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Analysis Of Hierarchical Storage Of Radiological Images Based On The Morse Model

One of the persistent problems facing radiology departments is storage and timely retrieval of images. Usually prudence and the law require that old studies be kept for years, which can often be difficult and costly. Digital storage of images poses even more difficult problems. The cost of rapid access storage is likely to force the development of hierarchical storage of images. This paper examines the problem of which images to migrate to secondary or tertiary storage and the cost of different approaches both in terms of dollars and probability of delayed access. The model used is based on P. M. Morse's model of library book circulation. The Morse model attempts to determine the probability distribution of future use based the past use. It assumes that usage is a Markov process and that the probability that usage will be any particular value is dependent on the previous year's use. Each year's probability distribution is Poisson with the mean governed by a constant decay factor and by a factor which is a multiple of the actual use in the preceeding year. This model will be used as a basis for theoretical analysis to determine the cost of different methods of assigning images to secondary storage.