Parallel imaging acceleration of EPIK for reduced image distortions in fMRI

Magnetic Resonance Imaging

Silva

et al. 2019

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Background Echo planar imaging (EPI) is one of the methods of choice in dynamic susceptibility contrast MRI (DSC‐MRI) because it provides a sufficient temporal resolution. However, the relatively long readout duration of EPI often imposes limitations on increased spatial coverage or the use of multiple contrasts. Purpose To develop a DSC‐MRI method using EPIK (EPI with keyhole) to provide dual‐contrast (TE1 and TE2) information with a higher spatial coverage than EPI. To compare results from the community‐standard EPI method and the proposed EPIK method. Study Type Prospective. Subjects One healthy subject and 17 brain tumor patients. Field Strength/Sequence 3 T/accelerated EPI and dual‐contrast EPIK sequences. Assessment After an initial evaluation using healthy in vivo images, the use of the proposed method for DSC‐MRI was verified with brain tumor patients. The parametric images (eg, CBF and CBV) and arterial input function (AIF), obtained from both the EPI and EPIK, were compared. Statistical Tests The ratio of AIF peak height of the proposed method to that of EPI was computed. The ratio computation was also performed for the time‐to‐peak (TTP) in the AIF curves. From the obtained CBF and CBV maps, the tumor‐to‐brain (TBR) ratio was also calculated for each imaging method and the results were compared. Results For the same temporal resolution (1.5 sec), EPIK yielded dual‐contrast (TEs of 13/33 msec) with an increased spatial coverage (24 slices) and less geometric distortions than EPI; EPI provided single contrast (TE of 32 msec) with 20 slices. The obtained parametric values (eg, AIF peak, TTP, and TBR) had similar characteristics between EPI and the proposed method. Data Conclusion The dual‐contrast data produced by EPIK in DSC‐MRI allowed T1‐corrected parametric images without the need of second contrast injection and an enhanced estimation of the AIF. Level of Evidence: 1 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:628–640.

Section: Discussionmentioning

confidence: 69%

Section: Discussionmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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confidence: 99%

See 3 more Smart Citations

Dynamic susceptibility contrast parametric imaging using accelerated dual‐contrast echo planar imaging with keyhole

Caldeira

Magnetic Resonance Imaging

Silva

et al. 2019

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Perfusion weighted imaging using combined gradient/spin echo EPIK: Brain tumour applications in hybrid MR‐PET

Shah

Silva

2019

Human Brain Mapping

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Advanced perfusion‐weighted imaging (PWI) methods that combine gradient echo (GE) and spin echo (SE) data are important tools for the study of brain tumours. In PWI, single‐shot, EPI‐based methods have been widely used due to their relatively high imaging speed. However, when used with increasing spatial resolution, single‐shot EPI methods often show limitations in whole‐brain coverage for multi‐contrast applications. To overcome this limitation, this work employs a new version of EPI with keyhole (EPIK) to provide five echoes: two with GEs, two with mixed GESE and one with SE; the sequence is termed “GESE‐EPIK.” The performance of GESE‐EPIK is evaluated against its nearest relative, EPI, in terms of the temporal signal‐to‐noise ratio (tSNR). Here, data from brain tumour patients were acquired using a hybrid 3T MR‐BrainPET scanner. GESE‐EPIK resulted in reduced susceptibility artefacts, shorter TEs for the five echoes and increased brain coverage when compared to EPI. Moreover, compared to EPI, EPIK achieved a comparable tSNR for the first and second echoes and significantly higher tSNR for other echoes. A new method to obtain multi‐echo GE and SE data with shorter TEs and increased brain coverage is demonstrated. As proposed here, the workflow can be shortened and the integration of multimodal clinical MR‐PET studies can be facilitated.

Mapping of whole‐cerebrum resting‐state networks using ultra‐high resolution acquisition protocols

Pais‐Roldán

Palomero‐Gallagher

et al. 2022

Human Brain Mapping

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Resting‐state functional magnetic resonance imaging (fMRI) has been used in numerous studies to map networks in the brain that employ spatially disparate regions. However, attempts to map networks with high spatial resolution have been hampered by conflicting technical demands and associated problems. Results from recent fMRI studies have shown that spatial resolution remains around 0.7 × 0.7 × 0.7 mm 3 , with only partial brain coverage. Therefore, this work aims to present a novel fMRI technique that was developed based on echo‐planar‐imaging with keyhole (EPIK) combined with repetition‐time‐external (TR‐external) EPI phase correction. Each technique has been previously shown to be effective in enhancing the spatial resolution of fMRI, and in this work, the combination of the two techniques into TR‐external EPIK provided a nominal spatial resolution of 0.51 × 0.51 × 1.00 mm 3 (0.26 mm 3 voxel) with whole‐cerebrum coverage. Here, the feasibility of using half‐millimetre in‐plane TR‐external EPIK for resting‐state fMRI was validated using 13 healthy subjects and the corresponding reproducible mapping of resting‐state networks was demonstrated. Furthermore, TR‐external EPIK enabled the identification of various resting‐state networks distributed throughout the brain from a single fMRI session, with mapping fidelity onto the grey matter at 7T. The high‐resolution functional image further revealed mesoscale anatomical structures, such as small cerebral vessels and the internal granular layer of the cortex within the postcentral gyrus.