Study Population

Between January 2010 and December 2014, 195 patients with aortic valve disease (aortic stenosis or regurgitation) or ascending aortic dilatation who required MDCT or MRI before surgery were prospectively recruited at a single tertiary center. Two-dimensional TTE and MDCT or MRI were performed at an interval of <1 week. Exclusion criteria were poor echocardiographic acoustic window ( n = 8); inability to hold the breath for 20 sec ( n = 7); known contrast allergy ( n = 6); impaired renal function (serum creatinine > 2 mg/mL) ( n = 10); presence of atrial fibrillation ( n = 5); asymmetric aortic root, defined as differences in the three cusp-to-cusp diameters > 10% by computed tomography or MRI ( n = 12); refusal to provide written informed consent ( n = 2); and claustrophobia or formal contraindication to MRI ( n = 5). Thus, the first 70 patients in whom MDCT and the first 70 in whom MRI was indicated for clinical purposes were included. Two-dimensional TTE was performed in all cases. The institutional review board of our institution approved the study, and all patients gave written informed consent.

Two-Dimensional Echocardiography

All patients underwent comprehensive grayscale harmonic imaging 2D TTE performed by two experienced echocardiographers (J.F.R.-P. and G.T.-T.) using high-quality commercially available ultrasound systems (Vivid 7 and Vivid E9; GE Vingmed Ultrasound AS, Horten, Norway). The aorta was measured at different levels in this specific order: sinuses of Valsalva (SVA), sinotubular junction (STJ), and proximal ascending aorta (AA). The ascending aortic diameter was determined 1 cm above the STJ, as previously described by Muraru et al . Images were acquired during breath-hold in the parasternal long-axis view. Diameters were measured at end-diastole (on the basis of the QRS complex for timing) using the L-L, I-I, and O-O conventions ( Figure 1 ) on an EchoPAC workstation (GE Healthcare, Little Chalfont, United Kingdom). All reported values represent the averages of at least three measurements in consecutive cardiac cycles. Aortic wall thickness was obtained by subtracting the I-I from the L-L measured diameters, as described by Muraru et al ., at all three levels. Assuming that the wall thickness was homogeneous, the average value at all levels was used. To assess intraobserver and interobserver variability, two experienced echocardiographers measured aortic root and ascending aortic diameters in 25 randomly- selected subjects. Intra- and interobserver variability was determined by measuring the aortic diameters in the same acquired image. Interacquisition variability was determined by measuring the diameters in two immediate consecutive studies by two different observers. In addition, aortic diameters were determined using harmonic imaging and fundamental imaging to determine differences in measurements.

Echocardiographic left parasternal long-axis view showing aortic measurements using different conventions: (A) I-I, (B) L-L, and (C) O-O.

MDCT

Seventy patients were scanned using 16- and 128-multidetector computed tomographic scanners (Sensation 16 and Somatom 128; Siemens Healthcare, Forchheim, Germany). Technical parameters were an axial field of view of 50 cm, longitudinal coverage of the entire thoracic aorta, table feed of 3.0 mm/rotation, gantry rotation time of 0.42 sec, tube voltage of 100 to 120 kV, tube current–time product of 400 to 450, and prospective x-ray tube modulation. A bolus of 80 to 100 mL of iodinated contrast material (Visipaque 320; Amersham Health, Little Chalfont, United Kingdom) followed by 50 mL of saline was administered through an arm vein (5 mL/sec). Automated detection of peak enhancement in the aortic root was used to time the scan. All images were acquired during an inspiratory breath-hold, with simultaneous registration of the patient’s electrocardiogram. Acquisition was centered at the 75% phase of the R-R cardiac cycle to ensure minimal motion artifacts. Axial data sets were transferred to a remote workstation (Leonardo; Siemens Healthcare) for evaluation. Maximal aortic diameter measurements at the SVA, STJ, and AA were generated using the double-oblique short-axis technique. The three cusp-to-commissure and the three cusp-to-cusp diameters were measured at the level of the aortic root ( Figure 2 A) and the two diameters (anteroposterior and laterolateral) at the rest of the aortic levels. Diameters were measured at the 75% phase of the R-R cardiac cycle using the I-I and O-O conventions. Inter- and intraobserver variability was also determined.

Aortic root diameters measured by MDCT (A) and MRI (B) using the I-I convention. The cusp-to-commissure diameters are displayed on the left images and the cusp-to-cusp diameters on the right.

MRI

Seventy patients were imaged using a 1.5-T system (Signa Excite; GE Healthcare). Images were obtained in synchronization with the electrocardiogram and in apnea. Steady-state free precession cine acquisitions were acquired in held expiration using the following parameters: field of view, 350 × 297 mm; matrix size 256 × 192; repetition time, <50 msec; and slice thickness, 6 mm. To acquire cine planes, coronal and sagittal oblique views of the aorta were reconstructed using the axial scouts. From these two planes, and using the double-oblique method, perpendicular images at the level of the SVA, STJ, and AA were obtained. Cine images were used for MRI measurements using the luminogram of the aorta at an end-diastolic frame. The three cusp-to-commissure and the three cusp-to-cusp diameters were measured at the aortic root level ( Figure 2 B) and the two diameters (anteroposterior and laterolateral) at the rest of the aortic levels. Diameters were measured using the I-I and O-O conventions. The measurements were taken using QMass version 5.5 (Medis, Leiden, The Netherlands) to manually define diameters and areas. Inter- and intraobserver variability were also determined.

Statistical Analysis

Continuous variables are expressed as mean ± SD. The Kolmogorov-Smirnov test was used to evaluate normality of distribution. Differences between groups for continuous parameters were assessed using Student’s t test if they were normally distributed or analysis of variance with Bonferroni correction for multiple comparisons and the Mann-Whitney U test if the distribution was not normal. Categorical variables are expressed as percentages, and differences between groups were assessed using χ ² tests. Agreement among different imaging techniques to establish aortic diameters was examined using mean absolute differences (assessed using paired-samples t test), intraclass correlation coefficients, and Bland-Altman analysis. Aortic diameter was divided into four groups at all different levels for comparisons to be made: normal (<40 mm), mildly dilated (40–44.9 mm), moderately dilated (45–49.9 mm), and severely dilated (≥50 mm), as previously described. A two-tailed P value < .05 was considered to indicate statistical significance. SPSS version 19.0 software version (SPSS, Chicago, IL) was used for the analysis.

Study Population

Between January 2010 and December 2014, 195 patients with aortic valve disease (aortic stenosis or regurgitation) or ascending aortic dilatation who required MDCT or MRI before surgery were prospectively recruited at a single tertiary center. Two-dimensional TTE and MDCT or MRI were performed at an interval of <1 week. Exclusion criteria were poor echocardiographic acoustic window ( n = 8); inability to hold the breath for 20 sec ( n = 7); known contrast allergy ( n = 6); impaired renal function (serum creatinine > 2 mg/mL) ( n = 10); presence of atrial fibrillation ( n = 5); asymmetric aortic root, defined as differences in the three cusp-to-cusp diameters > 10% by computed tomography or MRI ( n = 12); refusal to provide written informed consent ( n = 2); and claustrophobia or formal contraindication to MRI ( n = 5). Thus, the first 70 patients in whom MDCT and the first 70 in whom MRI was indicated for clinical purposes were included. Two-dimensional TTE was performed in all cases. The institutional review board of our institution approved the study, and all patients gave written informed consent.

Two-Dimensional Echocardiography

All patients underwent comprehensive grayscale harmonic imaging 2D TTE performed by two experienced echocardiographers (J.F.R.-P. and G.T.-T.) using high-quality commercially available ultrasound systems (Vivid 7 and Vivid E9; GE Vingmed Ultrasound AS, Horten, Norway). The aorta was measured at different levels in this specific order: sinuses of Valsalva (SVA), sinotubular junction (STJ), and proximal ascending aorta (AA). The ascending aortic diameter was determined 1 cm above the STJ, as previously described by Muraru et al . Images were acquired during breath-hold in the parasternal long-axis view. Diameters were measured at end-diastole (on the basis of the QRS complex for timing) using the L-L, I-I, and O-O conventions ( Figure 1 ) on an EchoPAC workstation (GE Healthcare, Little Chalfont, United Kingdom). All reported values represent the averages of at least three measurements in consecutive cardiac cycles. Aortic wall thickness was obtained by subtracting the I-I from the L-L measured diameters, as described by Muraru et al ., at all three levels. Assuming that the wall thickness was homogeneous, the average value at all levels was used. To assess intraobserver and interobserver variability, two experienced echocardiographers measured aortic root and ascending aortic diameters in 25 randomly- selected subjects. Intra- and interobserver variability was determined by measuring the aortic diameters in the same acquired image. Interacquisition variability was determined by measuring the diameters in two immediate consecutive studies by two different observers. In addition, aortic diameters were determined using harmonic imaging and fundamental imaging to determine differences in measurements.

Echocardiographic left parasternal long-axis view showing aortic measurements using different conventions: (A) I-I, (B) L-L, and (C) O-O.

MDCT

Seventy patients were scanned using 16- and 128-multidetector computed tomographic scanners (Sensation 16 and Somatom 128; Siemens Healthcare, Forchheim, Germany). Technical parameters were an axial field of view of 50 cm, longitudinal coverage of the entire thoracic aorta, table feed of 3.0 mm/rotation, gantry rotation time of 0.42 sec, tube voltage of 100 to 120 kV, tube current–time product of 400 to 450, and prospective x-ray tube modulation. A bolus of 80 to 100 mL of iodinated contrast material (Visipaque 320; Amersham Health, Little Chalfont, United Kingdom) followed by 50 mL of saline was administered through an arm vein (5 mL/sec). Automated detection of peak enhancement in the aortic root was used to time the scan. All images were acquired during an inspiratory breath-hold, with simultaneous registration of the patient’s electrocardiogram. Acquisition was centered at the 75% phase of the R-R cardiac cycle to ensure minimal motion artifacts. Axial data sets were transferred to a remote workstation (Leonardo; Siemens Healthcare) for evaluation. Maximal aortic diameter measurements at the SVA, STJ, and AA were generated using the double-oblique short-axis technique. The three cusp-to-commissure and the three cusp-to-cusp diameters were measured at the level of the aortic root ( Figure 2 A) and the two diameters (anteroposterior and laterolateral) at the rest of the aortic levels. Diameters were measured at the 75% phase of the R-R cardiac cycle using the I-I and O-O conventions. Inter- and intraobserver variability was also determined.

Aortic root diameters measured by MDCT (A) and MRI (B) using the I-I convention. The cusp-to-commissure diameters are displayed on the left images and the cusp-to-cusp diameters on the right.

MRI

Seventy patients were imaged using a 1.5-T system (Signa Excite; GE Healthcare). Images were obtained in synchronization with the electrocardiogram and in apnea. Steady-state free precession cine acquisitions were acquired in held expiration using the following parameters: field of view, 350 × 297 mm; matrix size 256 × 192; repetition time, <50 msec; and slice thickness, 6 mm. To acquire cine planes, coronal and sagittal oblique views of the aorta were reconstructed using the axial scouts. From these two planes, and using the double-oblique method, perpendicular images at the level of the SVA, STJ, and AA were obtained. Cine images were used for MRI measurements using the luminogram of the aorta at an end-diastolic frame. The three cusp-to-commissure and the three cusp-to-cusp diameters were measured at the aortic root level ( Figure 2 B) and the two diameters (anteroposterior and laterolateral) at the rest of the aortic levels. Diameters were measured using the I-I and O-O conventions. The measurements were taken using QMass version 5.5 (Medis, Leiden, The Netherlands) to manually define diameters and areas. Inter- and intraobserver variability were also determined.

Statistical Analysis

Continuous variables are expressed as mean ± SD. The Kolmogorov-Smirnov test was used to evaluate normality of distribution. Differences between groups for continuous parameters were assessed using Student’s t test if they were normally distributed or analysis of variance with Bonferroni correction for multiple comparisons and the Mann-Whitney U test if the distribution was not normal. Categorical variables are expressed as percentages, and differences between groups were assessed using χ ² tests. Agreement among different imaging techniques to establish aortic diameters was examined using mean absolute differences (assessed using paired-samples t test), intraclass correlation coefficients, and Bland-Altman analysis. Aortic diameter was divided into four groups at all different levels for comparisons to be made: normal (<40 mm), mildly dilated (40–44.9 mm), moderately dilated (45–49.9 mm), and severely dilated (≥50 mm), as previously described. A two-tailed P value < .05 was considered to indicate statistical significance. SPSS version 19.0 software version (SPSS, Chicago, IL) was used for the analysis.

Differences in Aortic Diameters Depending on Measurement Approach

Aortic Root Geometry

Cusp-to-cusp diameters were slightly larger than cusp-to-commissure diameters by MDCT and MRI ( Table 4 ). The mean cusp-to-commissure diameter was 34.5 ± 5.6 mm (95% CI, 33.1–35.8 mm; range, 25.3–50.9 mm), and the mean cusp-to-cusp diameter was 35.8 ± 5.7 mm (95% CI, 33.5–36.2 mm; range, 24.3–54.1 mm) ( P = .032) by MDCT. In the MRI group, mean diameters were 37.6 ± 4.3 mm (95% CI, 36.6–38.6 mm; range, 26.9–45.7 mm) and 39.2 ± 4.6 mm (95% CI, 38.1–40.3 mm; range, 28.9–48.5 mm), respectively ( P = .025).

Comparison of Aortic Diameters among Different Imaging Techniques

When aortic measurements using the O-O convention by MDCT and MRI were compared with those obtained by 2D TTE using the I-I convention (according to the current American College of Cardiology and AHA guidelines ), 2D TTE underestimated the MDCT and MRI cusp-to-commissure aortic root diameter by −3.7 ± 2.9 mm ( P < .0001) and −3.4 ± 2.4 mm ( P < .0001), respectively. Similar results were obtained at different aortic levels ( Supplemental Table 4 ). These underestimations persisted when the I-I convention by MDCT and MRI was used: −1.8 ± 2.6 mm ( P = .019) and −1.7 ± 1.2 mm ( P < .0001), respectively. However, no significant differences were observed when the L-L convention was used by 2D TTE: 0.7 ± 3.7 mm (95% CI, −0.1 to 1.5; P = .064) with MDCT and 0.3 ± 2.4 (95% CI, −1.5 to 2.7; P = .934) with MRI, as average in all aortic levels ( Table 5 ). The Bland-Altman analysis of the differences between 2D transthoracic echocardiographic diameters using different conventions versus multidetector computed tomographic and MRI internal diameters at different aortic levels is displayed in Supplemental Figure 1 .

Table 5

Differences between aortic diameters measured by MDCT and MRI versus echocardiography using different conventions

	NCC-Commissure	RCC-Commissure	LCC-Commissure	LCC-RCC	RCC-NCC	NCC-LCC	STJ	AA
MDCT I-I
TTE I-I	3.1 ± 2.8 ∗	1.6 ± 3.1 ∗	2.6 ± 3.6 ∗	1.8 ± 3.5 ∗	3.1 ± 2.2 ∗	3.5 ± 3.1 ∗	2.9 ± 1.4 ∗	3.2 ± 2.5 ∗
TTE L-L	0.5 ± 2.5	0.9 ± 2.6	−0.9 ± 3.3	−0.8 ± 3.1	−0.2 ± 2.4	−0.6 ± 2.3	−0.3 ± 1.2	−0.8 ± 2.2
TTE O-O	−3.8 ± 2.9 ∗	−5.3 ± 2.8 ∗	−4.2 ± 3.9 ∗	−5.1 ± 3.5 ∗	−3.8 ± 2.9 ∗	3.4 ± 2.8 ∗	−3.8 ± 2.1 ∗	−3.4 ± 2.7 ∗
MRI I-I
TTE I-I	1.6 ± 2.2 ∗	1.6 ± 2.2 ∗	1.7 ± 2.2 ∗	1.8 ± 2.5 ∗	3.1 ± 1.9 ∗	1.8 ± 2.3 ∗	3.1 ± 1.7 ∗	2.5 ± 1.4 ∗
TTE L-L	−0.3 ± 2.3	−0.4 ± 2.2	−0.4 ± 2.3	−1.2 ± 2.4	−0.1 ± 1.6	−0.5 ± 2.1	−0.3 ± 1.2	−0.2 ± 1.7
TTE O-O	−3.1 ± 2.2 ∗	−3.2 ± 2.7 ∗	−2.9 ± 2.5 ∗	−3.8 ± 2.8 ∗	−3.6 ± 1.9 ∗	−3.7 ± 2.2 ∗	−3.9 ± 1.5 ∗	−3.1 ± 1.6 ∗

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