Lecture 18 - Radiology Flashcards
What is a contrast agent?
Chemical agent given to patient for a scan
Why are patients given contrast agents for a scan?
Improves contrast resolution (ability to distinguish between different tissue types)
Helps characterise pathology
2 Types of contrast
Positive and Negative
What is Positive contrast? For X-ray modalities
Contrast agent is more radiopaque (blocks X-rays)
Like Iodine (CT Scans) and Barium (Heavy elements)
What is negative contrast of X-ray modalities?
Contrast agent mroe radiolucent(X-rays not blocked)
Not very common
Usually Air or CO2 used
Used in ultrasound sometimes
Characteristics for Contrast agent (6)
Biologically inert
Safe and non toxic
Stable for storage in body
Low osmolality and viscosity
Soluble in water
Cost effective
2 Types of Adverse reactions people can have with contrast agents
Idiosyncratic reactions
Non-Idiosyncratic reactions
Idiosyncratic reactions (about)
Acute (come about rapidly)
Severe reactions are rare
What puts people at high risk for idiosyncratic reactions?
Previous reactions to contrast
Asthma
Allergies
Idiosyncratic reaction definition
Cant be explained by drugs
Mostly unpredictable (only happens in susceptible patients)
Not affected by drug doses
Non-idiosyncratic reactions
Contrast extravasating (where contrast leaks into surrounding tissues) gives metallic taste/warmth
Nausea vomiting, Vasovagal syncope (fainting triggered by seeing something) , other CVS affects
Iodinated Contrast agents (CT)
May cause Contrast-induced nephropathy
So affects kidneys
Kidneys excrete iodine
if someone has hyperthyroidism should you use Iodine contrast agents?
No
Iodine is metabolised here
Gadolinium based agents
May cause Nephrogenic systemic fibrosis
Lots of scar tissue deposited everywhere
4 different types of projections in X-rays
AP (anteroposterior)
PA (posteroanterior)
Lateral
Oblique
