A S T I E N
G U E R I N ,
P H . D .
neuroimaging at the A. A. Martinos Center for Biomedical Imaging
h a t ' s
N e w
|[6/19/2014] MRM paper is out on SAR reduction for patients with deep brain stimulation using parallel transmission MRI.
My collaborator Yigitcan Eryaman has a paper this month in MRM on the use of the transmit degree-of-freedom of pTx coils for reduction of SAR at the tip of deep brain stimulation implants.
The idea of using pTx to reduce heating risks in DBS patients is not
completely new, but the method of this paper has the unique advantage
of not requiring an accurate simulation of the patient and the implant,
which is extremely difficult to perform as the lead geometry is not
generally known. Instead, Yigitcan computes
appropriate modes of excitation of the pTx array that lead to a small
B1+ artefact, which is used as a surrogate for SAR. Check it out...
[6/13/2014] New MRM paper on pTx pulse design for Simultaneous Multi-Slice (SMS).
I have a new paper in MRM this month about the design
of pTx RF pulses for SMS. In this work, I show that local SAR and peak
power constraints can be included in the pTx SMS design problem much
like in "standard" single slice imaging. The advantage of enforcing
these constraints explicitely in the SMS design problem is much more
pronouced however, because of the large SAR and power demands of these
pulses. Simulations in this paper show that this strategy allows the
pulse design algorithm to utilize the power amplifiers at their maximum
performance while satisfying all system and safety limits, which in
turns dramatically improves the quality of the multi-slice flip-angle
[4/22/2014] Two new MRM papers on SAR reduction using "dark modes" and comparison of pTx coils using EM simulation.
My collaborator Yigitcan Eryaman's paper on reduction of global and local SAR using "dark modes" of a transmit arrayt is out in early view
of MRM. The idea of this work is to build a transmit array using both
elements that create B1+ (loops) as well as elements that do not
(dipoles). Excitation of the dipole elements is optimized for SAR
reduction, not for flip-angle mitigation. My paper on simulation of pTx coils
is also out today.This paper is the result of a 3 years collaboration
with Siemens Healthcare that was aimed to determine the "best" parallel
transmit geometry for body imaging at 3 T. This is an enormous
amount of work, for which I developed an electromagnetic simulation
framework with my collaborator Peter Serano, which is based on the co-simulation technique of Mickael Kozlov and Robert Turner.
I also had to develop a pTx pulse design strategy that constrains power
and global and local SAR. Check this work out, there are many "learned
lessons" in it that will be of interest to coil builders and pulse
[3/24/2014] MRM paper on SAR constrained pTx pulse design is editor's pick!
My paper "Local specific absorption rate
(SAR), global SAR, transmitter power, and excitation accuracy
trade‐offs in low flip‐angle parallel transmit pulse design", published online last year in Magnetic Resonance in Medicine was one of 2 papers picked by the editor for the April issue.
[2/18/2014] New MRM paper on realistic head phantom.
Graedel's new paper on the temperature mapping of pTx pulses's SAR
distributions using a realistic head phantom is now available in early view of the journal Magnetic Resonance in Medicine.
[2/10/2014] 2014 ISMRM abstracts.
So the results
and it looks like our pTx collaboration between MGH and MIT is going to
be well represented in Milan next May. Oral presentations will include
(titles are not exact, you can search for the author last name in the
We have also several posters
and e-posters (again, titles not
- Ultimate SNR and
SNR calculations in non-uniform body models (Bastien Guerin);
- A new
framework for decoupling pTx coils with many channels (Zohaib Mahmood)
- PTx pulse design
for patients with deep brain stimulation implants (Yigitcan Eryaman);
- High throughput
evaluation of pTx coils using ultra-fast electromagnetic simulations
- Fast, robust
design of time-optimal gradient trajectories (Mathias Davids).
The Wald lab has many more exciting abstracts that
presented there, too many to list. Check the complete list on the ISMRM
- Large flip-angle Kt point pTx pulse
design with local SAR constraints (Filiz Yetisiz);
- Validation of local SAR reduction in
patients with deep brain stimulation implants using pTx (Bastien
- SAR-constrained pTx pulse design robust
to inaccuracies in the RF transmit chain (Adrian Martin);
design of RF and gradient waveforms for fast pTx inner volume
excitation based on a general parameterization of gradient trajectories