Approaches to interventional fluoroscopic dose curves

Abstract

Modern fluoroscopes used for image‐based guidance in interventional procedures are complex X‐ray machines, with advanced image acquisition and processing systems capable of automatically controlling numerous parameters based on defined protocol settings. This study evaluated and compared approaches to technique factor modulation and air kerma rates in response to simulated patient thickness variations for four state‐of‐the‐art and one previous‐generation interventional fluoroscopes. A polymethyl methacrylate (PMMA) phantom was used as a tissue surrogate for the purposes of determining fluoroscopic reference plane air kerma rates, kVp, mA, and variable copper filter thickness over a wide range of simulated tissue thicknesses. Data were acquired for each fluoroscopic and acquisition dose curve within each vendor's default abdomen or body imaging protocol. The data obtained indicated vendor‐ and model‐specific variations in the approach to technique factor modulation and reference plane air kerma rates across a range of tissue thicknesses. However, in the imaging protocol evaluated, all of the state‐of‐the‐art systems had relatively low air kerma rates in the fluoroscopic low‐dose imaging mode as compared to the previous‐generation unit. Each of the newest‐generation systems also employ Cu filtration within the selected protocol in the acquisition mode of imaging; this is a substantial benefit, reducing the skin entrance dose to the patient in the highest dose‐rate mode of fluoroscope operation. Some vendors have also enhanced the radiation output capabilities of their fluoroscopes which, under specific conditions, may be beneficial; however, these increased output capabilities also have the potential to lead to unnecessarily high dose rates. Understanding how fluoroscopic technique factors are modulated provides insight into the vendor‐specific image acquisition approach and may provide opportunities to optimize the imaging protocols for clinical practice.PACS number: 87.59.C‐

Comparison of image quality of an abdominal acquisition mode of angiography systems from four major manufacturers

“…The air kerma rate was in the range of 2.3-32.7 mGy/s. As already said, the air kerma rate for System C is very low, but the others correspond to values published in the literature [7] for 36 cm of PMMA for abdominal acquisition modes of five different angiography systems from three major manufacturers (17-50 mGy/s for 4 fr/s, which corresponds to values 13-38 mGy/s for 3 fr/s).…”

“…This is most likely a result of postprocessing, mainly high pass filtering. [7,30,31] This effect appeared also for System A for the static phantom.…”

“…The functioning of the ADRC for angiography systems is described in the literature. [3,[5][6][7] The frame length is chosen in such a way that the motion unsharpness is minimized (the frame length for the imaging of limb arteries would be too long for the imaging of coronary arteries). Higher voltage and higher spectral filtration can decrease the image contrast, but postprocessing may compensate for this, so it might not be apparent to the image observer.…”

“…[10][11][12] Thus the attenuation of the patient, preset detector dose value, performance of the X-ray tube and postprocessing are the main factors that influence the patient's dose and image quality. [3,6,7] Assessment of image quality of patient images is usually subjective, because it relies on human perception, albeit of highly trained individuals. Many of physical image quality tests are also subjective, and prone to inter-and intra-observer variability.…”

Angiographers no longer need to avoid digital zoom

“…We have observed similar characteristics in phantom studies with angiographic equipment from other manufacturers. The behaviour of X-ray tube voltage (kVp), filtration, focal spot and milli-amp seconds of tube current (mAs) as a function of attenuator thickness is well described in the literature (Lin, 2008;Wunderle, Rakowski, & Dong, 2016). An automatic dose increase with image magnification has been shown to be unnecessary for overall image quality or conspicuity of small vessels.…”