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Rationale and Objectives: The compression of cranial computed tomography scans was improved by using independent intra- and interframe compression techniques., Methods: For intraframe compression, an image was decomposed into four subimages, one subimage was chosen as a reference subimage, and three of the subimages were predicted from the reference subimage. The prediction error was encoded with a classified vector quantizer (CVQ) based on human visual perception characteristics. Interframe redundancy is exploited by a displacement estimated interslice (DEI) algorithm that encodes the differences between reference subimages from adjacent slices. This combined DEI/CVQ method was subjectively evaluated by 13 radiologists under a blinded protocol, and was compared to the CVQ method alone, the DEI method alone, the original images, and to a standard intraframe discrete cosine transform (DCT) compression method., Results: Only the combined DEI/CVQ method at 10:1 compression was not scored significantly different from the original images. At 15:1 compression, the DEI/CVQ method was scored significantly better than the 10:1 DCT and any other 15:1 compression methods., Conclusions: Compressed image quality is enhanced by exploiting inter- and intraframe redundancy, and by modeling some characteristics of human visual perception. The DEI/CVQ method is well-suited for progressive transmission, and thus, holds potential in teleradiology as well as picture archiving and communications systems.

Rationale and Objectives: The authors developed and subjectively evaluated an interslice compression algorithm that explores the redundancy among adjacent slices of an x-ray computed tomography (CT) scan. This algorithm has been compared to an intraslice compression algorithm based on the two-dimensional discrete cosine transform., Methods: Nine x-ray CT head images from three patients were compressed with this interslice method at compression ratios of 5:1, 10:1, and 15:1. The same images were also compressed with the intraslice method at the same ratios. Six radiologists judged quality of randomly selected compressed and decompressed images compared to that of the originals. The evaluation data were analyzed statistically with the analysis of variance and Tukey's multiple comparison. Kappa-like statistics (Williams index and O'Connell and Dobson indexes) were also calculated to measure the agreement among readers beyond the amount expected by chance., Results: The interslice coding algorithm showed significantly better quality than the intraslice method at significance level 0.05, even though there was no difference in the objective distortion measure (signal-to-noise ratio). Also, the quality of 10:1 compressed images with the interslice coding algorithm was not significantly different from that of the originals at level 0.05. While large variations in agreement occurred among readers, the overall agreement was statistically significant., Conclusions: By using adjacent slice information in compressing x-ray CT images, significantly better quality in compressed and decompressed images was achieved. While 10:1 compressed images with the interslice algorithm were not significantly different from the originals in quality at level 0.05, effect on diagnostic accuracy remains to be investigated.

CORRELATE is a new computer software program for CT that enables a radiologist to mark tumor margins on traditional CT cross-sectional images and then display the outline of that same tumor on CT ScoutView images. This function is particularly useful for radiation therapy planning because CORRELATE ScoutView images are in the same longitudinal plane as simulation radiographs used for tumor localization in radiation therapy. The impact of CORRELATE on the radiation therapy planning process was measured in 83 patients with various tumors. Therapy planning was performed before and after CORRELATE information was made available to the radiation therapist. CORRELATE information caused a change in the therapy plan in 77% of the cases and increased confidence in the therapy plan in an additional 22%. CORRELATE provides a useful and accurate tool for tumor localization.

The minicomputer that is part of a commercial CT scanner has been used to develop a general purpose computer-assisted education system. This allows instruction in radiology using the CT computer already installed in the radiology department. The computer software was designed as a course interpreter, allowing the courses themselves to be written in English. Images and educational text are stored on separate disk files and displayed by the interpreter.

How much does one need to know about the computer part of a computed tomographic or nuclear magnetic resonance system to select the best system and to use it effectively? Enough to comprehend how features or options relate to individual applications and needs. Besides acquiring some basic knowledge, one needs to consider upgradability, word size, and features of the image display controller, graphic input, array processor, and other hardware.

A computer software program (Seapit) was developed for precise determination of intracranial targets identified by stereotactic computed tomography (CT). This program was added to the software of a GE 8800 CT scanner to perform the following operations: millimetre precise calculation and display of the rectilinear coordinates of a target identified on axial CT images; preplotting of phantom target trajectories on the CT images or electronic radiographs; calculation of probe angles required to achieve various trajectories; display of a coordinate scale on each CT image to allow direct target determination without mathematical calculations; calculation of the intercommissural plane for functional neurosurgery. In a series of 100 patients undergoing stereotactic surgery, the Seapit program proved to be a superior and accurate method of target coordinate calculation. Preview display on the CT images of 'phantom' probes significantly enhanced the safety of stereotactic intervention.