Imaging Tool Detects Cancer Based on Electrical Abnormalities
Capacitance-based imaging technique spots small tumors and distinguishes cancer from inflammation.
A new imaging technique that measures the electrical properties of tissue could help diagnose cancer and monitor treatment responses, according to a recent study. The so-called dielectric imaging technique measures capacitance—the ability to store electric charge—using pin-type electrode arrays. As reported Oct. 13 in the journal Scientific Reports, the authors demonstrated that their method could detect small tumors, monitor the effects of an anti-cancer drug in real time, and distinguish cancer from inflammation in mice. However, the current setup is limited to the surface of the skin, so further research is needed to test if the technology can be adapted to image deep tumors.
“The study is important because it provides a noninvasive way to easily identify cancerous cells and distinguish cancerous cells from inflamed cells,” said Mark Golkowski, an associate professor of electrical engineering at the University of Colorado Denver, who was not involved in the study and whose research interests include medical applications of electromagnetic waves in the human body. “The broad implications are for easier and cheaper cancer diagnosis. This can help bring costs down and increase the success of early treatment.”
Currently, an imaging technique known as positron emission tomography (PET) is widely used in cancer diagnosis and therapeutic monitoring. However, PET can produce false positives because it does not easily distinguish cancer from inflammation, so it is often combined with diagnostic images generated by other techniques such as magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound, which can be expensive. Meanwhile, a noninvasive medical imaging technique called electrical impedance tomography (EIT), which uses body surface electrodes to stimulate the tissue and measure its response, can create conductivity images of the interior of the body that can be used for a wide spectrum of applications, including screening for breast cancer. But the resolution of EIT is poor compared to other imaging techniques such as CT and MRI.
To overcome these limitations, senior study author Kyung-Hwa Yoo of Yonsei University in South Korea and her collaborators set out to develop an electrical imaging technique to detect cancer cells that is simpler and more direct. Compared to healthy tissues, cancer tissues show a substantially increased capacitance for a variety of reasons, including higher cell density caused by cell proliferation. Capacitance is also affected by the altered metabolic activity, and higher water content and sodium concentration, of cancer cells compared to normal cells.
To measure capacitance, the researchers constructed a probe array of 10 × 10 pin-type electrodes 1.5 mm in length and placed 0.5 mm apart on a flexible plastic structure. When they placed the probe on the skin of tumor-bearing mice, the dielectric imaging technique detected small tumors just beneath the surface with a diameter of less than 3 mm. Moreover, the method tracked the reduction in cancer tissue volume following treatment with a chemotherapy drug called doxorubicin. Additional studies in mice showed that, unlike PET, dielectric imaging distinguished cancer from inflammation caused by bacterial infection.
“A simple measurement directly on the skin can identify the presence, shape and size of cancerous tissue,” Golkowski said. By contrast, previous methods that measured electrical properties to detect cancerous cells were indirect and complicated, and therefore had poor resolution, he explained. For example, to reconstruct EIT images from surface bioimpedance measurements, complicated nonlinear inverse problems have to be solved, a challenge the capacitance-based imaging eliminated. “The method in the current study is direct because a large number of small electrodes come into direct contact with the cells being diagnosed,” Golkowski said.
According to Jonathan Newell, a professor emeritus of biomedical engineering at the Rensselaer Polytechnic Institute in Troy, New York, the study was well designed and technically sound. “The weakness is that it’s basic work that will need a lot of additional development to be brought to have practical utility,” he said.
Another limitation is that the current setup can only be used on the surface of the skin, Golkowski explained. The authors acknowledge in the paper that the dielectric imaging system would need to be further developed and combined with instruments like endoscopes to diagnose a mass deep inside the body, such as in the throat or gastrointestinal tract.