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Coronary Artery Stent Evaluation by Combining Iterative Reconstruction and High-resolution Kernel at Coronary CT Angiography

Posted Oct 31, 2012 Updated Apr 10, 2023
By Yoshinori Funama PhD , Seitaro Oda MD , Daisuke Utsunomiya MD , Katsuyuki Taguchi PhD , Toshiaki Shimonobo RT , Yasuyuki Yamashita MD , Kazuo Awai MD
10 min read

Purpose

To evaluate stent lumen visualization by combining high-resolution cardiac kernel and the iterative reconstruction (iDose) on an anthropomorphic moving heart phantom and in patients at coronary computed tomography (CT) angiography.

Materials and Methods

We used the moving heart phantom and a 64 detector-row CT, retrospectively gated helical scanning, and image reconstruction. The heart rate was set at nonpulsating condition of 0 beats/min, 50 beats/min, and 80 beats/min. The 120-kV images were reconstructed in synchronization with electrocardiogram data using filtered back projection (FBP) or iDose algorithm and standard kernel/filter (CB) or high-resolution kernel/filter (CD). We measured image noise, the kurtosis, and stent lumen diameter in the phantom study. We also assessed the visual inspections by two radiologists.

Results

With cardiac motion at 50 and 80 beats/min, the difference of kurtosis improved with CD relative to CB ( P < .05). iDose algorithm with level 7 provided lowest noise, with no statistically significance in difference of the kurtosis relative to level 4 ( P > .05). Without cardiac motion at 0 beats/min, the stent lumen diameter measurements with CD kernel were better relative to CB kernel ( P < .05). In addition, no significant difference was found in stent lumen diameter between iDose level 4 and level 7 ( P > .05).

Conclusion

The use of iDose and a sharp kernel allowed improved stent visualization at a lower radiation dose.

Multidetector computed tomography coronary angiography (CTCA) with electrocardiogram (ECG) gating is an accurate noninvasive method to evaluate coronary artery disease . Additionally, current multidetector CT facilitates the reliable detection of in-stent stenosis compared to earlier generations of scanners . However, the issue of overestimating the actual degree of stenosis from blooming artifacts persists . The blooming effect on coronary CT angiographs is attributable to beam hardening; stent struts appear thicker than they are and they often overlap the vessel lumen . Therefore, the assessment of coronary artery stent patency is compromised by blooming artifacts. Compared to the standard reconstruction kernel, the high-resolution cardiac kernel reduces these artifacts and improves visualization of coronary artery stents although image noise is increased as spatial resolution is improved .

The new “iterative reconstruction algorithm (iDose)” involves two denoising components, an iterative maximum likelihood-type sinogram restoration method based on Poisson noise distribution and a local structure model fitting on image data that iteratively decreases uncorrelated noise . Therefore, iDose reduces noise with a limited effect on spatial resolution.

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Materials and methods

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Phantom

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Figure 1, The anthropomorphic moving heart phantom (a) is implanted with a coronary stent (b) . The inner luminal diameter of the stent is 3.0 mm. The degree of stenosis is 0%, 25%, and 50%.

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Retrospectively Gated Helical Scanning and Image Reconstruction

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Measurement of image noise

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Figure 2, Measurements of image noise and the stent lumen diameter. The mean computed tomography number for the phantom was 273 Hounsfield units (HU) (a) ; for the portion containing distilled water, it was 2.8 HU (b) . We acquired five consecutive images in the z direction for each helical scan. Image noise was measured on each image at three different portions of a region of interest (ROI 1, 2, 3). The stent lumen was measured on magnified (×3) images (c) .

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Measurement of kurtosis

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Figure 3, Computed tomography voxel attenuation profiles across the stent for standard kernel/filter (CB) and high-resolution kernel/filter (CD) kernels using multiplanar reformation (MRP) images.

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Measurement of the stent lumen diameter

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Visual inspection of phantom- and clinical images

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Table 1

Description of Stent Type, Manufacture, Material, Length, and Diameter of the Stents

Patient No. Stent Type Manufacturer Material Diameter (mm) Length (mm) 1 Liberté Boston Scientific Stainless steel 2.75 12 2 Tsunami Terumo Stainless steel 4.0 20 3 Xience Abbott vascular Stainless steel 3.0 28 4 Bx Velocity Cordis Stainless steel 3.0 13 5 Endeavor Medtronic vascular Stainless steel 3.0 24 6 Tsunami Terumo Stainless steel 3.0 15 7 Coreflex B. Braun Stainless steel 3.5 13 8 Xience Abbott vascular Stainless steel 3.0 15 9 Tsunami Terumo Stainless steel 3.0 10 10 Vision Guidant Cobalt-chromium alloy 3.5 18 11 Cypher Cordis Stainless steel 3.0 13 12 Endeavor Medtronic vascular Stainless steel 2.75 24

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Statistical analysis

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Results

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Figure 4, Image noise on images acquired at different effective current-time products and with different reconstruction algorithms without cardiac motion artifacts at a heart rate of 0 beats/min. CB, standard kernel/filter; CD, high-resolution kernel/filter; CT, computed tomography; FBP, filtered back projection; HU, Hounsfield units; iDose, iterative reconstruction algorithm.

Table 2

Difference of Kurtosis (Diff. kurtosis) between Each Kurtosis and Kurtosis at FBP with CB Kernel in Each Heart Rate on Images Obtained at 450 and 900 Effective mAs

Heart Rate (beats/min) 0 50 80 450 mAs FBP 0.00 0.00 0.00 CB iDose level4 0.03 0.13 −0.10 iDose level7 0.08 0.04 −0.09 Level 4 vs. level 7P = .651P = .102P = .148 FBP 2.34 2.21 1.98 CD iDose level 4 2.21 2.35 2.35 iDose level 7 2.33 2.33 2.46 level4 vs. level7P = .867P = .206P = .095 CB vs. CD_P_ < .05P < .05P < .05 CB −0.10 −0.05 −0.24 900 mAs FBP CD 2.63 2.40 1.90

CB, standard kernel/filter; CD, high-resolution kernel/filter; FBP, filtered back projection; iDose, iterative reconstruction.

Table 3

MLD, Standard Deviation, and ALN of the Stent Lumen Obtained by Two Radiologists

Heart Rate (beats/min) 0 50 80 MLD (mm) ALN (%) MLD (mm) ALN (%) MLD (mm) ALN (%) 450 mAs FBP 1.35 (0.11) 55.0 1.31 (0.15) 56.3 1.19 (0.01) 60.3 CB iDose level 4 1.39 (0.07) 53.7 1.24 (0.14) 58.7 1.19 (0.01) 60.3 iDose level 7 1.35 (0.05) 55.0 1.27 (0.11) 57.7 1.20 (0.01) 60.0 FBP 1.50 (0.03) 50.0 1.48 (0.05) 50.7 1.38 (0.02) 54.0 CD iDose level 4 1.49 (0.10) 50.3 1.57 (0.06) 47.7 1.42 (0.04) 52.7 iDose level 7 1.48 (0.03) 50.7 1.54 (0.08) 48.7 1.42 (0.04) 52.7 CB vs CD_P_ < .01P < .01P < .01 900 mAs CB 1.39 (0.07) 53.7 1.29 (0.18) 57.0 1.19 (0.01) 60.3 FBP CD 1.57 (0.03) 47.7 1.59 (0.04) 47.0 1.42 (0.07) 52.7

ALN, artificial lumen narrowing; CB, standard kernel/filter; CD, high-resolution kernel/filter; FBP, filtered back projection; iDose, iterative reconstruction; MLD, mean lumen diameter.

Figure 5, Coronary stent images in the longitudinal plane using different reconstruction algorithms and kernels. The images were acquired at a heart rate of 50 beats/min and at 450 and 900 effective mAs. Stent stenosis of 50% was most easily detected on longitudinal stent images acquired with iterative reconstruction algorithm (iDose) level 7 and the high-resolution kernel/filter (CD) kernel. CB, standard kernel/filter; FBP, filtered back projection.

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Table 4

Mean Visual Inspection Scores Assigned by Two Radiologists to Images Acquired with the FBP Algorithm and the CB and the CD Kernel and the iDose Level 7 Algorithm with the CD Kernel

Exam No. Mean Score FBP with CB FBP with CD iDose with CD 1 2 3 4 2 2 2 3 3 2 2 3 4 2 2 3 5 2.5 2 2.5 6 2.5 2 2.5 7 2 2 3 8 3 3 4 9 2 3 3.5 10 3 3 4 11 3 3 4 12 2.5 2.5 3.5 Mean 2.4 2.5 3.3

CB, standard kernel/filter; CD, high-resolution kernel/filter; FBP, filtered back projection; iDose, iterative reconstruction.

FBP with CB vs. FBP with CD: P > .05.

FBP with CB vs. iDose with CD: P < .05.

FBP with CD vs. iDose with CD: P < .05.

1 = poor, indicating that no clinical information could be obtained because the stent lumen and stent skeleton could not be identified because of severe artifacts; 2 = fair, indicating that the stent lumen was assessable but partially obscured because of moderate artifact, yielding insufficient information because in-stent patency was indeterminate; 3 = good, indicating that the stent skeleton was demonstrated with some degradation in the image quality because of small artifacts, yielding acceptable clinical information; 4 = excellent, indicating that the full length of the stent lumen was clearly assessable, artifacts were slight, and the clinical information yielded was very useful.

Figure 6, Representative clinical images acquired with the FBP algorithm with CB and CD kernels and the iDose level 7 algorithm with the CD kernel. CB, standard kernel/filter; CD, high-resolution kernel/filter; FBP, filtered back projection; iDose, iterative reconstruction algorithm.

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Discussion

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Academic Radiology, Volume 19, Issue 11
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