Multivariate analysis of the adjustment of the colour duplex unit for the differential diagnosis of lymph node alterations.

Intranodal angioarchitecture was used as criterion for the differential diagnosis of lymph node alterations by colour duplex sonography. The influence of the adjustment of the duplex unit on the diagnostic accuracy and on the rate of lymph nodes with detectable intranodal flow signals was tested. A total of 243 superficial lymph nodes in 127 patients were included in a retrospective study. Diagnoses were approved by histopathology (n = 173) or clinical follow-ups (n = 70 reactive lymph nodes). The intranodal angioarchitecture and sonomorphology were assessed. We used nonparametric discriminant analysis in order to define appropriate settings for transducer frequency, flow mode, power and threshold which result in the best diagnostic quality. Of the lymph nodes, 87 % displayed flow signals using a threshold of >/= 13 and the flow modes low or medium. Vascularisation was detected only in 47 % of the nodes assessed with different adjustments. Diagnostic accuracy dropped from 94 to 68-84 % if threshold was < 13 or power was less than -11 dB. An insufficient adjustment of the colour duplex unit decreases the chance of detecting intranodal flow signals and impairs the diagnostic quality of colour duplex sonography. Flow mode, power and threshold are the most important parameters which have to be adjusted properly.