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A pTx-based pulsed CEST presaturation scheme is proposed and validated by simulations and 7T in vivo imaging. Magn Reson Med 78:2216-2225, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

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For the first time, CEST images were compared with F-FET in a simultaneous MR-PET measurement. Imaging findings derived fromF-FET PET and APT CEST MRI seem to provide different biological information. The validation of these imaging findings by histological confirmation is necessary, ideally using stereotactic biopsy.

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.

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.

Full-waveform inversion (FWI) is a technique used to obtain high-quality velocity models of the subsurface. Despite the elastic nature of the earth, the anisotropic acoustic wave equation is typically used to model wave propagation in FWI. In part, this simplification is essential for being efficient when inverting large 3D data sets, but it has the adverse effect of reducing the accuracy and resolution of the recovered P-wave velocity models, as well as a loss in potential to constrain other physical properties, such as the S-wave velocity given that amplitude information in the observed data set is not fully used. Here, we first apply conventional acoustic FWI to acoustic and elastic data generated using the same velocity model to investigate the effect of neglecting the elastic component in field data and we find that it leads to a loss in resolution and accuracy in the recovered velocity model. Then, we develop a method to mitigate elastic effects in acoustic FWI using matching filters that transform elastic data into acoustic data and find that it is applicable to marine and land data sets. Tests show that our approach is successful: The imprint of elastic effects on the recovered P-wave models is mitigated, leading to better-resolved models than those obtained after conventional acoustic FWI. Our method requires a guess of V P ∕V S and is marginally more computationally demanding than acoustic FWI, but much less so than elastic FWI.

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