Listening to cancer cells

It's now possible to detect skin cancer cells present in blood samples by listening to the sound of melanoma cells. This new technique, named photoacoustic detection, uses a laser to make cells vibrate and ultrasound techniques to pick the sound of cancerous cells. This method is very precise but large clinical studies still need to be done.

According to researchers at the University of Missouri-Columbia, it's now possible to detect skin cancer cells present in blood samples by listening to the sound of melanoma cells. The scientists have used a method named photoacoustic detection, which uses a laser to make cells vibrate and ultrasound techniques to pick the sound of cancerous cells. This technique is so precise that it's possible to identify the spread of cancer even if there are only ten melanoma cells in a blood sample. Still, large clinical tests must be done before this method can be widely used. But read more...

John Viator, an Assistant Professor in the Department of Biological Engineering and member of the team of researchers, is working on this technique for a while. You can read two previous University of Missouri-Columbia news releases on the subject, "Doctors Use Sound to Battle Melanoma" (February 24, 2005) and "Professors Awarded $470,000 for Development of Cancer Detection Devices" (July 25, 2006).

Now, let's discover how the Optical Society of America (OSA) describes how this photoacoustic detection technique works.

[It]combines laser techniques from optics and ultrasound techniques from acoustics, using a laser to make cells vibrate and then picking up the characteristic sound of melanoma cells. In a clinical test, doctors would take a patient's blood sample and separate the red blood cells and the plasma.
In a healthy person, the remaining cells would be white blood cells, but in a melanoma patient the sample may contain cancer cells. To find out, doctors would put the sample in saline solution and expose it to rapid-fire sequences of brief but intense blue-laser pulses, each lasting just five billionths of a second.

But how is it possible to identify cancerous cells?

The sound waves produced by melanin are high-frequency ultrasounds, meaning that they cannot be heard by the human ear, even if amplified. However, researchers can pick them up with special microphones and analyze them with a computer. Other human cells do not contain pigments with the same color as melanin, so the melanin signature is easy to tell apart from other noises, said John Viator.

Below are two illustrations describing the method. On the left is a schematic layout of this design (Credit: OSA/Nature Photonics) while the experimental setup is shown on the left (Credit: John Viator). You'll find more explanations and other pictures by reading "Photoacoustic Detection of Circulating Tumor Cells."

Listening to cancer cells setup

This research work has been published by Optics Letters under the title "Photoacoustic detection of metastatic melanoma cells in the human circulatory system" (Volume 31, Issue 20, Pages 2998-3000, October 2006). Here is a link to the abstract.

It has also been commented by David Gevaux in the new journal Nature Photonics under the name "Laser-induced ultrasound can detect malignant cancer cells" (October 5, 2006). Here is an excerpt.

When a cell, suspended in a liquid, absorbs a laser pulse, the resulting heat generated causes it to rapidly expand and contract producing an acoustic wave that travels through the surrounding liquid. Detection of these waves after pulsed laser illumination indicates the presence of the light-absorbing cells -- in effect, laser-induced ultrasound. With this basic principle, [The researchers] fired 11–12-mJ light pulses with a wavelength of 450 nm at melanoma cells (a type of skin cancer) suspended in saline.

This new blood test is the object of a patent, "Photo-Acoustic Detection of Circulating Melanoma Cells" (PDF format, 1 page). But even if this blood test can lead to early diagnosis of metastasis, large clinical studies still need to be done. Meanwhile, the researchers are now working "to extend the reach of its technique to other types of cancer."

Sources: Optical Society of America news release, October 16, 2006; and various websites

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