Photoacoustic Microscopy Offers a Better Way for Orthopedic Surgeons to Separate Malignant from Healthy Tissue

Researchers from Sylvester Comprehensive Cancer Center at the University of Miami Miller School of Medicine, Caltech, and other institutions have successfully tested a more efficient way to identify cancerous bone tissue during surgery. Called photoacoustic microscopy, the technique uses light and sound to differentiate between cancerous and healthy tissue, offering surgeons a potential new tool to completely excise tumors without removing excess bone. The study was published in Nature Biomedical Engineering.

“We want to have surgical margins that remove all the tumor, including the microscopic cells,” said orthopedic oncologic surgeon Brooke Crawford, M.D., co-senior author on the paper. “At the same time, we want to remove as little bone as possible to preserve the patient’s quality of life.”

Creating precise surgical margins is tricky in any tissue, but particularly with bone. In most tissues, surgeons can shave small slices, freeze them, and send them to pathology to look for residual cancer cells. While this process extends the time patients are under anesthesia, it does give surgeons good insights into how much tissue they should remove to achieve safe margins.

Bone, however, is a different story. Before pathologists can review a sample, pathologists must initiate a cumbersome process called decalcification, which can take days. Without timely information, surgeons are forced to create two-centimeter margins to ensure all tumor cells are removed.

“Two centimeters can be a lot of bone,” said Dr. Crawford. “If the tumor is close to the knee, it could jeopardize the joint. For kids who are still growing, having precise margins could mean the difference between saving or losing a growth plate, and that kid not having to face limb length disparities their entire life.”

Applying Existing Technology to Cancer Surgery

Photoacoustics is an established technology that has been used in deep ocean studies and other areas. Recently it has been applied to cancer surgery, and this is the first time it has been tested on bone. The technique directs laser light at the tissue, which generates acoustic energy. By analyzing this sound wave, using deep learning and other advanced algorithms, the instrument can characterize the tissue being lit up.

“What’s really cool is that each cellular component, the proteins, mitochondria, cell nuclei, DNA, they all have their own specific signatures,” said Dr. Crawford. “We showed in this study that, within five to10 minutes, we can get data that tells normal bone from abnormal bone. We just have to apply the laser to the tissue.”

One of the beauties of the technology is its ease of use. Pathologists don’t have to perform any complex decalcification steps or stain the bone. The laser handles everything. In addition, photoacoustic microscopy can be applied to virtually any cancer, as well as other conditions.

“We could potentially look at it for infections, which is a big deal for patients who have total knee and hip replacements,” said Dr. Crawford. “We could also use it for fracture healing. There are many potential implications.”

The instrument was developed at Caltech, by Lihong Wang, Ph.D., co-senior author on the study. It is still housed in Pasadena, but Dr. Crawford and others are working to have one installed at the University of Miami for further study.

“This proof-of-concept study showed we can tell normal bone from abnormal,” said Dr. Crawford. “Now, we need to see if we can use it as a diagnostic tool instead of going through the time-consuming process of creating slides. Photoacoustic microscopy could give us some really fast answers.”

Tags: bone cancer, Dr. Brooke Crawford, Miller School of Medicine, Nature Biomedical Engineering, photoacoustic microscopy, Sylvester Comprehensive Cancer Center