Sunday, January 25, 2009

Use of Liquid crystals in high-resolution digital X-rays !

We have seen many applications of liquid crystals, but now something interesting like "X-ray light valve" (a term coined by Dr.John Rowlands). This finds importance because the use of liquid crystals reduces the cost of high-resolution digital X-rays by many folds. As the use of digital X rays is becoming essential (because its simple to analyse, manipulate and store-in comparison with the presently used ones). Most of them work by using a layer of amorphous selenium to convert the X-rays into electric charge. This charge image is then recorded using an array of transistors and other electronic components, akin to those used in some digital cameras.

X-rays cannot be easily focused, so X-ray machines work by recording the shadow of an object rather than a focused image. That means the recording medium, be it an electronic imager or conventional X-ray film, must be at least the same size as the object being scanned and this add to the cost of digitally imaging. Thanks to Dr.Rowland and his group for X-ray light valve-consisting of a layer of liquid crystal - which is opaque or transparent depending on whether an electric charge is present - covered with a layer of amorphous selenium. These layers are sandwiched between a pair of electrodes which generate an electric field across them. When an X-ray is taken, the rays that hit the selenium layer generate a charge which is drawn towards the liquid crystal by the electric field. This makes the liquid crystal transparent at those locations. The overall pattern of transparency and opacity can be read off the liquid crystal layer using a light-based digital scanner and presented as a digital image. This research is of significance because of the fact that it separates the read-out system from the X-ray mechanism.

As pulmonary tuberculosis is becoming an epidemic in the developing countries, development of this technique is a boon to the people.

When I was working for my Ph.D., my guide (Dr. Shankar C. Bennur  (now retired) Professor of Organic Chemistry, Karnatak University Dharwad, Karnatak, India) used to tell me that the liquid crystals will have many fold uses in the days to come. He did work (UFSC, Florianopolis, SC, Brazil) on the synthesis of many liquid crystals and used to tell me about his experience with this interesting field (which was at nascent stage). Whenever we used to get products (in my case, the compounds had methylene aminoxy methyl moiety) with low melting points, he  used to elaborate about  smectic point./long chain compounds.....Hope,  he will be happy about this innovative idea. Congrats Dr.Rowland......

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