Image Processing Reference
In-Depth Information
clinically applied cardiovascular CT providing 3-D data over the full cardiac cycle.
Using prospective gating, a stack of slices can be acquired with a high temporal
resolution (50 msec between frames) and a slice thickness of about 3-4 mm. EBCT
has been mainly applied clinically for detecting coronary calcium deposits. Limita-
tions of this system are that the spatial resolution in the transaxial direction is much
less than the in-plane resolution, there is a high noise level in the images, and the
geometry of the scanner is fixed, which does not allow acquisition of short-axis views.
Multislice CT (MSCT)[37,38] is less expensive and more widely available than
EBCT. MSCT is characterized by a higher spatial resolution in all directions and
can provide near-isotropic data sets within one breath hold, albeit at a lower temporal
resolution than can EBCT (150 msec between frames). Hence, with the recent advent
of multirow detectors, a faster imaging time is combined with higher resolution and
lower noise levels. MSCT effectively became feasible with 4-row detectors, enabling
spiral scanning of four slices at a time; nowadays 12- and 16-row detectors are
commonly available, and 64-row detector
gantries are under development. It is
expected that the increasing number of detectors in combination with improved
reconstruction algorithms will enable reduced acquisition times, and that image
quality and temporal and spatial resolution will further improve in the near future.
The near-isotropic resolution has two additional advantages: the data can be refor-
matted into any desired spatial orientation (such as the short-axis view) without
interpolation, and it gives an excellent definition of the coronary vessels [39,40].
Currently, MSCT is clinically used for examining coronary anatomy, for visual
coronary stenosis detection, and for assessing the amount of calcium in the coronar-
ies. Recent studies [41,42] indicate that already a 12-row CT enables detection of
coronary artery disease with 95% sensitivity and 93% specificity. However, as
almost on other modality, MSCT enables the combined assessment of left-ventric-
ular global and regional function and coronary function. It is therefore increasingly
used to detect coronary artery disease in combination with left-ventricular function,
and to screen asymptomatic patients with cardiovascular risk factors.
9.2.5
M
AGNETIC
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ESONANCE
I
MAGING
Cardiac magnetic resonance imaging [23] (MRI) is now an established, although
still rapidly advancing, technique providing information on the morphology and
function of the cardiovascular system [43]. Advantages of cardiac MRI include
a wide topographical field of view with visualization of the heart and its internal
morphology and the surrounding mediastinal structures, multiple imaging planes,
and a high soft-tissue contrast discrimination between the flowing blood and
myocardium without the need for contrast media or invasive techniques. Long-
and short-axis views of the heart, as used in echocardiography, can be obtained
routinely because arbitrary imaging planes can be selected.
In fact, cardiac MRI can be regarded as a collection of “MR modalities,”
each dedicated to different aspects of cardiac function. Multislice multiphase
short-axis scanning enables a detailed study of cardiac anatomy and global and
regional function, both at rest and under stress. Several researchers have used
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