An Electrical Impedance Tomography Based Probe for Intraoperative Surgical Margin Assessment

Prostate cancer has the highest incidence rate of cancer in men. Those with localized
tumors may undergo a radical prostatectomy. Positive surgical margins (cancer at
the edges of resected tissue) are associated with an increased risk of biochemical
recurrence and disease progression. This project aims to help create an efficient
surgical margin assessment probe compatible with robot-assisted laparoscopic surgery
that utilizes bioimpedance to identify positive surgical margins while the patient is
still in surgery.

Electrical impedance tomography creates an image based on the passive electrical
properties of the tissue. Previous research has indicated that benign and cancerous
prostatic tissue have sufficiently different electrical properties to be distinguished. A
probe compatible with surgical robots was developed, but concerns of the potential
for infection, noise from long cables, and a relatively lengthy data acquisition time
have led to a redesign.

The electrode array for a new probe design is presented here. The new probe
has dedicated voltage measurement and current source/sink electrodes and fewer
current drive patterns than the previous probe design. Simulations using ex vivo
data were examined to modify the electrode array design (4 current drive electrodes
was determined to be insufficient to localize inclusions, so the design was modified
to include 8). Simulations were also used to provide expected data for clinically
relevant scenarios to aid in hardware design and understand the expected utility of the device in a surgical setting.

These simulations indicate an ability to localize a 1
mm diameter cancerous inclusion against benign prostatic tissue (the most difficult
clinically relevant tissue contrast). Initial bench top experiments with the electrode
array are also encouraging, demonstrating an ability to localize a 2.38 mm diameter
aluminum rod in saline close to the electrode array surface.