Purpose: The resolution of x-ray fluoroscopy images is dependent on detector characteristics and x-ray focal spot penumbra blur. The purpose of this work was to investigate the influence of focal spot size and geometric magnification (M) on the modulation transfer function (MTF) of flat panel fluoroscopic imaging systems. Method and Materials: The MTF of was measured for two x-ray detectors, three different focal spot sizes, and M in the range 1.04 to 1.70. The MTF was measured both parallel and perpendicular to the cathode-anode direction using an angled edge device method. MTF spectra were used to calculate the noise equivalent aperture (NEA, mm2), which is the reciprocal of the 2D integral of the 1D MTF. Results: There were marked changes in MTF and NEA between systems and as a function of geometric magnification for the three focal spots. Comparing the two systems, that with the larger pixel size had higher NEA for all focal spots and magnification factors. For the nominal 0.4 mm focal spot, system resolution improved with magnification up to M=1.3 and then remained unchanged for 1.3 < M ≤ 1.7. For the 0.8 mm focal spot, the system resolution was largely unchanged in the range 1.04 ≤ M < 1.3 and then decreased for 1.3 < M < 1.7. For the 1.2 mm focal spot, the system resolution consistently decreased for all 1.04 < M ≤ 1.07. For all focal spots, resolution was better maintained in the direction parallel to the cathode-anode direction than in the orthogonal direction. Conclusion: Methods to assess the MTF and NEA of digital fluoroscopy systems were developed. The MTF and NEA demonstrated changes in resolution between the two detectors and three focal spot sizes, and with variable geometric magnification.

Purpose: Leaded eyewear is commonly recommended for physicians routinely performing interventional fluoroscopy procedures. However, radiation‐attenuating glasses and goggles can be heavy and uncomfortable. Recently, several new lightweight eyewear designs have become available. Two such designs were investigated to determine how well they are able to reduce eye dose under clinical conditions. Materials and Methods: The eye dose was measured using OSL nanodot dosimeters positioned on a Rando head phantom. The phantom was positioned next to an acrylic phantom to duplicate the position of an operator exposed to scattered x‐rays. Eye dose was measured with and without leaded eyewear in three different positions: head directed toward the scatter volume and angled 45 and 90 degrees. The eyewear investigated included standard style glasses with 0.75 mm lead equivalent lenses (Type A), sport‐wrap glasses with 0.75 mm lead equivalent lenses (Type B) and a panorama shield with 0.07 mm lead equivalent acrylic lenses (Type C). Results: With the phantom head directed toward the scatter volume, the eye dose was reduced by 90%, 88% and 61% for Type A, B and C, respectively. Each value is lower than expected from the attenuation of the lenses alone, indicating backscatter is a significant contribution. At 90 degrees, eye protection dropped somewhat for Type A (75%), significantly for Type B (31%), while remaining the same for Type C (61%). The poor protection afforded by Type B at 90 degrees was primarily due to limited side coverage. Conclusion: Even though the lead equivalent thickness of Type C is much lower than other designs tested, increased side coverage resulted in nearly equivalent eye dose reduction when side exposure was predominant. The use of 0.75 mm lead equivalent lenses appears to have diminishing returns given that backscatter and side exposure are a significant source of eye exposure.