An electromagnetic method for cancer detection

The availability of intraoperative detection techniques to surgeons performing curative resection of cancer has been shown to improve survival rates and patient outcomes. This work explores a technique for cancer detection with potential for intraoperative use which takes advantage of differences in the electromagnetic (EM) properties between cancerous and healthy tissue. Using time-varying EM fields, electrical eddy currents are generated in tissue samples and other conducting materials, and investigated using phase-sensitive detection. This work is among the first to utilize an EM method involving a phase sensitive scheme for detection of cancer.;A prototype EM probe consisting of a pair of coils is designed to detect changes in inductive coupling due to eddy currents when different materials are brought into the probe's vicinity. Experiments on colon cancer-bearing xenograft mice and human tissue excised during cancer surgeries demonstrate the probe's consistent ability to differentiate between healthy and cancerous tissue. Experiments on animal tissue show that both the conductivity and the internal structure of the specimen significantly affect the probe's response.;The probe's response to eddy current configurations that are fixed and well known are studied by performing experiments on individual wire loops, thus forcing the eddy currents to travel in well-defined paths. These experiments, along with an analytical model of the probe's response, help elucidate the interaction between the probe and biological samples. The analytical model uses an equivalent circuit of the probe interacting with a single wire loop under sinusoidal excitation. The self and mutual inductances of the circuit elements---driver coil, receiver coil, and loop---are calculated numerically from first principles. The numerical calculations are validated against published solutions of relevant problems. Once validated, the circuit element model is compared with experimental data for the wire loops. Good agreement is obtained between the data from the wire loop experiments and the analytical model for sinusoidal driver voltages.;The experiments on animal tissue, the supporting experiments on wire loops and the analytical model together provide insight into what governs the probe's behavior. In particular, both the electrical conductivity and internal structure of the specimen affect the paths of the eddy currents and emerge as critical quantities. This work shows that at the levels of conductivity present in tissue, an increase in sigma will lead to an increase in probe sensitivity relative to its null value. It is found that the probe is most sensitive to eddy current domains that are close to the size of the probe itself (i.e. on the order of several millimeters), and in a plane parallel to its face. Measurements on the tissue specimens show that the greatest sensitivity is obtained for sawtooth excitation. A significant conclusion of this work is that information contained in the phase shift of the induced voltage in the receiver coil relative to the voltage across the driver coil is substantially less ambiguous in detecting differences in tissue properties. This approach holds great promise for use in intraoperative detection of cancer, and its selectivity may be further enhanced when used in conjunction with monoclonal antibodies. The method may also be readily extended to imaging of surgically excised tissue and real-time tissue analysis in the operating room.