Diagnostic Tools

What does the 'strength' of the MRI magnet mean?

MRI magnet strength is measured in a scientific unit called a Tesla.  For short-hand we use the abbreviation 'T' for this.  So a 1.5T magnet is one-and-a-half-times stronger than a 1.0T magnet.  There are MRI's used in experimental research that are 17.0T as of 2014 and there are even stronger magnetic fields that have been created!  The earth's magnetic field at the equator is only about 3 micro-Tesla by comparison.

So what does this little crash-course in electromagnetism mean for my pet?  

Well, the strength of the magnet is one of the more important variables in MR imaging.  It has a major impact on the resolution of the image and the speed with which we're able to acquire that image.  For comparison sake: with our 1.5T magnet we are able to scan the brain in a domestic feline in less than 20 minutes with excellent resolution and detail.  Previously, I've worked with a 1.0T magnet that would take closer to an hour and the resolution wouldn't be nearly as good.

Sagittal image of a dog's brain at 1.5T

Of course, there are other variables that can be adjusted to gain better resolution in a weaker magnet, but it takes a longer time.  And, when anesthesia is involved, less time is always safer!  Also, one has to be careful to consider the computer post-processing that goes into making these weaker magnet's images look good.  Just like Photo-shop can make anyone look like a super-slim super-model; images from these weaker magnets can be sharpened and manipulated to make them look as good as those from the stronger magnets.  But this can lead to false results when we try to interpret them.  It's a little like trying to gauge what's real when looking at the cover of a magazine!

What is an EEG?

EEG is the acronym for electroencephalography.  

Which is definitely a word that needs an acronym ....

Electroencephalography is a method of using electrodes that can sense the flow of electricity within biological tissues to look at brain function.  The brain, spinal cord, heart, and some other special tissues in the body use electrical signals to communicate rapidly between the cells that make up those particular tissues.  With these special electrodes, we can watch this electrical current and deduce information from them with regard to certain diseases.  

The machine shows us the electrical activity as several lines on a screen.  In animals and people, EEG is primarily used to evaluate an individual for seizures or, sometimes, sleep disorders.  

Seizures look like 'spikes' followed by 'waves' as you can see here...

Seizures look like 'spikes' followed by 'waves' as you can see here...

We also use it for patients that are in status epilepticus.  This is a condition when a seizure lasts longer than 20 minutes or there are multiple seizures without a return to consciousness in between.  Left untreated, this can cause permanent brain damage!

We've actually had two patients at LOVN this year that were in status epilepticus when they came in, but weren't having any outward signs.  This is called non-convulsive status epilepticus and without our EEG we wouldn't have been able to recognize it.  What's more, we were able to treat both of these patients with medications and use the EEG to monitor the effect of the drugs.

When patients are having such prolonged seizures, we often have to put them under general anesthesia to stop the seizures.  Then we have to decide when to try and wake them up.  Without the EEG this would just be a guess.  But with our EEG we can monitor the read-out for continued seizures even though the patient is completely asleep.  So, now, we don't have to guess when it's safe to wake a patient up.  We know...

What is Magnetic Resonance Imaging?

Magnetic Resonance Imaging, or MRI, has been used since the late 1970's to image the human body.  Among the different ways that doctors have to image ourselves and our animal friends, the MRI is unique.  Unlike an x-ray, CAT scan, PET scan, or other radiologic techniques, the MRI doesn't use radiation to create the images.  Rather it relies on the magnetic properties of the tissues in our bodies.

When a patient is placed in the MRI machine, that individual is subjected to a strong magnetic field.  The MRI machine then pulses radiowaves into the part of the body we are inspecting and 'listens' for the return radiowaves the tissue gives off.  This lets us determine specific characteristics of the tissues we're looking at and gain unprecedented insight into the architecture and disease state of the body.  When we give an intravenous injection of contrast, this improves our ability to recognize and characterize the disease even more.

As MRI technology has improved, doctors have been able to find even more detail and have even begun to be able to see the functional activity of parts of the brain.  But some of the most exciting research is being done with diffusion-weighted imaging.  This technique allows us to distinguish 'strokes' from tumors and other diseases.  But in some of the very advanced MRI machines used in research, scientists are able to track the connections between parts of the brain and begin to understand the 'wiring' that makes us all the amazing manifestations of Life that we are.

Check out the Human Connectome Project for some amazing images!