Name:
Personal tutor:
Joshua Wong Rui Yen
Prof. Jem Hebden
The Pros and Cons of X-ray Computed Tomography (“CT”) and
Magnetic Resonance Imaging (“MRI”)
MRI and CT scans are diagnostic imaging techniques used to identify causes of
injuries or illnesses. While both generate a cross-sectional 3-D image of the
internal body, the two use different methodology – CT scanners make use of Xrays while MRI scanners utilize radio waves and powerful magnetic fields.1
Through this essay, the desirability of CT and MRI scans as diagnostic imaging
techniques is evaluated by exploring their pros and cons, specifically regarding
spatial resolutions, costs, diagnostic reliabilities, and safety.
In medicine, the ability to distinguish two structures in a small area of space
(high spatial resolution) is crucial to determine which technique more effective.
In this respect, CT scans are more appropriate than MRI scans because the
latter’s spatial resolution is limited primarily by a low signal level.
Secondly, CT scans are generally half the price of a MRI. This indicates that unless
the marginal medical benefit of using the MRI greatly outweighs the difference in
cost, CT scans are generally preferred in considering the cost effectiveness of the
process.
Despite these positive aspects of CT scans, they expose patients to harmful
ionizing radiation through the X-Rays used2. A CT scan exposes a patient to
approximately 2 to10 millisieverts (mSv) of radiation, which is up to 4 times
more than the exposure that an average person in the UK would experience
annually (2.7 mSv)3. Hence, CT scans could potentially cause radiation-induced
cancer. In contrast, an MRI is non-invasive, functions without ionising radiation
and there is no evidence thus far of any biological hazards regarding its usage. In
this sense, a MRI scan would be preferred over CT scan, especially when multiple
imaging examinations are required.
The effectiveness of the two techniques is dependent on the nature of organ
being scanned. CT scans are particularly useful in the diagnosis of bone-related
cases whereas MRIs are mainly used to view soft tissues. MRI scans are able to
distinguish between different types of soft tissues, for example, water bound
within cells gives a different MRI signal than free water.
Roughly 30,000 times stronger than the Earth’s magnetic field.
Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT
David J. Brenner, Carl D. Elliston, Eric J. Hall, and Walter E. Berdon
American Journal of Roentgenology 2001 176:2, 289-296
1
2
3http://www.hpa.org.uk/Topics/Radiation/UnderstandingRadiation/Understan
dingRadiationTopics/DoseComparisonsForIonisingRadiation/
Name:
Personal tutor:
Joshua Wong Rui Yen
Prof. Jem Hebden
Furthermore, while the CT scan can be completed in less than 5 minutes, MRI can
take as long as 90 minutes. This is why CT scanners are mostly found in
emergency rooms.
Unfortunately, some patients do not have the luxury of choice. Pregnant women,
for instance, are not advised to undergo CT scans as the X-rays may harm the
unborn child. On the other hand, patients with metal implants would not be
allowed to undergo a MRI because of the undesired interaction with powerful
magnetic forces. Claustrophobic and horizontally challenged patients would not
be comfortable within the MRI machines as they are small and narrow (Figure
1).
Figure 1. A patient inside a MRI scanner4
In conclusion, neither technique is plainly more advantageous than the other: the
MRI and CT scanners have complementary advantages and disadvantages. Thus
the nature of the injury and previous medical history and conditions should be
first assessed and discussed with the patient before a particular technique is
decided upon.
Word count: 547 words
4
http://thelactationlearningstation.files.wordpress.com/2012/07/mri-scan.jpg
Name:
Personal tutor:
Joshua Wong Rui Yen
Prof. Jem Hebden
Bibliography
CT and MRI of Coronary Artery Disease: Evidence-Based Review
Anil K. Attili and Philip N. Cascade
American Journal of Roentgenology 2006 187:6_supplement, S483-S499
Estimated Risks of Radiation-Induced Fatal Cancer from Pediatric CT
David J. Brenner, Carl D. Elliston, Eric J. Hall, and Walter E. Berdon
American Journal of Roentgenology 2001 176:2, 289-296
http://www.hpa.org.uk/Topics/Radiation/UnderstandingRadiation/Understand
ingRadiationTopics/DoseComparisonsForIonisingRadiation/
http://thelactationlearningstation.files.wordpress.com/2012/07/mri-scan.jpg