CT analysis of the use of the electrical impedance technique to estimate local oedema in the extremities in patients with lymphatic obstruction

The aim of the study is to establish the validity of the use of the electrical impedance technique for estimating local oedema in extremities through comparison with computed-tomography (CT) analysis. Eight healthy women (group 1) and nine women with unilateral leg oedema following chronic lymphatic obstruction (group 2) are examined sequentially utilising both methods. ‘Equivalent resistivities’ of extra- and intracellular fluid (RE and RI) are measured in the leg's upper portion with a multi-frequency impedance meter, and seven CT slices are taken in the same leg segments. In each slice, the ratios of interstitial fluid to subcutaneous tissue and to muscle are calculated using the CT number of plasma for interstitial fluid, and CT numbers of subcutaneous tissue and muscle of group 1 for ‘normal’ tissues. A decrease in RE and an increase in RI/RE, indicating extracellular fluid increase, are observed in oedematous legs in group 2 when compared with the left legs in group 1. Correspondingly, an increase in the ratios of interstitial fluid to subcutaneous tissue area and to total cross-sectional area is observed in the oedematous legs when compared with those of normal legs in CT analysis. Thus the multi-frequency impedance technique is effective in detecting local oedema in extremities.