In 1980 when DSA was introduced there was initial enthusiasm that the technique would, for the first time, enable the ability to perform angiographic procedures, on a wide spread basis, using an intravenous injection of contrast medium. Unfortunately, this enthusiasm rather quickly dissipated as it became evident that because of the overlap of arteries and veins on any single projection, multiple acquisitions were required for adequate diagnostic evaluations (each of these was associated with a very significant contrast medium dose as well as additional x-ray exposure). Quickly, the use of the real time digital imaging capabilities was adapted for use with intra-arterial contrast injections. Conventional DSA provides 2D images at variable frame rates (a time series). Similarly, X-ray fluoroscopy offers a 2D display at high frame rates. Over the last 3 decades, DSA has been used primarily in conjunction with intra-arterial injections for diagnostic purposes while other angiographic modalities such as CTA and MRA have been used in connection with intravenous injections. Although current 3D rotational DSA does provide a 3D reconstruction, the images contain no temporal information, and although vessel overlap can be overcome to some extent through the use of rotational views, the combination of arteries and veins in the reconstructed volume often makes optimal visualization difficult. Because of the geometrical constraints that limit positioning of the C-arm gantries fluoroscopy implemented using C-arm systems often cannot provide optimal views for delivery and deployment (working views) of interventional devices. This not only impairs the safety of some interventions but also often results in an inability to offer patients endovascular treatment, requiring that they undergo more invasive traditional surgical interventions. During the past several years we have developed MRA techniques involving sub-Nyquist acquisition and constrained reconstruction that permit acceleration factors up to 1000. These have removed the traditional tradeoffs between spatial and temporal resolution and have provided contrast-enhanced MRA techniques using as little as 1 cc of intravenous gadolinium and phase contrast techniques that have facilitated new applications such as non-invasive measurement of vascular pressure gradients 1-4. The principles of constrained reconstruction have also been extended to other areas of medical imaging where significant dose reductions or SNR increases have been reported 5-7. Many of these principles can be applied to X-ray DSA to greatly increase the rate at which 3D time resolved volumes can be obtained. We have recently developed a C-arm based 4D DSA method that provides a series of fully time resolved 3D DSA volumes (4D-DSA) at frame rates of up to 30/s with higher temporal and spatial resolution than current MRA and CTA techniques. We also have developed a 4D Fluoroscopy method that permits fluoroscopic viewing of virtual roadmaps at any desired angle without a need to reposition the C-arm gantries. The purpose of the proposed research is to validate these techniques and to bring them to a point where they are ready for wide spread dissemination and clinical usage.
The proposed work will provide new tools that will significantly expand the diagnostic utility and interventional capabilities of C-Arm x-ray systems while reducing X-ray exposure and iodinated contrast medium dose. The proposed techniques will provide a time-resolved series of 3D vascular volumes (4D-DSA) following a single contrast injection and will also permit real time fluoroscopic road map visualization from previously inaccessible view angles without requiring gantry movement (4D Fluoroscopy). The studies outlined in this project will provide the validation required to permit rapid translation of these techniques into clinical practice.
