Evaluation of new diagnostic procedures of medical thermography in-vivo experiments

Transcription

1 Evaluaion of new diagnosic procedures of medical hermography in-vivo experimens by M. Kaczmarek 1, J. Rumiński 1, A. Nowakowski 1, A. Renkielska, J. Grudziński, W. Sojek 3 (1) Deparmen of Biomedical Engineering, Technical Universiy of Gdansk, Naruowicza 11/1, Gdansk, Poland; phone: , fax , mariusz@biomed.ei.pg.gda.pl, jwr@ei.pg.gda.pl, anowak@ei.pg.gda.pl; () Deparmen of Plasic Surgery and Burns, Medical Universiy of Gdansk, Marii Sklodowskiej-Curie 3a, Gdansk, Poland, aren@amg.gda.pl; jgrud@amg.gda.pl, (3) Deparmen of Animal Physiology, Gdansk Universiy, 80-8 Gdansk, Kladki 4, Poland, wojek@bioech.univ.gda.pl. Absrac The advanages and disadvanages of acive hermography in medical diagnosics using differen hermal exciaions: halogen lamps as a heaing source and ice and a fan as cooling sources are discussed. A new procedure of issues hermal properies idenificaion and a new image processing mehod used o increase conras beween healhy and injured issues are described. In-vivo experimens prove validiy of proposed mehods. 1. Inroducion We have shown earlier [1,, 3] ha he acive, dynamic hermography can be applied in medical procedures for monioring he sae of he skin and subdermal issue srucure during burns reamen. I gives objecive, measurable raings of reamen procedures. Ses of burns of differen degree were induced in series of in-vivo experimens on domesic pigs in fully conrolled condiions (basing on he Singer model [4]). For injury classificaion acive hermography procedures were performed. The mehod proved o be non-conac, non-invasive, clean and non-sressing, allowing wide area of invesigaion and objecive documenaion for diagnosics and evaluaion of a reamen process. However he value of heaing exciaion energy is limied by maximum accepable skin emperaure, around 4 0 C, o avoid pain or any conflic wih herapeuic processes. In effec he hermographic signal is raher small wha is limiing accuracy of measuremens. The aim of his paper is o examine if he cooling procedure migh be regarded as more suiable for burn injury diagnosics allowing he use of higher ampliudes of skin emperaure changes (emperaure decrease). Would i be safe, and easy in use? For heaing procedure he incremen of emperaure is only 6 0 C on he surface while for cooling procedures he decremen of emperaure migh be 30 0 C wihou any risk for a paien. This big difference in surface emperaure change is very imporan for furher image processing including fiing algorihms as i allows o improve signal o noise raio. If we assume he noise a he level of C (wha is a ypical value for mos of good hermographic cameras) and emperaure ampliudes for heaing T h = 6 0 C and for cooling T c = 30 0 C, he signal o noise raio is improved 5 imes.. Organisaion of experimens Young, weighing 0-30 kilograms, living boars were used for in-vivo experimens performed according o all rules defined in Polish law for animal experimens. Skin burn wounds of conrolled deph were inroduced by samping a copper bar of he boar s back. 60

2 In his paper we are reporing only experimens where he bar of he emperaure 90 0 C was in ouch wih he skin for 5, 10 and 15 seconds. Animals were in full anaeshesia during he burn injury. For reference daa he full-hickness biopsies followed by hisopahologic analysis were performed, o know exacly he degree of infliced burns. The hermographic measuremens were aken 5 hours afer he burn was infliced and hen every 4 hours during he consecuive 3 days. The general arrangemen of he measuremen sysem is ypical for acive hermography experimens [1, 3]. We use he AGEMA Thermovision 900 hermographic sysem. The hermal resoluion of he sysem is C. For heaing we use a se of halogen lamps as an exciaion source. The power and ime of irradiaion is conrolled in a big span of values. In his experimen he pulsed mode of irradiaion and emperaure measuremens in he cooling phase were performed. Momenary maximal emperaures a he irradiaed, esed surfaces were no exceeding 48 0 C. For cooling he ice was applied, hold in a hin plasic bag in ouch wih a esed issue for 10 seconds. Thermographic measuremens were aken during he recovery ime while self-heaing of he issue is dominan, afer aking he ice off. For cooling we applied also an air fan allowing undisurbed hermal regisraion during he cooling as well as a he heaing phases. I seems o be a very convenien and safe echnique giving very promising resuls. The phase of forced cooling is followed by recovery o he seady condiions, wha in his paper is called naural heaing. The sar of regisraion and he parameers of hermographic sequences (repeiion rae and he end of regisraion ime) are dependen on an exciaion mehod and issue emperaure recovery mechanism. Depending on a case he speed of regisraion varies from several frames per second o one frame every several seconds. 3. Idenificaion procedure The way of applicaion of a hermal exciaion as well as hermal properies of esed issue play he major role for a shape of he observed emperaure profiles see Fig. 1. Assuming for living issue ha only he recovery phase following an exciaion is observed we may sudy he cooling process afer opical heaing exciaion or he rise of emperaure afer cooling in he case of he ice sress. For he air fan mehod boh - cooling and rising phases - can be observed. Two measurable processes - heaing and cooling - may be relaed o differen physiological phenomena. The observed dynamic processes leading o equilibrium afer pulse exciaion (heaing or cooling) may be characerised by differen ime consans. For he wo phases he equivalen hermal models are described by differen equaions. Assuming he wo-exponenial model one may ge he ime dependence of skin surface emperaure as: T min 1 τ1c τ c () T + T e + T e = (1) for he naural cooling process (afer exernal heaing o T max = T min + T 1 + T, where T min =T equilibrium ), and for he naural heaing recovery (afer cooling o he value T min ): + T 1 1 e + T e () = τ1h τh T Tmin 1 () where: τ 1, τ - ime consans, c - indicaes he cooling and h - indicaes he heaing phase. The wo componens hermal model are applied here o calculae he complex surface emperaure profiles of a wo-layer medium. Due o limied accuracy of measured emperaure changes (small signal o noise raio) for some cases i migh be sufficien o 61

3 use only he one layer model expressed by one exponen facor. In recorded picures, he differences beween pixels of differen hermal properies are displayed during he observaion ime as in he example shown in Fig. b. For he acquired daa he fiing curve procedure using he Levenberg-Marquard or he Gauss-Newon algorihm is applied o esimae he equivalen model parameers. Some examples of fiing he daa o he one componen exponenial model for he described exciaions are presened in Table 1. One can differeniae beween healhy and burned issues basing on values of ime consans τ. For burned issue he values are correlaed wih he burn deph. For comparing he efficiency of proposed exciaion mehods and for classificaion of invesigaed issues an objecive measure is needed. We define here, as he basic figure of meri for each pixel i, he injury index - II i : i II i ref τ τ = i ref (3) τ + τ where: τ i - ime consan a he pixel i, and τ ref he ime consan a he healhy area aken as a reference. The reference area should be placed as close o he burned issue as i is possible or migh be aken from a symmerical poin of a esed body. The injury index is close o zero for issues of hermal properies similar o he healhy issue. I falls down o minus 1 for issues characerised by rapid hea exchange, e.g. he places of high vascularisaion caused by ligh superficial burns. I rises up o 1 for issues characerised by slow hea exchange, wha is he case of deep burns. Injury index allows discriminaion of he sae of he injured skin (deph of burns). To compare efficiency of differen exciaion mehods he synheic image of τ 1 should be calculaed. Afer applicaion of segmenaion procedure he new image is composed of n regions of differen hermal properies, which are relaed o he esimaed values of he ime consans. As an addiional figure of meri he dispersion coefficien D may be defined basing on he formula: D = n n j = 1 = 1 j n j τ j τ n( n 1) (4) where: n he number of regions discriminaed in he synheic image of τ 1 afer j segmenaion; τ he mean value of a ime consan in he region j. The formula is using he same concep as he sandard deviaion and is showing dispersion of he values of ime consans. The resoluion of he segmened image is dependen on he accuracy of measuremens performed, leading o discriminaion of a higher number n. The dispersion coefficien D calculaed for all mehods of exciaion is presened in Table 1 and Fig. 3. The bes resuls are obained for he ice sress mehod (he bigges dispersion coefficien), comparable resuls are for he boh phases (cooling and heaing) of he air fan mehod. The wors is he opical (halogen) heaing mehod due o limied emperaure rise afer exciaion. In his case he ime consan values for differen degrees of injury are close o each oher, he dispersion coefficien is of he smalles value. The presened daa for differen exciaions were aken in differen places of injury herefore he conclusions given here should be proved in addiional series of experimens. 4. Resuls The daa in Table 1 are obained for arbirary chosen characerisic Conrol Poins of burn wounds shown in Fig. a. One layer equivalen hermal model (one exponen facor) equaion (1) is applied. Insead of emperaure he emied radiaion R in arbirary unis are aken for calculaions. The Conrol Poin 1 is characerised by burn condiions: he bar 6

4 emperaure 90 0 C for 15 seconds conac wih skin; he Conrol Poin he bar emperaure 90 o C for 10 seconds conac wih skin, ec. The Conrol Poin 4 is he reference poin represening a healhy skin. Conrol Poin Table 1: Esimaed model parameers for differen issue exciaions Hisopahol ogic resul - % of skin damage Air fan naural heaing Air fan - cooling phase R min R 1 τ 1 [s] II R min R 1 τ 1 [s] II 1 [90 o C/15s] 86.4% [90 o C/10s] 63.6% [90 o C/5s] 1.5% [healhy] 0.0% dispersion coefficien of τ Ice sress naural heaing Halogen exciaion - cooling phase 1 [90 o C/15s] 86.4% [90 o C/10s] 63.6% [90 o C/5s] 1.5% [healhy] 0.0% dispersion coefficien of τ Taking ino accoun he se of model parameers he ime consan τ seems o be he bes for issue classificaion. For he ice sress cooling procedure he ime consan τ 1 of a healhy issue is almos wo imes smaller comparing o he ime consan characerisic for he full hickness burn.this can be explained as an effec of desrucion of he microcirculaion blood sysem for he III-rd degree burns. The hea ranspor o he skin surface is in his case poor. Therefore o reurn o he equilibrium emperaure, i akes longer ime hen for he healhy issue or for a issue under a healing process, characerised by increased blood circulaion. Figs. 4a-d) show esimaed ime consans τ 1 for he whole area of invesigaion and for all exciaion mehods. The injury index synheic picures for he air fan mehod are shown in Fig. 5a and b. The dark areas (he injury under a healing process) on boh picures are slighly differen. In he firs picure sharp edges of injuries are clearly seen while in he second one he injury areas are bigger and diffused. I can be explained by he difference of hea ranspor mechanism. The forced air-cooling is a quie fas process and he hea flow is mainly wodimensional. Hea exchange is possible only by a hin film of issues on he surface while for naural heaing process he hea flow is slower and he 3-dimensional hea exchange, wih big influence of deeper issues should be aken ino accoun. One can see in Fig. b ha afer recovery ime lasing 4 minues (he same as for he cooling phase) surface issues are sill cooler hen a he equilibrium. 5. Conclusions Discriminaion beween ime consans characerisic for he heaing and cooling phases needs some more invesigaion and sudy of basic physiological processes. Thermal exciaion influences condiions of hea exchange. The beer hermal conac and he lower hermal resisance he faser hermal response! Ice will be cooling faser han air sream; radiaion will be dependen on emperaure differences beween a esed surface and he environmen, ec. Therefore here we only claim ha i is possible o quanify and classify a burn injury and indicae affeced issue surface basing on visualisaion of he 63

5 ime-consans and injury index disribuion. We see a special possibiliy of using he air cooling wih conrolled emperaure in wide range - from lower o high emperaures. I allows o use higher ampliudes of exernal exciaion similar o hose used in he ice sress mehod bu he air mehod is fully non-conac and sepic. The cooling mehods seem o be beer from he herapeuic poin of view in burns diagnosics han he heaing as he exernal heaing of issues may addiionally desroy deeper layers of he skin. The measuremen saring momen, promply afer emperaure exciaion, is of he highes significance for proper regisraion of hermograms. The oher problem is he ime period beween injury and diagnosic examinaion. To our experience he mos valuable resuls are obained during he firs and he second days following an acciden. The clinical mos valuable feaure of he mehod is deerminaion of he deph of a burned issue. Sill more experimens o se he hresholds of injury index for classificaion of issues for surgical or pharmacological reamen are necessary. Acknowledgemen A par of his work was financed by he KBN research gran 7T11E The auhors hank for he echnical help o Mr A. Galikowski. REFERENCES [1] NOWAKOWSKI A., KACZMAREK M., RUMINSKI J., HRYCIUK M., RENKIELSKA A., GRUDZINSKI J., SIEBERT J., JAGIELAK D., ROGOWSKI J., ROSZAK K., STOJEK W., Medical applicaions of model based dynamic hermography, Thermosense XXIII Proc. of SPIE, vol. 4360, 001, p [] RUMIŃSKI J., KACZMAREK M., NOWAKOWSKI A., Medical Acive Thermography A New Image Reconsrucion Mehod, Lecure Noes in Compuer Science, LNCS 14, Springer, Berlin-Heidelberg, 001, p [3] KACZMAREK M., NOWAKOWSKI A., RENKIELSKA A., Raing burn wounds by dynamic hermography, Proc. of QIRT 000, 000, p [4] SINGER A.J., BERRUTI L., THODE HC J.R., MCCLAIN S.A., Sandardised burn model using a muliparameric hisologic analysis of burn deph, Academic Emergency Medicine, vol. 7:1, 000, p

6 a) b) 38 5 Temperaure [ 0 C] Injured area Healhy area Temperaure [ 0 C] Injured area Healhy area Time [s] Time [s] Fig. 1. Time response of injured and healhy issues; a) for he opical heaing mehod; b) for he ice sress mehod a) Fig.. a) Invesigaion areas deails in Table 1, b) Time response of injured and healhy issues in Conrol Poins 3 and 4 for he air fan mehod (cooling and heaing phase) b) air fan - naural heaing ice sress - naural heaing air fan - cooling phase halogen heaing - naural cooling 100 air fan - naural heaing ice sress - naural heaing air fan - cooling phase halogen heaing - naural cooling 00 τ Dispersion Coefficien a) Conrol Poin Fig. 3. a) Esimaed ime consan τ 1 for differen exciaions, b) he dispersion coefficien calculaed for differen exciaions 0 b) Mehod 65

7 a) b) c) d) Fig. 4. Synheic images of esimaed τ 1 parameer for: a) he air fan naural heaing phase, b) he ice sress naural heaing phase, c) he air fan cooling phase, d) he halogen heaing cooling phase; all done for second day invesigaion a) b) Fig. 5. Injury index images for he air fan mehod for invesigaion done 48 hour following he injury creaion; a) cooling phase; b) naural heaing phase 66