Electrical properties of prostatic tissues: I. Single frequency admittivity properties

Abstract

Purpose: Electrical properties of the prostate may provide sufficient contrast for distinguishing malignant and benign formations in the gland. We evaluated how well these electrical properties discriminate cancer from noncancer tissues in the prostate.

Materials and methods: Electrical admittivity (conductivity and permittivity) was recorded at 31 discrete frequencies of 0.1 to 100 kHz from each of 50 ex vivo human prostates. A specifically designed admittivity probe was used to gauge these electrical properties from sectioned prostate specimens. The specific tissue area probed was marked to provide precise colocalization between tissue histological assessment and recorded admittivity spectra.

Results: Adenocarcinoma, benign prostatic hyperplasia, nonhyperplastic glandular tissue and stromal tissue were the primary tissue types probed. Mean cancer conductivity was significantly less than that of glandular and stromal tissues at all frequencies (p <0.05), while mean cancer permittivity was significantly greater than that of all benign tissues at 100 kHz (p <0.0001). ROC curves showed that permittivity at 100 kHz was optimal for discriminating cancer from all benign tissues. This parameter had 77% specificity at 70% sensitivity and an ROC AUC of 0.798.

Conclusions: The contrast in electrical admittivity properties of different prostate tissues shows promise for distinguishing cancer from benign tissues. Sensitivity and specificity exceed those reported for current prostate specific antigen screening practices at low prostate specific antigen, making this an attractive addition to the clinical armamentarium for identifying prostate cancer.

Figure 1

Individual coaxial electrode pair PCBs (A, bottom) and expanded view of electrodes (A, top) with complete tetrapolar admittivity probe assembly (B). Tissue sample is placed between 2 PCB electrodes. Voltage electrode diameter is 1 mm. Current electrode has inner and outer diameter of 2.5 and 3.5 mm, respectively. Ink drop is placed in each hole with tissue in place. After removal from probe straight pins are inserted through ink dots to define location probed. Pins remain in tissue during fixation to provide visual landmarks for pathologist to locate precise region probed (fig. 2). Modified from Halter et al. Scale represents cm (A).

Figure 2

Photomicrographs show 100% Str (A), Gl (B), BPH (C) and ACa (D) tissue types. Probed region corresponds to area between 2 visible pinholes remaining after tissue fixation and slide preparation. Note decreased Str content in more glandular tissue types, which we hypothesize largely influences tissue conductivity. Variability in gland size and configuration likely influences permittivity associated with different tissue types.

Figure 3

Mean conductivity and permittivity at 4 acquisition frequencies, including 0.1, 1, 10 and 100 kHz. Whiskers represent SE

Figure 4

AUC as function of signal frequency for conductivity (A) and permittivity (B). Note that inflection point or notch in all benign, BPH and Gl permittivity traces denotes frequency at which permittivity of cancer became greater than that of specific benign tissue (fig. 3).

Figure 5

ROC curves of conductivity (A) and permittivity (B) at optimal frequency. SN, sensitivity. SP, specificity