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View metadata, citation and similar papers at core.ac.ukbrought to you byCOREprovided by Journal of the Medical Sciences (Berkala ilmu Kedokteran)J Med Sci, Volume 47, No. 1, March: 12-19The characterization of NMR signal for bloodpressure monitoring system and its testingBambang Murdaka Eka Jati1*, Kusminarto1, Agung Bambang Setio Utomo1,Bambang Irawan21Department of Physics, Faculty of Mathematics and Natural Sciences, 2Department ofCardiology and Vascular, Dr. Sardjito General Hospital/Faculty of Medicine, UniversitasGadjah Mada, Yogyakarta, IndonesiaDOI: RACTA blood monitoring system based on NMR method has been designed on constructed.This set-up of equipment used magnetic permanent, radio frequency (RF), receivercoil (RC), function generator (FG), amplifier which included the filter, as well as theoscilloscope digital storage. The background of this research was based on the sensitivityof NMR signal. The signal must be separated from signals background. This method wasdone by adjusting the frequency on FG, which was connected to radio frequency (RF)coil, on empty sample. Subsequently, NMR signal was received by RC, and that signalcould be shown on oscilloscope at resonance condition. The true frequency on NMRsignal was Larmor frequency, and the other was background. The two variables of thisexperiment were the position of RF coil and the location temperature (20 up to 30oC).In conclusion, the resonance frequency of NMR signal (as Larmor frequency) was 4.7MHz (at static magnetic field of 1,600 gauss) and it could be separated from backgroundsignals (3.4 and 6.2 MHz), and that signal was almost constant to room temperature. Theequipment was used for sample testing. It gave systole/diastole data of 110/70 mmHg(on sphygmomanometer) that was similar to 17/9 mV (on NMR signal).ABSTRAKTelah dikembangkan alat pemantauan tekanan darah berdasar prinsip NMR. Pada riset inidiselidiki, apakah sinyal yang muncul di layar osiloskop benar-benar berasal dari tekanandarah sampel (pasien). Teknik pengukuran ini melibatkan instrumen berupa: magnetpermanen, koil radio frekuensi (RF), koil penerima (RC), fungsion generator (FG), amplifierbeserta filternya, dan unit pemantau berupa oscilloscope digital storage. Penelitian inidilatarbelakangi oleh adanya kekhawatiran bahwa sinyal NMR oleh nilai sistol dan diastolbersifat tumpang tindih dengan sinyal NMR oleh sumber lain atau latar. Penelitian inidilakukan dengan meneliti sebaran kuat medan magnet di sekitar magnet permanen (Bo).Kemudian, pada kawasan frekuensi FG terpilih yang bersesuaian dengan nilai medanmagnet statis guna menghasilkan sinyal NMR, ditampilkan sinyal NMR ketika koil RFkosong. Akhirnya, parameter sinyal itu dibandingkan dengan sinyal NMR ketika di dalamkoil RF berisi lengan sampel. Hasilnya, frekuensi larmor oleh momen dipol magnet spinproton atom hidrogen (Bo (1,6 0,2)102 gauss) pada aliran darah adalah berkisar 4,7MHz. Sedangkan, frekuensi yang menghasilkan sinyal latar (tidak peka terhadap perubahansuhu lingkungan) bernilai 3,4 dan 6,2 MHz. Artinya, sinyal latar tidak berpengaruh* corresponding author: b [email protected]
Bambang Murdaka E.J. et al., The characterization of NMR signal for blood pressure monitoring system and its testingterhadap sinyal NMR (oleh adanya tekanan darah arteri sampel). Dari uji coba, telah dapatditampilkan pula sinyal NMR sampel 17/9 mV yang bersesuaian dengan sistol/diastol(diukur dengan sphygmomanometer) 110/70 mmHgKeywords: NMR-characterization-blood pressure-monitoring-testingINTRODUCTIONThe relationships between physics andsome applied sciences is increasingly close.1,2For example, the cooperation between physicsand medical science is termed medicalphysics. Products of such cooperation aremedical equipments. These equipments aredesigned and constructed using physicscombined with medical information. Oneexample of the medical equipment productsis artery blood pressure monitoring system.The blood pressure is defined as the pressurein systemic circulation (heart – all organs –heart), but not that in small circulation (heart– lung – heart).3 Systemic circulation ischosen because the arteries and veins of thiscirculation are through some vital organs suchas brain and liver.The blood pressure monitoring systemcould be categorized into two main methods,namely invasive and non-invasive methods.The invasive method could be carried outby placing a device inside the arteries. Thismethod (such as that using catheter) is accurate,very small in the dimension of equipment,good for critical patients, but expensive.The non-invasive method is used by placingthe equipment outside of body organs. Thismethod is safe, the dimension of equipmentis not small enough, but it could be mobile.Unfortunately, this method is frequently notprecise. Therefore, this method could beused to monitor the health of people daily.Sphygmomanometer is one of the examples.The operation principle of catheteris different from sphygmomanometer.4,5The blood pressure monitoring system ofcatheter is continuous, and it is based on themeasurement of pulse blood flows. On theother hand, sphygmomanometer is based onthe measurement of turbulant blood flows.This means that the flows of blood in patientsare undisturbed in catheter measurement, butthey are disturbed in sphygmomanometermeasurement. The variances of blood pressure,which could be monitored, are systole/diastole,pulse on blood pressure, and the average ofblood pressure. The systolic phase of bloodpressure is caused by the contraction of theheart, and the diastolic phase is caused by therelaxation of the heart. The pulse on bloodpressure is the value of systole subtracted todiastole. The average blood pressure is theaverage of systole-diastole in one period.6,7We have previously carried out studieson blood pressure model using NMR.8,9 Thepresent study introduces a new technicalmethod for blood pressure monitoringsystem using NMR.10 The method appliedin the current study, which is based onpulse of blood flows, is similar to cathetermethod, but non-invasive, safe, and cheap.These characteristics are similar to those ofsphygmomanometer method. The presentresearch aimed at calibrating NMR signalsand test for the sample. It was carried out in3 steps. The first step was to know and checkthe reality of NMR signals by blood flows insampled arteries then it was compared to the13
J Med Sci, Volume 47, No. 1, March: 12-19background signals. The second step was tocharacterize the home made blood pressuremonitoring system. The third step was to do asample testing. It is expected that this homemade instrumentation could be used safely forblood pressure monitoring system.MATERIALS AND METHODSNuclear Magnetic Resonance (NMR)signals could be found by the transition of“magnetic dipole moment of spin proton onatomic hydrogen” (mdmspah) from the higherenergy level to the lower one.11-14 This transitionchanges the magnetic flux on radiation. Thismagnetic flux radiation is received by receivercoil (RC). The transition of mdmspah fromupper energy level to the lower one is calledrelaxation. The duration for relaxation iscalled relaxation time. A proton is a nucleusof hydrogen atom, and water molecule isdominated by hydrogen atoms. NMR processis based on mdmspah transition. Human organis dominated by water, and therefore NMRprocess could be applied on every humanorgan. Thus, it could be used to detect theflows of blood in arteries.15,16The workingprinciple of NMR device as blood pressuremonitoring system is shown in FIGURE 1.FIGURE 1a presents a picture of fluid (asmdmspah inside blood) flowing from left toright. Initially, the direction of mdmspahs israndom. Subsequently, at an area betweentwo magnetic poles N (north) and S (south)at about 1,600 gauss, some of mdmspahare oriented to minimum on their potentialenergy. For a moment, mdmspah is radiatedby electromagnetic (em) wave from radiofrequency (RF) coil. This radiation causessome of mdmspah in excitatory condition. RFcoil is connected to function generator (FG),and hence FG generates current in higher (inthe order of MHz) frequency. For a moment, attheir relaxation times, some of mdmspah relaxand go back to lower energy level. As long asmdmspah is in relaxation condition, mdmspahradiates magnetic flux. This magnetic flux isreceived by RC. Output of RC gives inductionvoltage, which is termed NMR signals. ThisNMR signal is connected to a filter (for signalsless than 20 Hz) and an amplifier (amplifyingsignals about 500 times). Finally, after theNMR signal is filtered and amplified, thissignal is shown on the screen of oscilloscopedigital storage. The blood flowing model in anarm could be seen in FIGURE 1.b.FIGURE 1. (a) The flowing model of mdmspah inside blood, (b) the flowing model of mdmspah in an arm.14
Bambang Murdaka E.J. et al., The characterization of NMR signal for blood pressure monitoring system and its testingThe NMR signal is received from bloodflow in arteries of an arm (FIGURE 1.b).However, other signals which look like NMRsignals probably disturb that signal. Theseother signals (termed as background signals)are probably different from NMR signal interms of resonance frequency. The sourceof background signal is probably ionic gas.According to kinetic theory, all atoms ormolecules vibrate, rotate, and translate. Ifthe temperature of the location is T (kelvin),the Stefan – Boltzmann constant is k, and thedegree of freedom (f) is 7, the kinetic energyis. If the molecules move at a speedof v, and the density of the molecules is, the1pressure is P ρv 2 . This means that these2ionic gases move inside the gap between Nand S of permanent magnetic poles as well asinside RF coil.The present experiment used someequipment, including home-made equipment.The equipment (shown in FIGURE 2a) wasteslameter and permanent magnet (1,300up to 1,800 gauss). Other equipment wasoscilloscope, FG, amplifier including the filter,RF coil, and RC (FIGURE 2b). The amplifier– filter and the coils (RF and RC) were homemade equipment. The room temperature wasmeasured by placing 2 thermometers at avertical position on static. The experimentof monitoring blood pressure of a sample isshown in FIGURE 2b.FIGURE 2.(a)(a) The experimental set up (b)experimental testing fora sample.15
J Med Sci, Volume 47, No. 1, March: 12-19The experiment was completed by puttingdata quantity of magnetic field as a function ofsome positions around the permanent magnet(FIGURE 3a, b). The magnetic distributionwas put along N – S poles and perpendicularfrom that axis. RF coil was empty. Theposition of RF coil was varied in the distancefrom permanent magnet. Subsequently, thesignal (similar to NMR signals) was seen onthe oscilloscope screen and saved in a flashdisc. The data of background signals were putat resonance frequency as a function of roomtemperature.RESULTSThe data of the present study are thedistribution of magnetic field strength (B)as a function of position and the frequencyof background signals as a function of roomtemperature, the effect of room temperature tothe background signals, and NMR signals fora sample testing. The magnetic distributionalong N – S poles axis is presented inFIGURE 3a. The other one, the distributionin perpendicular direction to that axis (N – S)poles is shown in FIGURE 3b. B on the rightand on the left places from those poles can beseen in FIGURE 4. In addition, the frequencyof background signal at 22 1oC is shown inFIGURE 5.FIGURE 3.The distribution of magnetic field strength: (a) along N–S pole axis, (b) rectangular to N – S pole axis.16
Bambang Murdaka E.J. et al., The characterization of NMR signal for blood pressure monitoring system and its testingFIGURE 4.The distribution of magnetic fieldstrength on right side place from S pole.FIGURE 5.Resonance frequency of B backgroundsignal.in inhomogeneity could be erased by placing thesample as artery on constant position. On theother hand, B is going down sharply for moredistant from the pole gap position. This meansthat the distribution of B from the permanentmagnet does not disturb other equipment suchas oscilloscope or FG. FIGURE 5 shows that thefrequency of background signal is 3.4 MHz and6.5 MHz. The frequency of this signal is verymuch different from NMR signal of mdmspahby flowing blood in arteries. On the other hand,resonance frequency of background signal isalmost independent from room temperature(FIGURE 6). Finally, the NMR signal (for bloodpressure monitoring system) is not disturbed bybackground signal and also it is not sensitive toroom temperature. An example of NMR signalfrom a sample testing can be seen in FIGURE7. The voltage of NMR signal is consistent withsystole (maximum voltage) – diastole (minimumvoltage) when blood was flowing inside arteriesin sampled arms. The frequency of NMR signalis 4.7 MHz. This value is consistent with larmorfrequency of mdmspah.DISCUSSIONIt can be seen from the data (FIGURES 3and 4) that the distribution of B along N – S polesis not homogenous. However, the magnetic fieldFIGURE 6.The background signal is constantat constant RF coil position, atroom temperature of 20 to 30oC.17
J Med Sci, Volume 47, No. 1, March: 12-19FIGURE 7. NMR signal (in mV) from a sample is similar to systole/diastole (110/70 mmHg).CONCLUSIONACKNOWLEDGEMENTSIt can be concluded that, first, thedistribution of magnetic field strength foraround 20 cm from the poles of permanentmagnet is too small. This means that thismagnet does not disturb other electronicequipment. Background signals could befound but these signals are not sensitive tocoordinate and room temperature. Second, itcould be measured that the background signalfrequency is 3.4 and 6.5 MHz. It means thatthe background signal does not disturb NMRsignal (about 4.7 MHz) which is produced bymdmspah from flowing blood in the arm of thesample artery. Third, the similarity of NMRsignal (in mV) to blood pressure (as measuredin mmHg using sphygmomanometer)from a sampled testing could be seen by anoscilloscope. It is expected that this researchcould be developed for bigger magnetic fieldstrength (more than 7,000 gauss) on maximalsensitivity of NMR signal. From the next stepof research, the equipment (NMR system)could be applied to measure blood pressure ontime for some condition of samples.The authors would like to express theirgratitude to Directorate Deneral of HigherEducation, Ministry of National Education,Universitas Gadjah Mada, and Vice Dean andDean of Faculty of Mathematics and NaturalSciences, Universitas Gadjah Mada for theirsupport for fellowship, helping on institutionfee, and Doctoral Dissertation ResearchGrant. The authors also would like to thankthe Head of Laboratory of Geophysics, BasicPhysics, Atomic Physics, and ELINS for theirshares of some equipments. To Mr Suryono,Mr Suparwoto, and Mr Djoko, we would liketo thank for their help on the instrumentations.And too Dr. Mirza for reviewing themanuspcript.18REFFERENCES1.2.Kusminarto. Fisika: Penerapannya dalam BidangMedis, Pidato Pengukuhan Jabatan Guru Besarpada FMIPA UGM. Yogyakarta: 2007.Brown BH, Smallwood RH, Barber DC, LawfordPV, Hose DR. Medical Physics and BiomedicalEngineering. London: IOP Publishing Ltd, 1999.http://dx.doi.org/10.1887/0750303689
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magnet statis guna menghasilkan sinyal NMR, ditampilkan sinyal NMR ketika koil RF kosong. Akhirnya, parameter sinyal itu dibandingkan dengan sinyal NMR ketika di dalam koil RF berisi lengan sampel. Hasilnya, frekuensi larmor oleh momen dipol magnet spin proton atom hidrogen (B o (1,6
