|
As Picture Archiving and Communication System (PACS) technology has matured, video image capture has become a
common way of capturing digital images from many modalities. While digital interfaces, such as those which use the
ACR/NEMA standard, will become more common in the future, and are preferred because of the accuracy of image
transfer, video image capture will be the dominant method in the short term, and may continue to be used for some time
because of the low cost and high speed often associated with such devices. Currently, virtually all installed systems use
methods of digitizing the video signal that is produced for display on the scanner viewing console itself.
A series of digital test images have been developed for display on either a GE CT9800 or a GE Signa MRI scanner. These
images have been captured with each of five commercially available image capture systems, and the resultant images
digitally transferred on floppy disk to a PC1286 computer containing Optimast' image analysis software. Here the images
can be displayed in a comparative manner for visual evaluation, in addition to being analyzed statistically. Each of the
images have been designed to support certain tests, including noise, accuracy, linearity, gray scale range, stability, slew
rate, and pixel alignment. These image capture systems vary widely in these characteristics, in addition to the presence or
absence of other artifacts, such as shading and moire pattern. Other accessories such as video distribution amplifiers and
noise filters can also add or modify artifacts seen in the captured images, often giving unusual results.
Each image is described, together with the tests which were performed using them. One image contains alternating black
and white lines, each one pixel wide, after equilibration strips ten pixels wide. While some systems have a slew rate fast
enough to track this correctly, others blur it to an average shade of gray, and do not resolve the lines, or give horizontal or
vertical streaking. While many of these results are significant from an engineering standpoint alone, there are clinical
implications and some anatomy or pathology may not be visualized if an image capture system is used improperly.
|
