Post on 02-Jan-2016
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EPIK for TRIMAGESeong Dae Yun1 and N. Jon Shah1,2
1Institute of Neuroscience and Medicine 4 Forschungszentrum Jülich
2Faculty of Medicine, Department of Neurology,
RWTH Aachen University
April 20, 2023 Slide 2Institute of Neuroscience and Medicine
Contents
Introduction: Dynamic MR Studies
Proposed Method and Results Imaging techniques: EPIK with Keyhole (EPIK) Experimental Results at 1.5T Experimental Results at 3T
Conclusions and Outlook
April 20, 2023 Slide 3Institute of Neuroscience and Medicine
Introduction: Dynamic MR Studies
Dynamic MR studies Studies of quantifying dynamically changing MR quantities Applications: fMRI, DWI, DSC-MRI*, etc.
Requisites Precise measurement of time-dependent features MR sequences: should provide high temporal/spatial resolution EPI has been widely used due to its relatively fast speed.
*DSC-MRI: Dynamic Susceptibility Contrast-MRI
For more improvements Require new imaging techniques
April 20, 2023 Slide 4Institute of Neuroscience and Medicine
Imaging technique: EPI with Keyhole (EPIK)*
Ke
yhol
eS
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par
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K-space trajectory of EPIK
Sparse regions Solid, dashed, find-dashed lines:
sampled at 1st, 2nd and 3rd scans Complete the region by sharing
Keyhole region Sampled at every scan
Acceleration potential Original total lines: 16 Sampled lines in EPIK: 8
- Sparse: 4- Keyhole: 4
* Zaitsev M et al., Magn Reson Med 2001
April 20, 2023 Slide 5Institute of Neuroscience and Medicine
Imaging technique: EPI with Keyhole (EPIK)
The continuity of signal decaying trajectory in EPIK prevents the occurrence of major image artefacts
Narrower PSF of EPIK than EPI spatial resolution should not be worse than that of EPI
April 20, 2023 Slide 6Institute of Neuroscience and Medicine
Reconstructed Images of EPIK at 1.5T
Comparison between standard EPI and EPIK Phantom: practically no difference in the spatial resolution In vivo: reduced geometric distortions (marked by white arrows)
EPI EPIK EPI EPIK
Phantom In vivo
April 20, 2023 Slide 7Institute of Neuroscience and Medicine
Demonstration of fMRI using EPIK at 1.5T
Visual stimulation fMRI with a simple block design Comparison between EPI and EPIK: nearly identical performance
EPI EPIKActivations with a t-score > 3.21
on selected two slices
April 20, 2023 Slide 8Institute of Neuroscience and Medicine
Dual-contrast EPIK (DC-EPIK) at 1.5T*
Extension of EPIK to a dual-contrast version Each scan (A, B, C …) acquires two different contrasts (TE1, TE2).
Key
hole
Spa
rse
Spa
rse
Key
hole
Spa
rse
K-space trajectory of EPIK
K-space trajectory redesigned for DC-EPIK
complex conjugate
Dual-contrasts (TE1, TE2) per scan (A, B, C …)
* Zaitsev M et al., Phys Med Biol 2005
April 20, 2023 Slide 9Institute of Neuroscience and Medicine
Acquisition of dual-contrasts (T1, T2*) using DC-EPIK
Dual-contrast EPIK (DC-EPIK) at 1.5T
T1
T2*
Sample recon-structed images
T1 map (top),R2
* map (bottom) Evolution of T1 (top) and R2
* (bottom) following contrast agent injection
April 20, 2023 Slide 10Institute of Neuroscience and Medicine
For more improvements in image resolution Ex.) 2-fold acceleration: every other line is skipped in the sampling. Missing lines are computed based on multi-channel data.
Parallel Imaging Acceleration of EPIK at 3T*
Key
hole
Spa
rse
Spa
rse
K-space trajectory of EPIK
K-space trajectory redesigned for 2-fold EPIK
Key
hole
Spa
rse
Spa
rse
* Yun S et al., NeuroImage 2013
April 20, 2023 Slide 11Institute of Neuroscience and Medicine
Parallel Imaging Acceleration of EPIK at 3T
Comparison between EPI, EPIK and 2-fold EPIK EPIK and 2-fold EPIK have reduced distortions than EPI.
EPI EPIK 2-fold EPIK
April 20, 2023 Slide 12Institute of Neuroscience and Medicine
Demonstration of fMRI at 3T
Visual stimulation fMRI with a simple block design Methods: EPI, EPIK and 2-fold EPIK comparable performance
EPI
EPIK
2-foldEPIK
April 20, 2023 Slide 13Institute of Neuroscience and Medicine
Accelerated DC-EPIK at 3T*
Combination of DC-EPIK and parallel imaging EPI : 128 x 128 (1.80 x 1.80 mm2) x 20 slices with single
contrastEPIK: 128 x 128 (1.80 x 1.80 mm2) x 24 slices with double contrasts
EPI (T2*) EPIK (T1) EPIK (T2
*)
Reduced image distortions
in EPIK than in EPI(see white arrows)
* Caldeira L et al., ISMRM 2014
April 20, 2023 Slide 14Institute of Neuroscience and Medicine
Estimation of AIF (Arterial Input Function) at 3T
Signal changes by contrast agent injection AIF estimation CBF maps: tumour is clearly identified in EPIK (T1)
Estimated AIF
EPIK (T1)
EPIK (T2*)
EPI (T2*)
CBF maps
April 20, 2023 Slide 15Institute of Neuroscience and Medicine
Finger Tapping fMRI using EPIK at 3T
Finger tapping with a simple block design EPI (64 x 64; 3.13 x 3.13 mm2), EPIK (96 x 96; 2.08 x 2.08 mm2) Advantages of EPIK: increased resolution, better functional contrast
EPI
EPIK
One-sample t-test Paired t-test (EPIK vs EPI; Control vs Motor)
April 20, 2023 Slide 16Institute of Neuroscience and Medicine
Finger Tapping fMRI using EPIK at 3T
(a) Conjunction analysis (b) EPIK > EPI Advantages of EPIK: about 4% better than EPI; smaller regions
April 20, 2023 Slide 17Institute of Neuroscience and Medicine
Induced by local changes of the main magnetic field due to different magnetic properties of tissue.
Especially pronounced in T2*-weighted sequences
with long echo time (=> EPI)
Typical EPI @ 1.5T: susceptibility artefacts
EPI: susceptibility-induced signal dropout
April 20, 2023 Slide 18Institute of Neuroscience and Medicine
High-Resolution EPIK (1x1mm) at 3T
April 20, 2023 Slide 19Institute of Neuroscience and Medicine
Ultra-High Resolution EPIK at 3T
EPIK FOV = 230x230mm; 0.8x0.8x1.5mm; 30 slices; TR/TE = 2200/30ms
Single Band Multi Band
April 20, 2023 Slide 20Institute of Neuroscience and Medicine
Sequence Interface/Image Reconstruction
EPIK has a virtually same user interface as EPI Like EPI, imaging parameters can be changed as a user like. Supported options
- ramp sampling- parallel imaging- partial Fourier- dual-contrast (T1, T2
*), multi-contrast (T1, T2*, T2
*, …)
Images are reconstructed with online reconstruction. Images are obtained in the same way as the standard sequence. Inevitable for high-resolution imaging due to its huge data size
April 20, 2023 Slide 21Institute of Neuroscience and Medicine
High-resolution EPIK at 3T (online reconstruction)
For EPI and EPIK, imaging parameters were optimised by pushing the limits towards highest possible resolution (TR/TE = 3000/35ms).
EPI: 192 x 192 (1.25 x 1.25 mm2), a slice out of 28 slices
EPIK: 240 x 240 (1.00 x 1.00 mm2), a slice out of 32 slices
April 20, 2023 Slide 22Institute of Neuroscience and Medicine
High-resolution fMRI at 3T
Visual stimulation fMRI with a simple block design LGN* and SC+ were better characterized by EPIK than EPI.
EPI
EPIK
Functional maps from a single subject Functional maps from a group (16 subjects)
*LGN: Lateral Geniculate Nucleus
+SC: Superior Colliculus
April 20, 2023 Slide 23Institute of Neuroscience and Medicine
Conclusions and Outlook
Conclusions EPIK outperforms EPI in terms of imaging speed, robustness
against geometric distortions. EPIK was validated with several dynamic MR applications. EPIK can be combined with other imaging techniques:
parallel imaging, partial Fourier, multiple echoes, etc.
Outlook The sequence and online reconstruction have been tested on
VB17 Needs to be transferred to RS2D. Any possible dynamic applications should profit from the
addressed advantages of EPIK.