A standardised clinical multicentric whole brain T2* mapping protocol at 3T
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 ΔB0 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.

Figures

Figure 1: Final 3D mGRE parameters fully compatible with the three main manufacturers.

Figure 2: Monte Carlo simulation done over 10k iterations based on a T2* extraction with experimental SNR obtained with Siemens 32 channels head coil array. The red box indicates the range of T2* target values (35-50 ms).

Figure 3: from left to right R2* maps (s-1) obtained with GE (MR Discovery 750), Siemens (Verio) and Philips (Achieva) systems.



Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)
3305