Biomedical Engineering Reference
In-Depth Information
the required amounts of nanoparticles or expected temperature
profiles.
Although magnetic nanoparticles are used as contrast agents
to enhance MR imaging techniques, the high concentrations
required for hyperthermia applications result in localized suscep-
tibility artifacts, which eliminate the possibility for quantifica-
tion. However, the ability to measure nanoparticle concentrations
based on differences in density has been demonstrated with
computed tomography (CT) imaging (Johannsen, Gneveckow,
Taymoorian, Cho et al. 2007). A comparison between signal
intensities from MRI and CT is included in Figure 17.12. CT
signal intensity is expressed in units of Hounsfield Units (HU).
Previous studies have demonstrated the capability to differentiate
nanoparticle deposits down to a concentration of approximately
4 mg Fe/ml, correlating to a signal intensity change of about 20
HU per mg Fe/ml (Wust et al. 2006). Thus CT imaging can be
used to measure nanoparticle distribution after injection and sub-
sequently determine appropriate field parameters and treatment
time. In addition, while traditional MR techniques are limited in
quantifying high concentrations of iron oxide nanoparticles, a
new approach, sweep imaging with Fourier transform (SWIFT)
MR, has demonstrated preliminary capabilities to image at greater
than 1 mg Fe/ml (Hoopes et al. 2012).
The NanoPlan module (MagForce Nanotechnologies AG,
Berlin, Germany) puts these methods to commercial use. The
software package allows physicians to calculate needle trajectories
and deposit locations for nanoparticle implantation, based on 3D
reconstructions obtained from previous imaging. Homogeneous
(a)
800
900
Undiluted
magnetic
fluid
700
MR TE 4
800
600
700
500
600
MR TE 4
MR TE 40
400
500
CT-Mean
300
400
200
300
MR TE 40
100
200
100
0
MR image wrap zone
0
-100
1000
100
10
1 0.1
Concentration Fe [g/l]
0.01
0.001
0.0001
0.0001
~0.01 - 0.4 mg Fe/ml
0.4
0.17
0.09
0.04
0.009
0
(b)
MR
CT
40
20
10
5
1
0
~1 - 40 mg Fe/ml
FIGURE 17.12
CT/MR signals in correlation with the concentrations of iron mass in the magnetic fluid (a) (From Gneveckow, U. et al.,
Medical
Physics
31, 2004); and CT/MR contrast images for Petri dishes containing varying concentrations of iron mass (b) (From Kalambur, V. S, S. Hui,
and J. C Bischof,
Proceedings of SPIE
, 6440, 2007.)
