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Medical Physics and Biomedical Engineering

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MPHY0037: Medical Electronics and Neural Engineering

Module information

Unit value: 0.5
Year of study: 3 or 4
Term: 2
Course organiser: Professor Nick Donaldson
Second examiner: Dr Anne Vanhoest

Purpose

This course brings together material from engineering, physics and physiology which is relevant to situations in which electronic devices are in direct contact with the body. Body contact is common in clinical practice with medical devices being used for recording bipotentials, such as ECG, and for stimulation. The course focusses on interaction with the nervous system. This is relevant to rehabilitation, intensive care, clinical neurophysiology, neuroprosthetics, etc. It should be useful:

  • To medical students who will encounter these applications in clinical practice
  • To students who intend to go on to biomedical research
  • To engineering students who go on to specify, design, test or use clinical electrical equipment.

Usually, there are about equal numbers from engineering, the sciences, and intercalated medical students.

Year 3 and Level 7 (previously called M-level) variants

This course, taught during term 2, forms part of the Electronics with Medical Electronics (MEng) and Medical Physics & Bioengineering (MSci and Intercalated BSc) undergraduate degrees. For Electronics with Medical Electronics students this is a compulsory 3rd year course and provides core information which will be drawn upon during the final year. It is an optional course for other 3rd and 4th year Electronic Engineering students, and 4th year Physics students. For Medical students it is also optional.

This course can be taken in Year 3 as MPHY3013 or in Year 4 as a Level 7 (previously called M-level) variant called MPHYM013. The two variants differ in the amount of coursework, and the pass mark for the Level 7 variant is 50%.

Aims

The taught material is not concerned with how the electronic devices work but what they must do for adequate performance and safety. No prior knowledge of electronics is necessary. However, some circuit theory including complex impedance is essential. This is a prerequisite and you should test your knowledge by doing the six quizzes before the start of term. If you have not used complex numbers before, you will have to learn this intriguing maths and you will benefit by the ease with which you will be able to do impedance problems during the course.

(The medical students are often apprehensive about complex impedance, having done little maths recently. However, my experience is that medical students are perfectly able to grasp this method and get high grades from this module.)

This year (2015-16) we are continuing with flipped lectures so that we have more time in class to do the sort of problems that come up in the exam. The five main topics that we will cover are: nerves (anatomy, biophysics, physiology), amplifiers and filters, electrodes, biopotential recording and stimulation. There are three practicals (which will take place in the Undergraduate Lab of the Department (Medical Physics & Biomedical Engineering) and there will be at least one visit to a local hospitals to see how the methods are applied. 

Our aim is to give about one hour of prep for each class and there are two classes per week (i.e.  maximum of 2 ×2 hours). This prep will include reading notes, doing coursework, writing up lab-work, but also watching movies on the applications in neural engineering.

Coursework will be set on Moodle as multiple-choice questions: as soon as you choose an answer, Moodle informs you whether you were correct and which the correct answer was, if you were wrong. This is aimed to help you learn and to get full marks you only have to attempt all the coursework.

Objectives

  • To impart knowledge and understanding of the origins of electrophysiological signals and their characteristics.
  • To impart knowledge and understanding of electrodes.
  • To impart knowledge and understanding of electrical stimulation.
  • To impart knowledge and understanding of electric shock hazards and safety devices.
  • To impart knowledge and understanding of the characteristics and limitations of biomedical amplifiers for acquisition of electrophysiological signals, and to demonstrate how these characteristics are derived from an understanding of electrophysiology, electrode properties and electrical hazards.
  • To enable students to apply knowledge of stimulators and biomedical amplifiers during laboratory practicals and develop laboratory skills.
  • To illustrate and emphasise practical applications by visits to local hospitals.
  • To develop problem solving and analysis skills using the knowledge accumulated from this course.
  • To facilitate and develop communication skills and group work.
  • To enable students to take responsibility for their own learning.

Teaching and exams

Hours specific to the course:

  • Lectures: 26 hours.
  • Private reading: 25 hours.
  • Problem classes/tutorials: 2 hours (more if requested).
  • Laboratory work: 12 hours (3 experiments: 3 x 3 hour "mini-labs", 3 hours writing up).
  • Hospital department visits: 2 hours (2 x 1 hour visits).
  • Problem sheets: 20 hours (3 problem sheets).
  • Revision: 20 hours.


For MPHY3013 students, the assessment will consist of:

  • 1 Unseen written examination (3 hours) worth 80% of the total course mark.
  • Coursework completed during term-time worth 20% of the total course mark.

For MPHYM013 students, the assessment will consist of:

  • 1 Unseen written examination (3 hours) worth 70% of the total course mark.
  • Coursework completed during term-time worth 20% of the total course mark.
  • Presentation of a Scientific paper worth 10% of the total course mark

Prerequisites

We assume that you have met the minimum entry requirements for our undergraduate degree programmes (i.e. A level Mathematics (grade A preferred), Physics and one other A level at ABB or above, or equivalent. If you feel you meet the prerequisites through a non-standard route, please contact the module organiser. All variants of the modules (MPHY3013 and MPHYM013) have the same prerequisites.

In past years, a particular difficulty for students on this course has been knowledge of transformers, complex number arithmetic and algebra, and its application to impedance calculations. We have therefore introduced six quizzes for students to do before the start of the course. To qualify for the course, you should pass 5 out of them (see Moodle page for more details).

Specific knowledge assumed

Mathematics: Familiarity with trigonometry, manipulation of equations, basic calculus, exponentials, log and loglog graphs.

Physics: Basic electricity theory: Ohm’s Law, Kirchhoff’s Laws, resistors and capacitors, resistivity. Prior understanding of amplifiers, alternating current theory and noise will be helpful.

Engineering: None

Anatomy & Physiology: None, though prior knowledge will be helpful.

Medicine: None.

Other: None, but be aware that success in this module requires an ability to use concepts that you have been taught before in unfamiliar situations.

Description

The lectures are in four groups: electrical safety, amplifiers, electrodes and nerves. There are three practicals (which take place in the Undergraduate Lab on the 6 th Floor of the Roberts Building) and usually two visits to local hospitals to see how the methods are applied (e.g. Clinical neurophysiology, Cochlear implants, UCH Equipment Management). Three question sheets are set for coursework.

The course begins with an overview of the subject of Medical Electronics, discussing its scope and relevance to Engineers and Medics.  Fundamental knowledge of physiological signal evolution and characteristics are reviewed. 

The section on safety considers electricity supply, physiological effects of electricity on the body, sources of electrical hazards, issues of safety and safety devices.

The following section is about biomedical amplifiers. Requirements and characteristics are described. Sources of interference are discussed with emphasis on 50Hz mains interference. 

The section on electrodes considers types of electrode and the resistance to ionic current flow in the tissue. The electrode-electrolyte interface is described at equilibrium and polarisable and non-polarisable electrodes are considered for silver/silver chloride and platinum respectively. Electrical models of the electrodes are introduced.  Volume conductor effects are discussed leading to a brief introduction to recorded neural signals.The next section imparts knowledge on electrical stimulation. The response of muscles to artificially-activated nerves is considered, the design of stimulators and functional uses.  Specifically, the behaviour of neurons is studied, by considering resting potentials and action potentials. Finally, applications of recording biopotential signals and electrical stimulation are considered. Examples include recording electrical signals from the heart (ECG), muscles (EMG), nerves (ENG) and brain (EEG) and the use of stimulators for defibrillators, pacemakers, cochlear implants and restoring loss of limb movement.

The course subject matter is conveyed through lectures, problem solving, student preparation and presentation of seminars and tutorials, demonstrations, "mini-labs" and recommended reading. The mini-labs provide the opportunity to study electrical activity generated by the students' own muscles (EMG) during movement and to measure nerve conduction velocity. They also develop practical skills, teach students to manage their time to achieve a required task, facilitate team work, and provide the opportunity to apply theoretical principles taught during the course.

Brief Syllabus

Lectures (3 hours per week during Term 2)

  1. Introduction to Medical Electronics.
  2. Electricity Supply and Sources of Hazard. Experimental results; Internal, External; Threshold levels; Electric Shock hazards (vacuum cleaner example, etc); Earth Leakage and "Patient" leakage; Isolation and circuit breakers.
  3. Biomedical Amplifiers. Characteristics of biomedical signals, common-mode interference, differential amplifiers, Common Mode Rejection Ratio, effect of source resistances.
  4. Electrodes. Terminology, Variety of Electrodes, Calculation of Resistances in Volume Conductor, Half-cell potentials, Reference Electrodes, Non-polarisable (silver-silver chloride electrode), Polarisable electrode (platinum), Circuit models of electrodes.
  5. Electrophysiology and electrical stimulation. Nerves, Nerve structure, Resting Potential, Action Potentials (regeneration), Action Potential (propagation), Volume Conductor Effects, Recorded nerve signals. Nerve stimulation due to current flow, response to stimulation (strength-duration curve, twitch response, tetanic contractions, force-pulse frequency effect, force-modulation frequency), design of stimulators, uses of muscle stimulation, simulation of neuron activation.
  6. Applications: Biopotential Signal Recording. EEG, ECG, EMG, ENG, ERG.
  7. Applications: Stimulation. Defibrillators, pacemakers, FES, cochlear stimulators.

Core Texts

  • R. H. S. Carpenter, Neurophysiology (3rd Edition), Arnold, 1996.
  • J. G. Webster (Editor), Medical Instrumentation - Application and Design, Houghton Miflin Co. Note: Third Edition £39.95. Beware that the Second Edition sells for the much inflated price of £75
  • B. H. Brown, R. H. Smallwood, D. C. Barber, P. V. Lawford and D. R. Hose, Medical Physics and Biomedical Engineering, Institute of Physics Publishing, 1999.