Thermography isa non-contact, non-destructive test method that utilizes a thermal imager todetect, display and record thermal patterns and temperatures across the surfaceof an object. Infrared thermography may be applied to any situation whereknowledge of thermal profiles and temperatures will provide meaningful dataabout a system, object or process.Since infraredradiation is emitted by all objects based on their temperatures, according tothe black body radiation law, thermography makes it possible to see one’senvironment with or without visible illumination. The amount of radiationemitted by an object increases with temperature; therefore thermography allowsone to see variation in temperature.

Thermography iswidely used in industry for predictive maintenance, condition assessment,quality assurance and forensic investigations of electrical, mechanical andstructural systems.In this context,we are mainly concentrating on the medical applications of Thermography. CONTENTS Chapter                      Title                                                                                        Page No.                                                       1.

                     INTRODUCTION                                                                                    1 2.                     LITERATUREREVIEW                                                                        2          3                      PHYSICSOF THERMOGRAPHY                                                        4                          3.1       Types of Thermography                                                               64.                     MEDICAL THERMOGRAPHY                                                           7                        4.1      Advantages                                                                                    8                        4.2        Limitations                                                                                     85                      THERMOGRAPHIC CAMERAS                                                           9                        5.1      Factors affecting Thermal Examination                                     9                   6                      APPLICATIONS OFTHERMOGRAPHY IN MEDICAL FIELD   11                          CONCLUSION                                                                                       15                        REFERENCES                                                                                       16                                                                                          LIST OF FIGURES   FigureNo                               Title                                                                            Page No 1.

1                  Thermographyimage of hands                                                            1                                                3.1                  Infrared spectrum                                                                                4 3.2                  Blackbody temperaturevariation                                                      6 4.1                  Block diagram of the IRThermography                                            7 4.2                  Temperature distributionscale                                                          8 5.1                  Thermographic Camera                                                                      10 5.2                  Thermal Image capture process                                                        10 6.1                  Breast thermography                                                                          11 6.

2                  Complete body thermogram                                                               14                              CHAPTER 1 INTRODUCTIONInfraredthermography is a non-contact imaging technique for visualising infraredradiation. The IR radiation emitted from an object has different intensitydepending on its surface temperature. An IR camera detector senses the IRradiation and electronically displays a visual image of the temperatures – athermal image or thermogram.Sinceinfrared radiation is emitted by all objects with a temperature above absolutezero according to the black body radiation law, thermography makes it possibleto see one’s environment with or without visible illumination. The amount ofradiation emitted by an object increases with temperature; therefore,thermography allows one to see variations in temperature.

When viewed through athermal imaging camera, warm objects stand out well against cooler backgrounds.Thereare three types of thermography: liquid crystal thermography (LCT), infraredthermography (IRT) and microwave thermography (MWT). The non-invasive and highresolution characteristics of the thermographic systems make them valuablediagnostic as well as therapeutic aids.  Fig. 1.1- Thermographyimage of hands (1)  Theinfrared ray is a kind of electromagnetic wave with a frequency higher than theradio frequencies and lower than visible light frequencies.Theinfrared region of the electromagnetic spectrum is usually taken as 0.77 and100 ?mfor convenience it is often split into near infrared (0.

77 to 1.5?m), middle infrared(1.5 to 6?m)and far infra (60-40?m)and far far infrared (40 to 100?m)Infraredrays are radiated spontaneously by all objects having a temperature aboveabsolute zero (-459.67 .Black body radiation law is theactual principle which works on thermography. A black body is an idealizedphysical body that absorbs all incident electromagnetic radiation.

Because ofthis perfect absorptivity at all wavelengths, a black body is also the bestpossible emitter of thermal radiation, which it radiates incandescently in acharacteristic, continuous spectrum that depends on the body’s temperature. Fig. 3.1 Infraredspectrum (2) Thermal images, or thermograms, are actually visualdisplays of the amount of infrared energy emitted, transmitted, and reflectedby an object. Because there are multiple sources of the infrared energy, it isdifficult to get an accurate temperature of an object using this method. Athermal imaging camera is capable of performing algorithms to interpret thatdata and build an image.

Although the image shows the viewer an approximationof the temperature at which the object is operating, the camera is actuallyusing multiple sources of data based on the areas surrounding the object todetermine that value rather than detecting the actual temperature.The total energy ‘W’ emitted by the objectand its temperature are related by the Stefan Boltzmann formula,                                                W=                                  WhereW = radiant flux density                                                                    StefanBoltzmann constant =5.64*10-2                                       T = Absolute temperatureBased on the intensity of the IR radiation,it determines the temperature of the object’s surface, and makes it visible forthe human eye with a thermal image. A thermal image allows us to sense thetemperature of an object or at least accurately tell its temperature relativeto its environment.This phenomenon may become clearer upon considerationof the formula:IncidentRadiant Power = Emitted Radiant Power + Transmitted Radiant Power + ReflectedRadiant Power;Where, Incident Radiant Power is theradiant power profile when viewed through a thermal imaging camera. EmittedRadiant Power is generally what is intended to be measured; TransmittedRadiant Power is the radiant power that passes through the subjectfrom a remote thermal source, and; Reflected Radiant Power isthe amount of radiant power that reflects off the surface of the object from aremote thermal source.This phenomenon occurs everywhere, all the time. It isa process known as Radiant Heat Exchange, since Radiant Power × Time equalsRadiant Energy.

However, in the case of Infrared Thermography, the aboveequation is used to describe the radiant power within the spectral wavelengthpass band of the thermal imaging camera in use. The Radiant Heat exchangerequirements described in the equation apply equally at every wavelength inthe Electromagnetic Spectrum.3.

1 Types ofThermographyThermography ismainly divided into two types, i.e.:-·        Active thermography·        Passive thermographyIn passive thermography, the feature ofinterest are naturally at a higher or lower temperature than the background.Passive thermography has many applications such as surveillance of people on ascene and medical diagnosis.Where as in active thermography, an energy isrequired to produce a thermal contrast between the feature of interest and the background.

The active approach is necessary in many cases given that the inspected partsare usually in equilibrium with the surroundings. Fig. 3.2 Blackbodytemperature variation (3)  CHAPTER 4. MEDICAL THERMOGRAPHYMedicalthermography is the estimation of spatial distribution of temperature on thebody surface. It is the only passive medical imaging modality, utilizingradiation energy produced by the body itself.

The human body absorbs IRradiation almost without reflection, and at the same time, emits part of itsown thermal energy in the form of infrared radiation. It often facilitatesdetection of pathological changes before any method of investigation.Infraredthermography is based on analysis of skin surface temperatures as a reflectionof normal or abnormal human physiology using a highly specialized IR- camera.Ina fraction of second, a large area of the body can be imaged to an accuracy ofless than 0.1  as well as a spatial resolution of 25-50micrometres and, dynamic responses to stimuli are easily documented.  Fig 4.1. Block diagramof the IR Thermography (4) 4.

1 Advantages•     It shows a visual picture so temperatures over a largearea can be compared.•     It is capable of catching moving targets in real time.•     It is able to find deterioration, i.e., highertemperature components prior to their failure. •     It can be used to measure or observe in areasinaccessible or hazardous for other methods.

•     It is a non-destructive test method. •     It can be used to find defects in shafts, pipes, andother metal or plastic parts.•     It can be used to detect objects in dark areas.

4.2 Limitations•     Quality cameras often have a high price range.•     Accurate temperature measurements are hindered bydiffering emissivity and reflections from other surfaces.•     Methods and instruments are limited to directlydetecting surface temperatures.   Fig 4.

2.Temperature distribution scale (5) CHAPTER 5. THERMOGRAPHICCAMERASA Thermographic camera is a non-contact device thatforms an image using infrared radiation, similar to a common camera that formsan image using visible light. Instead of the 450-750 nanometer range of thevisible light camera, infrared cameras operate in wavelength as long as 14000nm (14µm) An infraredcamera is a non-contact device that detects infrared energy (heat) and convertsit into an electronic signal, which is then processed to produce a thermalimage on a video monitor and perform temperature calculations. Heat sensed byan infrared camera can be very precisely quantified, or measured, allowing youto not only monitor thermal performance, but also identify and evaluate therelative severity of heat-related problems.

Images from infrared cameras tend to have a singlecolor channel because the cameras generally use a sensor that does notdistinguish different wavelengths of infrared radiation. Color cameras requirea more complex construction to differentiate wavelength and color has lessmeaning outside of the normal visible spectrum because the differentwavelengths do not map uniformly into the system of color vision used byhumans. Sometimes these monochromatic images are displayed in pseudo-color,where changes in color are used rather than changes in intensity to displaychanges in the signal. This is useful because although humans have much greaterdynamic range in intensity detection than color overall, the ability to seefine intensity differences in bright areas is fairly limited. This technique iscalled density slicing.5.

1 Factors affecting Thermal ExaminationVarious factors affects the thermal examinationprocess, at the time of thermal imaging process following aspects are to beconsidered and taken care.·        Ambient room temperature Type of equipment utilized Type of floor covering Presence or absence of windows which can alter room temperature. Type of heating or air conditioning for thermal regulation of the room. Usage of lotions, deodorants and cosmetics on the skin Ingestion of vasodilator and vasoconstrictor substances i.

e. Caffeine Medication taken by the patient.  Fig 5.1. ThermographicCamera (6)  Fig 5.2. Thermal Imagecapture process (7)Theinfrared ray is a kind of electromagnetic wave with a frequency higher than theradio frequencies and lower than visible light frequencies. Theinfrared region of the electromagnetic spectrum is usually taken as 0.

77 and100 ?mfor convenience it is often split into near infrared (0.77 to 1.5?m), middle infrared(1.5 to 6?m)and far infra (60-40?m)and far far infrared (40 to 100?m)Infraredrays are radiated spontaneously by all objects having a temperature aboveabsolute zero (-459.67 .Black body radiation law is theactual principle which works on thermography.

A black body is an idealizedphysical body that absorbs all incident electromagnetic radiation. Because ofthis perfect absorptivity at all wavelengths, a black body is also the bestpossible emitter of thermal radiation, which it radiates incandescently in acharacteristic, continuous spectrum that depends on the body’s temperature. Fig. 3.1 Infraredspectrum (2) Thermal images, or thermograms, are actually visualdisplays of the amount of infrared energy emitted, transmitted, and reflectedby an object.

Because there are multiple sources of the infrared energy, it isdifficult to get an accurate temperature of an object using this method. Athermal imaging camera is capable of performing algorithms to interpret thatdata and build an image. Although the image shows the viewer an approximationof the temperature at which the object is operating, the camera is actuallyusing multiple sources of data based on the areas surrounding the object todetermine that value rather than detecting the actual temperature.

The total energy ‘W’ emitted by the objectand its temperature are related by the Stefan Boltzmann formula,                                                W=                                  WhereW = radiant flux density                                                                    StefanBoltzmann constant =5.64*10-2                                       T = Absolute temperatureBased on the intensity of the IR radiation,it determines the temperature of the object’s surface, and makes it visible forthe human eye with a thermal image. A thermal image allows us to sense thetemperature of an object or at least accurately tell its temperature relativeto its environment.This phenomenon may become clearer upon considerationof the formula:IncidentRadiant Power = Emitted Radiant Power + Transmitted Radiant Power + ReflectedRadiant Power;Where, Incident Radiant Power is theradiant power profile when viewed through a thermal imaging camera. EmittedRadiant Power is generally what is intended to be measured; TransmittedRadiant Power is the radiant power that passes through the subjectfrom a remote thermal source, and; Reflected Radiant Power isthe amount of radiant power that reflects off the surface of the object from aremote thermal source.This phenomenon occurs everywhere, all the time. It isa process known as Radiant Heat Exchange, since Radiant Power × Time equalsRadiant Energy. However, in the case of Infrared Thermography, the aboveequation is used to describe the radiant power within the spectral wavelengthpass band of the thermal imaging camera in use.

The Radiant Heat exchangerequirements described in the equation apply equally at every wavelength inthe Electromagnetic Spectrum.3.1 Types ofThermographyThermography ismainly divided into two types, i.

e.:-·        Active thermography·        Passive thermographyIn passive thermography, the feature ofinterest are naturally at a higher or lower temperature than the background.Passive thermography has many applications such as surveillance of people on ascene and medical diagnosis.

Where as in active thermography, an energy isrequired to produce a thermal contrast between the feature of interest and the background.The active approach is necessary in many cases given that the inspected partsare usually in equilibrium with the surroundings. Fig. 3.2 Blackbodytemperature variation (3)  CHAPTER 4.

MEDICAL THERMOGRAPHYMedicalthermography is the estimation of spatial distribution of temperature on thebody surface. It is the only passive medical imaging modality, utilizingradiation energy produced by the body itself. The human body absorbs IRradiation almost without reflection, and at the same time, emits part of itsown thermal energy in the form of infrared radiation. It often facilitatesdetection of pathological changes before any method of investigation.Infraredthermography is based on analysis of skin surface temperatures as a reflectionof normal or abnormal human physiology using a highly specialized IR- camera.Ina fraction of second, a large area of the body can be imaged to an accuracy ofless than 0.1  as well as a spatial resolution of 25-50micrometres and, dynamic responses to stimuli are easily documented.  Fig 4.

1. Block diagramof the IR Thermography (4) 4.1 Advantages•     It shows a visual picture so temperatures over a largearea can be compared.•     It is capable of catching moving targets in real time.•     It is able to find deterioration, i.e., highertemperature components prior to their failure. •     It can be used to measure or observe in areasinaccessible or hazardous for other methods.

•     It is a non-destructive test method. •     It can be used to find defects in shafts, pipes, andother metal or plastic parts.•     It can be used to detect objects in dark areas. 4.2 Limitations•     Quality cameras often have a high price range.•     Accurate temperature measurements are hindered bydiffering emissivity and reflections from other surfaces.•     Methods and instruments are limited to directlydetecting surface temperatures.

   Fig 4.2.Temperature distribution scale (5) CHAPTER 5. THERMOGRAPHICCAMERASA Thermographic camera is a non-contact device thatforms an image using infrared radiation, similar to a common camera that formsan image using visible light.

Instead of the 450-750 nanometer range of thevisible light camera, infrared cameras operate in wavelength as long as 14000nm (14µm) An infraredcamera is a non-contact device that detects infrared energy (heat) and convertsit into an electronic signal, which is then processed to produce a thermalimage on a video monitor and perform temperature calculations. Heat sensed byan infrared camera can be very precisely quantified, or measured, allowing youto not only monitor thermal performance, but also identify and evaluate therelative severity of heat-related problems.Images from infrared cameras tend to have a singlecolor channel because the cameras generally use a sensor that does notdistinguish different wavelengths of infrared radiation. Color cameras requirea more complex construction to differentiate wavelength and color has lessmeaning outside of the normal visible spectrum because the differentwavelengths do not map uniformly into the system of color vision used byhumans.

Sometimes these monochromatic images are displayed in pseudo-color,where changes in color are used rather than changes in intensity to displaychanges in the signal. This is useful because although humans have much greaterdynamic range in intensity detection than color overall, the ability to seefine intensity differences in bright areas is fairly limited. This technique iscalled density slicing.5.1 Factors affecting Thermal ExaminationVarious factors affects the thermal examinationprocess, at the time of thermal imaging process following aspects are to beconsidered and taken care.·        Ambient room temperature Type of equipment utilized Type of floor covering Presence or absence of windows which can alter room temperature.

Type of heating or air conditioning for thermal regulation of the room. Usage of lotions, deodorants and cosmetics on the skin Ingestion of vasodilator and vasoconstrictor substances i.e. Caffeine Medication taken by the patient.  Fig 5.

1. ThermographicCamera (6)  Fig 5.2. Thermal Imagecapture process (7)      

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