Selected Abstracts from Published Medical Literature
Deep Vein Thrombosis

Thermography and DVT

The Thrombo-embolic Risk in Surgery. Hoffmann R. Department of Surgery, University Hospital, Zurich, Switzerland. Hepato-Gastroentrol (1991) 38, 272-278.

Thermography and plethysmography, a non-invasive alternative to venography in the diagnosis of deep vein thrombosis. Holmgren K, Jacobsson H, Johnsson H, Lofsjogard-Nilsson E. From the Department of Internal Medicine, the Department of Clinical Physiology and the Department of Diagnostic Radiology, Karolinska Hospital, Stockholm, Sweden. Journal of Internal Medicine (1990) 228, 29-33.

The combination of liquid crystal thermography and duplex scanning in the diagnosis of deep vein thrombosis. Kalodiki E, Marston R, Volteas N, Leon M, Labropoulos C, Fisher C, Christopoulos D, Touquet R, Nicolaides A. From Irvine Laboratory, Academic Surgical Unit and Department of Accidents and Emergency, St Mary's Hospital Medical School, London, U.K. European Journal of Vascular Surgery (1992) 6, 311-316.

Liquid crystal thermography as a screening test for deep vein thrombosis in patients with cerebral infarction. Cameron E, Sachdev D, Gishen P, Martin J. Departments of Medicine and Radiology, King's College School of Medicine and Dentistry, London and Romford Hospital, Essex, U.K. European Journal of Clinical Investigation (1991) 21, 548-550.

Thermal Imaging in the Investigation of Deep Venous Thrombosis. Harding R. St Woolos Hospital, Newport, U.K. EMBC95 paper

The Thrombo-embolic Risk in Surgery. 

Postoperative deep-vein thrombosis can lead to fatal pulmonary embolism on one side, and the development of a disabling postthrombotic syndrome, which can occur after some time. General thrombo-embolic prophylaxis can reduce the risk of postoperative thrombo-embolic complications. Predisposing factors include age, obesity, immobilization and recumbency. Cardiovascular diseases, malignant neoplasms, venous disorders, diseases associated with increased viscosity of blood, past deep-vein thrombosis and pulmonary embolisms, some infectious diseases with raised fibrinogen levels, and inherited or acquired clotting factor deficiency syndromes (antithrombin Ill, protein C. protein S) have an elevated risk of thrombosis. The surgery itself, when taking more than 20 minutes and performed under general anesthesia, is a major risk factor, as proven initiation of thrombosis is often on the operation table. Patients receiving regional or local anesthesia have a clearly reduced risk of thrombosis. After general surgery without thrombosis prophylaxis, a deep-vein thrombosis can be demonstrated by the fibrinogen uptake test in about 30 % of all patients over the age of 40. After abdominal surgery an incidence of thrombosis of 14-33 %, and after hip surgery an incidence of nearly 50 %, have been established by means of the fibrinogen uptake test. However only 10 % of these thromboses are expressed clinically. We therefore recommend Liquid Crystal Contact Thermography, which has a sensitivity of 94 % and a specificity of over 80 %, as a non-invasive, easily performed screening method in the diagnosis of deep-vein thrombosis.

Thermography and plethysmography, a non-invasive alternative to venography in the diagnosis of deep vein thrombosis.

One plethysmographic and two thermographic methods were evaluated against venography in 102 patients with suspected deep vein thrombosis (DVT). Seventy-one patients had venographically verified DVT, which in 21 cases was restricted to the calf. Plethysmography (PG) gave a sensitivity and specificity of 63 % and 94 %, respectively. The former was influenced by a limited sensitivity of 14 % in the sub-group with distal DVT. The sensitivity and specificity of temperature profiles (TP) were 87 % and 39 %, respectively, while the corresponding values for thermo-camera (TC) were 83 % and 55 %, respectively. Using a combined diagnostic approach of PG and TP, additional evaluation of posterior and lateral profiles and pattern recognition, 96 % sensitivity and 81 % specificity were reached. The combination of PG and TP will be an essential diagnostic complement when venography is not possible or inconclusive, as well as having a role in diagnostic screening in a large number of patients.

The combination of liquid crystal thermography and duplex scanning in the diagnosis of deep vein thrombosis.

One hundred patients with clinically suspected deep vein thrombosis (DVT) were studied by liquid crystal thermography (LCT), duplex scanning and venography. Liquid crystal thermography was found to have a negative predictive value of 97 % if performed within 1 week of the onset of symptoms. Duplex scanning had a sensitivity of 93 % and specificity of 91 % for all thrombi (proximal and calf). On the basis of these results a plan of investigation has been formulated that would avoid duplex scanning and venography in 39 of the 100 patients. Duplex scanning alone would be appropriate in 56 of the remaining 61 patients. Only six patients would be unsuitable for duplex scanning because of a very tense tender leg and require venography. The plan would miss one calf thrombus and result in treating three patients unnecessarily. This policy would be not only effective but also cost-effective.

Liquid crystal thermography as a screening test for deep vein thrombosis in patients with cerebral infarction.

Pulmonary embolism secondary to deep vein thrombosis is a frequent cause of death in stroke patients. In a multicentre study of deep vein thrombosis prophylaxis, 112 patients with cerebral infarction and leg paresis were given aspirin 300 mg three times a day (t.d.s.) alone or with dipyridamole 100 mg t.d.s. To screen for deep vein thrombosis liquid crystal thermography of the legs was performed daily for 15 days on all patients. Those patients with positive thermography underwent immediate X-ray venography of the appropriate limb as the definitive investigation for venous thrombosis.

Twenty-two patients had positive thermograms, of whom 16 had confirmed deep vein thrombosis as demonstrated by X-ray venography. Only 8 of the 22 had clinical signs of deep vein thrombosis and 2 of those had a negative venogram. Of the 14 patients with positive thermography but negative clinical signs 10 had positive venograms. Difference in the incidence of deep vein thrombosis in the two treatment groups was not demonstrated.

It is concluded that occult deep venous thrombosis is common after ischaemic stroke and it can occur without clinical signs. Liquid crystal thermography is a simple rapid and cheap screening test that will allow the detection of clinically unrecognized thrombosis.

Thermal Imaging in the Investigation of Deep Venous Thrombosis.

Preliminary assessment of clinically suspected deep venous thrombosis (DVT) of the lower limb by thermography avoids the need for over one third of venograms or duplex Doppler ultrasound scans. Clinical diagnosis of DVT is notoriously unreliable - hence the need for an accurate means of clinical investigation. Untreated DVT is dangerous as it can progress to pulmonary embolism (PE) which is frequently fatal or life-threatening. Treatment of DVT by anticoagulation poses risks of its own however, and should not be undertaken without a confirmed diagnosis. Thermal imaging is quick, simple, non- invasive, risk-free, cost-effective and highly sensitive in the initial investigation of suspected DVT; a negative thermogram excludes DVT and avoids the necessity for further investigation. Thermal imaging is, however, non-specific; a positive thermogram has a number of possible causes and is an indication for further assessment by venography or Doppler ultrasound to confirm or exclude DVT. Thermography should be considered the initial investigation of choice in clinically suspected DVT, proceeding to venography or Doppler ultrasound only when thermography is positive.


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