Development of a Mobile Tomographic Gamma Camera Based on Ectomography - Cardiotom

University dissertation from Stockholm : Elektrotekniska system

Abstract: 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 EctomographyThree 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.Keywords: acute studies, myocardial infarction,scintigraphy, mobile gamma camera, tomography.

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