Images in cardiovascular medicine. Coronary artery patency after metallic stent implantation evaluated by multislice computed tomography

Assessment of Coronary Stent In Vitro on Multislice Computed Tomography Angiography

OBJECTIVE

To assess the effect of tube voltage on the in-stent visibility of coronary stents in vitro on computed tomography (CT) angiography.

METHODS

A total of 6 vascular models (3 models without stenosis and 3 with stenosis) using 3 kinds of stent (Bx Velocity, Express2, and Driver) with an inner diameter of approximately 3.5 mm and filled with contrast material (CT attenuation, 450 Hounsfield units) were scanned by means of a 16-detector row CT. We assessed the visual stenosis evaluation and inhomogeneity of stent lumen in 4 orientations (0-, 30-, 60-, and 90-degree angles) relative to the z-axis of the scanner using 3 imaging techniques (120-kV tube voltage using a medium convolution kernel, 120-kV tube voltage using a convolution kernel for bone, and 140-kV tube voltage using a convolution kernel for bone). Statistical analysis involved F test with a statistical significance of P < 0.05.

RESULTS

The convolution kernel for bone made it easier to evaluate the stenosis inside the stents, although it increased the luminal inhomogeneity significantly (Bx Velocity and Express2, P < 0.005; Driver, P < 0.05). The luminal inhomogeneity tended to increase as the strut diameter and the weight per unit length increased. Using 120-kV tube voltage, the luminal inhomogeneity inside the stents was at the minimum in the angle of 0 degree relative to the z-axis, and at the maximum in the angle of 90 degrees, except for Driver. The 140-kV tube voltage was effective for the improvement of luminal inhomogeneity and visibility of in-stent stenosis compared with the 120-kV tube voltage.

CONCLUSIONS

The in-stent visibility of coronary stents on CT angiography can be improved by the use of 140-kV tube voltage with the convolution kernel for bone.

Evaluation of aortocoronary bypass stents with cardiac MDCT compared with conventional catheter angiography

OBJECTIVE

The objective of our study was to determine the accuracy of 16-MDCT for evaluation of stent patency and in-stent stenosis in venous coronary bypass grafts.

SUBJECTS AND METHODS

Fourteen patients who had previous stent placements in stenosed venous coronary bypass grafts underwent contrast-enhanced MDCT of the heart (collimation, 16 x 0.75 mm; 120 kV; 550 mAs(eff)) and invasive coronary angiography. A total of 20 stents were evaluated: Vessel and stent diameters proximal to, distal to, and at various sites inside the stent were measured on both techniques, and Bland-Altman plots and correlations were calculated. Image noise and image quality were also assessed applying a Student's t test for data comparison of image noise.

RESULTS

All 20 bypass stents were correctly classified as patent. Vessel diameters outside the stent showed an excellent correlation (r = 0.90) and in-stent diameters showed a good correlation (r = 0.72), with lower values for MDCT due to blooming artifacts. All significant in-stent stenoses were correctly classified.

CONCLUSION

In patients suspected of bypass in-stent stenosis, 16-MDCT may be considered as a valuable alternative to conventional angiography for evaluating bypass patency and in-stent stenosis.

Noninvasive assessment of coronary stents in patients by 16-slice computed tomography

BACKGROUND

The usefulness of thin-slice multi-detector computed tomography (MDCT) has been highly expected to assess the lumens of coronary artery stents. We evaluated the usefulness of 16-slice MDCT to assess the in-stent lumen after coronary artery stenting.

METHODS

In 42 consecutive patients after coronary artery stenting, retrospective ECG-gated CT-angiography using 16-slice MDCT (0.5-s rotation time, 16x0.625-mm detector collimation) was performed. The qualitative assessability of the lumens of 61 coronary stents (14 different types) by MDCT and the reasons for non-assessability were investigated. Furthermore, the evaluation of in-stent restenosis in 21 assessable stents of 16 patients, including quantitative density analysis by MDCT, was performed and the results were compared with those of conventional coronary angiography (CAG).

RESULTS

Of 61 stents, 42 (68.9%) were assessable. The assessability of diameter > or =3.5-mm stents made of stainless steel or cobalt was high (88.6%, 31/35), that of 3.0-mm stents was low (57.9%, 11/19) and all 2.5-mm stents were non-assessable due to partial volume effects and metal artifacts of stents. The lumens of stents made of tantalum were totally obscured and the metal artifacts of Bestent2 (gold markers) and S670 were severer than others. All non-assessable stents due to banding artifact and calcification were implanted in segment #1-3 and #6, respectively. In comparison to CAG, MDCT correctly detected the 5 in-stent restenoses and identified absence of restenoses was influenced strongly by the stent strut.

CONCLUSION

Despite some limitations, 16-slice MSCT is sufficiently useful for assessment of various coronary stents in patients and can detect in-stent restenoses of assessable stents with high accuracy in comparison to CAG.

Evaluation of coronary stents in vitro with CT angiography: effect of stent diameter, convolution kernel, and vessel orientation to the z-axis

BACKGROUND

The aims of the present study were to assess the effect of the stent diameter, convolution kernel, and vessel orientation to the z-axis on the evaluation of coronary stents, in vitro with computed tomography (CT) angiography.

METHODS AND RESULTS

Seven vascular models (2 models without stenosis, 2 with obstruction, and 3 with stenosis) with an approximate inner diameter of 3 or 4 mm, filled with contrast material (79 or 330 HU) were scanned with a 16-detector CT. The diameter measurement of the stent lumen and stenosis evaluation were both done in an orientation parallel to the z-axis of the scanner using 4 convolution kernels. The measured diameters of the stented lumen were 47-57% and 36-45% smaller than the actual inner diameter of the 3- and 4-mm diameter models, respectively. The diameter measurement of the stent lumen and visualization of the in-stent stenosis were improved by using convolution kernels with higher spatial resolution. The in-stent artifacts were evaluated in 4 orientations (0 degrees , 30 degrees , 60 degrees , 90 degrees ) to the z-axis. The artifact was the minimum in 0 degrees to the z-axis, and the maximum in 90 degrees .

CONCLUSION

Visualization of the lumen of a stent by CT is affected by its diameter, convolution kernel, and vessel orientation to the z-axis, and these factors should be taken into consideration in the stent evaluation.

Diagnosis of Coronary In-Stent Restenosis With Multidetector Row Spiral Computed Tomography

OBJECTIVES

The purpose of this study was to assess the accuracy of a new generation spiral multidetector computed tomography (MDCT) scanner (Brilliance 40, Philips Medical Systems, Cleveland, Ohio) in the diagnosis of coronary in-stent restenosis (ISR).

BACKGROUND

Noninvasive imaging of ISR would be clinically useful, but artifacts caused by metallic stent struts have limited the role of early generation MDCT scanners.

METHODS

We examined 65 patients (age 63 +/- 12 years, 48 [73.8%] men) with 111 implanted coronary stents who were referred for repeat invasive coronary angiography (ICA). Patients underwent 40-slice MDCT one to three days before scheduled ICA, using intravenous contrast enhancement. Images were reconstructed in multiple formats using retrospective electrocardiographic gating. Stents were viewed in their long and short axes and luminal contrast attenuation graded from MDCT grade 1 (minimal restenosis) to 4 (severe restenosis) by consensus of two observers.

RESULTS

In-stent restenosis (>/=60% luminal narrowing by quantitative coronary angiography) was found on ICA in 18 (16.2%) of the stented segments and in 16 (24.6%) patients. The MDCT findings correlated with ICA restenosis, with restenosis in only 1 of 59 (1.6%) MDCT grade 1 segments, but in more than three-quarters (12 of 15, 80%) of MDCT grade 4 segments (sensitivity 72.2%, specificity 92.5%, positive predictive value [PPV] 65.0%, negative predictive value [NPV] 94.5% [five stents not assessable by MDCT considered as restenosis]). Using MDCT grades 3 or 4 combined for restenosis, sensitivity of MDCT was 88.9%, specificity 80.6%, PPV 47.1%, and NPV 97.4%.

CONCLUSIONS

In-stent restenosis can be diagnosed with moderate sensitivity using a new generation 40-slice MDCT scanner. The high NPV implies a significant role for MDCT in excluding ISR.

Coronary Artery Stents in Multislice Computed Tomography

RATIONALE AND OBJECTIVE

The aim of this study was to systematically compare the ability to assess the coronary artery lumen in the presence of coronary artery stents in multislice spiral CT (MSCT).

METHODS

Ten different coronary artery stents were examined with 4- and 16-detector row MSCT scanners. For image reconstruction, a standard and a dedicated convolution kernel for coronary artery stent visualization were used. Images were analyzed regarding lumen visibility, intraluminal attenuation, and artifacts outside the stent lumen. Results were compared using repeated-measure analysis of variance.

RESULTS

Depending on stent type, scanner hardware, and convolution kernel, artificial lumen narrowing ranged from 20% to 100%. The convolution kernel had the most significant influence on the visibility of the stent lumen. Artificial lumen narrowing and intraluminal attenuation changes decreased significantly using the dedicated convolution kernel. In general, most severe artifacts were caused by gold or gold-coated stents.

CONCLUSIONS

Independent of the scanner hardware or dedicated convolution kernels, routine evaluation of most coronary artery stents is not yet feasible using MSCT.