Contributions to astronomical and medical information processing

A number of specific applications of digital information processing to astronomical speckle imaging and to physiological measurements in medicine are presented in this thesis. Astronomical speckle processing, a collection of information processing techniques in optical astronomy for high spatial resolution imaging through the Earth's atmosphere is reviewed in detail. The performance of simple shift-and-add [Bates and Cady 1980] is studied under conditions of partial isoplanatism and photon limiting. Partial isoplanatism is shown to attenuate and reduce the resolution of detail in the shift-and-add image, to a degree equivalent to the similar effects which occur with speckle interferometry. No spurious fine detail is generated in the shift-and-add image by partial isoplanatism. A variation of shift-and-add is proposed in which any bright, unresolved star serves as a reference object for the formation of a shift-and-add image of fainter detail within the same isoplanatic patch as the star. Computational and astronomical examples are presented demonstrating the potential of this proposal for forming high spatial resolution images of astronomical objects under partially isoplanatic conditions. Photon limiting is shown with the aid of computational examples to cause changes in the form of the shift-and-add image, including an increase of ghosting as the average number of photons per speckle image decreases. The performance of shift-and-add under photon-limited conditions with several different strategies for choosing single “brightest pixels” from speckle images with non-unique brightest pixels is compared. A new speckle imaging technique called zero-and-add is introduced and described. Zero-and-add compares the complex visibility zeros of individual one-dimensional speckle images to identify the complex visibility zeros, common to all of the speckle images, characterising the object. From these common zeros an image of the object is computed. The effects on zero-and-add of various types of deviation from isoplanatism in speckle images are investigated. A computerised system for long-term respiratory monitoring in hospitals is described. The system combines a non-invasive transducer of breathing motions, permitting continuous monitoring of respiratory activity for extended periods in clinical situations. with a general-purpose microcomputer that analyses the breathing motions breath-by-breath. The system has been designed as a tool for the study of the respiratory effects of different techniques of pain relief on hospital patients undergoing surgery. Preliminary clinical results obtained during the development of the system are presented. The system is potentially applicable in a wide variety of clinical and laboratory studies involving respiratory measurements. A suite of electronic hardware and computerised data processing algorithms for venous occlusion plethysmography [Seagar 1983a, Seagar et al 1984] has been integrated into a self-contained microprocessor-controlled system suitable for routine use in hospitals. The finished system is described. The system automates the acquisition and interpretation of venous occlusion plethysmographic measurements. It allows convenient, non-invasive measurements of limb blood circulation to be made in a wide variety of clinical and medical laboratory settings. Examples of clinical applications of the system in Christchurch hospitals are presented