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

---

Rebound Headache - Stop The Cycle

You've been getting headaches. Finally, you find some medications that... Read More

Bextra and Vioxx Withdrawal Spurs Price Increase Among Rivals

The market for painkillers is huge. People don't like pain... Read More

Back Pain & Muscle Pain - Effective & Natural Pain Treatment Alternatives

Pain and Stress. They seem almost to go hand in... Read More

?So? Which One Do I Use Doctor? Heat or Ice?

Heat has long been used to provide temporary relief of... Read More

Emotional Effects of Irritable Bowel Syndrome

Irritable bowel syndrome sufferers often find that they have to... Read More

Thalidomide

Thalidomide is responsible for causing more than 10,000 children to... Read More

Stem Cell Breakthrough: Can You Now Make Your Own?

Over the past few years, stem cells have been getting... Read More

An Introduction to Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a very common condition, but... Read More

Physicians, Chiropractors and Physical Therapist Agree on a New Treatment for Low Back Pain

One of the most prevalent and difficult health conditions to... Read More

Safely Mimicking the Effects of Accutane Without the Side-effects or Costs

Since 1982 Accutane has been a reliable, if not controversial,... Read More

Celebrex Side Effects Lawsuit Lawyer

The Food and Drug administration urges people to stop taking... Read More

FDA Orders Search Engines to Stop Online Pharmacies

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

The Arthritis Pain Reliever... A New Program That Just Might Make You Younger!

For years, it's been known that regular daily exercise is... Read More

Buy Electric Wheelchairs Online

Electric wheelchairs mobility for virtually any type of disability.Innovations have... Read More

Phenylpropanolamine (PPH) Lawyer: Decongestant Causes Stroke

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

Lipitor Side Effects

Lipitor is a drug intended to help lower cholesterol. The... Read More

Lunesta Withdrawal

Lunesta is a newly released sleeping pill. Marketed as a... Read More

Warning: Taking Bextra May Harm Your Health

Another Vioxx-like occurrence may be on the rise, as warnings... Read More

Death by Fluoride

A wee bit of fluoride makes teeth and dentists happy,... Read More

?Foot Pain Relief At Last!?

"As an arthritis specialist, one area that I see people... Read More

Bee Propolis: Synergisitc Health Care for the 21st Centruy

For well over a century modern science has progressed at... Read More

5 Risks to Avoid When Purchasing Discount Medicines Online

With the increasing price of prescription medications, many consumers are... Read More

Stem Cell Research

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

What Not to Tell Your Doctor?

For many years since medicine has been established as an... Read More

Lamictal Rash Lawyer

Lamictal, or lamotrigine, is an anti-seizure medication that has been... Read More

Treatment for High Blood Pressure

The treatment of high blood pressure is one of the... Read More

Phentermine Price Watch: Comparison Shop To Buy Phentermine At The Best Values Online

When compared with the other prescription diet pills, Phentermine is... Read More

Prescription Drugs from International Pharmacies Save Elderly Money

As pointed out by *Jack Shapiro, an internationally-known healthcare marketing... Read More

Online Pharmacies Are Becoming Increasingly Popular Due To Their Convenience And Discreetness

Leading online pharmacy companies are providing consumer with a secure,... Read More

A Look at the Different Acid Reflux Symptoms

Acid reflux symptoms vary in degrees of discomfort, from person... Read More

Online Pharmacies and the FDA

The FDA (Food and Drug Administration) is responsible for overseeing... Read More

Medical Billing PDA: 21st Century Convenience for Medical Practices

Medical Billing PDAOne of the first things I notice about... Read More

Why Our Healthcare System Isnt Healthy

Most people are well aware that an estimated 45 million... Read More