Pulseq: A rapid and hardwareâ independent pulse sequence prototyping framework

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/136354/1/mrm26235.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136354/2/mrm26235_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/136354/3/mrm26235-sup-0001-suppinfo.pd

Histological Correlates of Diffusion-Weighted Magnetic Resonance Microscopy in a Mouse Model of Mesial Temporal Lobe Epilepsy

Mesial temporal lobe epilepsy (MTLE) is the most common type of focal epilepsy. It is frequently associated with abnormal MRI findings, which are caused by underlying cellular, structural, and chemical changes at the micro-scale. In the current study, it is investigated to which extent these alterations correspond to imaging features detected by high resolution magnetic resonance imaging in the intrahippocampal kainate mouse model of MTLE. Fixed hippocampal and whole-brain sections of mouse brain tissue from nine animals under physiological and chronically epileptic conditions were examined using structural and diffusion-weighted MRI. Microstructural details were investigated based on a direct comparison with immunohistochemical analyses of the same specimen. Within the hippocampal formation, diffusion streamlines could be visualized corresponding to dendrites of CA1 pyramidal cells and granule cells, as well as mossy fibers and Schaffer collaterals. Statistically significant changes in diffusivities, fractional anisotropy, and diffusion orientations could be detected in tissue samples from chronically epileptic animals compared to healthy controls, corresponding to microstructural alterations (degeneration of pyramidal cells, dispersion of the granule cell layer, and sprouting of mossy fibers). The diffusion parameters were significantly correlated with histologically determined cell densities. These findings demonstrate that high-resolution diffusion-weighted MRI can resolve subtle microstructural changes in epileptic hippocampal tissue corresponding to histopathological features in MTLE

Corrigendum: Histological Correlates of Diffusion-Weighted Magnetic Resonance Microscopy in a Mouse Model of Mesial Temporal Lobe Epilepsy

In the published article, there were errors in affiliations 2 and 3. Instead of “Experimental Epilepsy Research, Department of Neurosurgery, Medical Center – University of Freiburg, Freiburg, Germany” and “Department Neurosurgery, Experimental Epilepsy Research, Medical Center, University of Freiburg, Freiburg, Germany,” they should be “Faculty of Medicine, University of Freiburg, Freiburg, Germany” and “Experimental Epilepsy Research, Department of Neurosurgery, Medical Center – University of Freiburg, Freiburg, Germany,” respectively. The authors apologize for these errors and state that this does not change the scientific conclusions of the article in any way. The original article has been updated

A comparison of Lenz lenses and LC resonators for NMR signal enhancement

High signal-to-noise ratio (SNR) of the NMR signal has always been a key target that drives massive research effort in many fields. Among several parameters, a high filling factor of the MR coil has proven to boost the SNR. In case of small-volume samples, a high filling factor and thus a high SNR can be achieved through miniaturizing the MR coil. However, under certain circumstances, this can be impractical. In this paper, we present an extensive theoretical and experimental investigation of the inductively coupled LC resonator and the magnetic Lenz lens as two candidate approaches that can enhance the SNR in such circumstances. The results demonstrate that the narrow-band LC resonator is superior in terms of SNR, while the non-tuned nature of the Lenz lens makes it preferable in broadband applications

Should patients with brain implants undergo MRI?

Patients suffering from neuronal degenerative diseases are increasingly being equipped with neural implants to treat symptoms or restore functions and increase their quality of life. Magnetic resonance imaging (MRI) would be the modality of choice for diagnosis and compulsory post-operative monitoring of such patients. However, interactions between the MR environment and implants pose severe health risks to the patient. Nevertheless, neural implant recipients regularly underwent MRI examinations, and adverse events were reported rarely. This should not imply that the procedures are safe. More than 300.000 cochlear implant recipients are excluded from MRI unless the indication outweighs excruciating pain. For 75.000 DBS recipients quite the opposite holds: MRI is considered essential part of the implantation procedure and some medical centres deliberately exceed safety regulations which they referred to as crucially impractical. MRI related permanent neurological dysfunctions in DBS recipients have occurred in the past when manufacturer recommendations were exceeded. Within the last decades extensive effort has been invested to identify, characterise, and quantify the occurring interactions. Today we are far from a satisfying solution to achieve a safe and beneficial MR procedure for all implant recipients. To contribute, we intend to raise awareness of a growing concern and want to summon the community to stop absurdities and instead improve the situation for the increasing number of patients. Therefore, we review implant safety in the MRI literature from an engineering point of view, with a focus on cochlear and DBS implants as success stories in clinical practice. We briefly explain fundamental phenomena which can lead to patient harm, and point out breakthroughs and errors made. We end with conclusions and strategies to avoid future implants from being contraindicated to MR examinations. We believe that implant recipients should enter MRI, but before doing so, we should make sure that the procedure is reasonable

Magnetic resonance imaging reveals functional anatomy and biomechanics of a living dragon tree

Magnetic resonance imaging (MRI) was used to gain in vivo insight into load-induced displacements of inner plant tissues making a non-invasive and non-destructive stress and strain analysis possible. The central aim of this study was the identification of a possible load-adapted orientation of the vascular bundles and their fibre caps as the mechanically relevant tissue in branch-stem-attachments of Dracaena marginata. The complex three-dimensional deformations that occur during mechanical loading can be analysed on the basis of quasi-three-dimensional data representations of the outer surface, the inner tissue arrangement (meristem and vascular system), and the course of single vascular bundles within the branch-stem-attachment region. In addition, deformations of vascular bundles could be quantified manually and by using digital image correlation software. This combination of qualitative and quantitative stress and strain analysis leads to an improved understanding of the functional morphology and biomechanics of D. marginata, a plant that is used as a model organism for optimizing branched technical fibre-reinforced lightweight trusses in order to increase their load bearing capacity

Fourier transform temporal diffusion spectroscopy

Temporal diffusion spectroscopy (TDS) currently uses the oscillating gradient spin echo (OGSE) experiment to measure the spectral density of translational velocity autocorrelation at single frequencies. Due to timing restrictions imposed by the transverse relaxation, the frequency selectivity and the sampling density of OGSE are limited, especially at low frequencies. We propose to overcome this problem by adopting the principles of Fourier transform spectroscopy. The new method of Fourier transform TDS (FTDS) uses two broadband gradient waveforms with different relative delays to make the spin echo attenuation sensitive to a broad range of diffusion frequencies with different harmonic modulations and calculates the spectrum by discrete Fourier transform. The method was validated by a measurement of diffusion spectra in highly restrictive tissues of a celery stalk and provided results consistent with OGSE, however, on a denser frequency grid.ISSN:1090-780

Use of simulated annealing for the design of multiple repetition time balanced steady-state free precession imaging

Balanced steady-state free precession is an ultrafast sequence with high signal-to-noise efficiency, but it also generates a strong fat signal which can mask important features. One method of fat suppression is to modify the balanced steady-state free precession spectrum using multiple repetition times to create a wide stopband over the fat frequency. However, with three or more pulse repetition times, the number of parameters creates a vast search space with many local minima of a cost function. We report on the initial results of using simulated annealing to find optimal sequences for two applications of multiple-pulse repetition time balanced steady-state free precession: positive contrast imaging and fat suppression

Fast multiecho balanced SSFP metabolite mapping of H-1 and hyperpolarized C-13 compounds

To investigate the feasibility of multiecho balanced steady-state free precession (bSSFP)-based fast chemical shift mapping hyperpolarized C-13 metabolites. The overall goal was to reduce total imaging time and to increase spatial resolution compared to common chemical shift imaging (CSI). A multiecho bSSFP sequence in combination with an iterative reconstruction algorithm was implemented. H-1 experiments were performed on phantoms and on a human volunteer in order to investigate the feasibility of the method on a system with metabolite maps that are known beforehand. C-13 experiments were performed in vivo on pigs, where CSI images were acquired also for comparison. Chemical shift images of three and four distinct H-1 resonance frequencies as well as chemical shift images of up to five hyperpolarized C-13 metabolites were successfully obtained. Fast metabolite mapping based on multiecho balanced SSFP in combination with an iterative reconstruction approach could successfully separate several H-1 resonances and hyperpolarized C-13 metabolites