Ingolf Sack

Current aortic magnetic‐resonance‐elastography (MRE) infers wall stiffness indirectly from waveguide effects. This study aimed to evaluate the feasibility of abdominal aortic MRE for direct assessment of wall stiffness and its dependence on segmental region, patient position, and hemodynamic parameters. This prospective study examined 11 healthy young male volunteers using MRE to evaluate two anatomical segments of the abdominal aorta: the supraceliac (SC) and infrarenal (IR) segments. The volunteers underwent examinations in both the supine and prone positions. An ECG trigger delay was implemented for MRE to minimize the blood signal in the lumen. Three‐dimensional wavefields were acquired at three mechanical frequencies (70, 80, and 90 Hz), and shear wave speed (SWS) maps were reconstructed as a stiffness surrogate. In addition, blood flow‐velocity MRI was performed assess hemodynamic parameters. Test–retest examinations were performed in a subgroup to evaluate repeatability of aortic MRE. Aortic wall MRE was successful in all participants with good repeatability (ICC = 0.76). Mean wall SWS was higher in SC than IR segments at supine (1.47 ± 0.07 vs. 1.39 ± 0.13 m/s, p = 0.035) and prone positions (1.40 ± 0.09 vs. 1.33 ± 0.10 m/s, p = 0.046) with higher values in supine SC segments ( p = 0.019). Flow measurements revealed higher peak velocity and peak flow in SC than IR segments (all p < 0.001) with significant effects of examination position on peak velocity and cross‐sectional area in SC (all p < 0.05). In prone position, peak velocity correlated negatively with aorta stiffness (SC: r = −0.75, p = 0.008; IR: r = −0.69, p = 0.019). This study demonstrated abdominal aortic MRE for directly depicting wall stiffness with minimal blood contribution. Segment‐specific aortic wall stiffness was sensitive to circulatory loading and vascular distensibility. In a clinical context, high‐resolution multifrequency MRE could serve as an imaging marker for vascular health and abdominal aortic risk stratification.

Conventional magnetic resonance imaging (MRI) often detects liver tumors after morphologic and vascular changes become apparent, whereas biomechanical alterations may precede visible tumor formation. Here, we evaluate multifrequency magnetic resonance elastography (mMRE)‐derived shear wave speed (SWS) and phase angle (ϕ) covering stiffness and viscosity as non‐invasive biomechanical imaging markers for liver cancer formation and progression in a translational rabbit model. VX2 liver tumor‐bearing New Zealand White rabbits underwent five longitudinal multiparametric MRI scans over 14 days, including mMRE at clinically relevant frequencies on a 3 Tesla scanner. SWS and ϕ maps were compared with apparent diffusion coefficient (ADC) maps, histopathology, and proteomics. Tumor SWS and ϕ increased 2–3 days after implantation and were significantly higher than liver at two weeks (SWS: p = .002; ϕ: p = .008). Tumor ADC decreased significantly only from days 11–13 onward (day 14: p = .02). Histopathology and proteomics demonstrated tumoral enrichment of collagen, proteoglycan, and glycosaminoglycan pathways compared to liver, suggesting matrix remodeling as a key contributor to increased stiffness and viscosity measured by mMRE. The early elevation of SWS and ϕ preceding ADC changes highlights mMRE as a promising tool for detecting tumor‐associated biomechanical remodeling and enabling earlier liver cancer diagnosis and monitoring beyond conventional MRI.

Extracellular volume fraction measured with photon-counting CT was used to accurately quantify liver fibrosis and enabled excellent stratification for fibrosis staging equivalent to MR elastography, using histopathologic findings as the reference.

Magnetic resonance elastography (MRE) is an established diagnostic tool for assessing liver and intestinal fibrosis. However, reliable biomechanical characterization of murine gastrointestinal (GI) tract remains challenging due to its small size, high compliance, and the lack of standardized protocols and reference data. Tabletop magnetic resonance elastography (ttMRE) provides a scalable, cost-effective ex-vivo approach to quantify viscoelastic properties of small samples using multifrequency shear wave measurements while preserving the tissue’s architecture. Here, we establish the first ttMRE protocol for the ex-vivo biomechanical assessment of the murine ileum and colon. The protocol enables measurements of shear wave speed and shear wave penetration frate in the frequency range between 0.8 to 4 kHz for viscoelastic dispersion analysis based on different rheological models. Among two-parameter models, the springpot model best fitted the experimental data yielding similar median shear modulus (µSP) values of 4.5 [3.8, 4.7] kPa and 4.8 [4.3, 5.4] kPa and power law-exponent 0.56 [0.52, 0.59] and 0.58 [0.57, 0.60] for colon and ileum, respectively. Our work establishes a ttMRE protocol and provides preliminary baseline values for murine intestinal biomechanical properties. The method may facilitate investigations of disease progression, extracellular matrix remodeling, and therapeutic response in mouse models of inflammatory bowel diseases.

Parotid tumors exhibit diverse biomechanical and microstructural characteristics that remain challenging to characterize noninvasively. This study aimed to investigate these properties using ex vivo tabletop magnetic resonance elastography (MRE) combined with multiparametric MRI, including relaxometry, diffusion‐weighted imaging, and fat quantification. Twelve patients (six males, six females; mean age 60.3 ± 11.2 years) undergoing parotid tumor resection were included. Resected specimens were assessed histopathologically according to the WHO Classification of Head and Neck Tumors (5th edition, 2022) and imaged within 36 h postresection using two‐dimensional Bessel‐MRE alongside T1 and T2 relaxometry, diffusion imaging, and fat fraction mapping. MRE‐derived parameters included shear wave speed (SWS), penetration rate (PR), elasticity ( μ ), and viscosity ( η ). Compared with adjacent normal tissue, pathological tissue demonstrated significantly higher SWS ( p = 0.014), elasticity ( p = 0.027), viscosity ( p = 0.037), and T1 relaxation time ( p < 0.001), along with reduced fat fraction ( p < 0.001). Penetration rate showed a near‐significant increase ( p = 0.065), whereas T2 exhibited no overall difference. Subtype analysis revealed that pleomorphic adenomas had significantly higher apparent diffusion coefficient (ADC) ( p = 0.008), T1 ( p = 0.008), and T2 ( p = 0.008) values than Warthin tumors, with greater deviation from normal tissue. Correlation analysis showed that in normal tissue, fat fraction strongly influenced variability in SWS, T1, and ADC, with ADC demonstrating a strong negative correlation with fat fraction ( r = −0.95, p < 0.001), limiting its interpretability without fat correction. In contrast, pathological tissue demonstrated a tightly coupled cluster of ADC, T1, and T2 ( r = 0.95–0.96, all p < 0.001) reflecting water content, independent of mechanical parameters. These findings indicate that ex vivo MRE combined with multiparametric MRI enables quantitative assessment of parotid tumor properties through complementary biomarkers reflecting distinct physical mechanisms. Although viscoelastic parameters alone were insufficient to differentiate all tumor subtypes, their integration with diffusion and relaxometry metrics provides a more comprehensive characterization of tumor microstructure. This multiparametric approach shows promise for translation to in vivo applications, potentially enabling improved noninvasive tumor characterization and informing surgical planning.

Magnetic resonance elastography (MRE) allows noninvasive measurement of tissue viscoelasticity and is increasingly applied to characterize soft tissue biomechanics. This study investigates unfertilized chicken eggs as a biologically significant and cost-effective prostate phantom for combined MRE and diffusion-weighted imaging (DWI). Eggs were measured in two thermal states (soft-boiled and hard-boiled) to systematically alter the protein network structure and thus the mechanical properties of the phantom. All specimens were embedded in agarose gel and scanned using a 3T clinical MRI scanner equipped with multifrequency MRE and DWI. Quantitative parameters including shear wave speed (SWS), loss angle (φ), and apparent diffusion coefficient (ADC) as surrogates for stiffness, fluidity and water diffusivity, respectively, were analyzed in distinct anatomic compartments (yolk, egg white and germinal disc). Across both thermal states, egg white consistently demonstrated significantly higher values for SWS (medians ranging from 2.56–3.50 m/s), φ (0.85–0.86 rad), and ADC (1745.7–1529.1 µm²/s) compared to yolk (SWS: 1.25–1.44 m/s; φ: 0.63–0.67 rad; ADC: 278.8–214.8 µm²/s; all p < 0.01). Thermal processing induced biophysical parameter changes but did not eliminate the overall compartmental contrast. Test–retest reproducibility was variable, ranging from poor to excellent across parameters and compartments. In conclusion, unfertilized chicken eggs may represent a stable and structurally heterogeneous biological phantom for MRE with consistent compartmental differentiation. The consistent contrast between yolk and egg white across different thermal states highlights their potential as a simplified two-compartment model for elastography-based imaging and methodological development.

Pancreatic ductal adenocarcinoma (PDAC) is characterized by a dense desmoplastic extracellular matrix (ECM) that contributes to tumor progression, therapeutic resistance, and poor patient survival. However, the relationship between in vivo imaging-derived mechanical properties, ex vivo tissue biomechanics, ECM architecture, and cellularity remains incompletely understood. Here, we combined pre-operative in vivo clinical magnetic resonance elastography (MRE) with ex vivo biomechanical testing of fresh human PDAC tissue and histopathological analyses. Nine patients undergoing pancreatic resection were prospectively enrolled. Quantitative MRE was performed pre-operatively to assess tissue stiffness through shear wave speed (c) and relative viscosity or fluidity through the loss angle (φ). Fresh tumor and adjacent non-malignant tissue biopsies were subsequently analyzed ex vivo by unconfined uniaxial compression testing to determine elastic moduli and stress relaxation halftime. Histological analyses quantified collagen-rich fibrous tissue area, cell nuclei density, and nuclear morphology. Tumor tissue exhibited significantly increased stiffness and collagen fraction compared with adjacent non-malignant tissue, together with reduced cellularity, smaller nuclear area and more elongated nuclei. Ex vivo stiffness positively correlated with collagen content and negatively correlated with patient survival. Reduced stress relaxation halftime, indicative of increased tissue viscosity, was associated with lower cellularity and elongated nuclei. Importantly, pre-operative MRE parameters of the intact surrounding environment correlated significantly with ex vivo tumor mechanics, cellular organization, and survival. Specifically, a softer and less viscous surrounding environment was associated with stiffer and more viscous tumors, with lower cellularity and elongated nuclei, and poorer prognosis. These findings demonstrate that MRE-derived mechanical biomarkers reflect underlying ECM remodeling and tumor mechanobiology in PDAC. Integrating in vivo imaging with ex vivo tissue mechanics and histopathology may improve non-invasive disease characterization and support biomechanically-informed therapeutic strategies.