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Florian Dittmann

Bio: Florian Dittmann is an academic researcher from Charité. The author has contributed to research in topics: Elastography & Magnetic resonance elastography. The author has an hindex of 8, co-authored 10 publications receiving 292 citations.

Papers
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Journal ArticleDOI
TL;DR: This work introduces an efficient way of processing wave images acquired by multifrequency magnetic resonance elastography (MMRE), which relies on wave number reconstruction at different harmonic frequencies followed by their amplitude-weighted averaging prior to inversion to reveal variations in tissue elasticity in a tomographic fashion.

109 citations

Journal ArticleDOI
TL;DR: To demonstrate the feasibility of in vivo wideband MR elastography (wMRE) using continuous, time‐harmonic shear vibrations in the frequency range of 10–50 Hz, high-performance liquid chromatography is used.
Abstract: Purpose To demonstrate the feasibility of in vivo wideband MR elastography (wMRE) using continuous, time-harmonic shear vibrations in the frequency range of 10–50 Hz. Theory and Methods The method was tested in a gel phantom with marked mechanical loss. The brains and livers of eight volunteers were scanned by wMRE using multislice, single-shot MRE with optimized fractional encoding and synchronization of sequence acquisition to vibration. Multifrequency three-dimensional inversion was used to reconstruct compound maps of magnitude |G*| and phase φ of the complex shear modulus. A new phase estimation, φ*, was developed to avoid systematic bias due to noise. Results In the phantom, G*-dispersion measured by wMRE agreed well with oscillatory shear rheometry. |G*| and φ* measured at vibrations of 10–25 HZ, 25–35 HZ, and 40–50 HZ were 0.62 ± 0.08, 1.56 ± 0.16, 2.18 ± 0.20 kPa and 0.09 ± 0.17, 0.39 ± 0.16, 0.20 ± 0.13 rad in brain and 0.89 ± 0.11, 1.67 ± 0.20, 2.27 ± 0.35 kPa and 0.15 ± 0.10, 0.24 ± 0.05, 0.26 ± 0.05 rad in liver. Elastograms including all frequencies showed the best resolution of anatomical detail with |G*| = 1.38 ± 0.12 kPa, φ* = 0.24 ± 0.10 rad (brain) and |G*| = 1.79 ± 0.23 kPa, φ* = 0.24 ± 0.05 rad (liver). Conclusion wMRE reveals highly dispersive G* properties of the brain and liver, and our results suggest that the influence of large-scale structures such as fluid-filled vessels and sulci on the MRE-measured parameters increases at low vibration frequencies. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

75 citations

Journal ArticleDOI
TL;DR: To develop a compact magnetic resonance elastography protocol for abdomen and to investigate the effect of water uptake on tissue stiffness in the liver, spleen, kidney, and pancreas.
Abstract: Purpose To develop a compact magnetic resonance elastography (MRE) protocol for abdomen and to investigate the effect of water uptake on tissue stiffness in the liver, spleen, kidney, and pancreas. Methods Nine asymptomatic volunteers were investigated by MRE before and after 1 liter water uptake. Shear-wave excitation at four frequencies was transferred to the abdomen from anterior and posterior directions using pressurized air drivers. Tomographic representations of shear-wave speed were produced by analysis of multifrequency wave numbers in axial and coronal images acquired within four breath-holds or under free breathing, respectively. Results Pre and post water, stiffness of the spleen (pre/post: 2.20 ± 0.10/2.06 ± 0.18 m/s) and kidney (pre/post: 1.93 ± 0.22/1.97 ± 0.23 m/s) was higher than in the liver (pre/post: 1.36 ± 0.10/1.38 ± 0.13 m/s) and pancreas (pre/post: 1.20 ± 0.12/1.20 ± 0.08 m/s), all P < 0.01. Accounting for four drive frequencies, water drinking only changed the splenic stiffness (–6%, P = 0.03), whereas in the frequency range from 50 to 60 Hz the effect became significant also in the pancreas (–6%, P = 0.04) and liver (+3%, P = 0.03). Elastograms of the kidney in coronal view clearly depicted higher stiffness in cortex than in medulla. Conclusion Tomoelastography reveals sensitivity of tissue mechanical properties to the hydration state of multiple abdominal organs within one scan and in unprecedented resolution of anatomical details. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

62 citations

Journal ArticleDOI
TL;DR: The distinct mechano-vascular properties of striatum tissue, as compared to the rest of DGM, may reflect elevated perfusion pressure, which could explain the well-known susceptibility of the putamen to hemorrhages.
Abstract: Viscoelastic properties of the brain reflect tissue architecture at multiple length scales. However, little is known about the relation between vital tissue functions, such as perfusion, and the ma...

47 citations

Journal ArticleDOI
TL;DR: To demonstrate the feasibility of in vivo multifrequency magnetic resonance elastography of the prostate using externally placed drivers, a novel MRE technique is developed that combines radiolysis, electrophysiology, and FISH.
Abstract: Purpose To demonstrate the feasibility of in vivo multifrequency magnetic resonance elastography (MRE) of the prostate using externally placed drivers. Methods Three pressurized-air drivers were used to excite shear waves within the prostate at vibration frequencies of 60, 70, and 80 Hz. Full 3D wave fields were acquired by multislice spin-echo echo-planar imaging in conjunction with tomoelastography wave speed recovery for generating full field-of-view stiffness maps. Twelve healthy volunteers were repeatedly scanned to analyze test–retest reproducibility. Five patients with suspected prostate cancer were investigated to demonstrate the clinical feasibility of the method. Results In healthy volunteers, the shear wave speed of the entire prostate was 2.24 ± 0.20 m/s with a repeatability coefficient of 0.14 m/s and 88% intraclass correlation coefficient. No significant difference between the peripheral zone (2.27 ± 0.20 m/s) and the central gland (2.22 ± 0.23 m/s) was observed. In patients, wave-speed maps displayed stiff regions consistent with the localization of suspicious masses detected by other imaging markers. Conclusions The proposed method provides reproducible quantitative maps of tissue stiffness throughout the pelvic region and can easily be integrated into clinical imaging protocols. Clinical stiffness maps display many details of potential interest for cancer diagnosis. Magn Reson Med, 2017. © 2017 International Society for Magnetic Resonance in Medicine.

30 citations


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Journal ArticleDOI
TL;DR: The authors review the technical basis, acquisition techniques, and results and limitations of US- and MR-based elastography techniques and discusses reliability, reproducibility, failure rate, and emerging advances.
Abstract: US and MR elastographic techniques have developed into accurate methods for quantitative, noninvasive diagnosis of liver fibrosis in a wide range of etiologies; however, interpretation of results should take into account potential confounding factors, pitfalls, and technical limitations.

191 citations

Journal ArticleDOI
TL;DR: The extent to which MRE has revealed significant alterations to the brain in patients with neurological disorders is assessed and discussed in terms of known pathophysiology, and the trends for future MRE research and applications in neuroscience are predicted.
Abstract: Neurological disorders are one of the most important public health concerns in developed countries. Established brain imaging techniques such as magnetic resonance imaging (MRI) and x-ray computerised tomography (CT) have been essential in the identification and diagnosis of a wide range of disorders, although usually are insufficient in sensitivity for detecting subtle pathological alterations to the brain prior to the onset of clinical symptoms-at a time when prognosis for treatment is more favourable. The mechanical properties of biological tissue provide information related to the strength and integrity of the cellular microstructure. In recent years, mechanical properties of the brain have been visualised and measured non-invasively with magnetic resonance elastography (MRE), a particularly sensitive medical imaging technique that may increase the potential for early diagnosis. This review begins with an introduction to the various methods used for the acquisition and analysis of MRE data. A systematic literature search is then conducted to identify studies that have specifically utilised MRE to investigate the human brain. Through the conversion of MRE-derived measurements to shear stiffness (kPa) and, where possible, the loss tangent (rad), a summary of results for global brain tissue and grey and white matter across studies is provided for healthy participants, as potential baseline values to be used in future clinical investigations. In addition, the extent to which MRE has revealed significant alterations to the brain in patients with neurological disorders is assessed and discussed in terms of known pathophysiology. The review concludes by predicting the trends for future MRE research and applications in neuroscience.

172 citations

Journal ArticleDOI
TL;DR: This work introduces an efficient way of processing wave images acquired by multifrequency magnetic resonance elastography (MMRE), which relies on wave number reconstruction at different harmonic frequencies followed by their amplitude-weighted averaging prior to inversion to reveal variations in tissue elasticity in a tomographic fashion.

109 citations

Journal ArticleDOI
TL;DR: Magnetic resonance elastography can reliably measure global and regional stiffness in the brain in vivo and is a promising tool for the preoperative assessment of intracranial tumors, as it can measure both tumor consistency and adherence to surrounding tissues.

103 citations

Journal ArticleDOI
TL;DR: This work presents a method for measuring the viscoelasticity in subcortical gray matter structures, including the amygdala, hippocampus, caudate, putamen, pallidum, and thalamus, based on incorporating high spatial resolution MRE imaging with a mechanical inversion scheme designed to improve local measures in pre‐defined regions (soft prior regularization [SPR].
Abstract: Viscoelastic mechanical properties of the brain assessed with magnetic resonance elastography (MRE) are sensitive measures of microstructural tissue health in neurodegenerative conditions. Recent efforts have targeted measurements localized to specific neuroanatomical regions differentially affected in disease. In this work, we present a method for measuring the viscoelasticity in subcortical gray matter (SGM) structures, including the amygdala, hippocampus, caudate, putamen, pallidum, and thalamus. The method is based on incorporating high spatial resolution MRE imaging (1.6 mm isotropic voxels) with a mechanical inversion scheme designed to improve local measures in pre-defined regions (soft prior regularization [SPR]). We find that in 21 healthy, young volunteers SGM structures differ from each other in viscoelasticity, quantified as the shear stiffness and damping ratio, but also differ from the global viscoelasticity of the cerebrum. Through repeated examinations on a single volunteer, we estimate the uncertainty to be between 3 and 7% for each SGM measure. Furthermore, we demonstrate that the use of specific methodological considerations-higher spatial resolution and SPR-both decrease uncertainty and increase sensitivity of the SGM measures. The proposed method allows for reliable MRE measures of SGM viscoelasticity for future studies of neurodegenerative conditions. Hum Brain Mapp 37:4221-4233, 2016. © 2016 Wiley Periodicals, Inc.

83 citations