Dual-energy subtraction angiography (DESA) using fast kV switching has received attention for its potential to reduce misregistration artifacts in thoracic and abdominal imaging where patient motion is difficult to control; however, commercial interventional solutions are not currently available. The purpose of this work was to adapt an x-ray angiography system for 2D and 3D DESA. The platform for the dual-energy prototype was a commercially available xray angiography system with a flat panel detector and an 80 kW x-ray tube. Fast kV switching was implemented using custom x-ray tube control software that follows a user-defined switching program during a rotational acquisition. Measurements made with a high temporal resolution kV meter were used to calibrate the relationship between the requested and achieved kV and pulse width. To enable practical 2D and 3D imaging experiments, an automatic exposure control algorithm was developed to estimate patient thickness and select a dual-energy switching technique (kV and ms switching) that delivers a user-specified task CNR at the minimum air kerma to the interventional reference point. An XCAT-based simulation study conducted to evaluate low and high energy image registration for the scenario of 30-60 frame/s pulmonary angiography with respiratory motion found normalized RMSE values ranging from 0.16% to 1.06% in tissue-subtracted DESA images, depending on respiratory phase and frame rate. Initial imaging in a porcine model with a 60 kV, 10 ms, 325 mA / 120 kV, 3.2 ms, 325 mA switching technique demonstrated an ability to form tissuesubtracted images from a single contrast-enhanced acquisition.
Cardiovascular disease is currently the leading cause of mortality worldwide. Digital subtraction angiography
(DSA) is widely used to enhance the visibility of small vessels and vasculature obscurred by overlying bone and lung fields
by subtracting a mask and contrast image. However, motion between these mask and contrast images can introduce artifacts
that can render a study non-diagnostic. This makes DSA particularly unsuccessful for cardiac imaging. A method called
dual-energy, or energy subtraction angiography (ESA), was proposed in the past as an alternative for vascular imaging,
however it was not pursued because experimental results suggested that image quality was deemed as poor and inferior to
DSA. Image quality for angiography comes down to iodine signal and noise. In this paper we investigate the fundamental
iodine signal and noise analysis of ESA and compare it to DSA.
Method: We developed a polyenergetic and monoenergetic theoretical model for iodine signal and noise for both
ESA and DSA. We validated our polyenergetic model by experiment where ESA and DSA images of a vascular phantom
were acquired using an x-ray system with a flat panel CsI Xmaru1215CF-MPTM (Rayence Co., Ltd., Republic of Korea)
detector. For ESA low and high applied tube voltages of 50 kV and 120 kV (2.5 mmCu), respectively, and for DSA the
applied tube voltage was 80 kV. Iodine signal-to-noise ratio (SNR) per entrance exposure was calculated for each iodine
concentration for both ESA and DSA.
Results: Our measured iodine SNR agreed well with theoretical calculations. Iodine SNR for ESA was relatively
higher than DSA for low iodine mass loadings, and as iodine mass loading increases iodine SNR decreases.
Conclusions: We have developed a model for iodine SNR for both DSA and ESA. Our model was validated with
experiment and showed excellent agreement. We have shown that there is potential for obtaining iodine-specific images
using ESA that are similar to DSA.