Radiology and contrast agent

Question 1

What is a contrast agent?

Answer 1

Chemical agent admisistered to the patient for a scan - essentially a dye

Question 2

What does a contrast agent do? (2)

Answer 2

Improves contrast resolution to help differentiate between different types of tissue
Helps characterise pathology

Question 3

What types of scan can we use contrast for?

Answer 3

Most commonly CT
MRI
Gastrograffin in abdominal X-rays
Angiograms - look at heart vessels
GI fluoroscopy e.g. barium swallows - take live pictures
Ultrasound

Question 4

How can contrast agents be given? (5)

Answer 4

Intravenously via cannula
Intraarterial (common for angiograms)
Orally
Rectally
Any cavity e.g. urinary bladder, gallbladder

Question 5

types of contrast used for X-ray based modalities

Answer 5

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

Question 6

What type of contrast agent is used in MRI?

Answer 6

Gadolinium based agents as they interfere with how protons behave in a magnetic field depending on which tissue takes them up

Question 7

What type of contrast agent is used in ultrasound?

Answer 7

Microbubbles - interact with sound waves from probe

Question 8

6 ideal characteristics for contrast agents

Answer 8

1. Biology inert - dont interfere with body functions
2. Safe and non-toxic
3. Stable for storage (good supply in hospital so not having to order each time) and within the body
4. Low osmolality (if high cells would suck up water where agent is) and viscosity
5. Soluble in water
6. Cost-effective

Question 9

2 types of adverse reactions to contrast agents

Answer 9

Idiosyncratic reactions
Non-idiosyncratic reactions

Question 10

What are the defining factors of idiosyncratic adverse reaction?

Answer 10

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

Question 11

Defining factors of non-idiosyncratic reactions

Answer 11

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)

Question 12

What problems can occur with iodinated contrast agents?

Answer 12

Kidneys : contrast induced nephropathy … as its excreted via kidneys

Question 13

What are the risk factors of giving an iodinated contrast agent?

Answer 13

Impaired kidneys, diabetes, heart failure, old, high volume of contrast (in angiogram)

Question 14

A patient with what condition should never be given iodinated contrast agents?

Answer 14

Hyperthyroidism : thyroid takes up iodine and uses it to secrete more thyroxine, damaging the patient more

Question 15

What problem can occur with gadolinium based agents?

Answer 15

Nephrogenic systemic fibrosis
Usually in patients with poor kidney function when lots of scar tissue is deposited everywhere

Question 16

4 possible projections in X-rays

Answer 16

Anteroposterior (AP) - X-ray targeted at anterior of patient with detector posterior
Posteroanterior (PA) - X-ray targeted posterior of patient with detector anterior
Lateral
Oblique

Question 17

Which x-ray projection can cause problems when viewing the heart?

Answer 17

AP - heart appears enlarged

Question 18

3 projections in CT/MRI

Answer 18

Axial - view from top of head of bottom of feet - like an ax has cut you in half
Coronal - frontal view - like a crown
Sagittal - s for side view