Jörg Felder1, Chang-Hoon Choi1, Stefan Schwan1, A. Avdo Celik1, Seong Dae Yun1, Nuno Andre da Silva1, Ana Maria Oros-Peusquens1, and N. Jon Shah1,2
1INM-4, Forschungszentrum Jülich, Jülich, Germany, 22Faculty of Medicine, Department of Neurology, JARA, RWTH Aachen University, Aachen, Germany
Synopsis
In translational
research going from animal model to in vivo human it is often desirable to
change as few experimental parameters as possible. For this purpose a unique
9.4 T animal scanner has been assembled consisting of a dedicated small bore
magnet and being operated with clinical software. Here we demonstrate an
initial performance analysis of the system as well as some more advanced image
acquisitions.Purpose
In translational
research going from animal model to in vivo human it is often desirable to
change as few experimental parameters as possible. However, clinical and animal
systems are currently not available from a single vendor. For this purpose a
9.4 T animal MRI system using clinical software platform has been
constructed consisting of components from different vendors as well as home-built
assemblies. It allows compiling MR pulse sequences once for the animal or the human
scanner and running them on both machines. A further advantage of the system presented
here is that tedious reprogramming of sequences for machines from different manufacturers
can be avoided. Moreover, the huge library of MR pulse sequences available on
the clinical platform becomes available for animal imaging on the dedicated,
small-bore preclinical scanner.
Methods
As a platform the Siemens
Syngo software (Siemens Healthcare GmbH, Erlangen, Germany) was chosen in
combination with the TaTS acquisition system modified with extra RF mixing
stages in order to operate at 400 MHz. It was connected to a 9.4 T,
210 mm bore actively shielded magnet and a 120 mm inner diameter
gradient insert (maximum gradient strength 600 mT/m, slew rate
4000 mT/m/ms) including second order shim coils (both: Agilent
Technologies, Santa Clara, USA). The gradient coils are driven from the clinical
gradient amplifiers using reduced output power while the shim coils are
connected to 10 A current sources (Resonance Research, Inc., Billerica,
USA) and interfaced with the Siemens system using a CAN to serial interface
converter. The RF system uses a proton amplifier set that delivers 1 kW
peak output power on a single channel or alternatively 4 x 250 W when the
system is operated in parallel transmit mode. For X-nuclei a broadband
1 kW amplifier is additionally available (both: Barthel HF-Technik GmbH,
Aachen, Germany). RF coils available include a fixed birdcage driven in
quadrature as a body coil, single-tuned birdcages for various X-nucleus imaging
as well as a set of proton receive surface coils. These are either home-built
or purchased (RAPID Biomedical GmbH, Würzburg, Germany). For triggering and
animal supervision a small animal monitoring and anesthesia system (Small
Animal Instruments, Inc., New York, USA/A.M. Bickford, Inc., New York, USA) is
connected to the clinical software platform. Modification in the software
include a scaling of 1:5 in gradient strength in order to mimic clinical
dimensions as well as disabling SAR and peripheral nerve stimulation monitoring
which is not required for animal investigations.
Results
Clinical quality assurance
(QA) protocols were adapted to the smaller field-of-view of the animal system
and tested on scaled down phantoms with the same solution as used in the human
sized versions, however. All QA protocols were within specifications (except
for the gradient regulator check which could not be prepared because of the modified
hardware). Initial experiments included the investigations of spinal cord
injuries in rats which were imaged using a turbo spin echo sequence, compare
Fig. 1. More examples of imaging and quantitative acquisitions carried
out in order to investigate system performance are shown in Fig. 2 and Fig. 3.
Discussion
The initial measurements
indicate that the performance of the home-built scanner is comparable to that
of commercial animal MRI systems. At the same time it operates with sequences
that have been compiled on a clinical platform making reprogramming of
sequences for animal purposes obsolete. This is a major factor since different
software platforms tend to split staff into different groups. Further extension
of the system is planned and currently integration of four channel parallel
transmit capability is being addressed. The intention is to use the animal
scanner as a test platform for parallel transmission with human applications in
mind as well as to elaborate animal applications using pTX.
Conclusion
A unique translational
platform for experiments from bench to bedside at 9.4 T has been created.
It allows investigation of animal models and human in vivo data with identical
imaging sequences.
Acknowledgements
No acknowledgement found.References
[1] Zaitsev, M. et. al. Mag.
Reson. Med. 2001;45:109-117.
[2] Oros-Peusquens. A. M. et.
al., Proc. ISMRM 19 (2011), 2755