1. What is a radiopharmaceutical?
1. Pharmaceutical is an element or compound that can be utilized by the body


2. Has specific biokinetics and will follow a specific a biodistribution (physiology)


3. Tagging a compound or chelating it makes it a radio + pharmaceutical = radiopharmaceutical


4. Tagging the compound does not alter the pharmaceutical's biodistribution of physiological properties


5. The radioactive tracer can be followed, in vivo, to determine specific physiological behavior of an organ in the body and/or determine the presence of disease

This lecture is something similar to one that was in CLRS 303. The modification here is to come up with radiopharmaceuticals that relate to the type of physiology mentioned in the paragraph.

1. Simple Diffusion/Passive Transport
1. High concentration moving to areas of low concentrations
2. Small molecules or atoms that can move across cell membranes without exerting any energy
3. After ^99mTcO₄^- is injection it moves from high concentration (vascular pool) into low concentrations (Interstitial fuild). Equilabrium is reached, however, as the kidneys excrete this compound, higher concentrations move from the interstitial fuild back into the vascular comparmtment.
4. Examples
   1. _________________
   2. _________________



 

2. Active Transport
1. Movement of a molecule of atom across a cell membrane
2. The process involves the expenditure of energy
3. Usually results in higher concentration of the involved element(s) that move and stay within the cell for a period of time
4. Examples: ________________
   



3. Compartmentalization
   1. Element of compound that becomes trapped in a "compartment" within the body
   2. Example ________________

4. Capillary/Arteriole Blockage
1. Trapping of particles (microembolization) in the arteriole structure of the vascular cavity
2. Example - _______________


5. Cell Sequestration
1. Splenic sequestration
2. Example - _______________



6. Phagocytosis
1. Cells that trap or "grab" particles
2. Example - _______________

7. Chemisorption
1. Binding of a chemical/substance to a solid surface forming a chemical bond with the molecule that comes in contact with that surface
2. Secondary requirement - Requires blood flow to that area for this process to occur
3. Example ________________


8. Metabolism
   1. ¹⁸FDG uptake
   2. Any cell that requires high levels of glucose can beause of its high metabolic rate will have significant uptake of FDG. FDG is a fake sugar that becomes trapped in the glycosis of process.
   3. Myocardial, brain tissue, and cancers are require high levels of glucose
9. Antibody/Antigen reaction
1. Lock and key relationship
2. The antibody's surface has a specific code on its surface that allows it to bond a specific antigen
3. Example ________________



10. Receptor/Binding
1. Bonding of compound to a specific receptor site
2. Similar to the antibody/antigen reaction, however, the radiopharmaceutical is not a monoclonal antibody
3. Example ________________


11. Chemotaxis
    1. ¹¹¹In labeled luekocytes
    2. Sites of Infection

1. Matching available instrumentation to the specifics of a radiopharmaceutical
1. Crystal thickness (3/8")
1. Crystal thickness relates to the efficiency of counting
2. Made for a 140 keV gamma
3. For a higher energy gamma, crystal thickness should be increased
4. Thickness of the crystal also relates to the resolution of the system - ideal for ^99m Tc

2. Pure gamma emitter
1. Reduces radiation burden to the patient
2. Mixed emitters that contain beta radiation will increase the radiation burden

3. Energy gamma
1. Crystal thickness of 3/8" is designed for 140 keV gamma
2. Energy gamma less than 100 keV will have greater attenuation in the body fewer will reach the crystal
3. Energy gamma higher that 200 keV reduces body attenuation, however, decreases the chance of being detected by the crystal

4. Count density
1. Greater the dose translates to more counts
2. More counts means increased count density resulting in better resolution

5. Half-Live
1. Shorter half-life allows for higher dose
2. Reduced radiation burden
3. Increased count density

6. Inexpensive and availability
1. Tc99m is readily available and inexpressive
2. Cyclotron produced radiopharmaceuticals are not as readily available and are usually more expensive

2. How does Tc99m fit into this equation? Evaluate the following:
1. Crystal thickness
2. Pure vs. mixed emitter
3. Energy gamma
4. Count density
5. Resolution
6. Radiation burden
7. Half-Life
8. Expense and availability