Cell Whisperer - Lasers Unlock the Secrets of the Blood

Red blood cells that are healthy look a lot like lifesavers. However, they have more dimples than holes in their middle. Red blood cells can become bloated if they are damaged or sick. The ability to detect an irregularity in the shape of red blood cells can help speed up diagnosis of certain types of cancer, blood diseases and blood bank alerts. This is done without ever having to touch any skin or drop any blood.

Photoacoustics, a new imaging technique that uses light and sound to create images may help make this dream a reality. It uses light and sound waves to produce images that are similar to ultrasound. Ryerson University, Toronto, used high-frequency sound waves in order to produce detailed images of red cells. This brings science closer to the future. Today's Biophysical Journal published the findings.

Photoacoustics is when a droplet of blood is put under a microscope which picks up the sounds made by cells. The laser beam is then focused at the samples by researchers. The laser pulse causes blood cells to absorb some energy and release it as sound waves. Scientists can use photoacoustics to get information about cell shape and structure because of blood's ability to absorb light differently at different wavelengths. "Think of it like a microphone," says study author Michael Kolios, a physics professor at Ryerson and Canada Research Chair in biomedical applications of ultrasound. "We just listen to what is happening."

This type of imaging is not yet capable of detecting red blood cell changes at the necessary level to determine if they are sick.

Kolios, along with his Ryerson colleagues, created a photoacoustic microscope that can detect extremely high frequencies. They can now recognize the shapes and sizes of red blood cells with greater precision than ever. They are opening the doors to a future where handheld medical scanners could be used to map cell shapes.

Because it was difficult for sensors to be strong enough to handle higher frequencies, photoacoustic researchers were limited to using frequencies under 100 megahertz. Low frequencies images didn't reveal much. However, investigators were able to find a cell in the image. A special ultrasound sensor, which can detect higher frequencies, enabled the Ryerson team to make use of higher frequency sound waves. The Ryerson team was able "see" red blood cells more clearly, allowing them to assess their health.

Because sound travels so unpredictable when it is in bodily cavities, doctors had to still look at the red blood cells beneath a slide. Medical professionals use very low frequencies to image a pregnant woman during an ultrasound. This is because high-frequency waves would reach her body but quickly scatter, and are absorbed by the tissue surrounding it. High frequencies used in photoacoustics will not produce a detailed image of something within the body's recesses.

Although there is still much to be done in technical areas, the researchers find the clarity and precision of images now made possible by photoacoustics encouraging. Lihong Wang (a Washington University in Saint Louis biomedical engineer) says the next step is to consider culling data from areas where blood vessels can be easily accessed, such as the arms. Wang states that this will stimulate new research. Wang suggests that we might look at photoacoustic data to quantify the shape of one blood cell.

One application of photoacoustics that may have a more immediate use is to examine blood samples in hospitals and blood banks before it's administered. Red blood cells can last for 42 days. Jason Acker is the associate director for development at Canadian Blood Services and assesses new technology. "Unlike milk where you can have it all day, but then it turns out to be sour," he says. He says that blood quality is not measured. It is only tested for hemoglobin, white blood cells, and contaminating bacteria. Kolios began talks with Canadian Blood Services regarding collaborating on the development of this technology that could help to assess the blood quality in blood banks.

Long-term, this work may be useful in diagnosing melanoma. Wang states, "I'm most excited by the potential for this work in vivo identification of circulating tumour cells," since this technology could detect cancer cells much faster than existing methods. Scientists would have to calibrate wavelengths to adapt the technology for this purpose. Red blood cells contain melanin which, being black, absorbs light differently, so scientists will need to calibrate these wavelengths. Scientists are excited about the future of this breakthrough, which could lead to earlier detection and lessinvasive treatment.