Compare and contrast MRI, CT Scan and Ultrasound

	CT	MRI:	Ultrasound
Expense	Expensive	Most expensive	Cheapest
Scan time	10-45 mins	Longest	Shortest
Availability (linked to waiting lists)	Most big hospitals can do it	So expensive that it only available in specialised units	Most widely available
Ionising - therefore increasing probability of cancer developing	Yes	No	No
Availability - due to trained operators as well as equipment		Least available	Most available
Contrast agents	nephrotoxic contrast agents, and adverse reactions to the iodinated contrast agents	the usual contrast agent [gadolinium chelates] has a good safety profile	None used
Contrast and detail in images	State-of-the-art spiral CT gives very detailed images - but not as good as MRI	MRI has better detection and descriptive powers than does CT. It provides excellent contrast that can reveal subtle variations in tissues of differing histology.	Detailed images are not obtained in Ultrasound of the quality of the other two - but we do get pretty good ones nowadays - see 3-d imaging!
Other considerations		The scan can be done in any direction, not just axially like CT scans.
Contraindications	Pregnancy - can't have ionising radiation scan if pregnant	Can't be used if patient has implanted metal like: pacemakers, aneurysm clips, heart valves, vascular stents