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Background:
Magnetic resonance elastography (MRE) is used to non-invasively estimate biomechanical tissue properties via the imaging of propagating mechanical shear waves. Several factors including mechanical transducer design, MRI sequence design and viscoelastic reconstruction influence data quality and hence the reliability of the derived biome...
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... approaches are based on piezoelectric elements. These setups can have either rigid 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t (rods) or more flexible (air or water) transmission of the shear waves into the object of interest (Hirsch et al., 2016a). The only available commercial transducer setup is based on pneumatic air and uses a passive acoustic driver (Yin et al., 2007). ...
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... 6 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... that the arrows point outwards to highlight the force generated by the rotating mass, not by the rotating axis. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 10 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... these issues are of little practical consequence for industrial applications of stepper motors like CNC machines, which do not need to operate at such precision for such sustained Page 11 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t periods of time. Our experiments however require far more stability over a prolonged period of time. ...
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... finite element method was used within the CHeart software ( Lee et al., 2016) to model steady-state Page 12 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t vibrational waves at 40 Hz in a 2D liver mesh using 2684 nodes and 5009 triangular elements. Linear viscoelasticity and isotropy were assumed and the storage and loss components of the shear modulus were set to 1.5 and 0.2 kPa, respectively, and assumed constant across the entire domain as well as over all frequencies (i.e. ...
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... acquisition was performed using a clinical 3T MR Scanner (Achieva, Philips, The Netherlands) with motion encoding gradients (MEGs) in three orthogonal directions and a fourth reference scan without MEGs to compensate for motion encoding from the imaging Phase images were processed offline. The processing pipeline performs phase unwrapping, reference scan subtraction and phase offset corrections according to slice number originating from the fact that one mechanical oscillation period encompasses several slice acquisitions (Garteiser et 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t al., 2013). We only accepted voxels with magnitude > 15% of the average magnitude of the area of interest and a total wave displacement amplitude > 10 μm. ...
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... factor was set Page 14 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t to 1.4. The readout bandwidth was 243 kHz. ...
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... readout bandwidth was 243 kHz. The acquisition times per encoding direction were 18 | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 16 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 16 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 18 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t and 5G show the reconstructed elasticity and viscosity with a 40 Hz signal in absence of noise. Fig. 5E and 5H show the same but with added (pseudorandom, uniformly distributed) noise (±3% of the transducer amplitude). ...
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... 18 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t and 5G show the reconstructed elasticity and viscosity with a 40 Hz signal in absence of noise. Fig. 5E and 5H show the same but with added (pseudorandom, uniformly distributed) noise (±3% of the transducer amplitude). ...
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... ROI in Fig. 5F highlights the region that is significantly impacted by the 2 nd harmonic which is shown to be a large portion of the (in absence of the 2 nd harmonic) accurately reconstructed region. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... ROI in Fig. 5F highlights the region that is significantly impacted by the 2 nd harmonic which is shown to be a large portion of the (in absence of the 2 nd harmonic) accurately reconstructed region. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 6B-D show the (B) accompanying x-component of the curl of the displacement, (C) elasticity [kPa] and (D) nonlinearity [%] maps. ROI measurements in the inclusions and background as found here and as reported by the manufacturer are shown in Table 1. Page 22 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. ...
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... 22 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t Table 1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 22 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t Table 1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 24 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t Nonlinearity is very low in the parenchymal organs of interest in these slices, i.e. liver and spleen and both organs are well visibly in the viscoelastic maps. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t Nonlinearity is very low in the parenchymal organs of interest in these slices, i.e. liver and spleen and both organs are well visibly in the viscoelastic maps. 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... the gravitational transducer delivers constant amplitude over a wide range of driving Page 27 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t frequencies typical to the clinical application of MRE (i.e. 40 -70 Hz). ...
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... key concepts are in place as safeguards: (1) should the rotational eccentric mass jam for any reason, the suddenly strongly increased torque will stall the stepper motor; (2) the eccentric mass consists of a single piece of CNC-lathed PTFE fixated to a PEEK rod by glue; should the glue bond fail, the rotating axis would spin inside and not turn the mass; moreover, there is no room for the rotating mass itself to fully detach from the rotating axis; (3) the transducer casing is made of a very strong plastic closed tightly using strong and resilient PEEK screws, ensuring that in the very unlikely event that any part Page 28 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t of the mass should come loose, little damage would be sustained by the casing. With respect to the eccentric mass, we plan to further improve this part by moving to a single piece of CNC-lathed PTFE that includes both rod and mass parts. ...
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... SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t the gravitational transducer provides substantially improved data for more reliable viscoelastic reconstruction. ...
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... 30 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
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... 30 of 32 AUTHOR SUBMITTED MANUSCRIPT -PMB-107642. R3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 A c c e p t e d M a n u s c r i p t ...
Citations
... 45 The total scan time will be approximately 45 min to estimate visceral and subcutaneous adipose tissue depot volume, hepatic and pancreatic fat content, as well as hepatic fibrosis and inflammation. [45][46][47] Individuals will be screened for contra-indications for MRI prior to inclusion in this study. In addition, vibration-controlled transient elastography (FibroScan) will be performed to investigate liver stiffness and steatosis. ...
Background
The spectrum of metabolic dysfunction-associated steatotic liver disease (MASLD) is highly prevalent, affecting 30% of the world’s population, with a significant risk of hepatic and cardiometabolic complications. Different stages of MASLD are accompanied by distinct gut microbial profiles, and several microbial components have been implicated in MASLD pathophysiology. Indeed, earlier studies demonstrated that hepatic necroinflammation was reduced in individuals with MASLD after allogenic faecal microbiota transplantation (FMT) from healthy donors on a vegan diet. Here, we further investigate the therapeutic potential of gut microbiome modulation using a syntrophic combination of next-generation beneficial bacteria with FMT in individuals with advanced MASLD.
Methods and analysis
This trial is a randomised, double-blind, placebo-controlled study investigating the therapeutic potential of lyophilised faecal microbiota capsules (LFMCs) in individuals with metabolic dysfunction-associated steatohepatitis. In this study, 48 participants will be randomised 1:1 to receive either healthy vegan donor LFMCs or placebo for 24 weeks. In addition, all participants will be supplemented with a set of next-generation beneficial bacteria, including Anaerobutyricum soehngenii , pasteurised Akkermansia muciniphila and Bifidobacterium animalis subsp. lactis , as well as fructo-oligosaccharides. A liver biopsy will be performed at baseline and at the end of the trial. In addition, participants will be assessed through MRI, FibroScan, blood tests, faecal samples and continuous glucose monitoring. The first participant was enrolled on 25 April 2023.
Ethics and dissemination
Ethical approval was obtained from the Medical Ethics Committee of the University Medical Centre of Amsterdam. The results of this study will be disseminated through peer-reviewed journals.
Trial Registration number
The trial is registered on clinicaltrials.gov ( NCT05821010 ).
... The generation of mono-frequent shear waves with sufficient amplitude and phase stability within the MRI environment is a nontrivial task. To date, several MRE transducer concepts have been proposed [13] with very different driving approaches: (I) currentdriven electromagnetic coils that oscillate due to the Lorentz force in the main B0-field [4,14,15]; (II) a pneumatic approach connecting an active driver with a membrane via a flexible tube [16]; (III) a pulse density-modulated approach using compressed air [17]; and (IV) the gravitational transducer concept [18]. For MRE to yield high-quality maps of biomechanical properties, the transducer needs to transmit a pure frequency spectrum. ...
... The generation of mono-frequent shear waves with sufficient amplitude and phase stability within the MRI environment is a nontrivial task. To date, several MRE transducer concepts have been proposed [13] with very different driving approaches: (I) current-driven electromagnetic coils that oscillate due to the Lorentz force in the main B0-field [4,14,15]; (II) a pneumatic approach connecting an active driver with a membrane via a flexible tube [16]; (III) a pulse density-modulated approach using compressed air [17]; and (IV) the gravitational transducer concept [18]. For MRE to yield high-quality maps of biomechanical properties, the transducer needs to transmit a pure frequency spectrum. ...
... The presence of the gearbox allows a reduction in the friction on the external driveshaft. The concept of a rotating eccentric mass has the advantage that the generated force grows quadratically with the increasing frequency, which leads to a vibrational amplitude independent of frequency [18]. This is in stark contrast to acoustically Sensors 2024, 24, 8038 3 of 14 driven (pneumatic) approaches which always experience a reduction in amplitude with increasing frequency. ...
MR elastography is a non-invasive imaging technique that provides quantitative maps of tissue biomechanical properties, i.e., elasticity and viscosity. Currently, hepatic MR elastography is deployed in the clinic to assess liver fibrosis in MAFLD patients. In addition, research has demonstrated MR elastography’s ability to non-invasively assess chronic liver disease and to characterize breast cancer lesions and brain tumors. MR elastography requires efficient mechanical wave generation and penetration, motion-sensitized MRI sequences, and MR elastography inversion algorithms to retrieve the biomechanical properties of the tissue. MR elastography promises to enable non-invasive and versatile assessment of tissue, leading to better diagnosis and staging of several clinical conditions.
... Most studies have chosen to employ an external actuator, such as a bite bar [14], a pneumatic cushion [15], or a head rocker [16] to produce vibrations to the head directly. The advantage of this direct vibration is that, by producing vibration as closely to the skull as possible, the generated shear wave can have enough energy to be transmitted through the skull into the brain [17], [18]. To date, the direct excitation methods have proven to be effective in several pilot neuroscience and clinical studies [19]. ...
Magnetic resonance elastography (MRE) of brain relies on inducing and measuring shear waves in the brain. However, studies have shown vibration could induce changes in cerebral blood flow (CBF), which has a modulation effect and can affect the biomechanical properties measured. Objective: This work demonstrates the initial prototype of the indirect excitation method, which can generate shear waves in the brain with minimal changes in CBF.
Methods
: A simple system was designed to produce stable vibrations underneath the neck. Instead of directly stimulating the skull, shear waves were indirectly transmitted to the brain through the spine and brainstem.
Results
: Phantom results showed that the proposed actuator did not interfere with the routine imaging sequence and successfully generated multifrequency shear waves. When compared with the conventional direct head stimulation method, brain MRE results from the proposed actuator showed no significant differences in terms of intraclass correlation coefficients (ICC) and coefficients of variation (CV). Moreover, the octahedral shear strain (OSS) generated by the indirect excitation in the frontal and parietal lobes decreased by 25.96% and 16.73% respectively. Evaluation of CBF in healthy volunteers revealed no significant changes for the indirect excitation method, whereas significant decreases in CBF were observed in four subregions when employing direct excitation.
Conclusion
: The proposed actuator offers a more accurate and comfortable approach to MRE measurements while causing minimal CBF alterations.
Significance
: This work presents the first demonstration of an indirect excitation brain MRE system that minimizes CBF changes, thus holding potential for future applications of brain MRE.
... 1,12 Mechanical and electromagnetic actuators have also been proposed to improve the vibration precision. 13,14 For MRE sequences, Spin Echobased Echo Planar Imaging (SE-EPI) and Gradient Recalled Echo (GRE)-based techniques are widely used. In addition, SE-EPI is fast and robust to iron overload in liver MRE. 15 In terms of inversion algorithms, Direct Inversion (DI), Local Frequency Estimation (LFE), Multifrequency Dual Elasto-Visco (MDEV) inversion, and k-MDEV are the most widely used. ...
... For vibration actuators, the mechanical system was also not included. 13 Finally, the integration of each MRE support system with its corresponding MRI system was treated as a singular entity for comparative analysis in this study. However, to avoid the influence of variable magnetic field strengths, differences in MRI scanner manufacturers, and distinct data acquisition protocols, MRE support systems should be interchanged between MRI scanners. ...
Background
Different MR elastography (MRE) systems may produce different stiffness measurements, making direct comparison difficult in multi‐center investigations.
Purpose
To assess the repeatability and reproducibility of liver stiffness measured by three typical MRE systems.
Study Type
Prospective.
Population/Phantoms
Thirty volunteers without liver disease history (20 males, aged 21–28)/5 gel phantoms.
Field Strength/Sequence
3.0 T United Imaging Healthcare (UIH), 1.5 T Siemens Healthcare, 3.0 T General Electric Healthcare (GE)/Echo planar imaging‐based MRE sequence.
Assessment
Wave images of volunteers and phantoms were acquired by three MRE systems. Tissue stiffness was evaluated by two observers, while phantom stiffness was assessed automatically by code. The reproducibility across three MRE systems was quantified based on the mean stiffness of each volunteer and phantom.
Statistical Tests
Intraclass correlation coefficients (ICC), coefficients of variation (CV), and Bland–Altman analyses were used to assess the interobserver reproducibility, the interscan repeatability, and the intersystem reproducibility. Paired t ‐tests were performed to assess the interobserver and interscan variation. Friedman tests with Dunn's multiple comparison correction were performed to assess the intersystem variation. P values less than 0.05 indicated significant difference.
Results
The reproducibility of stiffness measured by the two observers demonstrated consistency with ICC > 0.92, CV < 4.32%, Mean bias < 2.23%, and P > 0.06. The repeatability of measurements obtained using the electromagnetic system for the liver revealed ICC > 0.96, CV < 3.86%, Mean bias < 0.19%, P > 0.90. When considering the range of reproducibility across the three systems for liver evaluations, results ranged with ICCs from 0.70 to 0.87, CVs from 6.46% to 10.99%, and Mean biases between 1.89% and 6.30%. Phantom studies showed similar results. The values of measured stiffness differed across all three systems significantly.
Data Conclusion
Liver stiffness values measured from different MRE systems can be different, but the measurements across the three MRE systems produced consistent results with excellent reproducibility.
Evidence Level
1
Technical Efficacy
Stage 2
... Initially, imaging localizers were used to identify the position of the kidney with respect to the coils. A gravitational transducer [GT, King's College London, London, United Kingdom; liver transducer, see (Runge et al., 2018)] with a curved contact plate (15 × 11.5 cm) holding a gel pad towards the subjects was placed on the posterior-lateral abdominal wall next to the kidney. On top, a hook-and-loop fastener belt (width = 15 cm) was used to hold the GT in place. ...
... For example, the mean cortical thickness is reported to be 6 mm (Glodny et al., 2009). ii) To our knowledge, this is the first study to use a rotating eccentric mass to induce acoustic waves into the kidney (Runge et al., 2018;Manduca et al., 2021). So far, only pneumatic ( (Streitberger et al., 2014) were used. ...
... This finding might suggest the need to reduce the MEG strength on the left side, because high-amplitude shear waves can disturb the phase information and challenge unwrapping, and render the need for using a more complex disturbed-parameter system away from the pure elastic model (Piersol and Paez, 2009;Chen et al., 2023b). To our knowledge, no previous renal MRE study reported the ratio of curl over divergence (quantifying how well the assumption of a pure shear wave field is fulfilled) or non-linearity (indicating the presence of second upper harmonics) (Sinkus et al., 2005;Runge et al., 2018;Manduca et al., 2021). Van Schelt et al. (2023) used a GT to estimate pancreas stiffness and showed comparable results. ...
Introduction: Magnetic resonance elastography (MRE) is a non-invasive method to quantify biomechanical properties of human tissues. It has potential in diagnosis and monitoring of kidney disease, if established in clinical practice. The interplay of flow and volume changes in renal vessels, tubule, urinary collection system and interstitium is complex, but physiological ranges of in vivo viscoelastic properties during fasting and hydration have never been investigated in all gross anatomical segments simultaneously.
Method: Ten healthy volunteers underwent two imaging sessions, one following a 12-hour fasting period and the second after a drinking challenge of >10 mL per kg body weight (60–75 min before the second examination). High-resolution renal MRE was performed using a novel driver with rotating eccentric mass placed at the posterior-lateral wall to couple waves (50 Hz) to the kidney. The biomechanical parameters, shear wave speed (cs in m/s), storage modulus (Gd in kPa), loss modulus (Gl in kPa), phase angle ( Υ = 2 π atan G l G d ) and attenuation (α in 1/mm) were derived. Accurate separation of gross anatomical segments was applied in post-processing (whole kidney, cortex, medulla, sinus, vessel).
Results: High-quality shear waves coupled into all gross anatomical segments of the kidney (mean shear wave displacement: 163 ± 47 μm, mean contamination of second upper harmonics <23%, curl/divergence: 4.3 ± 0.8). Regardless of the hydration state, median Gd of the cortex and medulla (0.68 ± 0.11 kPa) was significantly higher than that of the sinus and vessels (0.48 ± 0.06 kPa), and consistently, significant differences were found in cs, Υ , and Gl (all p < 0.001). The viscoelastic parameters of cortex and medulla were not significantly different. After hydration sinus exhibited a small but significant reduction in median Gd by −0.02 ± 0.04 kPa (p = 0.01), and, consequently, the cortico-sinusoidal-difference in Gd increased by 0.04 ± 0.07 kPa (p = 0.05). Only upon hydration, the attenuation in vessels became lower (0.084 ± 0.013 1/mm) and differed significantly from the whole kidney (0.095 ± 0.007 1/mm, p = 0.01).
Conclusion: High-resolution renal MRE with an innovative driver and well-defined 3D segmentation can resolve all renal segments, especially when including the sinus in the analysis. Even after a prolonged hydration period the approach is sensitive to small hydration-related changes in the sinus and in the cortico-sinusoidal-difference.
... Particularly regarding driver systems, a variety of approaches have been used for brain MRE [11]. Recently, a novel MRE vibration transducer based on a rotational eccentric mass was introduced and successfully tested in a pre-clinical phantom study and in vivo human liver MRE, producing highly accurate vibrational waves without second-harmonic vibrations and thus high-fidelity data [19,20]. Nevertheless, the application of the MRE system to the brain warrants further research. ...
... Detailed imaging parameters of brain MRI are summarized in the Supplementary Methods. MRE was acquired using a gradient-recalled echo sequence with a Hadamard encoding scheme using a gravitational transducer based on a rotational eccentric mass as the driver system [19,20]. The motor and controller units of the driver system are located in the MRI control room, and a flexible rotating shaft connects the motor unit to a gravitational transducer. ...
... Currently, a driver system with a pneumatic actuator and head pillow is widely used in brain MRE because it is the only available commercial driver system [8]. However, potential errors in the reconstruction of biomechanical properties have been raised regarding the system, such as a decrease in the vibration amplitude or upper harmonicrelated inaccuracies [19]. In this context, a novel MRE driver system based on a rotational eccentric mass, termed a gravitational transducer, was recently introduced and proven to produce highly accurate vibrational waves without second-harmonic vibrations and to be accurately phase-locked with an MRE sequence [19]. ...
Objective:
To investigate the feasibility of assessing the viscoelastic properties of the brain using magnetic resonance elastography (MRE) and a novel MRE transducer to determine the relationship between the viscoelastic properties and glymphatic function in neurologically normal individuals.
Materials and methods:
This prospective study included 47 neurologically normal individuals aged 23-74 years (male-to-female ratio, 21:26). The MRE was acquired using a gravitational transducer based on a rotational eccentric mass as the driving system. The magnitude of the complex shear modulus |G*| and the phase angle ϕ were measured in the centrum semiovale area. To evaluate glymphatic function, the Diffusion Tensor Image Analysis Along the Perivascular Space (DTI-ALPS) method was utilized and the ALPS index was calculated. Univariable and multivariable (variables with P < 0.2 from the univariable analysis) linear regression analyses were performed for |G*| and ϕ and included sex, age, normalized white matter hyperintensity (WMH) volume, brain parenchymal volume, and ALPS index as covariates.
Results:
In the univariable analysis for |G*|, age (P = 0.005), brain parenchymal volume (P = 0.152), normalized WMH volume (P = 0.011), and ALPS index (P = 0.005) were identified as candidates with P < 0.2. In the multivariable analysis, only the ALPS index was independently associated with |G*|, showing a positive relationship (β = 0.300, P = 0.029). For ϕ, normalized WMH volume (P = 0.128) and ALPS index (P = 0.015) were identified as candidates for multivariable analysis, and only the ALPS index was independently associated with ϕ (β = 0.057, P = 0.039).
Conclusion:
Brain MRE using a gravitational transducer is feasible in neurologically normal individuals over a wide age range. The significant correlation between the viscoelastic properties of the brain and glymphatic function suggests that a more organized or preserved microenvironment of the brain parenchyma is associated with a more unimpeded glymphatic fluid flow.
... mm 3 resolution, 420×270×28 matrix, TR/TE=3000/80 ms) and T2-FLAIR sequences (turbo spin echo, 1×1×1 mm 3 resolution, 252×249×183 matrix, TR/TE=4800/320 ms, inversion time 1650 ms). For the MRE, a gravitational transducer was attached to the side of the subject's head to induce shear waves of 50 Hz in the brain 8 . Image acquisition was performed using a multi-shot gradient-echo MRE sequence, synchronized to the wave generator by a trigger A c c e p t e d M a n u s c r i p t 8 signal 9 . ...
Background:
Biomechanical tissue properties of glioblastoma tumors are heterogeneous, but the molecular mechanisms involved and the biological implications are poorly understood. Here, we combine magnetic resonance elastography (MRE) measurement of tissue stiffness with RNA sequencing of tissue biopsies to explore the molecular characteristics of the stiffness signal.
Methods
MRE was performed preoperatively in 13 patients with glioblastoma. Navigated biopsies were harvested during surgery and classified as ‘stiff’ or ‘soft’ according to MRE stiffness measurements (|G*|norm). Twenty-two biopsies from eight patients were analysed by RNA sequencing.
Results:
The mean whole-tumor stiffness was lower than normal-appearing white matter. The surgeon’s stiffness evaluation did not correlate with the MRE measurements, which suggests that these measures assess different physiological properties. Pathway analysis of the differentially expressed genes between ‘stiff’ and ‘soft’ biopsies showed that genes involved in extracellular matrix reorganization and cellular adhesion were overexpressed in ‘stiff’ biopsies. Supervised dimensionality reduction identified a gene expression signal separating ‘stiff ‘and ‘soft’ biopsies. Using the NIH Genomic Data Portal, 265 glioblastoma patients were divided into those with (n=63) and without (n=202) this gene expression signal. The median survival time of patients with tumors expressing the gene signal associated with ‘stiff’ biopsies was 100 days shorter than that of patients not expressing it (360 versus 460 days, hazard ratio: 1.45, P<0.05).
Conclusion:
MRE imaging of glioblastoma can provide non-invasive information on intratumoral heterogeneity. Regions of increased stiffness were associated with extracellular matrix reorganization. An expression signal associated with ‘stiff’ biopsies correlated with shorter survival of glioblastoma patients.
... Our actuator setup is position-sensitive and therefore we ensured that the volunteer's head was placed in a similar position on the driver setup during all follow-up examinations. Nevertheless, any other actuation setup (Runge et al., 2019;Smith et al., 2020;Qiu et al., 2021;Triolo et al., 2022) that achieves good wave penetration of the brain with high test-retest reproducibility is suitable for tomoelastography and can even further improve the consistency of cerebral MRE. Moreover, the transverse slice blocks were automatically aligned by the scanner. ...
Purpose: Magnetic resonance elastography (MRE) generates quantitative maps of the mechanical properties of biological soft tissues. However, published values obtained by brain MRE vary largely and lack detail resolution, due to either true biological effects or technical challenges. We here introduce cerebral tomoelastography in two and three dimensions for improved data consistency and detail resolution while considering aging, brain parenchymal fraction (BPF), systolic blood pressure, and body mass index (BMI).
Methods: Multifrequency MRE with 2D- and 3D-tomoelastography postprocessing was applied to the brains of 31 volunteers (age range: 22—61 years) for analyzing the coefficient of variation (CV) and effects of biological factors. Eleven volunteers were rescanned after 1 day and 1 year to determine intraclass correlation coefficient (ICC) and identify possible long-term changes.
Results: White matter shear wave speed (SWS) was slightly higher in 2D-MRE (1.28 ± 0.02 m/s) than 3D-MRE (1.22 ± 0.05 m/s, p < 0.0001), with less variation after 1 day in 2D (0.33 ± 0.32%) than in 3D (0.96 ± 0.66%, p = 0.004), which was also reflected in a slightly lower CV and higher ICC in 2D (1.84%, 0.97 [0.88–0.99]) than in 3D (3.89%, 0.95 [0.76–0.99]). Remarkably, 3D-MRE was sensitive to a decrease in white matter SWS within only 1 year, whereas no change in white matter volume was observed during this follow-up period. Across volunteers, stiffness correlated with age and BPF, but not with blood pressure and BMI.
Conclusion: Cerebral tomoelastography provides high-resolution viscoelasticity maps with excellent consistency. Brain MRE in 2D shows less variation across volunteers in shorter scan times than 3D-MRE, while 3D-MRE appears to be more sensitive to subtle biological effects such as aging.
... For this type of actuator, the entire unit has to be MR compatible and small enough to attach to the tissue of interest. The units are usually driven by air pressureor piezoelectric crystals (Brauck et al., 2007;Gordon-Wylie et al., 2018;Meinhold et al., 2019;Namani et al., 2009;Numano et al., 2013;E Ozkaya et al., 2021;Rossman et al., 2003;Runge et al., 2019;Uffmann et al., 2002;Z. Yin et al., 2017). ...
... Suga et al., 2003;Uffmann et al., 2001). Third, the actuator can apply the vibration directly to the tissue of interest, where a fully MR compatible, small actuation unit, usually driven by air pressureor piezoelectric crystals, are attached to the tissue of interest (Brauck et al., 2007;Gordon-Wylie et al., 2018;Namani et al., 2009;Numano et al., 2013;Rossman et al., 2003;Runge et al., 2019;Uffmann et al., 2002;Z. Yin et al., 2017). ...
Magnetic resonance elastography (MRE) is a technique for determining the mechanical response of soft materials using applied harmonic deformation of the material and a motion‐sensitive magnetic resonance imaging sequence. This technique can elucidate significant information about the health and development of human tissue such as liver and brain, and has been used on phantom models (e.g., agar, silicone) to determine their suitability for use as a mechanical surrogate for human tissues in experimental models. The applied harmonic deformation used in MRE is generated by an actuator, transmitted in bursts of a specified duration, and synchronized with the magnetic resonance signal excitation. These actuators are most often a pneumatic design (common for human tissues or phantoms) or a piezoelectric design (common for small animal tissues or phantoms). Here, we describe how to design and assemble both a pneumatic and a piezoelectric MRE actuator for research purposes. For each of these actuator types, we discuss displacement requirements, end‐effector options and challenges, electronics and electronic‐driving requirements and considerations, and full MRE implementation. We also discuss how to choose the actuator type, size, and power based on the intended material and use. © 2022 Wiley Periodicals LLC.
Basic Protocol 1 : Design, construction, and implementation of a convertible pneumatic MRE actuator for use with tissues and phantom models
Basic Protocol 2 : Design, construction, and implementation of a piezoelectric MRE actuator for localized excitation in phantom models
... Anatomical T1-weighted, T2-weighted and fluid attenuated inversion recovery (FLAIR) images, as well as DTI MRIs and MRE data, were acquired for five patients, using imaging parameters as in [59], also shown in Table S2. The MRE was performed using a gravitational transducer [60] attached on the side of the head, inducing shear waves of 50 Hz into the brain. The MRE acquisition lasted 5.5 min, with further details about acquisition and processing listed in reference [61]. ...
The purpose of this study is to develop a methodology that incorporates a more accurate assessment of tissue mechanical properties compared to current mathematical modeling by use of biomechanical data from magnetic resonance elastography. The elastography data were derived from five glioblastoma patients and a healthy subject and used in a model that simulates tumor growth, vascular changes due to mechanical stresses and delivery of therapeutic agents. The model investigates the effect of tumor-specific biomechanical properties on tumor anisotropic growth, vascular density heterogeneity and chemotherapy delivery. The results showed that including elastography data provides a more realistic distribution of the mechanical stresses in the tumor and induces anisotropic tumor growth. Solid stress distribution differs among patients, which, in turn, induces a distinct functional vascular density distribution—owing to the compression of tumor vessels—and intratumoral drug distribution for each patient. In conclusion, incorporating elastography data results in a more accurate calculation of intratumoral mechanical stresses and enables a better mathematical description of subsequent events, such as the heterogeneous development of the tumor vasculature and intrapatient variations in tumor perfusion and delivery of drugs.
