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Purpose Banding artifacts in images acquired by balanced steady-state free precession (bSSFP) remain a challenge in MRI as they considerably reduce image quality, and diagnostic value deteriorates accordingly. As the steady-state tolerates small shifts in frequency, it is possible to acquire frequency-modulated bSSFP. Unfortunately, standard reconstructions of such measurements suffer from signal loss. Our study proposes a multifrequency reconstruction and demonstrates its capability of suppressing banding artifacts while retaining the high signal level of standard bSSFP. Methods Numerical simulations in vitro and in vivo measurements were performed using both standard bSSFP and frequency-modulated bSSFP. The modulated data were reconstructed using a multifrequency approach consisting of three steps: phase correction, multiple reconstructions for different assumed frequencies, and maximum intensity projection. Results Although standard bSSFP measurements showed banding artifacts that compromised the image quality, standard reconstructions of frequency-modulated acquisitions suffered from signal loss. In contrast, images reconstructed from frequency-modulated data using the proposed multifrequency reconstruction showed no visual bandings and featured a higher signal-to-noise ratio (SNR). The SNR gain for phantom and in vivo measurements ranged from 1.23 to 1.49. Conclusions The presented multifrequency reconstruction for frequency-modulated bSSFP provides images showing no bandings and featuring high SNR in short scan times. Magn Reson Med 78:2226–2235, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

By combining intravoxel incoherent motion (IVIM) and diffusion tensor imaging (DTI) we introduce a new diffusion model called intravoxel oriented flow (IVOF) that accounts for anisotropy of diffusion and the flow-related signal. An IVOF model using a simplified apparent flow fraction tensor (IVOFf ) is applied to diffusion-weighted imaging of human kidneys. The kidneys of 13 healthy volunteers were examined on a 3 T scanner. Diffusion-weighted images were acquired with six b values between 0 and 800 s/mm(2) and 30 diffusion directions. Diffusivity and flow fraction were calculated for different diffusion models. The Akaike information criterion was used to compare the model fit of the proposed IVOFf model to IVIM and DTI. In the majority of voxels the proposed IVOFf model with a simplified apparent flow fraction tensor performs better than IVIM and DTI. Mean diffusivity is significantly higher in DTI compared with models that account for the flow-related signal. The fractional anisotropy of diffusion is significantly reduced when flow fraction is considered to be anisotropic. Anisotropy of the apparent flow fraction tensor is significantly higher in the renal medulla than in the cortex region. The IVOFf model describes diffusion-weighted data in the human kidney more accurately than IVIM or DTI. The apparent flow fraction in the kidney proved to be anisotropic.

Obtaining functional information on the human lung is of tremendous interest in the characterization of lung defects and pathologies. However, pulmonary ventilation and perfusion maps usually require contrast agents and the application of electrocardiogram (ECG) triggering and breath holds to generate datasets free of motion artifacts. This work demonstrates the possibility of obtaining highly resolved perfusion-weighted and ventilation-weighted images of the human lung using proton MRI and the SElf-gated Non-Contrast-Enhanced FUnctional Lung imaging (SENCEFUL) technique. The SENCEFUL technique utilizes a two-dimensional fast low-angle shot (FLASH) sequence with quasi-random sampling of phase-encoding (PE) steps for data acquisition. After every readout, a short additional acquisition of the non-phase-encoded direct current (DC) signal necessary for self-gating was added. By sorting the quasi-randomly acquired data according to respiratory and cardiac phase derived from the DC signal, datasets of representative respiratory and cardiac cycles could be accurately reconstructed. By application of the Fourier transform along the temporal dimension, functional maps (perfusion and ventilation) were obtained. These maps were compared with dynamic contrast-enhanced (DCE, perfusion) as well as standard Fourier decomposition (FD, ventilation) reference datasets. All datasets were additionally scored by two experienced radiologists to quantify image quality. In addition, one initial patient examination using SENCEFUL was performed. Functional images of healthy volunteers and a patient diagnosed with hypoplasia of the left pulmonary artery and left-sided pulmonary fibrosis were successfully obtained. Perfusion-weighted images corresponded well to DCE-MRI data; ventilation-weighted images offered a significantly better depiction of the lung periphery compared with standard FD. Furthermore, the SENCEFUL technique hints at a potential clinical relevance by successfully detecting a perfusion defect in the patient scan. It can be concluded that SENCEFUL enables highly resolved ventilation- and perfusion-weighted maps of the human lung to be obtained using proton MRI, and might be interesting for further clinical evaluation. Copyright © 2014 John Wiley & Sons, Ltd.

Purpose To iteratively correct for deviations in radial trajectories with no need of additionally performed calibration scans. Theory and Methods Radially acquired data sets—even when undersampled to a certain extend—inherently feature an oversampled area in the center of k-space. Thus, for a perfectly measured trajectory and neglecting noise, information is consistent between multiple measurements gridded to the same Cartesian position within this region. In the case of erroneous coordinates, this accordance—and therefore a correction of the trajectory—can be enforced by an algorithm iteratively shifting the projections with respect to each other by applying the GRAPPA operator. The method was validated in numerical simulations, as well as in radial acquisitions of a phantom and in vivo images at 3T. The results of the correction were compared to a previously proposed correction method. Results The newly introduced technique allowed for a reliable trajectory correction in each of the presented examples. The method was able to remove artifacts as effectively as methods that are based on data from additional calibration scans. Conclusion The iterative technique introduced in this paper allows for a correction of trajectory errors in radial imaging with no need for additional calibration data. Magn Reson Med 73:1151–1157, 2015. © 2014 Wiley Periodicals, Inc.

Purpose To investigate the influence of respiration on field maps for geometric distortion correction derived from two rapidly acquired consecutive echo planar images. Methods Displacement maps of the brains of seven healthy volunteers were acquired under breath hold and free breathing for a 64 × 64 pixel image matrix using phase labeling for additional coordinate encoding (PLACE). The maps were transformed into undistorted gradient echo space and analyzed with regard to standard deviation and absolute deviation from an accurate reference field map derived from a multiecho reference scan. Results Standard deviations between PLACE field maps and absolute difference from the reference field map are a factor of about 3 higher under free breathing than under breath hold. The mean deviation decreases from 3 pixels in the slice closest to the lung to 1 pixel in the most superior slice under free breathing and from 1 to