Room: AAPM ePoster Library
Many interventional procedures spend substantial time in increased dose acquisition modes such as digital subtraction angiography (DSA). Unlike fluoroscopy, DSA modes do not limit maximum exposure, representing areas where optimizing dose and image quality can be valuable. With systems using automatic exposure control (AEC), using conventional physics-based image quality metrics can be challenging. This work quantitatively characterizes image quality of DSA acquisitions that can be performed by a clinical imaging physicist.
Acquisitions were performed on a modern angiography system. Protocols used were for dialysis access placement, a high volume procedure with substantial occupational exposure. A patient-equivalent arm-phantom was positioned on the table, as well as an aluminum sheet. A 3 F/s acquisition using a low dose DSA protocol was performed, beginning with the arm phantom in the field of view (FOV), which sets the AEC parameters. Without interrupting the acquisition, the table is translated to image the other phantom, keeping the AEC constant. The acquisition was repeated using a low-dose fluoroscopy protocol. AEC modulates in fluoroscopy, but <5% tube parameter modulation was observed. The acquired images were processed offline to evaluate the edge spread function (ESF), line spread function (LSF), and module transfer function (MTF) for both modes.
Spatial resolution was evaluated for DSA and standard fluoroscopic techniques. The full-width half height (FWHM) of the DSA sequence (2.2 mm) was greater than that of the fluoroscopy sequence (1.2 mm), although the full-width tenth max (FWTM) was smaller (3.8 mm vs 4.3 mm). Shape of the ESF and LSF indicated edge-enhancement post-processing applied for fluoroscopy.
Technical imaging properties of fluoroscopic imaging can differ significantly between modes. Interventional procedures cover all body areas, and AEC being active, procedure specific phantoms need to be used to allow determination of appropriate image quality while maintaining patient and staff safety.
Funding Support, Disclosures, and Conflict of Interest: Sebastian Schafer is an employee of Siemens Healthineers.
DSA, Edge Spread Function, Dose