CT and MRI Scans in Neurological Practice: A Quick Overview

Before computed tomographic (CT) scans became available in the 1970s, there was no good method for imaging the brain. The available methods and technologies struck around the target without quite hitting the bull's-eye.

We had skull x-rays which imaged the bony brain-case, but not the brain itself. We had arteriograms which imaged the insides of blood-vessels supplying the brain. We had nuclear brain scans which imaged chunks of brain that were recently damaged. We had a particularly nasty test called a pneumoencephalogram (PEG) in which the doctor squirted air through a spinal tap needle and encouraged it to bubble around and inside the brain by turning the patient every which-a-way-including upside-down-while x-ray pictures showed where the air could and couldn't go. Finally, the most accurate method was not a physical picture at all, but a mind's-eye picture within the brain of an examining neurologist. Yet diagnoses still got made and patients did get treated.

CT scans revolutionized the practice of neurology. It's not that the other methods disappeared (well, yes, PEGs thankfully did disappear) but that CT scans vastly improved the accuracy of diagnosis and treatment. Even when CT scans didn't show the disease itself (e.g. multiple sclerosis or a fresh stroke) they assisted the diagnostic process by proving the absence of a brain tumor, abscess or hemorrhage that were also on the list of diagnostic possibilities.

CT scans did (and still do) this by sending x-ray beams through the head at various angles and collecting the x-ray beams on the opposite side that were not absorbed by the head. Then magic occurs. A series of images appear on a computer monitor or on x-ray film as if the head had been run through a giant salami-cutter and the slices were laid out flat and in sequence.

On CT pictures the different parts of the head are displayed in various shades of gray according to how much they absorb x-rays. The skull-bone absorbs x-rays the most and shows as the whitest component. At the other end of the gray-scale, the watery spaces in and around the brain absorb x-rays the least and show as the blackest components. The brain itself is somewhere in between, showing up in the mid-gray range. Abnormal components, like brain tumors and blood-collections, are identified not just by appearing in their own shades of gray, but also by their locations and shapes. Creating a second set of slices after the patient receives an infusion of intravenous dye provides an additional dimension to imaging not unlike that provided by the older, nuclear scans.

Then in the 1980s magnetic resonance imaging (MRI) scans burst upon the scene and astonished the medical community by not just imaging the brain itself, but by doing so in a brand-new way. Instead of imaging the extent to which the head's different components absorb x-rays, MRIs instead focus on water-molecules. To be more precise, MRIs image the rate at which spinning hydrogen-atoms of water molecules within different parts of the brain either line-up or fall out or alignment with a strong magnetic field. These differing rates of magnetization or de-magnetization are fed into a computer. Then magic occurs yet again. A series of slice-like images is created and displayed on a computer-screen or x-ray-type film in shades of gray. Abnormal structures, like brain-tumors or the plaques of multiple sclerosis, are displayed in their own shades of gray and are also recognizable by their shapes and locations. Obtaining another set of images after intravenous administration of gadolinium-the MRI equivalent of x-ray dye-also adds diagnostic information.

One of the virtues of MRI pictures is that they are based on physical principles totally different from those responsible for creating CT pictures. Thus, the MRI is good (or not so good) at showing different things than CTs. Another virtue is that MRIs can slice and dice the brain at different angles, while CTs slices are limited to just the horizontal plane. Yet another virtue of MRIs is that they are much better than CTs at imaging most diseases of the spine. Finally, MRIs are much more flexible than CTs: new bells, whistles and capabilities are being added all the time.

To the patient, the experiences of having a CT and of having an MRI greatly resemble each other. In both cases the patient lies horizontally on a flat table that moves into and out of an opening in the scanner that resembles a giant doughnut-hole. The doughnut-hole in the MRI machine is narrower, so claustrophobic patients need to inform their doctors if this might be a problem. The MRI machine is also noisier: a loud sound is created each time its radio-frequency coils turn on and off. For each kind of scan the technologist might stick a needle in the patient's vein to administer contrast-material.

Both tests are otherwise painless and are very safe with certain exceptions. Pregnant women who need a scan might have to do without one for fear of exposing the fetus to excessive x-rays in the case of the CT scan or to an excessive magnetic field in the case of the MRI. If push comes to shove, the woman is more likely to receive a CT scan because her abdomen can be draped with a lead shield that blocks passage of most x-rays, while there is no good method for blocking the magnetic field produced by an MRI machine.

A circumstance in which MRIs are simply not done is when the patient has a cardiac pacemaker. This is because the MRI machine's magnet might disrupt the pacemaker and stop the heart. No image is so necessary and valuable that this risk would be worth taking. Another circumstance in which an MRI is avoided is when the patient is critically ill. An unstable patient can be adequately monitored and supported while receiving a CT scan, but not while receiving an MRI.

Depending on the nature of the patient's problem, the doctor will usually order just one of the two types of scans and not the other, but in selected cases the magic of both kinds of scan might be needed.

(C) 2005 by Gary Cordingley

Gary Cordingley, MD, PhD, is a clinical neurologist, teacher and researcher who works in Athens, Ohio. For more health-related articles see his website at: http://www.cordingleyneurology.com

In The News:


pen paper and inkwell


cat break through


Stevens-Johnson Syndrome

Stevens Johnson Syndrome (SJS) is a severe and deadly allergic... Read More

Is the Mexican Pharmacy safe to buy drugs online?

Are you frustrated with the high prices of prescription drugs?... Read More

?Winning the War Against Rheumatoid Arthritis?

RA is a condition that forces half of patients to... Read More

Sinusitis: Sinus Infection Deals a Corporate KO

Sinusitis and Sinus Infection Starts with a Little SniffleYes, I... Read More

The Check Doctor Credentials Theory

In 2003, there where more than 890 million doctor visits... Read More

Thimerosal: Autism and Mercury Poisoning Side Effects?

Thimerosal is a preservative that is added to vaccines (has... Read More

Stem Cell Research

How To Buy Your Way Out Of An Early Death... Read More

4 Reasons Why You Should Use Canadian Pharmacies

Let's face it: purchasing prescription drugs in the U.S. can... Read More

10 Home Remedies For Arthritis Pain Relief

Your Remedy No. 1 ==============Stretch Gently for Strength and Mobility.When... Read More

Discipline Medicine

Most writers suffer from a lack of discipline. The urge... Read More

Irritable Bowel Syndrome: Simple Self-Help Tips

If you have been diagnosed with irritable bowel syndrome (IBS),... Read More

Mend Your Arthritis Pain Relief

GET TO KNOW YOUR ARTHRITISArthritis is referred to as the... Read More

Powerful Arthritis Pain Relief For All Of Us

When you ask what arthritis is, professinals will tell you... Read More

Medication Compliance Kit ... A Life Saver

Pill Proof LLC introduces the first, easy to use medication... Read More

Quitting Smoking: Planning To Succeed With Zyban!

Step One: The Big DecisionOne of the most frustrating things... Read More

Phenylpropanolamine (PPH) Lawyer: Decongestant Causes Stroke

Phenylpropanolamine, or PPH, used to be an active ingredient in... Read More

Over Medication; Grandma is on Drugs

It is very interesting this hypochondriac attitude which permeates our... Read More

An Addition For Practitioners - How to Help Your Patients and Your Practice

Please feel free to comment, so I may modify this... Read More

Catch The Wave

There has never been a better opportunity for chiropractic medicine?and... Read More

Healthcare Providers -- Its Time for Your Physical

I think this is a good time for a checkup,... Read More

Your Kidney Function Really Matters: A Lighter Look at What You Need to Know to Prevent Adverse Dru

When you (or loved ones) are taking prescription or over... Read More

Zicam Side Effects: Shortens Colds But Permanently Destroys Sense of Smell

Zicam is a homeopathic intranasal zinc remedy that is intended... Read More

How to Find a Drug Rehab in Florida?

When you're in need, the quickest way is the best:... Read More

The Neurological Exam: Evaluating the Master Organ

How does a mind contemplate itself? That's a philosophical question... Read More

The P Value And Its Significance

When diversifying an investment portfolio, one needs to consider investing... Read More

VIOXX Lawsuits

Vioxx is a prescription medication that has been used primarily... Read More

At Last! Good News For Gout Sufferers!

Gout, an arthritis affliction with its roots in antiquity, has... Read More

Signs of Suicide : Learn What They are and How to Deal with Them

The true numbers are probably much higher because many suicides... Read More

The Ease of Using a Motorized Wheelchair to Improve Mobility

No person likes to feel housebound and dependent on others.... Read More

?Do you suffer from Osteoarthritis? Here?s how to tell!?

The most common type of arthritis is osteoarthritis (OA). This... Read More

?Doc, my mouth is so dry all the time. What could be the problem??

Sjogren's syndrome is an autoimmune disorder ? a disorder in... Read More

Which Drug Addiction Treatment is the Best?

The answer is simple: there is no such thing as... Read More

FDA Orders Search Engines to Stop Online Pharmacies

How Does Online Pharmacies Affect Pharmacy Leaders?With cheaper drugs made... Read More