Bmi
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BIO-MEDICAL INSTRUMENTATION -THERMOGRAPHY
THERMOGRAPHY: • Process of recording true thermal images of surfaces of objects under study. • In medicine, thermography displays images representing thermal radiations of skin areas. • Accounts for the possible changes in skin emissivity, the images are considered as maps of temperature. • Types: Infrared thermography Liquid crystal thermography Microwave thermography
INFRARED THERMOGRAPHY: • Human skin emits IR rays as an exponential function of its absolute temperature & emissive properties of the skin temperature. • Radiant energy is emitted in broad band of wavelengths. • Carried out usually at 20°c after cooling period of 15 mins. • Photovoltaic or photo-conductive IR detectors are commonly used. • Photo-voltaic types: can be obtained only when in liquid nitrogen In Sb : sensitivity=> 3 to 6μm; peak Sensitivity: 5 μm. Pbx Sn1-x Te : sensitivity=> 8 to 13μm; peak sensitivity: 12μm.
• Pb Ti O3: Pyroelectric detector=> high sensitivity, high stability & operative at room temperature.(without N2)
OPERATION: Chopper is inserted in front of IR radiation detector. IR radys from body & black body enters detector surface thro optical focusing system. The cassegrain optical system collects extremely low energy IR radiations emanating from skin surface. Black body is connected with another thermal sensor for compensating. O/p from detector is amplified ->phase sensitive detector. Then to analog or digital meter & absolute temperature of an object is calibrated & displayed. Scanning time=> 1 or 2 sec for 600 scanning lines with horizontal resolution of more than 600 elements/line. Temperature resolution < 0.07°c at 1 milliradian of visual angle.
CHARECTERISTICS THERMOGRAPHIS EQUIPMENTS: • Short frame time (< 4secs)
• High resolution (>100,000 picture elements) • Small size light weight optical head. • Wide spectrum band detector near the wavelength of 10 microns. • Easy to handle. • Data for analyzing can be taken simultaneously in object thermograms. • Contain interfaces for image processing. • Absolute temperature measurable.
There are 2 types of IR cameras for medical purpose: • High-speed: shortens picture taking time, incapable of measuring absolute temperature. • High-resolution: superior to high-speed in terms of temperature resolution & image resolution EXAMPLES: Infra-eye, Thermoscope, Thermoviewer, Thermocamera & infra vision. Operation: • Special IR camera => scans the object & a display unit for displaying the thermal picture on screen • Camera contains optical system in the form of an oscillating flat plane mirror-> scans the field of view at very high speed horizontally &vertically & focuses IR radiations onto the chopper.
• a.c signals are modulated & demodulated further. • These are given to CRT in synch with scanning mechanism.
LIQUID CRYSTAL THERMOGRAPHY: • Liquid crystals -> compounds that exhibit color-temp sensitivity in cholesteric phase. • Scattering effect with material gives rise to iridescent colors; wavelength is influenced by small temperature changes. • Temperature sensitivity makes cholesteric liquid crystals useful for thermal mapping. • RED=>low temp. regions to VIOLET=>high temp. regions. • For IR: VIOLET=>low temp. regions to VIOLET=>high temp. regions.
MICROWAVE THERMOGRAPHY: • Modern microwave radiometers detect temp. change of 0.1K. • Skin is transparent &so can radiations extend to few cms depth in the skin. • Using microwave receiver with freq response from 1.7GHz to 2.5 GHz->penetration depth =1cm in tissues, 8cm in fat& bone. • Problem: emissivity of body=> part of radiation is reflected back-> error -> corrected by adding artificial microwave noise providing balance btw receiver &body surface.
MEDICAL APPLICATIONS: INFLAMMATION: • Inflammated skin shows high temperature coz of active metabolism & increase in local blood flow. • Tumors although easily cooled take time to recover the temp. while inflammation recovers soon. • Due to intake of antibiotics local temp drops. DISEASESOF PHERIPERAL VESSALS: • When arteries gets blocked blood flow of peripheral vessels either decreases or disappears-> low temp.
BURNS: 1st we have to decide the degree of sensitivity .1st degree burns register higher temp.3rd degree burns-> temp 2-3°c lower than normal value due to absence of blood flow. SKIN GRAFTS & ORGAN TRANSPLANTATION: Detected by blood flow, in kidney transplantation rejection causes a high temp. while malfunction of transplanted organs leads to low temp. ORTHOPEDIC DISEASES: Fractures, arthritis, bruises & sprains can be diagnosed by local temp. increase.
THERMOGRAPHY: • Process of recording true thermal images of surfaces of objects under study. • In medicine, thermography displays images representing thermal radiations of skin areas. • Accounts for the possible changes in skin emissivity, the images are considered as maps of temperature. • Types: Infrared thermography Liquid crystal thermography Microwave thermography
INFRARED THERMOGRAPHY: • Human skin emits IR rays as an exponential function of its absolute temperature & emissive properties of the skin temperature. • Radiant energy is emitted in broad band of wavelengths. • Carried out usually at 20°c after cooling period of 15 mins. • Photovoltaic or photo-conductive IR detectors are commonly used. • Photo-voltaic types: can be obtained only when in liquid nitrogen In Sb : sensitivity=> 3 to 6μm; peak Sensitivity: 5 μm. Pbx Sn1-x Te : sensitivity=> 8 to 13μm; peak sensitivity: 12μm.
• Pb Ti O3: Pyroelectric detector=> high sensitivity, high stability & operative at room temperature.(without N2)
OPERATION: Chopper is inserted in front of IR radiation detector. IR radys from body & black body enters detector surface thro optical focusing system. The cassegrain optical system collects extremely low energy IR radiations emanating from skin surface. Black body is connected with another thermal sensor for compensating. O/p from detector is amplified ->phase sensitive detector. Then to analog or digital meter & absolute temperature of an object is calibrated & displayed. Scanning time=> 1 or 2 sec for 600 scanning lines with horizontal resolution of more than 600 elements/line. Temperature resolution < 0.07°c at 1 milliradian of visual angle.
CHARECTERISTICS THERMOGRAPHIS EQUIPMENTS: • Short frame time (< 4secs)
• High resolution (>100,000 picture elements) • Small size light weight optical head. • Wide spectrum band detector near the wavelength of 10 microns. • Easy to handle. • Data for analyzing can be taken simultaneously in object thermograms. • Contain interfaces for image processing. • Absolute temperature measurable.
There are 2 types of IR cameras for medical purpose: • High-speed: shortens picture taking time, incapable of measuring absolute temperature. • High-resolution: superior to high-speed in terms of temperature resolution & image resolution EXAMPLES: Infra-eye, Thermoscope, Thermoviewer, Thermocamera & infra vision. Operation: • Special IR camera => scans the object & a display unit for displaying the thermal picture on screen • Camera contains optical system in the form of an oscillating flat plane mirror-> scans the field of view at very high speed horizontally &vertically & focuses IR radiations onto the chopper.
• a.c signals are modulated & demodulated further. • These are given to CRT in synch with scanning mechanism.
LIQUID CRYSTAL THERMOGRAPHY: • Liquid crystals -> compounds that exhibit color-temp sensitivity in cholesteric phase. • Scattering effect with material gives rise to iridescent colors; wavelength is influenced by small temperature changes. • Temperature sensitivity makes cholesteric liquid crystals useful for thermal mapping. • RED=>low temp. regions to VIOLET=>high temp. regions. • For IR: VIOLET=>low temp. regions to VIOLET=>high temp. regions.
MICROWAVE THERMOGRAPHY: • Modern microwave radiometers detect temp. change of 0.1K. • Skin is transparent &so can radiations extend to few cms depth in the skin. • Using microwave receiver with freq response from 1.7GHz to 2.5 GHz->penetration depth =1cm in tissues, 8cm in fat& bone. • Problem: emissivity of body=> part of radiation is reflected back-> error -> corrected by adding artificial microwave noise providing balance btw receiver &body surface.
MEDICAL APPLICATIONS: INFLAMMATION: • Inflammated skin shows high temperature coz of active metabolism & increase in local blood flow. • Tumors although easily cooled take time to recover the temp. while inflammation recovers soon. • Due to intake of antibiotics local temp drops. DISEASESOF PHERIPERAL VESSALS: • When arteries gets blocked blood flow of peripheral vessels either decreases or disappears-> low temp.
BURNS: 1st we have to decide the degree of sensitivity .1st degree burns register higher temp.3rd degree burns-> temp 2-3°c lower than normal value due to absence of blood flow. SKIN GRAFTS & ORGAN TRANSPLANTATION: Detected by blood flow, in kidney transplantation rejection causes a high temp. while malfunction of transplanted organs leads to low temp. ORTHOPEDIC DISEASES: Fractures, arthritis, bruises & sprains can be diagnosed by local temp. increase.
