Magnetism and Induction: Transcranial Magnetic Stimulation - Essay Example

DETAILS OF THE THESIS MAGNETISM AND INDUCTION:TRANSCRANIAL MAGNETIC STIMULATION OF THE PALCE? INDEX HEADINGPAGE NO. 1. INTRODUCTION 3 2. METHODOLOGY AND APPROACH 4 3. MAGNETISM 4 4. MAGNETIC FIELD 4 5. MAGNETIC FLUX AND FLUX DENSITY 5 6. ELECTRICAL CURRENT AND MAGNETIC FIELD 6 7. MAGNETIC POLARITY OF A COIL 7 8. ELECTROMAGNETIC INDUCTION 8 9. FARADAY’S LAWS OF ELECTROMAGNETIC INDUCTION 9 10. LENZ’S LAW 10 11. TRANSCRANIAL MAGNETIC STIMULATION 12 12. INTRODUCTION 12 13. TECHNICAL DETAILS 12 14. APPLICATION OF TMS 17 15. RISKS 18 16. RESULTS 19 17. ANALYSIS 19 18. DISCUSSION 19 19. CONCLUSIONS 20 20. RECOMMENDATIONS 20 21. REFERENCES 21 22. BIBLIOGRAPHY 22 23. APPENDIX 23 INTRODUCTION Childhood play sometimes becomes a subject of research when we grow up. Our present thesis is one such topic where we have to study the Theory and Applications of Magnetism and Induction along with its real time application in the medical field that is Transcranial Magnetic Stimulation (TMS). This topic is of great importance as in todays world majority of the population is suffering from psychological disorders and in particular with stress. The latest technology to treat this is through TMS. Its usage is important as it has more advantages than disadvantages. Various Universities like KIMS and various corporate hospitals like MAYO CLINIC are showing interest in its implementation and research. Though there is enough research already done on its working still much inquisitive research is to be done on harmful side effects. TMS definitely has a limitation in terms of the side effects it causes but the relief of the patient from the psychological disorders is above the harmful effects. This thesis helps nascent learners know about the technicalities of TMS and also patients that are curious to know about it. The main aim and objective of the thesis is study the working and applications of TMS and the properties of the instruments that are used like the theory of Magnetism and Induction and some Laws which govern them. To do this various books on the theory were studied and have come to a conclusion. The details and working of the TMS was a tedious job as there wasn’t enough information available due to security reasons both medically and in Law point of view. The figures to explain the true working of the fields are drawn in MS Office which would give a closer approach, sample data of a practical application on how to find TMS values is done with the help of a medical practitioner which proves their accuracy. The topics are explained with Block diagrams, nodal figures and tabular details to bring it close to real time application. METHODOLOGY AND APPROACH First and the foremost the technical details of the theories such as Magnetic and Electromagnetic field theories were explained with the help of various technical data available in books. Later the technical data and details regarding TMS were gathered. A real time implementation in which how the TMS is calculated and how the theories mentioned are applied is explained. A live example of how the procedure during the treatment is followed is shown with the help of figures. In text citation is done according to MLA style of citation. MAGNETISM The main two properties of a magnet are: It attracts small pieces of iron or other magnetic materials like Nickel and cobalt. When suspended freely in air by a silk thread, one end of the magnet always points towards the geographical north of the earth also called north pole, North seeking pole or N-pole. The other end of the magnet which points towards the geographical south of the earth is called the south pole, South seeking pole or S-pole. MAGNETIC FIELD The space around a magnet in which its influence can be felt is called the magnetic field. This magnetic field is the strongest near the poles of the magnet and gets weaker as we move away from the poles. A magnetic field is not seen but its existence can be shown by the effect it produces on magnetic materials like iron filings. Let us see this with a small practical example. Experiment: A bar magnet is placed on a glass sheet and some iron filings are sprinkled on the glass sheet, gently the glass sheet is tapped with tour fingers, now the iron fillings will arrange in a regular pattern of lines from north pole to the other as show. In the fig.1 Fig.1 Magnetic Lines of Force The lines along which the iron filings arrange is called magnetic lines of force. These lines of force are crowded near the poles indicating that the magnetic field is very strong here. Each particle of the iron filings becomes a tiny magnet under the influence of the magnetic field of the bar magnet and arranges itself along certain magnetic lines of force. MAGNETIC FLUX AND FLUX DENSITY The lines of magnetic force that emerge from the north pole of a magnet comprise what is called magnetic flux and is generally represented by the Greek letter Ø (phi). A strong magnet provides greater flux than a weak magnet. Flux density B is the number of magnetic lines of force that pass through the unit area of a section perpendicular to the direction of the magnetic flux. Mathematically, B= Ø/A ---------------------------- (1) Where A is the area through which a flux Ø passes. Flux density B is measured in terms of a unit called Gauss (G). A Gauss is equal to one line (also called Maxwell) per square centimeter. ELECTRICAL CURRENT AND MAGNETIC FIELD If a conductor carrying electric current is held over a magnetic needle, the north pole of the magnetic needle gets deflected at right angles to the current carrying conductors as in the fig.2.(a). If the direction of the current is reversed, the north pole of the magnetic needle gets deflected in the opposite direction as in fig.2 (b). This shows that a current carrying conductor develops around it a magnetic field whose direction depends on the direction of the flow of the current. Fig.2 Magnetic Effect of a current carrying conductor Let us observe a small practical example on magnetic field round a current carrying conductor. This can be demonstrated by piercing a copper wire through a piece of cardboard and sprinkling some iron filings on the card board. If the current is passed through wire from a battery and the cardboard tapped gently, the iron filings will arrange themselves in concentric circles around the wire as shown in fig. 3 Fig.3 Magnetic Field round a current carrying conductor MAGNETIC POLARITY OF A COIL A coil carrying current behaves like a bar magnet with the north pole at one end and south pole at the other. Whether a particular end becomes a north pole or a south pole can be determined by a number of methods. For instance let us take two of them; 1. END RULE. Looking at the end of the coil says a lot. If the electron flow (current is clockwise, the end will have north polarity, if anti-clockwise, the end will have south polarity as in the fig.4 (a) (b) Fig.4 End Polarity in a current carrying coil 2. LEFT HAND RULE If the coil or the solenoid is gripped with the left hand, wrap the fingers round the coil in the direction of the electron flow. The thumb will point in the direction of the north. This is because the electron flow is from the negative side of the voltage source through the coil and back to the positive terminal. ELECTROMAGNETIC INDUCTION It has already been shown how a current carrying conductor or coil has a magnetic field associated with it. This magnetic field is produced by the motion of electrons in the current carrying conductors. Similarly, if a conductor or a coil is moved in a magnetic field, the free electrons in the conductor are set into motion and current flows into the conductor or the coil when the circuit is closed. Electricity and magnetism are two interlinked phenomena and one cannot be separated from the other. The production of electricity from magnetism and vice versa is termed as Electromagnetic Induction. This can be demonstrated by simple examples as follows Experiment-1 A bar magnet is brought near a coil to which a sensitive micro ammeter (or a galvanometer) is connected. The setup is shown in fig.6 (a). The needle of the micro ammeter shows deflection as the bar magnet is brought near the coil and the magnetic lines of force cut the coil. When the magnet is held stationary near the coil the meter shows no deflection and the current flow stops. Now the magnet is moved away from the coil as shown in the fig.6 (b). The needle of the current meter again shows deflection but in opposite direction. The current flow stops again if the magnet is held stationary. The effect produced is the same if the magnet is kept stationary and the coil is moved towards or away from the magnet. Furthermore, if the magnet is moved in and out quickly, the current produced is stronger than when the magnet is moved slowly. Also, with a stronger magnet having greater flux density the current produced in the same coil is stronger that when a weak magnet is used. All the facts stated above are governed by a set of laws known as Laws of Electromagnetic Induction. There are two important laws of Electromagnet Induction 1. Faraday’s Law 2. Lenz’s Law. (a) (b) fig.6 Demonstration of electromagnet induction FARADAY’ SLAW OF ELECTROMAGNETIC INDUCTION Law 1 The production of induced emf or current in a coil by moving a magnet near it has already been said. The same effect can also be produced by placing two coils near each other as shown in fig.7(a). when the current flowing in the first coil called primary is changed, the magnetic flux linking the second coil is called secondary changed and induced emf is produced in it. The primary current can be changed either by a switching arrangement or by connecting some AC voltage across it. To enhance the effect of flux linkages the two coils are sometimes wound on a common magnetic material called the core. This in fact is the principle of transformers. Law 2 The magnitude of the induced emf depends on the rate of change of magnetic lines of force or the magnetic flux cutting the closed circuit. A higher emf is produced if the rate of change, i.e. the change of magnetic lines of force per second is higher. It can be proved that an emf of 1V is produced if the number of lines of force cutting a coil changes by magnetic linkage of 10 to the power of 8 lines per second. If the same change takes place in 1/10 of a second, the voltage induced will be 10V. The rate of change of flux can also be increased by increasing the number of turns in the coil. fig.7 (a) (b) Induced voltages indicating transformer action LENZ’S LAW This law determines the polarity or direction of the induced emf or induced current. The law states that the direction of the induced emf or current is such that its own magnetic field will oppose the change that produced the induced emf or current. In fig 4.17 when the north pole of a magnet is brought near the coil, the end of the coil facing the north pole also becomes a north pole due to induced current and tries to repel the north pole of the magnet that is responsible for inducing the current in the coil. When the magnet is withdrawn from the coil, the induced polarity is a south pole which tries to attract or bring back the north pole that has induced this polarity. By application of the end rule or the left hand rule the direction of the induced current in the above two cases can be found. (a) (b) Fig. 8 Lenz’s Law determines the polarity and the induced voltages TRANSCRANIAL MAGNETIC STIMULAION INTRODUCTION Transcranial magnetic stimulation (TMS) is the process of inducing electric current that flows within brain cells called neurons when the magnetic field is applied externally. It is in its nascent stage of evaluation as a potential treatment for depressive conditions. Initially single pulse TMS was developed as an investigative tool in Neurology. It was found that magnetic field when applied to various parts of the brain will stimulate and inhibit different areas and could change few functions of the brain. Neurologists were able to jot down different analysis of the functions associated with the various parts of the cerebral cortex as different frequencies appeared to have different physiological effects like lower frequencies were inhibitory and higher ones activating. TECHNICAL DETAILS It works on the principle of Induction where electric current is obtained across the insulating tissues of the scalp and the skull. A coil of wire that is shielded in plastic is held on the head. When this coils is energized by discharging a large capacitor rapidly equal rapid changing currents flow in the coil’s windings. This in turn develops magnetic field that is oriented orthogonally to the plane of the coil. This is clearly explained in Faraday’s Laws already stated in page no.7. The magnetic field generated impinges into the skin and the skull that induces an oppositely directed current in the brain that flows tangentially with respect to Skull. The currents induced in the structure of the brain stats activating the nearby nerve cells similar to the way the currents applied directly to the cortical surface. If we observe the path of the current it is very complex as the brain is a non uniform conductor with an irregular shape. The readings are precision with Stereotactic MRI based control while targeting TMS to get approximated to few millimeters. (Hannula et al., Human Brain Mapping 2005). Regarding the material of the coils used in TMS the core material should be either Magnetic Inert substrate (air-core coil design) or a solid ferromagnetically active material (solid core design). Let us see the practical values: Magnetic field : About 2 tesla on the coil surface and 0.5 on the cortex. Current rise time : Zero to peak, mostly 70-100 microseconds. Wave form : monopahsic or sometimes biphasic. Repetition rate for rTMS : if it is slow TMS it is below 1Hz, above 1Hz for rapid TMS TMS MODEL IDENTIFICATION TMS is usually paired with other methods like EEG and ECT to get the effective data. Typically the value of tms(t) is to be found. It is observed that due to the impulsive nature of TMS, output error (OE) which is also impulsive is observed (Ljung, 1999). The structure of the OE is as shown in the figure fig.9 From this we get that tms(t) = B(z)*u(t-1)/F(z)+v(t) ----------- (2) Fig.9 OE Model of the TMS Where v(t) is unitary impulse corresponding to the stimulus; B(z) and F(z) are two assigned polynomials. v(t) represents the stochastic part of the OE model. OE is observed with five of the samples before and thirty five samples after the stimulus on the single channel. Four models have been considered OE22, OE33, OE34 AND OE55 (the numbers denote the degree of polynomials B(z) and F(z)) the validity was conducted on nearly 15 stimuli. Table.1 is jotted for the results which shows Fit of the four models validated on the stimuli. Models OE33 and OE%55 represent the Highest mean Fit. When we the measured outputs and outs generated by OE33 and OE55 were compared it was observed that the measured outputs were closer to OE55. To further decide on precision if closely analyse the two zeros of B(z)F(z) in OE55 mostly superimpose to two poles as shown in the fig. it is necessary to cancel atleast two to be precise so OE55 reduces to OE33. Now almost all the parameters are reduced and obviously OE33 shall be used for TMS. To validate the process using signals from other channels, unlike EEG, TMS process is local ( the TMS induced artifact is higher in the electrodes close to the stimulation site), However, when identification procedure is repeated in other channels, OE33 is the most precise process. Fig.10 Poles and Zeros of B(z)F(z) in the OE55 model Table1 STIMULUS OE22 OE33 OE34 OE55 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 MEAN 37.5 22.2 40.0 51.2 52.1 60.7 52.8 60.3 54.6 37.8 37.7 57.7 13.8 32.9 40.9 43.61 35.2 26.1 50.1 58.1 54.1 61.2 61.0 67.2 58.6 41.2 39.6 48.7 23.3 47.7 57.8 48.66 60.5 75.3 70.9 62.0 56.2 48.6 24.8 25.0 18.0 7.9 5.6 10.3 60.9 57.7 43.2 41.79 53.6 39.1 60.1 69.6 68.6 73.8 68.7 72.7 64.8 51.1 48.9 52.6 27.7 50.8 62.1 57.61 Fit % of the OE process . APPLICATION OF TMS BRAIN MAPPING WITH TMS Fig.11 AIM : Brain mapping with TMS using a protocol based on ROBOT and techniques that are based on registration. PROCEDURE : The field of induced current which depends on the position related to the TMS coil is measured. The robot mounted coil is moved to the vertices of the 3D measurement grid. Power is supplied to the coil in literal means it is fired and the voltage induced in the small wire loop is measured. The field as a result depends on the coil used and the effects of TMS pulse on the nerve are experienced. The point to observe is that we measured the position of the wire loop, the nerve under observation with respect to the field. Position the coil at several points of the motoric cortex. Now fire it, the induced motor evoked potential (MEP) is measured over the targeted muscle. This induction is clear from the thumb rule already stated. The first field of measured voltages and the second field of MEPs using stochastic image registration metrics like mutual information(MI) and correlation ratio(CR) are noted. The transform that results is applied to the point of the wire loop of the first field to yield the predicted position of the motoric centre of the targeted muscle. Last but not the least the head of the subject to its 3D-MRdata is registered to embed the predicted motoric centre in the visualization of the subject’s brain. RISKS: Every new invention has both positive and negative effects. Till now we have seen its positive usage now let us observe adverse health problems and some common side effects while using TMS: Lightheadedness The noise during the treatment creates unnecessary discomfort. Tingling, spasms or twitching of facial muscles. Headache. Seizure Mania The uneven pulses may sometimes make the patient deaf. Structural changes in the brain RESULTS The thesis is based on study and analysis of Theories and working of supporting technology of TMS. The results of a real time application of TMS is studied and analysed with figures, equations and nodal diagrams. ANALYSIS The theories Magnetism and Induction are explained in detail whose fields of intensity are clearly shown with diagrams. TMS with its theories applied and working are shown with diagrams, equations and nodal diagrams. On the whole the aims and objectives of the thesis are achieved. DISCUSSION The significance of the obtained results is that TMS is emerging as a leading technology in treatment of psychological disorders internationally. Various laws such as Faraday’s laws, Lenz’s laws are gathered which play a major role in electromagnetic induction and in particular in applying this technology to the working of TMS. There are no assumptions and worst case scenarios as the thesis is completely based on practical real time application. My implication would be to wait till the research on TMS’s harmful effects is complete and then implement because the security of the patient is of primary importance. As there is chance of ECT ( Electric Convulsive Therapy) and EEG to come near to this result we shall also concentrate on them. The Advantage has an edge over disadvantages so a quality wait till the research is over will give doctor’s a fair chance of opportunity to excel. CONCLUSIONS Aims and objectives of the thesis are achieved to the best of knowledge. As assigned in the thesis by the curriculum the theories that govern the TMS are explained in detail. RECOMMENDATIONS The state of art that arise from the performed work is a wonderful explanation of the technology TMS which caters to the medical science’s achievement. This shall be applied on patients only if urgent and very much necessary as a quality wait to have the research completed will let unnecessary hazards that are not yet expected or assumed. Some of the major manufacturers of TMS Devices such as The Magstim Company, UK, MagVenture A/S Denmark and many more are all approved by FDA in US for the use on adult patients with major problems. REFERENCES Dhake, Aravind M, Television Engineering, Tata Mc Graw-Hill Publishing Co.ltd., New Delhi, 1979. Grob, Bernard, Basic Electronics, Fourth edition, International student edition, Mc Graw Hill Kogakusha Ltd., Tokyo, 1977. Grob, Bernard, Basic Television, principles and servicing, Fourth edition, International student edition, Mc Graw Hill Kogakusha Ltd., Tokyo, 1975. Hutson, Geoffrey H., Colour Television Theory, Mc Graw Hill Book Co. (UK) Ltd., 1971. Kevir Milton S. and Milton Kaufman, television Simplified, Seventh edition, Van Nostrand Reinhold Company, 1973. Infrapsych, 2009, Free Mental health Information, accessed on 10th May 2009, http://www.infrapsych.com/content/general/TMS.html. Paus, T,Imaging the Brain Before, During and after Transcranial Magnetic stimulation. Neuropsychologia, 1999: 37. Ljung L. System Identification: Theory For the User. PTR Prentice Hall; 1999. APPENDIX FIGURES 1. Fig.1 Magnetic lines of force. 5 2. Fig.2 Magnetic effect of a current carrying conductor 6 3. Fig.3 Magnetic field round a current carrying conductor 7 4. Fig.4 End polarity in a current carrying coil 7 5. Fig.6 Demonstration of electromagnetic Induction 9 6. Fig.7 Induced voltages indicating Transformer Action 10 7. Fig.8 The polarity and induced voltage 11 8. Fig.9 OE model of the TMS 14 9. Fig.10 poles and Zeros 15 10. Fig.11 Brain mapping with TMS 17 TABLE 1. Table.1 15 Read More