METHODS
Patient population
We searched our CMR database to identify all patients younger than 18
years of age who underwent a CMR exam before 2018. Patients were
included only if they had a normal RVOT anatomy, if they had static
balanced steady state free precession (bSSFP) images performed in the
strict transverse and sagittal views, and if they had 2D TTE images of
the RVOT in the PSAX and PLAX views within 6 months of their CMR exam.
The local ethics committee approved the study and written informed
consent was waived. The study was performed in accordance with the
ethical standards as laid down in the Helsinki Declaration as revised in
2013.
CMR measurements
CMR was performed on a 1.5 Tesla scanner (Magnetom Aera, Siemens Medical
Systems, Erlangen, Germany). Static bSSFP images were acquired during
free breathing and triggered to end-diastole. The typical imaging
parameters were as follows: in-plane spatial resolution 2.0 x 1.5
mm2, slice thickness 5 mm, interslice gap 0 mm, 1
average. The RVOT diameter was measured on the strict transverse and
sagittal views, perpendicular to the anterior wall of the RVOT, at the
level of the aortic valve, from inner edge to inner edge, as illustrated
in Figure 1.
TTE measurements
2D TTE was performed with commercially available echocardiography
machines (Sonos iE33, Philips, Andover, MA, USA; Vivid E9, GE
Healthcare, Milwaukee, WI, USA) using transducers of 5 and 8 MHz
according to patient size. The RVOT diameter was measured at
end-diastole in the PSAX and PLAX views, from inner edge to inner edge,
according to the published guidelines, as illustrated in Figure
2.[2]
Statistical analysis
The measurements were indexed to the body surface area (BSA) using the
Mosteller formula. The indexed diameters of the RVOT were confirmed to
be normally distributed using the Kolmogorov-Smirnov test. The mean,
standard deviation (SD) and reference range, using two SDs on either
side of the mean, were calculated for all measurements. The RVOT
diameter in the strict transverse view by CMR was compared with the RVOT
diameter in the similar PSAX view by 2D TTE, and the RVOT diameter in
the strict sagittal view by CMR was compared with the RVOT diameter in
the similar PLAX view by 2D TTE. The correlation between the
measurements was evaluated using the Pearson correlation coefficient,
and the strength of the relationship was interpreted according to the
published recommendations.[3] Agreement between the measurements was
evaluated using the Bland-Altman plot. Significant relationships between
the measurements were sought using the paired Student’s t -test.P values <0.05 were considered statistically
significant.