In-vitro assessment of coronary artery stents in 256-multislice computed tomography angiography

Background

The important detection of in-stent restenosis in cardiovascular computed tomography (CT) is still challenging. The first study assessing the in-vitro stent lumen visualization of the state of the art 256-multislice CT (256-MSCT), which was performed by our research group, yielded promising results. As the applied technical approach is not suitable for daily routine, we assessed the capability of the 256-MSCT and its different reconstruction kernels for the coronary stent lumen visualization employing a clinically applicable technique in a phantom study.

Results

The XCD kernel showed significantly lower artificial lumen narrowing (ALN) values (overall ALN < 40%) than the other reconstruction kernels (CC, CD, XCB) irrespective of the stent caliber. The ALN of coronary stents with a diameter >3 mm was significantly lower than of stents with a smaller caliber. The ALN difference between stents with a diameter of 3 mm and smaller ones was not statistically significant. Yet, the lumen visualization of the smaller stents was impaired by a halo effect. The XCD kernel showed more constant attenuation values throughout the different stent diameters than the other reconstruction kernels.

Conclusions

The 256-MSCT provides a good lumen visualization of coronary stents with a diameter >3 mm. The assessment of stents with a diameter of 3 mm seems feasible but has to be validated in further studies. The clinical evaluation of smaller stents cannot be recommended so far. The XCD kernel showed the best lumen visualization and should therefore be applied in addition to the standard cardiac reconstruction kernels when assessing coronary artery stents using 256-MSCT.

Diagnostic accuracy of 320-row multidetector computed tomography coronary angiography to noninvasively assess in-stent restenosis

OBJECTIVES

Percutaneous coronary intervention with stent implantation is routinely performed to treat patients with obstructive coronary artery disease. However, thus far, noninvasive assessment of in-stent restenosis has been challenging. Recently, 320-row multidetector computed tomography coronary angiography (CTA) was introduced, allowing volumetric image acquisition of the heart in a single heart beat or gantry rotation. The aim of this study was to evaluate the diagnostic performance of 320-row CTA in the evaluation of significant in-stent restenosis. Invasive coronary angiography (ICA) served as the standard of reference, using a quantitative approach.

MATERIALS AND METHODS

The population consisted of patients with previous coronary stent implantation who were clinically referred for cardiac evaluation because of recurrent chest pain and who underwent both CTA and ICA. CTA studies were performed using a 320-row CTA scanner with 320 detector-rows, each 0.5 mm wide, and a gantry rotation time of 350 milliseconds. Tube voltage and current were adapted to body mass index and thoracic anatomy. The entire heart was imaged in a single heart beat, with a maximum of 16-cm craniocaudal coverage. During the scan, the ECG was registered simultaneously for prospective triggering of the data. First, CTA stent image quality was assessed using a 3-point grading scale: (1) good image quality, (2) moderate image quality, and (3) poor image quality. Subsequently, the presence of in-stent restenosis was determined on a stent and patient basis by a blinded observer. Significant in-stent restenosis was defined as >or=50% luminal narrowing in the stent lumen or the presence of significant stent edge stenosis. Overlapping stents were considered to represent a single stent. Results were compared with ICA using quantitative coronary angiography. In addition, CTA stent image quality and diagnostic accuracy were related to stent characteristics and heart rate during CTA image acquisition.

RESULTS

The population consisted of 53 patients (37 men, mean age: 65 +/- 13 years) with a total of 89 stents available for evaluation. ICA identified 12 stents (13%) with significant in-stent restenosis. A total of 7 stents (8%) were of nondiagnostic CTA stent image quality, and were considered positive. Sensitivity, specificity, positive, and negative predictive values were 92%, 83%, 46%, and 98%, respectively on a stent basis. Five CTA studies (9%) were of nondiagnostic quality for the evaluation of in-stent restenosis and were considered positive. Sensitivity, specificity, positive, and negative predictive values were 100%, 81%, 58%, and 100%, respectively on a patient level. Stent diameter <3 mm as well as stent strut thickness >or=140 mum were associated with decreased CTA stent image quality and diagnostic accuracy. Heart rate during CTA acquisition and stent overlap were not associated with image degradation.

CONCLUSIONS

The present results show that 320-row CTA allows accurate noninvasive assessment of significant in-stent restenosis. However, stents with a large diameter and thin struts allowed better in-stent visualization than stents with a small diameter or thick struts. Consequently, noninvasive assessment of in-stent restenosis using CTA may be an attractive and feasible alternative particularly in carefully selected patients.

Coronary artery stent imaging with 128-slice dual-source CT using high-pitch spiral acquisition in a cardiac phantom: comparison with the sequential and low-pitch spiral mode

OBJECTIVE

To evaluate coronary stents in vitro using 128-slice-dual-source computed tomography (CT).

METHODS

Twelve different coronary stents placed in a non-moving cardiac/chest phantom were examined by 128-slice dual-source CT using three CT protocols [high-pitch spiral (HPS), sequential (SEQ) and conventional spiral (SPIR)]. Artificial in-stent lumen narrowing (ALN), visible inner stent area (VIA), artificial in-stent lumen attenuation (ALA) in percent, image noise inside/outside the stent and CTDIvol were measured.

RESULTS

Mean ALN was 46% for HPS, 44% for SEQ and 47% for SPIR without significant difference. Mean VIA was similar with 31% for HPS, 30% for SEQ and 33% for SPIR. Mean ALA was, at 5% for HPS, significantly lower compared with -11% for SPIR (p = 0.024), but not different from SEQ with -1%. Mean image noise was significantly higher for HPS compared with SEQ and SPIR inside and outside the stent (p < 0.001). CTDIvol was lower for HPS (5.17 mGy), compared with SEQ (9.02 mGy) and SPIR (55.97 mGy), respectively.

CONCLUSION

The HPS mode of 128-slice dual-source CT yields fewer artefacts inside the stent lumen compared with SPIR and SEQ, but image noise is higher. ALN is still too high for routine stent evaluation in clinical practice. Radiation dose of the HPS mode is markedly (less than about tenfold) reduced.