Tuesday, July 29, 2008

Dynamic MR Imaging of the Pituitary: Same tools, different technique (but wow, what a difference!)

Those of us who have suffered or still suffer with pituitary adenomas have heard way too many times "your MRI is normal". I did, for years. Yet, I ultimately did have a proven adenoma which caused my Cushing's disease. If the MRI had shown even an inkling of the tumor to the trained eye, perhaps a doctor would have taken my symptoms more seriously.

So, what makes a difference, then?
Two things made a huge difference for me. First, my current endocrinologist insisted on a dynamic MRI. Secondly, I sent the films and/or CDs to neurosurgeons who remove a lot of pituitary adenomas. What my local radiologist called a "normal" MR image of my pituitary was actually deemed NOT NORMAL by three world-renowned neurosurgeons.

(My local hospital is excellent, but they had never done a dynamic protocol with MR imaging. However, the Taper Imaging Center at Cedars-Sinaii Hospital in Los Angeles bent over backwards to prepare them through phone calls, emails, and reading materials. What a good group of folks! I've met several of them.)

What is a dynamic MRI?
In order to understand that, you need to first understand what an MRI is. Typically, pituitary MRI's are done "without contrast" and "with contrast". The Magnetic Resonance Imaging is done with no radioactivity (aka x-rays). It uses a strong magnetic field produced by a large magnet to send radio waves through the body which "jiggle" the body's atoms. When these atoms move back into place, they send out radio waves of their own which are picked up by the scanner and fed into a computer. This computer then uses programmed algorithms to turn them into pictures. To learn more about it, visit How Stuff Works.

A contrast is often used with MR imaging, especially of the head, to enhance the images. Solutions of gadolinium compounds are typically used as contrast agents. Tumors enhance after gadolinium is given because they tend to absorb the contrast agent either more quickly or less quickly than "normal" tissue. This leads to a "contrast" between the two types of tissue.

What makes a dynamic MRI different from any MRI using contrast?
Typically, a series of images are taken prior to contrast and then the MR imaging is stopped while contrast is injected. Once that is finished, the MRI proceeds with another series of images. With the dynamic protocol, the contrast is infused over a period of time while the MR imaging is taking place. In one study the gadolinium solution was injected via IV over a period of 180 seconds. In another study the gadolinium was dripped via IV between 2 and 3 minutes.

Why does that make a difference?

Pituitary tumors and normal gland tissue absorb the gadolinium at different speeds. The contrast between the normal tissue and tumor may be easier to see in the earlier images when compared to the later ones. Usually the pituitary adenoma enhances slower than the gland. (However, there have been documented cases of just the reverse if the tumor encases a blood supply.) When the tumor enhances slower, a "dark spot", in layman terms, shows up on the pituitary. These are called areas of "hypointensity". This is transitory and if not imaged as it happens, the tumor will enhance to match the gland. (In the picture, the upper image does not clearly show a tumor. The lower image shows the tumor well including its contact with the right internal carotid artery.)

Although I did not mention the strength of the MRI scanners being used, it's probably obvious that the stronger they are (measured in Tesla), the better they work. A 3T scanner is preferable if available, but the authors of the studies used scanners as low as 0.5T in their studies. A scanner is only as good as those operating it, those reading the scans, and the protocols used not matter how strong it is.

Pretty dynamic, huh?



For more information in prior threads, see:

Testing 101: Imaging

4 comments:

  1. This was very helpful, thanks!

    ReplyDelete
  2. thank you ..this will be very helpful.Joanne

    ReplyDelete
  3. I would be interested to know if using 3T scanners introduces artefacts which might reduce the accuracy of the dynamic sequence? The pituitary is very close to that problematic air filled sphenoid sinus etc.

    ReplyDelete
  4. Thank you. This is what i was looking for.

    ReplyDelete

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