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18 Publications visible to you, out of a total of 18
Physiologic Reduction of Hepatic Venous Blood Flow by the Valsalva Maneuver Decreases Liver Stiffness.

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OBJECTIVES: Liver stiffness increases after intake of food or water, suggesting that hepatic venous blood flow affects the results of elastographic measurements. This study investigated the correlation … between in vivo liver stiffness and hepatic blood flow using the Valsalva maneuver for reducing intrahepatic venous blood flow. METHODS: Intrahepatic changes in venous blood flow were assessed by sonography based on the pulsed wave Doppler velocity, vessel diameter assessment, and blood flow volume measurements in the portal vein and right hepatic vein. Time-harmonic elastography at 7 harmonic driving frequencies (30-60 Hz) was used to measure liver stiffness in the right liver lobe of 15 healthy volunteers. RESULTS: The right hepatic vein diameter, flow volume, and peak pulsed wave velocity decreased during the Valsalva maneuver from mean +/- SD values of 8.64 +/- 1.85 to 6.55 +/- 1.84 mm (P = .002), 0.53 +/- 0.23 to 0.37 +/- 0.26 L/min (P = .037), and 22.14 +/- 4.87 to 17.38 +/- 5.41 cm/s (P = .01), respectively. This maneuver decreased liver stiffness in all volunteers by a mean of approximately 13% from 1.71 +/- 0.22 to 1.48 +/- 0.22 m/s (P = .00006). CONCLUSIONS: Our results demonstrate that liver stiffness is sensitive to altered venous blood flow, which is of clinical importance when using elastography for evaluation of portal hypertension. Furthermore, our results indicate that accurate measurement of liver stiffness requires standardized breathing conditions to rule out effects of changes in hepatic blood flow on elastographic findings.

Authors: S. Ipek-Ugay, H. Tzschatzsch, J. Braun, T. Fischer, I. Sack

Date Published: 20th Mar 2017

Publication Type: Not specified

A compact 0.5 T MR elastography device and its application for studying viscoelasticity changes in biological tissues during progressive formalin fixation.

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PURPOSE: To develop a method of compact tabletop magnetic resonance elastography (MRE) for rheological tests of tissue samples and to measure changes in viscoelastic powerlaw constants of liver and … brain tissue during progressive fixation. METHODS: A 10-mm bore, 0.5-T permanent-magnet-based MRI system was equipped with a gradient-amplifier-controlled piezo-actuator and motion-sensitive spin echo sequence for inducing and measuring harmonic shear vibrations in cylindrical samples. Shear modulus dispersion functions were acquired at 200-5700 Hz in animal tissues at different states of formalin fixation and fitted by the springpot powerlaw model to obtain shear modulus mu and powerlaw exponent alpha. RESULTS: In a frequency range of 300-1500 Hz, unfixed liver tissue was softer and less dispersive than brain tissue with mu = 1.68 +/- 0.17 kPa and alpha = 0.51 +/- 0.06 versus mu = 2.60 +/- 0.68 kPa and alpha = 0.68 +/- 0.03. Twenty-eight hours of formalin fixation yielded a 400-fold increase in liver mu, 25-fold increase in brain mu, and two-fold reduction in alpha of both tissues. CONCLUSION: Compact 0.5-T MRE facilitates automated measurement of shear modulus dispersion in biological tissue at low costs. Formalin fixation changes the viscoelastic properties of tissues from viscous-soft to elastic-stiff more markedly in liver than brain. Magn Reson Med 79:470-478, 2018. (c) 2017 International Society for Magnetic Resonance in Medicine.

Authors: J. Braun, H. Tzschatzsch, C. Korting, A. Ariza de Schellenberger, M. Jenderka, T. Driessle, M. Ledwig, I. Sack

Date Published: 20th Mar 2017

Publication Type: Not specified

Tomoelastography of the abdomen: Tissue mechanical properties of the liver, spleen, kidney, and pancreas from single MR elastography scans at different hydration states.

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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 78:976-983, 2017. (c) 2016 International Society for Magnetic Resonance in Medicine.

Authors: F. Dittmann, H. Tzschatzsch, S. Hirsch, E. Barnhill, J. Braun, I. Sack, J. Guo

Date Published: 3rd Oct 2016

Publication Type: Not specified

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