EXPERIENCES WITH THERMOGRAPHY IN NEUROLOGIC PATIENTS

Real-time detection of vascular occlusion and reperfusion of the brain during surgery by using infrared imaging

OBJECT

Application of sensitive infrared imaging is ideally suited to observe blood vessels and blood flow in exposed organs, including the brain. Temporary vascular occlusion is an important part of neurosurgery, but the capacity to monitor the effects of these occlusions in real time is limited. In surgical procedures that require vascular manipulation, such as those involving aneurysms, arteriovenous malformations (AVMs), or tumors, the ability to visualize blood flow in vessels and their distribution beds would be beneficial. The authors recount their experience in the use of a sensitive (0.02 degrees C), high-resolution (up to 50 microm/pixel) infrared camera with a rapid shutter speed (up to 2 msec/frame) for localizing cortical function intraoperatively. They observed high-resolution images of cerebral arteries and veins. The authors hypothesized that infrared imaging of cerebral arteries, performed using a sensitive, high-resolution camera during surgery, would permit changes in arterial flow to be be seen immediately, thus providing real-time assessment of brain perfusion in the involved vascular territory.

METHODS

Cynomolgus monkeys underwent extensive craniectomies, exposing the frontal, parietal, and temporal lobes. Temporary occlusions of the internal carotid artery and middle cerebral artery branches (30 events) were performed serially and were visualized with the aid of an infrared camera. Arteries and veins of the monkey brain were clearly visualized due to cooling of the exposed brain, which contrasted with blood within the vessels that remained at core temperature. Blood flow changes in vessels were seen immediately (< 1 second) in real time during occlusion and reopening of the vessels, regardless of the duration of the occlusion. Areas of decreased cortical blood flow rapidly cooled (-0.3 to 1.3 degrees C) and reheated in response to reperfusion. Rewarming occurred faster in arteries than in the cortex (for a 20-minute occlusion, the change in temperature per second was 2 x 10(-2) degrees C in the artery and 7 x 10(-3) degrees C in the brain). Collateral flow could be evaluated by intraoperative observations and data processing.

CONCLUSIONS

Use of high-resolution, digital infrared imaging permits real-time visualization of arterial flow. It has the potential to provide the surgeon with a means to assess collateral flow during temporary vessel occlusion and to visualize directly the flow in parent arteries or persistent filling of an aneurysm after clipping. During surgery for AVMs, the technique may provide a new way to assess arterial inflow, venous outflow, results of embolization, collateral flow, steal, and normal perfusion pressure breakthrough.

Facial thermography, basis, protocol, and clinical value

Computerized electronic telethermography provides clinicians with a reliable evaluation of subtle body surface temperature changes that show underlying physical disorders characterized by pain. The first study population involved 4000 measurements of 100 volunteers at the Medical School of New Jersey. This study of normal volunteers evaluates the validity and reliability of using 0.5 degrees C skin surface temperature difference between opposite sides of the head as a minimum difference standard for recognition of a clinically significant thermographic abnormality. A second study population of over 300 patients with clinically suspected temporomandibular disorder were used. The authors used a standard thermographic protocol procedure that is approved by the Academy of Neuromuscular Thermography. Also discussed in detail are artifactual influences and trigger point detection. The clinical value of this information in the diagnosis and treatment of temporomandibular disorder patients is self evident.

Facial thermography in the diagnosis of cerebrovascular disease and in evaluation of carotid endarterectomy

Some 60% of strokes are due to extracranial occlusive arterial lesions, most frequently at the bifurcation of the common carotid artery. Since these lesions are accessible to endarterectomy, their prestroke diagnosis is very important. Facial thermography quickly supplies reliqble information on the circulatory area in which these lesions occur, and this information can be atraumatically obtained in an out-patient setting. The success rate of facial thermography versus aortic arch angiography was 83% and 80%, respectively, in our case material, and this rate corresponds with data in the literature. In a series of 23 patients with facial thermograms and angiograms obtained before and after endarterectomy, facial thermography proved to be a useful diagnostic and prognostic aid in neurological out-patient guidance after carotid endarterectomy. By virtue of its rapidity and atraumatic character, because it can be carried out by technicians and because the findings are suitable for computer data processing, facial thermography would seem to be suitable for potential stroke screening of a high-risk asymptomatic population.

Thermistor recording of forehead skin temperature as an index of carotid artery disease

Skin temperatures were recorded from the medial upper orbital area and above the nasal, mid and lateral portions of the brows in normal subjects and in patients with suspected cerebrovascular disease. Temperatures were reduced across the brow in patients with external carotid artery disease. Temperatures were lower than normal in the orbit in patients with internal carotid artery disease except when the internal carotid circulation was severely compromised. In such patients the supraorbital temperature was higher than normal, suggesting significant reversed flow via the supraorbital artery. With internal carotid occlusion, lateral brow temperatures suggested increases in external carotid flow. The interpretation of results was more reliable when temperatures were compared to normal values than when they were judged as differences between the two sides as is done in thermography.

Diagnostic thermography

Under standard and normalized environmental conditions, the thermal contrasts or patterns that exist on the exposed human skin are determined largely by the heat conducted to the skin locally from underlying organs, or variations in blood flow. These localized temperatures give rise to corresponding variations in the rates at which ir energy is radiated. Instruments are available that are capable of translating these differences in rates to photographic images or thermograms. In the absence of disease or pathology, there exists a normal thermal signature for each human. The presence of pathology grossly alters the thermogram and gives rise to a valuable diagnostic procedure-to a unique method of nondestructive testing or remote sensing.