Quantifying Left Ventricular (LV) End-Diastolic Volume Index (EDVI)
Determining the left ventricular (LV) end-diastolic volume index (EDVI) is essential to evaluating LV function. LV EDVI—the volume of blood in the LV 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. LV EDVI is derived from a series of parallel short axis slices or from one or more long axis slices (using geometric assumptions). A common method for determining LV EDVI, also used when quantifying right ventricular EDVI and discussed in greater detail below, involves the manual segmentation of contiguous short axis slices.
To quantify LV EDVI, first the height and weight of the patient are established and entered into the system. Second, the end diastolic phase of the cardiac cycle—wherein the LV volume is greatest—is determined. The selected LV end-diastolic phase that is used to quantify LV EDVI should match that which is chosen when quantifying the right ventricular EDVI. (However, end diastole is typically determined first using the LV series.) Generally, phase determinations should be made at the papillary muscle tips of the LV (Fig.1). For electrocardiogram(ECG)-gated images, end diastole is usually the last cardiac phase (Fig.1). Nevertheless, which cardiac phase uniquely matches end diastole may differ between individuals. Moreover, variations in ECG gating, heart rate, and/or other parameters might influence the exact phase designation of end diastole.
It is necessary to carefully define the LV base at end diastole, so that accurate LV contours are constructed. Determining the LV basal location from the short axis images alone may be difficult. Even though the presence of a clearly defined, muscular LV chamber is used as a marker for the basal extent of the LV, relying on this characteristic alone might be problematic due to ill-defined LV boundaries. Thus, incorporating positional information from long axis images might be required (Fig.2).
The LV endocardial contours are constructed manually by placing four points that create smooth, circular regions of interest; such traces include all LV blood and trabeculations (Fig.3). However, if traces are imprecise, the LV EDVI may be artificially altered (increased or decreased). To minimize the probability of such errors, endocardial contours should encompass as small an area as possible, while still including all of the LV blood. Once all traces are placed, software then sums the total LV blood volume to generate the LV EDVI.
The LV EDVI is employed in cardiac MRI analysis to indicate the extent, if any, to which the LV may be enlarged:
|Tb. Left Ventricular Enlargement|
|Degree of enlargement||Ventricular volume/EDVI (ml)|