Wednesday, July 22, 2015
Wisdom Wednesday: Magnetic Resonance Imaging
Magnetic resonance imaging or MRI was developed from nuclear magnetic resonance (NMR) in the 1970’s by Dr. Raymond Damadian. NMR had industrial uses for evaluating structural components. Dr. Damadian used NMR to study potassium ions in the human body and proposed that tumors could be visualized with the images he was able to generate.
In simple terms, an MRI is a giant electromagnet is which the patient is placed. The entire room is shielded in copper to block out external FM radio waves. When the magnet is turned on, all the water molecules in the body line up with the magnetic field. The water molecules also absorb FM radio waves generated by the MRI.
When the magnet is turned off the water molecules resume their normal orientation. This has two measurable effects: First, the molecules emit the same FM radio waves they absorbed. Second, the molecules “wobble” slightly as they reorient, creating their own magnetic field.
This data is stored in the computer showing where all the water molecules are located throughout the human body. The computer then can generate holographic images depicting the location of the water.
There are also two sets of images. The T1 views are created from the FM signal from the water molecules. The T2 images are built from the data from the magnetic “wobble”. Comparing the T1 to T2 images yields additional insight as the images highlight tissues quite differently.
Bone, being virtually devoid of water, is imaged as an absence of any signal. So MRI is quite limited in its’ ability to “see” bone. However, tumors, infection, and even fracture involve the inclusion of water so these pathologies actually light up very well on MRI.
The real advantage of MRI is the ability to see soft tissue. Soft tissue is quite high in water content, so high resolution images of the kidneys, lungs, spinal cord, and other tissues are created using MRI.
Damadian was initially criticized for his work and MRI was thought to be a passing fad in the medical community. Today, every hospital has an MRI and most communities have several free standing MRI units in addition. Although Damadian has patents on all the major advances in MRI technology over the past 40 years, the big corporations copied his work with each advance in violation of patent law. He tried to compete by opening his on facilities but could not afford to stay competitive and all the “Damadian MRI” facilities have closed.
Cost is real factor in MRI. The average study runs about $1500 compared to x-ray at $100 per study and CT scan at about $300 per study. I am often asked “Aren’t you going to order an MRI prior to any adjusting of the spine?” My standard reply is “You want me to do a $1500 study to demonstrate the need for a $60 adjustment?”
MRI, just like x-ray and CT scan, is not a screening procedure. However, if you paid over a million dollars to build an MRI unit, you need to pay for it. That, more than any other factor has led to the indiscriminate use of MRI as a screening tool.
The Bottom Line:
An MRI should be performed because the history, examination and other less expensive imaging studies fail to provide and accurate diagnosis and there is good evidence to believe that MRI may well provide the images to fill in the gaps. It should not be performed to meet the $2000 deductible on your automobile accident policy.