Correlation of Carotid Stenosis Diameter and Cross-Sectional Areas with CT Angiography
E.S. Bartletta,
S.P. Symonsb and
A.J. Foxb
a Department of Neuroradiology, Northwestern University, Chicago, Ill
b Department of Neuroradiology, Sunnybrook and Women’s College Health Sciences Centre, University of Toronto, Toronto, Ontario, Canada
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Fig 1. Quantification of a symmetric right carotid bulb stenosis. A, Axial CTA source image showing symmetric stenosis of the right carotid bulb (white arrow). B, Axial magnification of the symmetric right carotid bulb stenosis with measurement calipers (calipers marked [A], showing measurement of 0.21 cm [2.1 mm]). C, Axial magnification of the symmetric right carotid bulb stenosis with the AGFA Impax 4.5 VT measuring the cross-sectional 2D area of 0.02 cm2 (2.0 mm2).
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Fig 2. Quantification of an asymmetric right carotid bulb stenosis. A, Axial CTA source image showing asymmetric stenosis of the right carotid bulb (white arrow), with partially calcified posterior carotid bulb wall. B, Axial magnification of the asymmetric right carotid bulb stenosis with measurement calipers placed at the region of narrowest stenosis (calipers marked [A], showing measurement of 0.19 cm [1.9 mm]). C, Axial magnification of the asymmetric right carotid bulb stenosis with the AGFA Impax 4.5 VT measuring the cross-sectional 2D area of 0.03 cm2 (3.0 mm2). Note that the narrowest diameter is slightly smaller than on Fig 1, though the area is slightly larger than on Fig 1.
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Fig 3. Quantification of an irregular, asymmetric carotid bulb stenosis with calcification. A, Axial CTA source image showing an asymmetric stenosis (white arrow). B, Axial magnification of the asymmetric carotid bulb stenosis with measurement calipers placed at the region of narrowest stenosis (calipers marked [A], showing measurement of 0.27 cm [2.7 mm]). C, Axial magnification of the asymmetric carotid bulb stenosis with the AGFA Impax 4.5 VT measuring the cross-sectional 2D area of 0.14 cm2 (14.0 mm2).
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Fig 4. Quantification of a diminutive residual carotid bulb lumen. A, Axial CTA source image showing a diminutive left residual carotid bulb lumen with poor contrast filling (white arrow). B, Axial magnification of the residual carotid bulb lumen with measurement calipers placed at the region of narrowest stenosis (calipers marked [A], showing measurement of 0.11 cm [1.1 mm]). C, Axial magnification of the residual carotid bulb lumen with the AGFA Impax 4.5 VT. The VT could not accurately measure the cross-sectional 2D area of the lumen because there was very little contrast-filling of the diminutive carotid bulb. The difference in the HUs between the contrast-filled lumen and the surrounding tissues was not great enough for the VT to accurately measure the lumen.
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Fig 5. Quantification of a diminutive residual carotid bulb lumen. A, Axial CTA source image showing a diminutive right residual carotid bulb lumen (white arrow). B, Axial magnification of the residual carotid bulb lumen with measurement calipers placed at the region of narrowest stenosis (calipers marked [A], showing measurement of 0.10 cm [1.0 mm]). C, Axial magnification of the residual carotid bulb lumen with the AGFA Impax 4.5 VT, showing the cross-sectional 2D area of 0.02 cm2 (2.0 mm2). The HUs between the contrast-filled lumen and the surrounding tissues was great enough for the VT to accurately measure the lumen, despite the small lumen size.
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Fig 6. Pearson correlation between the calculated stenosis area (based upon the narrowest diameter) and the measured cross-sectional VT area of stenosis (mm2). The calculated area showed a trend of underestimating the area in comparison to the measured area. This trend is not surprising, because the calculated area is based upon the narrowest stenosis, which does not account for noncircular stenoses. Nonetheless, there was excellent correlation between these 2 methods of area quantification (correlation coefficient = 0.87; n = 176).
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Fig 7. Pearson correlation between the mean carotid stenosis narrowest diameter (mm) and the mean cross-sectional VT stenosis area (mm2). There was excellent correlation between the 2 stenosis quantification measures at 0.88 (n = 176). This supports the use of the narrowest diameter measurement to quantify carotid bulb stenosis, in lieu of the more precise cross-sectional area measurement. A regression curve was plotted over the data with an R2 value of 0.76, which indicates that the narrowest diameter has an excellent predictive ability to estimate the cross-sectional area (as defined by the VT).
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Fig 8. Pearson correlation between the mean carotid stenosis narrowest diameter (mm) and the mean calculated stenosis area (mm2). As anticipated, there was perfect correlation between the 2 methods of stenosis quantification at 1.0 (n = 176). A regression curve was plotted over the data, showing that the ability to predict the calculated area from the stenosis diameter is perfect with an R2 value of 1.0. This is expected, because the calculated area is based on the diameter measurements. The data provide a graphic example of the nonlinear relationship between the narrowest diameter and the area, which demonstrates that minimal changes in the diameter of the carotid lumen cause more dramatic changes in the area of the lumen.
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