79 Thermal Imaging
Thermal imaging cameras record electromagnetic radiation in the infrared spectrum, which is emitted by all matter as a function of its temperature, and those readings into a visible image. Infrared radiation lies between the visible and microwave portions of the electromagnetic spectrum (more specifically the wavelengths from 900 to 14,000 nanometers, or 0.9–14 µm). Any object that has a temperature above absolute zero (- 273.15o
C or 0 Kelvin) emits radiation in the infrared region. Even objects that we think of as being very cold, such as ice cubes, emit infrared radiation.
Figure 3. These thermal images show a hand after local anaesthetics were administered. The increase in temperature shows that the regional block is successful in the area that will be operated on. In this case the pink finger and the surrounding area show little to no rise in temperature, indicating that the ulnar nerve is not anaesthetized. General anaesthetics were therefore administered prior to surgery.
Results Confirm Usefulness of Method
From these results Niehof concluded that thermal imaging is the best method for regional block assessment. “Thermal imaging reaches higher accuracy values and maintains those high values for a longer period of time. And above all: it is a method that is completely objective, no patient input is required. At the same time it is extremely easy to use. All you need to do is point the FLIR thermal imaging camera and push the right button.”
According to Niehof local regional blocks should be assessed by a FLIR thermal imaging camera: “I don’t see why not. The price is not a limiting factor anymore. Given the fact that it will help decrease morbidity risk by avoiding unnecessary additional anaesthetics I would say that it is definitely worth the investment.”
“And thermal imaging cameras can be used for more than just this particular application”, continued Niehof. “Thermal imaging technology has seen use in the detection of certain infections, nerve damage and soft tissue injuries. Ongoing research is constantly revealing new and exciting ways to use thermal imaging technology as a medical monitoring and diagnostics tool.”
The existence of infrared was discovered in 1800 by astronomer Sir Frederick William Herschel. Curious to the thermal difference between different light colours, he directed sunlight through a glass prism to create a spectrum and then measured the temperature of each colour. He found that the temperatures of the colours increased from the violet to the red part of the spectrum. After noticing this pattern Herschel decided to measure the temperature just beyond the red portion of the spectrum in a region where no sunlight was visible. To his surprise, he found that this region had the highest temperature of all. This ‘invisible light’ he had discovered is now called infrared radiation.
Thermal imaging cameras are very similar to regular digital video cameras. Infrared radiation coming from an object or scene is focused by the optics onto an infrared detector. The detector sends the information to sensor electronics for image processing. The electronics translate the data coming from the detector into an image that can be viewed in the view finder or on a standard video monitor or LCD screen.
Using so-called ‘blackbodies’, objects with a known temperature, thermal imaging cameras can be calibrated so that the recorded intensity of infrared radiation can not only be used to produce an image, but also to determine the temperature of an objects or scene within the camera’s field of view. In other words: the thermal image is transformed in a thermographic image. Every pixel in the image is in fact a non-contact temperature measurement.
Thermal imaging detectors can be roughly devised in two categories: microbolometer detectors and quantum detectors. Microbolometer detectors are usually made of a metal or semiconductor material. They respond to infrared radiation in a way that causes a change of state in the bulk material (for example, resistance or capacitance), which allows for thermographic calibration. These detectors typically cost less to produce and have a broader infrared spectral response than quantum detectors, but they are influenced by incident radiant energy and are less sensitive than quantum detectors.
High-end thermal imaging cameras incorporate photon detectors, which operate on the basis of an intrinsic photoelectric effect. These materials respond to infrared by absorbing photons that elevate the material’s electrons to a higher energy state, causing a change in conductivity, voltage, or current. By cooling these detectors to cryogenic temperatures, they remain practically unaffected by incident radiant energy, ensuring high sensitivity and accuracy.
Don’t Fight to Get the Light Right
Chart 1. This chart shows the sensitivity of the thermal imaging (red), cold sensation (blue) and pin prick (green) assessment methods over time.
Olympus provides its versatile, powerful BX3 clinical microscope systems for analysis and disease diagnosis in pathology and cytology. The systems take advantage of Olympus’s new true colour LED illumination technology and built in Light Intensity Manager (LIM) to create images with accurately rendered colours. Histological and cytological stains appear exactly the same under the true colour LED as they do under daylight filtered halogen, facilitating a seamless transition for labs adopting the new, more efficient LED technology. True colour LEDs offer longer lifetimes, constant colour temperature at all voltages and reduced power consumption when compared to traditional halogen bulbs. In addition, the LIM improves user workflow and maximises consistency by automatically modulating light intensity when working with different magnifications. Such advantages make the BX3 systems with true colour LED illumination the logical choice for comfortable and efficient clinical microscopy.
The Olympus true colour LED approach utilises the most advanced mixed-matrix brightfield LED technology currently available to provide a colour rendering index very similar to that of halogen illumination. Stains such as Haematoxylin, Eosin and Papanicolaou look the same when using the Olympus LED as when using halogen light sources, while similar colours can be easily differentiated. These factors maximise the accuracy and reliability of diagnosis using the Olympus true colour LED illuminator.
Chart 2. This chart shows the specificity of the thermal imaging (red), cold sensation (blue) and pin prick (green) assessment methods over time.
Source: Galvin, E.M, et al, Thermographic temperature measurement compared with pin prick and cold sensation in predicting the effectiveness of regional blocks. Anesth Analg, 2006. 102(2): p. 598-604.
With a large number of clinical samples to screen, the optimisation of user workflow can significantly improve the efficiency of pathological analysis. For this reason, the Olympus true colour illumination system with LIM automatically modulates light intensity when changing objective lenses. This means that consistent illumination is maintained without the need for manual adjustment, saving a significant amount of time, while simplifying and improving the screening process. Automation is achieved using sensors mounted in the nosepiece that detect the objective lens in use and manipulate the LED intensity according to user defined preferences.
The flexible Olympus BX3 clinical microscopy systems with true colour LED illumination and LIM have been specifically developed to meet the needs of clinical microscopy, ensuring reliable diagnosis while maximising workflow efficiency.
Circle no. 246
INTERNATIONAL LABMATE - JANUARY/FEBRUARY 2012
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