CT Scan vs. MRI

CT Scan
MRI

A CT Scan (or CAT Scan) is best suited for viewing bone injuries, diagnosing lung and chest problems, and detecting cancers. An MRI is suited for examining soft tissue in ligament and tendon injuries, spinal cord injuries, brain tumors, etc. CT scans are widely used in emergency rooms because the scan takes fewer than 5 minutes. An MRI, on the other hand, can take up to 30 minutes.

An MRI typically costs more than a CT scan. One advantage of an MRI is that it does not use radiation while CAT scans do. This radiation is harmful if there is repeated exposure.

Comparison chart

CT Scan

MRI

Radiation exposure The effective radiation dose from CT ranges from 2 to 10 mSv, which is about the same as the average person receives from background radiation in 3 to 5 years. Usually, CT is not recommended for pregnant women or children unless absolutely necessary. None. MRI machines do not emit ionizing radiation.
Cost CT Scan costs range from $1,200 to $3,200; they usually cost less than MRIs (about half the price of MRI). MRI costs range from $1,200 to $4,000 (with contrast), which is usually more expensive than CT scans and X-rays, and most examining methods.
Time taken for complete scan Usually completed within 5 minutes. Actual scan time usually less than 30 seconds. Therefore, CT is less sensitive to patient movement than MRI. Depending on what the MRI is looking for, and where it is needing to look, the scan may be quick (finished in 10-15 minutes) or may take a long time (2 hours).
Acronym for Computed (Axial) Tomography Magnetic Resonance Imaging.
Effects on the body Despite being small, CT can pose the risk of irradiation. Painless, noninvasive. No biological hazards have been reported with the use of MRI. However, some may be allergic to the contrast dye, which is also inappropriate for those suffering from kidney or liver disorders.
Application Suited for bone injuries, Lung and Chest imaging, cancer detection. Widely used on Emergency Room patients. Suited for Soft tissue evaluation, e.g., ligament and tendon injury, spinal cord injury, brain tumors, etc.
Ability to change the imaging plane without moving the patient With capability of MDCT, isotropic imaging is possible. After helical scan with Multiplanar Reformation function, an operator can construct any plane. MRI machines can produce images in any plane. Plus, 3D isotropic imaging also can also produce Multiplanar Reformation.
Details of bony structures Provides good details about bony structures Less detailed compared to X-ray
Principle used for imaging Uses X-rays for imaging Uses large external field, RF pulse and 3 different gradient fields
Details of soft tissues A major advantage of CT is that it is able to image bone, soft tissue and blood vessels all at the same time. Much higher soft tissue detail as compare to CT scan.
Scope of application CT can outline bone inside the body very accurately. MRI is more versatile than the X-Ray and is used to examine a large variety of medical conditions.
Intravenous Contrast Agent Non-ionic iodinated agents covalently bind the iodine and have fewer side effects. Allergic reaction is rare but more common than MRI contrast. Risk of contrast induced nephropathy (especially in renal insufficiency (GFR<60), diabetes & dehydration). Very rare allergic reaction. Risk of reaction in those who have or have a history of kidney or liver disorders.
Comfort level for patient Seldom creates claustrophobia Anxiety, especially anxiety caused by claustrophobia, is common, as is tiredness or annoyance over having to stay still on a hard table for a long period of time.
Principle X-ray attenuation is detected by detector & DAS system, followed by math. model (back projection model) to calculate the value of pixelism that becomes a image. Body tissues that contain hydrogen atoms (e.g. in water) are made to emit a radio signal which are detected by the scanner. Search for "magnetic resonance" for physics details.
History The first commercially viable CT scanner was invented by Sir Godfrey Hounsfield in Hayes, United Kingdom. First patient's brain-scan was done on 1 October 1971. First commercial MRI was available in 1981, with significant increase in MRI resolution and choice of imaging sequences over time.
Image specifics Good soft tissue differentiation especially with intravenous contrast. Higher imaging resolution and less motion artifact due to fast imaging speed. Demonstrates subtle differences between different kinds of soft tissues.
Limitation for Scanning patients Patients with metal implants can get CT scan. A person who is very large (e.g. over 450 lb) may not fit into the opening of a conventional CT scanner or may be over the weight limit for the moving table. Patients with Cardiac Pacemakers, tattoos and metal implants are contraindicated due to possible injury to patient or image distortion (artifact). Patient over 350 lb may be over table's weight limit. Any ferromagnetic object may cause trauma/burn.

Contents: CT Scan vs MRI

How the scans work

An MRI of the left knee.
An MRI of the left knee.

How MRIs work

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 realign themselves after each RF alignment pulse. The collected data is reconstructed into a two-dimensional illustration through any axis of the body. Bones are virtually void of water and therefore do not generate any image data. This leaves a black area in the images. MRI scanners are best suited for imaging soft tissue.

The CT scan of a person's torso.
The CT scan of a person's torso.

How a CT Scan works

CT, Computerized Axial Tomography, uses x-rays 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 receives 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 polyethylene (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.

The following video explains how the different types of scans work — Ultrasound, CT scan, MRI and PET scan.

Pros and Cons

In this ABC News video, Paul Christo, M.D. at Johns Hopkins explains the use of MRI or CT scans for diagnosing problems related to the spine.


Advantages of MRI over CAT Scan

CT scans and cancer

The radiation from CT scans is harmful and repeated scans can even cause cancer. In a February 2014 article, the New York Times reported that

The radiation doses of CT scans (a series of X-ray images from multiple angles) are 100 to 1,000 times higher than conventional X-rays.
A single CT scan exposes a patient to the amount of radiation that epidemiologic evidence shows can be cancer-causing. The risks have been demonstrated directly in two large clinical studies in Britain and Australia. In the British study, children exposed to multiple CT scans were found to be three times more likely to develop leukemia and brain cancer. In a 2011 report sponsored by Susan G. Komen, the Institute of Medicine concluded that radiation from medical imaging, and hormone therapy, the use of which has substantially declined in the last decade, were the leading environmental causes of breast cancer, and advised that women reduce their exposure to unnecessary CT scans.

Advantages of CT Scan over MRI

Cost of Machines

Not surprisingly, there are various CT scanners available and there is a large variation in price depending upon the features and brand. This is a good pricing guide for CT scan machines. A vanilla 4-slice CT scanner costs $85,000 to $150,000. A 16-slice scanner costs $145,000 to $225,000 and the top-of-the-line 64-slice CTs can cost up to $450,000. The machines may typically need annual maintenance, which can cost tens of thousands of dollars.

MRI machines are available in 1.5 T and 3 T (T stands for Tesla) models. 3T models are more expensive but offer higher image quality and shorter scanning times. 1.5 T MRI scanners start at around $1 million and 3T models are 50% more expensive. Manufacturers may include accessories, such as a workstation to view images and contrast injectors, in their quotes for MRI scanners. (For a guide on MRI scanners, see here.)

References

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Comments: CT Scan vs MRI

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Anonymous comments (19)

May 12, 2014, 1:33pm

Very usefull info thanks

— 118.✗.✗.142
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January 27, 2009, 12:34am

only in your dreams

— 139.✗.✗.39
2

May 8, 2014, 9:13am

Thnkx it very usefull info

— 42.✗.✗.72
1

January 18, 2010, 9:22am

they cost up to thousand dollars. _-''

— 62.✗.✗.114
1

June 3, 2014, 5:07pm

Thanks. Information was very enlightening

— 66.✗.✗.142
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April 9, 2014, 6:37am

Thankyou for valueble information

— 103.✗.✗.38
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March 9, 2014, 6:03pm

Very helpful

— 166.✗.✗.53
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January 6, 2014, 10:47am

Thxs .. Information is clear and helps you to understand better why a ct or MRI as been chosen for patient diagnosis

— 149.✗.✗.38
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September 5, 2013, 12:33am

In Japan, because of socialized medicine, we pay about $50 for an MRI (the total cost is only $300). We pay about $400 per month in insurance, but that is for both my husband and I. It makes me wonder who is making a fortune in the US. The doctors?...Doctors in Japan are just as well off, not much difference there that I can see... Insurance companies? Medical Equipment distributors? The whole system is corrupt.

— 125.✗.✗.97
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March 21, 2013, 3:38pm

Great breakdown of the differences between CTScan and MRI Thank you!

— 24.✗.✗.173
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January 21, 2013, 4:42pm

Actually in Canada it is not free we pay VERY high taxes for this! But when I needed it socialized medicine saved me a fortune

— 204.✗.✗.251
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January 11, 2013, 9:45pm

Here in Canada, they're FREE [just like our medical, it's FREE too] BUT, try & get a Dr. to order it !! Actually, try to get a Doctor period !!!!! FREE ain't all it's cracked up to be..

— 69.✗.✗.82
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September 23, 2012, 3:32pm

love this website!

— 65.✗.✗.250
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February 27, 2011, 6:12pm

People from countries where the government provides "free" (or very inexpensive) healthcare for their citizens often act as if nobody paid for the treatments.
"I only paid 20 Euros!" or what ever. Do these people ever take a look at what the government takes out of their paycheck for taxes EVERY month?
Nothing is free - especially when governments are involved.
Good article - thank you!

— 184.✗.✗.70
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July 6, 2010, 4:04pm

The costs that are listed as associated with either scan are the costs of performing the scan itself and vary with the part of the body that is being scanned, not the cost to the patient directly. That has to do with insurance plans. Something to consider heavily is what kind of insurance plan you have (if any) as this will affect both how much you pay and how much the hospital will have to eat due to provider network discounts, etc. A doctor/hospital/clinic that is less than ethical in their practices may push you towards a less expensive test/treatment to cut costs on their end or if they feel you won't be able to pay it off. Do your own research and ask LOTS of questions before YOU make the decision on what kind of test/treatment YOU think is appropriate. I'm not saying that you should discount what doctors are telling you. In my opinion, most doctors are honest and have devoted themselves to keeping people healthy and free of pain. But second opinions never hurt anyone.

— 165.✗.✗.230
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October 8, 2009, 12:26pm

both are widely available in India : Ok???

— 121.✗.✗.215
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August 4, 2009, 3:44am

mine was free with my insurance....

— 99.✗.✗.175
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May 6, 2009, 4:03pm

In India...

— 59.✗.✗.248
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March 10, 2009, 1:36pm

not possible, even with full major medical insurance.

— 64.✗.✗.3
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