Biomedical Engineering Reference
In-Depth Information
6.6.3 Smart Contrast Agents
Smart contrast agents are referred to as activated or responsive agents. One such
example is EgadMe, a complex that contains a sugar moiety that prevents water
from coordinating with Gd
3+
. Enzymatic cleavage of this sugar by
b
-galactosidase
improves the accessibility of water to Gd
3+
, which results in an increase in the
relaxivity of the complex [
89
].
6.6.4 Contrast Agents for Labeling Cells
Contrast agents such as iron oxide particles conjugated to the TAT peptide [
90
]or
Gd-HPDO
3
A [gadolinium1,4,7-tris(carboxymethyl)-10-(2
0
-hydroxypropyl)-1,4,7,10-
tetraazacycl ododecane] [
91
,
92
], fall into this category. HP-DO3A is a neutral
(nonionic) gadolinium chelate. In order to meet the diverse requirements sketched
above, highly potent, innovative, specific and preferably multimodal contrast agents
are required.
6.6.5 MR Molecular Imaging and Drug Targeting of Atherosclerosis
with Contrast Agents
Angiogenesis plays an important role in providing the tumor with nutrients.
Antiangiogenic therapies are therefore believed to provide a powerful treatment
option for cancer. In atherosclerosis, the plaques contain angiogenic microvessels,
which are believed to play an important role in plaque development. Imaging
plaques and tumors with a
a
v
b
3-specific contrast agent is therefore of importance
for early detection, defining the severity of the disease, and following the effect of
therapy. Scanning electron micrographs of control fibrin clot and fibrin-targeted
paramagnetic nanoparticles bound to clot surface are shown in Fig.
27
. Recently,
Fig. 27 SEM images of (a) control fibrin clot (
arrow
s indicate fibrin fibrils), and (b) fibrin-targeted
paramagnetic nanoparticles bound to clot surface (
arrows
indicate fibrin-specific nanoparticle-bound
fibrin epitopes). (c, d) Thrombus in external jugular vein targeted with fibrin-specific paramagnetic
nanoparticles demonstrating dramatic T1-weighted contrast enhancement in gradient-echo image
(c) with flow deficit (
arrow
) of thrombus in corresponding phase-contrast image (d). (Adapted
from [
93
])
