Study Describes New Imaging Technique for Detecting Prostate Cancer

A new imaging technique that combines ultrasound and photoacoustic imaging of the prostate delivers detailed information about the prostate’s anatomy and cancer location, identifying some cancers that would be invisible to conventional imaging.

The approach, called transrectal ultrasound and photoacoustic device, or TRUSPA, may enable earlier detection of prostate cancer.

The new technology was described in a study titled “Simultaneous transrectal ultrasound and photoacoustic human prostate imaging,” which was published in the journal Science Translational Medicine.

Seeking the best ways to diagnose prostate cancer early is a continuous challenge for researchers and physicians. One strategy is to image the prostate using ultrasound, magnetic resonance imaging (MRI), or positron emission tomography (PET) scans, looking for physical changes that might indicate cancer. This can be useful, but there’s a catch.

“The problem is that cancer within the prostate quite often doesn’t lead to any anatomical changes until it’s quite large or has spread beyond the capsule of the prostate into the lymph nodes around it,” Sanjiv “Sam” Gambhir, MD, PhD, said in a press release. Gambhir is chairman of the Department of Radiology at Stanford University School of Medicine. “So for decades we’ve been looking for ways to analyze and image the prostate with greater detail to detect changes earlier on, safely, and at relatively low cost,” he said.

TRUSPA combines ultrasound with photoacoustic imaging (PAI) to create a picture of the different structures within the prostate, using ultrasound to get the shape and PAI to differentiate between different types of tissues.

The researchers also used an imaging agent called indocyanine green (ICG), which is already approved for human use by the U.S. Food and Drug Administration (FDA). Cancer cells in the prostate take up ICG more than non-cancer cells, and TRUSPA can identify cells that take up ICG. So, at least in theory, it makes any cancer that is present clearly visible in images.

“We opted for an imaging agent that was not specific to prostate cancer, but rather to cancerous tissues for our proof of principle,” Gambhir said, though he noted that “the idea moving forward is to heighten precision using a molecularly-targeted photoacoustic molecular imaging agent that binds specifically to prostate cancer cells.”

After doing a series of tests in their lab, including experiments using mice and using cancerous prostates from humans that had been surgically removed, the researchers conducted a small proof-of-principle study on 20 people who already had been diagnosed with prostate cancer via existing diagnostic tools (e.g., biopsy).

All participants were imaged with TRUSPA; half of them also had varying doses of ICG injected during the imaging.

TRUSPA created reasonably clear images of the prostate, and it was able to detect ICG — and thus, cancer — at most doses. In one patient, TRUSPA even differentiated between malignant and non-malignant cancer tissue, which was confirmed when that prostate was surgically removed later.

These data give the researchers a starting point for how best to design future studies, and they represent a proof-of-principle for using this imaging technique in people.

“Not only were we able to better understand TRUSPA imaging limitations in the patients, we also were likely seeing tumors that would have otherwise been invisible to conventional prostate ultrasound,” Gambhir said.

Gambhir added that the utility of TRUSPA also is being investigated outside of prostate cancer: “We’re now starting to explore TRUSPA for detecting ovarian cancer, thyroid cancer and skin cancer, too.”