Accuracy of dual-source computed tomography in quantitative assessment of low density coronary stenosis—a motion phantom study

Does the Tube Voltage Affect the Characterization of Coronary Plaques on 100- and 120-kVp Computed Tomography Scans

OBJECTIVE

The aim of this study was to compare the diagnostic performance of 100- and 120-kVp coronary computed tomography (CT) angiography (CCTA) scans for the identification of coronary plaque components.

METHODS

We included 116 patients with coronary plaques who underwent CCTA and integrated backscatter intravascular ultrasound studies. On 100-kVp scans, we observed 24 fibrous and 24 fatty/fibrofatty plaques; on 120-kVp scans, we noted 27 fibrous and 41 fatty/fibrofatty plaques. We compared the fibrous and the fatty/fibrofatty plaques, the CT number of the coronary lumen, and the radiation dose on scans obtained at 100 and 120 kVp. We also compared the area under the receiver operating characteristic (ROC) curve of the coronary plaques on 100- and 120-kVp scans with their ROC curves on integrated backscatter intravascular ultrasound images.

RESULTS

The mean CT numbers of fatty and fatty/fibrofatty plaques were 5.71 ± 36.5 and 76.6 ± 33.7 Hounsfield units (HU), respectively, on 100-kVp scans; on 120-kVp scans, they were 13.9 ± 29.4 and 54.5 ± 22.3 HU, respectively. The CT number of the coronary lumen was 323.1 ± 81.2 HU, and the radiation dose was 563.7 ± 81.2 mGy-cm on 100-kVp scans; these values were 279.3 ± 61.8 HU and 819.1 ± 115.1 mGy-cm on 120-kVp scans. The results of ROC curve analysis identified 30.5 HU as the optimal diagnostic cutoff value for 100-kVp scans (area under the curve = 0.93, 95% confidence interval = 0.87-0.99, sensitivity = 95.8%, specificity = 78.9%); for 120-kVp plaque images, the optimal cutoff was 37.4 HU (area under the curve = 0.87, 95% confidence interval = 0.79-0.96, sensitivity = 82.1%, specificity = 85.7%).

CONCLUSIONS

For the discrimination of coronary plaque components, the diagnostic performance of 100- and 120-kVp CCTA scans is comparable.

Quantification of uncertainty in the assessment of coronary plaque in CCTA through a dynamic cardiac phantom and 3D-printed plaque model

The purpose of this study was to develop a dynamic physical cardiac phantom with a realistic coronary plaque to investigate stenosis measurement accuracy under clinically relevant heart-rates. The coronary plaque model (5 mm diameter, 50% stenosis, and 32 mm long) was designed and 3D-printed with tissue equivalent materials (calcified plaque with iodine-enhanced lumen). Realistic cardiac motion was modeled by converting computational cardiac motion vectors into compression and rotation profiles executed by a commercial base cardiac phantom. The phantom was imaged on a dual-source CT system applying a retrospective gated coronary CT angiography (CCTA) protocol using synthesized motion-synchronized electrocardiogram (ECG) waveforms. Multiplanar reformatted images were reconstructed along vessel centerlines. Enhanced lumens were segmented by five independent operators. On average, stenosis measurement accuracy was 0.9% positively biased for the motion-free condition. Average measurement accuracy monotonically decreased from 0.9% positive bias for the motion-free condition to 18.5% negative bias at 90 beats per minute. Contrast-to-noise ratio, lumen circularity, and segmentation conformity also decreased monotonically with increasing heart-rate. These results demonstrate successful implementation of a base cardiac phantom with a 3D-printed coronary plaque model, relevant motion profile, and coordinated ECG waveform. They further show the utility of the model to ascertain metrics of CCTA accuracy and image quality under realistic plaque, motion, and acquisition conditions.

Stenosis quantification of coronary arteries in coronary vessel phantoms with second-generation dual-source CT: influence of measurement parameters and limitations

OBJECTIVE

The purpose of this study was to use second-generation dual-source CT to assess the influence of size, degree of stenosis, luminal contrast attenuation, and plaque geometry on stenosis quantification in a coronary artery phantom.

MATERIALS AND METHODS

Six vessel phantoms with three outer diameters (2, 3, and 4 mm), each containing three radiolucent plaques (72.2 HU) that simulated eccentric and concentric 43.8%, 75%, and 93.8% stenoses were made with a 3D printer system. These phantoms were filled with an iodine-saline solution mixture at luminal attenuations of 150, 200, 250, 300, and 350 HU and were attached to a cardiac motion simulator. Dual-source CT was performed with a standardized ECG-gated protocol (120 kV, 360 mAs per rotation) at a simulated heart rate of 70 beats/min. Two independent readers quantified the degree of stenosis using area-based measurements.

RESULTS

All measurements were highly reproducible (intraclass correlation, ≥ 0.791; p < 0.001). The mean measured degree of stenosis for a phantom with a 3-mm outer diameter at 250-HU luminal attenuation was 49.0% ± 10.0% for 43.8% stenosis, 71.7% ± 9.6% for 75.0% stenosis, and 85.4% ± 5.9% for 93.8% stenosis. With decreasing phantom size, measurement error increased for all degrees of stenosis. The absolute error increased for measurements at a low luminal attenuation of 150 HU (p < 0.001) and for low-grade stenoses compared with medium-and high-grade stenoses (p < 0.001).

CONCLUSION

The results are an overview of factors that influence stenosis quantification in simulated coronary arteries. Dual-source CT is highly reproducible and accurate for quantification of low-density stenosis in vessels with a diameter of 3 mm and attenuation of at least 200 HU for different degrees of stenosis and plaque geometry.

Accuracy of 128-slice dual-source CT using high-pitch spiral mode for the assessment of coronary stents: first in vivo experience

OBJECTIVE

To investigate the accuracy of 128-slice dual-source CT using high-pitch spiral mode (HPS) for the assessment of coronary stents.

METHODS

We conducted a prospective study on patients with previous stent implantation due to recurred suspicious symptoms of angina with positive findings at stress testing scheduled for coronary angiography (CA), while dual source computed tomography (DSCT) examinations were randomly done by one of the three different scan modes [HPS, sequential mode (SEQ), low-pitch spiral mode (LPS)] one week before CA examinations. The image quality, radiation dose and stent patency of DSCT were evaluated blinded to the results of CA.

RESULTS

180 patients with total 256 stents were enrolled in this study. There was no significant difference on the image quality of DSCT by HPS (1.4±0.5), SEQ (1.5±0.5) and LPS (1.3±0.6) (P>0.05). The noise of images reconstructed with B26f kernel in HPS is significantly increased than in SEQ/LPS (P<0.05), while no significant difference with images reconstructed with B46f kernel (P>0.05). Heart rate (HR) variability had a slight impact on the image quality for HPS (P<0.05), not for LPS/SEQ (P>0.05). In the assessment of stent restenosis compared with CA on per-stent basis, there was no significant difference on sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of DSCT using HPS (100%, 97.1%, 83.3%, 100%), LPS (92.3%, 95.9%, 80%, 98.6%) and SEQ (93.3%, 97.3%, 87.5%, 98.6%) (P>0.05). The effective dose of DSCT by HPS (1.0±0.5mSv) is significant less than that by SEQ (3.0±1.4mSv) or LPS (13.0±5.4mSv) (P<0.01).

CONCLUSIONS

DSCT using HPS provides good diagnostic accuracy on coronary stent patency compared with CA, similar to that by SEQ/LPS, whereas with lower effective dose in patients with HR lower than 65bpm.

Comparison between integrated backscatter intravascular ultrasound and 64-slice multi-detector row computed tomography for tissue characterization and volumetric assessment of coronary plaques

Background

The purpose of this study was to determine the cut-off values of Hounsfield units (HU) for the discrimination of plaque components and to evaluate the feasibility of measurement of the volume of plaque components using multi-detector row computed tomography (MDCT).

Methods

Coronary lesions (125 lesions in 125 patients) were visualized by both integrated backscatter intravascular ultrasound (IB-IVUS) and 64-slice MDCT at the same site. The IB values were used as a gold standard to determine the cut off values of HU for the discrimination of plaque components.

Results

Plaques were classified as lipid pool (n =50), fibrosis (n =65) or calcification (n =35) by IB-IVUS. The HU of lipid pool, fibrosis and calcification were 18 ± 18 HU (−19 to 58 HU), 95 ± 24 HU (46 to 154 HU) and 378 ± 99 HU (188 to 605 HU), respectively. Using receiver operating characteristic curve analysis, a threshold of 50 HU was the optimal cutoff values to discriminate lipid pool from fibrosis. Lipid volume measured by MDCT was correlated with that measured by IB-IVUS (r =0.66, p <0.001), whereas fibrous volume was not (r =0.21, p =0.059).

Conclusion

Lipid volume measured by MDCT was moderately correlated with that measured by IB-IVUS. MDCT may be useful for volumetric assessment of the lipid volume of coronary plaques, whereas the assessment of fibrosis volume was unstable.