Rüdiger Stirnberg

Ultra-high-field MRI promises major gains in BOLD sensitivity but introduces severe challenges such as RF field inhomogeneity, B0 field inhomogeneity, motion and vibration-induced field variations. We report the first whole-brain resting-state and task-based fMRI experiments at 11.7T. A 3D-EPI sequence was optimized using tailored parallel-transmit RF pulses, gradient reshaping to suppress vibration-induced B0 fluctuations, and prospective motion correction using servo navigation combined with retrospective phase equalization (PEERS). Four participants were scanned at 11.7T with whole-brain 1.2 mm isotropic resolution with servo navigation and PEERS that considerably reduced residual motion and increased temporal SNR. The Default Mode Network in resting state could be detected and a physiological-noise-dominated regime was identified. Four additional but different participants were scanned at 7T for tSNR comparison and validation of the protocol, data quality and processing pipeline. Task-based fMRI likewise was conducted at 11.7T and yielded robust, spatially specific activations across motor, visual, mathematical, and language networks, again with improved sensitivity and cleaner BOLD responses when using servo navigation and PEERS. These results demonstrate the feasibility and reliability of whole-brain human fMRI at 11.7T and constitute a first quality control milestone to further increase resolution at that field strength.

Purpose: Recent improvements in MRI gradient design and amplifiers, advanced MRI scanners are now routinely utilizing slew rates of several hundred T/m/s. However, full gradient performance cannot be exploited in high-resolution EPI due to peripheral nerve stimulation (PNS) limits. We aim to characterize and mitigate these PNS constraints using a simple sequence modification: PNS-optimized EPI gradient pulse shapes. Methods: PNS-Optimized Pulses for EPI (POPE): we selectively reduce the slew rate of gradient pulses at periods of high predicted PNS spikes, while leaving the rest of the waveform unchanged. Results: POPE allows 7%-35% faster imaging of EPI protocols resolutions of 1mm-0.3mm resolutions without exceeding predicted PNS. With such improvements, POPE allows robust 0.3 mm isotropic fMRI protocols that would have exceeded safety limits without it. Conclusion: POPE facilitates locally precise fMRI activation mapping on clinical 7T scanners at spatial resolution that were previously unattainable due to PNS limitations.

Purpose: To design and develop an 8‐channel transmit 32‐channel receive 11.7T head coil for the strongest human MRI scanner to date, demonstrate safety, and evaluate signal‐to‐noise ratio (SNR) gains compared to 7T, the most used ultra‐high‐field (UHF) platform. Methods: The transmit array design incorporated a folded‐end radiofrequency (RF) shield to mitigate wave propagation in the scanner bore. The receive array consisted of 32‐overlapped loops constructed on a helmet size‐matched with the industry standard 7T head coil. The transmit array was characterized using B ₁ ⁺ mapping and MR thermometry, whereas the receive array performance was evaluated by measuring SNR at 7T and 11.7T using a lightbulb‐shaped phantom filled with a tissue equivalent solution. Results: Loss due to wave propagation was 4.5% of the input power for the chosen RF shield. The mean magnitude of the complex correlations between the simulated and measured single channel B ₁ ⁺ maps was 94%, which highlights minimal interaction between the transmit and receive arrays. An SNR gain of three‐fold was achieved in the phantom centre. In the periphery, representing the cortex, the SNR gain was 2.65‐fold, and the average gain over the whole volume was a factor of 2.69. The g‐factors of the 11.7T array were lower than the reference 7T coil due to the distinct coil sensitivities at higher frequency. Conclusion: We report substantial SNR gains over the whole volume at 11.7T using a fully overlapped 32‐channel loop array. The central SNR gain of B ₀ ^2.14 agrees with the theoretical prediction, while we also gain supra‐linearly in the periphery.

Purpose: To integrate MR‐based servo navigation in MPRAGE and 3D‐TSE sequences and demonstrate its potential for prospective head motion correction in structural imaging. Methods: Repeated modules of servo navigators were inserted before each preparation pulse of MPRAGE and 3D‐TSE sequences (before‐prep) for rapid convergence of motion parameter estimation. Additionally, reference navigators were distributed along the imaging echo train to test a within‐echo train correction (within‐ET) with contrast‐matched models, enabling more frequent geometry updates. The methods were evaluated in instructed motion experiments and in high‐resolution scans at 7T. Results: Artifacts caused by instructed abrupt motion were clearly reduced in scans with servo navigation for both sequences using the before‐prep correction. Residual artifacts of rapid in‐train motion were further mitigated by the within‐ET correction in MPRAGE. In high‐resolution scans with minimal motion, servo navigation preserved fine anatomical details, while it improved image quality under involuntary motion in long acquisitions. Conclusion: Servo navigation provides accurate real‐time head motion correction for structural brain imaging.

Purpose: A modified interleaved flyback (miFB) approach is introduced, designed to mitigate flow artifacts caused by alternating readout polarities in Echo Planar Imaging (EPI), while preserving acquisition efficiency. Methods: We propose reconstructing odd and even echoes of 3D‐EPI separately. To this end, the respective missing lines are acquired in interleaved shots with inverted polarity and an additional gradient pre‐lobe. Thereby, high scan efficiency is maintained compared to unsampled flyback gradients. Our miFB approach is additionally combined with gradient moment smoothing and compared to the interleaved dual‐echo with acceleration (IDEA) method in phantom and in vivo scans at 7 Tesla. Results: Our results demonstrate a significant reduction in ghosting and signal dropout using the miFB approach, yielding comparable image quality to non‐EPI acquisitions while reducing acquisition time by approximately half. Conclusion: The miFB approach offers a substantial reduction in flow artifacts, allowing for decreased acquisition times in TOF‐MRA.

Purpose: To mitigate artifacts related to motion and field changes in high‐resolution ‐weighted human brain imaging using servo navigation at ultra‐high fields up to 11.7 T. Methods: MR‐based servo navigators were integrated into a segmented 3D‐EPI sequence to allow for prospective correction of involuntary head motion and first‐order shim changes. Seven subjects were scanned with whole‐brain protocols at 0.3 mm isotropic resolution with and without correction at 7 and 11.7 T. Validation was performed on detailed brain vasculature in scans with involuntary motion. Results: Blurring of small veins was reduced by servo navigation for all subjects and across field strengths. In case of involuntary large motion, the method preserved image quality, while uncorrected motion led to severe artifacts. In case of microscopic motion, reduced blurring and shading in the frontal lobe demonstrate the additional benefit of prospective field drift correction. Conclusion: Servo‐navigated segmented 3D‐EPI improves 0.3 mm isotropic whole‐brain ‐weighted imaging under realistic motion and field changes within 5.5 to 11 min scan time at 11.7 and 7 T.

Noninvasive measurement of the human brain’s angioarchitecture is essential for understanding functional neuroimaging signals, diagnosing cerebrovascular diseases, and tracking neurodegeneration. Ultrahigh-field MRI now enables mesoscopic (<0.5 millimeters) imaging, revealing vascular details previously inaccessible in vivo. Yet current approaches face two barriers: Scan times often exceed 40 minutes, and the conventional visualization methods remain limited for navigating the vasculature. Here, we present a fast whole-brain MRI protocol that resolves the venous network at 0.35 millimeters in under 7 minutes. We also introduce processing and visualization techniques that distinguish vessel types and more intuitively navigate the vasculature. These advances allow in vivo reproduction of the seminal vasculature images of Henri M. Duvernoy and provide whole-brain intracortical meso-vein maps in humans. Our methods lay the groundwork for detailed examination of vascular organization across individuals, brain regions, and cortical layers. More generally, these methods make mesoscopic imaging of angioarchitecture viable for broad neuroscientific and clinical applications.

Background: 7T MRI received FDA/CE clearance almost 7 years ago. However, until today, it has not yet been widely adopted in clinical routine. This is mainly due to field inhomogeneities that impede whole-brain coverage. Moreover, the long scan times often associated with high-resolution imaging are an additional limiting factor. Purpose: To combine calibration-free parallel transmit technology (pTx) using universal pulses (UP) with advanced imaging acceleration strategies to achieve homogenous multicontrast 7T MRI with whole-brain coverage and high spatial resolution in short scan time. Materials and Methods: Ten healthy volunteers were scanned both with conventional vendor-provided sequences and with custom sequences for anatomical whole-brain imaging [ -weighted, -weighted, FLAIR, and susceptibility-weighted]. The scan times for the 2 anatomical protocols were matched (25 minutes). In addition, a quantitative MRI protocol [multi-parametric mapping (MPM) and chemical exchange saturation transfer (CEST)] was scanned twice using custom sequences with conventional (circular polarized) and UPs, respectively, in a scan time of 2×25 minutes. Moreover, 4 patients with different neurological diseases were scanned, namely temporal lobe epilepsy, spinocerebellar ataxia, cerebral amyloid angiopathy, and glioblastoma. For the patients, only optimized custom sequences with UPs were acquired. Results: Compared with conventional implementations, the custom sequences provide strongly improved image homogeneity and quality with significantly higher SNR and CNR across the whole brain, including cerebellum and brain stem. Moreover, UPs improve the repeatability of derived quantitative parameters. The suggested protocol has additionally been successfully demonstrated in 4 patients with different neurological pathologies. Conclusions: Homogeneous whole-brain 7T MRI with high spatial resolution and high image quality is possible in clinically feasible scan times. The developed protocol can be applied without any expert knowledge and is ready for clinical use. The approach could largely extend applicability of UHF MRI in neuroradiology paving the way for increased routine use of 7T MRI.

Purpose: To present a new, fast MR imaging method for visualization and quantification of pulsatile displacement in brain tissue and fluid. Methods: The natural phase‐contrast of non‐balanced steady‐state free precession combined with careful tuning of the intrinsic spoiler gradients is harnessed to measure displacement along specific physical directions. Efficient segmented 3D‐EPI allows for whole brain coverage within TR = 0.15 s. Motion sensitive terms are added to the extended phase graph theory and simulations are used to optimize the sequence parameters and to calibrate the phase sensitivity. Pilot data on 4 healthy volunteers are acquired at 7T and analyzed after cardiac retrogating. A set of three 1‐min scans with spoiler gradients along orthogonal axes is required to estimate full 3D displacement vectors. Results: Simulations show that pulsatile displacements up to around 1 mm can be resolved with the proposed method. In vivo example data are in general agreement with predictions from simulations. The precision of the displacement measurements is estimated to be 0.01 mm using repeated scans of the same subject, and while estimated displacement values agree well with literature values for example tissue ROIs, the measurement accuracy needs to be further explored. The method provides a detailed view of the pulsatile motion along all three physical axes and with full 3D coverage of the brain. Conclusion: Brain Pulsation Imaging allows for quantitative measurements of displacement vectors through the cardiac cycle with whole brain coverage within 3–5 min. The method is robust and should have significant potential for clinical application.