Researchers at Purdue University have developed a new digital holographic imaging system to observe the response of tumours to anticancer drugs.
The new holograms, which use a laser and a charged couple device (CCD) to see inside tumour cells, allow scientists to determine the effect of anticancer drugs on tumours in a real-time 3D environment.
"This is the first time holography has been used to study the effects of a drug on living tissue," said David D. Nolte, the Purdue professor of physics who leads the team.
"We have moved beyond achieving a 3D image to using that image for a direct physiological measure of what the drug is doing inside cancer cells.
"This provides valuable information about the effects of various doses of the drug and the time it takes each dose to become significantly effective."
The cancer cells, which were grown independently in a bioreactor, are not harmed by the gentle laser used in the process.
Holography uses the full spectrum of information available from light to create a 3D image.
By shining a laser on the object and directly on the CCD chip of the digital camera, the system screens the pattern of light reflected back from the object and allows the camera to record very detailed information, including depth and motion on a scale of microns, or 0.0001 centimetres.
The scattered light waves reflected back from the object come together at the camera's detector and form what is called 'laser speckle'.
To the eye, this speckle appears as a random pattern of blotches of bright and dark, but the pattern changes if there is motion within the object.
The team detected the motion of organelles inside cancer cells. Organelles are tiny structures that perform internal cell functions and are a common target of anticancer drugs because they play a key role in the uncontrolled cell division that makes cancer lethal.
"Let's say there are 1,000 organelles reflecting light; the exact pattern of the laser speckle is sensitive to each organelle's location," said Professor Nolte.
"If one moves even one-half micron, the pattern changes. It is highly dynamic and sensitive to changes."
In addition to the technology's sensitivity to motion, the field of view is unique because of its 'dynamic range', the difference between the largest and smallest scale accessed.
"We can look at a fairly large section of the object, about a 30-micron-thick section of a 700-micron-thick tumour, at the same time we can retrieve information within the micron scale," Professor Nolte said.
"Biologists currently have to look at things on the cellular level through microscopes. With this technology, we can detect things on the cellular level and the tissue scale at the same time.
"In this case, the whole is greater than the sum of its parts. Tissue is more than just an accumulation of cells. It is a communication network in 3D that behaves differently than 2D cell cultures."
In 2002 Professor Nolte's group was the first to use holography to produce images inside tissue. The original technique used special semiconductor holographic film developed by the team as opposed to a CCD chip.
"At the time, the only way to capture the image was on this very expensive, very difficult to make film, but the CCD cameras kept getting better and better and reached the point where we could make the transition from holographic film to the CCD," he said.
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