Rationale and Objectives
Blooming artifact from calcified plaques often renders measurement of stenosis impossible on coronary computed tomographic angiography (CTA). We sought to evaluate the impact of modifying window level on reducing blooming artifact, and its impact on stenosis quantification.
Materials and Methods
We analyzed 125 calcified segments from 53 patients who underwent CTA and invasive coronary angiography (ICA). Segmental stenosis on CTA was measured using three window settings: width of 1000 Hounsfield units (HU) and level of 200 HU (“default”), 1500/200 HU (“widened”), and width and level based on the mean HU of the calcified plaque and pericoronary fat (“calcium-specific”). Segmental stenosis on ICA was quantified by a blinded experienced reader.
Results
ICA found ≥50% stenosis in 30 segments. Displaying segments with widened and calcium-specific settings improved overall accuracy of detecting ≥50% stenosis ( P ‘s < 0.001) by increasing the rate of accurately quantifying <50% stenosis ( P ‘s < 0.001), and improved correlation of stenosis quantification to ICA ( P ‘s < 0.05). There was no difference in stenosis quantification accuracy between widened and calcium-specific window settings. Limits of agreement between CTA stenosis quantification and ICA narrowed with widened and calcium-specific settings.
Conclusions
We showed for the first time that in calcified segments, widening display window width significantly improved CTA quantification of stenosis compared to ICA.
From the time of the introduction of coronary computed tomographic angiography (CTA) as a diagnostic tool, multiple studies have shown degradation in the accuracy of CTA when coronary arteries contain heavy calcification, resulting in significant reductions in both sensitivity and specificity . Calcification causes “blooming” artifact, which produces a falsely enlarged appearance of the plaque from partial-volume averaging effects . Blooming can be severe enough to render segments uninterpretable . Such difficulty has prompted some investigators to advise against performance of CTA when prior imaging has already documented a high coronary calcium score (CCS) .
When interpreting CTA image, the apparent size of calcification can be reduced by increasing display window width, potentially reducing blooming artifact. However, its impact on stenosis evaluation has not been investigated. We evaluated whether increasing the window width improved stenosis quantification of calcified coronary artery segments on CTA compared to invasive coronary angiography (ICA).
Materials and methods
Study Population
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Coronary Calcium Scoring
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CTA Performance and Evaluation
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ICA Performance and Evaluation
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Statistical Analysis
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Results
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Table 1
Characteristics of Patients and Coronary Artery Segments
Count (%) or Mean ± SD Median (Range)Patient characteristics: n = 53 Age 70 ± 9 71 (44–87) Men 32 (60) — BMI 26.7 ± 4.1 26.4 (18.9–35.5) Diabetes 16 (30) — Hypercholesterolemia 40 (75) — Hypertension 33 (65) — Currently smoking 5 (9) — Family CAD history 16 (30) — Asymptomatic 12 (23) — Typical angina 12 (23) — Total Agatston score 1309 ± 807 1160 (224–3255) Peak heart rate during CTA 70 ± 22 65 (44–187) Heart rate variation during CTA 11 ± 21 5 (0–134)Segment characteristics: n = 125 Left main 13 (10) — Left anterior descending 53 (42) — Circumflex 19 (15) — Right coronary 40 (32) — Agatston score of qualifying plaque 259 ± 210 187 (101–1027) Volume score of qualifying plaque 201 ± 159 154 (72–747) Calcium >180° arc at stenotic site 46 (37) — Multiple calcifications at stenosis 31 (25) — ≥50% Diameter stenosis by QCA 30 (24) —
BMI, body mass index; CAD, coronary artery disease; CTA, coronary computed tomographic angiography; QCA, quantitative coronary angiography; SD, standard deviation.
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Evaluable Segments: Reader 1
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Table 2
Performance of CTA Quantification Accuracy Using Different Window Settings in Evaluable Segment
Default (D) Widened (W) Calcium-specific (CS) Comparison P values W to D CS to D CS to W Reader 1 ( n = 113) With ≥50% stenosis on QCA 27 27 27 — — — Correctly found by CTA quantification 23/27 (85%) 22/27 (81%) 20/27 (74%) .596 .193 .407 With <50% stenosis on QCA 86 86 86 — — — Correctly found by CTA quantification 51/86 (59%) 72/86 (84%) 77/86 (90%) <.001 <.001 .096 CTA PPV 23/58 (40%) 22/36 (61%) 20/29 (70%) .043 .010 .510 CTA NPV 51/55 (93%) 72/77 (94%) 77/84 (92%) .861 .821 .657 Total accuracy by CTA 74/113 (65%) 94/113 (83%) 97/113 (86%) <.001 <.001 .394 CTA quantification within 10% of QCA 45/113 (40%) 66/113 (58%) 67/113 (59%) <.001 <.001 .846 Spearman correlation 0.53 0.63 0.64 .005 .012 .379 Reader 2 ( n = 117) With ≥50% stenosis on QCA 27 27 27 — — — Correctly found by CTA quantification 15/27 (56%) 13/27 (48%) 13/27 (48%) .435 .435 1.000 With <50% stenosis on QCA 90 90 90 — — — Correctly found by CTA quantification 62/90 (69%) 81/90 (90%) 82/90 (91%) <.001 <.001 .714 CTA PPV 15/33 (45%) 13/22 (59%) 13/21 (62%) .322 .238 .850 CTA NPV 62/74 (84%) 81/95 (85%) 82/96 (85%) .791 .769 .976 Total accuracy by CTA 77/117 (66%) 94/117 (80%) 95/117 (81%) <.001 <.001 .803 CTA quantification within 10% of QCA 43/117 (37%) 50/117 (43%) 53/117 (45%) .190 .063 .578 Spearman correlation 0.36 0.44 0.47 .028 .011 .101
CTA, coronary computed tomographic angiography; NPV, negative predictive value; PPV, positive predictive value; QCA, quantitative coronary angiography.
Table 3
Results of Bland–Altman Analysis of Agreement between CTA and QCA Using Different Window Settings
n Mean Difference (%) Lower Limit of Agreement (%) Upper Limit of Agreement (%) Range of Agreement Limits (%) Reader 1 Default 113 8.7 −25.0 42.4 67.4 Widened 113 0.5 −28.9 29.9 59.7 Calcium-specific 113 −1.5 −29.4 26.4 56.0 Reader 2 Default 117 4.6 −30.4 39.6 70.0 Widened 117 −5.7 −40.3 28.9 69.2 Calcium-specific 117 −7.4 −42.3 27.5 69.8
CTA, coronary computed tomographic angiography; QCA, quantitative coronary angiography.
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Evaluable Segments: Reader 2
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Uninterpretable Segments: Reader 1
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Uninterpretable Segments: Reader 2
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Potential Predictors of Improvement with Widened and Calcium-specific Window Settings
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Discussion
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Conclusions
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