Detection and Description of Tissue Disease: Advances in the Use of Nanomedicine for Medical Imaging - Harnessing Biomaterials in Nanomedicine: Preparation, Toxicity, and Applications - page 242

achieved by using contrast agents that selectively accumulate in
the diseased tissue, increasing the signal from that tissue, thus
distinguishing it from adjacent, normal, tissue. The increasing
ability of therapies to address specific subtypes of disease as well
as the associated increases in the cost of these therapies demands
a corresponding improvement in the ability to define disease,
preferably non-invasively, and to assess response to therapy in near
real time. Medical imaging has the ability to answer these demands
through increasingly specific contrast agents.
In the spectrum of available molecular imaging technologies,
nuclear medicine, using either single-photon or positron-emitting
tracers, provides the greatest sensitivity, with the ability to detect
targets that are present at the nanomolar level. The trade-off for
this high sensitivity is relatively lower resolution (5-10 mm) than
is available with magnetic resonance imaging (MRI), computed
tomography (CT), or ultrasound (US), all of which can achieve
anatomic resolution of 1 mm or less. However, MRI, CT, and US
require a much greater mass of contrast agent at the imaging site
to provide adequate diff erentiation between normal and diseased
tissue. An obvious way to provide this increase in mass is through
the use of targeted nanoparticles, which by their very nature deliver
a large mass of material to the target, assuming that the technical
challenges associated with delivering such a massive particle to an
in vivo target can be overcome. These challenges include evading
the body's defenses against particulate contaminants (including
the reticuloendothelial system), developing a particle that is small
enough not to be trapped in the capillary bed while still large
enough to provide an adequate signal once it reaches the target, and
overcoming the toxicological challenge inherent in administering
a significant mass of material intravenously. The development
of novel biomaterials off ers a great opportunity to overcome
these challenges. The aim of this review is to discuss the role of
biomaterials in development of contrast agents in two fields, CT and
US, their similarities and diff erences, and how the novel properties
of nanoparticles have facilitated this development.
Owing to the breadth of this subject and space limitations, this
review is not intended to be comprehensive, but rather to provide an
introduction to the requirements of the field, as well as an overview
of how advances in nanotechnology have exploited the unique
properties of biomaterials to address the challenges outlined above.