Demonstration of improved image resolution for larger focal spot sizes by decreasing anode angles in clinical settings

摘要

Image-guided neuro-endovascular interventional studies often require a high resolution image quality which requires theuse of small focal-spot sizes. There is always a tradeoff while choosing focal-spot sizes. The use of small- focal-spotsgives better spatial resolution but limits x-ray tube output and tube loading. The use of larger- focal-spots provides betterheat dissipation capacity and higher x-ray output but gives rise to geometric blurring hence loss of spatial resolution. Amethod has been proposed which incorporates the use of the line-focus principle that can achieve a smaller projectedfocal-spot while keeping the actual focal-spot size as the medium focal-spot. Here the gantry is tilted to reduce theeffective anode angle, hence the central axis is tilted producing a smaller projected focal-spot. This was tested byacquiring images of a Pipeline stent in the right jugular vein and a guidewire of a rabbit using a high-resolution CMOSbasedfluoroscopic detector with 75um pixels. Also the gantry was tilted in the anode-cathode direction shifting thecentral axis to the anode side of the beam and the rabbit was aligned with the new perpendicular ray. Acquired images,for small focal-spot, medium focal-spot, and 7-degree tilted medium focal-spot were compared. While small focal-spotimages demonstrated superior resolution, and both tilted and untilted medium focal spot images demonstrated lowernoise due to the increased tube output the tilted medium focal spot images exhibited improved resolution. Line profilesand quantitative measures of generalized relative object detectability confirmed the advantage of the tilted medium focalspotmethod above all.