Biomedical Engineering Reference
In-Depth Information
rate, and a smaller field of view. When screening the beating heart,
gating is necessary for both modalities in order to acquire data corre-
sponding to similar instants in the cardiac cycle, so that the anatomy
is approximately the same, assuming a periodic movement, for each
planar view.
- Phased arrays.
Real-time three-dimensional (RT3D) volumetric
imaging is the only true three-dimensional ultrasound modality [82-
87]. This technology, pioneered by Dr. Olaf Von Ramm and Dr. Stephen
Smith at Duke University, is fundamentally different from the former
generations of 3D systems as a volume is acquired with a 2D array of
pulse transmitter and receiver elements, enabling the cardiologist to
view moving cardiac structures from any given plane in real-time [82,
87-91]. Electronic scanning controls the acquisition depth allowing
real-time signal acquisition through a pyramidal shape volume. This
existing technique is still limited by hardware component size and
speed. The low spatial resolution and high noise level have prevented
this technology from meeting its initial expectation and reaching its
full potential. It remains, nevertheless, the only true 3D ultrasound
modality that can enable accurate temporal visualization of cardiac
deformation during a single cardiac cycle.
In current clinical practice, cardiologists use anatomical images from CT, US
and MRI modalities to quantify cardiac function through measurements of ven-
tricular volumes at end diastole (ED) which corresponds to the end of the blood
filling phase in the cardiac cycle, and end systole (ES) which corresponds to
the end of the blood ejection phase, stroke volume (SV) which is equal to the
difference of blood volumes and ED and ES and ejection fraction (EF) which
is equal to SV over ED volume. These measurements are performed via simple
visual inspection or manual tracing of 2D slices extracted from the 3D data.
A second phase of analysis of the images aims at analyzing myocardium wall
deformation and localization of abnormalities. Physiological images provided
by MUGA, SPECT and PET/SPECT modalities aim at quantifying myocardium
tissue blood perfusion for localization of ischemic tissue.
All these diagnostic tasks require the intervention of an expert cardiologist
familiar with the modality for quick visual inspection. A more detailed process-
ing of the data always require segmentation of the myocardium tissue versus
