In Doppler systems which automatically calculate the maximum frequency envelope and pulsatility index (PI) of umbilical artery Doppler waveforms there is the possibility of error in these parameters when the technical quality of the acquired waveform is low. Low quality waveforms may arise when there is an inapproprite set of physical parameters or when there are other sources of noise such as overlying vessels signals. In this thesis the effect of physical parameters on the envelope and on PI are investigated, and also methods for the detection of low quality waveforms are described and tested. A flow phantom which is able to produce realistic looking umbilical artery Doppler waveforms is described. This is based upon microcomputer control of a stepping motor/gear pump combination. The statistics of the Doppler spectra produced using artificial blood and human blood in the phantom are found to be identical. The effect of a number of physical parameters on the simulated umbilical artery waveforms produced using the phantom is investigated. The accuracy of estimation of the envelope and the PI is similar over a wide range of physical conditions. A suitable image processing algorithm for speckle reduction of Doppler waveforms is developed and it was found that both filtering of the envelope and also speckle suppression of the spectrum improved the accuracy of estimation of the envelope and of the PI. A number of quality indices based upon the degree of noise of the envelope are described. Using the flow device there is found to be a high correlation between the quality index values, and the errors in PI and errors in envelope estimation respectively. In a clinical trial the quality index values from umbilical arteries were compared with the waveform quality as assesed by a skilled observer. The clinical results show that quality indices are able to separate high and low quality waveforms when the indices are calculated from the unprocessed envelope, but not when calculated from the filtered envelope.

The first part of the thesis deals with new applications of neutron and nuclear physics to the detection and measurement of trace quantities of toxic elements, silicon and beryllium in human lungs. Reaction 28Si (n,n'gamma)28 Si has been used to measure small quantities of silicon in an anthropomorphic lung phantom. A satisfactory suppression of interferences from aluminium present in the experimental equipment from phosphorus present in the body and from hydrogen capture Compton continuum, was achieved with the use of pulsed neutron beams of energy in the range 5--10 MeV, The 2a detection limit, predicted on the basis of extrapolation of experimental results, is 150 mg of Si for a dose of 0.01 Sv, assuming the use of six Ge(Li) detectors, each having efficiency of 35%. The thesis gives also an account of experiments on build-up and decay of thermal neutron flux in small moderators exposed to bursts of fast neutrons, of energy 2.5 and 14 MeV. The technique of detection of beryllium in vivo utilized very low threshold of Be for photodisintegration. The photoneutrons, following a burst of bremsstrahlung with maximum energy not exceeding 2.220 MeV, are thermalized and either detected by a large array of BF3 detectors or captured by nuclei of hydrogen in the body and in the external moderator, so that the hydrogen capture radiation can be recorded. For a dose of 5 cGy this technique may lead to a detection sensitivity (2a) of 50--120 micrograms of Be. The second part of the thesis describes the technique of lyoluminescence dosimetry applied to the fast neutron beams. After analysis of factors affecting accuracy, precision and reproducibility of neutron dosimetry for gamma radiation fields, which have been tested in a series of international comparisons with other dosimetric techniques sponsored by IAEA, the results of in-house comparison with TLD are also included. Lyoluminescent phosphors, mannose and glutamine, have shown better reproducibility than individually calibrated TLD chips. Amino acids, isoleucine and valine are shown to be particularly good Lyo-luminescence phosphors for fast neutron beams, isoleucine having energy response very closely approximating that of ICRU muscle. The energy and dose responses of mannose, glutamine, valine and leucine were measured in the neutron energy range from about 1 MeV to 15 MeV. In addition, the thesis gives information on the use of lyoluminescent phosphors containing 6Li in the mapping of thermalized neutron radiation fields. It is suggested that lyoluminescent dosimeters can be used for mailed dosimeter intercomparisons between radiotherapy centres. One of the appendices to the thesis gives information on the properties and development of a neutron target based on 7LiD, intended for use on low energy cyclotrons accelerating deuteron beams.

This work attempts the formulation of a number of computer vision problems, often emerging when processing medical images, as optimisation problems. The ability of Genetic Algorithms, a global optimisation technique, to efficiently and reliably perform the required optimisations is assessed. Results are quantified and compared to other more established methods. The problem of anatomical object detection and extraction of their shape from 3D medical images is considered first. Two geometric primitives with parametrically controllable shape are used for geometric modelling and an adequate objective function is introduced to be optimised over the shape parameters. GAs are then employed to optimise the objective function. Quantified assessment of the results using two different anatomical objects is produced and comparisons to interactive object segmentation are made. The problem of texture based segmentation is also considered. The detection of texture is formalised as a problem of designing a mask that exploits relationships between the spectra of different classes of texture. Results are produced in the case of artificial patterns, natural texture and texture present in medical images, including modalities like MRI and X-rays. The results of the segmentation are compared to other better established texture discrimination techniques. Finally, the problem of noise suppression is formulated as a problem of stack filter configuration, a broad family of non-linear filters. Results are produced for different types of noise, including additive uncorrelated noise as well as multiplicative or gaussian and poisson noise. Results from the application of the configured filter are compared to those of other digital filters, commonly used for noise reduction.

My thesis is composed of two parts. Ultrasound hyperthermia is emphasised in part i, and surgical removal of tissues by ultrasonic surgical aspirator is emphasized in part ii. A hyperthermia system making use of overlapping five divergent ultrasonic beams has been developed in my studies. The system is microcomputer controlled. Tissue temperatures are monitored every 30 seconds during treatment with thermocouple arrays, and then the computer adjusts the hyperthermia applicator's output to reach and maintain the therapeutic temperature level in the treated volume. One of the features of the hyperthermia applicator design is that not only divergent field pattern is produced by individual transducer, but also ultrasonic beams are pointed to a focal region by the geometry of the applicator. Computer simulations of the field patterns generated by the applicator in nonabsorbing water medium and simulations of temperature distributions in soft tissue model have been done. Both direct visualization of field patterns in ink-water medium by using Sarvazyan method and measurements with thermocouple probe scanning across and along the field in water are consistent with the computer simulations. In-vitro experiments with pieces of meat and computer simulations of temperature distributions show that the hyperthermia system may be useful in cancer therapy. In-vitro experiments have demonstrated that a large volume of tissue at a few centimetres below the surface can be heat up. Animal experiments have also been carried out and the results are described. Effective blood flows and ultrasonic intensity distributions in the treated region have been estimated by using simplified bio-heat transfer equation. Thermal doses to tissue in treatments are also estimated. In addition, adverse effects of ultrasound on normal blood vessel walls are discussed, and the results of scanning electron microscopy of blood vessel walls are presented. In part ii a theoretical model for tissue fragmentation with ultrasonic surgical aspirator has been suggested. The number of cycles of vibrations required for the CUSA to fragment ox-liver is estimated. The calculated value is consistent with the experimental finding in the order of magnitude. A motor-driven vibrator/ aspirator has been developed in my studies. Its rate of removing ox-liver is comparable to that of the CUSA. Advantages and disadvantages of these two probes are discussed.

This thesis describes the general problems involved in the 'imaging' of gamma radiation, and the techniques employed in their attempted solution. Following an introduction to the subject in Part If where conventional 'scanners' and 'cameras' are described, Part II describes a simple experimental procedure which may be undergone in order to evaluate the smallest size of 'tumour' region that may be detected under any known set of simplified clinical conditions. The visual threshold characteristics of different display systems is an integral part of this technique, and is also described in this section. Part III is concerned with a novel theoretical approach to determine the spatial variation of gamma flux impinging upon the surface of a detector. This is calculated both with and without collimators. The modification of such a flux by the particular 'image transfer system' (i.e. type of detector moving or stationary) being used. Such calculations are compared to the experimental results of section II, and are found to agree closely. Part IV describes fundamental modifications to the image transfer system of the Anger Gamma Camera---with a view to improving the uniformity of the system. An attempt to produce a sensitive high-resolution stationary detecting and imaging system is described in Part V, where an Image Intensifier is optically coupled to a flat circular scintillator toy means of a novel high efficiency lens system. Two such lenses w6re designed---one with unity magnification and the other with a range of magnification from J to I so that a maximum field of view of 8" diameter may be accomodated.

Californium 252 sources were used in a clinical environment for neutron activation analysis studies for a period of * years. During this period changes in part body calcium in bone, in response to different treatment regimes, were measured in patients suffering from primary or secondary bond disease. Measurements were performed on peripheral bone, in particular the forearm, using two sources of 252Cf, minimum total activity 56 mCi, and a purpose built partial body counter. Optimisation of the irradiation geometry and the patient irradiation programme enabled calcium measurements to be performed with a precision of between 1.596 and 1.8% and a bone dose less than 3 rem. The following clinical studies were undertaken: the effect of c1-o hydroxyc1.ecalciferol on 19 patients undergoing chronic haemodialysis, the use of vitamin D2 or D3 in the treatment of 33 patients with potential anticonvulsant osteomalacia, the effect of lithium carbonate in 15 patients with manic depression and the efficacy of conventional treatments in combating thyrotoxic osteodystrophy. Apparatus was also development to measure calcium changes in the lumbar spine. Two 252Cf sources of total activity 200 mCi were used for irradiation and a whole body counter for detection of the induced activity. A precision of 2% was obtained for patient measurements, with a bone dose of 1.3 rem.

Ultrasonic techniques are very widely applied in medicine. Real-time two dimensional imaging is a technology which is extremely well-suited to medical applications since it enables moving structures to be observed and rapid searching through tissue structures to be performed. Three-dimensional (3D) ultrasonic imaging techniques have been developed but to date there has been very limited success in the development of real-time versions. The aim of this thesis is to study the feasibility of real-time 3D ultrasonic imaging to see if ways can be found to overcome the fundamental problem of sparcity of echo line data when a volume is scanned in real-time. The fundamental problem arises because conventional ultrasonic scanners have an upper limit of rate of generation of scan lines of around 10 KHz. The number of scan lines in each scanned volume is therefore low e.g. 2000 for a volume scan rate of 5 volumes per second. The aim of this thesis is to investigate whether or not modern electronic and image processing techniques can overcome this fundamental problem. During the first phase of our study, a microcomputer based C-scan test-rig system including hardware and software has been constructed to investigate the effectiveness of real-time image processing in compensating for the fundamental sparcity of echo data. This was investigated initially since C-scans suffer from the same sparcity of echo data as 3D scans. After the promising results obtained from this system using a number of image processing techniques, a hand-held 3D ultrasound system including hardware and software based on one of the commercial scanners (Dynamic Imaging C2000) has been constructed to extend our study to 3D. A number of test objects in addition to volunteers were scanned to investigate the feasibility of real-time 3D ultrasound imaging. Finally, a specification for real-time ultrasound imaging is discussed.

The project involves an experimental analysis of achievable accuracy in the different steps of radiotherapy, including investigations of the basic dosimetry chain, considering the individual steps concerned in dosimeter and treatment beam calibration and some aspects of treatment planning and dose delivery. The results are investigated from these various areas and are analysed in terms of overall achievable accuracy and its relationship to clinical requirements and to quality assurance programmes. It is concluded that required clinical accuracy can be achieved in radiotherapy treatment, but needs careful control at all stages of the radiotherapy process. In addition a previously-designed geometric phantom, developed for a UK national dosimetry intercomparison and audit system has been used to extensively test achievable accuracy of dosimetry and some basic treatment planning parameters and processes in one department. This has been used as the basis to develop an interdepartmental audit in Scottish and other radiotherapy centres (the so-called Scottish+ audit group, within the UK radiotherapy dosimetry audit network). Also a semianatomic phantom has been developed to allow reasonably realistic audit of various representative treatment sites. This has been constructed from epoxy-based tissue substitute phantom materials. It has been extensively tested before audit use, by measuring the whole range of possible irradiation situations on five megavoltage photon beams, calculating dose distributions using the Edinburgh in-house treatment planning system and CADPLAN, and comparing measured results to expected values. Some small differences can be linked to the phantom materials. Others can be linked to small discrepancies in the testing department, for example in planning data, machine performance, etc.

This thesis proposes that IOUSS is as accurate as IOE scanning in the detection of small metastases at the time of primary colon resection, and that IOE scanning in the follow up period will detect new metastases as they develop. Patients who have metastases detected in this way will be suitable for hepatic resection and have an improved 5 year survival. The detailed staging of patients with regard to hepatic metastases has been used to clarify the relationship between the presence of hepatic metastases, and elevation in the level of serum CEA. IOUSS is shown to be as accurate as IOE scanning in the detection of patients with metastases at the time of operation. IOUSS detects more patients with metastases than IOE, this difference does not reach statistical significance. IOE scanning can detect the appearance and growth of metastases in patients following colonic resection. IOE scanning cannot be used as a routine form of follow up as patients are reluctant to undergo repeated scans over a two year period, recruitment to this part of the study was very poor. IOE scanning and IOUSS are able to detect very small hepatic metastases as the only site of recurrence in patients following colonic surgery. Two patients with small metastases went on to have a hepatic resection. Unfortunately both of these patients died within 2 years of hepatic surgery. Early detection of metastases by IOE and IOUSS scanning did not therefore improve patients survival. The results of IOE scanning and IOUSS have been used to define levels of serum CEA which are likely to be related to the presence of hepatic metastases both at the time of colonic resection and during follow up. In conclusion IOUSS is a sensitive and accurate method of detecting hepatic metastases from colorectal cancer at the time of operation. This information could not be used to improve survival. The appearance of hepatic metastases is related to the elevation of serum CEA.

No description available.