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64-MDCT Coronary Angiography: Phantom Study of Effects of Vascular Attenuation on Detection of Coronary Stenosis

¹ Department of Radiology, Xuanwu Hospital of Capital Medical University, 45 Changchun St., Xuanwu District, Beijing 100053, China.
² CT Laboratory of GE Healthcare, Beijing Economic and Technology Development Area, Beijing, China.

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —Phantom system and balloon. Photographs show cardiac phantom system (A) and balloon (B) used to simulate left ventricle, attached tubes (simulated coronary arteries), and water-filled tank in which balloon is submerged. Phantom system consists of five components: driver, controller, fixed support, rubber balloon (phantom), and ECG simulator. Controller with ECG synchronizer drives balloon. Motion is achieved with four driver sequences: two speeds of fast emptying for systolic phase and fast and slow filling for diastolic phase. Balloon is filled with contrast medium to simulate contrast-enhanced heart. Acrylic tubes (mimicking coronary arteries) containing contrast medium are attached to balloon surface. Fabricated plaques are packed inside tubes to simulate stenosis. Ends of balloon are stabilized to fixed support at distance of 10 cm.

View larger version (147K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —Phantom system and balloon. Photographs show cardiac phantom system (A) and balloon (B) used to simulate left ventricle, attached tubes (simulated coronary arteries), and water-filled tank in which balloon is submerged. Phantom system consists of five components: driver, controller, fixed support, rubber balloon (phantom), and ECG simulator. Controller with ECG synchronizer drives balloon. Motion is achieved with four driver sequences: two speeds of fast emptying for systolic phase and fast and slow filling for diastolic phase. Balloon is filled with contrast medium to simulate contrast-enhanced heart. Acrylic tubes (mimicking coronary arteries) containing contrast medium are attached to balloon surface. Fabricated plaques are packed inside tubes to simulate stenosis. Ends of balloon are stabilized to fixed support at distance of 10 cm.

View larger version (91K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2 —Balloon filled with contrast medium simulates beating heart and simulated vessels during stenosis detection in cardiac phantom. A, Whole axial CT image shows placement of regions of interest. Four small objects attached to balloon are four acrylic tubes simulating coronary arteries. Circles indicate simulated vessels with stenosis. B, CT image with observer input shows selection of region of interest for 5-mm vessel.C, CT image shows segmentation whereby plaque used to simulate stenosis and contrast-filled lumen are separated from vessel wall and from each other.

View larger version (16K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —Accuracy of measured percentage stenosis. Values are means; error bars indicate mean ± 0.5 SD; light gray, 3-mm vessel diameter; dark gray, 5-mm vessel diameter. Graph shows effects of attenuation protocols of cardiac CT angiography (CTA) on accuracy of detection of 25% stenosis detection. High-attenuation (500 H) protocol resulted in underestimation of stenosis. Stenosis was especially difficult to detect in smaller vessels. Low-attenuation (200 H) protocol led to overestimation of stenosis detection within clinically acceptable limits, but imaging quality was much less reproducible than in other protocols.

View larger version (21K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —Accuracy of measured percentage stenosis. Values are means; error bars indicate mean ± 0.5 SD; light gray, 3-mm vessel diameter; dark gray, 5-mm vessel diameter. Graph shows effects of attenuation protocols of cardiac CTA on accuracy of detection of 50% stenosis. High-attenuation (500 H) protocol led to significant underestimation of stenosis for smaller vessels but was accurate in depicting larger vessels. Low-attenuation (200 H) protocol led to overestimation of stenosis within clinically acceptable limits, but imaging quality was not as reproducible as in other groups.

View larger version (21K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3C —Accuracy of measured percentage stenosis. Values are means; error bars indicate mean ± 0.5 SD; light gray, 3-mm vessel diameter; dark gray, 5-mm vessel diameter. Graph shows effects of attenuation protocols of cardiac CTA imaging on accuracy of detection of 75% stenosis. High-attenuation (500 H) protocol led to significant underestimation of stenosis in smaller vessels but was accurate in depicting larger vessels. Low-attenuation (200 H) protocol led to slight overestimation of stenosis. Imaging accuracy and stability did not differ significantly from moderate-attenuation protocols (300 and 350 H).

View larger version (53K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A —Phantom with simulated vessels with 50% stenosis. Results show low attenuation decreased contrast-to-noise ratio and caused overestimation of stenosis, especially in small vessels. High attenuation enhanced contrast-to-noise ratio but also caused severe partial volume effect. Thus larger stenosis in larger vessel was clearly depicted but stenosis was underestimated in smaller vessels. CT attenuation of 350 H is optimal for accurate quantification of stenosis in larger and smaller vessels. CT scan shows 3- and 5-mm coronary arteries under low-attenuation (200 H) protocol.

View larger version (52K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B —Phantom with simulated vessels with 50% stenosis. Results show low attenuation decreased contrast-to-noise ratio and caused overestimation of stenosis, especially in small vessels. High attenuation enhanced contrast-to-noise ratio but also caused severe partial volume effect. Thus larger stenosis in larger vessel was clearly depicted but stenosis was underestimated in smaller vessels. CT attenuation of 350 H is optimal for accurate quantification of stenosis in larger and smaller vessels. CT scan shows 3- and 5-mm coronary arteries under moderately-high-attenuation (350 H) protocol.

View larger version (45K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4C —Phantom with simulated vessels with 50% stenosis. Results show low attenuation decreased contrast-to-noise ratio and caused overestimation of stenosis, especially in small vessels. High attenuation enhanced contrast-to-noise ratio but also caused severe partial volume effect. Thus larger stenosis in larger vessel was clearly depicted but stenosis was underestimated in smaller vessels. CT attenuation of 350 H is optimal for accurate quantification of stenosis in larger and smaller vessels. CT scan shows 3- and 5-mm coronary arteries under high-attenuation (500 H) protocol.

View larger version (142K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5A —Phantom with simulated vessels with 25% stenosis. Results show low attenuation decreased contrast-to-noise ratio and thus caused overestimation of stenosis, especially in small vessels. High attenuation enhanced contrast-to-noise ratio but also caused severe partial volume effect on small stenosis, especially in small vessels. Intracoronary CT attenuation of 350 H was optimal for accurate quantification of coronary stenosis for larger and smaller vessels. CT scan shows 3- and 5-mm coronary arteries under low-attenuation (200 H) protocol.

View larger version (126K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5B —Phantom with simulated vessels with 25% stenosis. Results show low attenuation decreased contrast-to-noise ratio and thus caused overestimation of stenosis, especially in small vessels. High attenuation enhanced contrast-to-noise ratio but also caused severe partial volume effect on small stenosis, especially in small vessels. Intracoronary CT attenuation of 350 H was optimal for accurate quantification of coronary stenosis for larger and smaller vessels. CT scan shows 3- and 5-mm coronary arteries under moderately-high-attenuation (350 H) protocol.

View larger version (106K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5C —Phantom with simulated vessels with 25% stenosis. Results show low attenuation decreased contrast-to-noise ratio and thus caused overestimation of stenosis, especially in small vessels. High attenuation enhanced contrast-to-noise ratio but also caused severe partial volume effect on small stenosis, especially in small vessels. Intracoronary CT attenuation of 350 H was optimal for accurate quantification of coronary stenosis for larger and smaller vessels. CT scan shows 3- and 5-mm coronary arteries under high-attenuation (500 H) protocol.

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