Unit 3 Flashcards
(50 cards)
Contrast media are used in radiographic imaging to:
enhance the subject contrast of the area of interest
Radiographic images that demonstrate few density differences define:
low subject contrast
Any contrast agents, including barium, air, and injectable agents can be generally classified as:
positive and negative
Generally speaking, radiographic images are the result of x-ray photons being absorbed to varying degrees based on tissue density and thickness. There are five radiographic densities seen on radiographs: air or gas, water, fat, mineral, and metal. The lowest subject contrast between these five densities is between
water and fat.
Negative contrast agents
have low atomic numbers.
A double-contrast study of the colon is an example of
a high-contrast examination.
,
the use of both a negative and a positive contrast agent on the same image.
,
a barium sulfate and air examination.
Positive contrast agents
have high atomic numbers.
appear white on radiographs because of the degree of attenuation.
have a tendency to absorb x-ray photon energy to a great extent.
A common contrast agent used for MRI examinations is
gadolinium-DTPA.
For select examinations, air (negative contrast) and radiopaque contrast are used as a pair to outline mucosal linings, joint interspaces, and passageways. These examinations are considered
double-contrast studies.
All of the following are true of barium sulfate as a contrast agent EXCEPT
when mixed with water, it dissolves completely.
Barium sulfate would be contraindicated for a patient with
a suspected duodenal bulb perforation
Stomach examinations using barium sulfate have some degree of risk for patients who are
sedated
mentally disabled
potentially hypovolemic
Most adverse reactions to ionic, iodinated contrast agents are caused by
their osmolality.
An undesirable characteristic of ionic contrast agents is their
dissociation into a cation and an anion when dissolved in plasma
Nonionic iodine contrast agents differ from ionic agents in that nonionics
do not break down into a cation and an anion.
The ideal iodinated contrast agent would have what characteristic(s)?
1. High osmolality
2. Low osmolality
3. Nonionic chemical structure
4. Water solubility (hydrophilic)
2, 3, and 4
The osmotic effects of ionic contrast agents are a result of the movement of
water from the body’s cells into the bloodstream, causing increased blood volume and higher blood pressure.
After the injection of an ionic iodinated contrast agent into a patient for a renal study, the patient complains of a warm feeling and is starting to itch. You notice the patient is developing urticaria. As you monitor the patient, you should
closely monitor the patient and look for worsening signs such as vomiting and bronchospasm.
inform the radiologist or physician of the patient’s anaphylaxis.
Laboratory tests to assess a patient’s BUN and creatinine are used to determine the patient’s
renal function.
Contrast media that are high in osmolality can be harmful to patients with compromised renal function. Patients who commonly have compromised kidney function include
patients with diabetes.
elderly patients.
patients with renal disease.
Nonionic low-osmolality contrast agents have gained tremendous popularity with physicians as a safer choice for iodine contrast examinations. It is important to remember that nonionics
still pose a risk to renal function.
When using any type of contrast agent for a radiographic examination
a thorough medical history must be taken by the imaging professional.
A radiopharmaceutical is
a radioactive material used for nuclear imaging with a gamma camera.
A key distinction between radiographic studies and nuclear studies using radiopharmaceuticals is that
nuclear studies are generally more functional in nature.
,
radiographic examinations are more structural in nature.
both studies use ionizing radiation.
