Electron beam computed tomography: Challenges and opportunities

Abstract

In computed tomography (CT), a cross-sectional view is developed by measuring and analyzing the x-ray attenuation of a thin x-ray fan that rotates around the subject. There are two ways to make the x-ray fan. One is to physically rotate an x-ray tube around the subject. The other way is to scan an electron beam around a fixed tungsten anode ring that surrounds the subject. The medical application we address is to non-invasively determine risk of coronary disease in subjects who are symptom-free. Subjects lie still, holding their breath and drugs to lower heart rate are administered in order to reduce image blur. The advantage of electron beam CT imaging is speed. In addition to higher cost, the disadvantage is low x-ray source brightness so scan speed is limited by signal strength. We explore the possible improvement of using electrostatic rather than magnetic beam deflection incorporating a new method that provides little or no deflection aberrations even at large deflection angles. Since shielding electrical fields is very efficient, it is possible to operate a multitude of electron guns in close proximity each scanning a short segment of the anode ring. By modulating each gun at a signature frequency, all guns could operate simultaneously and x-ray signals can be separated by the modulation frequency. This idea should allow increasing x-ray scan speed by at least 10-fold. This would allow a cardiac CT scan to be made on a subject at elevated heartbeat while on a treadmill – a condition well known to accentuate heart malfunctions.