Overcoming x-ray tube small focal spot output limitations for high resolution region of interest imaging
2012
We investigate methods to increase x-ray tube output to enable improved quantum image quality with a higher
generalized-NEQ (GNEQ) while maintaining a small focal-spot size for the new high-resolution Micro-angiographic
Fluoroscope (MAF) Region of Interest (ROI) imaging system. Rather than using a larger focal spot to increase tubeloading
capacity with degraded resolution, we evaluated separately or in combination three methods to increase tube
output: 1) reducing the anode angle and lengthening the filament to maintain a constant effective small focal-spot size, 2)
using the standard medium focal spot viewed from a direction on the anode side of the field and 3) increasing the frame
rate (frames/second) in combination with temporal filter. The GNEQ was compared for the MAF for the small focal-spot
at the central axis, and for the medium focal-spot with a higher output on the anode side as well as for the small focal
spot with different temporal recursive filtering weights. A net output increase of about 4.0 times could be achieved with
a 2-degree anode angle (without the added filtration) and a 4 times longer filament compared to that of the standard
8-degree target. The GNEQ was also increased for the medium
focal-spot due to its higher output capacity and for the
temporally filtered higher frame rate. Thus higher tube output, while maintaining a small effective focal-spot, should be
achievable using one or more of the three methods described with only small modifications of standard x-ray tube
geometry.
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