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Purpose: An end-to-end differentiable 2D Bloch simulation is used to reduce T2 induced blurring in single-shot turbo spin echo sequences, also called rapid imaging with refocused echoes (RARE) sequences, by using a joint optimization of refocusing flip angles and a convolutional neural network.Methods: Simulation and optimization were performed in the MR-zero framework. Variable flip angle train and DenseNet parameters were optimized jointly using the instantaneous transverse magnetization, available in our simulation, at a certain echo time, which serves as ideal blurring-free target. Final optimized sequences were exported for in vivo measurements at a real system (3 T Siemens, PRISMA) using the Pulseq standard.Results: The optimized RARE was able to successfully lower T2 -induced blurring for single-shot RARE sequences in proton density-weighted and T2 -weighted images. In addition to an increased sharpness, the neural network allowed correction of the contrast changes to match the theoretical transversal magnetization. The optimization found flip angle design strategies similar to existing literature, however, visual inspection of the images and evaluation of the respective point spread function demonstrated an improved performance.Conclusions: This work demonstrates that when variable flip angles and a convolutional neural network are optimized jointly in an end-to-end approach, sequences with more efficient minimization of T2 -induced blurring can be found. This allows faster single- or multi-shot RARE MRI with longer echo trains.

Purpose: To evaluate the benefits and challenges of dynamic parallel transmit (pTx) pulses for fat saturation (FS) and water-excitation (WE), in the context of CEST MRI. Methods: "Universal" kT -points (for FS) and spiral non-selective (for WE) trajectories were optimized offline for flip angle (FA) homogeneity. Routines to optimize the pulse shape online, based on the subject's fields maps, were implemented (target FA of 110°/0° for FS, 0°/5° for WE at fat/water frequencies). The pulses were inserted in a CEST sequence with a pTx readout. The different fat suppression schemes and their effects on CEST contrasts were compared in 12 volunteers at 7T. Results: With a 25%-shorter pulse duration, pTx FS largely improved the FA homogeneity (root-mean-square-error (RMSE) = 12.3° vs. 53.4° with circularly-polarized mode, at the fat frequency). However, the spectral selectivity was degraded mainly in the cerebellum and close to the sinuses (RMSE = 5.8° vs. 0.2° at the water frequency). Similarly, pTx WE showed a trade-off between FA homogeneity and spectral selectivity compared to pTx non-selective pulses (RMSE = 0.9° and 1.1° at the fat and water frequencies, vs. 4.6° and 0.5°). In the brain, CEST metrics were reduced by up to 31.9% at -3.3 ppm with pTx FS, suggesting a mitigated lipid-induced bias. Conclusion: This clinically compatible implementation of dynamic pTx pulses improved the fat suppression homogeneity at 7T taking into account the subject-specific B0 heterogeneities online. This study highlights the lipid-induced biases on the CEST z-spectrum. The results are promising for body applications where B0 heterogeneities and fat are more substantial.

APTw CEST MRI suffers from long preparation times and consequently long acquisition times (~5 mins). Recently, a consensus on the preparation module for clinical APTw CEST at 3T was found in the community and we present a fast whole-brain APTw CEST MRI sequence following this consensus preparation of a pulsed rf irradiation of 2 s duration at 90% rf duty cycle and a B1,rms of 2 μT. After optimization of the snapshot CEST approach for APTw imaging regarding flip angle, voxel size and frequency offset sampling, we extend it by undersampled GRE acquisition and compressed sensing reconstruction. This allows 2 mm isotropic whole-brain APTw imaging for clinical research at 3T below 1:30 min. With this sequence, a fast snapshot APTw imaging method is now available for larger clinical studies of brain tumors.

A method of processing magnetic resonance data of a sample under investigation includes the steps ofprovision of the MR data being collected with an MRI scanner apparatus, and machine learning based data analysis of the MR data by supplying the MR data to an artificial neural network being trained with predetermined training data, wherein at least one image parameter of the sample and additionally at least one uncertainty quantification measure representing a pre diction error ofthe at least one image parameter are provided by output elements of the neural network. Furthermore, a magnetic resonance imaging (MRI) scanner apparatus being adapted for employing the method ofprocessing MR data is described.

Poster-Abstract

We present a fast whole-brain APTw CEST MRI sequence extending the snapshot CEST approach by undersampled acquisition and compressed sensing reconstruction. This allows push-button whole-brain APTw imaging with online reconstruction for clinical research at 3T.

We propose a method to reduce blurring in RARE sequences along phase en-coding direction due to T2 decay during k-space acquisition. A convolutional neural net-work is employed to map simulated RARE im-ages to the transversal magnetization of the central echo.

Seit den Arbeiten von Brodmann und seinen Zeitgenossen ist bekannt, dass verschiedene Hirnregionen aufgrund ihrer ein-zigartigen zyto- und myeloarchitektonischen Merkmale unterscheidbar und klassifizierbar sind. Hier habe ich in Kooperation mit einem interdisziplinären Team die Machbarkeit der Übertragung dieses klassischen Klassifizie-rungsansatz auf die MRT untersucht und dabei mehrere technologische Fortschritte genutzt: Ultrahochfeld-MRT, q-Raum-Trajektorienbild gebung, chemische Austausch-Sättigungs-MRT, sowie aktuelle neuronale Netzwerkarchi-tekturen. Es zeigte sich, dass eine globale Hirnklassifikation von 97 Hirnregionen mit einer Klassifikationsgenauigkeit von 60% möglich ist.

Purpose: To enable whole-brain quantitative CEST MRI at ultra-high magnetic field strengths (B0 ≥ 7T) within short acquisition times. Methods: Multiple interleaved mode saturation (MIMOSA) was combined with fast online-customized (FOCUS) parallel transmission (pTx) excitation pulses and B+1 correction to achieve homogenous whole-brain coverage. Examinations of 13 volunteers were performed on a 7T MRI system with 3 different types of pulse sequences: (1) saturation in circular polarized (CP) mode and CP mode readout, (2) MIMOSA and CP readout, and (3) MIMOSA and FOCUS readout. For comparison, the inverse magnetic transfer ratio metric for relayed nuclear Overhauser effect and amide proton transfer were calculated. To investigate the number of required acquisitions for a good B+1 correction, 4 volunteers were measured with 6 different B1 amplitudes. Finally, time point repeatability was investigated for 6 volunteers. Results: MIMOSA FOCUS sequence using B+1 correction, with both single and multiple points, reduced inhomogeneity of the CEST contrasts around the occipital lobe and cerebellum. Results indicate that the most stable inter-subject coefficient of variation was achieved using the MIMOSA FOCUS sequence. Time point repeatability of MIMOSA FOCUS with single-point B+1 correction showed a maximum coefficient of variation below 8% for 3 measurements in a single volunteer. Conclusion: A combination of MIMOSA FOCUS with a single-point B+1 correction can be used to achieve quantitative CEST measurements at ultra-high magnetic field strengths. Compared to previous B+1 correction methods, acquisition time can be reduced as additional scans required for B+1 correction can be omitted.

Chemical exchange saturation transfer (CEST) is an emerging mechanism to provide contrast in clinical magnetic resonance imaging (MRI). CEST agents are compounds that contain a pool of exchangeable or labile protons involved in exchange with the surrounding

Poster-Abstract

Poster-Abstract

Background Chemical exchange saturation transfer (CEST) is a novel MRI technique applied to brain tumor patients. Purpose To investigate the anatomic location dependence of CEST MRI obtained at 7T and histopathological/molecular parameters in WHO IV° glioma patients. Study Type Analytic prospective study. Population Twenty‐one patients with newly diagnosed WHO IV° gliomas were studied prior to surgery; 11 healthy volunteers were investigated. Field Strength/Sequence Conventional MRI (contrast‐enhanced, T2w and diffusion‐weighted imaging) at 3T and T2w and CEST MRI at 7T was performed for patients and both patients and volunteers. Assessment Mean CEST signal intensities (nuclear‐Overhauser‐enhancement [NOE], amide‐proton‐transfer [APT], downfield NOE‐suppressed APT [dns‐APT]), ADC values, and histopathological/molecular parameters were evaluated with regard to hemisphere location and contact with the subventricular zone. CEST signal intensities of cerebral tissue of healthy volunteers were evaluated with regard to hemisphere discrimination. Statistical Tests Spearman correlation, Mann–Whitney U‐test, Wilcoxon signed‐rank‐test, Fisher's exact test, and area under the receiver operating curve. Results Maximum APT and dns‐APT signal intensities were significantly different in right vs. left hemisphere gliomas (P = 0.037 and P = 0.007), but not in right vs. left hemisphere cerebral tissue of healthy subjects (P = 0.062‐0.859). Mean ADC values were significantly decreased in right vs. left hemisphere gliomas (P = 0.044). Mean NOE signal intensity did not differ significantly between gliomas of either hemisphere (P = 0.820), but in case of subventricular zone contact (P = 0.047). A significant correlation was observed between APT and dns‐APT and ADC signal intensities (rs = –0.627, P = 0.004 and rs = –0.534, P = 0.019), but not between NOE and ADC (rs = –0.341, P = 0.154). Histopathological/molecular parameters were not significantly different concerning the tumor location (P = 0.104–1.000, P = 0.286–0.696). Data Conclusion APT, dns‐APT, and ADC were inversely correlated and depended on the gliomas' hemisphere location. NOE showed significant dependence on subventricular zone contact. Location dependency of APT‐ and NOE‐mediated CEST effects should be considered in clinical investigations of CEST MRI.