| By :
Adrianna Noton
Knowledge of how photoacoustic imaging works and where it is used is a relatively recent field of study. The technology is a relatively recent innovation, and will hopefully allow medical practitioners in future to conduct highly detailed scans of a patient with a hand-held scanner rather than massive amounts of expensive and bulky technology which MRI (magnetic-resonance imaging) and CT scanning can often entail. The kind of information provided by this kind of technology produces images which are more detailed than those provided by previously-existing technologies. The technology can operate at depths of several centimetres in tissue, and it can be utilized to direct biopsy needles to affected areas much more swiftly than previous technologies would allow. It also has the potential in future to be able to detect the malignancy of tumors, and could even one day be used to monitor brain activity or to closely examine gene expression in cells. A photoacoustic image is made by shining pulses of laser light onto the section of tissue to be scanned. This allows the tissue to be heated by a very tiny amount, causing no damage but making the cells expand and contract. The temperature changes is minimal, and can be measured in thousandths of a degree. The cells' expansion causes them to emit sound waves which occur in the ultrasonic range, which are then measured by sensors. The information the sensors receive is then transmitted to a computer, and an image is then constructed by using triangulation. Images can be created in two or three dimensions. The technology was developed in the Soviet Union in the late 1980s, by scientist Alexander Oraevsky, working at the Soviet Academy of Sciences in Moscow, who had been examining techniques using lasers as part of a process of tissue removal. When he realized that his samples were also producing ultrasound, he began to examine its potential for other uses. One major positive about the technique is that it can scan to a depth of seven centimetres or so, handing it a clear advantage over other techniques such as confocal microscopy or optical-coherence tomography, which usually only operate effectively to a depth of just a millimetre or so. The way in which tissues absorb particular wavelengths of light also depends on the type of tissue. Blood also absorbs light in different ways depending upon whether it has been oxygenated or not. This means that there is a contrast agent naturally contained within the technique, and it can pick out organs such as veins especially well. One way in which the technique can be used is to detect brain lesions. This is achieved because it can recognize different tissues within the brain which have differing optical absorption properties. This has been demonstrated by experiments on mice. Perhaps its most crucial application, however, will be in the detection and treatment of cancer, particularly breast cancer. Previous technologies and techniques did not allow doctors to tell if tumors were benign or malignant without conducting invasive surgical procedures. How photoacoustic imaging works and where it is used could well develop into techniques which will save millions of lives in the future.
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