Processing of Medical Image Sequences

Abstract

Processing medical images has become a large and important application area of digital image processing techniques. Such techniques have been applied to a wide variety of images, namely X-ray images (a review of methods is given in [7.1]), scintigrams, ultrasonic and thermographic images, and microscopic image processing (as presented in [7.1]). A more general description of medical image processing is contained in [7.2]. As in other application areas, time sequence processing has developed relatively late, due to technical problems such as lack of memory and processing power, and probably due to a lack of concepts as well. However, the need has existed for some time [7.3]. Recent activities in time sequence processing in the medical field can be roughly classified into three categories: a) The determination of size, shape, volume, etc. of certain organs as a function of time. The input is a time sequence of images, and the output usually is a sequence of numbers or low-dimensional vectors, representing the time-behaviour of the measured values. These problems will be discussed in Sect.7.1. b) Functional imaging. Again the input is a time sequence of images, the output is a single image showing in condensed form the functioning, e.g. the velocity of the blood, etc., in human organs. This topic is presented in Sec t.7.2. c) Image enhancement. The input is a time sequence of images, and the output may be either a single image or a sequence of images, whose quality has beer improved with respect to noise, blurring, etc. In Sect.7.3 we will discuss a specific example of generating a single picture from a sequence showing improved noise and blurring properties. Finally, we shall briefly discuss image sequences that are not time sequences. Although work in this area is mostly in the beginning state, we fee it necessary to at least shortly review it here, because these may have some interesting cross-connection to time sequences. Examples to be discussed will be sequences with respect to spatial coordinates, and frequency characteristics of the image-generating signal (Sect.7.4). Since most activities as well as our own experience have been in the X-ray field, we will concentrate on X-ray images.