Quantitative assessment of in-stent dimensions: a comparison of 64 and 16 detector multislice computed tomography to intravascular ultrasound

Feasibility of improving vascular imaging in the presence of metallic stents using spectral photon counting CT and K-edge imaging

Correct visualization of the vascular lumen is impaired in standard computed tomography (CT) because of blooming artifacts, increase of apparent size, induced by metallic stents and vascular calcifications. Recently, due to the introduction of photon-counting detectors in the X-ray imaging field, a new prototype spectral photon-counting CT (SPCCT) based on a modified clinical CT system has been tested in a feasibility study for improving vascular lumen delineation and visualization of coronary stent architecture. Coronary stents of different metal composition were deployed inside plastic tubes containing hydroxyapatite spheres to simulate vascular calcifications and in the abdominal aorta of one New Zealand White (NZW) rabbit. Imaging was performed with an SPCCT prototype, a dual-energy CT system, and a conventional 64-channel CT system (B64). We found the apparent widths of the stents significantly smaller on SPCCT than on the other two systems in vitro (p < 0.01), thus closer to the true size. Consequently, the intra-stent lumen was significantly larger on SPCCT (p < 0.01). In conclusion, owing to the increased spatial resolution of SPCCT, improved lumen visualization and delineation of stent metallic mesh is possible compared to dual-energy and conventional CT.

Clinical evaluation of a commercial orthopedic metal artifact reduction tool for CT simulations in radiation therapy

PURPOSE

Severe artifacts in kilovoltage-CT simulation images caused by large metallic implants can significantly degrade the conspicuity and apparent CT Hounsfield number of targets and anatomic structures, jeopardize the confidence of anatomical segmentation, and introduce inaccuracies into the radiation therapy treatment planning process. This study evaluated the performance of the first commercial orthopedic metal artifact reduction function (O-MAR) for radiation therapy, and investigated its clinical applications in treatment planning.

METHODS

Both phantom and clinical data were used for the evaluation. The CIRS electron density phantom with known physical (and electron) density plugs and removable titanium implants was scanned on a Philips Brilliance Big Bore 16-slice CT simulator. The CT Hounsfield numbers of density plugs on both uncorrected and O-MAR corrected images were compared. Treatment planning accuracy was evaluated by comparing simulated dose distributions computed using the true density images, uncorrected images, and O-MAR corrected images. Ten CT image sets of patients with large hip implants were processed with the O-MAR function and evaluated by two radiation oncologists using a five-point score for overall image quality, anatomical conspicuity, and CT Hounsfield number accuracy. By utilizing the same structure contours delineated from the O-MAR corrected images, clinical IMRT treatment plans for five patients were computed on the uncorrected and O-MAR corrected images, respectively, and compared.

RESULTS

Results of the phantom study indicated that CT Hounsfield number accuracy and noise were improved on the O-MAR corrected images, especially for images with bilateral metal implants. The γ pass rates of the simulated dose distributions computed on the uncorrected and O-MAR corrected images referenced to those of the true densities were higher than 99.9% (even when using 1% and 3 mm distance-to-agreement criterion), suggesting that dose distributions were clinically identical. In all patient cases, radiation oncologists rated O-MAR corrected images as higher quality. Formerly obscured critical structures were able to be visualized. The overall image quality and the conspicuity in critical organs were significantly improved compared with the uncorrected images: overall quality score (1.35 vs 3.25, P = 0.0022); bladder (2.15 vs 3.7, P = 0.0023); prostate and seminal vesicles∕vagina (1.3 vs 3.275, P = 0.0020); rectum (2.8 vs 3.9, P = 0.0021). The noise levels of the selected ROIs were reduced from 93.7 to 38.2 HU. On most cases (8∕10), the average CT Hounsfield numbers of the prostate∕vagina on the O-MAR corrected images were closer to the referenced value (41.2 HU, an average measured from patients without metal implants) than those on the uncorrected images. High γ pass rates of the five IMRT dose distribution pairs indicated that the dose distributions were not significantly affected by the CT image improvements.

CONCLUSIONS

Overall, this study indicated that the O-MAR function can remarkably reduce metal artifacts and improve both CT Hounsfield number accuracy and target and critical structure visualization. Although there was no significant impact of the O-MAR algorithm on the calculated dose distributions, we suggest that O-MAR corrected images are more suitable for the entire treatment planning process by offering better anatomical structure visualization, improving radiation oncologists' confidence in target delineation, and by avoiding subjective density overrides of artifact regions on uncorrected images.

Association of metabolic syndrome and diabetes with subclinical coronary stenosis and plaque subtypes in middle-aged individuals

AIMS

  The presence of subclinical stenosed coronary segments and plaque subtypes has not been compared among those with metabolic syndrome, diabetes, or neither condition in middle-aged individuals. In select, intermediate-risk subjects, it may be reasonable to directly measure atherosclerosis burden by low-dose, multidetector-row computed tomographic coronary angiography.

METHODS

  We performed a cross-sectional analysis of 1024 consecutive, newly self-referred subjects (692 men, 332 women; mean age 53.0±9.7 years) who underwent health evaluation at the China Medical University Hospital. Participants had at least one cardiac risk factor, but no known coronary heart disease.

RESULTS

  Among our 1024 subjects, 135 had diabetes, 334 had metabolic syndrome and 555 had neither condition. The subjects with diabetes and those with metabolic syndrome had a higher prevalence of non-calcified, calcified and mixed-type plaques and stenosed coronary segments than the subjects with neither condition (P<0.05). The odds ratios for diabetes and the presence of any plaque, mixed plaque, calcified plaque and stenosed segment compared with neither metabolic syndrome nor diabetes were 2.893, 3.629, 2.099 and 2.036, respectively, all of which were significant (P<0.05). The odds ratio for metabolic syndrome and the presence of any plaque compared with neither metabolic syndrome nor diabetes was 1.606 (95% CI 1.063-2.426; P<0.05).

CONCLUSION

  In middle-aged subjects, diabetes was related to an increased risk of the presence of mixed plaques, calcified plaques and stenosed coronary segments. However, metabolic syndrome was related to an increased risk of the presence of any coronary plaque, but not related to stenosed coronary segments.

Assessment of in-stent restenosis using 64-MDCT: analysis of the CORE-64 Multicenter International Trial

OBJECTIVE

Evaluations of stents by MDCT from studies performed at single centers have yielded variable results with a high proportion of unassessable stents. The purpose of this study was to evaluate the accuracy of 64-MDCT angiography (MDCTA) in identifying in-stent restenosis in a multicenter trial.

MATERIALS AND METHODS

The Coronary Evaluation Using Multidetector Spiral Computed Tomography Angiography Using 64 Detectors (CORE-64) Multicenter Trial and Registry evaluated the accuracy of 64-MDCTA in assessing 405 patients referred for coronary angiography. A total of 75 stents in 52 patients were assessed: 48 of 75 stents (64%) in 36 of 52 patients (69%) could be evaluated. The prevalence of in-stent restenosis by quantitative coronary angiography (QCA) in this subgroup was 23% (17/75). Eighty percent of the stents were <or=3.0 mm in diameter.

RESULTS

The overall sensitivity, specificity, positive predictive value, and negative predictive value to detect 50% in-stent stenosis visually using MDCT compared with QCA was 33.3%, 91.7%, 57.1%, and 80.5%, respectively, with an overall accuracy of 77.1% for the 48 assessable stents. The ability to evaluate stents on MDCTA varied by stent type: Thick-strut stents such as Bx Velocity were assessable in 50% of the cases; Cypher, 62.5% of the cases; and thinner-strut stents such as Taxus, 75% of the cases. We performed quantitative assessment of in-stent contrast attenuation in Hounsfield units and correlated that value with the quantitative percentage of stenosis by QCA. The correlation coefficient between the average attenuation decrease and >or=50% stenosis by QCA was 0.25 (p=0.073). Quantitative assessment failed to improve the accuracy of MDCT over qualitative assessment.

CONCLUSION

The results of our study showed that 64-MDCT has poor ability to detect in-stent restenosis in small-diameter stents. Evaluability and negative predictive value were better in large-diameter stents. Thus, 64-MDCT may be appropriate for stent assessment in only selected patients.

Early- and long-term intravascular ultrasound and angiographic findings after bioabsorbable magnesium stent implantation in human coronary arteries

OBJECTIVES

This study aimed to evaluate the degradation rate and long-term vascular responses to the absorbable metal stent (AMS).

BACKGROUND

The AMS demonstrated feasibility and safety at 4 months in human coronary arteries.

METHODS

The PROGRESS-AMS (Clinical Performance and Angiographic Results of Coronary Stenting) was a prospective, multicenter clinical trial of 63 patients with coronary artery disease who underwent AMS implantation. Angiography and intravascular ultrasound (IVUS) were conducted immediately after AMS deployment and at 4 months. Eight patients who did not require repeat revascularization at 4 months underwent late angiographic and IVUS follow-up from 12 to 28 months.

RESULTS

The AMS was well-expanded upon deployment without immediate recoil. The major contributors for restenosis as detected by IVUS at 4 months were: decrease of external elastic membrane volume (42%), extra-stent neointima (13%), and intra-stent neointima (45%). From 4 months to late follow-up, paired IVUS analysis demonstrated complete stent degradation with durability of the 4-month IVUS indexes. The neointima was reduced by 3.6 +/- 5.2 mm(3), with an increase in the stent cross sectional area of 0.5 +/- 1.0 mm(2) (p = NS). The median in-stent minimal lumen diameter was increased from 1.87 to 2.17 mm at long-term follow-up. The median angiographic late loss was reduced from 0.62 to 0.40 mm by quantitative coronary angiography from 4 months to late follow-up.

CONCLUSIONS

Intravascular ultrasound imaging supports the safety profile of AMS with degradation at 4 months and maintains durability of the results without any early or late adverse findings. Slower degradation is warranted to provide sufficient radial force to improve long-term patency rates of the AMS.

Lack of widespread inflammation after contemporary PCI

BACKGROUND

The inflammatory response to percutaneous coronary intervention (PCI) contributes to restenosis. However, it is not known if advances in PCI have attenuated this response. This study sought to determine the prevalence of systemic inflammation immediately after contemporary PCI, and to identify the predictors of the acute proinflammatory response to PCI.

METHODS

Twenty seven consecutive eligible patients undergoing uncomplicated single lesion PCI were recruited. Clinical and procedural characteristics were collected. Neutrophil Mac-1 and plasma matrix metalloproteinase-9 (MMP-9) levels were measured by flow cytometry and ELISA.

RESULTS

Overall, neutrophils were de-activated post-procedure [median (IQR) Mac-1: 329(277-555) versus 423 (273-533) MFI, p=0.011] but MMP-9 was unchanged [2.6 (1.8-5.1) versus 2.0 (1.5-3.8) ng/ml, p=ns]. There was a heterogeneous inflammatory response: Neutrophils were activated in 6 (22%) patients, whilst plasma MMP-9 rose in 10 (37%) patients. Twelve (44%) patients had either neutrophil activation or increased MMP-9 level post-procedure. There was no relationship between these two biomarkers. Lesion length predicted both neutrophil activation (OR, 95%CI: 19.0, 2.0-178.0, p=0.010) and increased MMP-9 (16.0, 1.5-17.2, p=0.022), and lesion complexity predicted the latter (9.6, 1.5-62.2, p=0.018). Presentation with an acute coronary syndrome, diabetes mellitus, receipt of drug-eluting stent, and stent diameter were not associated with an acute inflammatory response to PCI.

CONCLUSIONS

In contrast to the balloon angioplasty era, widespread inflammation is absent in most patients after contemporary PCI. Lesion length and complexity predicted an inflammatory reaction, suggesting it to be primarily a response to vascular injury.

Coronary stent assessment on multidetector computed tomography: Source and predictors of image distortion

BACKGROUND

Metallic stent struts cause imaging artifacts on multidetector computed tomography (MDCT) which interfere with the assessment of in-stent coronary restenosis. We examined the degree of image distortion of implanted coronary stents on MDCT, comparing different stent types, sizes and orientation.

METHODS

We quantified stent dimensions and image distortion of 151 non-opacified coronary stents in 89 patients (81% men, age 65+/-10 years) who underwent MDCT with a 40 slice MDCT scanner. Stent dimension by MDCT was compared with measurements obtained from quantitative coronary angiographic (QCA) in the immediate post-implantation angiogram and with manufacturers' data.

RESULTS

Stent image quality was good for 107 stents (71%), moderate for 38 (25%) and poor in 6 (4%), 2 (<1%) of which were not assessable. Blooming artifact resulted in a mean MDCT luminal (inner) diameter 30+/-14% smaller than QCA diameter (2.0+/-0.5 vs 2.9+/-0.3 mm, p<0.001) and a mean outer diameter exceeding QCA by 31+/-14% (3.8+/-0.5 vs 2.9+/-0.3 mm, p<0.001). MDCT luminal stent diameter was unrelated to strut thickness or the vessel stented but appeared to be smaller for vertically orientated stents (p=0.017), cobalt alloy (vs stainless steel) (p=0.011) and also for different stent types (p=0.006).

CONCLUSION

The luminal dimension of implanted coronary stents, as visualized with 40 slice MDCT, was one third smaller than on invasive angiography. This decrease in visualized stent luminal diameter forms the basis for the difficulty in accurate assessment of in-stent restenosis by MDCT.

Effect of decrease in heart rate variability on the diagnostic accuracy of 64-MDCT coronary angiography

OBJECTIVE

The purpose of this study was to evaluate the effect of average heart rate and heart rate variability on the diagnostic accuracy of 64-MDCT in the assessment of coronary artery stenosis.

SUBJECTS AND METHODS

CT and invasive coronary angiography were performed on 114 patients (mean age, 62 years) referred for known coronary artery disease (n = 26), atypical chest pain (n = 58), and presurgical exclusion of coronary artery disease before abdominal aortic (n = 14) or cardiac valve (n = 16) surgery. The population was divided into two groups depending on median average heart rate (60.0 beats/min) and median heart rate variability (2.7 beats/min) during scanning. Heart rate variability was calculated as SD from the mean heart rate. Two blinded observers using a 4-point scale independently assessed the quality of images of each coronary artery segment and classified each segment as being stenosed (luminal diameter narrowing > 50%) or not. Invasive coronary angiography was used as the reference standard.

RESULTS

In 71 (62.3%) of the patients, 241 significant coronary artery stenoses were identified with invasive coronary angiography. In 11 (9.7%) of the patients, 1.6% (26/1,672) of the segments were not evaluable with CT. Overall sensitivity, specificity, and positive and negative predictive values in a patient-based analysis were 97%, 81%, 90%, and 95%, respectively. Image quality was better (p < 0.05) in the low average heart rate group than in the high average heart rate group, but diagnostic accuracy was comparable for the two groups. In contrast, image quality and diagnostic accuracy were significantly better (p < 0.01) among patients in the low heart rate variability group than in the high heart rate variability group.

CONCLUSION

Lower heart rate variability is associated with higher diagnostic accuracy of 64-MDCT coronary angiography.

Usefulness of 64-detector row computed tomography for evaluation of intracoronary stents in symptomatic patients with suspected in-stent restenosis

To determine whether 64-slice multidetector computed tomographic coronary angiography (MDCTA) can accurately assess the coronary artery lumen in symptomatic patients with previous coronary artery stents and potential in-stent restenosis (ISR). The primary aim was to determine the accuracy of binary ISR exclusion using MDCTA compared with invasive catheter angiography (ICA). Secondary aims were comparisons of stent dimensions measured using MDCTA and variables that affect accuracy. Forty patients with previous stent placement underwent both ICA and 64-slice MDCTA after elective presentation with chest pain, and ICA quantitative coronary angiographic data were used as the reference standard. Thirty-six men and 4 women (age 64 +/- 10 years; range 44 to 83) with 103 stents (2.8 +/- 1.6 stents/patient) were comparatively evaluated (stent exclusion rate 9.6%). There were 45 bare-metal and 58 drug-eluting stents (20 +/- 18 months after implantation) with an average diameter of 3.23 +/- 0.7 mm. Overall accuracy for the detection of significant ISR showed sensitivity, specificity, and positive and negative predictive values of 85%, 86%, 61%, and 96% for proximal stents > or =3 mm, which improved to 100%, 94%, 81%, and 100%; if the visible luminal diameter on MDCTA was <1.5 mm, accuracy decreased to 40%, 84%, 29%, and 90%, respectively. In conclusion, 64-slice MDCTA assessment of symptomatic patients with suspected clinically significant ISR is a realistic alternative to ICA if reference stent diameter is > or =2.5 mm and visible lumen cross-sectional diameter is > or =1.5 mm, for which a negative MDCTA result virtually excludes the presence of significant ISR.