FastCircularTomography DeviceforCardiac Imaging:ImageDeflection Mechanism and Evaluation

A circular tomography system forcardiac imaging isde- scribed andmeasurements ofthedetector system arepresented. Fast tomographic motion isobtained withacustom-made rotating focal spot X-ray tubecombined withservo-operated scanning mirrors that deflect theoptical imagebetween alarge field ofviewimageintensifier and television camera. Themotion ofthedeflection mirrors islocked in frequency andphasetotheposition ofthefocal spotwithprecision analog electronics. Initial measurements onthesystem components in- dicate that circular tomograms ofthebeating heart canbeobtained in 1/60satrates ashighas30/s. Imagedegradation duetofocal spot tracking error isminimal; however, theoptical temporal lagofaP-20 typeimage intensifier output phosphor results inafactor ofthree con- trast loss formillimeter-sized objects. Alinear system analysis incon- junction withthemeasured temporal stepresponse ofthephosphor is ingoodagreement withthemagnitude ofthis contrast loss.