Biomedical Engineering Reference
In-Depth Information
the regional infi ltration of infl ammatory cells in the presence or absence of
increased BBB permeability.
In another study, ferumoxtran-10 was compared with standard gadolinium
chelate-enhanced MRI in the evaluation of various CNS lesions, including lym-
phoma, multiple sclerosis, acute disseminated encephalomyelitis, and vascular
lesions. Here, the USPIOs showed quite different enhancement patterns among
the different lesions with infl ammatory components in comparison to gadolinium
chelate-based contrast agents. Hence, these two contrast agents might be comple-
mentary in MRI-based diagnoses of the CNS [226].
A few reports have also been made on the use of ferumoxides and ferumoxtran
for brain MRI in patients with primary and metastatic intracranial tumors [227,
228]. Histological examinations revealed the iron nanoparticles to be localized
mainly at the periphery of the lesions, with only minor iron staining of the tumor
[227]. Whilst, in comparison with gadolinium, the pattern of USPIO enhancement
was heterogeneous and variable, the USPIO agents seemed to enhance the
delineation of neovascularization. It was concluded that USPIO agents would
not replace gadolinium in brain tumor imaging, but might offer complementary
information to permit the differentiation between brain tumors and areas of radia-
tion necrosis [228] .
Recently, new clinical applications have emerged for magnetic nanoparticles.
Maier- Hauff
et al.
reported the details of clinical studies of thermotherapy using
aminosilane-coated iron oxide nanoparticles in patients with glioblastoma multi-
forme (an aggressive type of primary brain tumor). For this, magnetic nanopar-
ticles were injected into the tumor and the patients then exposed to an alternating
magnetic fi eld so as to induce particle heating. The process was monitored using
MRI, which allowed the calculation of the expected heat distribution within the
tumor, which depended on the magnetic fi eld strength. The study results showed
that MRI-controlled cranial thermotherapy using magnetic nanoparticles could be
safely applied to glioblastoma multiforme patients [229].
4.5.1.6
Blood Pool Imaging and MR Angiography
Blood pool contrast agents normally remain in the blood for a prolonged time,
and have longer half-lives and high relaxivities. High relaxivity is required to obtain
a stronger blood signal in MRI, and in turn improves the spatial resolution, while
a longer plasma half-life enables longer scan times and repetitive imaging to be
achieved. Each of these factors is very important in MR angiography (MRA), which
is used to examine blood vessels in various tissues and areas of the body [201,
230]. Blood pool contrast agents based on USPIO nanoparticles have found appli-
cation in the cardiovascular system and myocardial perfusion imaging [191, 231],
in assessments of the patient' s infl ammatory status [232], and even in cerebral
blood volume imaging [233].
Ferumoxtran, a superparamagnetic iron oxide-based blood pool imaging
contrast agent, has been shown to signifi cantly enhance (on average by 128%)
the image intensity gradients at the myocardial/blood pool interface [234].
Ferumoxtran-10 (AMI 227) has also been used to visualize and measure the
