used in tumours and at the site of inflammation; krypton (81Kr) – it is used in lung examination; iodine (20I) – it is used for thyroid examination.

🔹Gamma Imaging: The patient is positioned close to the collimator.

🔹Photopeak: It comprises pulses produced by the complete photoelectric absorption in the crystal of those gamma-ray photons. The patient is given an appropriate dose of radiopharmaceutical, usually by an intravenous injection.

🔹RIS: The technique of using radiolabelled antibodies to image and characterise the nature of the disease process in vivo is known as RIS.

🔹Radiotracers To Monitor Gene Therapy: Gene therapy is one of the most promising new treatments proposed for cancer. This general approach circumvents the inherent problem of delivering complex proteins to highly special tissues and subcellular compartments and exploits the tremendous stability and plasticity of the introduced gene sequences.

🔹SPECT: Most current gamma cameras can be used for both planar and tomographic imaging. They consist of a single–, dual- or triple-headed system, which is able to rotate 360° around the patient. A gamma camera with a parallel-hole collimator rotates slowly in a circular orbit around the patient lying on a narrow cantilever couch.

 

📌 MULTIPLE CHOICE QUESTIONS (MCQs)

💡Single emission computed tomography (SECT) was first introduced by ___ in 1963.

  1. Kuhl and Edwards
  2. Bender and Blau
  3. Anger
  4. Marshal and Kallmann

Answer: 1

💡99mTc and 99Tc are isomers and are indistinguishable, except in having

  1. Mass number
  2. Atomic number
  3. Energy states of nuclei
  4. Number of protons and neutrons

Answer: c

💡Iodine-123 decays wholly by electron capture and emits

  1. 160 keV gamma and beta particles
  2. 28 keV X-rays and beta particles
  3. 28 keV X-rays and 160 keV gamma and beta particles
  4. 160 keV gamma and 28 keV X-rays and no beta particles

Answer : d

💡Half-life of technetium-99m is

  1. 20 s
  2. 20 min
  3. 20 days
  4. 200,000 years

Answer: 4

💡Isotope imaging is indicated in the maxillofacial region for assessment of

  1. Extent of metastasis in tumour staging
  2. Salivary gland function in Sjögren syndrome
  3. Brain scans and investigation of the breakdown of blood-brain barrier
  4. Bone graft cases
  5. All of the above

Answer: 5

💡Advantages of nuclear medicine are

  1. Functional details
  2. More coverage area
  3. Computer analysis and image enhancement
  4. All of the above

Answer: 4

💡Radioisotopes used in conventional nuclear medicine are

  1. Technetium (99mTc)
  2. Gallium (67Ga)
  3. Iodine (20I)
  4. Krypton (81Kr)
  5. All of the above

Answer: 5

💡Technetium (99mTc) is the most commonly used isotope because of

  1. Gamma emission
  2. Short half-life
  3. Property to readily attach to different substances
  4. All of the above

Answer: 4

💡Components and principles of gamma imaging include

  1. Multihole collimator, crystal and monitor
  2. Photomultipliers and photopeak
  3. Pulse arithmetic (position logic) and pulse height analyser
  4. All of the above

Answer: 4

💡Radioimmunoscintigraphy is

  1. The technique of using radiolabelled autoantibodies to image and characterise the nature of the disease process in vivo
  2. The most promising new treatment for cancer, based on a strategy of delivering genes to promote the local production of a therapeutic protein in target tissue
  3. The technique that combines the anatomical detail provided by computed tomography with metabolic information provided by PET
  4. None of the above

Answer: 1

 

Oral Medicine and Radiology