11 Magnetic Resonance Spectroscopic Imaging (MRS)

Introduction of Speaker

Our next speaker is the one member of the faculty who you haven't met yet, and it's Verma.

She's an associate professor of radiology, radiation oncology and urology at the University of Cincinnati Medical Center.

She's gonna be talking about Mr. Spectroscopic Imaging.

Greeting and Overview

Good afternoon, it's my pleasure to be giving a talk to you this afternoon on Mr. Spectroscopy.

Before I begin, I just wanna get an idea as to who has used spectroscopy or uses in daily practice here?

So few hands, perhaps the audience listening would have some experience, but regardless, I think it is not extinct yet.

It is on the endangered species list, I believe.

Anyway, I hope to show you some of the uses for Mars spectroscopy.

I'm gonna go over what, why, where, and how a mar spectroscopy is used.

I put the how at the end because it is technically challenging and it does require some meticulous technique.

What is MR Spectroscopy?

Just gonna go into what it is since a lot of people don't use it.

It's a spectroscopy is available on all the different vendors have it, it has different names, pros, prostate, MRS or MRUI, depending on the vendor you use.

Just to kind of give you an example, this was one of the original functional sequences that we had.

We're looking at these metabolites are detected on based on the different resonance peaks.

We only had T two weighted imaging initially with spectroscopy.

But since diffusion DCA has arrived, really, you can see there's really no reason for Mr. Spectroscopy in this instance, you see a large lesion on T two weighted images that is anteriorly placed, has very low a DC, very nice enhancement.

So really, why do we need this?

But I'll show you some cases that most cases are not so obvious, so they're either very obvious cases or completely negative cases.

There's a big gray zone in especially the transition zone, and I hope to show you some examples of that.

So here you see a healthy metabolite pattern, and here's the abnormal.

What you must have heard a lot about choline and creatine peaks with citrate.

Healthy prostate has a lot of normal citrate, and just like other cancers, prostate cancer also, the membranes break down and produce choline.

The choline and creatinine peak are very closely placed, and that's why it's something that we put together, choline, creatinine, then poly means they're another ones that are present in healthy prostate tissue.

These are better all delineated on three Tesla as opposed to 1.5, but nevertheless, they're well seen on both 1.5 and three T.

And this is the cancer where you have high choline peak as opposed to the citrate.

Another example of in a left mid gland mass, you see a large mass in on T two here.

That's almost this extra capsule extension laterally.

And then this had very high choline plus creatinine citrate ratios.

And this was a very high grade tumor.

Spectroscopy as well has shown if you've seen several voxel together, higher incidents of more aggressive tumors, so it's associated with the Gleason grade as well.

So we look for choline and creatinine de citrate ratio of in at least two adjacent V expressed standard deviations above them mean of normal tissue.

Generally, we look at for three, but you need at least two.

And the key is to look at the spectra and not just the metabolic ratios, because the spectra, the background tissue is very important to evaluate as well.

Why Use MR Spectroscopy?

Why are we not using the so often?

This was a prospective trial that was done in 2004 and 2005 that they studied patients who had combined T two and 1.5 on 1.5 Tesla mr.

And really did not show any more benefit of T two witted imaging, if you included MR. Spectroscopy.

But there were some issues with this trial in the sense that the Akron study population consisted predominantly of lower risk patients, very small disease volume of disease and low grade disease.

And as you can see, the volume of tissue point less than point 0.5 ccs or so.

Also since then, three Tesla has come up and the spatial resolution has doubled on three Tesla as opposed to 1.5.

On 1.5 smaller tumors, low grade cancers were harder to delineate.

And also the acquisition time increased.

However, even on three Tesla, the acquisition time was even more if you to detect Until now.

I think now things have changed in the sense that now we can do a very fast Mr. Spectroscopy scan and you know, so if we do not get good data, well, you know, at least it's not 15 minutes in the scanner.

Where is MR Spectroscopy Useful?

Where is it useful?

One of the places it has shown us has been in transition zone.

So here's an example, for instance, is a T two weighted image that you see is a well is, you know, perhaps there's a low T two signal here that's somewhat ill-defined.

And yes, a DC shows some restriction, but it shows in this whole area.

And DCE is not useful here.

There's in fact, there's more enhancement in the peripheral zone here.

Spectroscopy does show that to be positive, so it can increase your confidence.

Again.

So this is one area, but not only that, and this was actually a Gleason seven.

There's been a recent paper in 2012 from the NY Megan group that showed that in the transition zone, a significant correlation with aggressiveness was found for choline plus creatinine citrate while this was lacking for the diffusion.

So as it is, the transition zone is so challenging to interpret that perhaps if you have this, it could only to help.

Now, the other thing is you could go back and say, well, okay, I'll show you this example.

Here's another example of T where T two abnormalities present, and here's an A DC that if you can see, it's somewhat speckled.

You do see some somewhat linear spots here, but so do you here, and DCE is not useful here.

T two do though you do see something.

And then in this case, there was high choline to citrate ratio here.

This patient, by the way, had low, mid he random biopsies.

He had a Gleason three plus three in his left mid gland, and that's why this was a staging MRI done.

But this lesion here is nicely seen on our spectroscopy.

Now, you could say that using our current version, you know, T two is dominant sequence.

So if you were to consider this partially circumscribed, something that you would worry, you would, you could biopsy it.

So it could still be useful in the current rads, but I think spectroscopy could add the in to increase the confidence.

There.

Another example of a lesion in the lar very large prostate, this was 115 ccs or so.

And there's a low T two markedly hypo intense nodule in the superiorly on the left side that does not really show much on on the A DC.

And the high B value exam was indeterminant on this because of ghosting artifacts and even the extrapolated B values did not work out.

But in this case, again, Mr. Spectroscopy was useful.

So there is a role if someone has it and wants to work on it, that it could be useful.

How about prostate cancer managed with active surveillance?

There are a couple of studies done on this.

This was originally this was for seven year study that show they followed patients for seven years on active surveillance.

I believe there were 114 some patients on this, in this study.

And they found that if you were to see a lesion, Mr Spectroscopy on the initial scan that those patients were more likely to progress to increase disease.

And so, for instance, this is a patient who has very small volume cancer, two millimeter in the left mid gland, and his spectroscopy is negative.

It's normal spectra.

He's less likely to progress as opposed to this patient who has now on T two, it's somewhat ill defined, kind of mildly hyperintense, on a DC, regardless of what it shows here, the spectroscopy showed very high choline to citrate, and this would be the in the study would've shown that would progress.

And there's another study done in eg they followed for even longer.

So that a couple of studies showing nice data long-term study showing nice data on active surveillance patients.

This is another study that is I believe done at the NIH and in this study, the initial 50, some patients only had MR spectroscopy and T two edit images.

So again, this was useful to follow those patients.

What about post-radiation recurrence?

And now DCEP just mentioned that is, it is the best sequence to evaluate recurrence.

However, what if the patients has renal insufficiency and such was the case?

So this is a patient with brachytherapy, 67-year-old who had Gleason seven, it was diagnosed in his left mid gland in 2003, and he went radiation seed implants.

And then he started to have a rise in his PSA.

So by the time 2011 rolled around his PSA was 2.9, and at the time of his exam was GFR was 20.

By the way, are fairly conservative in our practice.

We don't some practices will use gavis for fif for PSA, I mean of GFR of 15 and above.

We are conservative and we have it for 40 cutoff.

So we would not use contrast in this case.

And a mar spectroscopy really saved the day because as you can see on on T two, you do see some areas, but there's really no way to know where the tumor is.

A DC was not very useful, and he nicely, the peak peaks show up.

So what happens in radiation is you don't get any metabolites elsewhere.

And the meta, there's some metabolites just not necessarily get nice choline and sit citrate peaks, but the fact that you get some metabolite information and that was useful, and he went on to biopsy.

So hopefully I've shown you where it is useful or there's some value to it.

How to Perform MR Spectroscopy

So now I'm gonna perhaps bore you a little bit with how to do it because I do believe that how you do it makes the biggest difference in this.

End rectal coil is essential if you do spectroscopy.

And we do use Xylocaine gel as well.

You need to use some liquid pero carbon is something that I use personally, but barium is useful as well.

And then you do need to do a three plane load to check the coil position and coil position check is key.

By the way, so the couple of coils that are available, this is a the flexible expandable disposable coil by merad, and then there's a whole logic coil as well.

And these co equals are not platform specific, but they are field strength specific, and they're really under coils for all the major vendors.

So a little on how the placement is.

Dan had gone on a little earlier a little bit and talked about it, and it's I just wanted to emphasize that both on the sagittal plane and the axial plane on the axial plane, there should not be greater than 20% tilt or angulation, and then on sagittal plane to make sure that superior inferior regions are covered well.

Also the prostate analytic coil correction is a surface coil intensity correction program that corrects the high intensity close to the surface coil.

And all vendors have this.

And you also, if you use coil, you would be familiar with this on your system.

But just a few words on that, because this is what I believe is the Goldilocks approach here, where the coil correction is not done, you just cannot see the posterior part at all.

If it's overdone, you know, this is what happens.

You can, it can simulate tumor, so it has to be just right.

And so this is a little, it's very important, especially for spectroscopy.

It's important for just on T two as well.

But for spectroscopy, you need to really look at the coil correction.

So you obtain the three data set prostate with the voxels, the entire gland, as opposed to the single voxels that are used in neuro, the spectral of relative concentration and metabolites are what we view.

And then you do the MRI after the MRS, I mean MRS after the MRI, the T two weighted images.

So it's very important to do the volume that you're going to choose.

It should include the prostate and not much else.

Obviously, we wanna minimize the air interface and as well as the lipid interface, those are our enemies and spectroscopy, fat and water, air as well as the urine liquid can also be a problem.

And these sat very selective saturation bands are placed to avoid all of that.

So for instance, you find the base and you wanna start over there, but you wanna make sure you do not include the Sunil vesicles.

Why?

Because Sunil vesicles have phospholipids and they can really contaminate the entire data set.

And then you want you can go all the way down, but the volume of interest box, it should be placed around in the biggest part of the prostate.

And this is what it looks like with somewhat looks crazy with all the saturation bands, but those are important to cut out.

We're also looking at a oval structure and putting a rectangular box over it because that's what is available.

And so you have to cut out the extraneous using the saturation bands.

All right?

So we primarily evaluate the spectra, and then you look at the signal to noise.

If the signal to noise is low, then you have less confidence in the ratios.

And there's a fair amount of post-processing is done in the sense that this is not a spectra that the software produces.

And you say, okay, this these are the numbers there has, you have to interpret that spectra and spend some time on it.

There's some post-processing techniques, and all of that's included in the syllabus.

I've put in all the post-processing issues that come up and didn't really wanna go over details on the talk today, one of the things I do wanna emphasize though is the voxel shifting because there's to avoid partial volume effects that can occur.

And this is just an example showing that.

So here's a spectra where you see the markedly hypo intense nodule posteriorly.

And here with this spectra, if you were to just look at this, you would get some cancer here and some here.

And this is really a normal peak you get.

However, if you do this and focus more on the nodule itself, the spectra changes.

So there voxel shifting can be a very useful technique to use.

Conclusion

In conclusion, I think Mr. Spectroscopy has value in transition zone tumors, could be something we could use for active surveillance.

And several studies have shown usefulness test in that I think really in a big subset of patients in renal insufficiency, it would be something of high value because not only just for post-treatment, but now with focal therapy starting, those issues are gonna come up.

And if you have a large of a practice that evolves, you may find that useful.

Limitations.

Of course, there are many, the motion artifact, noise, time, cost, and physicist availability, of course is key.

Do work with your physicists and if they're willing to learn and go over this, it could only help.

So I think the entire study is better if the physicists are more keen on helping with your with your scanner shimming, et cetera.

So I find it a positive adjunct and I hope if you have time and interest that you would try it.

Thank you.