Midterm| Intro to CM Flashcards
Substances used in medical imaging to enhance visiblity of internal structures
Contrast Media/ Contrast Agent
Lead substrate was used to study the digestive system of the guinea pig which later proved to be toxic
1896
Walter Cannon used bismuth subnitrate in his series of experiments to study the digestive system. (Geese, cats, and 7y/o girl)
1896
Articles about the advantages of the inert and insoluble compound barium sulfate began to appear in the medical literatures. Its use increased rapidly because of its lack of toxicity, low cost, and availability
1910
Walter Dandy, a neurosurgeon, injected air to study the cerebral ventricles of children with hydrocephalus
1918
Water soluble ionated CM were introduced by Edgar Moniz. He injected sodium iodide into the cerebrovascular circulation by way of the carotid arteries.
1927
Atoms with high atomic numbers, such as iodine, could be placed on nontoxic water-soluble carrier molecules
1930
The degree of attenuation of an X-ray beam by an element is complex, but one of the major variables is the (1) in the path of the beam with which it can interact.
number of electrons
The number of electrons in the path of the beam is dependent upon three factors:
- Thickness of substance being studied
- Its density
- Number of electrons per atom of the element (which is equal to its atomic number)
CM are agents that are instilled into (1) or injected onto the (2) to enhance (3) in anatomic areas where low subject contrast exists.
- body orifices
- vascular system joints and ducts
- subject contrast
CM Types
Positive
Negative
Negative CM Mechanism of Action
Allows XR to pass through more easily compared to surrounding tissues resulting in darker appearances
Composed of low atomic number elements
Negative CM
Administered as gas or gas producing tablets, crystal or soda water, Air, carbon dioxide, oxygen
Negative CM
Why is negative CM rarely used alone as contrast agent
— Limited visibility: doesn’t provide enough detail to effectively visualize structures
— Less contrast differentiation: may not create strong enough differences b/n various tissues making it harder to identify abnormalities
— Pt preparation: Often requires careful pt preparation and specific positioning which can comoplicate its use as a standalone agent
Usually outlines soft tissue
Negative CM
Absorb less radiation, resulting in negative contrast or dark shadows.
Being lighter, they absorb fewer x-rays compared to soft tissues.
Air and gases
— provide a distinct outline of the surrounding tissues, which appear in lighter shades of gray
Air-filled cavities
Gases used for radiographic contrast must be (1) and (2) by the body
- non-toxic
- easily absorbed
CO2 meets these requirements and is preferred for its (1) compared to nitrogen.
- faster absorption
Available in small cartridges for individual use or in large, pressurized cylinders.
CO2
In the past, gas was injected into the spinal canal to visualize the (1). Procedure is called (2)
- brain’s ventricles
- Pneumoencephalography
Characteristics of CO2
— low Z
— safety: naturally occuring gas generally well-tolerated by pt; has low risk of allergic rx and is less likely to cause complication than other ionated CM
— reduces risk of nephrotoxicity: does not pose risk to kidney functions
— effective visualization
— ease of use: easily administered via specific delivery systems allowing for precise control over amount use and area being damaged
— rapid administration: thru respiration
Normal creatinine level
0.7 - 1.3
