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Clinically practical MR spectroscopy with "SENSE-able" scan times

Best Practice
Dydak, Ulrike, Ph.D. Zurich, Institute of Biomedical Engineering, University and ETH Switzerland

Clinically practical MR spectroscopy - with "SENSE-able" scan times - on horizon

Four to ten times faster studies promise mainstream spectroscopy use

Philipsã SENSE technique will become the cornerstone of clinically manageable MR spectroscopic imaging (MRSI) at both 1.5T and 3.0T, promising sophisticated 3D whole brain, high-resolution MRSI in 10-20 minutes and routine 2D MRSI in just two to five minutes, said Ulrike Dydak, Ph.D., of the Institute of Biomedical Engineering, University and ETH (Zurich). At Philips' Radiology MR Network Meeting in 2003, Dr. Dydak gave a presentation on the clinical potential of SENSE-MRSI (works-in-progress) ¹ particularly impressive at 3.0T ¹ featuring numerous examples of low scan time spectroscopy studies, boasting 24 x 24 and even 32 x 32 voxels.

 

The freedom to choose the desired grid and voxel sizes in MRSI has always been limited by cliniciansã preference for reasonable scan times. Therefore, if their idea of reasonable is two minutes, they must accept huge voxels and a grid of 8 x 8, which results in very poor spatial resolution in most cases, Dr. Dydak noted. The compromise has typically been slightly higher spatial resolution with a 16 x 16 grid (brain) or 8 x 8 x 16 grid (3D prostate), and significantly longer scan times.

SENSE to propel MR spectroscopy past barriers

SENSE brings many advantages to spectroscopic imaging, especially at 3.0T, Dr. Dydak said. SENSE-SI may be used by itself or combined with any of the existing fast SI techniques ¹ such as EPI, spiral MRSI (works-in-progress) and Turbo Spectroscopic Imaging (TSI) ¹ to enhance resolution or reduce scan time even further.

 

SENSE provides speed without compromise in MR spectroscopic imaging

In addition, unlike many fast sequences, SENSE imposes no restrictions on parameter choices, therefore users will be free to use short TEs, go to 3D or multislice acquisitions, and acquire high spectral and spatial resolutions ¹ all while scanning at a greatly accelerated rate, she said. At 3.0T, users employing SENSE-SI profit the most from the higher available SNR, because SENSE offers the possibility of fast SI without reliance on long spin or gradient echo trains, thus reducing T2-related signal loss. In addition, SENSE-SI scanning at 3.0T largely avoids RF deposition (SAR) limits that would be reached much faster at higher field strengths without SENSE.

Case studies show SENSE-SI scan time, resolution advantages

Dr. Dydak then treated attendees to a wealth of SENSE-SI images and spectra as evidence of SENSEãs contribution at both 1.5T and 3.0T. Dr. Dydak concluded by emphasizing that SENSE SI ¹ particularly for 3D high resolution SI ¹ will enable clinically manageable scan times. She added that SENSE represents an enabling technology for several applications that demand 3D imaging, such as longitudinal, post-interventional followup studies.

 

 

SENSE-SI at 1.5T A single slice measurement with a 32 x 32 grid (voxel < 1 ml) takes 30 minutes. SENSE SI at the same parameters takes just 7.5 minutes. Turbo-SI reduces scan time to 11 minutes, but SENSE-TSI reduces that to just three minutes - a ten-fold scan time reduction from SI to SENSE-TSI!SENSE-SI at 3.0T Similar study and parameters as at 1.5T. SI took 20 minutes, SENSE-SI yielded a four-fold reduction in scan time to five minutes. TSI took 10:34 min., SENSE-TSI only 2:46 min.
SENSE-SI at 1.5T
SENSE-SI at 3.0T
A single slice measurement with a 32 x 32 grid (voxel < 1 ml) takes 30 minutes. SENSE SI at the same parameters takes just 7.5 minutes. Turbo-SI reduces scan time to 11 minutes, but SENSE-TSI reduces that to just three minutes - a ten-fold scan time reduction from SI to SENSE-TSI!
Similar study and parameters as at 1.5T. SI took 20 minutes, SENSE-SI yielded a four-fold reduction in scan time to five minutes. TSI took 10:34 min., SENSE-TSI only 2:46 min.
SENSE-TSI at 1.5T A scout MRSI scan of a patient with an astrocytoma. The MRSI matrix was 24 x 24 and the voxel size approximately 1 ml. The scan time was only two minutes. All of the important information, such as the decrease in NAA and the increase in choline and lactate, are plainly visible in the metabolic maps.SENSE-TSI at 3.0T By exploiting the increased spectral resolution and SNR of higher field strength, even shorter scan times can be achieved. This example of a 24 x 24 voxel SENSE-TSI (TSE factor = 6) measurement shows that sub-minute measurements become realistic.Multislice SENSE-SI at 3.0T In a study of a patient with a glioma, four slices were acquired using a 24 x 24 grid and SENSE factor 4, yielding a scan time of 9:36 min., instead of the 40 minutes required for a non-SENSE-SI study. The SENSE-SI scan also produced high quality spectra, which clearly show the pathological changes.
SENSE-TSI at 1.5T
SENSE-TSI at 3.0T
Multislice SENSE-SI at 3.0T
A scout MRSI scan of a patient with an astrocytoma. The MRSI matrix was 24 x 24 and the voxel size approximately 1 ml. The scan time was only two minutes. All of the important information, such as the decrease in NAA and the increase in choline and lactate, are plainly visible in the metabolic maps.
By exploiting the increased spectral resolution and SNR of higher field strength, even shorter scan times can be achieved. This example of a 24 x 24 voxel SENSE-TSI (TSE factor = 6) measurement shows that sub-minute measurements become realistic.
In a study of a patient with a glioma, four slices were acquired using a 24 x 24 grid and SENSE factor 4, yielding a scan time of 9:36 min., instead of the 40 minutes required for a non-SENSE-SI study. The SENSE-SI scan also produced high quality spectra, which clearly show the pathological changes.
3D SENSE-SI at 1.5T In a volunteer, an eight-slice study with isotropic voxels (24 x 24 grid) of just 0.5 ml was acquired in 20 minutes. With conventional SI, this scan would have taken 80 minutes. The spectra even for these very small 8 x 8 x 8 mm voxels are exquisite, even in the basal ganglia.3D SENSE-SI at 3.0T In a patient with glioblastoma multiforme, clinicians acquired six slices with 24 x 24 voxels each and 0.8 ml voxel sizes. High spatial resolution was critical in this particular study. While the time required for a low resolution scan of this patient might take 15 minutes using conventional MRSI, this high resolution SENSE-SI study took only 14 minutes. A full hour would be required to obtain this resolution using standard SI techniques.3D SENSE-SI at 3.0T Another slice from the same measurement, 2 cm above the other slice. Observe how it is possible to differentiate voxels with elevated choline from voxels with normal metabolism which may lie next to each other. Had this been a single slice experiment, there would have been  immense partial volume effects, with the high lactate peak from the slice below concealing the fact that some of this tissue does not show lactate at all.
3D SENSE-SI at 1.5T
3D SENSE-SI at 3.0T
3D SENSE-SI at 3.0T
In a volunteer, an eight-slice study with isotropic voxels (24 x 24 grid) of just 0.5 ml was acquired in 20 minutes. With conventional SI, this scan would have taken 80 minutes. The spectra even for these very small 8 x 8 x 8 mm voxels are exquisite, even in the basal ganglia.
In a patient with glioblastoma multiforme, clinicians acquired six slices with 24 x 24 voxels each and 0.8 ml voxel sizes. High spatial resolution was critical in this particular study. While the time required for a low resolution scan of this patient might take 15 minutes using conventional MRSI, this high resolution SENSE-SI study took only 14 minutes. A full hour would be required to obtain this resolution using standard SI techniques.
Another slice from the same measurement, 2 cm above the other slice. Observe how it is possible to differentiate voxels with elevated choline from voxels with normal metabolism which may lie next to each other. Had this been a single slice experiment, there would have been immense partial volume effects, with the high lactate peak from the slice below concealing the fact that some of this tissue does not show lactate at all.


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Feb 10, 2005

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Achieva 1.5T, Achieva 3.0T, Intera 1.5T, Intera 3.0T
Brain, Neuro
 

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