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DIFFERENCES BETWEEN MRI ,X-RAY ,CT SCAN,ULTRASOUND

1. PRINCIPLE:CT scan uses an x-ray beam that slices through the patient.

MRI uses a magnetic field with radio frequencies introduced into it. When your body is placed

inside the magnetic field, the molecules of water in your body (hydrogen molecules) will start to

spin like a kid's top when he spins it. The top will begin to wobble as it slows down. Your

hydrogen molecules will start to wobble just like the top does at a certain rate of speed; the

stronger the magnetic field, the faster they will wobble and the weaker the magnetic field, the

slower they will wobble; it depends on the strength of the magnetic field. Then a radio

frequency is introduced into the magnetic field at the same rate of speed at which the "tops

wobble" causing the wobbling tops and radio frequency to sing out together sharing the same

signal frequency. (Thus the term resonance) That signal is used by the MRI computer to produce

the image.

Medical ultrasound or sonography is a medical-imaging technique based on exposing the

affected area to high frequency sound waves that produce pictures of organs and tissues inside

the body.

X-Rays make use of radiation to get an internal view of the body.

2. APPLICATIONS:CT Scan does not show you tendons and ligaments very well at all. CT scans provide better

images for bones structures,inner ear as it can easily detect tumors in the auditory canal and

cochlea.CTscans help diagnose bone tumors,bone fractures,internal injuries, internal bleeding &

blood clot and to monitor cancer and heart diseases. CT Scanning is useful for

screeningdiseases such as coloncancer,detecting injuries and abnormalities in the head, chest,

heart, abdomen and extremities. This technique is often combined with other techniques such

asMRI,and ultrasonography. CT is the preferred modality for cancer, pneumonia, and abnormal

chest x-rays. Bleeding in the brain, especially from injury, is better seen on CT than MRI. But a

tumor in the brain is better seen on MRI. CT shows organ tear and organ injury quickly and

efficiently. Broken bones and vertebral bodies of the spine are better seen on CT CT is far

superior at visualizing the lungs and organs in the chest cavity between the lungs. MRI is not a

good tool for visualizing the chest or lungs at all. Some patients who have received certain types

of surgical clips, metallic fragments, cardiac monitors or pacemakers cannot receive an MRI. MRI

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cannot be done in patients who are claustrophobic as the patient has to remain inside the noisy

machine for about 20-45 minutes.

Tendons and ligaments around the shoulder and knee are best seen by the physics used in MRI.

This is due to the density of the tissues that compose the tendons and ligaments. Spinal cord is

best seen by MRI for the same reason. The density of the spinal cord and the composition of it is

such that MRI physics can show it to us much better than CT.

X-Rays are largely used to examine broken bones. X-ray demonstrates the difference

between bone density and soft tissue.

Ultrasound applications are used for diagnostic applications such as visualizing muscles,

tendons, internal organs, to determine its size, structures, any lesions or other abnormalities.

Obstetric sonography is used to visualize fetuses during pregnancy. Other applications

of ultrasound include removing kidney and gall stones, lipectomy and other applications3. Radiation exposure:

In ct and X-ray moderate to high radiation and in MRI none. No radiation exposure in US

4. Cost:CT scans and X-rays, usually cost less than MRIs (with contrast). X-Ray is relatively cheaper than

MRI. Ultrasound is less expensive and comparatively safer technique than CT scans.

5. Acronym for :CT-Computer tomography, MRI- Magnetic Resonance Imaging. X-radiation or Rontgen

radiation

6. Effects on the body:Despite being small, CT can pose the risk of irradiation. CT scans are associated with the risk of

causing cancers, such as lung cancer, colon cancer and leukemia. This is mainly due to the use of

X-rays. No biological hazards have been reported with the use of the MRI. There are other

safety concerns associated with the use of contrast agents which are administered

intravenously. However, these disadvantages can be reduced with the use of lower doses.

Several studies have highlighted the harmful effects of ultrasound on pregnant mammals such

as mice though this effect has not yet been shown in humans. Also, increased exposure

to ultrasound waves leads to heating up of tissues, changes in pressure and other mechanical

disturbances. The powerful rays have the ability to create birth defects and diseases and can

also alter the DNA.The imaging effects or biological effects of x-rays can cause tissue cell injured

or even celldeath.So X-ray is doubled edged sword; in x-ray therapy it can help kill cancerous

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cells,at the same time it can damage normal body cells.Thus we mmust use x-rays in aproper

way and pay attention to protect patient as well as ourselves from high doses of x-rays

exposure. X-Rays used in CT scans usually have no harms.

7. Ability to change the imaging plane without moving the patient:Not present in CT scan. MRI machines can produce images in any plane. Ability to change the

imaging plane without moving the patient is present in US. While MRI and X-ray are both

imaging techniques for organs of the body, the difference is that MRI images provide a 3D

representation of organs, which X-Rays usually cannot.

8. Details of soft tissues:Less detailed compared to MRI. MRI is much higher detail in the soft tissues. US is detailed with

advanced technology

9.

Details of bony structures:CT Provides good details about bony structures. MRI is less detailed compared to CT scan.

US is usually not used for bony structures. Instead they are used for internal organs of the body

10.Time taken for complete scan:CT scan is usually completed within 5 minutes. MRI Scanning typically run for about 30 minutes.

Ultrasound usually takes about 10-15 minutes. Time taken for complete X-ray scan is a

few seconds.

11.Contrast agents: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 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 saferthan X-ray dye. Contrast agents for MRI are those

which have paramagnetic properties. One example is gadolinium. Iodine use may be associated

with allergic reactions. 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 have

paramagnetic properties, e.g.,gadolinium andmanganese.Due to the high contrast resolution

of CT scanning, differences between the tissues are more apparent compared to other

techniques.

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