scholarly journals In Vivo Quantification of Regional Circumferential Green Strain in the Thoracic and Abdominal Aorta by Two-Dimensional Spiral Cine DENSE MRI

2019 ◽  
Vol 141 (6) ◽  
Author(s):  
John S. Wilson ◽  
Xiaodong Zhong ◽  
Jackson Hair ◽  
W. Robert Taylor ◽  
John N. Oshinski
Keyword(s):  
Abdominal Aorta ◽  
Aortic Wall ◽  
Patient Specific ◽  
Peak Strain ◽  
Ssfp Cine ◽  
Green Strain ◽  
The Mean ◽  
Thoracic And Abdominal ◽  
Cine Dense

Regional tissue mechanics play a fundamental role in the patient-specific function and remodeling of the cardiovascular system. Nevertheless, regional in vivo assessments of aortic kinematics remain lacking due to the challenge of imaging the thin aortic wall. Herein, we present a novel application of displacement encoding with stimulated echoes (DENSE) magnetic resonance imaging (MRI) to quantify the regional displacement and circumferential Green strain of the thoracic and abdominal aorta. Two-dimensional (2D) spiral cine DENSE and steady-state free procession (SSFP) cine images were acquired at 3T at either the infrarenal abdominal aorta (IAA), descending thoracic aorta (DTA), or distal aortic arch (DAA) in a pilot study of six healthy volunteers (22–59 y.o., 4 females). DENSE data were processed with multiple custom noise reduction techniques including time-smoothing, displacement vector smoothing, sectorized spatial smoothing, and reference point averaging to calculate circumferential Green strain across 16 equispaced sectors around the aorta. Each volunteer was scanned twice to evaluate interstudy repeatability. Circumferential Green strain was heterogeneously distributed in all volunteers and locations. The mean spatial heterogeneity index (standard deviation of all sector values divided by the mean strain) was 0.37 in the IAA, 0.28 in the DTA, and 0.59 in the DAA. Mean (homogenized) peak strain by DENSE for each cross section was consistent with the homogenized linearized strain estimated from SSFP cine. The mean difference in peak strain across all sectors following repeat imaging was −0.1±2.3%, with a mean absolute difference of 1.7%. Aortic cine DENSE MRI is a viable noninvasive technique for quantifying heterogeneous regional aortic wall strain and has significant potential to improve patient-specific clinical assessments of numerous aortopathies, as well as to provide the lacking spatiotemporal data required to refine patient-specific computational models of aortic growth and remodeling.

scholarly journals Assessment of the regional distribution of normalized circumferential strain in the thoracic and abdominal aorta using DENSE cardiovascular magnetic resonance

2019 ◽  
Vol 21 (1) ◽  
Author(s):  
John S. Wilson ◽  
W. Robert Taylor ◽  
John Oshinski
Keyword(s):  
Cardiovascular Magnetic Resonance ◽  
Magnetic Resonance ◽  
Abdominal Aorta ◽  
Circumferential Strain ◽  
Aortic Wall ◽  
Medial Wall ◽  
Patient Specific ◽  
Axial Location ◽  
Aortic Pathology

Abstract Background Displacement Encoding with Stimulated Echoes (DENSE) cardiovascular magnetic resonance (CMR) of the aortic wall offers the potential to improve patient-specific diagnostics and prognostics of diverse aortopathies by quantifying regionally heterogeneous aortic wall strain in vivo. However, before regional mapping of strain can be used to clinically assess aortic pathology, an evaluation of the natural variation of normal regional aortic kinematics is required. Method Aortic spiral cine DENSE CMR was performed at 3 T in 30 healthy adult subjects (range 18 to 65 years) at one or more axial locations that are at high risk for aortic aneurysm or dissection: the infrarenal abdominal aorta (IAA, n = 11), mid-descending thoracic aorta (DTA, n = 17), and/or distal aortic arch (DAA, n = 11). After implementing custom noise-reduction techniques, regional circumferential Green strain of the aortic wall was calculated across 16 sectors around the aortic circumference at each location and normalized by the mean circumferential strain for comparison between individuals. Results The distribution of normalized circumferential strain (NCS) was heterogeneous for all locations evaluated. Despite large differences in mean strain between subjects, comparisons of NCS revealed consistent patterns of strain distribution for similar groupings of patients by axial location, age, and/or mean displacement angle. NCS at local systole was greatest in the lateral/posterolateral walls in the IAAs (1.47 ± 0.27), medial wall in anteriorly displacing DTAs (1.28 ± 0.20), lateral wall in posteriorly displacing DTAs (1.29 ± 0.29), superior curvature in DAAs < 50 years-old (1.93 ± 0.22), and medial wall in DAAs > 50 years (2.29 ± 0.58). The distribution of strain was strongly influenced by the location of the vertebra and other surrounding structures unique to each location. Conclusions Regional in vivo circumferential strain in the adult aorta is unique to each axial location and heterogeneous around its circumference, but can be grouped into consistent patterns defined by basic patient-specific metrics following normalization. The heterogeneous strain distributions unique to each group may be due to local peri-aortic constraints (particularly at the aorto-vertebral interface), heterogeneous material properties, and/or heterogeneous flow patterns. These results must be carefully considered in future studies seeking to clinically interpret or computationally model patient-specific aortic kinematics.

Direct calibration of a totally implantable pulsed Doppler ultrasonic blood flowmeter

1977 ◽  
Vol 232 (5) ◽  
pp. H537-H544
Author(s):  
H. V. Allen ◽  
M. F. Anderson ◽  
J. D. Meindl
Keyword(s):  
Linear Regression ◽  
Abdominal Aorta ◽  
Regression Line ◽  
Volume Flow ◽  
Flow Profile ◽  
Pulsed Doppler ◽  
Velocity Flow ◽  
The Mean ◽  
Best Fit

A totally implantable pulsed Doppler ultrasonic blood flowmeter has recently been developed to provide information on the velocity-flow profile in a vessel as well as its diameter. Volume flow can be indirectly obtained according to the formula: Q = (phi/4)(diam)2-v. In order to determine the accuracy of this estimate, in vivo direct bleedout measurements were performed on the abdominal aorta of six dogs with an overall accuracy in 77 trials of +2.0 +/- 8.7% (mean +/- 1 SD). The best-fit mean linear regression line was found to be: flowmeter output = 1.013-true flow + 5.1 ml/min. The scatter in the flowmeter's accuracy is thought to be due to small variations in the angle of the transducer. The source of the 2% overestimation in the mean accuracy could not be directly attributed to any one condition; the error is sufficiently small that in many cases it can be neglected.

Regional differences in vasculotoxic effects of cyclosporin in rats

1995 ◽  
Vol 73 (11) ◽  
pp. 1661-1668 ◽  
Author(s):  
Marleen Verbeke ◽  
Leo de Ridder ◽  
Johan Van de Voorde ◽  
Norbert Lameire
Keyword(s):  
Thoracic Aorta ◽  
Abdominal Aorta ◽  
Regional Differences ◽  
Treatment Schedule ◽  
Study Protocols ◽  
Relaxation Responses ◽  
Thoracic And Abdominal ◽  
And Control

Studies on cyclosporin-induced vasculotoxicity often yielded discrepant results, possibly as a result of differences in study protocols. The aim of the present study was to analyse cyclosporin-induced vasculotoxicity in arteries of different size and origin. Therefore, rats were treated with cyclosporin, 20 mg∙kg−1∙day−1, by gastric gavage for 10 days. In our previous studies, this treatment schedule induced renal functional impairment in vivo and an impaired relaxation response of thoracic aortic rings in vitro. Relaxation of various arteries (thoracic and abdominal aorta and carotid, renal, and interlobar arteries) from cyclosporin-treated and control rats in response to endothelium-dependent and -independent vasodilators was analysed. The thoracic aorta showed diminished endothelium-dependent and -independent relaxations; in the abdominal aorta no impairment was observed. Moreover, the dysfunction of the thoracic aorta seemed to be homogeneous along its length and showed an abrupt termination at the level of the diaphragm. In all other segments studied, no impairment of the relaxation responses was found. A similar pattern of vascular damage was found in rats treated with a very toxic cyclosporin treatment (50 mg∙kg−1∙day−1 s.c. × 7 days). The results indicate regional differences in cyclosporin-induced vasculotoxicity. The thoracic aorta, and in view of the fall of the renal blood flow, most likely also the renal resistance vessels, could be more susceptible than other vessels to cyclosporin-induced vascular dysfunction.Key words: cyclosporin, rat, arteries, vasorelaxation.

In-Vivo Obstetric Pressure Measurements for Patient-Specific Epidural Simulator

2014 ◽  
Author(s):  
Neil Vaughan ◽  
Venketesh N. Dubey ◽  
Michael Y. K. Wee ◽  
Richard Isaacs
Keyword(s):  
Needle Insertion ◽  
Epidural Needle ◽  
Patient Specific ◽  
Pressure Measurements ◽  
Epidural Pressure ◽  
Loss Of Resistance ◽  
New Finding ◽  
The Mean ◽  
Thickness Measurements

The aim of this study was to measure changing pressures during Tuohy epidural needle insertions for obstetric parturients of various BMI. This has identified correlations between BMI and epidural pressure. Also we investigated links between BMI and the thicknesses and depths of ligaments and epidural space as measured from MRI and ultrasound scans. To date there have been no studies relating epidural pressure and ligament thickness changes with varying Body Mass Indices (BMI). Further goals following measurement of pressure differences between various BMI patients, were to allow a patient-specific epidural simulator to be developed, which has not been achieved before. The trial has also assessed the suitability of our in-house developed wireless pressure measurement device for use in-vivo. Previously we conducted needle insertion trial with porcine for validation of the measurement system. Results showed that for each group average pressures during insertion decrease as BMI increases. Pressure measurements obtained from the patients were matched to tissue thickness measurements from MRI and ultrasound scans. The mean Loss of Resistance (LOR) pressure in each group reduces as BMI increases. Variation in the shape of the pressure graphs was noticed between two epiduralists performing the procedure, suggesting each anaesthetist may have a signature graph shape. This is a new finding which offers potential use in epidural training and assessment. It can be seen that insertions performed by the first epiduralist have a higher pressure range than insertions performed by second epiduralist.

scholarly journals Can we obtain in vivo transmural mean hoop stress of the aortic wall without knowing patient-specific material properties and residual deformations?

2018 ◽  
Author(s):  
Minliang Liu ◽  
Liang Liang ◽  
Haofei Liu ◽  
Ming Zhang ◽  
Caitlin Martin ◽  
...  
Keyword(s):  
Material Properties ◽  
Hoop Stress ◽  
Aortic Wall ◽  
Patient Specific ◽  
Membrane Stress ◽  
Penalty Approach ◽  
Thin Walled ◽  
Specific Material ◽  
Residual Deformations

AbstractIt is well known that residual deformations/stresses alter the mechanical behavior of arteries, e.g. the pressure-diameter curves. In an effort to enable personalized analysis of the aortic wall stress, approaches have been developed to incorporate experimentally-derived residual deformations into in vivo loaded geometries in finite element simulations using thick-walled models. Solid elements are typically used to account for “bending-like” residual deformations. Yet, the difficulty in obtaining patient-specific residual deformations and material properties has become one of the biggest challenges of these thick-walled models. In thin-walled models, fortunately, static determinacy offers an appealing prospect that allows for the calculation of the thin-walled membrane stress without patient-specific material properties. The membrane stress can be computed using forward analysis by enforcing an extremely stiff material property as penalty treatment, which is referred to as the forward penalty approach. However, thin-walled membrane elements, which have zero bending stiffness, are incompatible with the residual deformations, and therefore, it is often stated as a limitation of thin-walled models. In this paper, by comparing the predicted stresses from thin-walled models and thick-walled models, we demonstrate that the transmural mean hoop stress is the same for the two models and can be readily obtained from in vivo clinical images without knowing the patient-specific material properties and residual deformations. Computation of patient-specific mean hoop stress can be greatly simplified by using membrane model and the forward penalty approach, which may be clinically valuable.

Assessing Patient-Specific Mechanical Properties of Aortic Wall and Peri-Aortic Structures From In Vivo DENSE Magnetic Resonance Imaging Using an Inverse Finite Element Method and Elastic Foundation Boundary Conditions

2020 ◽  
Vol 142 (12) ◽  
Author(s):  
Johane H. Bracamonte ◽  
John S. Wilson ◽  
Joao S. Soares
Keyword(s):  
Magnetic Resonance Imaging ◽  
Finite Element Method ◽  
Finite Element ◽  
Magnetic Resonance ◽  
Aortic Wall ◽  
Patient Specific ◽  
Resonance Imaging ◽  
Displacement Fields ◽  
Inverse Finite Element Method

Abstract The establishment of in vivo, noninvasive patient-specific, and regionally resolved techniques to quantify aortic properties is key to improving clinical risk assessment and scientific understanding of vascular growth and remodeling. A promising and novel technique to reach this goal is an inverse finite element method (FEM) approach that utilizes magnetic resonance imaging (MRI)-derived displacement fields from displacement encoding with stimulated echoes (DENSE). Previous studies using DENSE MRI suggested that the infrarenal abdominal aorta (IAA) deforms heterogeneously during the cardiac cycle. We hypothesize that this heterogeneity is driven in healthy aortas by regional adventitial tethering and interaction with perivascular tissues, which can be modeled with elastic foundation boundary conditions (EFBCs) using a collection of radially oriented springs with varying stiffness with circumferential distribution. Nine healthy IAAs were modeled using previously acquired patient-specific imaging and displacement fields from steady-state free procession (SSFP) and DENSE MRI, followed by assessment of aortic wall properties and heterogeneous EFBC parameters using inverse FEM. In contrast to traction-free boundary condition, prescription of EFBC reduced the nodal displacement error by 60% and reproduced the DENSE-derived heterogeneous strain distribution. Estimated aortic wall properties were in reasonable agreement with previously reported experimental biaxial testing data. The distribution of normalized EFBC stiffness was consistent among all patients and spatially correlated to standard peri-aortic anatomical features, suggesting that EFBC could be generalized for human adults with normal anatomy. This approach is computationally inexpensive, making it ideal for clinical research and future incorporation into cardiovascular fluid–structure analyses.

VASCULAR CONNECTIVE TISSUE UNDER THE INFLUENCE OF THYROXINE

1961 ◽  
Vol 37 (2) ◽  
pp. 183-190 ◽  
Author(s):  
lb Lorenzen
Keyword(s):  
Aortic Valve ◽  
Connective Tissue ◽  
Abdominal Aorta ◽  
Aortic Wall ◽  
Physiological Saline ◽  
Clear Cut ◽  
Reparative Process ◽  
Hexosamine Content

ABSTRACT Male albino rabbits were injected with 1-thyroxine and physiological saline for 2 weeks. The resulting changes in the aortic wall were assessed grossly and microscopically and also by analysis of hexosamine, hydroxyproline, water, and calcium. Furthermore, the in vivo uptake of 35S sulphate was determined. Despite insignificant gross and microscopic changes, there was a clear-cut increase in hexosamine content and uptake of 35S sulphate, most pronounced in the first part of the aorta, from the aortic valve to the first intercostal arteries, and in the abdominal aorta. These changes were of the same nature as those seen following injections of epinephrine and of epinephrine plus 1-thyroxine. The lesions of the aortic wall might be due to thyroxine induced sensitization to endogenous epinephrine, and the accumulation of mucopolysaccharide probably indicates a reparative process.

scholarly journals Identification of in vivo nonlinear anisotropic mechanical properties of ascending thoracic aortic aneurysm from patient-specific CT scans

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Minliang Liu ◽  
Liang Liang ◽  
Fatiesa Sulejmani ◽  
Xiaoying Lou ◽  
Glen Iannucci ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Aortic Aneurysm ◽  
Thoracic Aortic Aneurysm ◽  
Aortic Wall ◽  
Inverse Methods ◽  
Ct Scans ◽  
Patient Specific ◽  
Accurate Identification ◽  
Anisotropic Mechanical Properties

Abstract Accurate identification of in vivo nonlinear, anisotropic mechanical properties of the aortic wall of individual patients remains to be one of the critical challenges in the field of cardiovascular biomechanics. Since only the physiologically loaded states of the aorta are given from in vivo clinical images, inverse approaches, which take into account of the unloaded configuration, are needed for in vivo material parameter identification. Existing inverse methods are computationally expensive, which take days to weeks to complete for a single patient, inhibiting fast feedback for clinicians. Moreover, the current inverse methods have only been evaluated using synthetic data. In this study, we improved our recently developed multi-resolution direct search (MRDS) approach and the computation time cost was reduced to 1~2 hours. Using the improved MRDS approach, we estimated in vivo aortic tissue elastic properties of two ascending thoracic aortic aneurysm (ATAA) patients from pre-operative gated CT scans. For comparison, corresponding surgically-resected aortic wall tissue samples were obtained and subjected to planar biaxial tests. Relatively close matches were achieved for the in vivo-identified and ex vivo-fitted stress-stretch responses. It is hoped that further development of this inverse approach can enable an accurate identification of the in vivo material parameters from in vivo image data.

scholarly journals On the computation of in vivo transmural mean stress of patient-specific aortic wall

2018 ◽  
Vol 18 (2) ◽  
pp. 387-398 ◽  
Author(s):  
Minliang Liu ◽  
Liang Liang ◽  
Haofei Liu ◽  
Ming Zhang ◽  
Caitlin Martin ◽  
...  
Keyword(s):  
Aortic Wall ◽  
Patient Specific ◽  
Mean Stress

Passage of labeled albumin into canine aortic wall in vivo and in vitro

1961 ◽  
Vol 200 (3) ◽  
pp. 622-624 ◽  
Author(s):  
Leroy E. Duncan ◽  
Katherin Buck
Keyword(s):  
Abdominal Aorta ◽  
Aortic Wall ◽  
Aortic Pressure ◽  
Ascending Aorta ◽  
Descending Aorta ◽  
Arterial Blood ◽  
Isolated Aorta ◽  
Abdominal Portion

The passage of labeled albumin into canine aortic wall in vivo and in vitro was studied. In vivo albumin entered the inner layer fastest in the ascending aorta and progressively less rapidly down the length of the aorta. In vitro, this gradient was partially preserved since albumin entered the inner layer of ascending aorta faster than that of descending aorta. The gradient was not completely preserved in vitro, since albumin entered the inner layer of abdominal aorta faster than that of descending thoracic aorta. The rapid entrance of albumin into the abdominal portion of the aorta in vitro appears to have been due to the maintenance of arterial blood pressure in the unusually dense capillary network of the abdominal aorta. The partial preservation of the gradient in the isolated aorta excludes phasic variation of intra- or extra-aortic pressure as a cause of the gradient.

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