PURPOSE:To compare a novel combined acquisition technique (CAT) of turbo-spin-echo (TSE) and echo-planar-imaging (EPI) with conventional TSE. CAT reduces the electromagnetic energy load transmitted for spin excitation. This radiofrequency (RF) burden is limited by the specific absorption rate (SAR) for patient safety. SAR limits restrict high-field MRI applications, in particular.MATERIAL AND METHODS:The study was approved by the local Medical Ethics Committee. Written informed consent was obtained from all participants. T2- and PD-weighted brain images of n = 40 Multiple Sclerosis (MS) patients were acquired by CAT and TSE at 3 Tesla. Lesions were recorded by two blinded, board-certificated neuroradiologists. Diagnostic equivalence of CAT and TSE to detect MS lesions was evaluated along with their SAR, sound pressure level (SPL) and sensations of acoustic noise, heating, vibration and peripheral nerve stimulation.RESULTS:Every MS lesion revealed on TSE was detected by CAT according to both raters (Cohen's kappa of within-rater/across-CAT/TSE lesion detection κCAT = 1.00, at an inter-rater lesion detection agreement of κLES = 0.82). CAT reduced the SAR burden significantly compared to TSE (p<0.001). Mean SAR differences between TSE and CAT were 29.0 (± 5.7) % for the T2-contrast and 32.7 (± 21.9) % for the PD-contrast (expressed as percentages of the effective SAR limit of 3.2 W/kg for head examinations). Average SPL of CAT was no louder than during TSE. Sensations of CAT- vs. TSE-induced heating, noise and scanning vibrations did not differ.CONCLUSION:T2-/PD-CAT is diagnostically equivalent to TSE for MS lesion detection yet substantially reduces the RF exposure. Such SAR reduction facilitates high-field MRI applications at 3 Tesla or above and corresponding protocol standardizations but CAT can also be used to scan faster, at higher resolution or with more slices. According to our data, CAT is no more uncomfortable than TSE scanning.

PurposeTo present a technique for non-contrast-enhanced in vivo imaging of the blood volume fraction of the human lung. The technique is based on the intravoxel incoherent motion (IVIM) approach. However, a substantial novelty is introduced here: the need for external diffusion sensitizing gradients is eliminated by exploiting the internal magnetic field gradients typical of the lung tissue, due to magnetic susceptibility differences at air/tissue interfaces.Materials and MethodsA single shot turbo spin-echo sequence with stimulated-echo preparation and electrocardiograph synchronization was used for acquisition. Two images were acquired in a single breath-hold of 10 seconds duration: one reference image and one blood-suppressed image. The blood volume fraction was quantified using a two-compartment signal decay model, as given by the IVIM theory. Experiments were performed at 1.5T in eight healthy volunteers.ResultsValues of the blood volume fraction obtained within the lung parenchyma (3616%) are in good agreement with previous reports, obtained using contrast-enhanced magnetic resonance angiography (33%), and show relatively good reproducibility.ConclusionThe presented technique offers a robust way to quantify the blood volume fraction of the human lung parenchyma without using contrast agents. Image acquisition can be accomplished in a single breath-hold and could be suitable for clinical applications on patients with lung diseases. J. Magn. Reson. Imaging 2015;41:1454-1464. (c) 2014 Wiley Periodicals, Inc.

PurposeParallel MRI methods are typically associated with a degradation of the signal‐to‐noise ratio (SNR). High scan time reduction factors are therefore restricted to applications with high intrinsic SNR. One possibility to increase the intrinsic SNR is to simultaneously excite several slices by means of multiband radio‐frequency (RF) pulses and subsequently separate the slices by parallel MRI reconstruction algorithms. However, the separation of closely spaced slices may suffer from severe noise amplification when there is insufficient coil sensitivity variation along the slice direction. The purpose of this work is to apply a phase‐constrained reconstruction for multiband experiments to minimize the noise amplification.MethodsPre‐defined phase differences between neighboring slices are induced and slice separation is performed by a phase‐constrained parallel MRI reconstruction. Phase differences between neighboring slices are tailored to achieve optimal slice separation with minimized noise amplification. The potential of the method is demonstrated through multiband in‐vivo experiments.ResultsNoise amplification in multiband phase‐constrained reconstructions is significantly reduced in comparison to standard multiband reconstruction when the phase difference between neighboring slices (distance = 12 mm) is 90°.ConclusionsMultiband phase‐constrained parallel MRI has the potential for accelerated multi‐slice imaging with an improved SNR performance. Magn Reson Med 69:974–980, 2013. © 2013 Wiley Periodicals, Inc.

OBJECT:Clinical 3 T MRI systems are rapidly increasing and MRI systems with a static field of 7 T or even more have been installed. The RF power deposition is proportional to the square of the static magnetic field strength and is characterized by the specific absorption rate (SAR). Therefore, there exist defined safety limits to avoid heating of the patient. Here, we describe a hybrid method to significantly reduce the SAR compared to a turbo-spin-echo (TSE) sequence.MATERIALS AND METHODS:We investigate the potential benefits of a combined acquisition technique (CAT) for high-field neuroimaging at 3 and 7 T. The TSE/EPI CAT experiments were performed on volunteers and patients and compared with standard TSE and GRASE protocols. Problems and solutions regarding T2 weighted CAT imaging are discussed.RESULTS:We present in vivo images with T2 and proton density contrast obtained on 3 and 7 T with significant SAR reduction (up to 60%) compared with standard TSE. Image quality is comparable to TSE but CAT shows fewer artifacts than a GRASE sequence.CONCLUSION:CAT is a promising candidate for neuroimaging at high fields up to 7 T. The SAR reduction allows one to shorten the waiting time between two excitations or to image more slices thereby reducing the overall measurement time.

INTRODUCTION: Proton MRI of the human lung is challenging due to low proton density, short T2, respiratory and cardiac motion. Single-shot turbo spin-echo (ssTSE) sequences can be used to mitigate the effects of T2 decay and T1 saturation and to achieve short acquisition times. This provides good signal-to-noise ratio (SNR) in the lungs and motion artifacts suppression. However, preparation schemes that induce phase shifts of the transverse magnetization, such as diffusion and T2 preparation, can result in the violation of the CPMG conditions and generate severe artifacts [1]. Here the application of a non-CPMG ssTSE sequence [2] to diffusionweighted (DW) and T2-weighted imaging of the human lung is presented. It is shown that this approach allows for apparent diffusion coefficient (ADC) and T2 mapping of the human lung in a single 10s breath-hold. METHODS: The non-CPMG ssTSE pulse sequence described in [2] was implemented on a 1.5T MR-scanner (Avanto, Siemens Healthcare, Erlangen, Germany). The sequence is based on a quadratic modulation of the phase cycle of the refocusing pulse train. This provides a stable signal amplitude along the echo train for both the inphase and out-of-phase components. Due to phase sign oscillation, two images need to be separately acquired from odd and even echoes and combined. Centric reordering was adopted to maximize the SNR. GRAPPA reconstruction [3], with acceleration factor 2, was used to reduce blurring due to T2 decay and specific absorption rate (SAR). The sequence was played with: a) diffusion sensitive preparation [4], based on the standard Stejskal-Tanner configuration, and b) T2 preparation, using an asymmetric spin echo scheme [5]. This was obtained by increasing the time between the excitation pulse and the first refocusing pulse by ΔTE. In vivo experiments were performed on a healthy volunteer using a six-channel phased-array body matrix in combination with a spine matrix. Imaging parameters: TR=6000ms, FOV=500x500mm, matrix size=128×128, voxel size=3.9×3.9mm, receive bandwidth=800Hz/pixel, inter-echo time=3.55ms, TA=480ms. For each kind of contrast (diffusion and T2) a breath-hold of less than 10s was sufficient to acquire two images, using: a) b=0-200s/mm for diffusion-weighting (with TE=45ms), and b) ΔTE=0-1ms for T2-weighting (with TE=16.5-17.5ms). ECG triggering in the diastolic phase was used to minimize the effect of blood pulsation on the signal refocusing. A separate breath-hold was necessary to acquire the calibration scan for GRAPPA reconstruction, using a standard gradient echo (GRE) sequence.

Introduction: Shorter scan times in MRI can be achieved by simultaneously exciting multiple slices. The individual slices can then be separated by applying dedicated parallel MRI algorithms [1]. The benefit over standard parallel MRI is an increased signal-to-noise-ratio (SNR) because a larger volume is excited. However, a reliable slice separation requires sufficient coil sensitivity variations along the slice direction. This requirement may not be met for closely spaced slices and hence the image quality may suffer from noise amplification due to high geometry factors. To overcome this problem, it has been proposed to improve the conditions for the parallel MRI reconstruction by shifting the individual approaches with respect to each other [2]. However, this approach requires dedicated RF phase-cycles and does not work for single-shot sequences such as EPI or HASTE.

Fig. 3: SNR (a) and δB1 (b) for BF = 4, 8, 16 and 32 with linear vs. centric encoding are compared for in vivo and phantom measurements. Rapid and low SAR B1-Mapping using a BURST-based Bloch-Siegert-Shift Sequence Alexander Gotschy, Uvo C. Hölscher, Thomas C. Basse-Lüsebrink, André Fischer, Morwan Choli, Thomas Kampf, Volker Sturm, Daniel Neumann, Volker Herold, Herbert Köstler, Dietbert Hahn, Guido Stoll, Wolfgang R. Bauer, and Peter M. Jakob Department of Experimental Physics 5, University of Würzburg, Würzburg, Germany, Department of Internal Medicine I, University of Würzburg, Würzburg, Germany, Research Center Magnetic Resonance Bavaria (MRB), Würzburg, Germany, Department of Neurology, University of Würzburg, Würzburg, Germany, Institute of Radiology, University of Würzburg, Würzburg, Germany

Purpose: To evaluate signal-to-noise ratio (SNR) and SNR efficiency in mixed-bandwidth acquisition (MBA). SNR efficiency describes the achievable SNR per unit time and is a basic aspect in clinical applications to optimize work flow. Materials and Methods: Corresponding simulations were performed and predictions of the theory verified in phantom experiments and volunteers. Specifically, SNR and SNR efficiencies were compared for an MBA fast low-angle shot (MBA-FLASH) sequence and traditional single-bandwidth acquisitions. Results:: MBAs result in an SNR penalty compared to single-bandwidth acquisitions for a given sampling time. Furthermore, the nonuniform distribution of noise characteristics in k-space introduced by MBA sequences caused potential changes in noise texture of the image. Conclusion: Overall, the MBA-FLASH imaging experiments in phantoms and healthy volunteers support the feasibility of using dual or multiple bandwidth acquisitions, which may be important in alternative imaging schemes that combine multiple acquisition techniques.

The purpose of this work is to demonstrate the functionality and performance of a PSF-based geometric distortion correction for high-field functional animal EPI. The EPI method was extended to measure the PSF and a postprocessing chain was implemented in Matlab for offline distortion correction. The correction procedure was applied to phantom and in vivo imaging of mice and rats at 9.4T using different SE-EPI and DWI-EPI protocols. Results show the significant improvement in image quality for single- and multishot EPI. Using a reduced FOV in the PSF encoding direction clearly reduced the acquisition time for PSF data by an acceleration factor of 2 or 4, without affecting the correction quality.