MRI vs X-ray - Difference and Comparison

Table of Contents

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.

Comparison chart

MRI versus X-ray comparison chart

	MRI	X-ray
Radiation exposure	None. MRI machines do not emit ionizing radiation.	Exposure to dangerous ionizing radiation.
Cost	MRI costs range from $1,200 to $4,000 (with contrast), which is usually more expensive than CT scans and X-rays, and most examining methods.	X-Ray is relatively cheaper than MRI (~70$ on average)
Time taken for complete scan	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).	A few seconds
Ability to change the imaging plane without moving the patient	MRI machines can produce images in any plane. Plus, 3D isotropic imaging also can also produce Multiplanar Reformation.	Does not have this ability
Details of bony structures	Less detailed compared to X-ray	Detailed images of bone structure on photographic film as bones absorb x-rays, and x-rays affect photographic film in the same way as light
Effects on the body	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.	The powerful rays have the ability to create birth defects and diseases and can also alter the DNA.
Application	Suited for Soft tissue evaluation, e.g., ligament and tendon injury, spinal cord injury, brain tumors, etc.	X-Rays are largely used to examine broken bones. Can also be used to detect diseased tissues.
Details of soft tissues	Provides much more soft tissue detail than a CT scan.	None - only bone and other dense tissue can be seen
Acronym for	Magnetic Resonance Imaging.	X-radiation or Rontgen radiation
Scope of application	MRI is more versatile than the X-Ray and is used to examine a large variety of medical conditions.	X-Ray is limited to examining a few body conditions only.
Principle	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.	X-rays attenuated (blocked) by denser tissue creates a shadow on the image.
Image specifics	Demonstrates subtle differences between different kinds of soft tissues.	Demonstrates the difference between bone density and soft tissue.
Detail	While an MRI is good at seeing soft tissue, however, it is a very specific test. Therefore it is not a viable option when searching for issues of unknown origin. CT is typically preferred when searching for cause of pain with unknown origin.	X-ray is not a very detailed exam, rather used to see bones and check for minor chest/sinus infection.

Methodology

X-Rays are beams of high frequency (has a wavelength between 10 and 0.1 nanometers) of the electromagnetic spectrum that can easily pass through low density (atomic number) material but not through materials that have high density. Therefore, solid objects like kidney stones and bones come out very clear in the X-Ray image.

MRI makes use of an oscillating magnetic field that is perpendicular to an extremely strong principle magnetic field along which the organ that needs to be scanned is placed. This oscillating field makes the hydrogen atoms within the organ to get magnetized in a direction that is perpendicular to the principle magnetic field.

An MRI of a left knee.

An X-ray of a left knee.

A chest X-ray.

An X-ray of the right foot

Applications

X-Ray technology is used to employ radiography and other techniques for diagnostic imaging. X-Rays are useful to detect pathology of the skeletal system and to detect certain diseases in the soft tissue. For example, identification of pneumonia, pulmonary edema, lung cancer or abdominal X-ray are all effective. They are helpful in detecting gallstones or kidney stones.

MRIs are used for distinguishing pathologic tissue from normal tissue. Unlike traditional X-Rays that use ionizing radiation, MRIs use non-ionizing radiation. MRIs offer excellent image clarity and different types of MRIs scans, such as MRA scans, enable taking different images with a great clarity.

Hazards posed

The most important problem with X-Rays is the danger they pose due to prolonged exposure. The radiation can cause damage to the soft tissues. X-Rays use radiation in order to get an internal view of the body and hence many X-Rays cannot be taken at a single time. The rays are so powerful that they can knock electrons off of the atoms when they hit them. The result is the production of ions that create many abnormal reactions in the body. X-Rays have the ability to alter DNA as well. But with the MRI several cross sectional images can be taken at the same time without creating any biological hazards.

Limitations

Other than radiation and its associated risks (especially for infants), there are few limitations for X-rays. It is a mature and well-established procedure.

MRIs on the other hand, can be disadvantageous for people who are claustrophobic. An examination can last up to 90 minutes, which some people may find difficult to handle. Patients with pacemakers or other metal objects can also not be examined MRI. Finally, MRI is considerably more expensive than an X-ray.