Optical tomography catches early-stage breast cancer

Near-infrared light used with ultrasound can zero in on early-stage breast tumors, potentially reducing the number of biopsies, according to a study in the October issue of Radiology.

The imaging combination can help physicians assess changes in tumor vasculature, better distinguishing between malignant and benign lesions, said Quing Zhu, Ph.D., an associate professor of electrical and computer engineering at the University of Connecticut.

"Optical tomography is best used for monitoring chemotherapy treatment and assessing changes of tumor vasculature during treatment," Zhu said.

The ability to measure tumor angiogenesis is especially helpful in highlighting early-stage cancers, as the vasculature in these lesions is not as heterogeneous or complex as that in larger tumors.

Zhu and colleagues prospectively studied 81 breast lesions in 65 consecutive women. The lesions were examined with a handheld probe consisting of an ultrasound transducer surrounded by near-infrared sensors. The device produces ultrasound images coregistered with optical data.

The researchers used light absorption measurements to help calculate total hemoglobin concentration. They then performed ultrasound-guided biopsy on the lesions.

Biopsy confirmed eight early-stage invasive tumors and 73 benign lesions. The average hemoglobin concentration in the early-stage tumor group was 88 micromol/L compared with 38 micromol/L for the benign group, a significant difference.

The sensitivity, specificity, positive predictive value, and negative predictive value of optical tomography were 100%, 96%, 73%, and 100%, respectively.

Some obstacles must be overcome before the technique can move into the clinical mainstream, according to Zhu. Most important, researchers must learn to deal with the distortion of near-infrared light caused by tissue and challenging interior spaces.

"Near-infrared light is very sensitive to tissue boundary conditions and changes its propagation path when the light wave hits the breast tissue and the chest wall conjunction. This problem occurs when imaging patients with small, dense breasts," he said.

The technique also cannot be used for imaging lesions that are very close to dark nipples because of the strong absorption of light by dark nipples.

Optical tomography requires careful execution, Zhu said. The optical instrument must have a good signal-to-noise performance, environmental light must be controlled to minimize background interference, and certain measurement procedures have to be followed to minimize any possible sources that may cause imaging artifacts.

For more information from the online Diagnostic Imaging archives:

Optical imaging sheds light on cancer's signature

Optical imaging keeps its light well hidden

Researchers examine light as new, fifth option for physiological imaging