= Cardiac short axis
A \b[cardiac short axis] is a transverse reference direction or imaging view relative to a specified <cardiac long axis>. For left-ventricular imaging, a short-axis <plane> is planned across the chamber rather than through its base-to-apex length. The chamber and anatomical landmarks must be specified; a patient's horizontal body plane is not automatically a <cardiac short axis> plane.
A primary cardiovascular <magnetic resonance imaging> protocol plans short-axis images using linked long-axis views and covers the ventricle from base to apex.<Standardized cardiovascular magnetic resonance imaging (CMR) protocols: 2020 update by Christopher M. Kramer and others>[General techniques, Left ventricular structure and function; Figures 1–2]{ref} A <cardiac short-axis stack> turns successive cavity outlines into volumetric information.
For an original geometrical construction, let $\boldsymbol u$ be the unit vector along the chosen <cardiac long axis>. A transverse <plane> through $r_0$ satisfies
$$
(r-r_0)\cdot\boldsymbol u=0.
$$
Parallel planes at different axial positions sample different portions of the ventricle. With measured cavity areas $A_i$ and represented slice thicknesses $\Delta z_i$, a simple volume estimate is $V\simeq\sum_i A_i\Delta z_i$.
An oblique slice also illustrates a useful caution. An ideal circular cylinder cut at angle $\theta$ away from its perpendicular section has an elliptical <cross-sectional area> $A_0/\cos\theta$. At $30^{\circ}$ this is about $15.5\%$ larger. This does not prove that an entire consistently acquired oblique stack overestimates volume: integrating all areas with the correct normal spacing and complete coverage still recovers volume. Orientation, spacing and coverage must be treated together. The major practical question is whether the chosen stack and <image segmentation> represent the complete intended cavity, not whether one slice happens to look circular.
Back to article page
