We investigated the physical properties of hybrid subtraction techniques by comparing their removal of motion artifacts, detectabilities of simulated vessels, and signal to noise ratio (SNR)with those of conventional temporal subtraction techniques.
Artifacts caused by gas motion were signific a ntly reduced by the hybrid subtraction. SNR of hybrid subtraction was approximately 45% to 30% of that for conv e ntional temporal subtraction.
It was confirmed that the SNR of hybrid subtraction images is improved slightly by image integration technique.
Clinical radiographs indicated that hybrid subtraction can improve the removal of motion artifacts.

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In this paper we compare the assumption of approximate analytic formula and real experimental data for excluding non diffraction element at liquid crystal device in sequence of two Fourier transformations.
We also experimentally demonstrate the simple realtime intensity inversion technique with liquid crystal.

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We have developed a consultation system on a personal computer to help radiologists in clinical decision makings. The system was applied to the CT diagnosis of pulmonary nodules (theme 1) and to the prediction of the outcome of radiation therapy to lung cancers (theme 2). It is our policy to construct a knowledge base with the cases which have been examined or treated in our department and for which detailed information has been derived. Knowledge base for theme 1 contains 127 pulmonary nodules, and that for theme 2 only 40 cases, which we think as a preliminary one. A knowledge base is a collection of the name of descriptive criteria, their significance, names and distributions of diseases to be differenciated. Significance of findings was appreciated by multivariate analysis (quantification analysis type 2).
In system design, it was considered that the system is expected not o n ly to tell a doctor what the diagnosis is but to communicate with him about the daignostic processing, it should be friendly to clinicians, and it can be easily accessed at the site of film reading.

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Recently, a new imaging method called digital X-ray imaging has been developed. It contains various kinds of X-ray generators and detectors which resulted in a confusion in terminology. Computed radiography is a newer concept which is also used to indicate several meanings for radiograpgy. The author attempts to define and classify the digital X-ray imaging and computed radiography.

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