Researchers have found an innovative way to use sound and light, or photoacoustic, imaging to diagnose ovarian tumors. The method may lead to a promising new diagnostic imaging technique to improve current standard of care for patients with ovarian cancer.
Ovarian cancer claims the lives of more than 14,000 women in the US each year, ranking fifth among cancer deaths in women.
Researchers recently conducted a pilot study using co-registered photoacoustic tomography with ultrasound to evaluate ovarian tumors in 16 patients. The findings appear in Radiology.
“When ovarian cancer is detected at an early, localized stage—stage 1 or 2—the five-year survival rate after surgery and chemotherapy is 70 to 90 percent, compared with 20 percent or less when it is diagnosed at later stages, 3 or 4,” says Quing Zhu, professor of biomedical engineering in the School of Engineering & Applied Science at Washington University in St. Louis and of radiology.
“Clearly, early detection is critical, yet due the lack of effective screening tools only 20-25 percent of ovarian cancers are diagnosed early. If detected in later stages, the survival rate is very low,” Zhu says.
In their approach, researchers use a transvaginal ultrasound to obtain information about ovarian tumors, but ultrasound lacks accuracy in diagnosis of ovarian masses, Zhu says.
Photoacoustic tomography, however, gives researchers a very detailed look at the tumor’s vasculature, or tumor angiogenesis, and blood oxygen saturation (sO2) by lighting up the tumor’s vasculature bed and allowing for more accurate diagnoses of ovarian masses seen by ultrasound.
Both tumor angiogenesis and tumor sO2 are related to tumor growth, metabolism, and therapeutic response.
For the study, Zhu and her team created a sheath with optical fibers that wrap around a standard transvaginal ultrasound probe. The optical fibers are connected to a laser. Once the probe is inside the patient, Zhu turns the laser on, which shines through the vaginal muscle wall.
With photoacoustic tomography, the light from the laser propagates, the tumor absorbs it, and it generates sound waves, revealing information about the tumor angiogenesis and sO2 inside the ultrasound-visible ovaries. A normal ovary contains a lot of collagen, Zhu says, but an ovary with invasive cancers has extensive blood vessels and lower sO2.
Information and assurance
The team used two biomarkers to characterize the ovaries: relative total hemoglobin concentration (rHbT), which is directly related to tumor angiogenesis, and mean oxygen saturation (sO2).
They found that the rHbT was 1.9 times higher for invasive epithelial cancerous ovaries, which make up 90 percent of ovarian cancers, than for normal ovaries. The mean oxygen saturation of invasive epithelial cancers was 9.1 percent lower than normal and benign ovaries. All five invasive epithelial cancerous ovaries, including two stage 1 and 2 cancers, showed extensive rHbT distribution and lower sO2.
“Physicians are very excited about this because it might bring significant change into current clinical practice,” Zhu says. “It is very valuable to detect and diagnose ovarian cancers at early stages. It is also important to provide information and assurance to patients that there is no worry about their ovaries, instead of removing a patient’s ovaries.
“This technology can also be valuable to monitor high-risk patients who have increased risk of ovarian and breast cancers due to their genetic mutations. The current standard of care for these women is performing risk reduction surgeries to remove their ovaries at some point, which affects their quality of life and causes other health problems,” Zhu says.
“We are very fortunate to participate in this research endeavor headed by Dr. Zhu,” says Cary Siegel, professor of radiology and chief of gastrointestinal/genitourinary radiology. “This photoacoustic imaging study has great potential to better identify ovarian cancers and may play a valuable role in screening high-risk patients and triaging patients for follow-up imaging or surgical excision.”
These initial results will need to be validated with more patients, Zhu says. The team is applying for funding to conduct a large clinical trial.
The National Institutes of Health and the Center for Strategic Scientific Initiatives at the National Cancer Institute funded the work.