1. Classification, Chemistry & Pharmacology of Contrast Agents
Chapter 6

2. Radiopaque Contrast Media: (ROCM) high-density pharmacologic agents used to visualize low-contrast tissues in the body.
Iodine (atomic number of 53)
Barium (atomic number of 56)
Both Barium and Iodine are effective photon absorbers in the human body.

3. Pharmacology of Iodinated ROCM
Radiopaque contrast media are available:
Parenteral
Enteral
Ionic
Nonionic
High-osmolality
Low-osmolality

4. Osmolality, Osmolarity, Osmotic Activity
Osmosis is the movement of water across a semi permeable membrane.
Osmolality: controls the distribution and movement of water between body compartment. (Measured in weight)
Osmolarity: same as osmolality only measured in volume.
Osmotic activity is the movement caused by osmosis.

6. A highly osmotic agent will attract water so that a dilutional effect can occur to equilibrate pressure between two permeable or semi permeable membranes.
A ROCM placed into the bloodstream will cause fluid from outside the bloodstream (extra- vascular space) to be drawn into the bloodstream (intra-vascular space).
This effectively dilutes osmotic particles until osmotic pressures equilibrate between the intra-vascular and extra-vascular spaces.

7. Intra-vascular Radiopaque Contrast Media
Categories
High-osmolality/ ionic ROCM
Consist of 3 iodine atoms and dissociate into two osmotically active particles when injected into the blood stream. (Ratio of 3:2)
Low-osmolality/ nonionic ROCM
Consist of 3 iodine atoms and do not dissociate, (Ratio of 3:0)
Low-osmolality/ ionic ROCM
Consist of 6 iodine atoms and dissociate into two osmotically active particles. (Ratio of 6:2 or 3:1)

8. High-osmolality/ ionic ROCM
Diatrizoate: Consist of 3 iodine atoms and dissociate into two osmotically active particles when injected into the blood stream. (Ratio of 3:2)

9. Low-osmolality/ nonionic ROCM
Iohexol/ Iopromide/ Iopamidol
Consist of 3 iodine atoms and do not dissociate, (Ratio of 3:1)

10. Low-osmolality/ ionic ROCM
Hexabrix/loxaglate
Consist of 6 iodine atoms and dissociate into two osmotically active particles. (Ratio of 6:2 or 3:1)

11. Distribution
Intravascular ROCM consist of large molecules with poor lipid solubility so that they do not cross cellular membranes well and thus remain in the blood system enhancing visibility of:
Veins and arteries
Heart and major thoracic vessels
Urinary tract
Brain vessels
Slight enhancement of the cerebrospinal area
This is usually blocked by a tight endothelial junctions that form a blood-brain barrier.

12. Excretion Majority Minority
Through the kidney system, excreted as urine in 24 hours or less with good renal function.
Minority
Through the intestine system, via the hepatic-biliary system. (one ROCM is eliminated principally by the hep-bil system and is thus used primarily for cholecystography and cholangiography.

13. Enteral Radiopaque Contrast Media
Aqueous Solutions
Water soluble iodinated contrast used when barium use would be potentially harmful. (gastrografin)
High rate of profuse diarrhea, systemic hypovolemia, dehydration and electrolyte imbalance.
Suspensions
Barium sulfate: it provides a more thorough visualization of structures. It is not water soluble.
Tablets
Cholebrine: used for GB visualization. The majority is excreted into the urine system in 48 hours, some via the biliary system into the feces.

14. CONTRAST VARIANCE