Analysis of left ventricular function, left ventricular outflow tract and aortic valve area using computed tomography: Influence of reconstruction parameters on measurement accuracy

Abstract

Objectives: Computed tomography (CT) allows reproducible assessment of left ventricular (LV) function, left ventricular outflow tract area (LVOT_area) and aortic valve area (AVA). We evaluated the influence of image reconstruction parameters on these measurements.

Methods: We analyzed 45 contrast-enhanced, retrospectively ECG-gated CT datasets acquired on a third-generation dual source system. A standard filtered-back-projection data set (20 cardiac phases (5% steps, 0-95%), 0.6-mm-slice thickness, 512 × 512 matrix) and eight reconstructions with modified slice thickness (1-8 mm), number of cardiac phases (5, 10), matrix size (256×256) and an iterative reconstruction (IR) algorithm were obtained. LV parameters (ejection fraction (EF), stroke volume (SV), end-diastolic (EDV), end-systolic volumes (ESV)), LVOT_area and AVA were assessed.

Results: Differences in LV parameters, LVOT_area and AVA, were only minimal between standard reconstructions and those with modified matrix size, IR algorithm and ≤2 mm slice thickness, while reconstructions with 8-mm slice thickness significantly overestimated SV (p < 0.001) and EDV (p = 0.016). AVA planimetry in reconstructions with ≥5 mm slice thickness was not feasible in 56% of patients. A decrease in the number of reconstructed phases (10 or 5) underestimated EF, SV, EDV, LVOT_area and AVA and overestimated ESV.

Conclusions: Modifications of reconstruction parameters (except a slice thickness ≤2 mm) have only a marginal effect on LV, LVOT_area and AVA assessment. However, a reduced number of reconstructions per cardiac cycle may significantly influence measurements.

Advances in knowledge: Substantial modifications in number of reconstructions per cardiac cycle significantly affect the assessment of LV function, LVOT_area and AVA also in modern CT scanners.

Figure 1.

(a) Automatic diastolic and systolic contour for LV functional assessment. (b–g) Assessment of left ventricular ejection fraction in a (b) standard reconstruction with 0.6-mm slice thickness, 20 phases of the cardiac cycle and 512 × 512 matrix size and modified reconstructions with (c) an iterative reconstruction algorithm, (D) a reduction in matrix size to 256 × 256, a reduction in the number of reconstructed phases of the cardiac cycles to (e) 10 (10% steps between 0 and 90%) and (f) 5 (20% steps between 0 and 80%) and (g) an increase of slice thickness to 8 mm.

Figure 2.

Box-plot diagrams for (a) left ventricular ejection fraction, (b) stroke volume, (c) end-diastolic and (d) end-systolic volume. Median, interquartile range and maximum and minimum values are presented. *, p < 0.05; ns, non-significant.

Figure 3.

(a) Correlation graph for left ventricular ejection fraction and (b) Bland-Altman analysis for left ventricular ejection fraction, stroke volume, end-diastolic and end-systolic volume for modified reconstructions with an iterative reconstruction, a reduction in matrix size to 256 × 256, a reduction of the phases of the cardiac cycle to 5 (20% steps between 0–80%) and an increase in slice thickness of 8 mm in comparison with the standard reconstruction.

Figure 4.

Manual assessment of LVOT area in a (a) standard reconstruction with 0.6-mm slice thickness, 20 phases of the cardiac cycle and 512 × 512 matrix size and modified reconstructions with (b) an iterative reconstruction algorithm, (c) a reduction in matrix size to 256 × 256, a reduction in the number of reconstructed phases of the cardiac cycles to (d) 10 (10% steps between 0 and 90%) and (e) 5 (20% steps between 0 and 80%). (f) An increase of slice thickness to 8 mm is not suitable for LVOT assessment due to an inaccurate outline.

Figure 5.

(a) Box-plot diagrams for LVOT area. Median, interquartile range and maximum and minimum values are presented. *, p < 0.05; ns, non-significant. (b) Bland-Altman analysis with corresponding correlation graph of LVOT area assessment for modified reconstructions with an iterative reconstruction, a reduction in matrix size to 256 × 256, a reduction of the phases of the cardiac cycle to 5 (20% steps between 0 and 80%) and an increase in slice thickness to 5 mm comparison with standard reconstruction.

Figure 6.

Manual assessment of AVA in a (a) standard reconstruction with 0.6 mm slice thickness, 20 phases of the cardiac cycle and 512 × 512 matrix size and modified reconstructions with (b an iterative reconstruction algorithm, (c) a reduction in matrix size to 256 × 256, a reduction in the number of reconstructed phases of the cardiac cycles to (d) 10 (10% steps between 0 and 90%) and (e) 5 (20% steps between 0 and 80%) and (f) an increase of slice thickness to 2 mm.

Figure 7.

(a) Box-plot diagrams for AVA. Median, interquartile range and maximum and minimum values are presented. *, p < 0.05; ns, non-significant. (b) Bland-Altman analysis with corresponding correlation graph of AVA assessment for modified reconstructions with an iterative reconstruction, a reduction in matrix size to 256 × 256, a reduction of the phases of the cardiac cycle to 5 (20% steps between 0 and 80%) and an increase in slice thickness to 2 mm comparison to standard reconstruction.