Micro-Angiographic Fluoroscope: Comparison for Different Input Phosphors

Although flat panel detectors are preferred for image-guided interventional endo-vascular treatments of stroke, they still have limitations in spatial resolution and excess additive noise, which restricts their low-dose performance. The Micro-Angiographic Fluoroscope (MAF), a CCD-based region-of-interest indirect X-ray imager recently developed, can meet the needs for high-resolution, high-sensitivity, real-time image guidance. Although the prototype MAF has better resolution (MTF) and detective quantum efficiency (DQE) than a standard flat panel detector, its performance could be improved by a change in the phosphor. The spatial resolution of such X-ray-to-light converting phosphors is limited by stochastic blurring and k-fluorescent X-ray reabsorption. Thinner phosphors generally improve resolution at the cost of lowering quantum detection efficiency (QDE) and increasing Swank noise, while thicker phosphors provide better absorption at the expense of spatial resolution. Two other Hamamatsu CsI(Tl) phosphors, 300- μm-thick HR, and 500- μm-thick HR, both without front reflective surface, were compared with the current 300- μm HL phosphor with front reflective surface. The phosphors were evaluated by comparing the MTF, NNPS, and DQE of the MAF detector used with each phosphor. All detector configurations showed linearity and quantum noise limited operation for a large range of exposures appropriate for both fluoroscopy and angiography. While the 300- μm HR type prototype demonstrated better resolution than the 500- μm HR type, the latter demonstrated better overall DQE and improved resolution compared to the original 300- μm HL, suggesting it would be the better choice for the MAF design.