CT of pediatric vascular stents used to treat congenital heart disease

OBJECTIVE. The purpose of our study was to assess the visibility of lumen narrowing of pediatric vascular stents using various CT dose parameters in an in vitro model. MATERIALS AND METHODS. Ten steel stents of varying designs and sizes commonly used in the treatment of congenital heart disease were implanted in polyvinyl chloride ( PVC) tubes and three of the 10 stents were partially obstructed with wax by filling 25% ( mild) to 60% ( moderate) of the lumen with contrast material. On a 64-MDCT scanner, the stents were scanned at tube voltages ( kVp) of 80, 100, and 120 and at tube currents (mA) of 40, 80, 120, and 160. CT measurements of inner-stent diameter, strut thickness, and percent lumen (in-stent) stenoses were compared with biplane fluoroscopy of digital angiography. RESULTS. The stent diameter and percent stenosis on all CT images were consistently smaller than measured on digital angiography but were highly correlated (r = 0.97; p < 0.0001) with improvement as stent diameter increased (93% agreement with digital angiography for 4-mm stent, up to 99% for 25-mm stent; p = 0.001). Moderate stenosis could be assessed better than mild stenosis ( 99% vs 91% agreement with digital angiography; p = 0.003). Increasing exposure settings improved CT correlation of all measurements for mA up to 120 and kVp up to 100 (98.1% agreement). Higher settings did not improve accuracy (93.9% for 160 mA at 120 kVp; p = 0.03). CONCLUSION. CT is feasible to assess lumen narrowing of pediatric vascular stents at a wide range of tube settings. The study suggests that it is possible to lower the radiation exposure settings without loss in image quality or accuracy in detecting in-stent stenoses.