This thesis investigates the feasibility of designing a simple nuclear medicine data processing system based on an inexpensive microcomputer system, which is affordable to small hospitals and to developing countries where resources are limited. Since the main need for a computer is to allow dynamic studies to be carried out, the relevant criteria for choosing the computer are its speed and memory capacity. The benchmark chosen for these criteria is renography, one of the commonest nuclear medicine procedures. The Acorn Archimedes model 310 microcomputer was found to meet these requirements, and a suitable camera-computer interface has been designed. Because of the need for ensuring that the gain and offset controls of the interface are set optimally before connecting to the camera, it was necessary to design a circuit which produces a test pattern on the screen for use during this operation. Having also developed and tested the data acquisition and image display software successfully, atttention was concentrated on finding ways of characterising and measuring the performance of the computer interface and the display device, two important areas which have been largely neglected in the quality control of camera-computer systems. One of the characteristics of the interface is its deadtime. A procedure has been outlined for measuring this by means of a variable frequency pulse generator and also for interpreting the data correctly. A theoretical analysis of the way in which the interface deadtime affects the overall count rate performance of the system has also been provided. The spatial linearity, resolution and uniformity characteristics of the interface are measured using a special dual staircase generator circuit designed to simulate the camera position and energy signals. The test pattern set up on the screen consists of an orthogonal grid of points which can be used for a visual assessment of linearity, while analysis of the data in memory enables performance indices for resolution, linearity and uniformity to be computed. The thesis investigates the performance characteristics of display devices by means of radiometric measurements of screen luminance. These reveal that the relationship between screen luminance and display grey level value can be taken as quadratic. Characterisation of the display device in this way enables software techniques to be employed to ensure that screen luminance is a linear function of display grey level value; screen luminance measurements, coupled with film density measurements, are also used to optimise the settings of the display controls for using the film in the linear range of its optical densities. This in turn ensures that film density is a linear function of grey level value. An alternative approach for correcting for display nonlinearity is by means of an electronic circuit described in this thesis. Intensity coding schemes for improving the quality of grey scale images can be effective only if distortion due to the display device is corrected for. The thesis also draws attention to significant variations in film density which may have their origins in nonuniformities in the display screen, the recording film, or in the performance of the film processor. The work on display devices has been published in two papers.

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Successful treatment of myocardial infarction requires anearly and accurate diagnosis. Recent studies have shown thatacute myocardial scintigraphy has a high predictive value forprognosis of myocardial events. Three dimensional (3D)perfusion data obtained with SPECT are however very rare in theemergency department (ED). We have developed a mobile tomographic system for myocardialscintigraphy, which can be used in the ED. The objectives ofthe studies presented were:     To develop software and hardware for a mobile tomographicgamma camera system: the Cardiotom     To demonstrate that a mobile tomographic system can beused in a clinical situation     To evaluate the limitations of Ectomography when usingfiltered back projection for reconstruction     To develop a method of reconstruction that compensatesfor the incomplete data acquisition associated with theacquisition geometry of Ectomography Three prototypes of a mobile tomographic gamma camera systemhave been designed and built at the Division of MedicalEngineering, which all have been used in a clinical setting.The systems are based on Ectomography, a limited view anglemethod, also developed by us. Instead of rotating the entiregamma camera detector around the patient as in SPECT, a slanthole collimator is rotated in front of a stationary detector.Since short imaging times are important in the ED and the heartonly occupies a small area of the detector, system sensitivityhas been increased by dividing the collimator into segmentswith different projection directions. In myocardial imaging, 4segments are used and within 10 minutes from the start ofacquisition, reconstructed short axis view sections areavailable for interpretation. Using the Cardiotom in an experimental animal study, weverified that the system could be used to quantify myocardialarea at risk and final infarct size. This conclusion was madefrom a comparison of images obtained from the Cardiotom andpathological staining of the myocardium, analysedpost-mortem. Inherent limitations of Ectomography were evaluated withboth phantom studies and computer simulated data, reconstructedusing filtered back-projection Results show that moderatedeviation from optimal position of the detector with respect tothe myocardium will have little or no influence on thediagnostic information when assessed from short axis sectionimages and polar tomograms. However, long axis section imagesappear elongated when reconstructed using filteredback-projection. We have shown that this elongation distortion can besuppressed using iterative reconstructions techniques, and wehave implemented such an algorithm, called three-dimensionalTotal Variation Expectation Maximisation (3DTV-EM). Resultswere that elongation distortion was reduced and depthresolution improved. The reconstruction technique was alsoevaluated for SPECT reconstruction and was found to decreasethe noise in reconstructed images, when compared to thetwo-dimensional TV-EM algorithm. Noise pattern were also foundto be more uniform for the 3DTV-EM algorithm compared totwo-dimensional TV-EM. In conclusion, we have shown that the Cardiotom may beuseful in a clinical acute setting, providing valuablediagnostic information. Rapid positioning is possible, sincemoderate deviation from optimal positioning will cause few orno artefacts. Image quality can be improved if iterativetechniques are used for image reconstruction instead offiltered back-projection. <b>Keywords</b>: acute studies, myocardial infarction,scintigraphy, mobile gamma camera, tomography.

A new gamma imaging method, Neutron Stimulated Emission Computed Tomography (NSECT), is being developed to non-invasively and non-destructively measure and image elemental concentrations in vivo. In NSECT a beam of fast neutrons (3 - 5 MeV) bombards a target, inelastically scattering with target nuclei and exciting them. Decay from this excited state produces characteristic gamma emissions. Collecting the resulting gamma energy spectrum allows identification of elements present in the target. As these gamma rays range in energy from 0.3 - 1.5 MeV, outside the useable energy range for existing gamma cameras (0.1 - .511 MeV), a new gamma imaging method must be developed. The purpose of this dissertation is to design and develop a near-field (less then 0.5 m) high-energy (0.3 - 1.5 MeV) gamma camera to facilitate planar NSECT imaging. Modifying a design implemented in space-based imaging (focus of infinity), a prototype camera was built. Experimental testing showed that the far-field space-based assumptions were inapplicable in the near-field. A new mathematical model was developed to describe the modulation behavior in the near-field. Additionally, a Monte Carlo simulation of the camera and imaging environment was developed. These two tools were used to facilitate optimization of the camera parameters. Simulated data was then used to reconstruct images for both small animal and human fields of view. Limitations of the camera design were identified and quantified. Image analysis demonstrated that the camera has the potential to identify regions of interest in a human field of view. / Dissertation

Staging is critical in the management of cancer. Sentinel lymph node (SLN) biopsy is one method used in the assessment of cancer spread. SLN procedures are standard practice in the management of some cancers although; these procedures have only recently been developed and refined. SLN procedures are commonly used in the management of melanomas and breast cancers in patients with no evidence of metastatic disease on clinical exam. SLN procedures include detection, localization, and assessment of SLNs. The detection/localization components vary in technique and rates of success. The procedures with the least number of detection/localization techniques generally include the use of blue dye or the use of a radiotracer with intraoperative gamma counting. The most complex procedures involve the use of blue dye, the use of a radiotracer with preoperative gamma imaging and preoperative gamma counting, intraoperative gamma counting, or some combination of these techniques. The ideal procedure for SLN would include all the listed techniques however; all facilities do not incorporate the most complete procedure, for different reasons. An investigation using a small FOV (5 in x 5 in) gamma camera intraoperatively for SLN procedures in melanoma and breast cancer patients was performed. A smaller FOV camera is capable of obtaining some of the same information as a conventional gamma camera. It is possible that centers, which do not or are not able to take advantage of preoperative imaging, may find the use of a smaller FOV gamma camera in the operating room useful. The investigation consisted of a total of 41 patients; it was split into two studies, Study 1: melanoma and study 2: breast cancer. The melanoma study found the added use of a smaller FOV camera under the parameters of this study to be minimal. Study 2 was broken into two branches; branch 1: camera/probe/dye and branch 2: probe/dye, for a comparison study. Comparing the two branches did not show the smaller FOV camera to reduce the time spent in the operating room versus using the probe and blue dye.

<p>Successful treatment of myocardial infarction requires anearly and accurate diagnosis. Recent studies have shown thatacute myocardial scintigraphy has a high predictive value forprognosis of myocardial events. Three dimensional (3D)perfusion data obtained with SPECT are however very rare in theemergency department (ED).</p><p>We have developed a mobile tomographic system for myocardialscintigraphy, which can be used in the ED. The objectives ofthe studies presented were:</p><p>    To develop software and hardware for a mobile tomographicgamma camera system: the Cardiotom</p><p>    To demonstrate that a mobile tomographic system can beused in a clinical situation</p><p>    To evaluate the limitations of Ectomography when usingfiltered back projection for reconstruction</p><p>    To develop a method of reconstruction that compensatesfor the incomplete data acquisition associated with theacquisition geometry of Ectomography</p><p>Three prototypes of a mobile tomographic gamma camera systemhave been designed and built at the Division of MedicalEngineering, which all have been used in a clinical setting.The systems are based on Ectomography, a limited view anglemethod, also developed by us. Instead of rotating the entiregamma camera detector around the patient as in SPECT, a slanthole collimator is rotated in front of a stationary detector.Since short imaging times are important in the ED and the heartonly occupies a small area of the detector, system sensitivityhas been increased by dividing the collimator into segmentswith different projection directions. In myocardial imaging, 4segments are used and within 10 minutes from the start ofacquisition, reconstructed short axis view sections areavailable for interpretation.</p><p>Using the Cardiotom in an experimental animal study, weverified that the system could be used to quantify myocardialarea at risk and final infarct size. This conclusion was madefrom a comparison of images obtained from the Cardiotom andpathological staining of the myocardium, analysedpost-mortem.</p><p>Inherent limitations of Ectomography were evaluated withboth phantom studies and computer simulated data, reconstructedusing filtered back-projection Results show that moderatedeviation from optimal position of the detector with respect tothe myocardium will have little or no influence on thediagnostic information when assessed from short axis sectionimages and polar tomograms. However, long axis section imagesappear elongated when reconstructed using filteredback-projection.</p><p>We have shown that this elongation distortion can besuppressed using iterative reconstructions techniques, and wehave implemented such an algorithm, called three-dimensionalTotal Variation Expectation Maximisation (3DTV-EM). Resultswere that elongation distortion was reduced and depthresolution improved. The reconstruction technique was alsoevaluated for SPECT reconstruction and was found to decreasethe noise in reconstructed images, when compared to thetwo-dimensional TV-EM algorithm. Noise pattern were also foundto be more uniform for the 3DTV-EM algorithm compared totwo-dimensional TV-EM.</p><p>In conclusion, we have shown that the Cardiotom may beuseful in a clinical acute setting, providing valuablediagnostic information. Rapid positioning is possible, sincemoderate deviation from optimal positioning will cause few orno artefacts. Image quality can be improved if iterativetechniques are used for image reconstruction instead offiltered back-projection.</p><p><b>Keywords</b>: acute studies, myocardial infarction,scintigraphy, mobile gamma camera, tomography.</p>

The optimisation of image quality in medical imaging techniques is a significant factor in favourable patient prognoses. The number of counts in a nuclear medicine image is one factor in determining the diagnostic value of the image. The current study aims to determine the variation in counts in whole-body bone scan images with patient height and weight. Three separate studies were undertaken as part of the investigation. First, 65 whole-body bone scans were analysed together with patient height, weight, age and sex. Weight was found to the most important anatomy influence on image counts. However, significant influences from patient sex and age meant that a useful relationship between image counts and patient anatomy based solely on height and weight could not be determined. For the second study, a model of General Electric Millennium MG gamma camera was created and validated within the SIMIND Monte Carlo software. The results indicate that the model is an accurate representation of the gamma camera. Third, the 4D NCAT whole-body patient phantom was modified to represent the average male and female clinical study participants. The phantoms were used in conjunction with the gamma camera model to simulate the whole-body bone scan procedure. The counts in the simulated images were consistent with the average measured counts of the clinical study indicating that it is feasible to use the NCAT phantom for nuclear medicine bone imaging. However, the phantom’s method of activity distribution should be refined to allow a more realistic distribution of activity throughout the skeleton.

Ce travail de thèse a été effectué dans le cadre de la collaboration CLaRyS, qui a pour objectif le développement d'une caméra gamma multi-collimatée et d'une caméra Compton pour les applications médicales notamment pour le contrôle en ligne de l’hadronthérapie. La caméra Compton pourrait également être utilisée en médecine nucléaire. L’objectif principal de ce travail de thèse était la caractérisation complète des détecteurs qui composent les caméras et le test des deux systèmes complets avec des faisceaux d’ions cliniques. En parallèle, des études en simulation ont permis d'estimer les performances de la caméra Compton à la fois pour le contrôle de l’hadronthérapie et la médecine nucléaire / This thesis work has been carried out within the CLaRyS French collaboration, which is involved in the development of a multi-collimated gamma camera and a Compton camera for the application in ion beam therapy monitoring through prompt-gamma detection and in nuclear medicine examinations. The main goal of the thesis was the complete characterization of the camera detector components, and the test of the whole systems on clinical ion beams. In parallel, simulation works have been performed to assess the performance of the Compton camera for the measurement of ion range during proton and carbon therapy, and for single photon emission computed tomography application in the nuclear medicine field