THE USE OF POWER DOPPLER ULTRASOUND IN THE DIAGNOSIS OF ISOLATED DEEPVENOUS THROMBOSIS OF THE CALF

While ultrasound has been well accepted as an accurate test for the di agnosis of both femoral and popliteal deep venous thrombosis (DVT), it s role in the detection of calf DVT has been less clear. There have be en variable results between studies in the accuracy of colour Doppler or compression sonographic techniques in demonstrating calf DVT. Many of these studies have suffered from high rates of technically inadequa te examinations. Power Doppler (colour Doppler energy) has a higher se nsitivity than conventional colour Doppler. It should therefore allow the detection of slow venous flow in patent vessels, that may not be d emonstrated by conventional colour Doppler. This should decrease the n umber of technically inadequate examinations as well as decreasing the false-positive rate of the test. A prospective blinded reader study w as undertaken comparing power Doppler to the gold standard venography, in the diagnosis of isolated calf deep venous thrombosis (DVT). Both examinations were successfully performed in 50 patients, in whom proxi mal DVT had been excluded by compression ultrasonography. Fifteen pati ents had positive evidence of an isolated calf DVT on the gold standar d technique, venography. Power Doppler demonstrated a sensitivity of 1 00%, a specificity of 79%, a positive predictive value of 71% and a ne gative predictive value of 100%, in detecting an isolated calf DVT. Th ere were no technically inadequate ultrasound examinations. Where veno us flow is demonstrated, power Doppler is a highly accurate test in ex cluding a calf DVT. The specificity of the test, however, is limited, as the absence of flow does not always signify a DVT.