Keywords: Elastography, Elastography, transducer, hardware, mre, elastography

Motivation: Design of a compact MRE transducer prototype that fits between patient and coil for direct stimulation of tissue.

Goal(s): The main goal of this study is to design and construct a new MRE transducer that can independently vary frequency and amplitude, is free of any magnetic parts and is suitable for cardiac MRE.

Approach: Using computer aided design (CAD) and different manufacturing processes, a functional transducer prototype was built that transforms pressurized air into gravitational force. 

Results: A prototype that can induce tissue vibrations is presented. Its effectivity was verified by acceleration and phantom measurements.

Impact: The transducer induces waves whose amplitude and frequency can be selected independently. Its shape minimizes the distance between coil and patient for reducing MR signal losses with a comparatively large surface area for efficient wave transmission, optimized for cardiac MRE.

Keywords: Elastography, Elastography, MRE, Liver, Stiffness, Repeatability, Reproducibility

Motivation: We want contribute to establish MR Elastography as a reliable imaging technique for liver characterization. 

Goal(s): To validate the repeatability and reproducibility of a novel, gravitational hepatic MRE system using a generalized multi-shot GRE-MRE sequence.

Approach: 57 health volunteers underwent 2D and 3D hepatic MRE scans on a 3T Siemens scanner. The repeatability was evaluated through repeated volunteer scans without repositioning, while reproducibility was performed by re-positioning the volunteer after each acquisition.

Results: The repeatability and reproducibility coefficients of 2D-MRE were 0.11, 0.20 and for 3D-MRE, 0.21, 0.24, respectively. Repeatability and reproducibility for the 2D-MRE to 3D-MRE cases were 0.44 and 0.45, respectively.

Impact: We evaluated a new MRE system provides sufficient mechanical vibration which results in high repeatability and reproducibility. This, in combination with the fast GRE-MRE sequence providing sufficient SNR and PNR, serves as a valuable solution.

Keywords: Elastography, Elastography

Motivation: Most current volumetric 3D MRE sequences are restricted to 2D slice acquisitions, but we propose a novel sequence for rapid 3D slab-selective MRE.

Goal(s): To demonstrate the feasilbility of a 3D slab-selective MRE sequence with an interleaved motion encoding scheme.

Approach: The proposed 3D MRE sequence allows the measurement of different wave offsets and motion encodings for a 3D slab in a single measurement with a constant repetition time, minimising total acquisition time.

Results: We show initial results of the proposed technique in a phantom and for a single breathhold 3D liver MRE in a healthy subject.

Impact: The proposed method can be applied for effiicient 3D high-resolution MRE. Applications include liver fibrosis and inflammation staging, but the sequence may also be used for brain MRE.

Keywords: Elastography, Elastography, Transient MRE, Wavelet, Brain trauma, broadband motion

Motivation: To test wavelet magnetic resonance elastography (MRE), a promising new technique, on its efficiency in detecting broadband tissue motion.

Goal(s): Evaluate the efficiency and reproducibility of broadband motion detection using wavelet MRE.

Approach: Transient motion in phantoms was reconstructed using both the inverse wavelet transform and standard deconvolution using MRE with various MEG lengths. The estimated displacements were compared. The reproducibility of brain transient motion measurements was assessed in vivo.

Results: Wavelet MRE demonstrated high efficiency and reproducibility for broadband motion detection. These findings suggest that wavelet MRE is a promising technique in brain trauma study.  

Impact: Wavelet magnetic resonance elastography is developed to detect broadband motion more accurately and efficiently and could be particularly useful in detecting transient motion during brain impact. This study aims to validate its efficacy and assess its repeatability.

Keywords: Diagnosis/Prediction, Brain, Dementia

Motivation: Normal pressure hydrocephalus (NPH) is a treatable cause of dementia. The treatment with ventriculoperitoneal shunt surgery can lead to sustained improvement in about 80% of cases. However, due to the invasive nature of surgery, improving the predictability of outcomes is imperative.

Goal(s): To assess magnetic resonance elastography (MRE) as a non-invasive tool to predict surgical outcomes in NPH.

Approach: Pre-surgical stiffness and damping ratio pattern scores were used as features to train classification models that predict clinical improvement following shunt placement. 

Results: MRE is a promising noninvasive tool for prediction of surgical outcomes in normal pressure hydrocephalus.

Impact: MRE demonstrates promise as a prognostic tool for prediction of surgical outcomes in NPH. If successfully translated to clinic, this would provide patients with non-invasive alternative.  

Keywords: Elastography, Elastography, TURBINE fMRI, Functional MR Elastography

Motivation: To accurately characterize temporal dynamics of stiffness changes in the human brain in response to neural activity.

Goal(s): To understand the relationship between neurovascular (BOLD) and neuromechanical (stiffness) response to long (24s) and short (4s) stimulus durations.

Approach: We used a 3D TURBINE concurrent fMRI-fMRE sequence, which enabled full-brain coverage and faster acquisition of MRE time-series at shorter block duration (4s) in an attempt to decouple hemodynamic effects from the stiffness response.

Results: At a long (24s) block duration, the BOLD effect impacts brain stiffness while at a short (4s) duration no significant BOLD or stiffness response was observed.

Impact: Our preliminary findings suggest that brain stiffness is impacted on the same timescale as BOLD. Our future work aims to achieve higher temporal and signal SNR to decouple neurovascular (BOLD) response from neuromechanical (fMRE) response.

Keywords: Elastography, Elastography, Cardiac, free-breathing, 3D

Motivation: Cardiac magnetic resonance elastography (cMRE) has potential for clinically vital quantitative imaging of myocardial stiffness, but for it to become clinically viable in patients with heart failure or shortness of breath, free-breathing techniques need to be developed. 

Goal(s): To demonstrate the feasibility of 3D free-breathing cMRE. 

Approach: A 3D MRE sequence (TURBINE-MRE) was utilized for data acquisition. Physiologic signals were recorded and used to partition data into distinct cardiac and respiratory states. With a specified signal model, we iteratively reconstructed image volumes for all states. 

Results: Stiffness estimates throughout the cardiac cycle were successfully obtained in two volunteers, demonstrating successful free-breathing 3D cMRE. 

Impact: Free-breathing cMRE will enable quantitative imaging of myocardial stiffness in a significant number of patients who are not able to perform long breath-holds. A 3D TURBINE-MRE acquisition enables temporal resolution of the heart's elastic properties throughout the cardiac cycle.

Keywords: Elastography, Elastography, Arterial Spin Labeling

Motivation: We are motivated to understand the impact of blood flow on the mechanical properties of brain tissue for applications in neurodegenerative pathophysiology.

Goal(s): Our goal was to establish a novel postprocessing framework for correlation of structural and functional properties characterized by MR elastography (MRE) and pulsed arterial spin labeling (PASL).

Approach: We obtained MRE and PASL in 8 healthy controls, segmented the brain, and conducted regional correlation analyses of elastograms and perfusion maps.

Results: After successful data processing and validation, we found significant inverse correlations in the cortical gray matter, some cortex regions, as well as a similar nonsignificant trend in other regions.

Impact: These study results, which show a perfusion–stiffness relationship in some brain regions, point to an underlying biological mechanism relating vasculature and viscoelastic properties; however, this research direction needs further investigation, more subjects, and improved ASL techniques to strengthen regional analysis.

Keywords: Elastography, Brain

Motivation: Changes in the relationship between MRE and DTI metrics in small white matter structures could indicate alterations in brain microstructure due to white matter damage.

Goal(s): This study aims to determine correlations between metrics measured by MRE and DTI at 7T in the healthy human brain.

Approach: MRE and DTI acquisitions were performed on 14 young, healthy volunteers at 7T, and Shear Stiffness, Damping Raio, FA and RD were calculated for each person.

Results: Significant correlations were found in small, highly anisotropic, brain regions between Shear Stiffness or Damping Raio and FA or RD.

Impact: The high resolutions achieved at 7T for both MRE and DTI allow us to investigate microstructural relationships in small, highly-anisotropic, brain regions. Changes in these metrics or relationships between these metrics could indicate alterations in microstructure integrity, suggesting potential damage.

Keywords: Elastography, Elastography

Motivation: MR elastography can estimate anisotropic mechanical properties of fibrous white matter, traditionally using multi-excitation approaches. Multi-frequency elastography from a single driver is more common and could expand measurements of anisotropy.

Goal(s): Our goal was to compare mechanical anisotropy from multi-frequency and multi-excitation reconstructions.

Approach: Transversely isotropic parameters were reconstructed using simulated and in vivo multi-frequency wave data, then compared between approaches and against ground truth maps. Adolescent and adult measurements were compared in white matter regions.

Results: Multi-frequency elastography performed comparably with the multi-excitation approach in simulations. Higher shear anisotropy was observed in adults compared to adolescents, with no differences in tensile anisotropy.

Impact: This study demonstrates that multi-frequency magnetic resonance elastography can reliably estimate anisotropic mechanical properties from single driver data, enabling broader application. Quantifying developmental changes in anisotropy of white matter provides new insights into brain mechanics during maturation.

Keywords: Elastography, Elastography, muscle stiffness, oral posture, phase gradient technique, Zygomaticus major

Motivation: The MR elastography (MRE) phase-gradient (PG) technique allows measurement of tissue stiffness for small structures.

Goal(s): To use the PG technique to measure oral postural related changes in stiffness of the zygomaticus major (ZM) muscle in a small cohort of participants.

Approach: The phase image of the first harmonic of Fourier-transformed, directionally filtered MRE wave images was analysed. The gradient of the change in phase along a 1D-profile drawn in the direction of the long axis of ZM corresponds to the wavenumber and provides a measure of ZM stiffness.  

Results: ZM stiffness increased significantly in mouth-open posture compared to mouth-closed posture.

Impact: The feasibility of using the PG technique to measure oral posture related changes in the stiffness of ZM has been demonstrated. The method can potentially be applied to support the development of surgical treatments to rectify impaired oral posture.

Keywords: Elastography, Elastography

Motivation: Although the feasibility of intestinal MR elastography has recently been demonstrated, the influence of bowel distension through oral contrast agents on gut viscoelastic properties remains elusive.

Goal(s): To investigate the influence of oral contrast agent-based bowel distension on the viscoelastic properties of the gut in healthy volunteers.

Approach: Healthy volunteers were scanned using MR enterography and MR elastography before and after the ingestion of 1000 ml of 2 % mannitol solution as oral contrast agent.

Results: Our results suggest that the bowel distension in MR enterography has no systematic impact on viscoelastic tissue properties of the terminal ileum.

Impact: This study suggests that bowel distension in MR enterography has no systematic impact on the assessment of viscoelastic tissue properties of the terminal ileum. Consequently, future studies investigating inflammatory bowel disease using intestinal MR elastography do not need to account for potential biases related to pre-stretched bowel walls after oral ingestion of contrast agents.

Keywords: Elastography, Contrast Mechanisms

Motivation:  It is not widely available to real MR elastography (r-MRE) for clinical because of external elastography equipment. 

Goal(s): To assess the staging value of virtual MR elastography (v-MRE) preoperatively in rectal adenocarcinoma (RA).

Approach: Relationship between shift ADC (sADC) from IVIM and real shear-wave speed (C_r-MRE), inversion of the equation for generating virtual shear-wave speed (C_v-MRE), and assessment of pathological stages in RA patients.

Results:  In diagnosing T, N and P stage, the virtual MR elastography has potential to replace real MR elastography.

Impact: This study overcomes the shortcomings of real MR elastography and facilitates MR elastography to be used in clinical practice.

Keywords: Elastography, Pediatric, Liver Fibrosis

Motivation: Hepatic stiffness (HS), detected by MR elastography (MRE), is a biomarker for hepatic fibrosis. Liver MRE requires breath-holding (BH), which is challenging in children or people with liver disease. Spin-echo echo-planar-imaging (SE-EPI) MRE can quantify HS rapidly(~10 s), even with iron overload.

Goal(s): To evaluate free-breathing (FB) SE-EPI MRE without respiratory triggering or motion compensation in terms of agreement, repeatability, and measurable liver area [%] with respect to BH SE-EPI MRE.

Approach: BH and FB SE-EPI MRE were acquired in 23 children and 2 adults with liver biopsy.

Results: FB SE-EPI MRE provided fast, accurate, and repeatable HS with high measurable liver area.

Impact: The free-breathing (FB) MR elastography (MRE) of the liver based on spin-echo echo-planar-imaging (SE-EPI) produced accurate and repeatable hepatic stiffness with respect to standard breath-held SE-EPI MRE. FB SE-EPI MRE can be useful for populations who cannot hold their breath. 

Keywords: Elastography, Elastography, diagnosis/prediction, machine learning

Motivation: Pathology of steatotic liver disease is characterized by fat burden, inflammation, and ballooning. Mechanical properties of tissue acquire by 2D-MRE has improved the detection of this disease. However, 3D-MRE, an improvement over 2D-MRE is not widely adopted by clinicians.

Goal(s): We aimed to compare the predictive capabilities of these two in risk factors associated with this disease using machine learning to help motivate clinicians to use 3D-MRE.

Approach: Use machine learning to determine the predictive capabilities of 2D-MRE and 3D-MRE.

Results: Results showed 3D-MRE best predicts steatohepatitis, inflammation, and ballooning.

Impact: The demonstrated predictive value of 3D-MRE in identifying those with certain risk factors allows clinicians to better plan treatment for patients with steatotic liver disease.

Keywords: Elastography, Contrast Mechanisms, MRE, OC Pulse,Stiffness estimation

Motivation: Preclinical Magnetic Resonance Elastography (MRE) in small animal models offers valuable insights but often requires invasive methods. This study aims to develop non-invasive MRE for small animal liver examinations.

Goal(s): The specific goal is to compare conventional MEG-based MRE with OC-RARE MRE in terms of signal quality and motion encoding.

Approach: A non-invasive MRE setup was created for in vivo mouse liver studies. Both MEG and OC-RARE MRE were tested on four healthy mice.

Results: OC-RARE MRE showed superior Signal-to-Noise Ratios and improved wave visualization. Notable standard deviations highlight challenges. Nevertheless, OC-RARE MRE holds promise for small animal MRE research advancement.

Impact: hese results underscore a novel wave motion encoding strategy, offering substantial benefits for short T2 tissue studies, potentially reducing high technical error rates and fostering MRE's broader clinical application.