Suitability of single tissue dielectric constant measurements to assess local tissue water in normal and lymphedematous skin

Previous reports described the use of average tissue dielectric constant (TDC) measurements to assess local tissue water and its change. Our goal was to determine if a single TDC measurement could be used in place of the average of multiple measurements. The comparison criteria used to test this was the extent to which single and averaged measurements yielded similar TDC values in both normal and lymphedematous tissue. Measurements were made in two groups of women; a control group (n = 20) and a group with unilateral arm lymphedema (n = 10). In the control group, TDC was measured to multiple depths (0.5-5.0 mm) on both ventral forearms and to a depth of 2.5 mm on the lateral thorax on both body sides. In the lymphedematous group, TDC was measured on both ventral forearms to a depth of 2.5 mm. Results showed that the 95% confidence interval for differences between single and averaged TDC values was less than +/-1 TDC unit and that the limits of agreement between methods was less than +/-2.5 TDC units (+/-6.5%) for each condition, site and depth measured. This finding suggests that where this level of agreement is acceptable suitable clinical assessments can be made using a single TDC measurement.