Mitglied der Helmholtz-Gemeinschaft EPIK for TRIMAGE Seong Dae Yun 1 and N. Jon Shah 1,2 1 Institute of Neuroscience and Medicine 4 Forschungszentrum Jülich 2 Faculty of Medicine, Department of Neurology, RWTH Aachen University

19 October 2015Slide 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

19 October 2015Slide 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 improvementsRequire new imaging techniques

19 October 2015Slide 4Institute of Neuroscience and Medicine Imaging technique: EPI with Keyhole (EPIK) * Keyhole Sparse K-space trajectory of EPIK  Sparse regions  Solid, dashed, find-dashed lines: sampled at 1 st, 2 nd and 3 rd 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

19 October 2015Slide 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

19 October 2015Slide 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 Phantom In vivo

19 October 2015Slide 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 EPIEPIK Activations with a t-score > 3.21 on selected two slices

19 October 2015Slide 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 (TE 1, TE 2 ). Keyhole Sparse Keyhole Sparse K-space trajectory of EPIK K-space trajectory redesigned for DC-EPIK complex conjugate Dual-contrasts (TE 1, TE 2 ) per scan (A, B, C …) * Zaitsev M et al., Phys Med Biol 2005

19 October 2015Slide 9Institute of Neuroscience and Medicine  Acquisition of dual-contrasts (T 1, T 2 * ) using DC-EPIK Dual-contrast EPIK (DC-EPIK) at 1.5T T1T1 T2*T2* Sample recon- structed images T 1 map (top), R 2 * map (bottom) Evolution of T 1 (top) and R 2 * (bottom) following contrast agent injection

19 October 2015Slide 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 * Keyhole Sparse K-space trajectory of EPIK K-space trajectory redesigned for 2-fold EPIK Keyhole Sparse * Yun S et al., NeuroImage 2013

19 October 2015Slide 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. EPIEPIK 2-fold EPIK

19 October 2015Slide 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-fold EPIK

19 October 2015Slide 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 mm 2 ) x 20 slices with single contrast EPIK: 128 x 128 (1.80 x 1.80 mm 2 ) x 24 slices with double contrasts EPI (T 2 * )EPIK (T 1 )EPIK (T 2 * ) Reduced image distortions in EPIK than in EPI (see white arrows) * Caldeira L et al., ISMRM 2014

19 October 2015Slide 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 (T 1 ) Estimated AIF EPIK (T 1 ) EPIK (T 2 * ) EPI (T 2 * ) CBF maps

19 October 2015Slide 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 mm 2 ), EPIK (96 x 96; 2.08 x 2.08 mm 2 )  Advantages of EPIK: increased resolution, better functional contrast EPI EPIK One-sample t-testPaired t-test (EPIK vs EPI; Control vs Motor)

19 October 2015Slide 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

19 October 2015Slide 17Institute of Neuroscience and Medicine Induced by local changes of the main magnetic field due to different magnetic properties of tissue. Especially pronounced in T 2 * -weighted sequences with long echo time (=> EPI) Typical 1.5T: susceptibility artefacts EPI: susceptibility-induced signal dropout

19 October 2015Slide 18Institute of Neuroscience and Medicine High-Resolution EPIK (1x1mm) at 3T

19 October 2015Slide 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 BandMulti Band

19 October 2015Slide 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 (T 1, T 2 * ), multi-contrast (T 1, T 2 *, T 2 *, …)  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

19 October 2015Slide 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 mm 2 ), a slice out of 28 slices EPIK: 240 x 240 (1.00 x 1.00 mm 2 ), a slice out of 32 slices

19 October 2015Slide 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

19 October 2015Slide 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.