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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

par

seS

par

se

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.