The main objective of the facial edema evaluation is providing the needed information to determine the effectiveness of the anti-inflammatory drugs in development. This paper presents a system that measures the four main variables present in facial edemas: trismus, blush (coloration), temperature, and inflammation. Measurements are obtained by using image processing and the combination of different devices such as a projector, a PC, a digital camera, a thermographic camera, and a cephalostat. Data analysis and processing are performed using MATLAB. Facial inflammation is measured by comparing three-dimensional reconstructions of inflammatory variations using the fringe projection technique. Trismus is measured by converting pixels to centimeters in a digitally obtained image of an open mouth. Blushing changes are measured by obtaining and comparing the RGB histograms from facial edema images at different times. Finally, temperature changes are measured using a thermographic camera. Some tests using controlled measurements of every variable are presented in this paper. The results allow evaluating the measurement system before its use in a real test, using the pain model approved by the US Food and Drug Administration (FDA), which consists in extracting the third molar to generate the facial edema.
Inflammation is understood as the body's protective response to injuries [
The rapid advances in the inflammatory diseases knowledge and the related medicine have led to new medical treatments and have reduced the suffering in millions of patients [
In the anti-inflammatory drugs, development is necessary to identify specific biomarkers and measure the progression of the inflammatory disease to evaluate the medical results and the safety of the treatment; however, the developed measurement systems do not have an adequate reliability.
Currently there are five representative cardinal signs of inflammation [ Swelling: increased interstitial fluid and edema formation. Blushing: redness, due mainly to the phenomena of increasing pressure by vasodilation. Heat: increment of temperature in the swelled area due to the vasodilatation and increased local consumption of oxygen. Pain: the pain appears as a consequence of releasing substances capable of causing the activation of nociceptors, such as prostaglandins. Lost or decreased function (trismus).
Figure
Inflammatory process.
The development of drugs to control and reduce inflammation caused by damage to the human body is continuously performed. These drugs, called nonsteroidal anti-inflammatory drugs (NSAIDs), are a group of drugs that block the prostaglandins synthesis provoking the following effects: anti-inflammatory, analgesic (reduce pain), and antipyretic (reducer fever), [
Within the research and development of anti-inflammatory drugs, there are generic models to analyze their effects. The third molar extraction pain model is recognized by the US Food and Drug Administration (FDA), and it is frequently used to evaluate analgesic and anti-inflammatory drugs [
The techniques currently used to measure the effectiveness of anti-inflammatory drugs are based on vernier calipers. Other techniques are based on using the length of a thread to measure the inflammation distance strategically located between some marked points in the face of the patient or to measure the distance between two points strategically located on the face.
Based on the need to obtain accurate measurements of the effectiveness of anti-inflammatory drugs, the techniques currently used to measure the signs present in the postoperative edema, due to a third molar extraction, require a technological improvement to get more reliable and trustworthy measurements of these variables.
This paper focuses on the current scientific interest over the area of pathological inflammatory diseases related to the development of a reliable system that allows studying the measurement of four main variables that influence an adequate edema evaluation: trismus, blushing, temperature, and inflammation, having as a possible application the measurement of the effectiveness of the anti-inflammatory drugs.
After the extraction of the third molar, the attack on the oral and perioral soft tissues and detachment of the flap and bone trauma are responsible for the inflammation that, under normal conditions, is more intense 72 hours after the extraction. After this period, inflammation begins to subside and decreases during 48 or 72 hours [
Determining the effectiveness of anti-inflammatory drugs is currently based on measuring only two of the variables presented in the postoperative edema: swelling and trismus, by using different techniques.
Historically, different methods to measure trismus have been used. van Gool et al. [
Currently, trismus assessment is carried out by measuring the maximum interincisal opening using normal and digital Vernier calipers.
Figures
Trismus measurement with different tools.
Caliper vernier
Millimeter ruler
Inflammation is a three-dimensional volumetric change difficult to evaluate. Some of the methods that have been used to determine the swelling due to the third molar extraction are as follows. Laskin method [ The distance in centimeters from the bottom edge of the earlobe to the midpoint of the symphysis Hirota, called: horizontal distance to the symphysis (DHS). The distance in centimeters from the bottom edge of the earlobe to the external angle of the mouth, called: horizontal distance to the corner (DHC). The distance in centimeters from the palpebral outboard angle to the goniaco angle, called: vertical distance (DV).
Figure
Distances used in the Laskin method to measure inflammation.
Other methods to measure inflammation are based on the following. Calibrators [ Photographic method and cephalostat [ Facebows are complicated handling equipments, such as the ones used by Petersen [
Inflammation measurement by vernier calibrators.
Inflammation measurement by photographic method and cephalostat.
Inflammation measurement by facebow.
There is an area of
The trismus is evaluated by measuring the maximum interincisal opening. The proposal presented in this paper is based on the measurement of trismus through digital image processing using the MATLAB software.
The developed technique requires locating the face of a person in a digital image, which is acquired at a fixed distance between the camera and the person by using a metric reference standardized to this distance. Once the image of the person mouth opening is ready, it is necessary to select the distance in the image to be measured using two points selected by the user.
The pixels of the selected distance are converted to centimeters by using the MATLAB software. The pixels to centimeters conversion resolution of the selected distance in the opening mouth image is defined by the distance between the camera and the captured face image. Figure
Algorithm used to convert pixels to centimeters.
The proposed technique can achieve reliability similar to the techniques that use digital Vernier calipers. In the conversion process from pixels to centimeters, a centimeter can be represented by different pixel heights of an image, such as
The average of the opening mouth image is between 7 and 8 centimeters, for an
This research aims to measure the change in the color (blushing) of the area affected by edema by analyzing histograms of the facial color images.
A digitized image is simply an array of numbers, where every number represents the value of a pixel.
The histogram of an image (
All the colors are derived from a combination of the RGB (red, green, and blue) colors in different proportions. The color of every pixel in an RGB digital image corresponds to a value between 0 and 255 assigned to every RGB channel for every pixel; that is, every pixel has a value assigned to every color channel (red, green, and blue), and the combinations of these different colors emerge. If the value of a pixel is R255 + G255 + B0, red and green are mixed resulting in yellow. If the value of a pixel is the combination of
Histograms have very different aspects depending on the image content. A histogram is probably the best tool to adjust and to analyze digital images allowing knowing the range of the pixels for every RGB channel; in addition, it provides information about the changes in the intensity values that the same image suffers over time.
The methodology consists of the following steps. A person is placed in a cephalostat that allows standardizing the position of the color images, allowing taking similar pictures. Different images are taken from the face of the person to whom different shades of blush are applied to simulate changes in coloration due to edemas. The obtained color images are processed using MATLAB to obtain the RGB histograms for every one of the images in order to analyze the changes in the color of the facial skin affected by edema. Comparisons are made about the RGB histograms of the images with different tones of blush; the result is a correlation between 0% and 100%. If the color is similar between two images, the correlation is approximately 100%; if the color between two images is too different, the correlation is about 50% or 60% for every channel.
The application of infrared thermography to study the effectiveness of anti-inflammatory drugs is used for detecting temperature changes in the area between the jaw and the temporo-mandibular joint, and this measurement is performed during the evaluation period after the extraction of the third molar.
The images (thermograms) are captured by the FLIR i7 thermographic camera which provides information about the changes in the surface temperature of the patient's facial area once the third molar was extracted. The alteration in temperature corresponds to the radiation generated due to the changes in the internal cellular metabolism.
The process used to obtain the thermograms is as follows. The patient is placed in a cephalostat to position and immobilize the patient's head in a fixed relationship to the digital camera. This equipment standardizes the thermal images (thermograms). Some thermographic images (thermograms) are taken and stored in the PC for further analysis. Every thermogram provides basic information about the temperature in every one of the areas of the face images that suffered injuries, having the option to select only a specific area of interest to obtain the average temperature of the specified zone as well as the maximum and minimum temperatures.
The application of a thermographic camera to evaluate changes in the temperature of an edema enables the user to obtain a comprehensive and reliable measurement about the edema evolution, so temperature measurement can be used in the evaluation of the effectiveness of anti-inflammatory drugs.
The technique proposed in this paper consists in measuring inflammation through a three-dimensional reconstruction of the area affected by facial edema using the structured light technique (fringe projection). This reconstruction can provide measurements of the inflammation evolution through the variations in centimeters or millimeters of the inflammation.
The proposal consists in performing three-dimensional reconstructions of the interest area of a laptop or PC, a digital camera (CCD technology), a mini projector, a cephalostat to immobilize the head of the person and to standardize the photographs, software image processing software (MATLAB).
The CCD camera and the mini projector are mounted on a base which allows the mobility and adjustment of both elements.
Figure
Process of the tridimensional digitizing technique using structured light.
In the inflammation measurement process, the person is placed in a cephalostat that allows taking photographs in the same position every time. Later, the structured light patterns (fringe grill) are sent from the PC to the projector, and pictures of the face are taken with the camera in the same plane of the projection.
Images are recorded and the necessary processing techniques to achieve the 3D reconstruction are applied. Using these techniques allows obtaining the wrapped phase map, the unwrapped phase map, and the real measurements in centimeters or millimeters using triangulation.
The result of the first step is a three-dimensional reconstruction of the affected area. It is necessary to compare these results to the three-dimensional reconstructions of the same area once the inflammation has evolved to obtain the difference in inflammation between two different 3D reconstructions, showing the inflammation evolution.
The proposed digitizing method uses an algorithm developed in MATLAB. A grayscale fringes grill is generated by using cosine values and a
Equation (
Once both wrapped phase maps are obtained (reference and swelled facial surfaces), their subtraction is performed. The result of this subtraction is the swelling difference.
The next step consists in obtaining an unwrapped phase map, meaning that the phase map of the surface is represented by values between 0 and
Applying the algorithm path-dependent method developed in MATLAB the unwrapped phase map is obtained. It is necessary to convert the values of the unwrapped phase map to centimeters or millimeters by applying (
Once the unwrapped phase map is expressed in terms of
To verify the accuracy of the trismus measuring system, some initial tests were made to measure the diameter of five different Mexican currencies and, based on the fact that their diameters are standardized and accurate, the measurement comparisons between the real value and the measured value are very reliable. Figure
Diameter of the five different currencies used to validate the developed algorithm.
Table
Diameter measurements.
Diameter measurement of Mexican currencies | |||||
---|---|---|---|---|---|
50 cent cm | 1 peso cm | 2 pesos cm | 5 pesos cm | 10 pesos cm | |
Real diameter | 2.2 | 2.1 | 2.3 | 2.55 | 2.8 |
Measured diameter | 2.196 | 2.0984 | 2.2936 | 2.5476 | 2.7976 |
Absolute error | 0.004 | 0.0016 | 0.0064 | 0.0024 | 0.0024 |
Relative error | 0.18% | 0.07% | 0.27% | 0.09% | 0.08% |
In Table
Using the MATLAB guide interface a photograph showing the mouth of the person is selected. Once the image has been chosen, the distance to measure is selected by using the ginput command; this command allows selecting the image first point and saves its location in a [
When the distance in pixels corresponding to one centimeter is obtained, a division between the distance in pixels of the mouth opening and the distance in pixels corresponding to one centimeter is made. The result of this division is the maximum mouth opening distance (trismus) in centimeters. Figure
Trismus measurement using the algorithm developed. The maximum mouth opening distance is 7.3627 cm.
Several tests were conducted to verify the trismus measurement system. Since the average size of the opening mouth images, used to measure the trismus, is from 7 to 8 centimeters, if an
In the trismus measurement methodology a person opens his mouth at different distances (maximum opening, half opening, and almost closed).
Figure
Trismus measurement for a picture concerning a mouth almost closed. The distance of the mouth opening is 2.9707 cm.
Figure
Trismus measurement for a picture concerning a half mouth opening. The distance of the mouth opening is 4.1716 cm.
Figure
Trismus measurement for a picture concerning a maximum mouth opening. The distance of the mouth opening is 5.9584 cm.
In the blushing measurement test three different shades of blush were used to simulate changes in skin color caused by facial edema. In this paper only the results corresponding to the third shade of blush (bigger color difference) are presented (Figure
Selected area corresponding to the bigger color difference.
Figures
(a) Comparison of the red channel histograms between the reference image and the image with shade of blush. (b) Comparison of the green channel histograms between the reference image and the image with shade of blush. (c) Comparison of the blue channel histograms between the reference image and the image with shade of blush.
The results obtained in the blush comparison between the reference image and the image with the shade of blush are as follows: correlation percentage of red channel: 93.8694%, correlation percentage of green channel: 90.379%, correlation percentage of blue channel: 88.8141%.
In the final tests the temperature was increased and decreased in the area where the facial edema was simulated in order to generate the different temperatures present during facial edema.
Figure Maximum temperature: 36.1°C. Minimum temperature: 32.4°C. Average temperature: 35.1°C.
Temperature measurement of a face at normal temperature.
Figure
Temperature measurement of a face having an injury.
The interest area is marked within the rectangle and the results are the maximum, the minimum, and the average temperatures. Maximum temperature: 36.6°C. Minimum temperature: 34.3°C. Average temperature: 35.8°C.
Figure Maximum temperature: 37.1°C. Minimum temperature: 34.4°C. Average temperature: 36.1°C.
Temperature measurement of the face with increased temperature.
Figure Maximum temperature: 36.3°C. Minimum temperature: 33.9°C. Average temperature: 35.5°C.
Temperature measurement of the face returned to its normal temperature after the temperature was increased.
To verify the accuracy of three-dimensional reconstruction system twenty reconstructions of a pyramid with a maximum height of 43 mm were performed. Figure
Fringe projection on the pyramid.
Figure
Wrapped phase map.
Figure
Unwrapped phase map.
Figure
Three-dimensional reconstruction of the pyramid whit real values of height.
Table
Pyramid height measures.
Number of reconstruction | Maximum height (pyramid) | Absolute error | Relative error |
---|---|---|---|
1 | 4.2889 | 0.0111 | 0.2581% |
2 | 4.2891 | 0.0109 | 0.2535% |
3 | 4.2894 | 0.0106 | 0.2465% |
4 | 4.2897 | 0.0103 | 0.2395% |
5 | 4.2905 | 0.0095 | 0.2209% |
6 | 4.2912 | 0.0088 | 0.2047% |
7 | 4.2913 | 0.0087 | 0.2023% |
8 | 4.2924 | 0.0076 | 0.1767% |
9 | 4.2931 | 0.0069 | 0.1605% |
10 | 4.2936 | 0.0064 | 0.1488% |
11 | 4.3051 | 0.0051 | 0.1186% |
12 | 4.3066 | 0.0066 | 0.1535% |
13 | 4.3079 | 0.0079 | 0.1837% |
14 | 4.3086 | 0.0086 | 0.2000% |
15 | 4.3087 | 0.0087 | 0.2023% |
16 | 4.3099 | 0.0099 | 0.2302% |
17 | 4.3103 | 0.0103 | 0.2395% |
18 | 4.3107 | 0.0107 | 0.2488% |
19 | 4.3212 | 0.0212 | 0.4930% |
20 | 4.3218 | 0.0218 | 0.5070% |
| |||
Real maximum height real | 4.3 | ||
Average of the absolute error | 0.01008 | ||
Average of the relative error | 0.2344% | ||
Standard deviation |
|
||
Average of the maximum height measured | 4.301 |
Table
Figure
Equipment experimental arrangement of the three-dimensional reconstruction system.
An algorithm for the three-dimensional reconstruction using the fringe projection technique is developed in MATLAB. Figure
Algorithm for the three-dimensional reconstruction.
Several tests were performed using different objects to validate the three-dimensional reconstruction. Some of the used objects were a pyramid, a mask, and the shape of a child. Initially only simple three-dimensional reconstructions of the objects were performed without obtaining actual measurements of the objects height.
The advantage of the proposed technique is that it can provide more complete and accurate measurements, allowing obtaining the values
Finally, to measure the swelling in the face of a person, the inflammation was simulated by filling the mouth with air (maximum and medium values), and the placing of a ball on the cheek, increasing the volume of the facial area allowing measuring the difference between two reconstructions (reference reconstruction and the increased volume).
Figures
(a) Reference face. (b) Maximum inflammation fringe projections.
Figures
Wrapped and unwrapped phase map corresponding to the selected area of interest.
Figure
Difference in inflammation between the three-dimensional reconstruction of the reference and the maximum inflammation.
In the process to improve anti-inflammatory drugs, it is necessary to use techniques and equipment to obtain reliable measurements of the variables that determine its effectiveness: trismus, temperature, blushing, and swelling. Based on the need to improve the traditional measurement techniques an integral system is developed, and it can deliver the measurement of the four variables present in the inflammatory process once the model of the third molar extraction is applied.
To measure swelling the structured-light three-dimensional reconstruction technique is selected based on the study of its characteristics, advantages, and disadvantages. The main advantages are the scanning speed and the accuracy (±0.030 mm).
This technique cannot be used with transparent and reflective surfaces because light does not infer in them the same as in the opaque reflection. In this research the interest areas do not have the properties of transparency or reflectivity, so this technique is suitable for the desired application.
The implementation of this technique provides a 0.1 mm maximum error adequate to validate the precise evolution of inflammation and by consequence the effectiveness of anti-inflammatory drugs.
Based on the operating principle of the colorimeter which is the application of three color filters: red (R), green (G), and blue (B), the proposal of this research is to make a system to obtain the color difference of patient face images and to make a comparison of the histograms corresponding to the RGB channels, making it possible to identify changes in the face coloration under different swelling levels. It can be concluded that the system allows obtaining accurate results while the illumination of the environment is controlled, that is, under normal test situations because the measurements are usually performed under controlled protocols.
The implementation of a technique to convert pixels to centimeters, using digital image processing, allows a measurement equal or more accurately than the techniques using digital verniers but with the advantage that the proposed system does not require contact with the mouth the patient. By applying the proposed system the measurement of trismus allows obtaining a 0.03 mm error.
Finally, to measure temperature, the proposal is based on using a thermal camera which characteristics allow measuring temperature changes in the affected zone by the postoperative edema with an accuracy of 0.2°C and a sensitivity of 0.1°C.
The proposed system to measure the variables present in the facial edema requires placing the patient in a cephalostat and taking the pictures without touching the patient's face, avoiding modifying the affected area.
The processing time is not a drawback in this
This section presents one of the algorithms developed for this project, the trismus measurement main algorithm as follows: [ [ hline = line( pixel_distance =
None of the authors or coauthors of this paper have a direct financial relation with MathWorks, and the use of the MATLAB software is as a tool for the algorithms development.