842 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 35, NO. 10, OCTOBER 1988 Multispectral Imaging of Burn Wounds: A New Clinical Instrument for Evaluating Burn Depth MARTIN A. AFROMOWITZ, MEMBER, IEEE, JAMES B. CALLIS, DAVID M. HEIMBACH, LARRY A. DESOTO, AND MARY KAYE NORTON Abstract-A real-time video imaging system (the imaging burn depth indicator, or IBDI) is described which can discriminate areas of burn wounds expected to heal in three weeks or less from the day of injury from those areas not expected to heal in that time period. The analysis can be performed on or about the third day postburn on debrided burn wounds. The relative diffuse reflectivity of the burn wound is measured in the red, green, and near infrared wavelength bands and an algorithm established previously is used to translate this optical data into burn healing probabilities. The IBDI produces a true-color and a false-color image of the burn. The false-color image consists of up to four colors, each of which in- dicates a distinct range of probability that the area of the burn so col- ored will heal within 21 days. Over 100 burn wound sites were studied. Burn sites were evaluated on day three postburn by our instrument and by the attending physi- cian. Overall, the IBDI was more accurate in predicting burn healing than were the attendiag physicians. For wounds judged to be difficult to assess, the IBDI’s burn healing predictions were 86 and 79 percent accurate for wounds of intermediate depth which healed in less than 21 days and more than 21 days, respectively. The predictions of the surgeon were 71 and 48 percent accurate by comparison. BACKGROUND S EARLY excision plays an ever increasing role in A bum management, knowledge of the time required for healing becomes crucial. If small to moderate sized bums that will not heal within three weeks are excised and grafted within the first five days postbum, the patient could be discharged as soon as the donor sites heal. The entire hospitalization would rarely extend as long as three weeks. On the other hand, if the bum can heal on its own in less than three weeks, the patient can be spared oper- ation, donor sites, and blood transfusions. In general, such superficial bums heal without scarring, and the hospital- ization is no more than three weeks. Incomplete knowl- edge of the wound can lead to erroneous diagnoses, of Manuscript received January 28, 1988; revised May 2, 1988. This work was supported by the U.S. Army Medical Research and Development Command under Contract DAMD-17-85-C-5106. M. A. Afromowitz and L. A. DeSoto are with the Department of Elec- trical Engineering, University of Washington, Seattle, WA 98195. J. B. Callis is with the Department of Chemistry, University of Wash- ington, Seattle, WA 98195. D. M. Heimbach is with the Department of Surgery, University of Washington, Seattle, WA 98195. M. K. Norton was with the Center for Bioengineering, University of Washington, Seattle, WA 98195. She is presently with Advanced Tech- nology Laboratories, Bothell, WA 98041. IEEE Log Number 8822626. course. A wound estimated to be superficial enough to heal in three weeks, that eventually requires grafting or does not heal for four or more weeks, markedly prolongs the patient’s hospital stay. Conversely, wounds that are quite superficial are sometimes incorrectly classified and needlessly excised with the attendant risks of surgery. For all these reasons, an early accurate estimate of healing time becomes a crucial factor in modem burn manage- ment. The instrument we have developed is intended to im- prove the accuracy of early bum diagnosis, thereby in- creasing the likelihood of appropriate bum wound man- agement. The imaging bum depth indicator (IBDI) is based on several years of experimental and theoretical re- search conducted at the University of Washington on the optical properties of bum wounds [1]-[5]. Our studies sought to verify and extend the work of Anselmo and Za- wacki [6], [7] whose early near infrared and visible mul- tispectral photographic work on burns suggested a corre- lation between optical reflectivity and burn healing. In our earlier work, a small noncontacting bedside re- flectometer was developed, and used to measure the red- to-infrared and green-to-infrared diffuse reflectivity ratios of selected sites on bum wounds. Key results of this ear- lier research are summarized below: Measurements of the optical reflectivity of bum wounds on the third day postbum in the red, green, and near infrared bands were shown to be strongly correlated with time-to-healing. In one major clinical study of 569 bum sites, our optical bum wound characterization anal- ysis discriminated with 77 percent accuracy between bum sites that would or would not heal within 21 days of in- jury. Obvious superficial and obvious full thickness bums were excluded from the study. These results contrast with an experienced bum surgeon’s 50 percent correct identi- fication rate on the same group of patients on day three postbum. A Kubelka-Munk model of the optical properties of clean (debrided) bum wounds indicated that the back- scattering of red, green, and near infrared light from a wound is a function of the thickness of the denatured col- lagen layer at the surface of the wound (eschar), the vol- ume fraction of blood in the tissue just below this dena- tured layer where vascular structures are still patent, and the oxygen saturation of this perfusing blood. These pa- 0018-9294/88/1OO0-0842$01 .OO @ 1988 IEEE
Transcript
842 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 35, NO. 10, OCTOBER 1988
Multispectral Imaging of Burn Wounds: A New Clinical Instrument for Evaluating Burn Depth MARTIN A. AFROMOWITZ, MEMBER, IEEE, JAMES B. CALLIS, DAVID M. HEIMBACH,
LARRY A. DESOTO, AND MARY KAYE NORTON
Abstract-A real-time video imaging system (the imaging burn depth indicator, or IBDI) is described which can discriminate areas of burn wounds expected to heal in three weeks or less from the day of injury from those areas not expected to heal in that time period. The analysis can be performed on or about the third day postburn on debrided burn wounds.
The relative diffuse reflectivity of the burn wound is measured in the red, green, and near infrared wavelength bands and an algorithm established previously is used to translate this optical data into burn healing probabilities.
The IBDI produces a true-color and a false-color image of the burn. The false-color image consists of up to four colors, each of which in- dicates a distinct range of probability that the area of the burn so col- ored will heal within 21 days.
Over 100 burn wound sites were studied. Burn sites were evaluated on day three postburn by our instrument and by the attending physi- cian. Overall, the IBDI was more accurate in predicting burn healing than were the attendiag physicians. For wounds judged to be difficult to assess, the IBDI’s burn healing predictions were 86 and 79 percent accurate for wounds of intermediate depth which healed in less than 21 days and more than 21 days, respectively. The predictions of the surgeon were 71 and 48 percent accurate by comparison.
BACKGROUND S EARLY excision plays an ever increasing role in A bum management, knowledge of the time required
for healing becomes crucial. If small to moderate sized bums that will not heal within three weeks are excised and grafted within the first five days postbum, the patient could be discharged as soon as the donor sites heal. The entire hospitalization would rarely extend as long as three weeks. On the other hand, if the bum can heal on its own in less than three weeks, the patient can be spared oper- ation, donor sites, and blood transfusions. In general, such superficial bums heal without scarring, and the hospital- ization is no more than three weeks. Incomplete knowl- edge of the wound can lead to erroneous diagnoses, of
Manuscript received January 28, 1988; revised May 2, 1988. This work was supported by the U.S. Army Medical Research and Development Command under Contract DAMD-17-85-C-5106.
M. A. Afromowitz and L. A. DeSoto are with the Department of Elec- trical Engineering, University of Washington, Seattle, WA 98195.
J . B. Callis is with the Department of Chemistry, University of Wash- ington, Seattle, WA 98195.
D. M. Heimbach is with the Department of Surgery, University of Washington, Seattle, WA 98195.
M. K. Norton was with the Center for Bioengineering, University of Washington, Seattle, WA 98195. She is presently with Advanced Tech- nology Laboratories, Bothell, WA 98041.
IEEE Log Number 8822626.
course. A wound estimated to be superficial enough to heal in three weeks, that eventually requires grafting or does not heal for four or more weeks, markedly prolongs the patient’s hospital stay. Conversely, wounds that are quite superficial are sometimes incorrectly classified and needlessly excised with the attendant risks of surgery. For all these reasons, an early accurate estimate of healing time becomes a crucial factor in modem burn manage- ment.
The instrument we have developed is intended to im- prove the accuracy of early bum diagnosis, thereby in- creasing the likelihood of appropriate bum wound man- agement. The imaging bum depth indicator (IBDI) is based on several years of experimental and theoretical re- search conducted at the University of Washington on the optical properties of bum wounds [1]-[5]. Our studies sought to verify and extend the work of Anselmo and Za- wacki [6], [7] whose early near infrared and visible mul- tispectral photographic work on burns suggested a corre- lation between optical reflectivity and burn healing.
In our earlier work, a small noncontacting bedside re- flectometer was developed, and used to measure the red- to-infrared and green-to-infrared diffuse reflectivity ratios of selected sites on bum wounds. Key results of this ear- lier research are summarized below:
Measurements of the optical reflectivity of bum wounds on the third day postbum in the red, green, and near infrared bands were shown to be strongly correlated with time-to-healing. In one major clinical study of 569 bum sites, our optical bum wound characterization anal- ysis discriminated with 77 percent accuracy between bum sites that would or would not heal within 21 days of in- jury. Obvious superficial and obvious full thickness bums were excluded from the study. These results contrast with an experienced bum surgeon’s 50 percent correct identi- fication rate on the same group of patients on day three postbum.
A Kubelka-Munk model of the optical properties of clean (debrided) bum wounds indicated that the back- scattering of red, green, and near infrared light from a wound is a function of the thickness of the denatured col- lagen layer at the surface of the wound (eschar), the vol- ume fraction of blood in the tissue just below this dena- tured layer where vascular structures are still patent, and the oxygen saturation of this perfusing blood. These pa-
0018-9294/88/1OO0-0842$01 .OO @ 1988 IEEE
AFROMOWITZ et al . : MULTISPECTRAL IMAGING OF BURN WOUNDS 843
rameters are in turn assumed to correlate with bum depth and burn healing time.
Correlation of the reflection data with the healing outcomes of 569 bum sites permitted us to establish a use- ful algorithm. The probability of healing within three weeks of the day of injury P for any bum site is given by the following expression:
P = ex/(l + ex)
wherex = -7.22 - 5.11 ( G / Z R ) + 9.22 ( R / Z R ) , and R , G, and IR denote the red, green, and near infrared re- flectivity of the bum site, measured on the third day post- bum. The sources of light for the R , G, and IR measure- ments were standard light emitting diodes, having center wavelengths of approximately 635, 565, and 880 nm re- spectively.
The accuracy of prediction of bum healing based on this optical reflection technique is independent of patient age, sex, race, size of bum, burn etiology, or bum loca- tion.
APPROACH TO THE PROBLEM Utilization of the optical reflectometer approach to pre-
dicting bum healing in the clinical setting requires map- ping each new bum on gridded charts showing the body outlines, and making careful measurements of the reflec- tion ratios, point by point, at a number of sites. This tech- nique is fairly time consuming for large bums, especially where diverse surface coloration may indicate significant bum depth variation across the wound. We saw a need to automate the process and to provide images of bum wounds with the healing probabilities automatically dis- played.
Our approach to the problem of automating the char- acterization of bum wound healing time, or equivalently, bum depth, was to develop a real-time video system [8] that could measure the red, green, and near infrared re- flectivity of an entire bum area, and calculate on a point by point basis the probability of bum healing in three weeks. An image of the bum area is displayed on a color video monitor, showing by false color our estimate of the probability that each area will heal within three weeks. This information, along with other clinical signs, can be used to plan the management of the bum wound.
Documentation of the bum is made easy by permitting the operator to freeze either a true-color picture of the bum or the corresponding false color reflectivity analysis on a video monitor, and take an instant 8 X 10 in color picture of either image for study or inclusion in the pa- tient’s file. Patient information or other data can be placed in a title window which appears on the bottom of the video screen, so that each hard copy picture can be readily iden- tified.
DESCRIPTION OF THE INSTRUMENT The overall block diagram of the IBDI is shown in Fig.
1. A solid-state monochrome silicon charge-coupled de- vice (CCD) video camera (Pulnix model TM-3410-0; 16
Motor Signal
Processor Unit
A Color Monitor Color Printer
Fig. 1. Block diagram of the imaging bum depth indicator (IBDI).
mm lens) with disabled automatic gain control is focused on the bum wound. The camera sees the subject through a color filter wheel, which rotates in front of the camera lens at 300 r/min. The wheel contains four different filters which transmit narrow-band red, green, blue, and near infrared light. Fig. 2 shows the normalized spectral pass- bands of our filter combinations. The filters were selected to yield a close correspondence to the red and green spec- tra of the LED’s used in the reflectometer described above. The IR band was allowed to be considerably wider in the present instrument. No significant deterioration in system performance was noted however. The filters used in each quadrant are as follows:
Green: Wratten Filter 61 plus 700 nm cutoff Red: Wratten Filter 25R plus 700 nm cutoff NIR: Wratten Filter 87C. The long wave cutoff filter for the visible images was
necessary since the Wratten filters have passbands in the near infrared. The long wave cutoff in the near infrared image is provided by the intrinsic fall off of the sensitivity of the silicon CCD device at about 1100 nm. Neutral den- sity filters were also placed in the IR and red sectors to approximately equalize the response of the camera to each wavelength band when it was focused on a white card illuminated by our quartz-halogen flood lamp.
The rotation of the filter wheel must be synchronized to the 60 Hz vertical drive signal. An indexing pulse is gen- erated optically at the same point of each revolution of the filter wheel. This indexing pulse is used to determine if the wheel is positioned correctly so that acquisition of each frame will occur while the proper filter is wholly in front of the camera lens. When the system is first turned on, it is necessary for the rotational rate of the filter wheel to be different from its synchronized rate so that the wheel can automatically reach the proper position with respect to the vertical drive signal. The filter wheel is driven by a 60 Hz synchronous motor, which is powered by a signal derived from the 15.75 kHz horizontal drive. When the filter wheel in not in its proper position with respect to the vertical drive, the filter wheel motor is powered by a signal at 59.77 Hz, which causes the wheel to rotate
844 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 35, NO. 10, OCTOBER 1988
Passbands of Filters used in Color Wheel
4
400 son m n 7nn xnn vno inno 1 1 0 0
W a ~ d e n ~ l h . in nm
Fig. 2. Normalized spectral passbands of the filter combinations used in the filter wheel.
slightly slower than normal, eventually drifting into a synchronous position. When the synchronous position is achieved, the filter wheel motor is powered at 60 Hz, and the synchronous position is maintained. The maximum time to achieve synchronization is less than 5 s.
The video signals acquired by the camera are digitized and processed in the signal processing unit (SPU). The SPU is designed around the Intel Multibus system. The video portion of the SPU consists of one RGB-512 and three FB-5 12 cards manufactured by Imaging Technol- ogy, Inc. The RGB-512 contains a high-speed 8 bit A/D and three high-speed D/A converters. The RS-170 video signal from the camera is applied to the A/D input and digitized in real time. The resolution of the RGB-512 is 480 by 512 pixels. The digitized output of the A/D is transferred to the three FB-512 frame buffers, each of which contains 256 kbytes of memory. The frame buffers can be commanded to continuously acquire an image or to acquire an image starting at the next vertical interval after the command. The frame buffers also send data back to the D/A converters on the RGB-512 where they are converted to the analog red, green, and blue signals suit- able to drive the color monitor (Panasonic MT-1340G).
The SPU also contains the Intel iSBC 86/30 computer circuit card used to control the system and to do the image processing calculations. The iSBC 86/30 contains an 8086 microprocessor, 128 kbytes of random access memory (RAM), an ASCII serial port, and parallel ports. The sys- tem software is contained in two erasable programmable read-only memories (2732 EPROM’s). When the system is tumed on, a bootstrap loader in EPROM loads an ex- ecutable program into RAM from a load module also stored in EPROM. The loader then transfers control to the system software for execution.
The SPU interfaces with an RS-232 terminal (Qume model QVT-101). Activating certain function keys on the terminal control the operation of the system.
In the first mode of operation, the operator holds a stan- dard white reflector card in the camera’s field of view. The instrument measures the intensity of light reflecting off this card in the three wavelength bands used to predict
burn healing. This procedure calibrates the instrument’s response to the red, green, and near infrared illumination spectrum of the flood lamp. It should be noted that since the algorithm established for predicting the bum healing probability contains only ratios of reflected intensities, changes in the absolute intensity of illumination on either the reference card or subject caused by varying distances to the light source are of little concern as long as 1) the light levels are within the linear range of the CCD and the associated digitizing circuitry, and 2) the light levels are high enough to provide a good S I N ratio.
In a second mode of operation, video frames of the sub- ject are acquired sequentially through the red, green, and blue filters, once each revolution.of the filter wheel. These frames are displayed on the color inonitor as a true-color image of the selected bum site at a rate of 5 images per s. This mode is used for camera setup, focusing, etc. At a keyboard command, the true-color image can be frozen on the monitor. This permits the operator to make a hard copy of the true-color image of the bum under investi- gation. Although our RGB filters do not meet NTSC stan- dards, the true-color image displayed by the monitor is certainly acceptable for qualitative purposes.
Another keyboard command places the system in the third mode of operation, and causes three successive video frames to be acquired sequentially through the red, green, and near infrared filters. These frames are digitized and stored in the frame buffers. The microprocessor in the SPU then analyzes the information in these three frames, pixel by pixel, and determines the probability of bum healing for that pixel based on the algorithm established previ- ously. The instrument then displays, within 30 s, a false- color image of the bum wound in which the colors indi- cate selected ranges of probabilities of bum healing. In- tensity (gray -level) information is maintained in the false- color image to enhance the recognizability of the features in the image. The meanings of the colors used in the false- color image can be controlled by a simple set-up proce- dure. Patient information can be typed onto the terminal and displayed in a window superimposed on the color im- ages. Hard copy 8 X 10 in photographs or transparencies of the color monitor screen can be obtained simply by loading a film plate into an attached Polaroid Videoprinter 8, exposing the film, and processing the plate in an instant film processor. Alternatively, photographs may be taken of the monitor directly. A complete description of the sys- tem, including details of the software, may be found in
The SPU, color monitor, hard copy unit, user terminal and storage areas for the camera, tripod, lights and film are fully enclosed in a mobile cabinet with dimensions of approximately 5 x 4 X 3 ft ( L x H x 0). During use, the camera apparatus and high intensity lamp are mounted on tripods separate from the main system cabinet and con- nected to it by a 25 ft cable which allows for flexibility in placing the apparatus in a patient’s room.
It is important to assure that the subject is illuminated primarily by one light source with a broad and featureless
[91.
AFROMOWITZ et al.: MULTISPECTRAL IMAGING OF BURN WOUNDS 845
spectrum. Incandescent sources are better that fluorescent sources, which contain fairly sharp spectral peaks. This assures that the spectra selected by the color filters will not be significantly modified by the spectrum of the source. In addition, the light source should be placed ap- proximately behind the camera, so that the camera does not see shadowed regions on curved surfaces of the sub- ject.
CLINICAL TRIAL After the IBDI was built, we embarked upon a year-
long clinical study [9] conducted at the Harborview Bum Center, Harborview Medical Center, Seattle. We had two objectives for this study. The primary objective was to evaluate the prediction accuracy of the IBDI and to com- pare this accuracy with that of the attending bum surgeon. The second objective was to evaluate the operational as- pects of the IBDI, including ease of use, reliability, and physician acceptance in the bum center environment.
Approximately 40 patients admitted to the Harborview Bum Center ranging in age from six months to 82 years of age were involved in the clinical study. Any patient with a new bum of greater than approximately 5 percent total body surface area was eligible to participate. How- ever, data are presented on only 32 of those patients with a total of 112 sites imaged. Due to various factors includ- ing infection, the inability to obtain follow-up informa- tion on certain patients, and lack of surgical information for some of the grafted bums, eight patients had to be eliminated from the study.
The protocol began when a patient was admitted and ended when the wound itself had healed, a time span usu- ally no longer than 30 days. Upon admission to our study, the bum site was sketched on body part diagrams to per- mit relocation for follow-up. The number of bum sites to be evaluated on each bum wound was chosen at the time of imaging and numbered on the gridded body part sheet. The sites were selected in order to best represent the com- plexity and extent of the bum.
All images were taken on the third day postburn since previous studies [3], [SI had demonstrated that during the first 48 h after injury, bum wounds are unstable. The im- ages were taken after either the morning or afternoon hy- drotherapy and debridement (commonly referred to as tanking) so that the wounds would be free of organic slough, medication, or antibacterial creams. For each bum site we obtained a true-color image, a false-color image, and a measurement of the redhnfrared and greedinfrared reflectivity ratios, provided by the reflectometer used in the previous studies [3]-[5]. The false-color images gen- erated by the IBDI were composed of four colors, which represent the following:
Blue = an area with a 75-100 percent probability of healing within 21 days.
Green = 50-75 percent probability of healing within 21 days.
Yellow = 25-50 percent probability of healing within 21 days.
Red = 0-25 percent probability of healing within 21 days.
It is important to note that the colors displayed in the false-color image have significance only within areas of the bum wound. Outside the wound, the pigmentation of the skin can cause any of the four colors to be displayed.
At the time of imaging, one of three attending bum sur- geons was asked to make a clinical assessment of each bum site, stating either that the bum site will heal within 21 days or will not heal within 21 days. The physicians were not given any information about the IBDI’s healing prediction, to avoid biasing their judgments. The sites were monitored for final outcome by follow-up with the patient at clinic appointments which were scheduled reg- ularly after discharge. For those sites which were not grafted, the number of days to healing was recorded. For those bum sites which were grafted, the surgeon was asked to confirm or modify his earlier clinical assessment at the time of excision and grafting. A research nurse was present during these surgical procedures to assure that the surgeon knew precisely which sites we were interested in, and to record the surgeon’s comments.
In addition to the data described above, additional pa- tient information was obtained in order to determine if any other factors were significant in assessing bum depth. These are
1) age and sex of patient, 2) the body site according to six categories, 3) the etiology of the bum according to four categories, 4) the total body surface area of the bum (TBSA), and 5 ) a medical history and any possible complications. Race was not included since the pigmented epidermis
is generally sloughed in the early course of debridement and does not contribute to the optical properties of a wound.
RESULTS We include several sets of images, both true-color and
false-color, to demonstrate the quality of the output of the IBDI. Figs. 3-5 illustrate three bums of different etiology and depth. For each bum wound, the upper photograph presents a true-color image of the bum and the lower pho- tograph shows the corresponding false-color image. As discussed previously, all images were taken on the third day postburn.
In the first pair of photographs [Fig. 3(a) and (b)], a contact bum on the palm of an 82-year-old female is shown. The bum is clearly superficial. A visual indication of this classification is the red, vascularized appearance of the wound. The false-color image is purely blue (greater than 75 percent probability of healing within 21 days) showing the uniformity of the site. This bum site com- pletely reepithelialized within six days.
The second pair of photographs [Fig. 4(a) and (b)] shows a scald bum on the foot of a 65-year-old black, diabetic female. The bum sites vary in depth as demon- strated by the different false colors. The area on the lateral side of the foot was a bum of superficial thickness with
846
was correct in this
and fluids had begun oozing from the site. We propose that the use of crossed polarizers on the light source and
able to use autografts. the IBDI's pixel by pixel resolution would be of' great value in detemiining which sites abso-
848 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 35, NO. 10, OCTOBER 1988
TABLE I PHYSICIAN VERSUS IBDI
All 112 sites
Predicted to Heal in < 21 Days Predicted to Heal in > 2 1 Days
correctly. This confirms that the bandwidth of the near infrared measurement is not a sensitive parameter in our healing prediction algorithm.
DISCUSSION OF RESULTS AND CONCLUSIONS The quantitative analysis of results presented in the pre-
ceding section depends to some degree on qualitative as- sessments. For example, the number of days to healing is really only accurate to within one day. This judgment is further suspect because it was often made by the untrained out-patients and reported to the project nurse. In the case of grafted burns, where days-to-healing has no meaning, the bum surgeon was twice asked to make a healing pre-
diction for each site, once on postburn day three, and once again during excision. It was this latter assessment, as to whether the surgeon still thought the burn site would or would not heal within 21 days if not excised, that was recorded as the outcome for that site. While in surgery, the physician is able to make conclusive determinations of burn depth since he is able to tangentially excise the burn until a viable bed of tissue is reached. Absolute burn depth, of course, must be regarded in the context of the normal total skin thickness at that body site in order to predict burn healing potential. Thus, the burn healing pre- diction, even in surgery, is a subjective assessment based upon the experience of the surgeon, absent excision down to subcutaneous tissue. As a result, the accuracy of the instrument’s predictions on intermediate depth burns that were grafted prior to 21 days postburn cannot be known with certainty. In this study, there were at most 20 sites out of a total of 112. Furthermore, if a burn is a mosaic bum having partial and full thickness areas, the general practice is to graft the entire site. Therefore, sites which would have healed on their own were sometimes grafted and categorized as a nonhealing site. This is often true of sites on the periphery of a burn. This introduced a source of error and bias in the data as well.
Since three different bum surgeons made site predic- tions for this study, we were able to observe differences in prediction accuracy. The percentages of accurate pre- dictions made by the three surgeons (as assessed by the number of correct predictions divided by the total number of predictions made) ranged from 53-89 percent. Thus, there is a large variation in burn healing prediction accu- racy even for experienced bum surgeons. And this finding cannot be attributed to the surgeons consistently assessing “easy” or “difficult” burns, as line 5 of Table IV shows there is no correlation between the burn surgeons and the patient or wound variables.
AFROMOWITZ et ai . : MULTISPECTRAL IMAGING OF BURN WOUNDS 849
Table IV also offers some insight into a possible source of error on the part of the physicians. As noted above, the physicians’ predictions were correlated ( r = 0.50) with the type of bum. On the other hand, the prediction of the IBDI was essentially uncorrelated ( r = 0.10) with this variable. Since the accuracy of prediction of the IBDI ex- ceeded that of the surgeons, we are forced to conclude that the surgeons may be variably predisposed to view certain types of bums as being deeper, and other types of bums as shallower than they really are. The data suggests that the IBDI, which is not subject to this prognostication bias, could be used to the advantage of the patient in re- ducing the incidence of unnecessary surgery in the first case, and permitting earlier tangential excision and re- duced hospitalization time in the second case.
Our clinical experience with the imaging bum depth in- dicator at Harborview Bum Center has been extremely positive. All the surgeons and staff who observed the op- eration of the instrument were eager to see it remain in the hospital, and wanted to have it integrated into the nor- mal patient assessment procedure. We believe, however, that the prototype IBDI can be improved in several areas, and that this should be done before it is released for un- supervised clinical use.
In the first place, the system does not alarm the user in the event that the video signals are too large (leading to saturation of the digitizer) or too small (causing excessive quantization errors because of low S I N ratio). This mod- ification is deemed essential to provide a system as free as possible from operator-induced imaging errors. In ad- dition, as mentioned above, a polarized light source and cross-polarized imaging filter would significantly reduce the problem of specular reflection and glare from the skin surface which occurs most frequently on moist wound surfaces.
REFERENCES
M. A. Afromowitz, D. M . Heimbach, and M. W. Bums, 111, “Electro- optic bum depth indicator,” XI1 Int. Conf. Med. Biol. Eng.; V Int. Conf. Med. Phys., Jerusalem, Aug. 19-24, 1979. M. A. Afromowitz, “Early characterization of bum injuries,” in Proc. Int. Burn Res. Con$, US Army Inst. Surg. Res. (US Army Med. R & D Command), San Antonio, TX, Jan. 19-21, 1983, p. 47. G. S. Van Liew, “A statistical and optical analysis of light reflectances off bum injured skin, ” Master’s thesis, Univ. Washington, Seattle, WA, 1984. D. M. Heimbach, M. A. Afromowitz, L. H. Engrav, J. A. Marvin, and B. Perry, “Bum depth estimation-Man or machine,” J . Trauma, vol. 24, p. 373, 1984. M. A. Afromowitz, G . S. Van Liew, and D. M. Heimbach, “Clinical evaluation of bum injuries using an optical reflectance technique,” IEEE Trans. Biomed. Eng., vol. BME-34, p. 114, Feb. 1987. V. J. Anselmo and B. E. Zawacki, “Infrared photography as a diag- nostic tool for the bum wound,” Proc. Soc. Photo-Optical Instrum. Eng . , vol. 40, p. 181, 1973. -, “Multispectral photographic analysis: A new quantitative tool to assist in the early diagnosis of thermal bum depth,” Ann. Biomed. Eng . , vol. 5 , p. 179, 1977. L. A. DeSoto, “A bum depth imaging system,” Master’s thesis, Univ. - _ . Washington, Seattle, WA; 1986.
cator,” Master’s thesis, Univ. Washington, Seattle, WA, 1987. [9] M. K. Moore, “A clinical evaluation of the imaging bum depth indi-
Martin A. Afromowitz (S’63-M’69-M’81) re- ceived the B.S. , M.S., and Ph.D. degrees in elec- trical engineering from Columbia University, New York, NY, in 1965, 1966, and 1969, respectively.
He spent five years at Bell Telephone Labora- tories, Murray Hill, NJ, working on 111-V semi- conductor LED’s and laser structures. In 1974 he joined the Center for Bioengineering, University of Washington, Seattle, and two years later be- came a Research Assistant Professor in the De- partment of Electrical Engineering. He is now an
Associate Professor of Electrical Engineering and an Adjunct Associate Professor of Bioengineering. His research interests include medical instru- mentation, optical fiber sensors, and microfabrication.
James B. Callis received the B.S. degree in chemistry from the University of California, Davis, and the Ph.D. degree in physical chemistry from the University of Washington, Seattle, in 1965 and 1970, respectively.
He undertook postdoctoral studies in biophys- ical chemistry at the University of Washington (1970-1972) and the University of Pennsylvania, Philadelphia (1972-1973). His first academic ap- pointment was in 1975 at the Department of Pa- tholoev in the Universitv of Washington’s Medi- ”< -
tal School. In 1978, he returned to the Chemistry Department as Director of Analytical Services. He was appointed to Research Associate Professor in 1980, promoted to Research Professor in 1984 and to Professor in 1986. His major research interest is in instrumentation for optical spectroscopy. He is currently developing new types of laser-based chromatographic de- tectors, a high-resolution infrared microscope and novel imaging and spec- troscopic devices for medical diagnosis. In 1984, a new dimension was added to his work when he and his colleague B. Kowalski founded the Center for Process Analytical Chemistry. Research for this organization involves development of ultraminiature spectrometers based upon novel transform concepts.
David M. Heimbach received the B.A. and M.D. degrees from Come11 University, Ithaca, NY. He was trained at Parkland Memorial Hospital, Uni- versity of Texas Southwestem Medical School, and at the University of Glasgow, Glasgow, Scot- land.
He joined the University of Washington, Se- attle, in 1974, and is currently a Professor in the Department of Surgery and Director of the Uni- versity of Washington Bum Center at Harborview Medical Center.
Dr. Heimbach is immediate past president of the American Bum Asso- ciation.
Larry A. DeSoto was born in Fort Worth, TX, in February 1949. He received the B.S. degree in electrical engineering from Louisiana Tech Uni- versity, Ruston, LA, in 1970, and the M.S. de- gree in electrical engineering from the University of Washington, Seattle, WA, in 1986.
From 1971 until 1980 he was employed in the military engineering division of the Western Elec- tric company based in Greensboro, NC. From 1980 until 1985, he was assigned to Bell Tele- phone Laboratories in Whippany, NJ, where he
850 IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING, VOL. 35, NO. 10, OCTOBER 1988
participated in the development of signal processing software for military surveillance applications. He is currently a Ph.D. student in electrical en- gineering at the University of Washington. His primary research interest is in medical imaging.
Mary Kaye Norton was born in Seattle, WA. She received the B.S. degree in biology and chemistry in 1985 from Gonzaga University, Spokane, WA, and the M.S.E. degree in bioengineering with an emphasis in medical instrumentation from the University of Washington, Seattle, in 1987.
She is presently employed with Advanced Technology Laboratories as a Regulatory Affairs Associate working with product development/ manufacturing compliance to federal medical-de- vice reeulatins. Her research interests include de- w
velopment of protocols for validating clinical imaging systems and assess- ing clinical feasibility from an engineering perspective.
