Thorsten Honroth1, Cristoffer Cordes1,2, Saulius Archipovas1, Daniel Christopher Hoinkiss1, Matthias Günther1,2,3, and David Porter1
1Fraunhofer MEVIS, Bremen, Germany, 2University of Bremen, Bremen, Germany, 3mediri GmbH, Heidelberg, Germany
Synopsis
A platform-independent
rapid clinical prototyping environment for MR sequences is demonstrated. Fully
interactive product-like sequences can be defined without coding or compiling
software. They are saved as plain text files and run by a generic pre-installed
software module at the scanner that never needs modifications by a user. Sub-groups
of sequence elements can be exported as macros
and reused in other sequences.Purpose
Platform-independent design of MR sequences helps especially
non-technical users and supports multi-center studies.
Several promising approaches already exist: ODIN1 and SequenceTree2 allow to create dynamic sequences that interact with the user via the
scanner user interface (UI) but need (at least for the Siemens platform) a
compiling of an executable vendor specific sequence program. JEMRIS3 together with Pulseq4 do not require recompilation of the scanner
interpreter but they only generate static sequences which cannot react on user
input from the scanner UI5.
We present a software solution for rapid
clinical prototyping of MR sequences that combines both advantages described
above: Creating fully interactive sequences without recompiling source
code.
Methods
The software has been developed for and tested with a Siemens Magnetom
Skyra 3T system (Siemens Healthcare, Erlangen, Germany). A generic program
(driver) that runs on this scanner has been developed. It comprises the following
features:
For non-technical users: No compiling of software is
necessary for a user and almost all tasks can be solved without coding.
Product-line behavior of sequences: Calculations
of a sequence necessary for certain parameters or timings are handled by so
called connections in this software. A
connection consists of input
parameters, a formula and the output parameter. Input parameters can be
parameters of other sequence elements or parameters from the scanner UI like
the echo time (TE). This way, an interactive sequence, which can react on
parameter changes from the scanner UI, can be created.
Modularity & Reusability: Sequence elements like ADC events
or gradient pulses can be bundled and saved as so called macros that can be reused in other sequences (fig.1). Fast exchange
of readout or preparation modules between sequences is possible. Macros
together with loops and single sequence elements are incorporated into a tree
which represents the sequence structure.
Scripting support: Advanced users can add special functionality
to their sequences by adding scripts in the language Lua which does not require
compiling.
Automatic calculations: Parameters required by the scanner
sequence framework, such as scan duration and RF pulse energy, are calculated
automatically.
Platform-independence: The underlying
sequence design can be performed from without reference to a specific scanner
platform.
Generic scanner driver:
The structure of the sequence, its parameters, connections, optional scripts and
constituent macros are saved as plain text files (fig.2). Together, these files
contain the platform-independent definition of the sequence. At the scanner,
they are loaded by a generic pre-installed software module, here called driver, which provides the corresponding interactive sequence. The
driver is only compiled once and needs no further changes when switching
between sequences.
As a demonstration, a spoiled gradient echo sequence and an echo planar
imaging (EPI)6 sequence have been developed, which can be configured at
the scanner using standard sequence parameters. For example, the spoiled
gradient echo can react to user-specified repetition times (TR) and echo times
(TE). Both sequences use the same driver
at the scanner: Only different text files for the sequence definitions are used
and thus, no new code compilation is necessary. For the EPI sequence, phase correction scans have been integrated.
Two healthy volunteers have been scanned on a Siemens Skyra 3T system (Siemens Healthcare, Erlangen, Germany).
All images have been reconstructed on site using the manufacturer’s reconstruction
software.
Results
Fig.3 shows images acquired using the spoiled gradient echo sequence
using different TR and TE. The contrast changes clearly with the modification of the parameters.
Fig.4 shows four slices acquired using the EPI sequence. Adequate image quality has been achieved.
Discussion
The software is still preliminary work and might have limitations that
are not obvious at the moment but that may lead to e.g. some future restructuring
of the software.
Future work will include the development of further scanner drivers,
also for different vendors.
Conclusion
A new approach to platform-independent MR sequence development has been
demonstrated. It provides the advantage of producing product-like sequences and
can react on UI interaction at the scanner while eliminating the need for modifying
or recompiling the vendor-specific program that runs on the scanner.
Acknowledgements
No acknowledgement found.References
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2004.
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3. Stöcker et al., MRM 64:186-193, 2010.
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5. Stöcker et al., Proc ESMRMB
32:515-516, 2015.
6. Stehling et al., Science 254:43-50, 1991.