Background
Hypertrophic cardiomyopathy (HCM) remains the commonest cause of sudden cardiac death among young athletes. Differentiating between physiologically adaptive left ventricular (LV) ...hypertrophy observed in athletes' hearts and pathological HCM remains challenging. By quantifying the diffusion of water molecules, diffusion tensor imaging (DTI) MRI allows voxelwise characterization of myocardial microstructure.
Purpose
To explore microstructural differences between healthy volunteers, athletes, and HCM patients using DTI.
Study Type
Prospective cohort.
Population
Twenty healthy volunteers, 20 athletes, and 20 HCM patients.
Field Strength/Sequence
3T/DTI spin echo.
Assessment
In‐house MatLab software was used to derive mean diffusivity (MD) and fractional anisotropy (FA) as markers of amplitude and anisotropy of the diffusion of water molecules, and secondary eigenvector angles (E2A)—reflecting the orientations of laminar sheetlets.
Statistical Tests
Independent samples t‐tests were used to detect statistical significance between any two cohorts. Analysis of variance was utilized for detecting the statistical difference between the three cohorts. Statistical tests were two‐tailed. A result was considered statistically significant at P ≤ 0.05.
Results
DTI markers were significantly different between HCM, athletes, and volunteers. HCM patients had significantly higher global MD and E2A, and significantly lower FA than athletes and volunteers. (MDHCM = 1.52 ± 0.06 × 10−3 mm2/s, MDAthletes = 1.49 ± 0.03 × 10−3 mm2/s, MDvolunteers = 1.47 ± 0.02 × 10−3 mm2/s, P < 0.05; E2AHCM = 58.8 ± 4°, E2Aathletes = 47 ± 5°, E2Avolunteers = 38.5 ± 7°, P < 0.05; FAHCM = 0.30 ± 0.02, FAAthletes = 0.35 ± 0.02, FAvolunteers = 0.36 ± 0.03, P < 0.05). HCM patients had significantly higher E2A in their thickest segments compared to the remote (E2Athickest = 66.8 ± 7, E2Aremote = 51.2 ± 9, P < 0.05).
Data Conclusion
DTI depicts an increase in amplitude and isotropy of diffusion in the myocardium of HCM compared to athletes and volunteers as reflected by increased MD and decreased FA values. While significantly higher E2A values in HCM and athletes reflect steeper configurations of the myocardial sheetlets than in volunteers, HCM patients demonstrated an eccentric rise in E2A in their thickest segments, while athletes demonstrated a concentric rise. Further studies are required to determine the diagnostic capabilities of DTI.
Evidence Level
1
Technical Efficacy Stage
2
The identification and management of incidental findings is becoming increasingly problematic, particularly in relation to brachial plexus imaging because the prevalence is unknown. Therefore, we ...aimed to estimate the prevalence of incidental findings in symptomatic patients undergoing MRI of the brachial plexus.
This retrospective cohort study included all children and adults who underwent MRI over a 12-year period, in a tertiary care centre in the UK. An incidental finding was any abnormality which was not a direct injury to or disease-process of the brachial plexus. An "incidentaloma" was defined by the need for further investigation or treatment. Multivariable logistic regression was used to estimate the odds ratio (OR) of an "incidentaloma". To estimate which factors were associated with the incident rate ratio (IRR) of incidental findings, multivariable Poisson regression was used.
Overall, 502 scans (72%) reported incidental anomalies. Although the number of MRIs performed per annum increased by 23%, the prevalence of "incidentalomas" remained static (
= 0.766). Musculoskeletal incidental findings were the most prevalent (63%) and when identified, there were a median of 3 incidental anomalies per patient. Overall, 125 (18%) anomalies were "incidentalomas" which required further investigation or treatment. The odds of having further investigation or treatment was strongly related to the frequency of incidental findings adjusted OR 1.16 (95% CI 1.08, 1.24) and when a tumour was identified adjusted OR 2.86 (95% CI 1.81, 4.53). The number of incidental findings recorded per scan increased when trainees co-reported with consultants adjusted IRR 0.36 (95% CI 0.05, 0.67) and in the presence of a tumour adjusted IRR 0.39 (95% CI 0.28, 0.49).
The prevalence of clinically important incidental findings on brachial plexus MRI is lower than organ-specific imaging, but still 18% of scans identified an 'incidentaloma' which required further investigation or treatment.
This cohort study shows that approximately 1 in 5 symptomatic patients undergoing a brachial plexus MRI had a clinically important incidental findings, which required further investigation or treatment. This information can be used to inform patients consenting to clinical or research imaging.
Changes in composition of the intestinal microbiota are linked to the development of obesity and can lead to endothelial cell (EC) dysfunction. It is unknown whether EC can directly influence the ...microbiota. Insulin‐like growth factor‐1 (IGF‐1) and its receptor (IGF‐1R) are critical for coupling nutritional status and cellular growth; IGF‐1R is expressed in multiple cell types including EC. The role of ECIGF‐1R in the response to nutritional obesity is unexplored. To examine this, we use gene‐modified mice with EC‐specific overexpression of human IGF‐1R (hIGFREO) and their wild‐type littermates. After high‐fat feeding, hIGFREO weigh less, have reduced adiposity and have improved glucose tolerance. hIGFREO show an altered gene expression and altered microbial diversity in the gut, including a relative increase in the beneficial genus Akkermansia. The depletion of gut microbiota with broad‐spectrum antibiotics induces a loss of the favourable metabolic differences seen in hIGFREO mice. We show that IGF‐1R facilitates crosstalk between the EC and the gut wall; this crosstalk protects against diet‐induced obesity, as a result of an altered gut microbiota.
SYNOPSIS
It remained unclear if gut endothelial cells can directly influence the microbiota. Here, endothelial specific over‐expression of IGF‐1R is shown to promote advantageous remodelling of the gut microbiota upon high fat diet, which protects against the development of obesity.
Mice overexpressing insulin like growth factor‐1 receptors in the endothelium (hIGFREO) are protected against obesity.
Protection against obesity is in part due to remodelling of the intestinal microbiota due to endothelium‐enterocyte crosstalk.
Altered microbial diversity in the gut leads to a relative increase in the beneficial genus Akkermansia.
Microbiota depletion using broad‐spectrum antibiotics attenuates advantageous metabolic phenotypes of hIGFREO mice.
It remained unclear if gut endothelial cells can directly influence the microbiota. Here, endothelial specific over‐expression of IGF‐1R is shown to promote advantageous remodelling of the gut microbiota upon high fat diet, which protects against the development of obesity.
Myocardial infarction, or heart attack, is the leading cause of mortality globally. Although the treatment of myocardial infarct has improved significantly, scar tissue that persists can often lead ...to increased stress and adverse remodeling of surrounding tissue and ultimately to heart failure. Intra‐myocardial injection of biomaterials represents a potential treatment to attenuate remodeling, mitigate degeneration, and reverse the disease process in the tissue. In vivo experiments on animal models have shown functional benefits of this therapeutic strategy. However, a poor understanding of the optimal injection pattern, volume, and material properties has acted as a barrier to its widespread clinical adoption. In this study, we developed two quasistatic finite element simulations of the left ventricle to investigate the mechanical effect of intra‐myocardial injection. The first model employed an idealized left ventricular geometry with rule‐based cardiomyocyte orientation. The second model employed a subject‐specific left ventricular geometry with cardiomyocyte orientation from diffusion tensor magnetic resonance imaging. Both models predicted cardiac parameters including ejection fraction, systolic wall thickening, and ventricular twist that matched experimentally reported values. All injection simulations showed cardiomyocyte stress attenuation, offering an explanation for the mechanical reinforcement benefit associated with injection. The study also enabled a comparison of injection location and the corresponding effect on cardiac performance at different stages of the cardiac cycle. While the idealized model has lower fidelity, it predicts cardiac function and differentiates the effects of injection location. Both models represent versatile in silico tools to guide optimal strategy in terms of injection number, volume, site, and material properties.
In preclinical models, intramyocardial injection of biomaterials has been shown to attenuate disease progression of cardiac tissue after a heart attack. Nonetheless, a poor understanding of the optimal injection pattern, volume, and material properties has posed a challenge to clinical adoption of this strategy. In this study, we developed two quasi‐static finite element simulations of the left ventricle to investigate the mechanical effect of intramyocardial injection.
Myocardial microstructure and its macroscopic materialisation are fundamental to the function of the heart. Despite this importance, characterisation of cellular features at the organ level remains ...challenging, and a unifying description of the structure of the heart is still outstanding. Here, we optimised diffusion tensor imaging data to acquire high quality data in ex vivo rabbit hearts in slack and contractured states, approximating diastolic and systolic conditions. The data were analysed with a suite of methods that focused on different aspects of the myocardium. In the slack heart, we observed a similar transmural gradient in helix angle of the primary eigenvector of up to 23.6°/mm in the left ventricle and 24.2°/mm in the right ventricle. In the contractured heart, the same transmural gradient remained largely linear, but was offset by up to +49.9° in the left ventricle. In the right ventricle, there was an increase in the transmural gradient to 31.2°/mm and an offset of up to +39.0°. The application of tractography based on each eigenvector enabled visualisation of streamlines that depict cardiomyocyte and sheetlet organisation over large distances. We observed multiple V- and N-shaped sheetlet arrangements throughout the myocardium, and insertion of sheetlets at the intersection of the left and right ventricle. This study integrates several complementary techniques to visualise and quantify the heart’s microstructure, projecting parameter representations across different length scales. This represents a step towards a more comprehensive characterisation of myocardial microstructure at the whole organ level.
Biomimetic phantom for cardiac diffusion MRI Teh, Irvin; Zhou, Feng-Lei; Hubbard Cristinacce, Penny L. ...
Journal of magnetic resonance imaging,
March 2016, Letnik:
43, Številka:
3
Journal Article
Recenzirano
Odprti dostop
Purpose
Diffusion magnetic resonance imaging (MRI) is increasingly used to characterize cardiac tissue microstructure, necessitating the use of physiologically relevant phantoms for methods ...development. Existing phantoms are generally simplistic and mostly simulate diffusion in the brain. Thus, there is a need for phantoms mimicking diffusion in cardiac tissue.
Materials and Methods
A biomimetic phantom composed of hollow microfibers generated using co‐electrospinning was developed to mimic myocardial diffusion properties and fiber and sheet orientations. Diffusion tensor imaging was carried out at monthly intervals over 4 months at 9.4T. 3D fiber tracking was performed using the phantom and compared with fiber tracking in an ex vivo rat heart.
Results
The mean apparent diffusion coefficient and fractional anisotropy of the phantom remained stable over the 4‐month period, with mean values of 7.53 ± 0.16 × 10‐4 mm2/s and 0.388 ± 0.007, respectively. Fiber tracking of the 1st and 3rd eigenvectors generated analogous results to the fiber and sheet‐normal direction respectively, found in the left ventricular myocardium.
Conclusion
A biomimetic phantom simulating diffusion in the heart was designed and built. This could aid development and validation of novel diffusion MRI methods for investigating cardiac microstructure, decrease the number of animals and patients needed for methods development, and improve quality control in longitudinal and multicenter cardiac diffusion MRI studies. J. MAGN. RESON. IMAGING 2016;43:594–600.
Cardiac diffusion tensor imaging (DTI) is an emerging technique for the in vivo characterisation of myocardial microstructure, and there is a growing need for its validation and standardisation. We ...sought to establish the accuracy, precision, repeatability and reproducibility of state‐of‐the‐art pulse sequences for cardiac DTI among 10 centres internationally. Phantoms comprising 0%–20% polyvinylpyrrolidone (PVP) were scanned with DTI using a product pulsed gradient spin echo (PGSE; N = 10 sites) sequence, and a custom motion‐compensated spin echo (SE; N = 5) or stimulated echo acquisition mode (STEAM; N = 5) sequence suitable for cardiac DTI in vivo. A second identical scan was performed 1–9 days later, and the data were analysed centrally. The average mean diffusivities (MDs) in 0% PVP were (1.124, 1.130, 1.113) x 10−3 mm2/s for PGSE, SE and STEAM, respectively, and accurate to within 1.5% of reference data from the literature. The coefficients of variation in MDs across sites were 2.6%, 3.1% and 2.1% for PGSE, SE and STEAM, respectively, and were similar to previous studies using only PGSE. Reproducibility in MD was excellent, with mean differences in PGSE, SE and STEAM of (0.3 ± 2.3, 0.24 ± 0.95, 0.52 ± 0.58) x 10−5 mm2/s (mean ± 1.96 SD). We show that custom sequences for cardiac DTI provide accurate, precise, repeatable and reproducible measurements. Further work in anisotropic and/or deforming phantoms is warranted.
There is a growing need for validation of pulse sequences for cardiac diffusion tensor imaging (DTI). We show, in a multicentre study involving 10 sites, that custom sequences for cardiac DTI based on motion‐compensated spin echo and stimulated echo acquisition mode provide accurate, precise and reproducible measurements.
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