Elmar Laistler

Dynamic ASL and T2*‐weighted MRI in exercising calf muscle at 7 T: A feasibility study

The aim of this study was to develop a measurement protocol for noninvasive simultaneous perfusion quantification and T2*‐weighted MRI acquisition in the exercising calf muscle at 7 Tesla.

Exercising calf muscle T₂∗ changes correlate with pH, PCr recovery and maximum oxidative phosphorylation.

Skeletal muscle metabolism is impaired in disorders like diabetes mellitus or peripheral vascular disease. The skeletal muscle echo planar imaging (EPI) signal (SEPI) and its relation to energy metabolism are still debated.

A form-fitted three channel 31P, two channel 1H transceiver coil array for calf muscle studies at 7 T

To enhance sensitivity and coverage for calf muscle studies, a novel, form‐fitted, three‐channel phosphorus‐31 (31P), two‐channel proton (1H) transceiver coil array for 7 T MR imaging and spectroscopy is presented.

Magnetic resonance microimaging of human skin vasculature in vivo at 3 Tesla.

MRI can be used to investigate human skin microvasculature in vivo, provided adequate spatial resolution. Therefore, the sensitivity of the experiment has to be optimized to achieve sufficient signal‐to‐noise ratio (SNR) within reasonable measurement time to minimize motion artifacts, improve patient comfort and save costs. In this work, the high sensitivity of a 15 mm surface coil and the signal strength of a 3 Tesla scanner, together with a three‐dimensional gradient echo sequence and post‐processing have been combined to obtain high SNR. Images of human skin with isotropic spatial resolution of 100 μm were acquired within 10 min and the cutaneous vasculature could be visualized in 3D [Correction made here after initial online publication.], based on three averaged scans. The presented method can be used for diagnosis and, due to its non‐invasiveness, treatment monitoring of vascular pathologies in the skin, such as inflammation, vascular malformation, or neoangiogenesis in superficial tumors. Magn Reson Med, 2011.

Power Balance and Loss Mechanism Analysis in RF Transmit Coil Arrays

To establish a framework for transmit array power balance calculations based on power correlation matrices to accurately quantify the loss contributions from different mechanisms such as coupling, lumped components, and radiation.

Novel inductive decoupling technique for flexible transceiver arrays of monolithic transmission line resonators.

This article presents a novel inductive decoupling technique for form‐fitting coil arrays of monolithic transmission line resonators, which target biomedical applications requiring high signal‐to‐noise ratio over a large field of view to image anatomical structures varying in size and shape from patient to patient.

Skeletal muscle ATP synthesis and cellular H(+) handling measured by localized (31)P-MRS during exercise and recovery.

31P magnetic resonance spectroscopy (MRS) is widely used for non-invasive investigation of muscle metabolism dynamics. This study aims to extend knowledge on parameters derived from these measurements in detail and comprehensiveness: proton (H+) efflux, buffer capacity and the contributions of glycolytic (L) and oxidative (Q) rates to ATP synthesis were calculated from the evolutions of phosphocreatine (PCr) and pH. Data are reported for two muscles in the human calf, for each subject and over a wide range of exercise intensities. 22 subjects performed plantar flexions in a 7T MR-scanner, leading to PCr changes ranging from barely noticeable to almost complete depletion, depending on exercise protocol and muscle studied by localized MRS. Cytosolic buffer capacity was quantified for the first time non-invasively and individually, as was proton efflux evolution in early recovery. Acidification started once PCr depletion reached 60–75%. Initial and end-exercise L correlated with end-exercise levels of PCr and approximately linear with pH. Q calculated directly from PCr and pH derivatives was plausible, requiring fewer assumptions than the commonly used ADP-model. In conclusion, the evolution of parameters describing cellular energy metabolism was measured over a wide range of exercise intensities, revealing a relatively complete picture of muscle metabolism.

Dynamic PCr and pH imaging of human calf muscles during exercise and recovery using (31) P gradient-Echo MRI at 7 Tesla.

Simultaneous acquisition of spatially resolved 31P‐MRI data for evaluation of muscle specific energy metabolism, i.e., PCr and pH kinetics.

A novel coil array for combined TMS/fMRI experiments at 3 T

To overcome current limitations in combined transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) studies by employing a dedicated coil array design for 3 Tesla.

High-sensitivity TMS/fMRI of the Human Motor Cortex Using a Dedicated Multichannel MR Coil

Purpose To validate a novel setup for concurrent TMS/fMRI in the human motor cortex based on a dedicated, ultra‐thin, multichannel receive MR coil positioned between scalp and TMS system providing greatly enhanced sensitivity compared to the standard birdcage coil setting. Methods A combined TMS/fMRI design was applied over the primary motor cortex based on 1 Hz stimulation with stimulation levels of 80%, 90%, 100%, and 110% of the individual active motor threshold, respectively. Due to the use of a multichannel receive coil we were able to use multiband‐accelerated (MB=2) EPI sequences for the acquisition of functional images. Data were analysed with SPM12 and BOLD‐weighted signal intensity time courses were extracted in each subject from two local maxima (individual functional finger tapping localiser, fixed MNI coordinate of the hand knob) next to the hand area of the primary motor cortex (M1) and from the global maximum. Results We report excellent image quality without noticeable signal dropouts or image distortions. Parameter estimates in the three peak voxels showed monotonically ascending activation levels over increasing stimulation intensities. Across all subjects, mean BOLD signal changes for 80%, 90%, 100%, 110% of the individual active motor threshold were 0.43%, 0.63%, 1.01%, 2.01% next to the individual functional finger tapping maximum, 0.73%, 0.91%, 1.34%, 2.21% next to the MNI‐defined hand knob and 0.88%, 1.09%, 1.65%, 2.77% for the global maximum, respectively. Conclusion Our results show that the new setup for concurrent TMS/fMRI experiments using a dedicated MR coil array allows for high‐sensitivity fMRI particularly at the site of stimulation. Contrary to the standard birdcage approach, the results also demonstrate that the new coil can be successfully used for multiband‐accelerated EPI acquisition. The gain in flexibility due to the new coil can be easily combined with neuronavigation within the MR scanner to allow for accurate targeting in TMS/fMRI experiments.