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32-channel coil boosts 3.0T neuro imaging at Kennedy Krieger

Best Practice
Prof. Barker, Peter, D.Phil. Baltimore, Md, F.M. Kirby Research Center for Functional Brain Imaging at Kennedy Krieger Institute USA
Prof. Mori, Susumu, Ph.D. Baltimore, Md, F.M. Kirby Research Center for Functional Brain Imaging at Kennedy Krieger Institute USA
Pekar, James, Ph.D. Baltimore, Md, F.M. Kirby Research Center for Functional Brain Imaging at Kennedy Krieger Institute USA

The F.M. Kirby Research Center for Functional Brain Imaging at the Kennedy Krieger Institute (Baltimore, Maryland, USA) is a general resource center for neuro imaging. It provides 3.0T and 7.0T imaging for Kennedy Krieger, for Johns Hopkins University School of Medicine and for the University of Maryland.
 32-channel SENSE Head coil Kennedy Krieger Institute
32-channel SENSE Head coil
Kennedy Krieger Institute

Kennedy Krieger Institute sees significantly better fMRI, DTI, spectroscopic imaging with the 32-channel SENSE Head coil

The Center recently began using the 32-channel SENSE Head coil in its neuro studies on the Achieva 3.0T X-series. Because the 32-channel coil provides increased SNR, clinicians can either scan faster or get higher spatial resolution or temporal resolution, depending on the particular study.

Peter van Zijl, PhD, is the Director of the F.M. Kirby Research Center at Kennedy Krieger and Professor of Radiology at the Johns Hopkins University School of Medicine. He explains how the coil benefits studies done at the Institute.

High SENSE factors become practical

"With the 8-channel coil we wouldn't do parallel imaging in multiple directions because noise was much bigger," says Dr. van Zijl. "The 32-channel coil now enables using SENSE in multiple directions and with higher SENSE acceleration factors. This is particularly an advantage for 3D acquisition techniques."

Dr. van Zijl emphasizes that the high SENSE acceleration factors achieved with the coil do not compromise image quality. "For anatomical imaging, we have applied SENSE acceleration factors of 6, and the images are still beautiful. So, for instance, we can easily do a 3D FFE at 0.7 x 0.7 x 0.7 mm in about 4 minutes, which is much better than the 1 x 1 x 1 mm in about 6 minutes that we used to do with the 8-channel coil."

"In spectroscopy, we have gone as high as a SENSE acceleration factor of 9. The quality of these spectroscopic images is still better than with the 8-channel coil using lower acceleration factors, because there is less lipid contamination. These are the most impressive spectroscopic images that I have seen in my whole life," he says, "and I have seen a lot of them." "This coil's design enables very good quality images over the whole of the brain, even without the front section. I have not seen that in any other coil ," says Dr. van Zijl.



 Peter Barker, D.Phil. Susumu Mori, PhD James Pekar, PhD
Peter Barker, D.Phil.
Susumu Mori, PhD
James Pekar, PhD

Significantly faster spectroscopy promotes clinical acceptance

Peter B. Barker, D.Phil., Professor, Department of Radiology at Johns Hopkins University School of Medicine, is working on several neuroimaging projects at the Institute. These include using MR Spectroscopy Imaging (MRSI) to assess rare metabolic diseases in children, such as leukodystrophies and Rett syndrome.

"There are two main advantages to this 32-channel coil," says Dr. Barker. "Improved SNR and improved SENSE reconstruction performance. These are critical for demanding experiments such as multi-voxel spectroscopy. The coil is also very comfortable for the patient."

With the conventional 8-channel coil, Dr. Barker did not use SENSE factors higher than 2 or 3 for 2D-MRSI, because of low SNR and artifacts becoming more apparent. "With the new 32-channel coil, we routinely do a SENSE factor of 6 for MRSI," he says. "This reduces a conventional 30-minute MRSI scan to just five minutes. Recently, we acquired some 3-minute 2D-MRSI scans with a SENSE factor of 9. The data were surprisingly good for such a short scan time."

The applications of MRSI might be expanded as clinicians become aware of its feasibility. "Widespread adoption of clinical applications has been hampered by a lack of commercially available optimized pulse sequences and analysis tools," says Dr. Barker. "Philips now provides an outstanding package for both single and multi-voxel spectroscopy."


 32-channel coil
SF 2 x 1.5 = 3 32-channel coil
SF 2 x 3 = 6
32-channel coil SF 2 x 1.5 = 3
32-channel coil SF 2 x 3 = 6
 8-channel coil
SF 2 x 1.5 = 3 8-channel coil
SF 2 x 3 = 6
8-channel coil SF 2 x 1.5 = 3
8-channel coil SF 2 x 3 = 6

High SENSE factors for MRSI. Detailed comparisons by Dr. Henry Zhu
with Dr. Barker show that the 32-channel coil choline spectroscopic
scan with SENSE factor 6 has better quality and is faster than the
8-channel coil scan with SENSE factor 3.


SENSE-MRSI of high-grade tumor. The left frontoparietal lesion shows very characteristic spectra of a high grade glioma, with a high Cho signal and a decrease in NAA. Note that the lesion shows FLAIR/T2 hyperintensity in a region which closely matches the NAA reduction. Individual spectra are shown from the normal right side (blue) and the abnormal region (red). Achieva 3.0T with 32-channel SENSE Head coil.

Parallel imaging has improved DTI

Susumu Mori, PhD, Professor at Johns Hopkins University School of Medicine, is a world leader in using DTI to characterize human white matter anatomy, and its abnormalities in conditions such as multiple sclerosis, stroke, brain tumors and cerebral palsy.

"While DTI is an extremely powerful method to delineate white matter anatomy, it's easily affected by patient motion," says Prof. Mori. "To minimize this motion effect, it is essential to use a rapid imaging technique such as single-shot echo-planar imaging (EPI). DTI, therefore, inherits many issues related to single-shot EPI, such as low spatial resolution and image distortion."

In the past 10 years, DTI has been drastically improved by the introduction of SENSE parallel imaging. SENSE enables shorter echo times for high SNR, less distortion, and higher spatial resolution.

New coil enables higher resolution and less distortion in DTI

"SENSE was literally a 'dream' technology for DTI," says Prof. Mori. "However, there is a limitation in increasing the SENSE factor. Depending on the coil geometry, a SENSE factor higher than 2 often leads to artifacts. With the 32-channel SENSE Head coil, however, we can now push the boundary in DTI. First, the new coil allows a higher SENSE factor; a SENSE factor of 3 produces clean, artifact-free images. Second, it provides higher SNR, which leads to shorter scanning time and/or higher image resolution."

"In the past, we spent at least 9 minutes for DTI with 2.5 mm resolution, but now the scanning time is reduced to about 4.5 minutes with 2.2 mm resolution," says Prof. Mori. "This time reduction is the key for DTI scans to be accepted as a routine clinical scan, where time efficiency is so crucial."


 SENSE 2 SENSE 3
SENSE 2
SENSE 3

Images with different SENSE factors. The red outline from the SENSE 3 image is superimposed on the SENSE 2 image, highlighting the improvements near the temporal lobes. This clearly shows that distortion is significantly reduced with the higher SENSE factor.


The 32-channel SENSE Head coil enables high resolution DTI, which was not possible several years ago. These DTI images with 1.9 mm isotropic resolution, 66 slices were obtained in 5:21 min. scan time.


High resolution DTI allows detailed fiber-tracking. The
small pixel size in combination with high SENSE factor
allows detailed visualization of complex anatomy in the
mid-brain region. Five fiber bundles are shown:
cortico-spinal tract (cst, blue), medial lemniscus (ml,
green), superior-, medial-, and inferior-cerebellar
peduncles (scp, pink; mcp, red; icp, orange).

Faster scans, smaller voxels particularly important in pediatric fMRI

In Kennedy Krieger's functional MRI (fMRI) studies, the new 32-channel head coil far outperforms the previous coil. "In standard fMRI the new coil works very well," says Dr. van Zijl. "The SNR is much better, and we can go to higher spatial resolution."

James J. Pekar, PhD, is Research Scientist at Kennedy Krieger and Associate Professor in the Russel H. Morgan Department of Radiology and Radiological Science at Johns Hopkins University School of Medicine. In his fMRI work, Dr. Pekar often works with children who have ADHD, autism, dyslexia and other brain-related disorders.

There are special challenges in working with children. Investigators design child-friendly paradigms with stimuli and tasks that are age appropriate. Faster scan times are of great importance in children, who often cannot stay still for long periods of time. The higher SENSE factors also produce smaller voxels for better localization.

"We're currently optimizing fMRI acquisitions using the new 32-channel coil," says Dr. Pekar. "Previously, our default fMRI exam used 3 mm isotropic resolution. Our initial scans with the new coil show better results using 2 mm isotropic voxels."

"The new coil provides higher temporal SNR with 3 mm isotropic voxels," he says, "But the 2 mm isotropic voxels show higher t-values in a block-design activation paradigm, which is due to reduced partial volume effects when using smaller voxels."


 3 x 3 x 3 mm 2 x 2 x 2 mm
3 x 3 x 3 mm
2 x 2 x 2 mm
High resolution improves BOLD-fMRI. This right-hand finger-tap block-design experiment demonstrates better localization of the activation and higher t-values (arrows) when resolution is increased from 3 x 3 x 3 mm to 2 x 2 x 2 mm using the 32-channel head coil.

Increasing to more than 32 coil elements will add less benefit

"Adding even more coil elements will not have a similar impact as moving from 8 to 32," says Dr. van Zijl. "There's a point of diminishing gain per added coil element as this follows an exponential curve. Changing from 1 to 8 will give more than a doubling in SNR, increasing from 8 to 16 may provide 50% more, and from 16 to 32 probably another 10%. Even if you would go from 32 to 64, you would probably gain only 10% in SNR. So, I think 32 channels is about right."

References

1 Mori, S., Wakana, S., Poetscher, N. L. M, van Zijl, P. C. M.
MRI Atlas of Human White Matter, First Edition.
Elsevier Science. (2005).




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