Diagnostic Thermography

What is Thermography?• In medicine, is the measurement of body heat emitted by the skin• Is a non – invasive, diagnostic imaging procedure involving the detection

of and recording of cutaneous thermal patterns using instruments which can provide visual and quantitative documentation of these temperature measurements. Because thermography detects pathophysiologic changes in cutaneous temperature, it may be used as an integral part of the physical examination or, alternatively, as an adjunct to that examination.

• Thermal patterns are displayed on the skin and detected by the infrared sensor of the camera. Interpreted as temperature data it is transmitted into the computer where all images are stored as picture, where red means hot and blue means cold.

• The interpretation of these temperatures and thermal patterns can be important in the development of diagnostic impression.

• It may contribute to a diagnosis and patient management by aiding in the determination of the site and degree of lesion, the type of functional disorder, and the prognosis for treatment outcomes, as well as assisting in the determination of the most effective course treatment through continual case evaluation.

Why Thermography?• Thermography can detect the increased metabolic heat associated

with increased vascularity of most suspicious growth, and can sense the thermal signal – often years in advance of the mass detected on x – ray.

• Thermography is appropriate an germane to any healthcare practice whenever the treating professional feels a physiological imaging is needed for diagnosis or case management. It provides information about acute as well as chronic conditions and can be useful in distinguishing aggravated from residual tissue injury.

• Because the temperature of human skin changes in response to disorders in the underlying tissue, conditions such as poor circulation, swelling, and cancer are visible with cameras sensitive to infrared heat.

• Variations in skin temperature depend on the number of blood vessels and their nearness to the body surface under observation, among other factors.

Physiological Basis Blood flow allows core temperature to come to the surface or not, and will change the temperature of the skin territorially. Each area of the body has a particular cutaneous – cordal connection by the sympathetic nervous system. The alteration of the thermal content of a territory occurs based upon alterations of this nervous control. Only the dermal blood flow changes explain the heart seen on the surface of the body. The heat of a muscle, joint, or a bone is not conducted to the dermal tissues and cannot influence the dermal temperature recorded by thermography. Conduction of heat from the deeper portions of the body to the surface does not occur or create changes in the surface temperature. However, there are neurochemical processes in the dermis which can block the normal sympathetic control of blood flow in the skin, such as histamines, prostaglandins, and myovascular receptor inhibitors of mast cells. These, however, can be easily differentiated from neural control by clinical correlation.

• Areas of the surface of the body are recorded as symmetrical. The frontal areas, the thumbs, the great toes, the knees, the buttocks, the posterior shoulders should be contra laterally symmetrical and isothermic. If there is a difference, it is described as a delta T and means simply the difference in temperature. In order to interpret thermographic patterns, one must know the normal pattern. The normal pattern of the skin surface is symmetrical, and it is thought that the 95 percentile range in the normal subject deviates less than 0.3 °C. Uematsu and others have established the normal patterns of the human surface temperature.

• The hands are usually colder than the shoulders. The buttock and the feet are the coldest in the lower body, followed by the anterior knees. The thenar side of a given hand is usually warmer than the hypothenar, and the fingers are cooler than the palm.

• It has been shown that the surface temperature of the human body is symmetrical. It is a reflection of blood flow in the dermal microcirculation, and the control of this microcirculation is autonomic and specifically, sympathetic. The major basis of clinical thermography is the correlation of temperature recordings with various conditions from disease and injury as it relates to autonomic function.

Emissivity

• Emissivity is a term representing a material's ability to emit thermal radiation. Each material has a different emissivity and it can be quite a task to determine the appropriate emissivity for a subject. A material's emissivity can range from 0.00 (completely not-emitting) to 1.00 (completely emitting); the emissivity often varies with temperature.

• A black body is a theoretical object which will radiate infrared radiation at its contact temperature. If a thermocouple on a black body radiator reads 50 °C, the radiation the black body will give up will also be 50 °C. Therefore a true black body will have an emissivity of 1.

• Since there is no such thing as a perfect black body, the infrared radiation of normal objects will appear to be less than the contact temperature. The rate of emission of infrared radiation will thus be a fraction of the true contact temperature. This fraction is called emissivity.

• Some objects have different emissivities in long wave as compared to mid wave emissions. Emissivities may also change as a function of temperature in some materials.

• To make a temperature measurement of an object, the thermographer will refer to the emissivity table to choose the emissivity value of the object, which is then entered into the camera. The camera's algorithm will correct the temperature by using the emissivity to calculate a temperature that more closely matches the actual contact temperature of the object.

• If possible the thermographer would try to test the emissivity of the object in question. This would be more accurate than attempting to determine the emissivity of the object via a table. The usual method of testing the emissivity is to place a material of known, high emissivity, in contact with the surface of the object. The material of known emissivity can be as complex as industrial emissivity spray which is produced specifically for this purpose or it can be as simple as standard black insulation tape, emissivity 0.97. A temperature reading can then be taken of the object with the emissivity level on the imager set to the value of the test material. This will give an accurate value of the temperature of the object.

• The temperature can then be read on a part of the object not covered with the test material. If the temperature reading is different, the emissivity level on the imager can be adjusted until the object reads the same temperature. This will give the thermographer a much more accurate emissivity reading. There are times, however, when an emissivity test is not possible due to dangerous or inaccessible conditions. In these situations the thermographer must rely on tables.

• he usual method of testing the emissivity is to place a material of known, high emissivity, in contact with the surface of the object. The material of known emissivity can be as complex as industrial emissivity spray which is produced specifically for this purpose or it can be as simple as standard black insulation tape, emissivity 0.97. A temperature reading can then be taken of the object with the emissivity level on the imager set to the value of the test material. This will give an accurate value of the temperature of the object. The temperature can then be read on a part of the object not covered with the test material. If the temperature reading is different, the emissivity level on the imager can be adjusted until the object reads the same temperature. This will give the thermographer a much more accurate emissivity reading. There are times, however, when an emissivity test is not possible due to dangerous or inaccessible conditions. In these situations the thermographer must rely on tables.

How is Thermography used?Two of the most exciting, yet overlooked, diagnostic procedures of this century are Digital Infrared Thermal Imaging (DITI) and Contact Regulation Thermography (CRT), otherwise simply termed thermography. Dr. Ali Meschi is a board- certified naturopathic physician at the forefront of this technique. "Thermography is a non-invasive, objective [and] nonradiative tool that uses [body heat] to diagnose the causes of a host of health conditions," he explains. Because it uses no radiation, it is completely safe. Utilizing high speed computers and very accurate thermal imaging cameras, body heat is processed, recorded and translated by a computer. The image map it produces can then be analyzed on screen, printed or sent via e-mail.

• During the thermography procedure 112 electrodes are placed on the patient's body to acquire temperature readings. Two different readings are taken. First, the patient sits in a fairly cool, but not uncomfortable, room for 10 minutes. Then, the first temperature readings of the face/head, teeth and neck are taken by gently touching the body part's surface with the probe. The patient is then asked to remove her clothes from the waist up to create "cold stress" at about 68 degrees Farenheit and complete the first reading of the 112 data points. Then, the patient stands in her underwear another 10 minutes. After this period, the second reading of the data points is taken and the test is concluded.

• Doctors use the image map acquired from these readings to determine if abnormal hot or cold areas are present. These hot and cold areas can relate to a number of conditions for which the FDA, Bureau of Medical Devices, has approved the thermography procedure. These include screening for breast cancer, extra-cranial vessel disease (head and neck vessels), neuro-musculo-skeletal disorders and vascular disease of the lower extremities. In the past decade, a number of advancements have brought thermal imaging to the diagnosis forefront.

• "Thermography measures the heat from one's body. Metastatic cancers create heat, which can be imaged by digital infrared imaging. This is due to the metabolic activity of the tumor tissue as compared with the temperature of tissue adjacent to the tumor and in the opposite breast. By comparing the breast in question with the normal breast, which acts as the patient's own control, abnormal heat signatures associated with the metabolism of the tumor can be easily detected."

• Cancer tumors produce a chemical which promotes the development of blood vessels supplying the area where the tumor resides. Also, normal blood vessels under the control of the sympathetic nervous system are essentially paralyzed, causing an increase in blood vessel size. The blood increase in the region simply means more heat.

• Since "thermal imaging has demonstrated in numerous studies to be capable of measuring these heat signatures years before conventional technologies can see a mass, the procedure uses no radiation, compression of breast tissue and is totally safe, thermography or DITI/CRT provides a safe early warning detection system, “Meschi adds. A monthly self exam, annual physical exam, yearly thermal imaging and mammography, when indicated, increase the effectiveness of early detection to greater than 95 percent.

Advantages of thermography

• 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 deteriorating, 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 see better in dark areas

Limitations and disadvantages of thermography

• Due to the low volume of thermal cameras, quality cameras often have a high price range (often US$6,000 or more)

• Images can be difficult to interpret accurately when based upon certain objects, specifically objects with erratic temperatures, although this problem is reduced in active thermal imaging.

• Accurate temperature measurements are hindered by differing emissivities and reflections from other surfaces.

• Most cameras have ±2% accuracy or worse and are not as accurate as contact methods.

• Only able to directly detect surface temperatures