Diagnostic ultrasound ( PDFDrive )

54 PART I Physics
A B 5 μm
FIG. 3.1 Contrast Agents for Ultrasound. (A) Perluoropropane bubbles with a protein shell (Optison, GE Healthcare, Milwaukee, WI), shown
here against a background of red blood cells. (B) Lipid-coated microbubbles of perluoropropane gas (Deinity, Lantheus Medical Imaging, North
Billerica, MA) are shown under a dark-ield microscope.
in real time. his chapter aims to provide both a tutorial and a
reference for the practical use of contrast agents for these
indications.
FIG. 3.2 Bubbles Are Relatively Large as Contrast Agents and
Remain Within the Blood Pool. Intravital microscopy of luorescently
labelled perluoropropane bubbles (Deinity, Lantheus Medical Imaging,
North Billerica, MA) shows them in capillaries, being transported much
as red blood cells nearby (arrows). (Courtesy of J. Lindner, Oregon
Health Sciences Center.)
REQUIREMENTS AND TYPES
he principal requirements for an ultrasound contrast agent are
that it should be easily introducible into the vascular system, be
stable for the duration of the diagnostic examination, have low
toxicity, and modify one or more acoustic properties of tissues
that can be detected by ultrasound imaging. Although it is
conceivable that applications will be found for ultrasound contrast
agents that will justify their injection into arteries, the clinical
context for contrast ultrasonography requires that these agents
be capable of intravenous administration and intact passage
through the heart and lungs. hese are demanding speciications
that have been met only in the past decade. he technology
universally adopted is that of encapsulated bubbles of gas that
are smaller than red blood cells and therefore capable of circulating
freely in the pulmonary and systemic vasculature.
Contrast agents act by their presence in the vascular system,
from where they are ultimately metabolized (“blood pool” agents),
or by their selective uptake in tissue ater a vascular phase. Of
the properties of tissue that inluence the ultrasound image, the
most important are linear and nonlinear backscatter coeicient,
attenuation, and acoustic propagation velocity. 2 Most agents
enhance the echo by increasing as much as possible the backscatter
of the tissue that bears them, while increasing the attenuation