David Gay1, Marie Chupin1,2, Jean-François Mangin1,3, Cyril Poupon1,4, Hugo Dary1, Takoua Kaaouana2, Paulo Loureiro de Sousa5, Christine Delmaire6, Ludovic De Rochefort7, Jean-Marie Bonny8, and Alexandre Vignaud4
1CATI Multicenter Neuroimaging Platform, cati-neuroimaging.com, Paris, France, 2ICM - Institut du Cerveau et de la Moelle Epinière, Paris, France, 3CEA, DSV, I2BM, NeuroSpin, UNATI, Gif-sur-Yvette, France, 4CEA, DSV, I2BM, NeuroSpin, UNIRS, Gif-sur-Yvette, France, 5Université de Strasbourg, CNRS, ICube, FTMS, Strasbourg, France, 6Neuroradiology, CHRU Roger Salengro, Lille, France, 7Université Paris-Sud, CNRS, IR4M UMR8081, Université Paris-Saclay, Orsay, France, 8INRA, UR370 QuaPA, Saint-Genès Champanelle, France
Synopsis
The purpose of this work is to report the
implementation of a T2* map in multicenter neuroimaging studies. We focus on T2*
because it is an endogenous biomarker for paramagnetic products like iron or
melanin, which is very interesting to assess, among other diseases, Parkinson’s
disease. We developed a MR sequence which meets several specific
requirements. This sequence is accessible on 3 major manufacturer 3T MRI
scanners and ensures good measurement accuracy at a standard millimeter
isotropic resolution. This “universal” sequence allows to acquire, in a
reliable and repeatable way, T2* maps of the whole brain.Purpose of the study
The CATI (Centre pour
l’Acquisition et le Traitement automatisé des images) is a French national platform that supports large
multicenter neuroimaging studies. In this specific context, the CATI is developing a quantitative MRI
solution, more suitable for lesion characterisation or follow up studies than conventional T1-, T2- or T2*-weighted MR
images. The purpose of this work was to define an acquisition protocol
dedicated to T2* which is the first step towards standardization. T2* is an
endogenous biomarker of paramagnetic materials like iron or melanin, of particular interest to investigate Parkinson’s
Disease (PD) [1]. The dedicated MRI protocol
will
have to meet several
specific requirements: 1. being compatible with
product sequences provided by the three main manufacturers of 3T MRI
scanners without
any optional license ; 2. providing whole
brain coverage at a standard millimeter isotropic resolution with
identical sequence parameters; 3. ensuring
a good measurement accuracy and reproducibility
(error rate lower than 5% in the range of 35 to 50ms [1]) using a 32 channel
receive array coil; 4. lasting less than ten
minutes to be suitable for clinical
routine.
Materials and Methods
Acquisitions have been done on 3T MRI systems from the three major manufacturers (Siemens Healthcare, Erlangen; GE
Healthcare, Milwaukee, WI, USA; Philips Healthcare, Best, Netherlands). The
parameters of a 3D multi Gradient Echo Recalled (mGRE) sequence were
iteratively optimized until a set fulfilling the requirements listed above was
found. T2* maps were then estimated by a complex reconstruction in order to take into account fat signal and
macroscopic ΔB
0 contribution [2]. A unique Python code was used,
independent of manufacturers, to ensure that no difference was introduiced by image
post-processing. Finally, in order to evaluate the sequence sensitivity, a
Monte Carlo simulation study was performed. Calculations were based on the use
of 32 channel head coils and considering experimental Signal to Noise Ratio
(SNR) retrieved from in vivo acquisitions and realistic T2* values, thus
providing the expected performance of the optimized parameter set.
Results
Figure 1 summarizes the 3D mGRE sequence parameters
compatible with MRI scanners of the three main manufacturers. The major
limitations were related to the number
of echoes that could be tuned and to the available data storage space. Monte
Carlo simulations performed to evaluate the
T2* sensitivity, robustness and reproducibility
are displayed in figure 2. The results indicate a
high accuracy level for T2*
values in the range 35-50 ms, keeping the error rate below 5% for this range. R2*
(1/T2*) maps obtained for the three manufacturers
are displayed in figure 3.
Discussion
We successfully
managed to implement a sequence that meets with our specific requirements. This
“universal” sequence, tuned for 32 channel head
coils, can be acquired with all 3T MRI systems from the three main manufacturers
and allows to build T2* maps that are reliable and repeatable for a large range
of values, particularly for the values
(35-50ms) expected for PD in deep brain regions [1]. This standardized protocol will soon be installed on the MRI systems of
French and European partners belonging to the CATI network and investigating
PD.
Acknowledgements
No acknowledgement found.References
[1] Ulla M, Bonny JM. Is R2* a new MRI biomarker for the progression of
Parkinson’s disease? A longitudinal follow-up. PLOS one, 2013.
[2] Hernando D, Reeder SB. R2* mapping in the presence of macroscopic B0 field variations. Magnetic Resonance in Medicine, 2011.