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Full-Text Articles in Mechanical Engineering

Cerebrospinal Fluid Dynamics In The Cervical Spine: Importance Of Fine Anatomical Structures, S. Pahlavian, T. Yiallourou, R. Tubbs, A. Bunck, M. Goodin, Francis Loth, M. Raisee, Bryn Martin Apr 2015

Cerebrospinal Fluid Dynamics In The Cervical Spine: Importance Of Fine Anatomical Structures, S. Pahlavian, T. Yiallourou, R. Tubbs, A. Bunck, M. Goodin, Francis Loth, M. Raisee, Bryn Martin

Dr. Bryn Martin

No abstract provided.


Cerebrospinal Fluid Hydrodynamics In Type I Chiari Malformation, Nicholas Shaffer, Bryn Martin, Francis Loth Apr 2015

Cerebrospinal Fluid Hydrodynamics In Type I Chiari Malformation, Nicholas Shaffer, Bryn Martin, Francis Loth

Dr. Bryn Martin

The objective of this study was to review past studies that have used engineering analysis to examine cerebrospinal fluid hydrodynamics in cranial and spinal subarachnoid spaces in both healthy humans and those affected by type I Chiari malformation. Methods: A PubMed search of literature pertaining to cerebrospinal fluid hydrodynamics was performed with a particular focus on those that utilized methods such as computational fluid dynamics or experimental flow modeling.


Task-Specific And General Cognitive Effects In Chiari Malformation Type I, Philip Allen, James Houston, Joshua Pollock, Christopher Buzzelli, Xuan Li, A. Harrington, Bryn Martin, Francis Loth, Mei-Ching Lien, Jahangir Maleki, Mark Luciano Apr 2015

Task-Specific And General Cognitive Effects In Chiari Malformation Type I, Philip Allen, James Houston, Joshua Pollock, Christopher Buzzelli, Xuan Li, A. Harrington, Bryn Martin, Francis Loth, Mei-Ching Lien, Jahangir Maleki, Mark Luciano

Dr. Bryn Martin

Our objective was to use episodic memory and executive function tests to determine whether or not Chiari Malformation Type I (CM) patients experience cognitive dysfunction.


Construction And Validation Of A Complaint Model Of The Cerebrospinal Fluid System With Fluid Filled Syrinx, Bryn Martin, Wojciech Kalata, John Oshinski, Francis Loth, Thomas Royston Apr 2015

Construction And Validation Of A Complaint Model Of The Cerebrospinal Fluid System With Fluid Filled Syrinx, Bryn Martin, Wojciech Kalata, John Oshinski, Francis Loth, Thomas Royston

Dr. Bryn Martin

No abstract provided.


Pathological Biomechanics Of Cerebrospinal Fluid Pressure In Syringomyelia: Fluid Structure Interaction Of An In Vitro Coaxial Elastic Tube System, Bryn Martin, Richard Labuda, Thomas Royston, John Oshinski, Bermans Iskandar, Francis Loth Apr 2015

Pathological Biomechanics Of Cerebrospinal Fluid Pressure In Syringomyelia: Fluid Structure Interaction Of An In Vitro Coaxial Elastic Tube System, Bryn Martin, Richard Labuda, Thomas Royston, John Oshinski, Bermans Iskandar, Francis Loth

Dr. Bryn Martin

Full explanation for the formation and pathogenesis of syringomyelia (SM), a neurological pathology characterized by the formation of a cystic cavity (syrinx) in the center of the spinal cord (SC), has not yet been given. The SM pathology forms a coaxial elastic tube system with the inner tube formed by the spinal cord having a syrinx and the outer tube formed by the spinal column (dura and vertebrae).


The Influence Of Coughing On Cerebrospinal Fluid Pressure In An In Vitro Syringomyelia Model With Spinal Canal Stenosis, Bryn Martin, Francis Loth Apr 2015

The Influence Of Coughing On Cerebrospinal Fluid Pressure In An In Vitro Syringomyelia Model With Spinal Canal Stenosis, Bryn Martin, Francis Loth

Dr. Bryn Martin

Five in vitro models were constructed which were representative of various pathologies of the spinal canal (SC) associated with syringomyelia (SM). The models were subjected to a cough type flow impulse while monitoring the pressure environment in the syrinx and subarachnoid space (SAS) regions of the model. The results indicated that conditions can arise during a cough which would provide pressure forces to encourage cerebrospinal fluid (CSF) movement into the syrinx cavity.


A Multimode Sonic And Ultrasonic Diagnostic Imaging System With Application To Peripheral Vascular Characterization, Todd Spohnholtz, Thomas Royston, Yigit Yazicioglu, Bryn Martin, Francis Loth Apr 2015

A Multimode Sonic And Ultrasonic Diagnostic Imaging System With Application To Peripheral Vascular Characterization, Todd Spohnholtz, Thomas Royston, Yigit Yazicioglu, Bryn Martin, Francis Loth

Dr. Bryn Martin

No abstract provided.


Hydrodynamic And Longitudinal Impedance Analysis Of Cerebrospinal Fluid Dynamics At The Craniovertebral Junction In Type I Chiari Malformation, Bryn Martin, Wojciech Kalata, Nicholas Shaffer, Paul Fischer, Mark Luciano, Francis Loth Apr 2015

Hydrodynamic And Longitudinal Impedance Analysis Of Cerebrospinal Fluid Dynamics At The Craniovertebral Junction In Type I Chiari Malformation, Bryn Martin, Wojciech Kalata, Nicholas Shaffer, Paul Fischer, Mark Luciano, Francis Loth

Dr. Bryn Martin

Elevated or reduced velocity of cerebrospinal fluid (CSF) at the craniovertebral junction (CVJ) has been associated with type I Chiari malformation (CMI). Thus, quantification of hydrodynamic parameters that describe the CSF dynamics could help assess disease severity and surgical outcome. In this study, we describe the methodology to quantify CSF hydrodynamic parameters near the CVJ and upper cervical spine utilizing subject-specific computational fluid dynamics (CFD) simulations based on in vivo MRI measurements of flow and geometry. Hydrodynamic parameters were computed for a healthy subject and two CMI patients both pre- and post-decompression surgery to determine the differences between cases. For ...


Characterization Of The Discrepancies Between Four-Dimensional Phase-Contrast Magnetic Resonance Imaging And In-Silico Simulations Of Cerebrospinal Fluid Dynamics, Soroush Heidari, Alexander Bunck, Francis Loth, R. Tubbs, Theresia Yiallourou, Jan Kroeger, Walter Heindel, Bryn Martin Apr 2015

Characterization Of The Discrepancies Between Four-Dimensional Phase-Contrast Magnetic Resonance Imaging And In-Silico Simulations Of Cerebrospinal Fluid Dynamics, Soroush Heidari, Alexander Bunck, Francis Loth, R. Tubbs, Theresia Yiallourou, Jan Kroeger, Walter Heindel, Bryn Martin

Dr. Bryn Martin

The purpose of the present study was to compare subject-specific magnetic resonance imaging (MRI)-based computational fluid dynamics (CFD) simulations with time-resolved three-directional (3D) velocity-encoded phase-contrast MRI (4D PCMRI) measurements of the cerebrospinal fluid (CSF) velocity field in the cervical spinal subarachnoid space (SSS). Three-dimensional models of the cervical SSS were constructed based on MRI image segmentation and anatomical measurements for a healthy subject and patient with Chiari I malformation. CFD was used to simulate the CSF motion and compared to the 4D PCMRI measurements. Four-dimensional PCMRI measurements had much greater CSF velocities compared to CFD simulations (1.4 to ...


Quantitative Comparison Of 4d Mri Flow Measurements To 3d Computational Fluid Dynamics Simulation Of Cerebrospinal Fluid Movement In The Spinal Subarachnoid Space, Theresia Yiallourou, Leonie Asboth, J. Kroeger, David Maintz, A. Bunck, Nikolaos Stergiopulos, Bryn Martin Apr 2015

Quantitative Comparison Of 4d Mri Flow Measurements To 3d Computational Fluid Dynamics Simulation Of Cerebrospinal Fluid Movement In The Spinal Subarachnoid Space, Theresia Yiallourou, Leonie Asboth, J. Kroeger, David Maintz, A. Bunck, Nikolaos Stergiopulos, Bryn Martin

Dr. Bryn Martin

Computational fluid dynamic (CFD) simulations have provided detailed information about the complex flow and pressure field within the cerebrospinal fluid (CSF) system. The solutions of these simulations are sensitive to boundary conditions and thus need validation with in vivo measurements. However, validation of CFD flow results and MRI CSF flow measurements have been limited to through-plane pcMR measurements.


Impact Of Aortic Grafts On Hemodynamics: A 1d Computational Assessment, O. Vardoulis, E. Coppens, Bryn Martin, P. Reymond, N. Stergiopulos Apr 2015

Impact Of Aortic Grafts On Hemodynamics: A 1d Computational Assessment, O. Vardoulis, E. Coppens, Bryn Martin, P. Reymond, N. Stergiopulos

Dr. Bryn Martin

Vascular prostheses currently used in aortic replacement surgery do not have the same mechanical properties as human arteries. In vivo studies have revealed that aortic grafts augment heart load and alter blood pressure and flow waveforms. A one-dimensional model of the arterial tree was developed in order to analyze the different mechanisms by which grafts placed in the ascending aorta (proximal) and descending aorta (distal) affect hemodynamics. Graft compliance and properties were based on in vitro tests


A Coupled Simulation Of Spinal Cord Blood Flow And Cerebrospinal Fluid Motion In The Spinal Subarachnoid Space Based On In Vivo Measurements, Bryn Martin, Philippe Reymond, Olivier Baledent, Jan Novy, Nikos Stergiopulos Apr 2015

A Coupled Simulation Of Spinal Cord Blood Flow And Cerebrospinal Fluid Motion In The Spinal Subarachnoid Space Based On In Vivo Measurements, Bryn Martin, Philippe Reymond, Olivier Baledent, Jan Novy, Nikos Stergiopulos

Dr. Bryn Martin

A preliminary coupled 1-D model of the systemic arterial tree and cerebrospinal fluid (CSF) system was constructed. The systemic tree model includes arteries greater than 2 mm in diameter and a simplified spinal cord vasculature. Coupling of the arterial tree and CSF system is accomplished by a transfer function based on in vivo cerebral blood flow (CBF) and CSF pulsation measurements in 17 young healthy adults.


Spinal Subarachnoid Space Pressure Measurements In An In Vitro Spinal Stenosis Model: Implications On Syringomyelia Theories, Bryn Martin, Richard Labuda, Thomas Royston, John Oshinski, Bermans Iskandar, Francis Loth Apr 2015

Spinal Subarachnoid Space Pressure Measurements In An In Vitro Spinal Stenosis Model: Implications On Syringomyelia Theories, Bryn Martin, Richard Labuda, Thomas Royston, John Oshinski, Bermans Iskandar, Francis Loth

Dr. Bryn Martin

Full explanation for the pathogenesis of syringomyelia (SM), a neuropathology characterized by the formation of a cystic cavity (syrinx) in the spinal cord (SC), has not yet been provided. It has been hypothesized that abnormal cerebrospinal fluid (CSF) pressure, caused by subarachnoid space (SAS) flow blockage (stenosis), is an underlying cause of syrinx formation and subsequent pain in the patient.


Syringomyelia: A Review Of The Biomechanics, N. Elliott, C. Bertram, Bryn Martin, A. Brodbelt Apr 2015

Syringomyelia: A Review Of The Biomechanics, N. Elliott, C. Bertram, Bryn Martin, A. Brodbelt

Dr. Bryn Martin

Syringomyelia is a neurological disorder caused by the development of one or more macroscopic fluid-filled cavities in the spinal cord. While the aetiology remains uncertain, hydrodynamics appear to play a role. This has led to the involvement of engineers, who have modelled the system in silico and on the bench. In the process, hypotheses from the neurosurgical literature have been tested, and others generated, while aspects of the system mechanics have been clarified. The spinal cord is surrounded by cerebrospinal fluid (CSF) which is subject both to the periodic excitation of CSF expelled from the head with each heartbeat, and ...


Coupled Vibration Of A Fluid‐Filled And Submerged Vascular Tube With Internal Transitional/ Turbulent Flow Due To A Constriction, Yigit Yazicioglu, Thomas Royston, Todd Spohnholtz, Bryn Martin, Francis Loth Apr 2015

Coupled Vibration Of A Fluid‐Filled And Submerged Vascular Tube With Internal Transitional/ Turbulent Flow Due To A Constriction, Yigit Yazicioglu, Thomas Royston, Todd Spohnholtz, Bryn Martin, Francis Loth

Dr. Bryn Martin

No abstract provided.


Mr Measurement Of Cerebrospinal Fluid Velocity Wave Speed In The Spinal Canal, Wojciech Kalata, Bryn Martin, John Oshinski, Michael Jerosch-Herold Apr 2015

Mr Measurement Of Cerebrospinal Fluid Velocity Wave Speed In The Spinal Canal, Wojciech Kalata, Bryn Martin, John Oshinski, Michael Jerosch-Herold

Dr. Bryn Martin

Noninvasive measurement of the speed with which the cere-brospinal fluid (CSF) velocity wave travels through the spinal canal is of interest as a potential indicator of CSF system pressure and compliance, both of which may play a role in the development of craniospinal diseases. However, measurement of CSF velocity wave speed (VWS) has eluded researchers primarily due to either a lack of access to CSF velocity measurements or poor temporal resolution.


Syringomyelia Hydrodynamics: An In Vitro Study Based On In Vivo Measurements, Bryn Martin, Wojciech Kalata, Francis Loth, Thomas Royston, John Oshinski Apr 2015

Syringomyelia Hydrodynamics: An In Vitro Study Based On In Vivo Measurements, Bryn Martin, Wojciech Kalata, Francis Loth, Thomas Royston, John Oshinski

Dr. Bryn Martin

A simplified in vitro model of the spinal canal, based on in vivo magnetic resonance imaging, was used to examine the hydrodynamics of the human spinal cord and subarachnoid space with syringomyelia. In vivo magnetic resonance imaging (MRI) measurements of subarachnoid (SAS) geometry and cerebrospinal fluid velocity were acquired in a patient with syringomyelia and used to aid in the in vitro model design and experiment. The in vitro model contained a fluid-filled coaxial elastic tube to represent a syrinx.


Transverse Vibration Of Prestressed Beams: An Experimental Technique For The Determination Of Dynamic Viscoelastic Material Properties Of Tissue Mimicking Materials, Yigit Yazicioglu, Bryn Martin, Karen Navarro-Castillo, Umit Kutluay, Thomas Royston Apr 2015

Transverse Vibration Of Prestressed Beams: An Experimental Technique For The Determination Of Dynamic Viscoelastic Material Properties Of Tissue Mimicking Materials, Yigit Yazicioglu, Bryn Martin, Karen Navarro-Castillo, Umit Kutluay, Thomas Royston

Dr. Bryn Martin

An experimental dynamic material property identification technique is presented that is based on the theoretical formulations of a vibrating pre-stressed beam. The technique determines the viscoelastic material properties of tissue mimicking materials that govern their dynamic behavior. Results are presented for a silicone based material (CF11-2188 Nusil Silicone Technology, Carpinteria, CA) that is in the form of a thick string held between fixed supports under tensile pre-stress.


Acoustic Radiation From A Fluid-Filled, Subsurface Vascular Tube With Internal Turbulent Flow Due To A Constriction, Yigit Yazicioglu, Thomas Royston, Todd Spohnholtz, Bryn Martin, Francis Loth, Hisham Bassiouny Apr 2015

Acoustic Radiation From A Fluid-Filled, Subsurface Vascular Tube With Internal Turbulent Flow Due To A Constriction, Yigit Yazicioglu, Thomas Royston, Todd Spohnholtz, Bryn Martin, Francis Loth, Hisham Bassiouny

Dr. Bryn Martin

The vibration of a thin-walled cylindrical, compliant viscoelastic tube with internal turbulent flow due to an axisymmetric constriction is studied theoretically and experimentally. Vibration of the tube is considered with internal fluid coupling only, and with coupling to internal-flowing fluid and external stagnant fluid or external tissue-like viscoelastic material. The theoretical analysis includes the adaptation of a model for turbulence in the internal fluid and its vibratory excitation of and interaction with the tube wall and surrounding


Towards Non-Invasive Assessment Of The Elastic Properties Of The Spinal Aqueduct, Bryn Martin, Thomas Royston, John Oshinski, Francis Loth Apr 2015

Towards Non-Invasive Assessment Of The Elastic Properties Of The Spinal Aqueduct, Bryn Martin, Thomas Royston, John Oshinski, Francis Loth

Dr. Bryn Martin

Analytical models are developed for cerebrospinal fluid (CSF) pressure wave propagation speed based on viscoelastic properties and geometry of the subarachnoid space (SAS). The models were compared to experimental tests on various compliant coaxial tube phantom models of the spinal SAS having different thicknesses and mechanical properties, with the ultimate goal of developing a noninvasive in vivo technique for determining the elastic properties of the spinal aqueduct.


Where Do We Stand On The Relationship Between Tau Biomarkers And Mild Cognitive Impairment?, Bryn Martin, Philip Allen Apr 2015

Where Do We Stand On The Relationship Between Tau Biomarkers And Mild Cognitive Impairment?, Bryn Martin, Philip Allen

Dr. Bryn Martin

We present an editorial on a recent publication by Amlien et al. [2013] in which diffusion tensor imaging (DTI) was used to quantify longitudinal decreases in fractional anisotropy (FA) and increased radial diffusivity (DR) in patients with mild cognitive impairment (MCI). These longitudinal alterations were found to be greater in MCI patients with high cerebrospinal fluid (CSF) tau levels at baseline and greater than healthy controls. Amlien et al. concluded that tau levels were an important early biomarker for predicting rate of disease progression and outcome. The results of this study are an interesting finding for possible predictive use ...


Assessment Of Aortic Graft Impact On Hemodynamics, Orestis Vardoulis, Bryn Martin, Philippe Reymond, Nikos Stergiopulos Apr 2015

Assessment Of Aortic Graft Impact On Hemodynamics, Orestis Vardoulis, Bryn Martin, Philippe Reymond, Nikos Stergiopulos

Dr. Bryn Martin

In vivo studies have revealed that aortic grafts augment heart load and alter blood pressure and flow waveforms [1]. A one-dimensional model of the arterial tree was developed in order to analyze the different mechanisms by which proximal and distal aortic grafts affect hemodynamics. Graft compliance and properties were based on in vitro tests. Predicted pressures at the aortic root were compared for the control, proximal and distal graft case.


Magnetic Resonance 4d Flow Analysis Of Cerebrospinal Fluid Dynamics In Chiari I Malformation With And Without Syringomyelia, Alexander Bunck, Jan Kroger, Alena Juettner, Angela Brentrup, Barbara Fiedler, Gerard Crelier, Bryn Martin, Walter Heindel, David Maintz, Wolfram Scwindt, Thomas Niederstadt Apr 2015

Magnetic Resonance 4d Flow Analysis Of Cerebrospinal Fluid Dynamics In Chiari I Malformation With And Without Syringomyelia, Alexander Bunck, Jan Kroger, Alena Juettner, Angela Brentrup, Barbara Fiedler, Gerard Crelier, Bryn Martin, Walter Heindel, David Maintz, Wolfram Scwindt, Thomas Niederstadt

Dr. Bryn Martin

Objective

To analyse cerebrospinal fluid (CSF) hydrodynamics in patients with Chiari type I malformation (CM) with and without syringomyelia using 4D magnetic resonance (MR) phase contrast (PC) flow imaging.


Mr Measurement Of Pulse Wave Velocity In The Spinal Canal, Bryn Martin, Francis Loth, Wojciech Kalata, John Oshinski Apr 2015

Mr Measurement Of Pulse Wave Velocity In The Spinal Canal, Bryn Martin, Francis Loth, Wojciech Kalata, John Oshinski

Dr. Bryn Martin

Non-invasive measurement of pulse wave velocity (PWV) in the cerebrospinal fluid (CSF) system is of interest as a potential indicator of subarachnoid space pressure and compliance, both of which play a role in the development of craniospinal diseases. However, measurement of PWV has eluded researchers primarily due to either a lack of access to CSF velocity measurements or to poor temporal resolution.


Hydrodynamics Of Cerebrospinal Fluid In Spinal Canal With Chiari Malformation And Syringomyelia, Wojciech Kalata, Bryn Martin, Josh Oshinski, Francis Loth Apr 2015

Hydrodynamics Of Cerebrospinal Fluid In Spinal Canal With Chiari Malformation And Syringomyelia, Wojciech Kalata, Bryn Martin, Josh Oshinski, Francis Loth

Dr. Bryn Martin

No abstract provided.


Method For Dynamic Material Property Characterization Of Soft-Tissue-Mimicking Isotropic Viscoelastic Materials Using Fractional Damping Models, Bryn Martin, Umit Kutluay, Yigit Yazicioglu Apr 2015

Method For Dynamic Material Property Characterization Of Soft-Tissue-Mimicking Isotropic Viscoelastic Materials Using Fractional Damping Models, Bryn Martin, Umit Kutluay, Yigit Yazicioglu

Dr. Bryn Martin

No abstract provided.


The Effect Of Continuous Positive Airway Pressure On Total Cerebral Blood Flow In Healthy Awake Volunteers, Theresia Yiallourou, Celine Odier, Raphael Heinzer, Lorenz Hirt, Bryn Martin, Nikolaos Stergiopulos Apr 2015

The Effect Of Continuous Positive Airway Pressure On Total Cerebral Blood Flow In Healthy Awake Volunteers, Theresia Yiallourou, Celine Odier, Raphael Heinzer, Lorenz Hirt, Bryn Martin, Nikolaos Stergiopulos

Dr. Bryn Martin

Continuous positive airway pressure (CPAP) is the gold standard treatment for obstructive sleep apnea. However, the physiologic impact of CPAP on cerebral blood flow (CBF) is not well established. Ultrasound can be used to estimate CBF, but there is no widespread accepted protocol. We studied the physiologic influence of CPAP on CBF using a method integrating arterial diameter and flow velocity (FV) measurements obtained for each vessel supplying blood to the brain.


Ventricle Equilibrium Position In Healthy And Normal Pressure Hydrocephalus Brains Using An Analytical Model, K. Shahim, J. Drezet, Bryn Martin, S. Momjian Apr 2015

Ventricle Equilibrium Position In Healthy And Normal Pressure Hydrocephalus Brains Using An Analytical Model, K. Shahim, J. Drezet, Bryn Martin, S. Momjian

Dr. Bryn Martin

The driving force that causes enlargement of the ventricles remains unclear in case of normal pressure hydrocephalus (NPH). Both healthy and NPH brain conditions are characterized by a low transparenchymal pressure drop, typically 1 mm Hg. The present paper proposes an analytical model for normal and NPH brains using Darcy’s and Biot’s equations and simplifying the brain geometry to a hollow sphere with an internal and external radius. Self-consistent solutions for the large deformation problem that is associated with large ventricle dilation are presented and the notion of equilibrium or stable ventricle position is highlighted for both healthy ...


Comparison Of 4d Phase-Contrast Mri Flow Measurements To Computational Fluid Dynamics Simulations Of Cerebrospinal Fluid Motion In The Cervical Spine, Theresia Yiallourou, Jan Robert Kroger, Nikolaos Stergiopulos, David Maintz, Bryn A. Martin, Alexander C. Bunck Apr 2015

Comparison Of 4d Phase-Contrast Mri Flow Measurements To Computational Fluid Dynamics Simulations Of Cerebrospinal Fluid Motion In The Cervical Spine, Theresia Yiallourou, Jan Robert Kroger, Nikolaos Stergiopulos, David Maintz, Bryn A. Martin, Alexander C. Bunck

Dr. Bryn Martin

Cerebrospinal fluid (CSF) dynamics in the cervical spinal subarachnoid space (SSS) have been thought to be important to help diagnose and assess craniospinal disorders such as Chiari I malformation (CM). In this study we obtained time-resolved three directional velocity encoded phase-contrast MRI (4D PC MRI) in three healthy volunteers and four CM patients and compared the 4D PC MRI measurements to subject-specific 3D computational fluid dynamics (CFD) simulations. The CFD simulations considered the geometry to be rigid-walled and did not include small anatomical structures such as nerve roots, denticulate ligaments and arachnoid trabeculae. Results were compared at nine axial planes ...


Information Theoretic Analysis For Input Vector Selection In Black Box Modeling, Bryn Martin, Peter Meckl, Benjamin Zwissler Apr 2015

Information Theoretic Analysis For Input Vector Selection In Black Box Modeling, Bryn Martin, Peter Meckl, Benjamin Zwissler

Dr. Bryn Martin

No abstract provided.