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
System for automatic CO2 injection in angiography
Angiodroid
Usually used for insufflation in GI procedures; can also be involved in imaging contexts
E-Z EM CO2 Insufflator
Ppositive CM Mechanism of Action
Higher density than surrounding tissues, leads to greater absorption of XRs, makes the areas appear lighter
Ppositive CM examples
Barium sulfate
Iodinated contrast
Iodine and Barium Atomic number
Iodine: 53
Barium: 56
TYPES OF POSITIVE CM COMPOUNDS
- Metallic Salts
- Organic Iodide
After Roentgen’s discovery of X-rays, improving image contrast was essential for better clarity
Metallic Salts
Elements with high atomic numbers were identified to enhance radiopacity in X-ray imaging.
Metallic Salts
Initially used to develop the first angiogram on an amputated hand
These heavy metals were found to be unsafe for use in living patients
Barium salts
Bismuth
Lead
An inert inorganic salt, now safely used for radiographic imaging of the GI tract.
It is administered either orally or rectally for GI studies
Barium Sulfate
Main advantage:
- high quality images
- ulcer, tumor, bloackages in GI track visualization
Barium Sulfate
Derived from iodine-containing organic compounds
Organic iodides
Number of particles in solution per kilogram of water.
Osmolality
It is responsible for the adverse effects of contrast media; risk is reduced when the this is lowered.
Osmolality
Is a measure of the resistance of fluid to flow.
Viscosity
Agents with — tend to be more viscous
high iodine concentration
Main advantage:
- high contrast resolution
- rapid clearance (quickly excreted by kidneys)
Organic iodides
Types of organic iodides
a. Oily CM/ Ethiodized oil
b. Water- soluble iodine compound
These are specialized contrast agents that were developed for studies in which absorption of contrast into the surrounding tissues, or mixing of contrast with body fluids, is not desired.
Oily CM/ Ethiodized oil
Principal use of ethiodized oil today
lymphography
Injected directly into the lymphatic system typically through small incision near a lymph node or lymphatic vessel
Oily CM/ Ethiodized oil
Most frequently used contrast agents
Water-soluble iodine compound
These agents are carbon-based organic chemicals containing iodine atoms and various other elements.
Water-soluble iodine compound
Water-soluble iodine compound osmolality range
300 mOsm/kg to over 1000 mOsm/kg
Types of Water-soluble iodine compound
- Ionic Contrast Media/ High Osmolality CM (HOCM)
- Non-Ionic Contrast Media/ Low Osmolality CM (LOCM)
Composed of iodinated benzoic acid derivatives
HOCM
Historically relied upon for radiographic and CT imaging
HOCM
Consists of a positively charged cation and a negatively charged anion, and they are strong acids that fully dissociate in solution.
HOCM
Consists of a positively charged cation and a negatively charged anion, and they are strong acids that fully dissociate in solution.
HOCM
Higher likelihood of allergic reactions
HOCM
Significantly hyperosmotic to body fluids, which can lead to adverse effects, including cardiac events, vein cramping, pain, and abnormal fluid retention
HOCM
Often utilized for angiography and urography
HOCM
Examples of HOCM
Diatrizoate
Iothalamate
Less concentrated, resulting in a lower incidence of allergic reactions, making it more expensive
LOCM
Its osmolality is closer to that of human plasma at similar iodine concentrations, contributing to fewer adverse reactions
LOCM
Has wide spread application
LOCM
Examples of LOCM
Ionexol
Iopamidol
Ioversol
(Io-nex-vers-pam)
Special contrast agent for MRI
gadolinium diethylenetriaminepentaacetic acid (gadolinium-DTPA)
This CM is a metallic and magnetic agent that will affect the signal intensity used to image the anatomic area of interest
gadolinium diethylenetriaminepentaacetic acid (gadolinium-DTPA)
CM for UTZ are usually — that affect the soundwave to enhance UTZ contrast
gas-filled microbubbles
Positive and negative CM are used together
Double Contrast studies
Coats the part under study
Positive CM
Fills the space and permits vizualization through gaseous medium
Negative CM
Mucosal liningare well visualized
Negative CM
