ABSTRACT OF PHD THESIS

Transcription

1 TECHNICAL UNIVERSITY OF CLUJ-NAPOCA FACULTY OF ELECTRICAL ENGINEERING Ig. Ştefa Gergely ABSTRACT OF PHD THESIS Research ad implemetatio of medical electroic equipmet, to use i cardiology Thesis committee: PRESIDENT: MEMBERS - Prof.dr.ig. Ioa TÂRNOVAN - dea, Faculty of Electrical Egieerig, Techical Uiversity of Cluj-Napoca; - Prof.dr.ig. Radu CIUPA - coducător ştiiţific, dea- Faculty of Electrical Egieerig, Techical Uiversity of Cluj-Napoca; - Prof.dr.ig. Alexadru MOREGA - reviewer, Polytechic Uiversity of Bucharest; - Cercet. Şt.I dr.ig. Valer ALMĂŞAN - reviewer, I.N.C.D.T.I.M. Cluj-Napoca; - Prof.dr.ig. Marius N. ROMAN - reviewer, Faculty of Electrical Egieerig Techical Uiversity of Cluj-Napoca; SCIENTIFIC COORDINATOR: Prof. dr.ig. Radu CIUPA 20

2 Chapter. Itroductio The thesis is divided ito five chapters, refereces ad 20 appedices. The cotributios to umerical aalysis of the PCG sigal (PhooCardioGraphs), this thesis aims to cotribute to solvig problems or improvig the diagosis of heart pathologies. So the thesis addresses the complex issue of developmet support ad developmet of mathematical algorithms required for classifyig cardiac pathologies usig PCG sigal. Also made cotributios, thesis has the objective of substatially fills a gap i the way of characterizatio of a PCG sigal. The marketig of prevetio i cardiology equipmet has grow due to icreasig computig power at the portable device. The itroductio of high-speed microcotroller with itegrated DSP module makes possible to carry these devices with icreasigly smaller dimesios. Edpoits of the thesis are:. Developmet of the first algorithms applicable i a portable computer system for the characterizatio of PCG sigals. 2. Research, desig ad realizatio of a prototype electroic equipmet for complex aalysis of the PCG sigals. Thus defied objectives give a practical research that has come followig itermediate steps:. Developig the mathematical support for PCG sigal aalysis; 2. Desig ad testig of a algorithm for time-frequecy scalogram represetatio; 3. Desigig ad testig a multi-resolutio algorithm for etropy aalysis of PCG sigal; 4. Desig ad testig of a shape recogitio algorithm for evaluatig the sigal evelope to classify cardiac pathology; 5. Isertig a patter recogitio algorithm used i 2D images based o Fourier trasform covolutio matrix of image cotet; 6. Software algorithm by umerical sigal processig tools (DSP); 7. Desig ad realizatio of a operatig system software for medical equipmet with color graphics display capability; 8. Desig ad practical implemetatio of a prototype hardware system for medical equipmet, capable to perform complex aalysis of PCG sigals. Coclusios Chapter : There were preseted a umber of pathologies as itroductory module to detectable PCG pathology sigals, the differeces betwee soud accompaied by cardiac activity ad cardiac murmur. There are preseted the cases that lead to murmur, ad may be associated with a certai type of heart disease or pathology class. Aalysis of existig equipmet by meas phoocardiography ivestigatio led to the idea to ivestigate ad make a series of algorithms by which to detect cardiac pathologies ad the they are implemeted i a portable system. Thus were established geeral criteria uder which it was possible to udertake research. The PCG sigal aalysis system had to be uder autoomic computig capacity to determie the type or class of pathology at least detected. Usig te PCG sigals with differet pathologies were sufficiet to begi research i this area.

3 Chapter 2. Medical sigal processig usig moder mathematical methods Wavelet fuctios are used to covert the sigal to be aalyzed i a represetatio iteded to highlight some features much better origial sigal. This trasformatio of the sigal is called wavelet trasform, which strictly mathematical poit of view fuctio is a covolutio of the sigal wavelet aalysis. I sigal aalysis, wavelet trasform ca meet two possible roles: it ca be traslated alog the sigal may suffer compressio or extesio by rescalig respectively. The wavelet fuctios are localized both i frequecy ad i time by shiftig ad scalig fuctio without a projectio over the etire trasformed. Aother importat aspect is that i terms of umber of calculatios ecessary for the Fourier trasform is required whe performig mathematical O( log2) operatios o wavelet trasform by fast algorithms ca be reduced to Ooperatios. Each iteratio of the decompositio of the sigal is called octave that ca assimilate a set of two FIR filter type. A wavelet trasform filter is built-pass type (TJ) ad the other is type-pass (TS). By direct applicatio of wavelet trasformed o a discrete sigal, we obtai a double umber of poits for the half vector trasform. Because the umber of samples after every iteratio trasforms is equal to the umber of samples of the origial sigal, it was proceeded to a decimatio of two. Scalig behavior sequece is a sequece of wavelet pass filter ad a filter is goig up where both filters are ormalized to have sum equal to 2. I some applicatios, sequeces are ormalized to have equal amout 2 remais orthogoal to each other. Sice i this case a umber of coefficiets will exceed the ed samples, there will be remaiig at the ed of the retur sigal coefficiets at the begiig to avoid the pheomeo of distortio to the limit. It ca you build a recostructio algorithm particularly useful for aalysis of perfect recostructio filters. Thus: Yields: x m t S t T t x m m. m, m, m, (2.) m, k m,2 k m, k m, 2 k 2 k 2 t S c t T b t After rearagig the terms of equatio 2.2: S m, c2ksm, k b 2kTm, k 2 k 2 k The family of Daubeschies fuctios plays a importat role i sigal aalysis because it is most ofte used to break dow ito compoet sub-bad sigals. Usig wavelet db4 requires calculatig scalig coefficiets. Coefficiets are calculated usig equatio 2.3, the scalig equatio for a fuctio with four wavelet coefficiets is writte: (2.2) (2.3) t c t c 2t c 2t 2 c 2t 3 (2.4) Ad the wavelet fuctio with the correspodig equatio results: t c t c 2t c 2t 2 c 2t 3 (2.5)

4 Coclusios Chapter 2: A summary was preseted of how the mathematical eed for research i digital sigal processig PCG. From the aalysis of this type of sigal a eed to use wavelet trasform as the oly effective way to achieve the desired results. Usig wavelet trasform as a startig poit i aalyzig a sigal havig characteristics very difficult to put ito evidece led to the eed to go through a complex mathematics which was oly recetly published. To deepe this material, the PhD studet had to make a selectio of mathematical methods for implemetig best practice developed i computer algorithms. Buildig a well-structured mathematical device led to the selectio ad testig of the optimal wavelet fuctio preseted i the thesis. Sice the wavelet trasform algorithms uderlyig desig experiece, to complete properly the mathematical apparatus was required mathematical theory coverig elemets, i parallel with the desig ad testig of the dedicated algorithms. Wavelet trasform algorithms usig time domai were developed based o sigal filtratio theory. This was doe to allow the covolutio algorithm for the DSP hardware. Chapter 3. PCG sigal characterizatio algorithms The extremely complex structure of the PCG sigal by aalogy with a iformatio carrier sigal, is characterized by a low frequecy amplitude modulated sigal, followed by a frequecy modulatio "carrier" geerated by the cardiac activity at differet times i relatio to the movemet of valves, ad fially the phase modulatio sigal is added to all compoets. The most importat parameter is the frequecy of PCG sigal that is i the rage 62Hz - 800Hz. I this chapter the origial algorithms that allow aalysis ad characterizatio of PCG sigals i terms of spectral, temporal compoets ad layout of the sigal evelope are specific to the cardiac pathologies. So the presetatio of aalysis algorithms through the followig steps: Determiatio of the spectral wavelet packets; Wavelet decompositio aalysis by evaluatig the partial Shao etropy; Accurate heart rate detectio for sigals with pathology; PCG sigal multirate samplig; Detectio of sigal evelope; Coversio of two-dimesioal correlatio of PCG sigals. After calculatig the etropy of wavelet trasform coefficiets, it ca be defied the set of referece vectors to determie the Euclidea distace betwee aalyzed sigal ad each referece sigal. I mathematical form, a referece sigal becomes the Shao etropy values i a matrix, which icludes approximatio coefficiets ad those of detail. So the etropy of each level of decompositio will replace the matrix lies. This method drastically reduces the amout of memory used to store referece sigal associated with cardiac pathology. The simulatios doe to characterize the PCG sigals by calculatig Shao etropy, were made o a umber of 0 sigals belogig to differet pathologies icludig some differet classes. The simplest algorithm used i patter recogitio is the Euclidea distace calculatio. A set of predetermied referece arrays is computed by calculatig the Euclidea distace betwee each of the matrices ad matrix pathology referece sigal acquired. The method of calculatig the Euclidea distace betwee two matrices is give i equatio 3.: 3

5 d m pij qij qij pij i j 2, (3.) There is the fial form of the PCG sigal correlatio algorithm, icludig the algorithms developed i previous subsectios 3.4, 3.5 respectively 3.6. Thus accurate determiatio of heart rate is preseted i sectio 3.4 i order to determie the relatioship betwee heart rate sigal to be aalyzed ad the referece sigal. The value of ratio betwee the two sigals will idicate the re-samplig factor used for traslatio i time of PCG sigal give i sectio 3.5. The correlatio algorithm is show i Figure 3.. Figure 3. The correlatio algorithm Coclusios Chapter 3: It was preseted a set of algorithms for processig digital sigal PCG, who are part of the three methods of pathologic classificatio. The first method ivolved the aalysis of spectral cotet of the PCG sigal ad the based o a complex algorithm; frequecy spectrum is displayed o a color LCD display. This method of evaluatig a sigal is addressed to medical persoel who ca iterpret the created time-frequecy scalogram. The secod method ivolves aalysis of statistically calculatig the sigal so that the Shao etropy of wavelet decompositio o each level, showig a specific value for each pathology i part. This desity acts as a iformatio figerprit of the sigal which allows automatic pathology classificatio of the detected PCG sigal. The third method is the most complex drive by the large umber of algorithms, so that the correlatio sigal is acquired with a series of referece sigals stored i the SD memory system created for this purpose. PCG sigal correlatio method icludes a algorithm accurate heart rate detectio usig autocorrelatio fuctio. Determiig the precise heart rate is dictated by the eeds of rescalig temporal wavelet decompositio level of three to brig the acquired sigal to the same HBR value of the referece sigal. Last step is to precisely detect the sigal evelope PCG Hilbert trasform usig a discrete sigal. The correlatio sigal is prepared by covertig the sigal ito a two-dimesioal vector, makig the actual sigal i a two-dimesioal image. This method opeed the way to the methods of imagig especially for shape recogitio. The sum of these preseted umerical processig methods is a importat step i the processig of a sigal virtually uapproachable by traditioal methods of umerical processig. 4

6 Cap.4 Research, desig ad implemetatio of electroic medical equipmet The fuctioal diagram of the device is divided ito two modules. This module idetifies (orth side) i which is the DSP microcotroller ad the (south-master) module which maages the flow of data withi the device. Each module is composed by a Microchip microcotroller series. Block diagram of the device is show i Figure 4.3. Figure 4.3 Block diagram of the PCG sigal aalyzer The electrical diagram has bee desiged usig the CAD capabilities of the Labceter-Proteus program, i which we geerated the ecessary missig compoets, from libraries. After exportig the et list files we have moved to the PCB desig. Complete wirig diagram is show i Appedix. Due to the large umber of data ports used i the scheme was ecessary to defie rules for trackig ad geeratig the list uder semi automatic routig procedure. The total duratio of CAD computig was 8 miutes without icludig the duratio of checkig of the arraged paths correctess started i maual mode. The prited circuit boards are preseted i Appedix 3 ad 4. The wirig desig is completed by a set of Gerber files exported i RS274X format. The two PCB circuits were assembled i a professioal way by usig HAL (Hot Air Levelig), fiish double layer, o-pb solder mask by the compay AR-Elektroik i Germay. All SMD compoets were soldered maually. The 3D simulatios ca be see i Appedix 2 ad the fial realizatio of both sides of the prited circuit board havig all the compoets, placed ca be see i Figure 4.5: 5

7 Figure 4.5 The PCB board of the electroic device I Figure 4.30 we ca see the medical device i operatio. Figure 4.6 The PCG sigal aalyser DSP module is the basic compoet of the microcotroller dspic30f602 ad is specialized i the executio of fast istructios such as additio, subtractio ad multiplicatio. The ext equatio is fudametal i digital sigal processig ad as a mathematical poit of view it is based o the covolutio operatio. The developmet is desiged so that it carries out all sigal aalysis processes usig equatio 4.: N i0 S a b (4.) i i Recursive FIR filter implemetatio ca be doe easily by usig modulo addressig type programmig which provides after begiig of the routie the retur of the address used to the filter coefficiets. Hilbert trasform calculatio assumes a similar algorithm but to simplify the modulo addressig type, due to the reduced umber of Hilbert coefficiets by isertig i the loop list the ecessary zero values. The itegrated aalog-digital coverter circuit is a 2-bit SAR structure. Coversio speed ca reach up to 500Khz. The developed prototype uses a samplig rate of 8KHz, otherwise low frequecy resolutio which is a audio stadard. The Natioal Istrumets LabWidows CVI platform uses a set of commuicatios protocols implemeted with NI-VISA. This protocol is a 6

8 set of applicatio programmig iterfaces for high-level (API) i order to provide commuicatio iterfaces to a PC with various tools attached. The USB protocol allows that the applicatios writte, to trasfer the SD referece sigals, the programmig of the graphical elemets used by the device, the direct readig of RAM ad also the readig of the fial results followig the assessmet of PCG sigal. The commuicatio is specific to this device ad was created exclusively for this applicatio to access the SD memory through a USB protocol. Coclusios C4: It was preseted a electroic device for sigal acquisitio ad umerical processig of the PCG sigals. It was researched, desiged ad made practical by usig moder electroic desig. There were preseted the two major compoets of this device structure, which icludes operatig system software created for this purpose. The hardware structure comprises a color graphic LCD display that ca display a graphical user-friedly meu drive by a set of three keys to access the operatig system. Data storage is doe by usig a SD memory card, which has the advatage of virtually ulimited memory space relative to the size of geerated files. These files are geerated from blocks with a total size of 64KB each. A commuicatio protocol was developed a high speed USB device desiged thereby servig the exchage of iformatio with the host program residet o a PC. The operatig system is autoomous i operatio but durig the test routies are emulated by trasferrig computer data to microcotroller DSP. The thesis is withi the field of digital sigal processig ad was completed by the desig ad realizatio of a DSP system developmet capability. This developmet system was desiged for the acquisitio ad aalysis of PCG sigal ad ed with the characterizatio ad recogitio of cardiac pathologies. So the whole thesis cotais the theoretical apparatus ecessary for the desig, calculatio ad completio of practical algorithms for this type of sigal aalysis. Iitial processig of the sigal was made by wavelet trasform to perform spectral decompositio PCG sigal while carryig out data compressio to reduce the umber of calculatios i the DSP processig. The characterizatio of the PCG sigal that has a very complex structure was achieved through the implemetatio of three methods. Thus the first method provides a timefrequecy represetatio through a PCG sigal scalogram. Thus PCG sigal is coverted ito a graphical form more easily iterpreted by your cardiologist. A secod method of characterizatio of PCG sigal is by calculatig the statistical type of iformatio desity wavelet decompositio levels. The Shao etropy calculatio method uses the sigal sequece results after wavelet decompositio of the PCG sigal. The third method used to characterize the sigal is by the coversio based o the sigal obtaied i a two-dimesioal vector form. Thus PCG sigal is processed as a 2D image. The resultig images were decomposed ito a referece sigal with a specially writte program. The refereces sigal results were also used i the matchig algorithms i images processig. Cap.5 Origial cotributios The resultig algorithms were tested by simulatio programs desiged i C laguage usig LabWidows CVI Natioal Istrumets eviromet. After the simulatios, it was switched to recompile the programs for the microcotroller implemetatio. The fial DSP routies will be made after o board emulatio of the computer algorithms. The persoal cotributios are idicated as referred to the full versio of the thesis: Ow method for wavelet decimatio filterig algorithm implemeted i laguage C, o the basis of multi-resolutio theoretical wavelet trasform (sectio 2.0) 7

9 Ow method for determiig the wavelet fuctio by calculatig the recostructio error, suitable for performig sigal decompositio PCG (sectio 2., Table 2., Table 2.2, Figure 2.4, Figure 2.5.) Ow ad origial method to implemet time-frequecy scalogram o a embedded micro system usig color graphic display features (sectio 3.2, Figure 3.8, Figure 3.). Summary of results is show i Figure 5.. Desigig GUI buildig program for displayig time-frequecy scalogram (Appedix 2). Ow statistical evaluatio method by calculatig multi-resolutio decompositio of the Shao etropy partial applicatio of Euclidea distace. (Sectio 3.3 Table 3., Table 3.2, Figure 3.4, Figure 3.5) Summary of results is show i Figure 5.2. Ow method for determiig precise heart rate i a pathological coditios with oise sigals, by autocorrelatio of the level three wavelet decompositio (sectio 3.4, Figure 3.8) Utreated origial method i other literature, the traslatio time of PCG sigals multirate fractioal samplig. This method preserves all the origial features of the sigal amplitude. Summary of results is show i Figure 5.3. Utreated origial method i other literature to determie the evelope of the PCG sigal usig Hilbert trasforms. Summary of results is show i Figure 5.4. Utreated origial method i other literature, the PCG sigal correlatio methods as digital imagig. Summary of results is show i Figure 5.6. Desig of a multifuctio developmet system havig PCG sigal processig capabilities by usig DSP module (sectio 4.2.3, Figure 4.29) Desig of a software iterface for programmig graphical color LCD display DEM2860 (sectio 4..4, Figure 4.7, Figure 4., Figure 4.2) Desigig the program eeded to covert RGB565 LCD display (Appedix 3) Support program for calculatig FIR filters coefficiets for the Q.5: calculatig badpass iput filter ad FIR filters for calculatig the multirate samplig (Appedix ) Desigig a multipurpose program for commuicatio betwee the host program istalled i a PC ad the electroic equipmet (Appedix 2) Developmet ad implemetatio of a commuicatio protocol for devices desiged by usig USB2 iterface i the Medical Egieerig departmet (Appedix 5) Performig various circuits based o microcotrollers for use by studets of the Medical Egieerig Departmet. Promote the idea of aalysis device display features local PCG sigals Writig of 6 scietific articles published o the PCG sigal aalysis, ECG, ad portable devices equipped with complex data aalysis capabilities. 8