SU‐E‐I‐12: Assessment of Absorbed Dose and Image Quality Using Cone Beam CT On An X‐Ray Angiography System

Abstract

Purpose: Cone beam CT (CBCT) acquisitions using interventional X‐ray Angiography (XA) systems are becoming more prevalent. Patient dose should be considered when performing these studies. This work assesses absorbed radiation dose and image quality from CBCT acquisitions on an XA system. Methods: CBCT acquisitions of a CIRS tissue equivalent abdomen phantom and the Gammex ACR CT phantom were performed at 3 detector dose settings using a 90 kVp, 210 degree, 420 view, 8 second acquisition on a Siemens Artis Zee system. Radiation dose was measured using a Radcal 0.6cc ionization chamber positioned at central and peripheral locations in the abdomen phantom. Patient absorbed dose was estimated via a weighted average of the peripheral (2/3) and central (1/3) doses. Image quality was assessed via the standard deviation of the reconstructed image pixel values in a homogeneous region of the ACR CT phantom and contrast to noise ratio (CNR) measurements of the polyethylene rod to the background. For comparison, absorbed dose was measured with the same setup on a standard CT system using a clinical abdomen and pelvis protocol. Results: Estimates of patient absorbed dose for the CBCT acquisitions were 38, 26, and 15 mGy at detector dose settings of 540, 360 (default) and 200 nGy per view. The image noise at different dose settings was consistent with a 0.5 power law relationship. The absolute value of the CNR was determined to be 6.1 (540 nGy), 5.5 (360 nGy) and 3.7(200 nGy). The absorbed dose estimate for the abdomen and pelvis standard CT was 9 mGy. Conclusion: Absorbed dose from cone beam CT acquisitions on an interventional XA system is greater than that of a standard CT. The necessary image quality for a given CBCT imaging task and the potential for dose reduction should be assessed in accordance with ALARA principles. Research Grant: Siemens AG