CT Scan vs MRI - Difference and Comparison

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	CT Scan	MRI
Cost:	CT Scan costs range from $1200 to $3200 - they are usually cheaper than MRIs but not always if done at a hospital	MRI costs range from $1200 to $4000 - they are usually more expensive than CT scans
Details of bony structures:	Provides good details about bony structures	Less detailed compared to CT scan
Ability to change the imaging plane without moving the patient:	Not present	MRI machines can produce images in any plane
Radiation exposure:	Moderate - high radiation	None
Principal used for imaging:	Uses X-rays for imaging	Uses magnets and radio waves to create the images.
Time taken for complete scan:	Usually completed within 5 minutes	Scanning typically run for about 30 minutes.
Details of soft tissues:	Less detailed compared to MRI	Much higher detail in the soft tissues

1 Working of MRI vs. CT Scan
- 1.1 MRI
- 1.2 CT Scan
2 MRI vs. CT scan - Advantages of MRI
3 MRI vs. CT Scan - Advantages of CT Scan over MRI
4 References

[edit] Working of MRI vs. CT Scan

[edit] MRI

Using a very powerful magnet and pulsing radio waves the detection coils in the MRI scanner read the energy produced by water molecules as they mis-align themselves after each RF alignment pulse. The collected data is reconstructed into a two dimentional illustration through any axis of the body. Bone is virtually void of water and therefore does not generate any image data. This leaves a black area in the images. MRI scanners are best suited for imaging soft tissue.

[edit] CT Scan

CT, Computerized Axial Tomgraphy, uses xrays to generate images of the body, including bone. In the CT scanner the x-ray tube, (source) rotates around the patient laying on the table. On the opposite side of the patient from the tube is the x-ray detector. This detector recieves the beam that makes it through the patient. The beam is sampled via some 764 channels, (approximate number of channels). The signal received by each channel is digitized to a 16 bit value and sent to the reconstruction processor. Measurements are taken about 1000 times per second. Scan rotations are usually 1 to 2 seconds long. Each view/channel chunk of scan data is compared to calibration scan data of air, water and polyethelyne, (soft plastic) previously acquired in the exact same relative location. The comparisons allow the image pixels to have a known value for a particular substance in the body regardless of differences in patient size and exposure factors. The more samples, or views, the better the picture.

[edit] MRI vs. CT scan - Advantages of MRI

A CAT scan uses X rays to build up a picture. MRI uses a magnetic field to do the same and has no known side effects related to radiation exposure.
MRI has much higher detail in the soft tissues.
One of the greatest advantages of MRI is the ability to change the contrast of the images. Small changes in the radio waves and the magnetic fields can completely change the contrast of the image. Different contrast settings will highlight different types of tissue
Another advantage of MRI is the ability to change the imaging plane without moving the patient. Most MRI machines can produce images in any plane.
Contrast agents are also used in MRI but they are not made of iodine. There are fewer documented cases of reactions to MRI contrast and it is considered to be safer than x-ray dye.
For purposes of tumor detection and identification, MRI is generally superior. However, CT usually is more widely available, faster, much less expensive, and may be less likely to require the person to be sedated or anesthetized.
CT may be enhanced by use of contrast agents containing elements of a higher atomic number than the surrounding flesh (iodine, barium). Contrast agents for MRI are those which have paramagnetic properties. One example is gadolinium. Iodine use may be associated with allergic reactions.

[edit] MRI vs. CT Scan - Advantages of CT Scan over MRI

CT is very good for imaging bone structures.
Some patients who have received certain types of surgical clips, metallic fragments, cardiac monitors or pacemakers cannot receive an MRI.
The time taken for total testing is shorter than taken by MRI
MRI cannot be done in patients who are claustrophobic as the patient has to remain inside the noisy machine for about 20-45 minutes
It is cheaper than an MRI.