Lec 10 Radiopharmaceuticals and Contrast Media

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Section 1

Question Answer
Isotopes Elements that contain equal numbers of protons (atomic number) but different numbers of neutrons in their nuclei (different mass numbers).
atomic numberequal numbers of protons
mass numbersnumbers of neutrons
Radioactive isotopesunstable isotopes – Isotopes that decompose or decay, by emission of nuclear particles, into other isotopes of the same or different elements. – Decay is characteristic for a particular isotope, and continues until a stable isotopic level is achieved.
RadioisotopesNaturally occurring and may be artificially produced.
RadioisotopesProduction usually involves the bombardment of atomic nuclei with subatomic particles, i.e. neutrons or electrons, to produce unstable nuclei of the same or a different element.
Accelerator/CyclotronRadionucleide Production:bombard the target nucleus with particles that have been accelerated to a high velocity
Alpha Particles (α, 4𝐻𝑒+2)The heaviest and slowest of all radioactive emissions.
Alpha Particles (α, 4𝐻𝑒+2)Most highly charged nuclear species giving it a very high ionizing power upon interaction with air or other media.
Alpha Particles (α, 4𝐻𝑒+2)Usually emitted only from elements having atomic numbers greater than 82.
Alpha Particles (α, 4𝐻𝑒+2)Low penetrating power, therefore useless in biological applications
Beta particles (β-)Described as an electron of nuclear origin
Beta particlesnegatively charged species having the mass of an electron
Beta particles (β-)Moves faster and has more penetrating power than alpha particles
Positrons (β+)• Less common • Identical to the electron with the exception of having a positive charge. • Has little importance in biological applications since they are very short-lived species.
Positrons (β+) • Undergo annihilation reactions with electrons to produce gamma radiation or annihilation photons: β+ +e- -> 2γ
Gamma Radiation (γ)Photon of electromagnetic radiation
Gamma Radiation (γ)• The rays are of short wavelength similar to x-rays, and travel at the speed of light. • No mass and no charge, but they are of very high energy, giving them excellent penetrating power.
Gamma Radiation (γ)• Ionizing power is poor, however, can interact with atoms and molecules in a particular medium to produce ions and free radicals secondarily by dislodging electrons from orbitals.

Section 2

Question Answer
K-Capture type of radiation produced by isotopes with an unstable proton/neutron ratio but with insufficient energy to emit positron. • Similar to gamma rays seen in the emission of x-rays
Mev (Million of electron volts) One electron volt (ev) is defined as the energy acquired by an electron when accelerated through a potential of one volt.
curie (c).activity of radioisotope is expressed(?) Equivalent to the amount of radioactive material providing 3.7 X 1010 atomic disintegrations per second (dps). – The millicurie, mc, (3.7 X 107 dps) and the microcurie, um, (3.7 X 104 dps) are used most frequently in pharmaceutical or medicinal applications.
dependent on the concentrationThe rate of isotopic decay is(?) of the radioactive atoms present.
Exposure Dose: roentgen (r)– The amount of radiation available for interaction with some target material. – Unit: (?)
Absorbed Dose: Radiation absorbed dose (rad)– Measures the amount of energy transferred to a particular medium. – Unit: (?)
1 rad 100ergs/g of absorbing medium
Relative Biological Effectiveness (RBE)Expresses the relative effects of each type of radiation particle on tissue.
RBE 1X-ray and gamma ray
rem (Roentgen Equivalent Man)RBE x rad:Commonly used to determine doses received by those working radioisotopes and participating in required monitoring programs for radioactive protection.
Geiger-Muller Counter (GM)An instrument designed to measure the extent of ionization being produced by radiation.
CathodeThe negatively charged electrode.
CathodeThe cathode attracts cations or positive charge. • The cathode is the source of electrons or an electron donor.
AnodeThe anode is the positively charged electrode.
Anode• The anode attracts electrons or anions. • The anode may be a source of positive charge or an electron acceptor.

Section 3

Question Answer
emitting beta or gamma radiation.Preparations containing radioisotopes which are used internally for therapeutic and diagnostic purposes.
RadiopharmaceuticalsUsually concentrated in certain organs or cells (e.g., 131I in thyroid tissue) – “hot spots” vs “low spots”
Contrast Mediaa substance that is used to enhanced the contrast between the structures or fluids within the body, especially in medical imaging
X-rays and CT Scansatoms or molecules that have a large number of electrons, increasing the chance of stopping x-rays
MRI (Magnetic Resonance Imaging)Compounds that alter the relaxation times of atoms within body tissues.
SPECT :Single-photon emission computed tomographyGamma and beta emitters that allow visualization of tissues.
PETPositron Emission TomographyGamma and beta emitters that allow visualization of tissues.
Diatrizoate MeglumineProvides contrast enhancement of the bladder
IodipamideUsed for visualization of the gallbladder & biliary ducts
Gadopentate Dimeglumineas a contrast agent in MRI for visualization of brain, blood vessels, spinal and other disorders
Ferumoxidesa sterile colloidal suspension of superparamagnetic iron oxide associated with dextran in Water for Injection

Section 4

Question Answer
Chromium Cr-51 Edetate Injectiondetermination of GFR
Cyanocobalamin (Co-57 or Co-58)diagnosis of pernicious anemia
Ferrous Fe-59 Citrateiron metabolism and RBC formation

Section 5

Question Answer
Technetium RadiopharmaceuticalsMost commonly used metal atom in radiopharmaceuticals – Has a 6-hour half life – Versatile chemistry that allows it to be chelated with a variety of compounds (but not all)
99mTc Albumin Aggregated InjectionLung scanning
99mTc Sulfur Colloid InjectionImaging areas of functioning reticuloendothelial cells
99mTc Labeled RBCCardiac pool pumping
99mTc Methylene DiphosphateBone imaging
99mTc PyrophosphateCardiac infarct imaging
99mTc SestamibiImaging of myocardial perfusion, breast tumor
99mTc Sulfur Colloid cooked in scrambled eggsGastric emptying imaging
99mTc - bicirumabDeep vein thrombosis

Section 6

Question Answer
Cyanocobalamin Co 57 CapsulesPernicious anemia
125I Serum Albumin InjectionBlood volume determination
Iodohippurate 131I InjectionRenal function
Sodium Chromate Cr 51 InjectionBlood volume determination
Sodium Iodide 131I Capsules/SolutionThyroid function, thyroid inhibitor
Sodium pertechnate 99mTc InjectionBrain and thyroid scanning
Sodium Phosphate 32P SolutionOcular tumor localization & antipolycythemia