Image Processing Reference
In-Depth Information
approaches to left-ventricular modeling have suggested true 3-D global and local
shape indices based on surface properties.
In practice, assessment of cardiac function still relies on simple global vol-
umetric measures such as LVV and LVM, and EF. These and other basic param-
eters will be presented in the following text:
Left Ventricular Volume (LVV): This is a basic parameter required to derive
other LV indices such as, e.g., EF. Angiocardiography and echocardio-
graphy have been traditionally used to assess this quantity. In the latter
case, three approaches have been applied to represent the LVV: (a) as
the volume of a single shape (e.g., truncated ellipse); (b) as the sum of
multiple smaller volumes of similar configuration (e.g., Simpson's
method), and (c) as a combination of different figures [14]. The achieved
accuracy in the assessment of LVV with echocardiography varies
widely with the model used to represent the LV. The best results have
been obtained using Simpson's rule in which
in vitro
studies have
revealed a relative error ranging from 5.9% to 26.6% depending on the
particular implementation and the number of short-axis slices used in
the computation [14]. It has been shown that echocardiography consis-
tently underestimates ventricular cavity, whereas angiocardiography
consistently overestimates the volumes [14]. In a recent study by Lorenz
et al. [48] with a canine model and autopsy validation, it has been
shown that cine MRI is a suitable and accurate method to estimate RVV
and LVV. In this study, MR-based and autopsy volumes agreed to within
6 ml, yielding no statistically significant differences.
Left Ventricular Mass (LVM): Left-ventricular hypertrophy, as defined by
echocardiography, is a predictor of cardiovascular risk and higher mortality
[14]. Anatomically, LV hypertrophy is characterized by an increase in
muscle mass or weight.
LVM is mainly determined by two factors: chamber volume and wall
thickness. There are two main assumptions in the computation of
LVM: (a) the interventricular septum is assumed to be part of the LV
and (b) the volume,
V
m
, of the myocardium is equal to the total volume
contained within the epicardial borders of the ventricle,
V
t
(
epi
), minus
the chamber volume,
V
c
(
endo
); LVM is obtained by multiplying
V
m
by the density of the muscle tissue (1.05 g/cm
3
)
v
=
v
() (
epi
−
v
endo
)
(9.1)
mt
c
LVM
=×
105
.
V
m
(9.2)
LVM is usually normalized to the total body surface area or weight in order
to facilitate interpatient comparisons. The normal values of LVM nor-
malized to body weight are 2.4
±
0.3 g/kg [48].
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