Thermal imaging (thermography)

In 1960, military engineer R. Lawson tested a secret device for that time night vision device and accidentally sent the receiving lens of the device to the lady sitting opposite him with an open neckline. A thermogram of the breast appeared on the screen of the device. This phenomenon interested the major. Having understood the prospects of this direction, he left the service and already in 1961 together with R. Barnes developed and successfully applied the first installation for medical thermography in practice.

Indications for conduction

The most applicable areas of diagnostic use of thermal imaging are as follows.

• Recognition of premalignant and neoplastic lesions of pectorals, thyroid glands, orbits and certain skin diseases.
• Diagnosis of joint diseases.
• Identification of the initial and / or advanced stages of stenotic / occlusive lesions of the carotid, subclavian, femoral and popliteal arteries.
• Diagnosis of venous dyskirculation in the extremities and scrotum.

As can be seen from this list, the "neurological aspect" of studies is represented only by the identification of carotid insufficiency. In no way minimizing the significance of revealing stenotic / occlusive lesions of carotid arteries, as is well known, often proceeding without manifestations or malosymptomatically, we consider ourselves entitled to significantly expand the range of thermographic studies in neurology.

It is known that the classics of neurology were considered an indispensable condition for examining the patient in a nude, so as not to miss any of the hypotrophy, dysraphia, etc.

Just as the basis for a neurological examination is the definition of various asymmetries from the cranial nerves, motor and / or sensitive sphere, the detection of anisothermia of different parts of the patient's body is the essence of thermography. 

If we take into account that thermography is an extremely high-sensitivity method (measuring accuracy up to 0.01 ° C) with relatively lower specificity, the analysis of thermograms becomes a creative process, requiring an indispensable clinical analysis of the situation in each specific case.

For example, the anisothermy of the orbital region can be caused by completely different processes - from plugging of the carotid artery to the tumor of the upper glandular gap, from the lagophthalmus to the cluster migraine. Given the simplicity, short-term, safety, painlessness and accessibility of thermal imaging, the diagnosticians consider this technique to be ideal for mass non-random examinations of the population for detection of early stages of oncological, vascular, inflammatory diseases of the thoracic, thyroid gland, kidneys, joints, scrotum, limbs.

At the same time, highly sensitive corporal thermography would be indispensable for rapid orientation selection of patients: with anisothermia of the head, these are the most likely patients of a neurologist, neurosurgeon, ophthalmologist or otolaryngologist, with temperature asymmetry of the neck or breast glands, patients are referred to an endocrinologist or an oncologist, faces with anisothermia of the limbs are probable patients with angiologists.

Method of conducting

Thermography - registration of invisible infrared radiation. The maximum of the radiation is 9.5 μm. According to the Stefan-Boltzmann law, the amount of radiated energy is proportional to the fourth power of the absolute temperature: W = T ⁴.

Infrared radiation of the skin does not depend on race, pigmentation and other individual characteristics. The temperature of the body surface depends on 3 main factors: the features of vascularization, the level of metabolic processes and the differences in thermal conductivity.

To date, 3 modifications of the infrared radiation detection are used.

• Thermography captures the thermogenesis of the most superficial layers of the skin (0.5-1.5 mm).
• Infrared radiometry in the centimeter and decimeter range (wavelength 17 cm with a frequency band of 1.5-2.0 kHz) makes it possible to obtain information about the deep structures of the body.
• The film thermography with the use of contact liquid crystal strips detects the thermal radiation of the outer layers of the skin with a thickness of 0.3-0.8 mm.

There are basic types of thermal imaging devices.

• Thermographs that use liquid nitrogen to cool the temperature sensitive sensor. These devices allow you to obtain a distant picture of the infrared luminescence of the investigated part of the human body. They are good for examining planned patients in a hospital and / or polyclinic, but are of little use for use in urgent medicine, especially at the patient's bedside. A significant limitation is the need for a constant presence of a sufficiently scarcely volatile liquid nitrogen.
• Thermographs not requiring the use of liquid nitrogen. Such devices give a non-contact map of infrared activity map of the investigated spectrum. Especially convenient are portable thermographs - universal devices for emergency medicine: examination at home, in the ambulance, in the ward, in the hospital, in the clinic, in the intensive care unit, in the operating room. These devices are portable, highly sensitive, fairly easy to maintain. The sensitivity of these systems is quite high and reaches hundredths of a degree.
• Contact thermography based on liquid crystal films. There are domestic and foreign analogs. Advantages - less cost of research, no need to use liquid nitrogen. Disadvantages - laboriousness, the ability to use only on a flat surface, the need for a dense uniform contact with the dry surface of the skin, the complexity of use in urgent medicine. This modification of thermal imaging has a lower sensitivity - about 0.5 ° C.
• Infrared radiometry, or thermotomography. The thermograph of this type has a special antenna recording ultra-high frequency bands, which allows to measure the temperature of the body structures up to 17 cm to an accuracy of 0.1 ° C. Unfortunately, this device is very sensitive to interference, therefore the results become reliable only when working in a special screened camera.

Evaluation of results

Normally, the distribution of the temperature activity of identical parts of the body in humans is strictly uniform. Therefore, the essence of medical thermography is, in principle, reduced to identifying, localizing and determining the degree of thermal asymmetries and their clinical evaluation. In healthy people, the features of symmetrical heat distribution are noted. So, the orbital region, face covers, lips, neck are usually warmer (look like light areas) than the nose, upper forehead, outer segments of the face (dark areas).

In parallel, the most typical and constant temperature gradients of the thermograms of the head and extremities are taken into account.

• Horizontal orbital gradient. Normally, with uniform infrared illumination of the orbits, the temperature of the inner corner of the eye is 0.3-0.7 ° higher than the outer one.
• Longitudinal gradient of the upper extremities. The shoulder is usually 0.5-0.7 ° "hotter" than the rear of the hand.
• Longitudinal thermal gradient of the lower extremities. In most healthy people, the temperature of the thigh is 0.6-1.1 ° above the foot temperature.

These gradients are relative. If the orbital is the most constant, then the "finite" anisothermies are variable. This especially applies to the hands - the main "heat exchanger" of the body. The thermogenesis of brushes is most susceptible to fluctuations due to innervation, psychoemotional, medicinal and cold effects.

A number of pathological conditions causing changes in the infrared activity of different parts of the patient's body.

Blockage of the internal carotid artery or stenosis of more than 70%, as it were, is accompanied by hypothermia of the orbit on the occlusion side with a thermal gradient of 1.5-2.7 °. During carotid endarterectomy, there is a direct relationship between the "luminosity" of the orbit and the supraorbital region (the zone of vascularization of the angular and supra-lateral arteries) and the degree of narrowing of the lumen of the carotid artery. When the lumen of the internal carotid artery narrowed, more than 60% noted a decrease in the infrared radiation of the orbital region homolateral to stenosis.

E. Wood, with the combined use of thermography and angiography, showed that when the collateral for the occluded internal carotid artery is the homolateral external carotid artery, its short-term clamping further enhances the "cooling" of the orbit on the side of the affected artery.

Cluster headache during examination in the period of exacerbation gives a marked increase to 1.5-2.0 ° luminescence on the side of the "clusters of pain."

On the contrary, a rare but extremely curious pathogenetically cold migraine (ace cream headache), arising from the proven spasm of the internal carotid syphon, gives a pronounced transient hypothermia of the orbit on the side of the pain.

Temporal arteritis, as a rule, is accompanied by the identification of "tight" hyperthermia in the projection of the superficial temporal artery.

Persistent pronounced hypothermia such as the Harlequin mask is characteristic of the syndrome of Barraker-Simons.

Characteristic changes in the thermogram of the head in venous cerebral dyscirculation - pulsating exophthalmos, the syndrome of Tholos-Hunt and the Melkersson-Rosenthal syndrome. In the latter case, hyperemia of the lips and tongue with exacerbation of edematous syndrome gives a clear hyperthermia, leveling with pathogenetic therapy.

The most common forms of facial lesions are prozopoparez and trigeminal neuralgia. They emit indefinite thermographic signs - from pronounced local hyperthermia in the superciliary with exacerbation of the neuralgia of the first branch of the trigeminal nerve to relative hypothermia on the side of the pains of the second and third branches. Prozoparaze for the most part does not lead to significant anisothermia of the face.

In patients with exacerbation of the vertebral artery syndrome, the areas of hyperthermia in the paravertebral zone C ₄ -C ₅ on the side of the pain syndrome are most often noted .

When studying the thermograms of extremities in patients with acute impairment of cerebral circulation, we first noticed pronounced early hypothermia in the left extremities in patients with right hemispheric hemorrhages. On the one hand, this phenomenon allows the probable localization of the hematoma in case of a deep coma, on the other hand - confirms the well-known thesis about the functional asymmetry of the hemispheres with the predominance of the centers of vegetative regulation in the right hemisphere.

In the part of observations of patients with the posterior form of syringomyelia, we first recorded an anisothermia of the torso as a semi-jacket, confirming the segmental-dissociated sensitivity disorder in this disease.

The most striking changes in thermograms were noted with metastatic lesions.

Reynaud's syndrome produces marked asymmetric changes on the thermograms of the hands, especially after a sample with cooling, when instead of quickly warming the hands after a 10-minute immersion in cold water, the fingers do not warm up as normal (due to the rapid opening of arteriovenous shunts), and long remain hypothermic .

For most patients with vibration disease, in contrast to Raynaud's syndrome, symmetrical hypothermia of the hands is more characteristic, up to a "thermal amputation" during exacerbation.

As already mentioned, the thermogenesis of the brushes is dynamic. In this connection, the most important aspect of thermal imaging of brushes is the possibility of using dynamic thermography and ultrasound in antinicotin propagation.

Hot feet are typical for patients with erythromelalgia. Very informative thermography with the dynamic observation of patients with angiopathies of the distal parts of the lower extremities of different genesis, it demonstrates the effectiveness or inadequacy of drug and / or drug treatment.

The next two aspects of thermal imaging are important not only for urgent neurology, but also for emergency medicine. First, we are talking about the possibility of non-invasive diagnosis of subclinical stages of iatrogenic thrombophlebitis. With dynamic thermal imaging and ultrasonic duplex monitoring of the catheterized vein, post-injection phlebitis appeared on the 2nd day of continuous catheterization in 50% of patients. Areas of hyperthermia along the catheterized vein, recorded on the thermogram, along with a violation of venous outflow from ultrasound duplex, reflect the development of iatrogenic phlebitis. Timely treatment allows to prevent the further development of phlebotrombosis, and repeated thermal imaging control - to evaluate the effectiveness of preventive treatment.

No less important is dynamic thermal imaging and ultrasound observation of venous circulation in the lower extremities in patients with hemiplegia. Studies supplemented by ultrasound dopplerotrophy, duplex study and coagulation tests showed that 60% of patients with hemiplegia develop prethrombotic conditions already on the 2nd-3rd day of stroke, and 6 times more often in the paralyzed lower limb. This is understandable, because in neurological patients, the clinical recognition of phlebopathies is difficult due to disorders of sensitivity and motor sphere. Moreover, this is often combined with speech impairment. Because of this, unlike patients in the therapeutic and surgical departments, neurological patients generally do not present alarming complaints of swelling, pain and similar feelings. Therefore, if dynamic thermography and ultrasound methods reveal even initial signs of venous outflow disturbance, urgent preventive treatment is needed to prevent the development of such a formidable complication of urgent medicine as pulmonary embolism.

Studies of recent years have convincingly shown that if the death of a person as an individual, but not of an organism, is inextricably linked with brain death, then cerebral death is fully associated with the cessation of intracerebral blood flow and the registration of the so-called stop phenomenon, which until now was established only with the help of contrast cerebral angiography. Obviously, such an unsafe and difficult procedure for seriously ill patients is unacceptable.

Non-invasive ultrasonic methods and thermography are obviously more ethical, accessible and informative.

[1], [2], [3]