Radiology and contrast agent Flashcards
What is a contrast agent?
Chemical agent admisistered to the patient for a scan - essentially a dye
What does a contrast agent do? (2)
Improves contrast resolution to help differentiate between different types of tissue
Helps characterise pathology
What types of scan can we use contrast for?
Most commonly CT
MRI
Gastrograffin in abdominal X-rays
Angiograms - look at heart vessels
GI fluoroscopy e.g. barium swallows - take live pictures
Ultrasound
How can contrast agents be given? (5)
Intravenously via cannula
Intraarterial (common for angiograms)
Orally
Rectally
Any cavity e.g. urinary bladder, gallbladder
types of contrast used for X-ray based modalities
Positive : more radiopaque (blocks X-rays), tend to be heavy elements like iodine or barium
Negative : contrast is more radiolucent (doesn’t block x-rays so things appear less bright), tend to be lighter materials like air or CO2
What type of contrast agent is used in MRI?
Gadolinium based agents as they interfere with how protons behave in a magnetic field depending on which tissue takes them up
What type of contrast agent is used in ultrasound?
Microbubbles - interact with sound waves from probe
6 ideal characteristics for contrast agents
- Biology inert - dont interfere with body functions
- Safe and non-toxic
- Stable for storage (good supply in hospital so not having to order each time) and within the body
- Low osmolality (if high cells would suck up water where agent is) and viscosity
- Soluble in water
- Cost-effective
2 types of adverse reactions to contrast agents
Idiosyncratic reactions
Non-idiosyncratic reactions
What are the defining factors of idiosyncratic adverse reaction?
Unpredictable - can’t say which patient can react to do
Can’t be explained by side effects of the drug (reaction is inexplicable)
Not dose dependent
Happens in less than an hour and ranges from mild to life threatening
Defining factors of non-idiosyncratic reactions
Contrast extravasation (contrast pools in soft tissue), metallic taste or sensation of warmth
Nausea and vomiting and other CVS effects
Higher dose = more likely to have reaction
Delayed reaction (1 hour to 1 week)
What problems can occur with iodinated contrast agents?
Kidneys : contrast induced nephropathy … as its excreted via kidneys
What are the risk factors of giving an iodinated contrast agent?
Impaired kidneys, diabetes, heart failure, old, high volume of contrast (in angiogram)
A patient with what condition should never be given iodinated contrast agents?
Hyperthyroidism : thyroid takes up iodine and uses it to secrete more thyroxine, damaging the patient more
What problem can occur with gadolinium based agents?
Nephrogenic systemic fibrosis
Usually in patients with poor kidney function when lots of scar tissue is deposited everywhere