Thermography increases with temperature; therefore thermography allows one

Thermography is
a non-contact, non-destructive test method that utilizes a thermal imager to
detect, display and record thermal patterns and temperatures across the surface
of an object. Infrared thermography may be applied to any situation where
knowledge of thermal profiles and temperatures will provide meaningful data
about a system, object or process.

Since infrared
radiation is emitted by all objects based on their temperatures, according to
the black body radiation law, thermography makes it possible to see one’s
environment with or without visible illumination. The amount of radiation
emitted by an object increases with temperature; therefore thermography allows
one to see variation in temperature.

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Thermography is
widely used in industry for predictive maintenance, condition assessment,
quality assurance and forensic investigations of electrical, mechanical and
structural systems.

In this context,
we are mainly concentrating on the medical applications of Thermography. CONTENTS 

Chapter                      Title                                                                                        Page No.                                                       

1.                     INTRODUCTION                                                                                    1 2.                     LITERATURE
REVIEW                                                                        2          3                      PHYSICS
OF 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 OF
THERMOGRAPHY IN MEDICAL FIELD   11                          CONCLUSION                                                                                       
15                        REFERENCES                                                                                       
16                                                                                          LIST OF FIGURES 

 

Figure
No                               Title                                                                            Page No 1.1                  Thermography
image of hands                                                            1                                                3.1                  Infrared spectrum                                                                                
4 3.2                  Blackbody temperature
variation                                                      
6 4.1                  Block diagram of the IR
Thermography                                            7 4.2                  Temperature distribution
scale                                                          
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

 INTRODUCTION

Infrared
thermography is a non-contact imaging technique for visualising infrared
radiation. The IR radiation emitted from an object has different intensity
depending on its surface temperature. An IR camera detector senses the IR
radiation and electronically displays a visual image of the temperatures – a
thermal image or thermogram.

Since
infrared radiation is emitted by all objects with a temperature above absolute
zero according to the black body radiation law, thermography makes it possible
to see one’s environment with or without visible illumination. The amount of
radiation emitted by an object increases with temperature; therefore,
thermography allows one to see variations in temperature. When viewed through a
thermal imaging camera, warm objects stand out well against cooler backgrounds.

There
are three types of thermography: liquid crystal thermography (LCT), infrared
thermography (IRT) and microwave thermography (MWT). The non-invasive and high
resolution characteristics of the thermographic systems make them valuable
diagnostic as well as therapeutic aids.

 

Fig. 1.1- Thermography
image of hands (1)

 

 The
infrared ray is a kind of electromagnetic wave with a frequency higher than the
radio frequencies and lower than visible light frequencies.

The
infrared region of the electromagnetic spectrum is usually taken as 0.77 and
100 ?m
for 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)

Infrared
rays are radiated spontaneously by all objects having a temperature above
absolute zero (-459.67

.Black body radiation law is the
actual principle which works on thermography. A black body is an idealized
physical body that absorbs all incident electromagnetic radiation. Because of
this perfect absorptivity at all wavelengths, a black body is also the best
possible emitter of thermal radiation, which it radiates incandescently in a
characteristic, continuous spectrum that depends on the body’s temperature

.

Fig. 3.1 Infrared
spectrum (2)

 

Thermal images, or thermograms, are actually visual
displays of the amount of infrared energy emitted, transmitted, and reflected
by an object. Because there are multiple sources of the infrared energy, it is
difficult to get an accurate temperature of an object using this method. A
thermal imaging camera is capable of performing algorithms to interpret that
data and build an image. Although the image shows the viewer an approximation
of the temperature at which the object is operating, the camera is actually
using multiple sources of data based on the areas surrounding the object to
determine that value rather than detecting the actual temperature.

The total energy ‘W’ emitted by the object
and its temperature are related by the Stefan Boltzmann formula,

                                                W=

                                 Where
W = radiant flux density

                                 

                                 

Stefan
Boltzmann constant =5.64*10-2

                                       T = Absolute temperature

Based on the intensity of the IR radiation,
it determines the temperature of the object’s surface, and makes it visible for
the human eye with a thermal image. A thermal image allows us to sense the
temperature of an object or at least accurately tell its temperature relative
to its environment.

This phenomenon may become clearer upon consideration
of the formula:

Incident
Radiant Power = Emitted Radiant Power + Transmitted Radiant Power + Reflected
Radiant Power;

Where, Incident Radiant Power is the
radiant power profile when viewed through a thermal imaging camera. Emitted
Radiant Power is generally what is intended to be measured; Transmitted
Radiant Power is the radiant power that passes through the subject
from a remote thermal source, and; Reflected Radiant Power is
the amount of radiant power that reflects off the surface of the object from a
remote thermal source.

This phenomenon occurs everywhere, all the time. It is
a process known as Radiant Heat Exchange, since Radiant Power × Time equals
Radiant Energy. However, in the case of Infrared Thermography, the above
equation is used to describe the radiant power within the spectral wavelength
pass band of the thermal imaging camera in use. The Radiant Heat exchange
requirements described in the equation apply equally at every wavelength in
the Electromagnetic Spectrum.

3.1 Types of
Thermography

Thermography is
mainly divided into two types, i.e.:-

·        
Active thermography

·        
Passive thermography

In passive thermography, the feature of
interest are naturally at a higher or lower temperature than the background.
Passive thermography has many applications such as surveillance of people on a
scene and medical diagnosis.

Where as in active thermography, an energy is
required 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 parts
are usually in equilibrium with the surroundings

.

Fig. 3.2 Blackbody
temperature variation (3)

 

 

CHAPTER 4.

MEDICAL THERMOGRAPHY

Medical
thermography is the estimation of spatial distribution of temperature on the
body surface. It is the only passive medical imaging modality, utilizing
radiation energy produced by the body itself. The human body absorbs IR
radiation almost without reflection, and at the same time, emits part of its
own thermal energy in the form of infrared radiation. It often facilitates
detection of pathological changes before any method of investigation.

Infrared
thermography is based on analysis of skin surface temperatures as a reflection
of normal or abnormal human physiology using a highly specialized IR- camera.In
a fraction of second, a large area of the body can be imaged to an accuracy of
less than 0.1

 as well as a spatial resolution of 25-50
micrometres and, dynamic responses to stimuli are easily documented.

 

Fig 4.1. Block diagram
of the IR Thermography (4)

 

4.1 Advantages

•     
It shows a visual picture so temperatures over a large
area can be compared.

•     
It is capable of catching moving targets in real time.

•     
It is able to find deterioration, i.e., higher
temperature components prior to their failure.

•     
It can be used to measure or observe in areas
inaccessible or hazardous for other methods.

•     
It is a non-destructive test method.

•     
It can be used to find defects in shafts, pipes, and
other 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 by
differing emissivity and reflections from other surfaces.

•     
Methods and instruments are limited to directly
detecting surface temperatures.

 

 

Fig 4.2.
Temperature distribution scale (5)

 

CHAPTER 5.

THERMOGRAPHIC
CAMERAS

A Thermographic camera is a non-contact device that
forms an image using infrared radiation, similar to a common camera that forms
an image using visible light. Instead of the 450-750 nanometer range of the
visible light camera, infrared cameras operate in wavelength as long as 14000
nm (14µm)

 An infrared
camera is a non-contact device that detects infrared energy (heat) and converts
it into an electronic signal, which is then processed to produce a thermal
image on a video monitor and perform temperature calculations. Heat sensed by
an infrared camera can be very precisely quantified, or measured, allowing you
to not only monitor thermal performance, but also identify and evaluate the
relative severity of heat-related problems.

Images from infrared cameras tend to have a single
color channel because the cameras generally use a sensor that does not
distinguish different wavelengths of infrared radiation. Color cameras require
a more complex construction to differentiate wavelength and color has less
meaning outside of the normal visible spectrum because the different
wavelengths do not map uniformly into the system of color vision used by
humans. Sometimes these monochromatic images are displayed in pseudo-color,
where changes in color are used rather than changes in intensity to display
changes in the signal. This is useful because although humans have much greater
dynamic range in intensity detection than color overall, the ability to see
fine intensity differences in bright areas is fairly limited. This technique is
called density slicing.

5.1 Factors affecting Thermal Examination

Various factors affects the thermal examination
process, at the time of thermal imaging process following aspects are to be
considered 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. Thermographic
Camera (6)

 

Fig 5.2. Thermal Image
capture process (7)The
infrared ray is a kind of electromagnetic wave with a frequency higher than the
radio frequencies and lower than visible light frequencies. The
infrared region of the electromagnetic spectrum is usually taken as 0.77 and
100 ?m
for 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)Infrared
rays are radiated spontaneously by all objects having a temperature above
absolute zero (-459.67

.Black body radiation law is the
actual principle which works on thermography. A black body is an idealized
physical body that absorbs all incident electromagnetic radiation. Because of
this perfect absorptivity at all wavelengths, a black body is also the best
possible emitter of thermal radiation, which it radiates incandescently in a
characteristic, continuous spectrum that depends on the body’s temperature.

Fig. 3.1 Infrared
spectrum (2) Thermal images, or thermograms, are actually visual
displays of the amount of infrared energy emitted, transmitted, and reflected
by an object. Because there are multiple sources of the infrared energy, it is
difficult to get an accurate temperature of an object using this method. A
thermal imaging camera is capable of performing algorithms to interpret that
data and build an image. Although the image shows the viewer an approximation
of the temperature at which the object is operating, the camera is actually
using multiple sources of data based on the areas surrounding the object to
determine that value rather than detecting the actual temperature.The total energy ‘W’ emitted by the object
and its temperature are related by the Stefan Boltzmann formula,                                                W=

                                 Where
W = radiant flux density                                 

                                 

Stefan
Boltzmann 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 for
the human eye with a thermal image. A thermal image allows us to sense the
temperature of an object or at least accurately tell its temperature relative
to its environment.This phenomenon may become clearer upon consideration
of the formula:

Incident
Radiant Power = Emitted Radiant Power + Transmitted Radiant Power + Reflected
Radiant Power;

Where, Incident Radiant Power is the
radiant power profile when viewed through a thermal imaging camera. Emitted
Radiant Power is generally what is intended to be measured; Transmitted
Radiant Power is the radiant power that passes through the subject
from a remote thermal source, and; Reflected Radiant Power is
the amount of radiant power that reflects off the surface of the object from a
remote thermal source.This phenomenon occurs everywhere, all the time. It is
a process known as Radiant Heat Exchange, since Radiant Power × Time equals
Radiant Energy. However, in the case of Infrared Thermography, the above
equation is used to describe the radiant power within the spectral wavelength
pass band of the thermal imaging camera in use. The Radiant Heat exchange
requirements described in the equation apply equally at every wavelength in
the Electromagnetic Spectrum.3.1 Types of
ThermographyThermography is
mainly divided into two types, i.e.:-·        
Active thermography·        
Passive thermographyIn passive thermography, the feature of
interest are naturally at a higher or lower temperature than the background.
Passive thermography has many applications such as surveillance of people on a
scene and medical diagnosis.Where as in active thermography, an energy is
required 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 parts
are usually in equilibrium with the surroundings.

Fig. 3.2 Blackbody
temperature variation (3)  CHAPTER 4. MEDICAL THERMOGRAPHYMedical
thermography is the estimation of spatial distribution of temperature on the
body surface. It is the only passive medical imaging modality, utilizing
radiation energy produced by the body itself. The human body absorbs IR
radiation almost without reflection, and at the same time, emits part of its
own thermal energy in the form of infrared radiation. It often facilitates
detection of pathological changes before any method of investigation.Infrared
thermography is based on analysis of skin surface temperatures as a reflection
of normal or abnormal human physiology using a highly specialized IR- camera.In
a fraction of second, a large area of the body can be imaged to an accuracy of
less than 0.1

 as well as a spatial resolution of 25-50
micrometres and, dynamic responses to stimuli are easily documented. 

Fig 4.1. Block diagram
of the IR Thermography (4) 4.1 Advantages•     
It shows a visual picture so temperatures over a large
area can be compared.•     
It is capable of catching moving targets in real time.•     
It is able to find deterioration, i.e., higher
temperature components prior to their failure. •     
It can be used to measure or observe in areas
inaccessible or hazardous for other methods. •     
It is a non-destructive test method. •     
It can be used to find defects in shafts, pipes, and
other 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 by
differing emissivity and reflections from other surfaces.•     
Methods and instruments are limited to directly
detecting surface temperatures.  

Fig 4.2.
Temperature distribution scale (5) CHAPTER 5. THERMOGRAPHIC
CAMERASA Thermographic camera is a non-contact device that
forms an image using infrared radiation, similar to a common camera that forms
an image using visible light. Instead of the 450-750 nanometer range of the
visible light camera, infrared cameras operate in wavelength as long as 14000
nm (14µm) An infrared
camera is a non-contact device that detects infrared energy (heat) and converts
it into an electronic signal, which is then processed to produce a thermal
image on a video monitor and perform temperature calculations. Heat sensed by
an infrared camera can be very precisely quantified, or measured, allowing you
to not only monitor thermal performance, but also identify and evaluate the
relative severity of heat-related problems.Images from infrared cameras tend to have a single
color channel because the cameras generally use a sensor that does not
distinguish different wavelengths of infrared radiation. Color cameras require
a more complex construction to differentiate wavelength and color has less
meaning outside of the normal visible spectrum because the different
wavelengths do not map uniformly into the system of color vision used by
humans. Sometimes these monochromatic images are displayed in pseudo-color,
where changes in color are used rather than changes in intensity to display
changes in the signal. This is useful because although humans have much greater
dynamic range in intensity detection than color overall, the ability to see
fine intensity differences in bright areas is fairly limited. This technique is
called density slicing.5.1 Factors affecting Thermal ExaminationVarious factors affects the thermal examination
process, at the time of thermal imaging process following aspects are to be
considered 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. Thermographic
Camera (6) 

Fig 5.2. Thermal Image
capture process (7)