A Review of Recent Application of Medical Thermography in Human Body for Medical Diagnosis
Hamidreza Shirzadfar*, Fateme Ghasemi and Melika Shahbazi
Department of Biomedical Engineering, Sheikhbahaee University, Esfahan, Iran
*Correspondence to: Dr. Hamidreza Shirzadfar
Citation: Shirzadfar H, Ghasemi F, Shahbazi M (2018) A Review of Recent Application of Medical Thermography in Human Body for Medical Diagnosis. SCIOL Biomed 2018;2:102- 120
To the medical view, temperature is a good indicator to determine the body's health condition. Human body is able to keep and fix its temperature while the environmental temperature might be different. Thermal variations, even in some degrees, are considered as a bright sign of a probable disease. Body controls the temperature by a physiological process which is called the "Thermoregulation". Temperature between 36.3-37.5 ℃ can be considered as the normal temperature.
In this study the infrared thermography (IRT) is used. IRT is a quick, non-contact and non-invasive replacement for determining and the ordinary monitoring of the body's clinical temperature. Everything with higher temperatures (more that absolute zero) cause electromagnetic radiation, known as infrared radiation or thermal radiation. IRT experiments require an infrared camera, a tripod, a display board and the image processing unit. Nowadays the displaying and the processing of the image are digitally done by a special computer and the special software packages. Today the images which are captured by a camera are directly conducted to a digital computer in which the images are processed. The need to establish a normal thermal images database, captured from all the possible parts of human body, is recognized.
Operating with IRT needs the studying of many issues that can affect the diagnosis by thermal image explanation. Attempts to control a huge amount of issues might look impossible but the simplicity of the introduction to these issues is an important step in many fields. These issues are divided in three main groups: Environmental reasons, individual reasons and the technical reasons.
Thermography gave a high visual ability to the physician and it is supportive in arthritis diagnosis (joints inflammation), vascular disease, blood flow disorders (e.g. in dialysis), cancers like breast cancer, thrombus caused by diabetes, dermal temperature changes with different reasons and thermal modeling of the different parts of the body, pregnancy issues diagnosis and procreation, dentistry, etc.
In this paper it is tried to study the performance of the thermal cameras and also the ability and advantages of the thermal imaging in various disease diagnosis and the methods of image processing.
Infrared thermography, Image processing, Blood stream, Breast cancer, Diabetes, Varicocele, Ocular surface thermo, Rheumatics
A passing over thermo issue
Human body depends on thermodynamic rules. Thermodynamics is a branch of natural science that debates on the heat and its portion to energy and work and has four basic rules . Firstly the three thermodynamic rules were compiled but it seems to there would be a fourth rule called the "zeroth law" that is because the first, the second and the third rule had their own place and were not as basic as this law. First law generally says that the energy and the matter are not created and will not be dissolved, just their form converts from solid, liquid, gas and plasma and the input of each machine is equal to the output. In fact the potential energy of a system is isolated, stable and equal is the difference of the given heat to the system and the work done by system on the environment:
Which, ΔU is the change in internal energy U of the system. Q is the net heat added to the system and W is the net work done by the system.
The second law essentially states that the energy is followed by disorder (entropy) a moves from its own source. In this condition there is a natural route for convection, the heat goes from the hot part to the cold part in the body. You cannot create the permanent heat flow without adding energy to the system. For a system, you must add energy for further work and the portion of temperature to work never becomes 1, because there is energy loss. In other words the second law describes the path of doing a process.
According to the third law, all the events stop at the absolute zero temperature (minus 273 ℃). At this temperature the molecules kinetics and the kinetics energy are stopped. In fact there will be no energy. By the first law we believe that the matter/energy is not made and not dissolved but it can change its form, for example transforms from solid to liquid, gas or plasma and reshape to the previous form again but the amount of the matter/energy remains stable. The second law states that although the amount of the matter/energy remains identical, the quality decreases through the time. Thermodynamic zeroth rule is more basic than the previous three laws and is discovered after them and it simply states that if the system 1 and system 2 are thermo balancing with the system 3, it can be understood that the system 1 and system 2 themselves are in thermo balancing too .
In a human being, heat is produced from the energy within the food [1,3]. To keep the inner temperature in 37 ℃ (Celsius degrees), for a human, the environmental conditions determine if this temperature is too high, too low or it's fine. If in static mode, body doesn't return heat to the environment, for example in a fully thermo-insulated place, human body increases 1 degree each hour and the person dies in some hours . In a study, Gulyaev and his cooperators showed that in most of healthy people the temperature of hands, legs and the face raises after being motionless, because in still state causes relaxation and redistribution of blood which increases the body skin temperature. They observed the auto-oscillations, caused by the alteration in sympathetic system and the bloodstream, in thermography of hands and legs . In a heat wave or wearing preserving clothes, less heat rate is lost and it is important to make sure that the correct rate of heat is returned to the environment or is out in other ways. In cool conditions, using cloths or other mechanisms; It is possible to hold heat inside the body. The air temperature, radiation temperature, humidity and air movement are the four fundamental and circumferential variables that impress the human respond to the thermal circumstance .
Heat is transferred from the hot point to the cold point based on thermal differences, through conduction, transferring and radiation. Heat can be reached or lost without changes in temperature by transforming liquid to gas (evaporation) and gas to liquid (condensation) which is called the latent heat. Heat transferring to environment using all these mechanisms and losing the unstable heat is crucial especially when the environment temperature is near or higher than the body temperature . In a molecular level, temperature can be considered as the kinetic energy in a body. If the thermal energy is lost the temperature falls and if it enters the body it will be increased. Humans are trying to hold the body temp to 37 ℃. Some degrees deviation from this can have serious issues. So the human body temperature severely affected by the temperature of liquids and solids around him/her .
In addition to the impression of air temperature on the human body temperature, also there is the effect of radiation heat. Heat is transferred among all solids through radiation and the pure heat flow from a hot solid to a cold one, depends on the absolute thermal difference between them. Heat alludes to the cold or hot form of a solid or liquid. This is corresponded to the heat ingredients (for example the average kinetic energy). Yet, heat also depends on properties like thermal capacity and the mass. The feeling of hot or cold is a psychological phenomenal, however there are physiological mechanisms that respond to the temperature, the temperature feeling depends on issues like pre-experiences, individual differences and the temperature alteration rate. In present there are three temperature scales in common. Practical values (Celsius and sometimes called synthesis) and Fahrenheit and the absolute temperature (kelvin) . The inner temperature must be held at 37 ℃ to balance the body and the environment temperature. Normally, heat transfer to the body and heat production in body must be balanced by the heat outputs from the body. It does not mean that a stable condition happens, as far as a stable condition requires changes in temperature and the body temperature and the heat exchange way are various, the point is that there will be an active balance for a steady temperature. If the heat production was more than the heat output, the body temperature increases and if the heat output was high the temperature falls .
The thermal balance equation for the human body can be indicated in many forms. Yet, all equations have a unique basic concept and include three terms: Heat production in body, heat transfer and heat store. Metabolism measure of the body (M) provides energy for mechanical work (W) and the rest is released as heat (for example M-W). Heat can be transferred by conduction (K), transmission (c), radiation (R) and evaporation (E). When all are combined, it represents the production rate, loss rate and heat storage rate. For human body in thermal balance (for example the stable temperature), the heat storage value is zero (S = 0). If there would be a pure heat increment the storing will be positive and the body temperature will rise. If there would be a pure heat loss the storing will be negative, and the body temperature will fall .
Heat production in the body corresponds to individual activity. Generally, oxygen is absorbed then transmitted to cells via the blood that is used to feed. Most of the released energy is thermal units. Depending on the activity, some of the works are done. The required energy for mechanical work is different from about zero (for most of actions) to more than 25% of the whole metabolism measure .
Thermal importance in body
In medical respect, temperature is a good health condition indicator [1,3,4]. Human body is able to hold its temperature and fix it while the environment temperature is different. Therefore, the body can be divided in two parts: Inner core and the outside circumstance. The inner core temperature is kept in a specific bound (about 33-42 ℃). Regulation of the inner core temperature is essential for natural performance of the human body. Metabolism and the muscular flexibility during sports are the main sources of the heat in the body core. Heat is transferred from the core to the outer parts by bloodstream in veins which means the blood reaches the core temperature and loses it in circumferential parts specifically on skin [1,3]. Temperature change even in some degrees is considered as a bright symptom of a probable issue. Body controls the temperature with a physiological process that it is called thermoregulation. Temperature 36.3-37.5 ℃ can be assigned as normal temperature and the temperatures higher than this limit must be considered as symptom of a probable issue .
Bloodstream is the main mechanism of the heat transfer in human body. Dermal heat and the blood flow around it can be described by the equation below also known as Pennes bio-heat : The Pennes bio thermo equation is used for determining the amount of the radiated heat over the surface of the cancer cells and the blood flow around it.
In which the pt is tissue compression, ct tissue special heat, T tissue temperature, t the time, ωb blood's profusion rate, cb blood special heat, Ta arterial blood temperature, K tissue thermo conductance and x is the distance from the skin .
Infrared ray discovery by Sir William Herschel in 1800 was quickly followed by the first thermal image capturing by his son John Herschel that brightened the new dimensions in thermo measuring field . In 1934, Hardy explained the physiological role of infrared radiation from the human body and suggested that the human body can be assumed as a radiator with the black cover . He established the diagnostic importance of thermal measuring using the infrared technology which smoothed the path for using infrared thermography (IRT) in medical science .
Digital infrared medical imaging or the clinical thermography is based on the precise analysis of the skin surface temperature as a reflection of the normal or abnormal physiology of the human . There are different techniques which provide the field of inner imaging of the human body from outside. For example, we can externally inject and track the radioactive isotopes to the body. Radiology uses interactions of the x ray and the matter for imaging the inner structure of the body, but these techniques have disadvantages like respectively high costs, low sensitivity and x ray dangers, especially when being radiated for a long time. Due to the danger, diagnostic methods including no radiation are used . In fact the thermography method only records the natural radiation from the skin surface and does not have harmful effects of the radiation and it is suitable for repetitive and longtime use. There has been a research on human and the animals for half a century which shows the correlation between thermal patterns and the medical condition. The temperature of a part of the body is the production of the cellular metabolism and the local blood flow and the temperature increment is usually the result of these issues and the body's abnormal temperature is the natural indicator of the disease .
In the human body thermal energy is transferred from the inner organs to the surfaces and the outer parts. For this thermal energy transfer, the blood is usually at the higher temperatures than the surfaces and the outer parts. Thermography provides the field of detecting the bloodstream at these levels.
Blood is the main heat convertor in the body, thus the diagnosed pathologies are generally corresponded to the changes in bloodstream. In some disease process, the increment or decrement of the blood flow in the targeting tissue causes the difference in surface temperature [1,3,9].
In 1963 Lawson and Chughtai published a paper that indicated the direct relation of skin temperature in breast cancer with blood flow and metabolism increment . Gautherie and fellows reported that in the natural tissue of the breast there is linear curve that the temperature gradually increases from skin to the depth of the tissue whereas in a breast with cancer wastage the conduction curve has angles. Results indicating that there is something in this breast tissue that releases much heat. Studies shows that in tissue physiological changes occur before the pathological changes and premature thermography of breast raucousness which might cause cancer, has a potential role .
Features like being non-invasive and high-resolution thermography diagnosis are worthwhile and also effective in cure process. The ability of indirect heat measuring is an important clinical tool. Because of the ability in measuring the small heat difference, practical thermography is an important medical diagnosis device. Thermography has given a high-level sight to the physician and in diagnosis of arthritis (joints inflammation), vascular disease, bloodstream disorder (for example in dialysis), cancer among breast cancer, thrombus of diabetes, skin temperature changes with different reasons and also thermal modeling of different parts of body and in diagnosis of pregnancy issues and reproducing [3,11,12].
All the stuff with temperatures higher than the absolute zero cause electromagnetic radiation which is defined by the Stefan-Boltzmann. This rule states that the whole radiation from a thing is directly related to the thing's area, radiation scale and the amount of it. The wavelength of this radiation is in the range of 0.75-1000 µm. This vast range can be dividing into three more little groups :
Near infrared or NIR range (0.75-1.5 µm)
Medium infrared or MIR range (1.5-5.6 µm)
Far infrared or FIR (5.6-1000 µm)
Thermal difference even in small scales may cause spreading of significant number of photons which need special equipped thermography to detect. Human eye is able to detect electromagnetic waves with wavelength of 3500-7000 Å. Thermal ray spread by the body is usually formed of greater wavelengths. Therefore, human eye is not able to detect such radiations. Special cameras are used for recording these radiations and computers are used for processing recorded images to create an understanding image for human eye [1,3,4].
During the first decade after the development of IRT, the research about the use of IRT in human was commonly concentrating on the application of it as diagnostic tools. Still, IRT was replaced by newer and more precise technologies (e.g. X-ray and magnetic resonance imaging). Recent technical advances in infrared cameras made new human applications (of IRT beyond the diagnostic techniques) possible. Therefore, the infrared cameras produce the thermal images with electromagnetic waves; We must notice that optic rules (optical physics) are suitable for image creation. Also the thermal energy, temperature and convection are titled as the infrared radiation source and the thermodynamic rules must be mentioned and determined .
According to the thermal radiation theory, black matter is assumed as an imaginary thing that absorbs all of the contacting radiation and continuous spectrum according to the Punk's rule. The combination of Plunk's rule for all of the frequencies the Stefan-Boltzmannis resulted, which shows the whole power of the black matter :
Which E is the whole spreading power (W/m2), σ is the Stefan-Boltzmann constant which is σ = 5.676 × 10-8 W/m2K4, T is the absolute temperature (K). For real levels the Stefan-Boltzmann is corrected like this:
Ε is the surface radiation in steady wavelength and at the absolute temperature T .
With rising of the new generation of detectors, NIR regions and MIR are still used in medical thermography . First modern infrared detector equipped with lead-sulfide (Pb-S) sensor, initially was developed for military applications at the Second World War But later this technology was published for non-military applications and afterwards IRT was used in medical science also in the non-destruction test (NDT) field. In IRT, the thermal patterns on the surface of the things are monitored . Below layers defections cause abnormal thermal patterns which shows the presence of these defections. Similarly, in medical programs, because of the presence of abnormal thermal patterns in clinical patients these patterns on the skin surface are observed and studied . The emitted infrared beam from a surface depends on the experiment conditions like humidity, air flow and the environment temperature. Therefore, the thermography experiments, especially in medical applications that change in some degrees, must be operated at controlled environments. To compare thermographic images, a standard protocol must be followed. Clark and colleagues have presented a draft version of such a standard . Recently, Ring and Ammer have reported that IRT can only produce reliable results in medical applications that meet certain standards. Fortunately, they described the details of the main standards for the test room, temperature control, subject information processing, imaging system, image capture, image processing and analysis of the results. These standards are very useful for researchers in pursuing researches in the field of medical thermography .
During the thermographic tests, people are kept in a comfortable environment, such that mild heat stress leads to contractions of the blood vessels of the skin that increase blood pressure, and hot spots are clearly visible due to underlying abnormalities . Amalu and colleagues reported that the temperature and humidity of the test room should be controlled in such a way that people do not "get into a condition of trembling or itchiness". It is recommended that people avoid exposure to direct sunlight and use cosmetics and antiperspirants before the thermography test. According to the parts of the body that should be examined, the body may be bare or normal. The Figure1 and Figure 2 shows a probationary scheme .
IRT experiments require an infrared camera, a tripod, a display, and an image processing unit. Today, digital image processing and processing is done using a dedicated computer and software packages. The development and principles of the operation of infrared detectors and sensors are described in detail by Zhang, et al. and Jones [19,20]. First-generation cameras used a single-element detector and two scan mirrors to produce images. This generation of cameras suffered from a bleaching problem (e.g. high intensity saturation). Two scanners with a large linear array or a small 2-D array are used as detectors, and the time delay integration algorithm is used to enhance the image on second-generation cameras. Third-generation cameras are non-mirrored, with a focal plane array detector (FPA) and image processing is operated on the chip, which increases the reliability and sensitivity of these systems .
Thermal detectors are divided into two categories: Cooled and uncooled. Modern developments in solid state systems have made the way for the production of newer detectors with better accuracy and clarity. At present, the thermal sensitivity of the cooled cameras is about 0.05 ℃ compared to 0.01 ℃ uncooled cameras. These cameras have many advantages, including space and high temperature precision, portability and compression. In addition, these lightweight cameras, produced by thin-film silicon technology, are cheaper than cooled infrared cameras. Uncooled modern digital infrared cameras have extremely improved thermal imaging [22-24].
Classifying the effective factors
Working with IRT requires the examination of many factors that can affect the evaluation or interpretation of thermal images. Trying to control a large number of factors may not be possible, but the simplicity of familiarity with these factors is an important step in many areas. These factors are divided into three main groups: (According to Figure 3).
1. Environmental factors: Those who are involved with the assessment site. The first group is the factors related to the natural environmental features that the IRT assessment takes place. Environmental factors are very important and unlike individual factors, they are more controllable (such as room size, ambient temperature, relative humidity, atmospheric pressure and radiation source).
2. Individual factors: Those that is relevant to the assessment of the individual and his personal characteristics that can affect the temperature of the skin. These factors are related to the intrinsic factors (inherent factors of the person's main characteristics and primarily to the biological and anatomical parameters such as gender, age, roundabout rhythm, hair density, skin irradiation, metabolic rate, genetics and emotions) and outer factors (such as drug or drug therapy, alcohol, tobacco, stimulants, food consuming, ointment and cosmetics, etc.). The number of factors per person is very complex and attempts to control all of them are now impossible.
3. Technical factors: Factors associated with equipment used during IRT assessment. (Such as accuracy, reliability, protocol: Distance/history/camera position/camera features/temperature range/resolution/calibration range, ROI selection, software and statistical analysis).
The number of factors that affect the temperature of the skin in humans is very much. Failure to control all of these factors can be considered as one of the weakest infrared thermography (IRT) points .
Image processing, data analysis and numerical modelling
In a review article in 2002, Jones and Plassmann discussed the importance of image processing techniques in the IRT. Today, images captured by a camera are directly redirected to a digital computer, where images are processed. The need to create a database of natural thermal images has been identified from all possible parts of the human body. Ring and his colleagues have discussed the technical challenges for building a database for the medical IR digital medical image. Fujimasa and her collaborator developed an Internet-based image database. Ring and his colleagues have developed the Anglo-Polish reference database of thermal medical imagery. In order to compare several thermal images, Vardasca developed an interactive lookup based on the methods of comparing the regions of interest (ROI = regions of interest) in multiple thermal images, with ROIs aligned semi-automatically. Data Acquisition Software plays an important role in IRT. Plassmann and Ring have developed the thermal imaging software (BTHERM), which can capture and manipulate images from both older and modern digital cameras. A new version of CTHERM software has also been developed by Plassmann and Murawski, which runs on a modern computer. Newer software such as Altair and Matlab, with more options for automatic image processing, are very fast and useful.
Thermal waves are exponentially reduced in an environment, and hence the thermal effects of abnormalities are often subtle. The thermal images also suffer from a relatively low noise signal (SNR = signal-to-noise ratio) .
Therefore, image processing in IRT is of great importance. Different filters (in both time and frequency domains) and algorithms to minimize noise, reduce blur and retain edges in thermal images are used. Gulyaev and his colleagues proposed four basic numerical operations in the thermography to increase the accuracy of extracted data from it. These four operations are :
i) Subtraction of background in each frame of interest.
ii) Construction of temperature time profile at chosen point or regions.
iii) Spatio-temporal projections of image sequences.
IV) Calculation of time derivative of temperature data Thermal image processing.
The importance of digital image processing (DIP) and algorithms has two main areas of application: Visual image enhancement for further analysis and image data processing for storage, transmission, and presentation for automated auto-view. Recently, several algorithms and techniques have been developed to obtain more accurate and more detailed information from images using DIP. Heat images are kind of digital image that require image processing. The thermal image processing is performed in several steps: recording, pre-processing and segmentation as shown in Figure 4.
First, the thermal camera is used to capture heat images, and as the white thermal noise (low frequency noise) is caused by fluctuations in heat exchange, filtering is used as a pre-processing step to reduce noise. Several techniques, including the histogram of the gray levels for the entire image, were presented by Wiecek, et al.  to improve the process of further image processing .
Infrared breast thermography is usually taken in a larger area. Therefore, before processing, unnecessary areas and fields should be removed from the thermograms. Then, the thermal images turn into black and white images. The black and white conversion of the thermogram is followed by segmentation of the target area (ROI). In the analysis of thermal images, ROI division plays a crucial role, but extraction of ROI from the infrared thermal image is very complicated. To put objects and boundaries in thermal images, partitioning is done in order to partition the thermal image into several sections as a set of pixels or super-pixels .
After the division, it is possible to extract the measurable features and important features of the thermal image. The extracted features of the image can help to distinguish different areas in a single image. These features can be low-level or high-level features. Low-level features are extracted directly from the amount of image intensity. To reduce the computational time, the selected features of the important vectors should be reduced using appropriate algorithms. Finally, the shape may require a series of thermal images (recorded) to measure temporal changes in temperature. The average temperature, spatial variation, time variation and frequency variation are used and can compare the different regions of an object .
Carcinoma or vicious tumor is normally hotter than the around tissue and due to "black matter" theory it absorbs any light radiated to it (based on Plunk radiation law) [3,10]. Radiation distribution is a function of temperature, wavelength or the radiation frequency. With body temperature increment the radiation compression or spreading in all frequencies increases.
Following issues cause cancer cells produce heat:
1. Higher metabolic in most of cancer cells in comparison to the normal cells.
2. Veinization: Cancer tumor needs nutritious ingredients, so it produces chemical heat to increase the growth of blood vessels which feed the tumor also it makes normal blood vessels wide to provide more blood for tumor growth.
Tumors cause the increment in blood flow and metabolism which brings local stains with high temperatures in place that can be detected via infrared thermography [3,4]. Breast cancer is one of the most prevalent cancers that if diagnosed quick, the chance of a successful cure increases. Currently in diagnosis of breast cancer developed equipment like clinical breast experiments, mammography and ultrasonography are used. Ultrasonography and clinical breast experiments are the helpful tools in breast screening, especially for ladies with compressed breasts, fibrocystic breasts, pregnant and lactative. None of screening tools have fine prediction but a mixture of tools that include thermography indicates the increment of sensitivity and its properties [3,4,9,11].
Thermography is able to track breast cancer 8-10 years earlier than mammography and it is placed as a complementary method beside mammography. Thermogram of each woman is as unique as her fingerprints and never changes by the time . Breast thermogram is used in routine checkup. In routine checkup, first a basic thermogram of the patient is provided and the next thermograms are compared with this basic thermogram. Figure 5 shows the routine check-up of a healthy referrer and it is seen that the thermal profile of the breasts was stable for two years .
Figure 5: Routine check-up of a healthy referrer; a) Basic thermogram; b) After 6 months; c) After one year; d) After two years. View Figure 5
Infrared thermography of the breast is a non-invasive method that does not include compressing the tissue or radiating the breast and it is done by evaluating the physiological performance through measuring the breast tissue with high resolution. In fact, thermography does not represent information about the morphological features of the breast, but it gives operational information about the thermal and vascular condition of the tissue .
There has been a study that indicates the effectiveness of IRT in primary diagnosis of the breast cancer and the case is a heap in the right breast of a woman and the result of mammography in detecting the heap was negative. Figure 6a shows a full view of this woman's breasts. In the Figure 6b, it is clearly seen that in the heap location high temperature is observed rather around.
Thermography in varicocele
Varicocele is the abnormal dilatation and twisting in the vessel network above the testicles [26,27]. The cause of varicocele is the return of blood flow to the inner sperm vein that happens because of the lack of enough venous valves or congenital insufficiency. Because the hydrostatic pressure on the left is high as a result of high perpendicular evacuation on the left inner sperm vein to the renal vein, very often varicocele occurs in the left .
The Figure 7 presents the varicocele anatomy.
Rarely prevalence of it happens in under 10-years-old but in young adults it is 15% and in infertile men 20% to 40%. In those who refer with second infertile, had kids before, the prevalence is up to 70%. 90% of the cases is in the left and in 10% of the cases is in both sides. The cause of this phenomenon is the long length of the left testicle blood evacuation vein to the renal vessel and also more vertical angle to right. Varicocele is the most prevalent recoverable infertile cause in men. The reason of its development is the disorder in venous evacuation or insufficiency of venous valves of the testicles. There are different theories about the mechanism of damaging the testicles which the most important ones are: Testicles temperature rise or decrement of blood flow and oxygen transferring or transition of renal stuff and metabolites and ultra-renal glands to testicles or a composition of these. Varicocele can cause deduction in the growth of testicles then shrinking the testicles. Also by affecting sperms causes decrease in their movement and number and morphologic change (apparent shape). The varicocele does not affect sexual power or pre-ejaculation directly.
Understanding and foreseeing the act of varicocele is still beyond the exiting diagnosis abilities. Thermography of testicle sack, by common diagnosis patterns, can help in choosing the kind if cure and surgery. Thermography as a non-invasive method, purposive, practical, short-time and low-cost in diagnosis of varicocele is presented. In Figure 8 pattern a is related to the high temperature limited to the twisting location pampiniform and Figure 9 pattern b is the temperature increase and non-limited to the twisting pampiniform .
About half of people with diabetes are hospitalized because of the leg issues that are the most common to diabetes. Main reasons of these issues are low blood flow (vascular disorder) and the loss of feeling or weakness (neuropathy). Diabetes and vascular disorder both cause changes in skin temperature that make the IRT a proper tool for diagnosis of diabetes neuropathy or the vascular disorder. In a study they found out that all these patients have abnormal thermal patterns in their legs and hands like temperature decrement in toes, foot bones and fingers. Sun and fellows studied a relation between the temperature of the sole and the sympathetic disorder in patients facing diabetes. They found out that the people facing diabetes have thermal average of (30.2 ± 1.3 ℃ degrees) respect to healthy people (26.8 ± 1.8 ℃). Researches show that thermal disorders caused by sympathetic damages in diabetes people legs can be detected using IRT in pre-levels. The Figure 10 shows the thermal images . In Figure 10a, the sole is divided in six regions. a) Hallux (huge finger); b) Small finger; c) Bow; d) Lateral edge; e) Ankle; f) Heel. In Figure 7 the cold spots are seen in fingers. Figure 10a is related to a 38-year-old man with 6 years of non-neuropathy diabetes history and Figure 10b is related to a 26-year-old lady with about 4 years of non-neuropathy diabetes history .
Hypodermal diseases generally cause inflammation that in person brings an abnormal thermal pattern on the skin. Therefore, IRT might be considered as a proper method for studying the skin issues (wart detection, leprosy and the depth of the burnt location, etc.) .
Diagnosis of rheumatics
Arnold and fellows reported that the IRT technology is an excellent way for measuring the skin temperature in different joints. IRT is used in diagnosis and evaluation of recovery in Raynaud phenomena, gout and arthritis (joints inflammation). Also, methods based on thermography are introduced for measuring joints inflammation, measuring the effects of anti-inflammation anti-steroids drugs (Aspirin indomethacin) in rheumatoid arthritis affected patients .
Diagnosis of dry eye syndrome and ocular issues
In ophthalmology, thermography is used to study and observe the eye physiology, ocular issues and surgery. Multiple relations between the ocular surface thermo (OST) and some of physiological changes and ocular pathology are easily done via thermography. OST is not only affected by physiological changes and ocular pathology, but some outer issues can also alter it. For example, the rise in room temperature to 1 ℃ may cause the ocular temperature increment (0.2-0.15 ℃).
By using IRT, Morgan and fellows recorded the thermography of the patient's eye and the control of eye dryness. In comparison to controls they found out that the average eye surface temperature in normal people (31.94 ± 0.54 ℃) in comparison with people with dry eye (32.38 ± 0.69 ℃) is higher.
Horizontal temperature passes through the geometrical center of the eye and the human eye elements analysis indicated that temperature at the center of the surface of the cornea is low. Yet, experimental studies showed that the temperature at the center point of cornea is a little lower than the surface, and these observations were checked in many people. In Figure 11 we see that the temperature distribution in normal people eye is symmetrical and has little changes in the geometric center of the cornea. This may be because of the tearing fluid current which causes decrease in the cornea temperature [3,29].
Thermal imaging has been widely used in dentistry. In 1996, Gratt, et al.  developed a new classification system using a thermogram for people with chronic oral anxiety. The selected anatomical regions are classified according to the three normal, warm and cold conditions, which have the value of temperature difference (temperature difference of right and left region) between 0-0.25 ℃, more than 0.35 ℃ and less than 0.35 ℃. Shevelev, et al.  examined the heat expansion process during teeth bone digestion using thermal imaging. Bennington, et al.  used thermal imaging to monitor the changes in bone temperature during the drilling process to prepare the implant site. Madura, et al.  in laboratory conditions, used thermal imaging to study the thermal effect of the use of laser Nd: YAG in the root of the tooth during the sterilization process [30,32-34].
Infants and children
One of the most important uses of the image is the use of it in infants and children. Because of the problems with identifying infant's diseases, this type of imaging can clearly illustrate its role. For example, one of these cases is the use of imaging in the constipation process in children, as presented in Figure 12; Constipation process by thermal imaging is presented .
Character test and brain imaging
Gulyaev, et al.  examined the thermal pattern from the personality and mental state of the mind. They observed that the distribution of temperature at the tension level depends on the concentration and mental activity. Shevelev in his proposal explained imaging the brain function, a new method for cortical brain thermal imaging, called thermoencephaloscopy (TES). He points out the main mechanism behind the TES for neurological activity, local metabolism and local brain blood flow, which has detectable changes in temperature production. This method involves active (hot) and inactive (cold) regions of the cerebellum. He found that this technique was able to detect activation sequences in specific cortical areas. Studies show that glial source brain tumors have a higher temperature of 0.5-2 ℃ than their surrounding (natural tissue). An example of the Melanoma cancer of the skin in the scalp is shown in Figure 13 [31,36,37].
Thermography has also been widely used in women. Birnbaun and Kliot have suggested that women's illnesses may have the greatest potential for the application of thermography, including pregnancy period, when the female reproductive system undergoes significant changes in size, vessels, and volume increase of the uterus during this period leads to an increase in the number and size of blood vessels. Menczer and Eskin applied a thermal imaging test to the cases of women. In this experiment, the temperature at the nipple level and at a constant level at the top and bottom of the nipple for 4 weeks before delivery and in the first four days after maternity was measured. According to reports, those who complain of postpartum pain have a higher temperature than non-painful afterbirth. According to these comments, postpartum pain is mainly caused by intravenous and lymphatic swelling and/or ACINI filling with milk, and both processes, directly or indirectly, increase arterial blood vessels and increase body temperature, a as a result thermal imaging is provided as an effective tool for the diagnosis of postpartum pain. In Figure 14, we can see a thermogram and sonogram of the large cystic septum in the abdomen [38-41].
Manginas and his colleagues studied the possibility of thermography in people with coronary artery disease (CAD) and in patients undergoing cardiac transplantation (TX). They performed thermal thermography on 16 subjects with CAD, 19 Heart transplants and six people without structural heart disease. They compared the left ventricular and right ventricular temperature and found that CAD people have significantly higher temperature difference (0.19 ± 0.11 ℃) than those with TX (0.10 ± 0.06 ℃) and the control group (0.07 ± 0.04 ℃). It has also been reported that the thermography can detect first signs of Atherosclerosis and can therefore act as a primary indicator of a heart attack. In many cases of thermal operation, thermal imaging has been used as an additional observation method. Madjid and colleagues used internal thermography to identify vulnerable plaques [42-43].
Diagnosis of liver disease
Mansfield and colleagues used thermal imaging to detect liver metastases that cause abnormal temperature patterns at the skin surface. Knobel and colleagues used thermal imaging to measure the body temperature of the incubated baby in order to determine the relationship between necrotizing Enterocolitis and the body temperature in preterm infants. It was observed that the mean difference in temperature in the abdominal and chest area was higher in preterm newborns with NEC. Milonov, et al.  used thermography with an electric thermometer in people with liver-parasitic diseases. In this study, the disease multilocular hydatid and unilocular hydatid have been observed. Their research shows that thermal imaging is a useful tool for detecting suppurating cysts. Bhatia and colleagues reviewed infants and children with acute and chronic liver disease using thermal imaging and found out that 96% of people have abnormal stomach thermograms [44,45].
Deep vein thrombosis
One of the most important complications in hospitalized patients is the development of deep vein thrombosis. Deep vein thrombosis refers to the formation of a blood clot in one of the deep veins. Some parts of the clot, isolated in the blood vessels of the different limbs, especially in the lungs, cause ambulatory blockage. Venous thromboembolism, which includes deep thrombosis and pulmonary embolism, is a major cause of mortality in the hospital, which can be greatly prevented. Studies have shown that the incidence of venous thrombosis in hospitalized patients is one percent in healthy subjects. Deep vein thrombosis and its associated problems account for 10% Hospital deaths. During a prospective, clinical diagnostic study, the value of two non-invasive tests one using colored duplex ultrasound and the other fluid crystal contact thermography was performed for deep vein thrombosis. The SPE for duplex method was 95% and sensitivity is equal to 18%, but in the LCCT method, the SPE is 85% and the sensitivity is 75%. According to the abundance of DVT after surgery on the legs, especially pelvic surgery, postoperative screening for the DVT should be mandatory. It has been established that the LCCT is low-cost and a non-invasive test with a negative predictive value of 94%. In Figure 15, the sample of thermal imaging of the varicose vein is shown [46-50].
With the advent of a new generation of infrared detectors, infrared thermal imaging is becoming a precursor of a precise medical diagnostic tool for measuring the abnormal patterns of the thermal pattern. In addition, the high sensitivity to the temperature, spatial resolution, and the contactless nature and remote imaging, IRT is a completely harmless imaging method. Thermal images can be stored digitally and then processed by using different software to reach the existing thermal pattern. The interpretation of pseudo-colored thermographs is relatively simpler and faster. Studies have so far shown that IRT can successfully be used to diagnose breast cancer, diabetes, diseases associated with pathology of the blood, dentistry, diabetic neuropathy, and so on.
In this paper, firstly, the performance of the thermal cameras and its physical principles has been evaluated and further processed into images and factors affecting the thermography. Also, the thermal imaging position in diagnosing breast cancer has been studied both in the field of hardware and in the field of software. The use of thermal imaging in the field of women during pregnancy has been studied. After breast cancer, diagnosis of diabetic neuropathy is another important issue of thermal imaging. Thermal imaging in the lower limbs, including peripheral vascular disease (deep vein thrombosis), has also been considered. One of the things that can be used with a thermal imaging system is screening to isolate people from epidemics such as the flu. It examines the effect of thermal imaging in children, including its ability to constipate children. The need to use thermal imaging to diagnose the diseases that are recommended is of particular importance. In addition, the thermal imaging system can be used as a good complement to the diagnosis.
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