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Papers by Liam Morris

Abdominal Aortic Aneurysms (AAA) is one of the major cardiovascular diseases that can lead to dea... more Abdominal Aortic Aneurysms (AAA) is one of the major cardiovascular diseases that can lead to death if left untreated. An AAA is defined as a permanent and irreversible localised dilation of the infrarenal aorta. Aneurysms can result from accidents, arteriosclerosis, and high blood pressure or as a congenital disease. There are currently two surgical treatments for acute AAA, open surgery or minimally invasive repair (also known as the endovascular repair procedure). The objective of both methods is to isolate the aneurysm sac from the systemic blood pressure and flow to minimise the risk of arterial wall rupture [1]. Preliminary results for endovascular procedures have been promising with short-term results comparable with conventional surgical repair. This is especially the case for patients with small and medium sized AAAs. Long-term results are not so encouraging with stent graft migration, endoleaks, material failure and aneurysm rupture all being reported [2]. A well known complication with this endovascular procedure is the late migration of the graft in which most of the migrations are diagnosed after the first 12 months after the procedure. Multi-factors, including iliac bifurcation angle, stent graft size, blood pressure, stent graft wall compliance, iliac branch curvature, and neck length have been reported to influence device migration. The drag force acting on the bifurcated stent grafts (SG) is one of the main reasons for stent graft migration [3].

Abdominal aortic aneurysm (AAA) represents an asymptomatic cardiovascular type of disease, that i... more Abdominal aortic aneurysm (AAA) represents an asymptomatic cardiovascular type of disease, that is diagnosed in elder people over 60 years old. It is characterised by a ballooning of the abdominal aorta, which grows, at different rates in different patients. If left untreated, it will rupture causing severe internal bleeding, which can lead to shock or death [1]. Medical devices such as bifurcated stent grafts (SG) are used for the treatment of this disease. To help improve SG performance, biomedical engineers design benchtop models for testing.

Progress In Electromagnetics Research B

Phantoms provide valuable test platforms for developing medical devices. Solid materials in parti... more Phantoms provide valuable test platforms for developing medical devices. Solid materials in particular allow fabrication of stable and robust models. This paper presents a novel, anatomically realistic, multi-layered head phantom made from dielectrically accurate, stable, easily mouldable, low-cost tissue-mimicking materials for testing of microwave diagnostic systems. Also incorporated is a mechanism for inserting reconfigurable lesions and a novel circulatory system modelling physiology. Tissue-mimicking materials composed of graphite, carbon black, and polyurethane with small volumes of acetone or isopropanol were fabricated and dielectric properties were measured across the 1-8.5 GHz band. The tissuemimicking material properties were adjusted until their dielectric properties matched those of reference values for target tissues of interest, thereby emulating: weighted aggregates of head tissues external to the brain, tissues comprising the brain, and blood. 3D printed anatomically realistic head and brain moulds cast the phantom mixtures for each layer. Cylindrical holes in the brain layer allow insertion of pathological lesion phantoms, such as haemorrhages. Tubing embedded in the brain layer forms a symmetrical loop providing a novel simplistic model of circulation. The resulting head phantom is anatomically realistic, dielectrically stable, enables pathology modelling, and has, uniquely, a circulatory loop. This novel head phantom provides a valuable test platform for microwave diagnostic studies.

Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, 2016

Coronary artery disease is one of the leading causes of cardiovascular deaths worldwide. Approxim... more Coronary artery disease is one of the leading causes of cardiovascular deaths worldwide. Approximately 70% of patients requiring coronary revascularisation receive endovascular stents. The endovascular procedure is the preferred option due to its minimally invasive nature when compared to open heart surgery. Stent delivery is paramount for the success of the endovascular procedure. Catheter delivery forces within tortuous blood vessels can produce vasoconstriction and injury, resulting in reactive intimal proliferation or distal embolisation associated with end-organ ischaemia and infarction. Trackability is evaluated by most medical device companies for further development of their delivery systems. Relevant device design attributes must be tested in settings which simulate aspects of the intended use conditions, such as vessel geometry and compliance. Various tortuosity parameters are used to facilitate endovascular intervention planning. This study assessed the significance and c...

The Journal of the Louisiana State Medical Society : official organ of the Louisiana State Medical Society

A 52-year-old hypertensive female transferred from an outside hospital to our unit for management... more A 52-year-old hypertensive female transferred from an outside hospital to our unit for management of an acute coronary syndrome. She presented initially with sudden onset severe chest pain radiating to the neck, right jaw, and right arm, associated with nausea and shortness of breath.

ASME 2009 Summer Bioengineering Conference, Parts A and B, 2009

ABSTRACT Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Associat... more ABSTRACT Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal

ASME 2011 Summer Bioengineering Conference, Parts A and B, 2011

ABSTRACT The circle of Willis (CoW) is a complex arterial network comprising of major cerebral ar... more ABSTRACT The circle of Willis (CoW) is a complex arterial network comprising of major cerebral arteries that converge to form a pentagonal arrangement as shown in Figure 1(A). This arterial network supplies oxygen-enriched blood to the brain. An incomplete CoW can exist in up to 50% of cases [1]. These missing vessels can be accommodated by the collateral flow feature within the CoW configuration. In certain circumstances, anatomical variations within the CoW can result in undesirable flow patterns [2–3]. It is unclear from the literature what effects these variations can have on blood flow collision paths within a complete CoW.

Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine, 2014

The variation in computational assumptions for analysing abdominal aortic aneurysm haemodynamics ... more The variation in computational assumptions for analysing abdominal aortic aneurysm haemodynamics can influence the desired output results and computational cost. Such assumptions for abdominal aortic aneurysm modelling include static/transient pressures, steady/transient flows and rigid/compliant walls. Six computational methods and these various assumptions were simulated and compared within a realistic abdominal aortic aneurysm model with and without intraluminal thrombus. A full transient fluid-structure interaction was required to analyse the flow patterns within the compliant abdominal aortic aneurysms models. Rigid wall computational fluid dynamics overestimates the velocity magnitude by as much as 40%-65% and the wall shear stress by 30%-50%. These differences were attributed to the deforming walls which reduced the outlet volumetric flow rate for the transient fluid-structure interaction during the majority of the systolic phase. Static finite element analysis accurately app...

International journal for numerical methods in biomedical engineering, 2013

Endovascular repair is now a recognised procedure for treating abdominal aortic aneurysms. Howeve... more Endovascular repair is now a recognised procedure for treating abdominal aortic aneurysms. However, post-operative complications such as stent graft migration and thrombus may still occur. To assess these complications numerically, the correct input boundary conditions, which include the full human aorta with associated branching, should be included. Four patient-specific computed tomography scanned bifurcated stent grafts (SGs) were modelled and attached onto a full human aorta, which included the ascending, aortic arch and descending aortas. Two of the SG geometries had a twisted leg configuration, while the other two had conventional nontwisted leg configurations. Computational fluid dynamics was completed for both geometries and the hemodynamics assessed. The complexity of the flow patterns and secondary flows were influenced by the inclusion of the full human aorta at the SG proximal section. During the decelerating phase significant recirculations occurred along the main body ...

International journal for numerical methods in biomedical engineering, 2013

ASME 2009 Summer Bioengineering Conference, Parts A and B, 2009

ASME 2012 Summer Bioengineering Conference, Parts A and B, 2012

ABSTRACT The CABER group is based at the University of Limerick and for the past 15 years has pri... more ABSTRACT The CABER group is based at the University of Limerick and for the past 15 years has primarily focused on cardiovascular hemodynamics research. A key element of the group’s research has always been in the application of CFD to idealized and patient specific geometries. Recently the group has changed commercial CFD software’s and so currently has access to 2 packages, Star-CCM+ 6.02.007 and Ansys Fluent 12.1.4. For this challenge it was therefore decided to compare both software packages and also to examine variability between users. The Fluent simulations were conducted by postgraduate researcher Adrian Lynch and the Star CCM software was utilized independently by postgraduate researchers Jennifer Costello and Leonard Browne.

Biomechanical Systems Technology, 2007

CHAPTER 7 NUMERICAL AND EXPERIMENTAL TECHNIQUES FOR THE STUDY OF BIOMECHANICS IN THE ARTERIAL SYS... more CHAPTER 7 NUMERICAL AND EXPERIMENTAL TECHNIQUES FOR THE STUDY OF BIOMECHANICS IN THE ARTERIAL SYSTEM THOMAS P. O&#x27;BRIEN, MICHAEL T. WALSH, LIAM MORRIS, PIERCE A. GRACE, EAMON G. KAVANAGH and TIM M. McGLOUGHLIN∗ Centre ...

ASME 2007 Summer Bioengineering Conference, 2007

ABSTRACT Abdominal aortic aneurysm (AAA) is treated with two methods — open repair and endovascul... more ABSTRACT Abdominal aortic aneurysm (AAA) is treated with two methods — open repair and endovascular repair. The endovascular method has many advantages over open repair, such as shorter hospital stays, non-invasiveness and shorter recovery times but there have been several reported problems with these devices, including graft migration, endoleaks and limb occlusion. Graft migration occurs in approximately 10% of grafts [1] while limb occlusion occurs in 11% of cases [2]. The consequence of endoleaks and migration not being treated may be the ultimate rupture of the aneurysm. The occlusion of iliac graft limbs can lead to peripheral vascular problems such as ischemia and gangrene. Some of the influencing factors on migration, occlusion and endoleaks are fluid, drag, stent-graft angulation and flow characteristics such as Deans flow.