Week Five!

Hi everyone!

This week on the fifth week of my internship, I explored the differences between MRI machines themselves. The Scottsdale campus of Mayo Clinic has around four MRI’s with a power of 1.5 Tesla while the Phoenix campus has around seven 1.5 Tesla MRI’s and a few more MRI’s with powers of 3 Tesla. Without going too much into the physics of it, a Tesla is the standard unit of magnetic flux density and is equivalent to one kilogram per second squared per ampere.

But what’s the distinction between the 1.5T vs. 3T? Is a 3T MRI twice as good as a 1.5T MRI? Sure, as far as the magnetic field strength is concerned. Price-wise a 3T MRI is also usually double the cost of a 1.5T. However, a 3T MRI is not necessarily twice as adept as the 1.5T. There are many drawbacks to a 3T even if its stronger magnetic field will allow for better image clarity. For example the scan times for a 3T are much longer and as my project explores, the longer the time the scans take, the more likely patients are to quit the scans unfinished, causing an inaccurate diagnosis or other problems.

A 1.5T MRI is adequate for the majority of scan that are done on all MRI’s today so there isn’t much of a necessity for the 3T’s. But since the stronger magnetic field of the 3T increases the signal available which is what actually creates the image, the definition of the scans produced on the 3T are actually better. However, they are better at a cost and that cost is the increased scan times.

In every MRI scan there is always image noise. While image noise is not actually a sound, it interferes with the signals given out to create images and actually comes from the patient’s body and other electronics inherent in the MRI. Ideally, there would be no noise present but this isn’t possible so the goal is to have more signal in making the image than noise which can affect the quality of the image. The 3T and 1.5T both achieve this but in different ways. A 3T MRI gives out more signal or more molecules that are resonating in the greater magnetic field strength and it drowns out the image noise. The 1.5T, on the other hand, uses multi-channel phased array coils that gets closer to the part of the body that is being scanned to create an image that isn’t as “noisy”.

Below are images of the average 1.5T MRI vs the 3T MRI and as you can see there are differences on the outward appearance and not just the internal workings of the two scanners.

I hope to explore more on the image interpretation side of things next week at Mayo Clinic and I’ll see you all then!