Matthias Günther

Fraunhofer Institute for Digital Medicine MEVIS | MEVIS · Fraunhofer-Institute for Medical Image Computing

This article focuses on clinical applications of arterial spin labeling (ASL) and is part of a wider effort from the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group to update and expand on the recommendations provided in the 2015 ASL consensus paper. Although the 2015 consensus paper provided general guideline...

Complex engineered systems are often equipped with suites of sensors and ancillary devices that monitor their performance and maintenance needs. MRI scanners are no different in this regard. Some of the ancillary devices available to support MRI equipment, the ones of particular interest here, have the distinction of actually participating in the i...

The German National Cohort (NAKO) is a multidisciplinary, population-based prospective cohort study that aims to investigate the causes of widespread diseases, identify risk factors and improve early detection and prevention of disease. Specifically, NAKO is designed to identify novel and better characterize established risk and protection factors...

Introduction Magnetic resonance imaging (MRI) of the brain could be a key diagnostic and research tool for understanding the neuropsychiatric complications of COVID-19. For maximum impact, multi-modal MRI protocols will be needed to measure the effects of SARS-CoV-2 infection on the brain by diverse potentially pathogenic mechanisms, and with high...

We demonstrate a constraint-based approach of MRI sequence development in the vendor-independent MRI pulse sequence development framework gammaSTAR and demonstrate this concept in arterial spin labeling by optimizing the timings of the background suppression pulses to minimize the signal contribution of chosen T1 values in the human brain. This con...

Assessment of liver perfusion can yield valuable information about diseases like carcinoma and cirrhosis. Arterial spin labeling enables contrast-free measurements of liver perfusion with the drawback of increased motion sensitivity. Since timed breathing protocols prolong scan times, a novel prospective motion correction technique is presented, ad...

Purpose: Measurements of liver perfusion yield valuable information about certain diseases like carcinomas and cirrhosis. To assess perfusion, noninvasive arterial spin labeling (ASL) MRI has the potential to become an important alternative to contrast agent-based methods. Unfortunately, ASL perfusion-weighted images are highly susceptible to brea...

Background: Reproducible image quality is of high relevance for large cohort studies and can be challenging for magnetic resonance imaging (MRI). Automated image quality assessment may contribute to conducting radiologic studies effectively. Purpose: The aims of this study were to assess protocol repetition frequency in population-based whole-bo...

Background Clinical diagnosis of frontotemporal dementia (FTD) remains a challenge due to the overlap of symptoms among FTD subtypes and with other psychiatric disorders. Perfusion imaging by arterial spin labeling (ASL) is a promising non-invasive alternative to established PET techniques; however, its sensitivity to imaging parameters can hinder...

Metamaterials, in particular 2D metasurfaces, offer great potential to advance the measurement efficiency in Magnetic Resonance Imaging (MRI) and to overcome some limitations due to physiological restriction that hamper technically feasible developments. In particular, the signal-to-noise ratio (SNR) in MRI can be improved significantly in a multi...

Multiple echo-time arterial spin labelling (multi-TE ASL) offers estimation of blood–tissue exchange dynamics by probing the T2 relaxation of the labelled spins. In this study, we provide a recipe for robust assessment of exchange time (Texch) as a proxy measure of blood–brain barrier (BBB) integrity based on a test-retest analysis. This includes a...

Object In this work, we present a technique called simultaneous multi-contrast imaging (SMC) to acquire multiple contrasts within a single measurement. Simultaneous multi-slice imaging (SMS) shortens scan time by allowing the repetition time (TR) to be reduced for a given number of slices. SMC imaging preserves TR, while combining different scan ty...

Purpose Arterial spin labeling allows noninvasive measurement of cerebral blood flow by magnetically labeling inflowing blood, using it as endogenous tracer. Unfortunately, sensitivity to subject motion is high due to the subtractive nature of arterial spin labeling, which is especially problematic if Cartesian segmented 3D gradient and spin echo (...

Background Advances in the understanding of the pathophysiology of frontotemporal dementia (FTD) and related disorders, along with the development of novel candidate disease modifying treatments, have stimulated the need for tools to assess the efficacy of new therapies. While perfusion imaging by arterial spin labeling (ASL) is an attractive appro...

Over almost five decades of development and improvement, Magnetic Resonance Imaging (MRI) has become a rich and powerful, non-invasive technique in medical imaging, yet not reaching its physical limits. Technical and physiological restrictions constrain physically feasible developments. A common solution to improve imaging speed and resolution is t...

The mismatch in the spatial resolution of Arterial Spin Labeling (ASL) MRI perfusion images and the anatomy of functionally distinct tissues in the brain leads to a partial volume effect (PVE), which in turn confounds the estimation of perfusion to a specific tissue of interest such as grey or white matter. This confound occurs because the image vo...

Over almost five decades of development and improvement, Magnetic Resonance Imaging (MRI) has become a rich and powerful, non-invasive technique in medical imaging, yet not reaching its physical limits. Technical and physiological restrictions constrain physically feasible developments. A common solution to improve imaging speed and resolution is t...

Assessement of CBF using Arterial Spin Labeling (ASL) can yield valuable functional information regarding different neuropathological diseases like tumors and stroke without exogenous contrast agents. However, being a subtractive technique, ASL shows high sensitivity to motion artifacts. ASL in combination with a 3D GRASE PROPELLER (3DGP) readout a...

Commercial MRI software that is shipped with an MRI scanner is typically not suited for research and development in state-of-the-art MRI imaging schemes. In particular, the advanced MR imaging requires both high computing power and dedicated frameworks for (iterative) algorithms. Reconstruction frameworks tend to be rather optimized for MR reconstr...

Liver perfusion can give valuable functional information about diseases like carcinoma and cirrhosis. Arterial Spin Labeling allows non-invasive assessment of liver perfusion without exogenous contrast agents being especially helpful in patients with renal failure. ASL in abdominal organs like liver faces increased challenges due to low perfusion r...

Simultaneous multi-contrast imaging (SMC) can be used to combine acquisition of diffusion-weighted (DW) and T2*-weighted (T2*W) images into a single scan. Compared to conventional single-contrast imaging, SMC reduces the total scan time and improves image registration. However, saturation effects can reduce SNR and alter contrast. In this study, th...

Magnetic resonance imaging (MRI) is the primary clinical tool to examine inflammatory brain lesions in Multiple Sclerosis (MS). Disease progression and inflammatory activities are examined by longitudinal image analysis to support diagnosis and treatment decision. Automated lesion segmentation methods based on deep convolutional neural networks (CN...

The emergence of data driven approaches such as Deep Learning has led to novel application of various aspects of science and engineering. It has recently entered the field of ultrasound image beamforming. In this work we investigate neural networks tailored to create images of the quality of multiple compounded plane wave excitations from the data...

Classical ultrasound reconstruction applies model driven approaches to obtain ultrasound images from ultrasound raw data. With the emergence of Deep Learning however data driven approaches become feasible and can be explored. These can be used to take shortcuts in the reconstruction, directly learning the relationship between raw data and image dat...

In this work, numerical simulation results regarding an automatically self-detuning signal enhancement plate (DSEP) for use in magnetic resonance imaging at 3T field are presented. The DSEP is composed of a linear alignment of wire resonators milled on a suitable PCB and inductively coupled to a varactor-loaded detuning loop. Eigenmode simulations...

MR sequence development is either based on complex, platform-specific solutions or restricted by fixed sequence structures together with a strict hierarchical implementation of loops. This abstract introduces event-based traversing of gammaSTAR sequences together with a buffered real-time execution at the scanner. The concept provides easy implemen...

The presented automated inner-scan timing adjustment for subject-specific pCASL measurements can reduce uncertainties in perfusion quantification. The high variability of arterial transit times often leads to undesired arterial transit delay (ATD) artifacts. The method evaluated here allows the optimal FL-bolus duration to be individually adjusted...

This study introduces a subject-specific automated approach for optimization of background suppression (BS) in 3D pseudo-continuous arterial spin labeling perfusion imaging. Optimised timing of BS related FOCI pulses is calculated from the T1 spectrum, obtained from a M0 scan of the organ of interest. Results show strong suppression of brain tissue...

This abstract compares quantified perfusion values of the standard model and a new dispersion model based on an AIF using the ASLIF-sequence. For different ATTs, the voxel´s signal was simulated using the dispersion model. The simulations show that the standard model overestimates the signal. This may result from lack of dispersion effects especial...

We present a dedicated RF-measurement setup consisting of custom-build Tx/Rx coils, an automated positioning system and a vector network analyzer that is suitable for an efficient characterization of MR-metamaterial devices which is crucial during the design stage. We measure complex scattering parameters over a large volume in air and obtain dispe...

PurposeWe investigate the feasibility of reconstructing ultrasound images directly from raw channel data using a deep learning network. Starting from the raw data, we present the network the full measurement information, allowing for a more generic reconstruction to form, as compared to common reconstructions constrained by physical models using fi...

Arterial spin labeling (ASL) has undergone significant development since its inception, with a focus on improving standardization and reproducibility of its acquisition and quantification. In a community-wide effort towards robust and reproducible clinical ASL image processing, we developed the software package ExploreASL, allowing standardized ana...

Background: The German National Cohort (NAKO) is an interdisciplinary health study aimed at elucidating causes for common chronic diseases and detecting their preclinical stages. This article provides an overview of design, methods, participation in the examinations, and their quality assurance based on the midterm baseline dataset (MBD) of the re...

Arterial spin labeling (ASL) has undergone significant development since its inception, with a focus on improving standardization and reproducibility of its acquisition and quantification. In a community-wide effort towards robust and reproducible clinical ASL image processing, we developed the software package ExploreASL, allowing standardized ana...

Purpose: To introduce a new sequence description format for vendor-independent MR sequences that include all calculation logic portably. To introduce a new MRI sequence development approach which utilizes flexibly reusable modules. Methods: The proposed sequence description contains a sequence module hierarchy for loop and group logic, which is...

Cerebrovascular changes, including reduced cerebral blood flow (CBF), occur early in the development of Alzheimer disease and may accelerate disease progression. This randomized, double-blind, placebo-controlled study investigated how 6 months of treatment with the calcium antagonist nilvadipine would affect CBF in patients with mild-to-moderate Al...

The sensitivity to subject motion is one of the major challenges in functional MRI (fMRI) studies in which a precise alignment of images from different time points is required to allow reliable quantification of brain activation throughout the scan. Especially the long measurement times and laborious fMRI tasks add to the amount of subject motion f...

A deep neural network for reconstruction of SMS data without the need of additional reference data to calibrate for the spatial encoding information of the multi-coil receiver is presented. Noise-propagation through the reconstruction process is investigated in form of g-factors. Simulations with pseudo-multiple replicas showed robustness and stabi...

We present a prototype exemplifying conceptual web-based workflow with services and applications which allow MR sequence developers to collaboratively create and work on MR sequences. By automating various error-prone tasks that usually overwhelm new and existing users and focusing on an interplay of web-services and applications, we introduce a no...

Introduction There is evidence suggesting a detrimental effect of asymptomatic carotid artery stenosis on cognitive function even in the absence of ischemic cerebral lesions. Hypoperfusion has been suggested as pathophysiological mechanism causing cognitive impairment. We aimed to assess cognitive performance and cerebral perfusion changes in patie...

We present a method to efficiently separate signal in magnetic resonance imaging (MRI) into a base signal S0, representing the mainly T1-weighted component without T2*-relaxation, and its T2*-weighted counterpart by the rapid acquisition of multiple contrasts for advanced pharmacokinetic modelling. This is achieved by incorporating simultaneous mul...

Simulation of MR signal for different parameter settings to estimate the resulting image contrast. ACS with FA = 5° (blue) and ACS with FA = 90° were used to calculate SG/SSG kernels and to reconstruct image data (FA = 5°) of a phantom containing differently CA-doped sub-volumes. All other imaging parameters were kept constant, i.e. TR = 30 ms. (TI...

Subject #2. Dynamics of the measured signal (TE1, TE2, TE3) (top left) and separated signal components (S0, T2*) (bottom left) during the CA bolus phase in a single voxel (AIF ROI). In contrast to the AIF the extravasation process into muscle tissue is selected from a larger ROI (tissue ROI) removing underestimation of the dynamic signal (TE = 0 ms...

Subject #2. Evaluation of different SMS reconstruction approaches. Four representative slices from one MB slice group are shown as maps for the normalized subtraction error compared to a single-band acquisition (top) and for the g-factor resulting from the SMS reconstruction (bottom). Histograms below each map summarize the respective metric across...

Subject #3. Dynamics of the measured signal (TE1, TE2, TE3) (top left) and separated signal components (S0, T2*) (bottom left) during the CA bolus phase in a single voxel (AIF ROI). In contrast to the AIF the extravasation process into muscle tissue is selected from a larger ROI (tissue ROI) removing underestimation of the dynamic signal (TE = 0 ms...

Subject #3. Evaluation of different SMS reconstruction approaches. Four representative slices from one MB slice group are shown as maps for the normalized subtraction error compared to a single-band acquisition (top) and for the g-factor resulting from the SMS reconstruction (bottom). Histograms below each map summarize the respective metric across...

Subject #4. Evaluation of different SMS reconstruction approaches. Four representative slices from one MB slice group are shown as maps for the normalized subtraction error compared to a single-band acquisition (top) and for the g-factor resulting from the SMS reconstruction (bottom). Histograms below each map summarize the respective metric across...

Slice profiles for 24 slices of 5 mm thickness (1 mm gap) after MB excitations with MB = 4 (solid) compared to the corresponding slice profiles after SB excitations (dashed) (a). Data was taken in homogeneous cylinder-phantom (T1 = 106 ms) where full longitudinal relaxation was guaranteed (TR = 1800 ms), such that the signal levels for both excitat...

Acquisition of 24 slices in a compound phantom (structure-phantom and bottle-phantom) as shown in (a). Images of SB excitation are given as reference. The slice thickness was set to 5 mm (1 mm gap). The colored difference maps in (b) and (c) show the SB images which were compared to SG/SSG reconstructions after MB excitation (MB = 4, CAIPIRINHA shi...

Subject #4. Dynamics of the measured signal (TE1, TE2, TE3) (top left) and separated signal components (S0, T2*) (bottom left) during the CA bolus phase in a single voxel (AIF ROI). In contrast to the AIF the extravasation process into muscle tissue is selected from a larger ROI (tissue ROI) removing underestimation of the dynamic signal (TE = 0 ms...

Imperfections and their effects in the MB RF-pulse. (DOCX)

Comparison of slice profiles at the identical spatial locations resulting from two separate single-band excitations (dashed) versus a multiband pulse (MB = 2; solid). The dependency of slice profiles of the FA for a given TR/T1 is demonstrated. Slice profiles were acquired in a cylindrical phantom (T1 = 106 ms) for a ratio of TR/T1 = 0.3 which is s...

The robustness of the reconstruction with respect to S0 (top rows) and T2* (bottom rows) were quantified by a linear model (b0, b1). Slice-GRAPPA (left) and split slice-GRAPPA (right) were compared as well as different SNR-levels (1, 5 and 10 avg.) and combinations of echo times to derive the ACS from (ACS111, ACS123). The signal differences are de...

The unwrapping of simultaneous multi-slice images without extra reference data is presented. A trained deep neural network disentangles overlapping image content and creates the final magnitude images. The results are compared to established techniques (split slice-GRAPPA) where correct reference data are missing.

This study introduces an image-based technique for prospective motion correction in multiband fMRI utilizing multislice-to-volume image registration. Motion detection is based on a single multiband excitation and readout, which allows a high temporal resolution and does not depend on the repetition time or the total number of slices. Results show h...

Background Under current guidelines, intravenous thrombolysis is used to treat acute stroke only if it can be ascertained that the time since the onset of symptoms was less than 4.5 hours. We sought to determine whether patients with stroke with an unknown time of onset and features suggesting recent cerebral infarction on magnetic resonance imagin...

Background: Changes in cerebral perfusion during migraine with aura (MA) have been assessed mainly using dynamic susceptibility contrast (DSC) magnetic resonance perfusion imaging. A contrast agent-free method to assess these changes would be desirable. We assessed changes in cerebral perfusion during MA using arterial spin labeling (ASL) perfusio...

Background Focused ultrasound (FUS) is entering clinical routine as a treatment option. Currently, no clinically available FUS treatment system features automated respiratory motion compensation. The required quality standards make developing such a system challenging. Methods A novel FUS treatment system with motion compensation is described, dev...

The unwrapping of simultaneous multi-slice images without extra reference data is presented. A trained deep neural network disentangles overlapping image content and creates the final magnitude image. The results are compared to established techniques where correct reference data are missing.

Purpose: The clinical utility of FDG-PET in diagnosing frontotemporal dementia (FTD) has been well demonstrated over the past decades. On the contrary, the diagnostic value of arterial spin labelling (ASL) MRI – a relatively new technique – in clinical diagnosis of FTD has yet to be confirmed. Using simultaneous PET/MRI, we evaluated the diagnosti...

A new multi-echo imaging sequence for dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has been developed. To achieve a temporal resolution of 1.3 s a simultaneous multislice (SMS) acquisition has been added to a multi-contrast, segmented echo-planar imaging (EPI) sequence. The purpose of this sequence is to separate the MR signal int...

A fully automated workflow for image-based quality assessment (QA) was set up in a large, multi-center cohort whole-body MR imaging study, part of the National Cohort Study Germany NAKO. Study design, data management, workflow, and objectives have been described previously. Standardized quality assessment including technical aspects like program an...