title: Implantable electrode structures and their RF effects in MRI machines

authors: McCabe, Steven Owen

subjects: Deep Brain Stimulator (DBS)

abstract: Medical implants incorporating long insulated conductors can generate a serious heating hazard to a patient undergoing a Magnetic Resonance Imaging (MRI) scan. Under the high-power RF field from an MRI machine, the conductors can behave as antennas and concentrate energy into small regions of body tissue, leading to excessive joule heating. Neurostimulator implants that employ long electrode leads such as those for Deep Brain Stimulation (DBS) and Spinal Cord Stimulation (SCS), are highly susceptible to this RF hazard. Patients with these implants are generally contraindicated from MRI.

This thesis examines the heating phenomenon and identifies a variety of methods to mitigate the hazard and gain implant leads MRI safety. Techniques such as thin insulation, surface roughening, and auxiliary decoy filars are explored, with the latter shown to be especially effective at providing safety. Designs are first modelled with electromagnetic simulation software then experimentally proven inside of a gelled saline phantom within a 3T MRI machine. A lab-based measurement method is also established to enable rapid low-cost testing of prototype lead designs.

text: Implantable electrode structures and their RF effects in MRI machines Medical implants incorporating long insulated conductors can generate a serious heating hazard to a patient undergoing a Magnetic Resonance Imaging (MRI) scan. Under the high-power RF field from an MRI machine, the conductors can behave as antennas and concentrate energy into small regions of body tissue, leading to excessive joule heating. Neurostimulator implants that employ long electrode leads such as those for Deep Brain Stimulation (DBS) and Spinal Cord Stimulation (SCS), are highly susceptible to this RF hazard. Patients with these implants are generally contraindicated from MRI.

This thesis examines the heating phenomenon and identifies a variety of methods to mitigate the hazard and gain implant leads MRI safety. Techniques such as thin insulation, surface roughening, and auxiliary decoy filars are explored, with the latter shown to be especially effective at providing safety. Designs are first modelled with electromagnetic simulation software then experimentally proven inside of a gelled saline phantom within a 3T MRI machine. A lab-based measurement method is also established to enable rapid low-cost testing of prototype lead designs.

year: 2019

title: The effects of alkaline digestion, bleaching and ultrasonication treatment of fibre on 3D printed harakeke fibre reinforced polylactic acid composites

authors: Beg, Mohammad Dalour Hossen

subjects: Biocomposites

abstract: This paper documents an investigation of the effects of fibre treatment on New Zealand flax (harakeke) fibre reinforced polylactic acid (PLA) composites. The raw fibre was alkali digested, followed by bleaching and then modified with ultrasonication. Alkali treatment removed lignin and other non-cellulosic components and partially separated fibre bundles while bleaching further removed lignin and improved the separation of elementary fibres, resulting in microfibres with a cellulose content 92 wt%. With subsequent ultrasonication, microfibrils could be seen partially separated (defibrillation) at fibre surfaces. Treated fibres were compounded with PLA at a fibre loading of 30 wt% and extruded into composite filaments. Filaments from alkali, bleached and ultrasonication-treated fibres had smooth surfaces, which translated into high-quality printability along with good mechanical performance. The combination of chemically treated microfibres with selective surface defibrillation using ultrasonication and fibre alignment induced by the printing process resulted in 3D printed samples with a tensile strength of 79 MPa and Young’s modulus of 8.7 GPa, which are the highest values reported so far for 3D printed PLA-based composites reinforced with short fibres.

text: The effects of alkaline digestion, bleaching and ultrasonication treatment of fibre on 3D printed harakeke fibre reinforced polylactic acid composites This paper documents an investigation of the effects of fibre treatment on New Zealand flax (harakeke) fibre reinforced polylactic acid (PLA) composites. The raw fibre was alkali digested, followed by bleaching and then modified with ultrasonication. Alkali treatment removed lignin and other non-cellulosic components and partially separated fibre bundles while bleaching further removed lignin and improved the separation of elementary fibres, resulting in microfibres with a cellulose content 92 wt%. With subsequent ultrasonication, microfibrils could be seen partially separated (defibrillation) at fibre surfaces. Treated fibres were compounded with PLA at a fibre loading of 30 wt% and extruded into composite filaments. Filaments from alkali, bleached and ultrasonication-treated fibres had smooth surfaces, which translated into high-quality printability along with good mechanical performance. The combination of chemically treated microfibres with selective surface defibrillation using ultrasonication and fibre alignment induced by the printing process resulted in 3D printed samples with a tensile strength of 79 MPa and Young’s modulus of 8.7 GPa, which are the highest values reported so far for 3D printed PLA-based composites reinforced with short fibres.

year: 2023-03

title: Defining indigenous trade: A working paper incorporating Māori and indigenous perspectives

authors: McLellan, Georgia

abstract: This working paper is part of a New Zealand Government–funded research project titled ‘Tauhokohoko: Enabling mana motuhake through Indigenous trade’ (Tauhokohoko), which was developed by the University of Waikato and Te Rōpū Taumata Charitable Trust (Te Taumata). The paper was prepared by the Tauhokohoko Research Aim 1.3 team and sets out a working definition of ‘Indigenous trade’.

The Tauhokohoko Research Aim 1.3 team acknowledges that the term ‘Indigenous’ can be problematic, since it collectivises the experiences of all Indigenous peoples. The project acknowledges the diverse realities of Indigenous peoples and strives to use the term in an inclusive way. Despite the existence of fraught relations between Indigenous peoples and postcolonial trade practices, Indigenous peoples have always had their own trade practices and relations grounded in Indigenous ways of being, knowing and doing. Within contemporary economies, Indigenous peoples are increasingly turning to international trade to meet their economic, social and cultural aspirations.

The Tauhokohoko Research Aim 1.3 team believes that Indigenous trade, when practiced in the right way, can be used as a tool for enhancing Indigenous self-determination and collective wellbeing. This paper outlines a tentative definition of ‘Indigenous trade’ for research purposes and provides grounded examples of Indigenous trade that fit within that tentative definition. The Tauhokohoko project is concerned primarily with the involvement of Indigenous peoples in international trade as a financial activity; however, the tentative definition encompasses financial, non financial, tangible and non-tangible forms of exchange. The paper ends by outlining the key literature that informs the working definition of ‘Indigenous trade’, including perspectives on the origins of international trade and Indigenous trade, international business and entrepreneurship, and Indigenous economies.

text: Defining indigenous trade: A working paper incorporating Māori and indigenous perspectives This working paper is part of a New Zealand Government–funded research project titled ‘Tauhokohoko: Enabling mana motuhake through Indigenous trade’ (Tauhokohoko), which was developed by the University of Waikato and Te Rōpū Taumata Charitable Trust (Te Taumata). The paper was prepared by the Tauhokohoko Research Aim 1.3 team and sets out a working definition of ‘Indigenous trade’.

The Tauhokohoko Research Aim 1.3 team acknowledges that the term ‘Indigenous’ can be problematic, since it collectivises the experiences of all Indigenous peoples. The project acknowledges the diverse realities of Indigenous peoples and strives to use the term in an inclusive way. Despite the existence of fraught relations between Indigenous peoples and postcolonial trade practices, Indigenous peoples have always had their own trade practices and relations grounded in Indigenous ways of being, knowing and doing. Within contemporary economies, Indigenous peoples are increasingly turning to international trade to meet their economic, social and cultural aspirations.

The Tauhokohoko Research Aim 1.3 team believes that Indigenous trade, when practiced in the right way, can be used as a tool for enhancing Indigenous self-determination and collective wellbeing. This paper outlines a tentative definition of ‘Indigenous trade’ for research purposes and provides grounded examples of Indigenous trade that fit within that tentative definition. The Tauhokohoko project is concerned primarily with the involvement of Indigenous peoples in international trade as a financial activity; however, the tentative definition encompasses financial, non financial, tangible and non-tangible forms of exchange. The paper ends by outlining the key literature that informs the working definition of ‘Indigenous trade’, including perspectives on the origins of international trade and Indigenous trade, international business and entrepreneurship, and Indigenous economies.

year: 2025-12-10