Comparison of beam‐hardening and K‐edge filters for imaging barium and iodine during fluoroscopy

Abstract

This study investigated the dose reduction performance of several beam-hardening and K-edge filter materials for the imaging of barium or iodine during fluoroscopy. A computer model was developed to simulate the effect of added filtration on entrance exposure rate (Xp), integral dose rate (Di), contrast (C), signal to noise ratio (SNR), imaging performance per dose (SNR2/Di), and tube load. The model incorporated the response characteristics, in both manual and automatic control modes of operation, of fluoroscopic systems to increasing or decreasing x-ray intensity at the input of the image intensifier. Input parameters to the computer model included choice of filter material and thickness, a barium or iodine test object, tube potential, phantom thickness, a CsI input phosphor, and a set of algorithms for controlling the fluoroscopic system. In all cases, the performance of systems with added filtration was judged with respect to a reference system operating under comparable conditions. In general, either beam-hardening or K-edge filters provided a significant reduction in entrance exposure and integral dose rates, but with an attendant increase in tube load. For a fluoroscopic system constrained to follow a representative automatic brightness control algorithm, added filtration provided a reduction in entrance exposure and integral dose rates for all phantom or uniformly distributed barium thickness. However, the imaging performance per dose, in some cases, decreased rapidly and was less than that of the reference system at large thicknesses. Only as change in the algorithm controlling the kVcp and mA operating points on the fluoroscopic system provided an imaging performance per dose greater than the reference system's at large thicknesses. The practical implementation of adding filtration to fluoroscopic systems is most simply accomplished with beam-hardening filters rather than K-edge filters. However, the systems with K-edge added filtration can provide slightly better performance when used over a limited range of phantom thicknesses such as the range normally associated with pediatric patients.

Investigation of the Practical Aspects of an Additional 0.1 Mm Copper X-Ray Spectral Filter for Cine Acquisition Mode Imaging in a Clinical Care Setting

“…That Monte Carlo experiment used phantoms of thickness 10 to 30 cm and was performed to maintain fixed image quality. Similarly, Gagne et al (1994) predicted a maximum 25% improvement in dose efficiency (SNR 2 /absorbed dose) attributable to a 0.195 mm Cu filter. That work used a barium rather than iodine contrast target.…”

“…In particular, skin dose increases as the proportion of low energy photons in an x-ray beam increases. X-ray spectral filters, metallic films or sheets, placed between the x-ray source and patient can substantially reduce x-ray dose rate by preferentially attenuating low energy x rays (Burgess 1984;Nagel 1989;Carrier and Béïque 1992;Gagne et al 1994;Martin 1995;Massoumzadeh et al 1998). However, these filters can also be expected to reduce image quality through a decrease in contrast between tissues or tissue and contrast medium (Burgess 1984;Nagel 1989;Gagne et al 1994;Massoumzadeh et al 1998).…”

Dose optimization in cardiac x‐ray imaging

“…31,29 Gadolinium (Gd) has had positive reviews for dose optimization, demonstrating enhanced contrast for iodine and barium imaging while substantially reducing radiation dose. 32 Gadolinium oxysulphide (Gd 2 O 2 S) compound filters have shown substantial dose reductions with minimal loss of contrast at lower peak tube voltage; 33 an improvement in dose efficiency of 40% was reported using 140 mg cm −2 Gd 2 O 2 S. 19 Gadolinium has been recommended for pediatric x-ray imaging, 34,35 and specifically for cardiac iodine-based pediatric imaging 36,37 because of a concern for tube loading relating to adults. The reason for this is that reduction in beam in-tensity from using Gadolinium filtration must be compensated for by higher radiographic factors in order to obtain adequate x-ray images, and for x-ray systems of the past, tube loading was an issue when higher factors were used.…”

Optimisation of Image Quality and Dose

“…For the contrast meal, a material with high specific mass density is used (Ba, K-edge at 37.4 keV). Gagne et al (1994) call the IQF a measure of imaging performance per dose. They have evaluated, for the imaging of a barium test object that the maximum of the squared signal-to-noise ratio (SNR 2 ) per dose for water-phantom thicknesses of 10-30 cm lies in the range of 59.5-63 kV.…”