Quantifying Right Ventricular (RV) End-Diastolic Volume Index (EDVI)
The right ventricular (RV) end-diastolic volume index (EDVI) is of great value when assessing RV function. RV EDVI—the volume of blood in the RV at end load filling indexed for body surface area (ml/m2)—may be quantified, either manually or automatically, using cardiac magnetic resonance imaging (MRI) software. It is obtained from a series of parallel short-axis slices or from one or more long-axis slices (using geometric assumptions). A common method for determining RV EDVI, also used when quantifying left ventricular (LV) EDVI and discussed further below, involves the manual segmentation of contiguous short-axis slices.
LV EDVI is often acquired before RV EDVI. Quantifying the LV EDVI involves obtaining the patient’s height and weight, selecting the end-diastolic phase of the cardiac cycle, tracing all LV images (ranging from the base to the apex) within the end-diastolic phase, and summing (by software) the total LV volume at end diastole. (For further details about how to quantify LV EDVI, please see End-Diastolic Volume Index under Left Ventricle.)
To determine RV EDVI, the patient’s height and weight data also are required by the software. The end-diastolic phase used to determine LV EDVI is held constant when quantifying RV EDVI: the same end-diastolic phase is utilized for both ventricular analyses. Furthermore, as in the LV EDVI analysis, accurate traces of the RV, from the base to the apex, are crafted throughout end diastole. Software then sums the total RV volume at the end-diastolic phase.
It is necessary to define the RV base at end diastole, so that accurate RV contours are constructed. Determining the RV basal location from the short-axis images alone is sometimes difficult. Even though the presence of a clearly defined RV chamber is used as a marker for the basal extent of the RV, relying on this characteristic alone might be problematic due to ill-defined RV boundaries and potential RV-overlap with the right atrium (Fig.1). Thus, incorporating positional information from long axis images is sometimes required (Fig.1).
If cardiac gating is correct and arrhythmias are absent, the same end-diastolic phase should be selected for each short-axis slice (Fig.2). An advantage of selecting the same phase for all end-diastolic slices is that, if difficulties (due to artifacts, arrhythmias, and/or limited time for analysis) arise when drawing contours on a given slice(s), software may interpolate, estimating the RV EDVI without including the problematic slice(s).
Using manual segmentation the RV endocardial contours are drawn as smooth, triangular regions of interest; traces include all RV blood and trabeculations (Fig.3). However, this may artificially alter RV EDVI. To minimize the probability of errors, the endocardial traces should encompass as small an area as possible, while still including all of the RV blood.
Once all traces are crafted, software then sums the total RV blood volume, acquiring RV EDVI.
RV EDVI is employed in cardiac MRI analysis to indicate the extent, if any, to which the RV may be enlarged or shrunken:
|Tb. Right Ventricular Enlargement|
|Degree of enlargement||Ventricular volume (ml)|