Image Processing Reference
In-Depth Information
of the lesion to be demonstrated can be accomplished by positioning an intravascular
catheter through which the contrast medium is guided and injected. Angiocardio-
graphy is usually good for anatomic delineation of lesions but is much less satis-
factory for the determination of their severity and the degree of hemodynamic
disturbance they have produced. This technique has been used for a long time to
assess ejection fraction (EF) and ejection volumes (EV) [10] based on simplified
geometric models [11-13] of the LV, but most radiologists use visual assessment
based on experience [17].
9.2.2
C
ARDIAC
U
LTRASOUND
Two-dimensional ultrasonic (US) imaging of the heart, or
echocardiography
[18,24], allows the anatomy and movements of intracardiac structures to be
studied noninvasively. The application of pulsed- and continuous-wave Doppler
principles to 2-D echocardiography (2DE) permits blood flow direction and
magnitude to be derived and mapped onto a small region of interest of the 2DE
image. In color-flow Doppler mapping (CFM), the pulsed-wave signal with
respect to blood velocity and direction of flow throughout the imaging plane is
color-coded and produces a color map over the 2DE image. One of the limiting
factors of 2DE is the ultrasound window (presence of attenuating tissues in the
interface between the US transducer and the organ of interest). To overcome this
problem,
transesophageal echocardiography
can be used, which can provide
high-quality color-flow images at the expense of being invasive.
Three-dimensional echocardiography (3DE)[19] is a relatively new develop-
ment in the U.S. that allows 3-D quantitation of organ geometry because the
complete organ structure can be imaged. This technique has been used to compute
LVV and LVM [25-30] and to perform wall motion analysis [31].
9.2.3
I
SOTOPE
I
MAGING
Isotopes have been used to study left-ventricular function and myocardial perfusion.
Radionuclide techniques for monitoring global and regional ventricular function fall
into two major categories: (a) first-pass studies, in which an injected bolus dose is
monitored during its first passage through the heart and great vessels, and (b) gated
equilibrium studies, in which the tracer mixes with the blood pool before data collec-
tion. First-pass acquisitions are typically 2-D, whereas gated equilibrium studies can
be 2-D or 3-D (single-photon emission computed tomography — SPECT). Isotope
imaging can be used to assess parameters like EF [32] and regional wall motion analysis
[32-34]. It is also used to study myocardial perfusion [35] in cases of ischemia or
myocardial infarction, and to assess myocardial viability. The overwhelming majority
of radionuclide studies performed for perfusion assessment employ SPECT.
9.2.4
C
ARDIAC
C
OMPUTED
T
OMOGRAPHY
Computed tomography (CT) is rapidly gaining ground as a routine cardiovascular
modality. Electron beam computed tomography (EBCT)[36] was the first type of
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