Local tissue water assessed by tissue dielectric constant: anatomical site and depth dependence in women prior to breast cancer treatment-related surgery.

Assessing local tissue water using tissue dielectric constant (TDC) values is useful to evaluate oedema/lymphoedema features and their change. Knowledge of anatomical site and tissue depth dependence of TDC values could extend this method's utility. Our goal was to compare TDC values obtained at anatomically paired sites and to investigate their depth dependence. In 22 women (12 awaiting surgery for breast cancer and 10 cancer-free control subjects), four sites (mid-forearm, mid-biceps, axilla and lateral thorax) on both body sides were measured with a 2.5-mm sampling depth probe. Also, at forearm, four different probes with sampling depths of 0.5, 1.5, 2.5 and 5 mm were used. TDC values range between 1 for zero water to 78.5 for 100% water. Site comparisons showed TDC values (mean+/-SD) to be largest at axilla (36.4+/-8.9), least at biceps (21.6+/-3.5) and not different between forearm and thorax (24.3+/-4.0 versus 24.8+/-5.0). Group comparisons showed slightly greater values in patients at forearm and biceps (P<0.05) but no group difference at other sites. Dominant-non-dominant side comparisons showed no significant difference in paired-TDC values in either group at any site. Forearm TDC values decreased with increasing depth from 36.4+/-4.8 at 0.5 mm to a minimum of 21.4+/-3.9 at 5.0 mm, with a sharp decline between 1.5 and 2.5 mm. The composite findings suggest that TDC measurements have the necessary features for usefully assessing oedema/lymphoedema and its change on limbs and at body sites not routinely amenable to assessment by other techniques. The depth dependence feature provides additional flexibility to investigate oedematous or lymphoedematous conditions.