Laura Barlow, RTMR
MRI Technologist Supervisor at the University of British Columbia MRI Research Center, 3T facilities. She has been working with MRI for a decade. Her current role focuses on the field of advanced neuro research.
At the UBC MRI Research Centre, which is currently staffed by 70 principal investigators, the majority of studies and clinical trials are brain research, with MSrelated research as a principle area of interest. The center installed a 3.0T Ingenia Elition scanner in December 2018 as a successor of their Achieva 3.0T, with the intention to use it for all future research studies.
Multiple sclerosis or MS is a neurodegenerative disease that is characterized by myelin degradation, resulting in cognitive and motor deficits. According to Dr. Shannon Kolind, MR imaging for diagnosis and monitoring of MS is moving to higher field strength and using more 3D sequences, as reflected in the CMSC guidelines [1-3].
At UBC, a lot of the MS-related work focuses on myelin imaging. “We're born with very little myelin and that increases as the brain grows, which is important for nerve signal propagation. Multiple sclerosis on the other hand, degenerates the myelin with the opposite effect. So, myelin has a really important role in brain function, and having a tool that measures myelin can be extremely useful, we feel,” says Dr. MacKay.
Myelin water imaging (MWI) is a breakthrough technique that was pioneered at UBC for measuring myelin content in the brain, in vivo. “Because the T2 time of water in myelin is much shorter than the T2 of water in the intraand extracellular spaces, we can separate out the myelin water signal.”
The techniques for measuring myelin have changed a lot over the years. “Since we are using the Elition, our myelin water images are much better. We're now acquiring 1 x 2 x 5 mm voxels and displaying at 1 x 1 x 2.5 mm. For a whole brain we can now measure the fraction of water in the myelin component in only about five or six minutes,” Dr. MacKay says.
Dr. Kolind says that Ingenia Elition has opened up a world of different options and features and it has been tremendously exciting to discover how these can benefit their protocols. “Switching from our old scanner to Elition is like jumping from a flip phone to the latest smart phone,” she adds.
“The biggest jump is being able to turn on Compressed SENSE; it has definitely made sequences faster, allowing us to fit in more types of images. However, in most studies one or two scans are the main focus, so we can also stick to the time and apply Compressed SENSE to improve the resolution or even the coverage. For example, instead
of limiting MWI to the brain, even without the cerebellum, we can now spend about the same amount of time and scan the whole brain and the cervical spinal cord, which is a huge boost for us.”
Dr. Rauscher says, “For MWI we perform 3D T2 with 32 or more echoes. This used to take a long time, but with Compressed SENSE we can decrease this to ten minutes for the whole head. Because of the large field of view (FOV) on the readout direction, we even get information from the brainstem, which we previously missed when we were using the GRASE approach. Having the whole head scan is nice because it has spatial resolution, orientation and FOV that are comparable to the standard 3D clinical MS scans, including the FLAIR and 3D T2, and a 3D T1 for brain volume.”
| | With SENSE | | With Compressed SENSE |
| Acquired resolution: | 1 x 2 x 5 mm3 | → | 1.5 x 2 x 3 mm3 |
| Number of echoes: | 32 or 48 | → | 56 |
| Echo spacing: | 10 ms or 8 ms | → | 7 ms |
Also Dr. Rauscher considers it a huge advantage that he can simply try things on the Elition that would require pulse programming on different MRI systems, such as their old Achieva system. “For example, adding pre-pulses or turning a conventional 3D T2 scan into an accelerated GRASE scan with multiple echoes have been very easy thanks to the enormous flexibility with the Elition’s graphic user interface,” he says.
“In the past, MWI scans were often limited due to time constraints,” says Dr. Kolind, “because it was a difficult acquisition and complicated analysis. But with the Elition, we can perform MWI without having to do any programming modifications.”
For Dr. Kolind, the Elition excels in advanced neuroimaging for two main reasons. “It's image quality and access to so many different imaging parameters. We’re involved in several multi-center studies, and we can always easily identify the images that came from our Elition scanner, because they are just so beautiful – even though it seems like we’ve set our parameters similarly to other study participants. And as a physicist, being able to do many things, for instance to push resolution and save time, is really helpful.”
According to Dr. MacKay, MWI images benefit from Elition’s high quality gradients. “We need good gradients because we want to be able to do multi-echo sequences that have short TE times.”
Dr. Rauscher says, “With better gradients we can use a shorter echo spacing on the spin echo, so we get better sampling of the rapidly decaying myelin signal, which typically has T2 of around 10-20 milliseconds at 3 Tesla. If we can reduce echo spacing from about 8 to 5-6 milliseconds, we get a much better sampling of the short decay component and increase our SNR, which is a big advantage. The same is true for multi-echo gradient echo which we use for susceptibility mapping and for mapping venous vessels in MS.”
In practice, Ingenia Elition allows the team to do things now that were not possible before: “There are some scans that we didn’t do before, because the scans were taking too long. With Elition we can combine scans that would have been prohibitively long on the old scanner.
The Elition scanner at UBC has helped researchers decrease scan times and has paved the way for extended scanning possibilities. “We can now achieve more of our scanning goals in the same time,” says Dr. Rauscher. “Patients can typically stay in the scanner for about 45 minutes. So, with the faster scan times, we can now add more scans into one session.
He says the accelerated scanning is achieved via the use of Compressed SENSE and MultiBand SENSE. “We can use Compressed SENSE acceleration factors of about 10 on a 3D FLAIR for instance, which is quite remarkable compared with what we saw with the Achieva. With 3D FLAIR, we can push the spatial resolution to 0.3 cubic mm and it works. Previously, our 3D FLAIR scans lasted about 8 minutes, but now with Elition they are five minutes. The SNR is also visibly better. Our SWI and QSM scans look fantastic. Also, since a lot of neuroimaging is EPI based, using the MultiBand SENSE technique can increase temporal resolution and make it possible to run complicated DTI scans relatively quickly.”
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