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MultiTransmit helps improve SNR and CNR in spine imaging

Best Practice
Filippi, Christopher, M.D. Fletcher Allen Health Care • USA

The University of Vermont (Burlington, Vermont, USA) has been investigating how spine imaging at 3.0T benefits from MultiTransmit parallel RF transmission. Spines of healthy volunteers of all ages from in and around the University have been scanned using Achieva 3.0T TX, with very good results for image quality and speed.
 Christopher Filippi, MD
Christopher Filippi, MD

Christopher G. Filippi, MD, is the Tampas Green and Gold Professor of Radiology, Section Head of Neuroradiology, Director of MRI and Medical Director of the University of Vermont MRI Center for Biomedical Imaging. His study1 looks at overall image quality improvements with MultiTransmit in thoracic and lumbar spine MRI. He says consistently high image quality and improved SNR and CNR were the main reasons that adding MultiTransmit to their 3.0T system was so important.

“MultiTransmit was shown to help obtain consistently high image uniformity in our routine 3.0T body and breast imaging. We have also applied MultiTransmit for spine to see if it would improve image quality, and it does. MultiTransmit technology allows for RF shimming to correct B1 inhomogeneity, which makes for a better image.”


Images show vastly improved uniformity, SNR and CNR

“With MultiTransmit we have achieved better signal-to-noise and contrast-to-noise ratios (SNR and CNR) on every thoracic and lumbar spine sequence we’ve tested so far,” Dr. Filippi says. “RF shimming provides more flip angle uniformity across the FOV, so SAR is more uniformly distributed, and you get rid of areas of dielectric shading that occur often in routine spine imaging at 3.0T, where either the signal drops out or is too bright. In all the spine sequences we use, there are improvements with MultiTransmit.”

In a recent study1, Dr. Filippi performed lumbar axial and sagittal T1 scans with ten volunteers
as well as axial and sagittal lumbar T2 scans with another nine volunteers. He found that
– in addition to better uniformity – CNR and SNR increase considerably. “It depends upon
the sequence, but for sagittal T1, CNR was up 53% and SNR was up 19%; for axial T1, CNR
improvement was 48% and SNR was 23%; for sagittal T2, CNR was 38% better and SNR was
20%; and for axial T2, CNR was 18% better and SNR was fully 100% better. Obviously,
this represents improved image quality for all people we’ve scanned so far.”
 without MultiTransmit with MultiTransmit
without MultiTransmit
with MultiTransmit

Focal disc herniation

2D axial T2-weighted TSE without and with MultiTransmit in thoracic spine of 21-year-old male.
The scan without MultiTransmit is undiagnostic. Achieva 3.0T TX, 15-channel SENSE Spine coil.
In-plane resolution 0.47 mm x 0.47 mm, 24 slices of 4 mm thickness, FOV 150 mm, scan time 3:33 min.
 without MultiTransmit with MultiTransmit
without MultiTransmit
with MultiTransmit

Lumbar spine

2D axial T2-weighted TSE without and with MultiTransmit in 47-year-old male. With MultiTransmit the nerve roots are well visualized, while without MultiTransmit these could not be confidently visualized and the scan is undiagnostic. Achieva 3.0T TX, 15-channel SENSE Spine coil. In-plane resolution 0.47 mm x 0.47 mm, 24 slices of 4 mm thickness, FOV 150 mm, scan time 3:33 min.
 without MultiTransmit with MultiTransmit
without MultiTransmit
with MultiTransmit

Normal sagittal spine

2D Sagittal T2-weighted TSE without and with MultiTransmit in 22-year-old female. Without
MultiTransmit, the scan takes longer and the spinal cord was not confidently visualized, so the scan was undiagnostic. Achieva 3.0T TX, 15-channel SENSE Spine coil. In-plane resolution 0.47 mm x 0.47 mm, 12 slices of 4 mm thickness, FOV 320 mm, scan time 4:33 min. without 3:54 min. with MultiTransmit.

MultiTransmit also speeds up spine exams

Although he was focusing on image quality, Dr. Filippi has certainly noticed speed improvements.
“We see faster scan times with MultiTransmit, especially on axial images. When using the
MultiTransmit parallel transmission and RF shimming, we can essentially do more axial slices
per given TR. We can better control SAR, and thus scan faster in the axial plane. We’ve had
40% reductions in that scan time.”

Clinical benefits

The clinical benefits of the higher image quality provided by MultiTransmit are significant.
“Traditional spine image quality at 3.0T is fraught with a greater degree of artifactual loss of signal, particularly in the lumbo-sacral junction, conus medullaris, and thoracolumbar junction. Now, MultiTransmit provides improvements in CNR and SNR that improve quality of these types of scans at 3.0T.”

In the MultiTransmit lower thoracic spine images Dr. Filippi evaluated, he saw several disc herniations that might otherwise have been missed. “With routine imaging, you may not have seen these herniations, but with MultiTransmit there was a clear herniation that was easier to detect.”

“MultiTransmit also allows scanning patients much more quickly, which is important because
many are in pain and they don’t tolerate imaging well,” he adds.

With better image quality and shorter scans, is 3.0T the future of spine imaging? “Absolutely,
MultiTransmit or parallel transmission MR really provides much faster scan times and better image
quality,” says Dr. Filippi. “The door is open to start using it as well in other exciting areas like
DTI of the spinal cord in the thoracic and conus regions. Having more rapid scan times without
loss of SNR or CNR is really significant.”

Future research will include MultiTransmit

The next phase of Dr. Filippi’s study is to determine whether MultiTransmit helps improve lesion conspicuity and detection. “In addition, we’d like to focus on continuing our earlier research on DTI of the conus region in adults and we plan to focus on the tethered spinal cord in children. Regardless of what happens next in our research, the fact that we have significantly better SNR and CNR sort of mandates the use of MultiTransmit. It’s just a better way to image.”


View ExamCard:

References

CG Filippi, Grand Isle, JM Johnson, M Carlson, HN Burbank, GF Alsofrom, T Andrews.
Improvement in Lumbar Spine MR Imaging at 3.0T with the Use of Parallel Transmission (MultiTransmit)
MR RSNA 2010 abstract


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Aug 3, 2011

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Best Practice
Achieva 3.0T TX
CNR, lumbar spine, MultiTransmit, Neuro, SNR, spine, thoracic spine
 

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