Comparison of long and short axis quantification of left ventricular volume parameters by cardiovascular magnetic resonance, with ex-vivo validation

Abstract

Background: The purpose of the study was to compare the accuracy and evaluation time of quantifying left ventricular (LV), left atrial (LA) volume and LV mass using short axis (SAX) and long axis (LAX) methods when using cardiovascular magnetic resonance (CMR).

Materials and methods: We studied 12 explanted canine hearts and 46 patients referred for CMR (29 male, age 47 ± 18 years) in a clinical 1.5 T CMR system, using standard cine sequences. In standard short axis stacks of various slice thickness values in dogs and 8 mm slice thickness (gap 2 mm) in patients, we measured LV volumes using reference slices in a perpendicular, long axis orientation using certified software. Volumes and mass were also measured in six radial long axis (LAX) views.LV parameters were also assessed for intra- and inter-observer variability. In 24 patients, we also analyzed reproducibility and evaluation time of two very experienced (> 10 years of CMR reading) readers for SAX and LAX.

Results: In the explanted dog hearts, there was excellent agreement between ex vivo data and LV mass and volume data as measured by all methods for both, LAX (r² = 0.98) and SAX (r² = 0.88 to 0.98). LA volumes, however, were underestimated by 13% using the LAX views. In patients, there was a good correlation between all three assessed methods (r² ≥ 0.95 for all). In experienced clinical readers, left-ventricular volumes and ejection fraction as measured in LAX views showed a better inter-observer reproducibility and a 27% shorter evaluation time.

Conclusion: When compared to an ex vivo standard, both, short axis and long axis techniques are highly accurate for the quantification of left ventricular volumes and mass. In clinical settings, however, the long axis approach may be more reproducible and more time-efficient. Therefore, the rotational long axis approach is a viable alternative for the clinical assessment of cardiac volumes, function and mass.

Figure 1

Mold of explanted dog heart and long axis CMR images. Left: Mold of the left ventricle and left atrium of an explanted dog heart. Right: Six ex vivo CMR long axis views of the mold-filled heart. Contours are shown for the subendocardial border of the left atrium and left ventricle.

Figure 2

LV function analysis in short axis images using long axis views as a cross-reference. Left panel: Diastolic mid-ventricular short axis view with contours. Right upper panel: Example long axis reference view in a 4-chamber orientation. Right lower panel: Example long axis reference view in a 2-chamber orientation. The orange lines represent the location of the cross-sectional long axis views used for measurements.

Figure 3

LV function analysis in long axis images using short axis views as a cross-reference. Left panel: Diastolic long axis view with endocardial contour. Right upper panel: Example short axis reference view in a 3-chamber orientation. Right lower panel: Example short axis reference view in short axis orientation. The orange lines represent the location of the cross-sectional views used for measurements.

Figure 4

Correction of atrial volume next to the mitral valve. Left panel: Diastolic basal short axis view with contours. The green contour encircles the atrial portion of the volume in this slice and is excluded from the ventricular volume. Right upper panel: Example long axis reference view in a 2-chamber orientation. Right lower panel: Example long axis reference view in a 4-chamber orientation. The orange lines represent the location of the cross-sectional long axis views used for measurements.

Figure 5

Bland-Altman analysis of left ventricular volume. Overall bias and 95% limits of agreement between mold data and different methods for LV volume determination. Standard compared to CMR measurements using radial (top left), short axis 10 mm (top right), short axis 8 mm (bottom left), and short axis 5 mm (bottom right) techniques. The long axis method showed the least amount of variation and was on average closest to the real volume.

Figure 6

Bland-Altman analysis of left ventricular mass. Overall bias and 95% limits of agreement between mold data and different methods for LV volume determination. Standard compared to CMR measurements using radial (top left), short axis 10 mm (top right), short axis 8 mm (bottom left), and short axis 5 mm (bottom right) techniques.

Figure 7

Bland-Altman analysis of left atrial volume. Overall bias and 95% limits of agreement between mold data and different methods for LV volume determination. Standard compared to CMR measurements using radial (top left), short axis 10 mm (top right), short axis 8 mm (bottom left), and short axis 5 mm (bottom right) techniques.