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Purpose: To improve 2D noncontrast‐enhanced MRA by using a helical time‐of‐flight (TOF) acquisition technique and a slice‐super‐resolution reconstruction. Methods: The TOF technique is combined with a helical trajectory with golden‐angle-based radial projection reordering. A continuous spatial shift in slice direction is realized by adjusting the frequency of the excitation pulse between the individual projections. The limited resolution along the shift direction is improved by a deconvolution with simulated slice profile. The helical TOF (hTOF) was compared in vivo with a conventional 2D and 3D TOF. Results: Results from in vivo experiments on the carotid show that the visual resolution in slice direction can be improved by using hTOF and the slice‐super‐resolution reconstruction. The vessels appear up to 1.5 times sharper and can be better separated from each other. Compared to 2D TOF images, the stair step artifacts are strongly reduced in reformatted hTOF images, whereas measurement time is decreased by at least 35%. Compared to 3D TOF, the hTOF offers a higher blood‐to‐background contrast, better visualization of smaller vessels, and reduced measurement time. Conclusion: The hTOF benefits from a 2D acquisition and a 3D reconstruction, which makes it a promising technique for the noncontrast‐enhanced imaging of the carotid.

Aims Dynamically phase-cycled radial balanced steady-state free precession (DYPR-SSFP) is a method for efficient banding artifact removal in bSSFP imaging. Based on a varying radiofrequency (RF) phase-increment in combination with a radial trajectory, DYPR-SSFP allows obtaining a banding-free image out of a single acquired k-space. The purpose of this work is to present an extension of this technique, enabling fast three-dimensional isotropic banding-free bSSFP imaging. Methods While banding artifact removal with DYPR-SSFP relies on the applied dynamic phase-cycle, this aspect can lead to artifacts, at least when the number of acquired projections lies below a certain limit. However, by using a 3D radial trajectory with quasi-random view ordering for image acquisition, this problem is intrinsically solved, enabling 3D DYPR-SSFP imaging at or even below the Nyquist criterion. The approach is validated for brain and knee imaging at 3 Tesla. Results Volumetric, banding-free images were obtained in clinically acceptable scan times with an isotropic resolution up to 0.56 mm. Conclusion The combination of DYPR-SSFP with a 3D radial trajectory allows banding-free isotropic volumetric bSSFP imaging with no expense of scan time. Therefore, this is a promising candidate for clinical applications such as imaging of cranial nerves or articular cartilage.

Simultaneous multislice imaging (SMS) using parallel image reconstruction has rapidly advanced to become a major imaging technique. The primary benefit is an acceleration in data acquisition that is equal to the number of simultaneously excited slices. Unlike in-plane parallel imaging this can have only a marginal intrinsic signal-to-noise ratio penalty, and the full acceleration is attainable at fixed echo time, as is required for many echo planar imaging applications. Furthermore, for some implementations SMS techniques can reduce radiofrequency (RF) power deposition. In this review the current state of the art of SMS imaging is presented. In the Introduction, a historical overview is given of the history of SMS excitation in MRI. The following section on RF pulses gives both the theoretical background and practical application. The section on encoding and reconstruction shows how the collapsed multislice images can be disentangled by means of the transmitter pulse phase, gradient pulses, and most importantly using multichannel receiver coils. The relationship between classic parallel imaging techniques and SMS reconstruction methods is explored. The subsequent section describes the practical implementation, including the acquisition of reference data, and slice cross-talk. Published applications of SMS imaging are then reviewed, and the article concludes with an outlook and perspective of SMS imaging. Magn Reson Med 75:63–81, 2016. © 2015 The Authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance.

Purpose Balanced steady-state free precession (bSSFP) imaging suffers from banding artifacts due to its inherent sensitivity to inhomogeneities in the main magnetic field. These artifacts can be removed by the acquisition of multiple images at different frequency offsets. However, conventional phase-cycling is hindered by a long scan time. The purpose of this work is to present a novel approach for efficient banding removal in bSSFP imaging. Theory and Methods To this end, the phase-cycle during a single-shot radial acquisition of an image was dynamically changed. Thus, each projection is acquired with a different frequency offset. Using conventional radial gridding, an artifact-free image can be reconstructed out of this dataset. Results The approach is validated at clinical field strength [3.0 Tesla (T)] as well as at ultrahigh field (9.4T). Robust elimination of banding artifacts was obtained for different imaging regions, including brain imaging at ultrahigh field with an in-plane resolution of 0.25 × 0.25 mm2. Besides banding artifact-free imaging, the applicability of the proposed technique for fat-water separation is demonstrated. Conclusion Dynamically phase-cycled radial bSSFP has the potential for banding-free bSSFP imaging in a short scan time, in the presence of severe field inhomogeneities and at high resolution.

A promising approach for the simultaneous quantification of relative proton density (M0), T1, and T2 is the inversion-recovery TrueFISP sequence, consisting of an inversion pulse followed by a series of balanced steady-state free precession acquisitions. Parameters can then be obtained from a mono-exponential fit to the series of images. However, a segmented acquisition is usually necessary, which increases the total acquisition time considerably. The goal of this study is to obtain M0, T1, and T2 maps using a single-shot acquisition, with T1 and T2 measurements in brain that are consistent with the published literature, with a 20-fold speed improvement over the segmented approach, and at a clinically relevant spatial resolution. To this end, a single-shot inversion-recovery TrueFISP sequence was combined with a radial view-sharing technique. The parameters M0, T1, and T2 were then obtained on a pixel-wise basis from a three fit parameter to the signal evolution. The accuracy of this method for quantifying these parameters is demonstrated in vivo. In addition, further corrections to the quantification necessary owing to other experimental factors, namely magnetization transfer and imperfect slice profiles, were developed. Including additional scans necessary for these corrections in the measurement protocol, the required scan time is increased from approximately 6 to 18-28 s per slice.