Two years ago the Section on Structural Biology acquired a Zeiss EM902, the first commercially available microscope to incorporate on imaging energy- loss spectrometer. The main thrust of the project--and the reason for procuring one of these instruments--has been to exploit its potentialities for imaging relatively thick specimens in vitreous ice. Preservation of the native structures of biological macromolecules by rapid freezing, and maintaining them in an aqueous environment (ice) during imaging has potentially been one of the most important breakthroughs of the last twenty years, and the Zeiss EM902 has considerable potential to advance this area of research. CLS proposed a computer system based on the MicroVAX II to acquire data from the EM902. A Dage-MTI SIT-66 camera provided by Zeiss and incorporated into the microscope is used for image acquisition. Multiple images are averaged for image intensification because the microscope is often operated under minimal dose conditions. The video output from the camera is fed to a frame grabber and image processing board (Data Translation DT 2651 and 2658) connected to the MicroVAX I/O bus. A FORTRAN acquisition program using DT-IRIS subroutines has been developed. One out of every four video frames (CCIR standard) are acquired and averaged in real time in a 512 x 512 matrix. The averaged image is stored on disk in the same format used by the CLS image processing facility, thereby allowing extensive computer image processing to be performed with the highly developed PIC software package on either the large VAX system in the DCRT or locally on a MicroVAZ III. Either system may be accessed by a network connection. DECNET is used to transfer images on a 56K bit/sec link to the DCRT VAX and a local area VAX cluster connection enables local image transmission.
