CLINICAL RESEARCH
Diagnostic Accuracy of Coronary In-Stent Restenosis Using 64-Slice Computed TomographyComparison With Invasive Coronary Angiography
Mariko Ehara, MD*,
Masato Kawai, RT,
Jean-François Surmely, MD,
Tetsuo Matsubara, MD,
Mitsuyasu Terashima, MD,
Etsuo Tsuchikane, MD,
Yoshihisa Kinoshita, MD,
Tatsuya Ito, MD,
Yoshihiro Takeda, MD,
Kenya Nasu, MD,
Nobuyoshi Tanaka, MD,
Akira Murata, MD,
Hiroshi Fujita, MD,
Koyo Sato, MD,
Atsuko Kodama, MD,
Osamu Katoh, MD and
Takahiko Suzuki, MD
Department of Cardiology, Toyohashi Heart Center, Toyohashi, Japan
Manuscript received June 26, 2006;
revised manuscript received October 23, 2006,
accepted October 30, 2006.
* Reprint requests and correspondence: Dr. Mariko Ehara, Toyohashi Heart Center, Department of Cardiology, 21-1, Gobutori Oyamacho, Toyohashi-City, Aichi 441-8530, Japan. (Email: momomar{at}muc.biglobe.ne.jp).
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Abstract
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OBJECTIVES: This study sought to evaluate the diagnostic accuracy of coronary binary in-stent restenosis (ISR) with angiography using 64-slice multislice computed tomography coronary angiography (CTCA) compared with invasive coronary angiography (ICA).
BACKGROUND: A noninvasive detection of ISR would result in an easier and safer way to conduct patient follow-up.
METHODS: We performed CTCA in 81 patients after stent implantation, and 125 stented lesions were scanned. Two sets of images were reconstructed with different types of convolution kernels. On CTCA, neointimal proliferation was visually evaluated according to luminal contrast attenuation inside the stent. Lesions were graded as follows: grade 1, none or slight neointimal proliferation; grade 2, neointimal proliferation with no significant stenosis (<50%); grade 3, neointimal proliferation with moderate stenosis ( 50%); and grade 4, neointimal proliferation with severe stenosis (75%). Grades 3 and 4 were considered binary ISR. The diagnostic accuracy of CTCA compared with ICA was evaluated.
RESULTS: By ICA, 24 ISRs were diagnosed. Sensitivity, specificity, positive predictive value, and negative predictive value were 92%, 81%, 54%, and 98% for the overall population, whereas values were 91%, 93%, 77%, and 98% when excluding unassessable segments (15 segments, 12%). For assessable segments, CTCA correctly diagnosed 20 of the 22 ISRs detected by ICA. Six lesions without ISR were overestimated as ISR by CTCA. As the grade of neointimal proliferation by CTCA increases, the median value of percent diameter stenosis increased linearly.
CONCLUSIONS: Binary ISR can be excluded with high probability by CTCA, with a moderate rate of false-positive results.
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Abbreviations and Acronyms
| | CI = confidence interval | | CT = computed tomography | | CTCA = computed tomography coronary angiography | | %DS = percent diameter stenosis | | ICA = invasive coronary angiography | | ISR = in-stent restenosis | | MSCT = multislice computed tomography | | NPV = negative predictive value | | PPV = positive predictive value |
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Indications for percutaneous coronary intervention have been expanding over the years, and in particular since the introduction of drug-eluting stents, which have been shown to reduce considerably the occurrence of restenosis compared with other devices. However, restenosis still occurs in about 4% to 10% according to the lesion complexity, a large number of patients (1–4). A noninvasive detection of in-stent restenosis (ISR) would result in an easier and safer method of detecting and following up such patients. Computed tomography (CT) is nowadays the leading noninvasive modality for imaging coronary arteries. Multislice computed tomography (MSCT) computed tomography coronary angiography (CTCA) with 16-slice technology has already been in the spotlight as a promising means of diagnosing de novo lesion of coronary artery disease compared with invasive coronary angiography (ICA) (5–12), with a sensitivity of 82% to 95% and a specificity of 82% to 98%. However, concerning coronary segments after stenting, only a few studies have dealt with its diagnostic accuracy (13–16). The resolution of the former-generation scanners was not enough to show the steady outcome for stented sites.
Recently 64-slice MSCT, the latest generation in current usage, has offered an improved spatial and temporal resolution. The accuracy of 64-slice MSCT to diagnose de novo coronary artery disease is also promising; however, segments after stenting were again excluded in most of the populations of previously published data.
The goal of the present study is to evaluate the diagnostic accuracy of coronary binary ISR with 64-slice MSCT compared with ICA. We also investigated the correlation of the visual estimation of ISR by CTCA with quantitative coronary angiography by ICA.
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Methods
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Patient population.
Between October 2004 and August 2005, 81 consecutive patients with prior coronary stent implantation in 125 lesions underwent CTCA with an interval of >3 months since the latest stenting. Exclusion criteria for MSCT examination were as follows: renal insufficiency (serum creatinine >1.5 mg/dl), allergy to contrast media, atrial fibrillation or other rhythm irregularity, and inability to perform breath hold. An ICA was performed in all patients within the interval of 1 month of the MSCT examination. All patients gave written informed consent, and the study protocol was approved by the hospital ethics committee.
Scan protocol of CTCA.
All patients were scanned on a 64-slice scanner (SOMATOM Sensation 64 Cardiac, Siemens Medical Solutions, Forchheim, Germany). When necessary, beta-blocker (metoprolol 20 to 60 mg) was administered for heart rate control. Use of nitroglycerin before scanning was left to the physicians' discretion. A bolus of contrast media (iopamidol, 300 mg iodine/ml or 370 mg iodine/ml, Schering AG, Berlin, Germany; iopromide, 300 mg iodine/ml, Shering AG; Omnipaque, 300 mg iodine/ml or 350 mg iodine/ml, Daiichi Pharmaceutical Co., Ltd., Tokyo, Japan) was injected into an antecubital vein, followed by flushing with 20 to 50 ml saline. To reduce the incidence of adverse reaction, the sort of contrast media was selected for each patient considering previous usage. The proper amount of the contrast media and injection speed were determined according to the patient's body weight, scan time, and heart rate. The start delay was automatically defined using bolus tracking software equipped in the scanner. The region of interest was placed within the ascending aorta, and the scan was started when the CT density reached 120 HU higher than the baseline CT density. The scan was performed between the tracheal bifurcation and diaphragm with the following parameters: collimation width 64 x 0.6 mm, rotation time 330 ms, tube voltage 120 kV, effective tube current 800 mA, table feed 11.5 mm/rotation, and pitch 0.2.
Data acquisition and image reconstruction of CTCA..
Image reconstruction was retrospectively gated to an electrocardiogram, and the optimal cardiac phase showing the minimum motion artifact was individually determined. Depending on the heart rate during the examination, axial slices were reconstructed synchronized to the electrocardiogram by a monophase (heart rate <70 beats/min) or biphase (heart rate 70 beats/min) reconstruction algorithm using data from 1 or 2 consecutive heart beats. When necessary, R-wave indicators were manually repositioned to improve the quality of synchronization. To optimize in some cases the image quality, different cardiac cycle phases were selected for different coronary segments.
As previously described (16), 2 sets of images were reconstructed with different types of convolution kernels: the first set was reconstructed with a smooth or medium-smooth kernel (B20f, B25f, or B30f), with a slice thickness of 0.75 mm (increment 0.4 mm), and the second set was reconstructed with a sharp (Heartview, Siemens Medical Solutions) kernel (B46f), with a slice thickness of 0.6 mm (increment 0.3 mm). Spatial resolution is 0.33 mm. For delineating low-contrast objects such as coronary lumen or vessel wall, we used images generated with the smooth or medium-smooth kernel, whereas to observe the stented segment, we used both of the images that were generated with smooth and sharp kernels. Figure 1
shows the difference between 2 types of convolution kernels.
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Figure 1 Stent Images With 2 Different Convolution Kernels
A Cypher stent (3.5 x 13 mm) in the left main artery. (A) A multiplanar reformatted image, long-axis image generated with a smooth kernel (B30f), with 0.75-mm slice thickness (increment 0.4 mm). (B) A cross-sectional image generated with a smooth kernel. (C) A multiplanar reformatted image, long-axis image generated with a sharp kernel (B46f), with 0.6-mm slice thickness (increment 0.3 mm). (D) A cross-sectional image generated with a sharp kernel. A and B are suitable for delineating low-contrast objects such as coronary lumen or vessel wall, whereas C and D clearly visualize the high-density objects such as stent struts, but sometimes make much noise.
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The CTCA data sets generated with a smooth or medium-smooth kernel were transferred to offline workstations (Wizard, Siemens Medical solutions, Forchheim, Germany) for image analysis. Maximum-intensity projection with 6- to 10-mm slice and multiplanar reformatted reconstructions were made for observation of whole coronary artery. Datasets generated with a sharp kernel were transferred to Wizard for maximum intensity projection and multiplanar reformatted reconstruction images of stented segments, and to another workstation (Aquarius NetStation, Terarecon Inc., San Mateo, California) for volume rendering images.
ICA procedure and analysis.
The ICA was performed with standard techniques, and at least 2 different views were obtained for each main vessel. All stented segments (including the 5 mm proximal and distal to stent edges) were evaluated by a skilled observer who was blinded to the results of CTCA. Quantitative coronary angiography was performed, and percent diameter stenosis (%DS) was calculated using CMS (MEDIS, Leiden, the Netherlands), which was defined as reduction of minimal lumen diameter compared with the vessel diameter estimated with proximal and distal reference. Segments were classified into 4 groups according to %DS: Slight included segments with <25% in %DS, mild with 25 and <50%, moderate with 50 and <75%, and severe with 75%. Binary ISR was defined as %DS 50% (moderate or severe) in stented segment on ICA.
Validation, semiquantitative analysis, and morphological ISR classification on CTCA compared with ICA.
Referring to a report by Gasper et al. (14), contrast attenuation inside and at both edges of stents compared with the vessel lumen was regarded as neointimal proliferation. Adequately reconstructed CTCA images of stented segments were visually classified into 4 grades using the following criteria (Fig. 2): grade 1, none or slight neointimal proliferation; grade 2, mild neointimal proliferation but no significant restenosis (<50% narrowing); grade 3, moderate neointimal proliferation with significant restenosis (50% narrowing); grade 4, neointimal proliferation with severe stenosis or total occlusion (75% narrowing or occlusion). Two experienced observers who were blinded to the patients' clinical information as well as to the ICA findings evaluated the grade of CTCA independently, and when the readings of the observers differed, a consensus was reached and used in the final analysis. All segments were blindly analyzed twice by each observer to evaluate the intraobserver reproducibility.
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Figure 2 Semiquantitative Classification of CTCA
The white lines on the figures show the sites of stents. A to D are Grade 1 (none or slight neointimal proliferation). (A) Two Cypher stents placed in the left main artery (3.5 x 18 mm) and the proximal left anterior descending artery (LAD) (3.5 x 23 mm). (B) A cross-section of the Cypher stent placed in the left main (LM) artery. (C) A cross-section of a Cypher stent placed in the LM. (D) Invasive coronary angiography (ICA) of the left coronary artery (LCA). E to G are Grade 2 (mild neointimal proliferation but no significant restenosis [<50% narrowing]). (E) A Cypher stent (3.5 x 23 mm) placed in the proximal LAD. (F) A cross-section. (G) An ICA of the LCA. H to J are Grade 3 (moderate neointimal proliferation with significant restenosis [50% narrowing]). (H) A Cypher stent (3.5 x 23 mm) placed in the proximal right coronary artery (RCA). (I) A cross-section. (J) An ICA of the RCA. K to M are Grade 4 (neointimal proliferation with severe stenosis or total occlusion [75% narrowing or occlusion]). (K) A Cypher stent (3 x 28 mm) placed in the proximal LAD. (L) A cross-section. (M) An ICA of the LCA. CTCA = computed tomographic coronary angiography.
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Grades 3 and 4 were considered binary ISR on CTCA, and a segment-based and patient-based validation compared with the result of quantitative coronary angiography were performed for the diagnostic accuracy of CTCA. Correlation of the visual estimation with %DS was also evaluated. Pattern of ISR was classified according to the Mehran classification (17).
Statistical analysis.
Quantitative variables are described as mean ± SD. Categorical variables are presented as numbers and percentages. Comparison of quantitative variables were performed by one-way analysis of variance for normally distributed variables. The chi-square test was used for comparing frequency of occurrence. Statview version 5.0 (Abacus Concepts Inc., Berkeley, California) was used for data analysis. A probability value of <0.05 was considered to indicate statistical significance. Interobserver and intraobserver agreements were expressed as Cohen kappa statistics. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for CTA to detect significant stenosis were calculated from chi-square test of contingency, and 95% confidence intervals (CIs) were calculated from binomial expression.
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Results
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Patient characteristics, scan condition, and stent parameters.
Among 81 patients, 63 were male and 18 were female, the mean age was 67 ± 9 years of age (range 44 to 88 years), and 25% were on a beta-blocker daily or received it before the CT procedure. Two patients had a status post-coronary artery bypass surgery, but no stents were implanted in the grafts. The mean heart rate during scanning was 70.2 ± 12.2 beats/min (range 45 to 101 beats/min). The total amount of contrast media was 73.5 ± 10.6 ml (range 60 to 126 ml), and scan time was 13.2 ± 1.5 s (range 10.3 to 20.0 s). The estimated radiation exposure was 12.1 mSv. Patient characteristics and scan condition are shown in Table 1. An ICA was performed in all patients with an interval of 3 ± 5 days (range 0 to 24 days) of the CT procedure.
In total, 125 images of stented lesions (163 stents, 1.3 per lesions on average) were obtained. Thirty-nine lesions were located in the right coronary artery, 12 in the left main coronary artery, 45 in the left anterior descending artery, and 29 in the left circumflex artery. One hundred and fourteen lesions (91%) had an average stent diameter of 3 mm. There were 38 lesions (30%) with 2 overlapping stents, but no stents deployed inside other stents (Table 2).
According to stent cell type, 80 stents of 163 (49%) were closed cell and 83 (51%) were open cell: according to strut thickness, thick (0.005 inches) versus thin (<0.005 inches) was 86 (53%) versus 77 (47%) (Table 2). One hundred and fifty-eight (97%) stents were made of 316L stainless steel, 1 cobalt chrome, 2 nitinol, and 2 tantalum. The population had 33 (20%) drug-eluting stents (all Cypher stents, Cordis Corp., Miami, Florida) and 130 (80%) bare-metal stents.
Binary ISR diagnosis: CTCA compared with ICA.
Binary ISR was observed on ICA in 24 stented segments (19%) in 20 patients. The CTCA image quality was adequate in 110 stented segments (71 patients) of the 125 stented segments (81 patients). In these 110 assessable segments, 22 binary ISRs were diagnosed in 19 patients on ICA.
Of these 22 binary ISRs diagnosed on ICA, 20 (17 patients) were correctly detected by CTCA. Similarly, among 88 assessable lesions that had no ISR, 82 were correctly ruled out by CTCA (Table 3). To estimate the overall accuracy, including the 15 unassessable segments (2 with ISR and 13 without ISR on ICA), we assigned those segments as having binary ISR, because restenosis could not be excluded by CTCA. When including unassessable segments, sensitivity was 92% (22 of 24, 95% CI 81 to 100), specificity was 81% (82 of 101, 95% CI 74 to 89), PPV was 54% (22 of 41, 95% CI 39 to 69), and NPV was 98% (82 of 84, 95% CI 95 to 100). The predictive accuracy was 83%. When excluding unassessable segments, the sensitivity was 91% (20 of 22, 95% CI 79 to 100), specificity was 93% (82 of 88, 95% CI 88 to 98), PPV was 77% (20 of 26, 95% CI 61 to 93) and NPV was 98% (82 of 84, 95% CI 95 to 100). The predictive accuracy was 93%. The kappa-values of interobservers and intraobservers for the CTCA evaluation of stenosis were 0.85 and 0.92, respectively.
Subanalysis according to the target vessel, lesion location, presence of 2 overlapping stents, and mean stent diameter are also shown in Table 3. The presence of overlapping stents did not influence the rate of adequate CTCA images, nor the overall accuracy of 82% for both sorts of lesions.
On the patient-based analysis, 10 patients had poor image quality in all of the stented segments. One of these patients had 2 binary ISRs, whereas the other 9 had no binary ISR. For the overall population, sensitivity was 90% (18 of 20), specificity 79% (48 of 61), PPV 58% (18 of 31), and NPV 96% (48 of 50). The predictive accuracy was 81%. When excluding unassessable patients, sensitivity and specificity of CTCA to detect binary ISR were 89% (17 of 19) and 92% (48 of 52), and PPV and NPV were 81% (17 of 21) and 96% (48 of 50). The predictive accuracy was 92% (Table 3).
Failure to detect binary ISR occurred in 4 lesions in 3 patients. Two ISRs in the same patient were missed because of unassessable CTCA images. A further 2 ISRs located in the left circumflex artery in 2 patients were missed by CTCA (false negative). In the first case, 2 overlapping stents (2 Cypher, 3.5 mm in diameter and 23 mm in length) were placed from the left main to the proximal left circumflex artery, in a severely calcified lesion. Binary ISR occurred in the bifurcation of the left main artery. In the second case, ISR in a single stent implanted in the proximal left circumflex artery (3 x 14 mm, DuraFlex, Avantec Vascular Corp., Sunnyvale, California) was not detected because of severe motion artifact. Concerning the 6 falsely detected ISRs, 2 were located in single stents of the proximal right coronary artery with motion artifact, 2 were in the proximal left ascending artery with moderate calcification (1 had overlapping site), 1 was in the mid-left ascending artery with no calcification but overlapping site, and 1 was in the mid-left circumflex artery with no calcification or overlapping but motion artifact as well.
Comparison between ICA and CTCA for the type of ISR based on the morphologic classification (Mehran classification) is shown in Table 4.
Semiquantitative CTCA grade versus %DS on ICA..
Table 5
shows the correlation of class of %DS on ICA and semiquantitative CTCA grade. There was a significant difference in the frequency of %DS classes with CTCA grades (p < 0.0001). All of the 14 stented lesions regarded as grade 4 on CTCA were diagnosed as ISR on ICA. On the other hand, half of grade 3 lesions (6 of 12) on CTCA had no ISR (false positive) on ICA. Two lesions diagnosed as moderate ISR by ICA were classified by CTCA as grade 1 lesions (1 of 38) or as grade 2 lesions (1 of 46). Concerning the 15 unassessable lesions, 2 lesions in 1 patient were diagnosed as moderate ISR by ICA. Graphic representation of CTCA grade versus ICA class is shown in Figure 3. The median value of %DS increases as the grade increases from 1 to 4.
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Figure 3 Correlation of Grades on CTCA With %DS
Graphic representation of grades on coronary angiography by computed tomography versus class on invasive coronary angiography is shown. The median value and quartiles are shown beside the plots. As the grade increases from 1 to 4, the median value of percent diameter stenosis (%DS) increases linearly. Abbreviations as in Figure 2.
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Unassessable segments.
Among all 125 stented segments, 15 (12%) were evaluated as unassessable. Only 2 segments in 1 patient had binary ISR on ICA. Nine segments were located in the left ascending artery, 4 in the left circumflex artery, and 2 in the right coronary artery. Eight segments were in the proximal site, and 7 were in the middle or distal site. Nine unassessable stented segments were with open cell, 10 with thick strut, and 13 with 3.0- or 3.5-mm average diameter. Reduction of image quality was caused by extensive imaging artifacts generated by metallic struts themselves, motion artifact, calcification, or low opacification. In addition, in all unassessable stents, the CT density of stented lumens were <300 HU, which indicates lower opacification. Moderate to severe calcification was observed in 9 of those lesions. Stents implanted were 2 Cypher, 2 Bx Velocity (Cordis Corp.), 2 Express 2 (Boston Scientific, Maple Grove, Minnesota), 2 NIR (Boston Scientific, Galway, Ireland), 2 Wiktor (Medtronic Inc., Minneapolis, Minnesota), 1 DuraFlex, 1 MultiLink Penta (Abbott Vascular, Temecula, California), 1 S660, 1 Palmaz-Schuz Spiral (Johnson & Johnson Interventional System, New Brunswick, New Jersey), and 1 MultiLink Tristar (Abbott Vascular).
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Discussion
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The main results of our study can be summarized as follows: 1) For the overall population, binary ISR can be safely ruled out by CTCA (NPV of 98%), but because of a 12% rate of unassessable lesions, the positive predictive value is low. 2) When excluding unassessable lesions, diagnosis or exclusion of binary ISR is obtained with a high accuracy on a segment-based and patient-based analysis. The high sensitivity (91%) and NPV (98%) have a moderate rate of false-positive results.
An ISR is the major long-term complication of percutaneous coronary treatment and can be divided into 2 main causes: neointimal proliferation and mechanical causes. Until now, only invasive methods were able to diagnose ISR (18,19). A noninvasive detection of ISR would be of clinical importance in the treatment and follow-up of coronary artery disease. The CTCA is less invasive and less expensive than ICA, which reduces physical, mental, and economical stress, as well as potential complications, especially for patients who require repeat coronary angiography. Because of a low ISR rate with drug-eluting stents, the indication of percutaneous coronary intervention widely extended to more challenging cases such as left main lesions, chronic total occlusion, bifurcations, long lesions, and small vessels. A routine follow-up in these at-risk populations with a reported ISR rate ranging from 8% to 25% may be preferred (2–4,20,21).
The most important features of a test for it to be useful in the clinical setting is its reliability of not missing the cases having the disease (sensitivity), in this case ISR, and achieving this with reasonably few falsely overdetected cases (specificity). Additionally, when the events searched for have a low occurrence rate, as is now the case for simple lesions treated with drug-eluting stents, a correct exclusion of restenosis (high NPV) allows focus on the small number of patients with a positive test result, in whom invasive angiography would be performed to confirm and treat the ISR, or definitively exclude it.
As for any imaging modalities, MSCT provides information about anatomy and lumen size, but does not provide information about whether a stenosis is flow limiting. However, nonsignificant in-stent neointimal proliferation is very unlikely to be flow limiting, allowing a noninvasive follow-up of these types of lesions. On the other hand, lesions classified as binary ISR will need further evaluation to clarify their pathophysiological significance, and this can be performed either noninvasively (i.e., myocardial perfusion scanning) or invasively (i.e., fractional flow reserve). Our results show that 64-MSCT correctly excludes binary ISR. However, the PPV for the overall population is low. As a result, nearly 1 of 2 patients sent for angiography after ISR detection by CTCA will have with a false-positive result.
It also should be emphasized that this study is a semiquantitative approach, and that a quantitative analysis probably would show a variation in the stenosis severity when expressed in absolute numbers. However, these variations in absolute stenosis severity between ICA and CTCA do not affect the binary decision for ISR, which is the most clinically relevant information. Additionally, the decision of how to treat ISR also depends on its pattern (focal, diffuse, proliferative, occlusive), which was adequately classified by CTCA in our study.
Based on this study, we think that 64-MSCT has a role to play in the detection of binary ISR. The best candidates for such an examination probably include patients with atypical symptoms. In these patients, a normal CTCA that excludes restenosis with a high probability would allow deferment of angiography. Asymptomatic patients should be followed up only clinically, and patients with typical symptoms should be referred directly for angiography.
The relatively high rate of ISR observed in our study is explained by the predominant use of bare-metal stents (82%), and also by a high proportion of treated complex lesions. Several studies reported the influences of stent morphology and stent diameter on the rate of ISR (22–24). Additionally, stent morphology influences its CT visualization as well as the underlying lumen, which may affect the ability of CTCA to detect ISR. In our study, no statistically significant differences according to stent morphology for the detection of ISR could be shown. This study was, however, not powered to answer such subanalysis, and differences according to stent morphology therefore cannot be excluded.
As mentioned earlier, causes of ISR can be divided mainly into 2 areas: neointimal proliferation and mechanical causes. The MSCT allows depicting finely the stent structure in a 2- and 3-dimensional way. An MSCT can detect stent fracture or deformity, as well as proper stent overlap and the effect of using the kissing balloon technique between the stent struts (25). These CT advantages became possible after improvement of the scanner's spatial and temporal resolution (26,27).
Challenges in CTCA.
Our analysis showed that CTCA had 6 false-positive segments. The main reasons for overestimation is calcification, overlapping of stents, and motion artifact. Similarly, we had 12% unassessable segments. Although in most part this problem is caused by inadequate resolution, we have some room for improvement.
Former MSCT generations were unable to depict fine objects with a high CT density, such as calcium or metallic structures, which generate artifacts. Therefore, many investigators had excluded candidates after stent implantation from their study population. Recently some investigators reported detection of ISR (13–16,28–32), and others presented in vitro stent depiction using MSCT (27,33). However, there are very few data on the visualization of in vivo stent structure. The improved resolution of 64-MSCT allows us to overcome most of those limitations.
To improve stent visibility and to decrease artifact, specific reconstructions were performed. In addition to reconstruction with ordinary field of view, phase of cardiac cycle, and convolution kernel (B20f or B30f, smooth or medium-smooth kernel), we made additional reconstructions stent by stent with another convolution kernel (B46f, HeartView kernel) in limited field of view (16). These reconstructions were repeated usually in a few different phases for each stent until a satisfactory image was obtained. A smooth kernel is suitable for delineating vessel lumen, vessel wall, and surrounding tissue, whereas a sharp kernel (HeartView kernel) is good at visualizing objects located next to fine and high-density obstacles such as calcium deposit or stent. The same reconstruction protocols were performed for each stented segment by both observers, with an excellent reproducibility, as shown by the low interobserver and intraobserver variability.
Moreover, we tried to get adequate heart rate control with beta-blocker administration if necessary, and with patient relaxation. Also, adequate examination explanation, rehearsal of breath-hold, and tools for body holding ensure better image quality, and consequently a better diagnostic accuracy. Examination preparation is particularly important in cases after stenting. The initial extra time spent for preparation or reconstruction allows saving a greater amount of time and energy for the analysis and interpretation of images with an adequate quality. One of the future challenges is to reduce the radiation doses, because it is currently higher than for ICA. On the other hand, the contrast media amount was similar to the amount used for ICA.
This study has some limitations. First, many different sort of stents were implanted, and the number of each stent was too small for proper comparison between stents. Second, we took approximately 8 months to collect the subjects, so that slight changes may have occurred in the opacification of contrast media, preparation of beta-blocker, or other procedure steps.
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Summary and Conclusions
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On a segment-based analysis including unassessable segments, sensitivity, specificity, PPV, and NPV were 92%, 81%, 54%, and 98%, respectively. One-hundred and ten of 125 stented segments (88%) were adequately assessable. On the patient-based analysis, 71 of 81 patients (88%) had adequate images on CTCA, and the sensitivity, specificity, PPV, and NPV were 90%, 79%, 58%, and 96%, respectively. Binary restenosis can be excluded with high probability by CTCA, with a moderate rate of false-positive results. Consequently, we think that CTCA has a role to play in the subset of patients with atypical symptoms.
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