Determining the stage of organisation and natural history of venous thrombosis using computer analysis

In vitro studies have shown that as the organisation of a thrombus progresses its ultrasound appearance becomes more echogenic. When diagnosing a deep vein thrombosis (DVT) using duplex ultrasound, an estimation of the degree of organisation of the thrombus is made by assessing its echogenicity. This method is purely subjective and has many pitfalls.

A study was performed on 100 proximal DVTs from 89 patients diagnosed by duplex ultrasound. These images were transferred to a computer and standardised using, the adobe Photoshop. The thrombus in the image frame was outlined and the grey scale median (GSM) calculated. The grey scale median which is a measure of the echogenicity of the thrombus (indicating the degree of organisation), varied considerably from patient to patient.

The results show that the level of organisation of a thrombus on initial diagnosis is unrelated to the clinical signs or duration of symptoms of the patient. This has further implications when considering a therapy regimen based on the duration of symptoms (e.g. thrombolysis). Additionally, the age of the patient, predisposing factors and bulk of the thrombus appear to be unrelated to the value of the grey scale median at the initial visit. The initial grey scale median values were then compared to those at a one week's follow-up examination. Those with a low initial value of the grey scale median were found to increase, indicating further organisation, as expected. However, patients with higher initial grey scale median values were found to fluctuate, some increasing and some decreasing. The increase the grey scale median was due to a more homogenous appearance across the thrombus as the organisation process became more established. A decrease in grey scale median indicated areas of lysis occurring within the thrombus.

Measuring the value of the grey scale median is a quantitative way of assessing the degree of organisation of a deep vein thrombosis. This can be used to asses the suitability of patients for various treatment regimen. It is also a useful means of assessing the long-term implications of different therapies and could aid in determining the long-term outcome for the patient.