Single-breath-hold photoacoustic computed tomography (SBH-PACT) is a novel, light-based technology that could disrupt current breast-screening technologies, according to results of a pilot study in Nature Communications. SBH-PACT is quick, painless, and uses no radiation.
“By developing this advanced breast imaging modality, we provided a promising tool for future clinical use including not only in screening, but also in diagnostic studies to determine extent of disease, to assist in surgical treatment planning, and to assess responses to neoadjuvant chemotherapy,” wrote the investigators, led by Lihong V. Wang, PhD, Caltech Optical Imaging Laboratory, Andrew and Peggy Cherng Department of Medical Engineering, California Institute of Technology, Pasadena, CA.
Results from several large clinical trials have stressed the importance of detecting breast cancer early for survival benefit. However, current technologies for detecting such cancers leave much to be desired.
PACT renders the functional optical contrast of diffuse optical tomography plus the high spatial resolution of ultrasonography. The rich contrast of PACT secondary to optical absorption allows it to be used for structural, functional, and molecular imaging.
In plain terms, PACT-SMH focuses laser pulses on oxygen-rich hemoglobin in blood vessels during the breast scan, which causes vibrations. The vibrations are then picked up by ultrasonic sensors. These ultrasonic signals are used to reconstruct a detailed volumetric image via 3-D back projection, including the dense and convoluted vascular networks, or “knots,” typical of breast tumors.
During this diagnostic test, the patient lies on an examination table with the breast comfortably surrounded in a mesh of ultrasound sensors. The procedure takes 15 seconds, or a single breath hold, with few artifacts from breathing. Furthermore, the high-imaging speed of PACT-SMH permits more dynamic examination, including photoacoustic elastography.
SBH-PACT, which is the novel PACT system invented by Dr. Wang and co-investigators, exceeds current limitations in PACT technology in the following areas:
- Sufficient penetration depth to accommodate most breast sizes and skin colors
- High spatial resolution to reveal detailed angiographic structures
- High temporal resolution to minimize motion artifacts and enable dynamic or functional studies
- Minimal limited-view artifacts
- Sufficient noise-equivalent sensitivity and contrast-to-noise ratio to detect breast masses
In the current pilot study, SBH-PACT was used in seven patients with breast cancer and one healthy control; breast cup sizes ranged from B to DD, and the patients’ skin pigmentation ranged from light to dark.
The team was able to identify eight of the nine breast tumors present by means of blood vessel anatomy, and then they confirmed the findings using ultrasound-guided biopsy. In addition, the team created an algorithm that lit up tumors automatically. Ultimately, SBH-PACT caught tumors in all breast types, including denser breasts, which is a current limitation of mammography.
“The technique developed by Dr. Wang and his colleagues combines light and sound to peer noninvasively into tissues without the radioactivity of an X-ray,” said Behrouz Shabestari, PhD, director of the Program in Optical Imaging at the National Institute of Biomedical Imaging and Bioengineering, Bethesda, MD. “PACT is also superior to MRI, which is expensive and sometimes requires the injection of contrast agents, commonly gadolinium. Gadolinium cannot be used in individuals with kidney disease and has recently been shown to accumulate in the bones and brain with unknown long-term effects.”
This study was funded by the National Institute of Biomedical Imaging and Bioengineering.
To read more about this study, click here.