9.2 - Radiology + contrast agents

Question 1

What is a contrast agent

Answer 1

• Chemical agent given to patient for scan
• Improves contrast resolution
• This allows better differentiation between different tissue types
• Helps characterise pathology

Question 2

What are some common scan types (no details, just names)

Answer 2

• CT (computed tomography)
• MRI (magnetic resonance imaging)
• Gastrograffin (abdominal x-rays)
• Angiograms
• GI fluoroscopy (eg barium swallows)
• Ultrasound

Question 3

What are some of the ways that contrast can be given

Answer 3

• Intravenously
• Intraarterially
• Orally
• Rectally etc

Question 4

What are the different types of contrast

Answer 4

x-ray based
☞ positive contrast: more radiopaque (blocks x-rays) eg iodine or barium
☞ negative contrast: more radiolucent (doesn’t block x-rays). Used less commonly. Eg air or CO2
MRI
- Gadolinium based agents are used
- These interfere with how protons behave in magnetic field

ultrasound
- Microbubbles used
- these interact with sound waves

Question 5

What are some ideal characteristics for contrast agents

Answer 5

• Biologically inert → shouldn’t affect normal physiological functions
• Safe + non-toxic
• Stable
• Low osmolality and viscosity
• Soluble in water → can travel in blood
• Cost-effective

Question 6

Idiosyncratic vs non-idiosyncratic reactions

Answer 6

idiosyncratic
- cannot be explained by drug’s known mechanism of action
- Acute, within 1 hour
- Severity range from mild to life threatening
- Higher risk if previous reaction to contrast, asthma or other allergies
- Mostly unpredictable + very rare
- Symptoms can include: urticaria (rash), bronchospasm, angioedema (swelling under skin), laryngeal oedema, anaphylaxis, cardiopulmonary arrest

non-idiosyncratic
- More common
- Contrast extravasation (leakage, causing damage to surrounding tissues), funny taste or sensation of warmth
- Nausea + vomiting, vasovagal syncope (fainting), arrythmia, bradycardia
- Can be a delayed reaction, most commonly skin reactions

Question 7

Projections in x-rays

Answer 7

all based on where x-ray tube is in relation to the patient
- Anteroposterior (AP): patient has back to x-ray detector
- Posteroanterior (PA): patient is facing x-ray detector
- Lateral: patient is side-on
- Oblique: at an angle

Question 8

What position of x-ray does the heart appear abnormally enlarged

Answer 8

Anteroposterior (AP) ie patient has back to x-ray detector and is facing x-ray tube

Question 9

Projections in CT/MRI

Answer 9

• Axial: divides into top and bottom
• Coronal: divides into back and front
• Saggital: divides into right and left