CT Scan vs MRI
A CT Scan and an MRI are different in the way they work, levels of harmful radiation, the equipment used, their cost and in the situations they are best suited for.
Comparison chart
| Improve this chart | CT Scan | MRI |
|---|---|---|
| Principle: | X-ray attenuation was detected by detector & DAS system, follow by math. model (back projection model) to calculate the value of pixelsm then become a imag. | Makes use of the fact that body tissue contains lots of water (and hence protons) which gets aligned to large magnetic field to produce net MDM vector.The decay of MDM is detected as MR signal. |
| Details of soft tissues: | Less tissue contrast compared to MRI | Much higher detail in the soft tissues |
| 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: | with capability of MDCT, after helical scan with Mlti-plane Reformation function. operator can constructe any plane. | MRI machines can produce images in any plane |
| Principal used for imaging: | Uses X-rays for imaging | Uses large external field,RF pulse and 3 different gradient fields |
| Effects on the body: | Despite being small, CT can pose the risk of irradiation. | No biological hazards have been reported with the use of the MRI. |
| Acronym for: | Computed tomography | Magnetic Resonance Imaging |
| 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. |
| Cost: | CT Scan costs range from $1,200 to $3,200; they usually cost less than MRIs. | MRI costs range from $1200 to $4000 (with contrast); which is usually more than CT scans and X-rays, and most examining methods. |
| Radiation exposure: | Moderate to high radiation | None |
| Time taken for complete scan: | Usually completed within 5 minutes | Scanning typically run for about 30 minutes. |
| Disadvantages: | 1.Uses ionizing radiation | 1.More scanning time 2.Patient with metallic implants are not recommended 3.Patient with phobia required to give anesthesia during scan |
| Application: | Suited for bone injuries,Lung and Chest imaging,cancer detection | Suited for ligament and tendon injury,spinal cord injury,brain tumors |
| History: | The first commercially viable CT scanner was invented by Sir Godfrey Hounsfield in Hayes, United Kingdom; the first patient brain-scan was done on 1 October 1971. | |
| Image specifics: | Demonstrates subtle differences between the different kinds of soft tissues. |
Contents |
edit How the scans work
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. 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.
edit CT Scan
CT, Computerized Axial Tomography, 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 Pros and Cons
edit Advantages of MRI over CAT Scan
- 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 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. A CT scan costs $1,200 to $3,200 while an MRI can cost up to $4,000.
edit Video Explaining the Difference
This video explains all the different types of scans: Ultrasound, CT scan, MRI and PET scan. It's queued up to begin at the point where it explains CT scans and MRIs.
edit Related Articles
edit Examples (pictures) of MRI and CT Scan
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