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Purpose: To introduce a new method for in-phase zero TE (ipZTE) musculoskeletal MR imaging., Methods: ZTE is a 3D radial imaging method, which is sensitive to chemical shift off-resonance signal interference, especially around fat-water tissue interfaces. The ipZTE method addresses this fat-water chemical shift artifact by acquiring each 3D radial spoke at least twice with varying readout gradient amplitude and hence varying effective sampling time. Using k-space-based chemical shift decomposition, the acquired data is then reconstructed into an in-phase ZTE image and an out-of-phase disturbance., Results: The ipZTE method was tested for knee, pelvis, brain, and whole-body. The obtained images demonstrate exceptional soft-tissue uniformity free from out-of-phase disturbances apparent in the original ZTE images. The chemical shift decomposition was found to improve SNR at the cost of reduced image resolution., Conclusion: The ipZTE method can be used as an averaging mechanism to eliminate fat-water chemical shift artifacts and improve SNR. The method is expected to improve ZTE-based musculoskeletal imaging and pseudo CT conversion as required for PET/MR attenuation correction and MR-guided radiation therapy planning., (© 2019 International Society for Magnetic Resonance in Medicine.)

Purpose: Simultaneous multi-slice (SMS) imaging is an advantageous method for accelerating MRI scans, allowing reduced scan time, increased slice coverage, or high temporal resolution with limited image quality penalties. In this work we combine the advantages of SMS acceleration with the motion correction and artifact reduction capabilities of the PROPELLER technique., Methods: A PROPELLER sequence was developed with support for CAIPIRINHA and phase optimized multiband radio frequency pulses. To minimize the time spent on acquiring calibration data, both in-plane-generalized autocalibrating partial parallel acquisition (GRAPPA) and slice-GRAPPA weights for all PROPELLER blade angles were calibrated on a single fully sampled PROPELLER blade volume. Therefore, the proposed acquisition included a single fully sampled blade volume, with the remaining blades accelerated in both the phase and slice encoding directions without additional auto calibrating signal lines. Comparison to 3D RARE was performed as well as demonstration of 3D motion correction performance on the SMS PROPELLER data., Results: We show that PROPELLER acquisitions can be efficiently accelerated with SMS using a short embedded calibration. The potential in combining these two techniques was demonstrated with a high quality 1.0 × 1.0 × 1.0 mm 3 resolution T 2 -weighted volume, free from banding artifacts, and capable of 3D retrospective motion correction, with higher effective resolution compared to 3D RARE., Conclusion: With the combination of SMS acceleration and PROPELLER imaging, thin-sliced reformattable T 2 -weighted image volumes with 3D retrospective motion correction capabilities can be rapidly acquired with low sensitivity to flow and head motion. Magn Reson Med 80:496-506, 2018. © 2017 International Society for Magnetic Resonance in Medicine., (© 2017 International Society for Magnetic Resonance in Medicine.)

Purpose: A new multicontrast echo-planar imaging (EPI)-based sequence is proposed for brain MRI, which can directly generate six MR contrasts (T 1 -FLAIR, T 2 -w, diffusion-weighted (DWI), apparent diffusion coefficient (ADC), T2*-w, T 2 -FLAIR) in 1 min with full brain coverage. This could enable clinical MR clinical screening in similar time as a conventional CT exam but with more soft-tissue information., Methods: Eleven sequence modules were created as dynamic building blocks for the sequence. Two EPI readout modules were reused throughout the sequence and were prepended by other modules to form the desired MR contrasts. Two scan protocols were optimized with scan times of 55-75 s. Motion experiments were carried out on two volunteers to investigate the robustness against head motion. Scans on patients were carried out and compared to conventional clinical images., Results: The pulse sequence is found to be robust against motion given its single-shot nature of each contrast. For excessive out-of-plane head motion, the T 1 -FLAIR and T 2 -FLAIR contrasts suffer from incomplete inversion. Despite lower signal-to-noise ratio (SNR) and resolution, the 1-min multicontrast EPI data show promising correspondence with conventional diagnostic scans on patients., Conclusion: A 1 min multicontrast brain MRI scan based on EPI readouts has been presented in this feasibility study. Preliminary data show potential for clinical brain MRI use with minimal bore time for the patient. Such short examination time could be useful (e.g., for screening and acute stroke). The sequence may also help planning conventional brain MRI scans if run at the beginning of an examination. Magn Reson Med 79:3045-3054, 2018. © 2017 International Society for Magnetic Resonance in Medicine., (© 2017 International Society for Magnetic Resonance in Medicine.)

Purpose: The purpose of this study was to develop an X-Band electron paramagnetic resonance imaging protocol for visualization of oxidative stress in biopsies., Methods: The developed electron paramagnetic resonance imaging protocol was based on spin trapping with the cyclic hydroxylamine spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine and X-Band EPR imaging. Computer software was developed for deconvolution and back-projection of the EPR image. A phantom containing radicals of known spatial characteristic was used for evaluation of the developed protocol. As a demonstration of the technique electron paramagnetic resonance imaging of oxidative stress was performed in six sections of atherosclerotic plaques. Histopathological analyses were performed on adjoining sections., Results: The developed computer software for deconvolution and back-projection of the EPR images could accurately reproduce the shape of a phantom of known spatial distribution of radicals. The developed protocol could successfully be used to image oxidative stress in six sections of the three ex vivo atherosclerotic plaques., Conclusions: We have shown that oxidative stress can be imaged using a combination of spin trapping with the cyclic hydroxylamine spin probe cyclic hydroxylamine spin probe 1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine and X-Band EPR imaging. A thorough and systematic evaluation on different types of biopsies must be performed in the future to validate the proposed technique., (© 2014 Wiley Periodicals, Inc.)

Purpose: A two-dimensional fat navigator (FatNav) image is proposed, designed for future use as a means of prospective motion correction of head-nodding motion., Methods: The proposed FatNav module comprised a fat-selective excitation, followed by an accelerated echo planar imaging readout played out in one central sagittal plane. Step-wise motion experiments with different acceleration factors, blip polarity, and matrix sizes were performed. The accuracy of motion estimates derived from the FatNav data was assessed using water-based, distortion-free, spoiled-gradient echo images as the gold standard. The duration of the FatNav module was 10 ms to 20 ms. Volunteer data were acquired on a 3T system using an 8-channel radiofrequency coil., Methods: It is shown that acceleration factors of R = 8 are feasible for FatNav data. Best results are obtained when parallel imaging calibration data is matched in terms of both geometric distortions and signal content. For head rotations up to about 15 mm and 20 degrees, mean absolute errors of the motion estimates using FatNav data were about 0.5 mm and 1 degree., Conclusion: FatNav is advantageous in that it leaves most of the brain water magnetization unaffected and left to the host pulse sequence. Furthermore, high acceleration factors are possible with FatNav, which reduces estimation bias and the navigator duration., (© 2014 Wiley Periodicals, Inc.)

Purpose: Three-dimensional (3D) multislab diffusion-weighted echo-planar imaging (EPI) has been suggested as an alternative for high-resolution diffusion-weighted imaging. In this work, the key components of the sequence are investigated, optimal scan parameter settings suggested, and a signal-to-noise ratio (SNR) analysis, comparing 2D diffusion-weighted EPI and 3D multislab diffusion-weighted EPI, is performed., Methods: Slab profiles were measured using 3D multislab EPI to investigate slab profile saturation effects with respect to TR, T1 and overlap between slabs. For short TR values, two methods to reduce the slab banding artifacts are proposed. Moreover, the SNR for 2D and 3D multislab (3D-MS) DWI have been simulated for various anatomical coverages and slab thicknesses., Results: Simulated 3D multislab scans were shown to be more SNR-efficient than a corresponding 2D scan, for all investigated anatomical coverages and slab thicknesses. Slab banding artifacts being negligible for long repetition times (TRs) were strong for a TR of 2000 ms, proving that they stem from T1 -saturation effects. This banding was largely reduced by the suggested correction methods., Conclusion: In the low TR regime, T1 -saturation effects between adjacent slabs need to be taken in consideration to avoid slab-banding artifacts for multislab sequences. With the proposed correction methods the difference between the SNR-optimal TR and the TR where slab-banding artifacts become acceptable is reduced., (© 2014 Wiley Periodicals, Inc.)

Purpose: Vulnerable atherosclerotic plaques are structurally weak and prone to rupture, presumably due to local oxidative stress. Redox active iron is linked to oxidative stress and the aim of this study was to investigate the distribution of Fe(III) in carotid plaques and its relation to vulnerability for rupture., Methods: Atherosclerotic plaques from 10 patients (three asymptomatic and seven symptomatic) were investigated. Plaque vulnerability was classified using ultrasound and immunohistochemistry and correlated to Fe(III) measured by electron paramagnetic resonance spectroscopy., Results: Large intra-plaque Fe(III) variations were found. Plaques from symptomatic patients had a higher Fe(III) concentration as compared with asymptomatic plaques (0.36 ± 0.21 vs. 0.06 ± 0.04 nmol Fe(III)/mg tissue, P < 0.05, in sections adjoining narrowest part of the plaques). All but one plaque from symptomatic patients showed signs of cap rupture. No plaque from asymptomatic patients showed signs of cap rupture. There was a significant increase in cap macrophages in plaques from symptomatic patients compared with asymptomatic patients (31 ± 11% vs. 2.3 ± 2.3%, P < 0.01)., Conclusion: Fe(III) distribution varies substantially within atherosclerotic plaques. Plaques from symptomatic patients had significantly higher concentrations of Fe(III), signs of cap rupture and increased cap macrophage activity., (Copyright © 2013 Wiley Periodicals, Inc.)

Purpose: To acquire isotropic high-resolution, signal-to-noise ratio (SNR) efficient, 3D encoded diffusion-weighted MRI data., Methods: Multiple Fourier encoded slabs were combined into one full volume, using a generalized autocalibrating partially parallel acquisitions (GRAPPA) accelerated diffusion-weighted 3D multislab echo planar imaging (EPI) sequence with 2D phase navigation and in-plane motion correction., Results: Reconstructed data with 1.5-mm(3) nominal resolution is presented and shown under the influence of motion and with variable slab thicknesses. The SNR efficiency between diffusion-weighted 3D multislab EPI and DW 2D ss-EPI is compared. Finally, a 1.3-mm(3) full brain scan with 45 diffusion directions is presented., Conclusions: Diffusion-weighted 3D multislab EPI has been presented as an alternative sequence for high-resolution and high-SNR full brain coverage diffusion studies. Compared with the gold standard 2D diffusion-weighted single-shot Echo Planar Imaging, the SNR efficiency is significantly higher., (Copyright © 2012 Wiley Periodicals, Inc.)

In this work, diffusion weighting and parallel imaging is combined with a vertical gradient and spin echo data readout. This sequence was implemented and evaluated on healthy volunteers using a 1.5 and a 3 T whole-body MR system. As the vertical gradient and spin echo trajectory enables a higher k-space velocity in the phase-encoding direction than single-shot echo planar imaging, the geometrical distortions are reduced. When combined with parallel imaging such as generalized autocalibrating partially parallel acquisition, the geometric distortions are reduced even further, while also keeping the minimum echo time reasonably low. However, this combination of a diffusion preparation and multiple refocusing pulses during the vertical gradient and spin echo readout, generally violates the Carr-Purcell-Meiboom-Gill condition, which leads to interferences between echo pathways. To suppress the stimulated echo pathway, refocusing pulses with a sharper slice profiles and an odd/even crusher variation scheme were implemented and evaluated. Being a single-shot acquisition technique, the reconstructed images are robust to rigid-body head motion and spatially varying brain motion, both of which are common sources of artifacts in diffusion MRI., (Copyright © 2012 Wiley Periodicals, Inc.)