Hi Hareesh,
Have you made your decision on what CT scannner, 64 slice you would be going for? Have you looked at dual-sourced models? 256 slices would be also be available in the market in future, but as yet they have not been evaluated to be declared superior to current 64 slices. I do expect 64 slice to be a "standard CT" as their prices come down gradually and the 256 slice to be the the "high end CT" in the coming years. ECRI has done a recent evaluation study on CT 64 slice technology and is worth looking into.
www.ecri.org