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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!
Spatial Resolution (the ability to distinguish two structures an arbitrarily small distance from each other as separate)
CT provides good spatial resolution

MRI provides comparable resolution to CT with far better contrast resolution (the ability to distinguish the differences between two arbitrarily similar but not identical tissues).

The basis of this ability is the complex library of pulse sequences that the modern medical MRI scanner includes, each of which is optimized to provide image contrast based on the chemical sensitivity of MRI.

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

 

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