Simultaneous Optimization of MP2RAGE T₁‐weighted (UNI) and FLuid And White matter Suppression (FLAWS) brain images at 7T using Extended Phase Graph (EPG) Simulations

Abstract

Purpose The MP2RAGE sequence is typically optimized for either T1‐weighted uniform image (UNI) or gray matter–dominant fluid and white matter suppression (FLAWS) contrast images. Here, the purpose was to optimize an MP2RAGE protocol at 7 Tesla to provide UNI and FLAWS images simultaneously in a clinically applicable acquisition time at <0.7 mm isotropic resolution. Methods Using the extended phase graph formalism, the signal evolution of the MP2RAGE sequence was simulated incorporating T2 relaxation, diffusion, RF spoiling, and B1+ variability. Flip angles and TI were optimized at different TRs (TRMP2RAGE) to produce an optimal contrast‐to‐noise ratio for UNI and FLAWS images. Simulation results were validated by comparison to MP2RAGE brain scans of 5 healthy subjects, and a final protocol at TRMP2RAGE = 4000 ms was applied in 19 subjects aged 8–62 years with and without epilepsy. Results FLAWS contrast images could be obtained while maintaining >85% of the optimal UNI contrast‐to‐noise ratio. Using TI1/TI2/TRMP2RAGE of 650/2280/4000 ms, 6/8 partial Fourier in the inner phase‐encoding direction, and GRAPPA factor = 4 in the other, images with 0.65 mm isotropic resolution were produced in <7.5 min. The contrast‐to‐noise ratio was around 20% smaller at TRMP2RAGE = 4000 ms compared to that at TRMP2RAGE = 5000 ms; however, the 20% shorter duration makes TRMP2RAGE = 4000 ms a good candidate for clinical applications example, pediatrics. Conclusion FLAWS and UNI images could be obtained in a single scan with 0.65 mm isotropic resolution, providing a set of high‐contrast images and full brain coverage in a clinically applicable scan time. Images with excellent anatomical detail were demonstrated over a wide age range using the optimized parameter set.

Extent of piriform cortex resection in children with temporal lobe epilepsy

“…The application of 7-Tesla MRI that allows the acquisition of sub-millimetric structural and functional data may provide an opportunity for further study. 27,28 Conclusions This is the first study that suggests that a greater extent of resection of the temporal portion of PC is associated with a greater chance of seizure freedom in children with TLE and hippocampal atrophy. However, in a cohort of children with TLE with or without hippocampal atrophy, this association between the extent of resection of the temporal PC and postoperative seizure freedom was not found.…”

“…Investigation is limited by the resolution achievable with current clinically available MRI imaging in this region and the complexity of stereotactic electroencephalography recording in this zone where perforating vessels pose a high clinical risk. The application of 7‐Tesla MRI that allows the acquisition of sub‐millimetric structural and functional data may provide an opportunity for further study 27,28 …”

Pushing MP2RAGE boundaries: Ultimate time‐efficient parameterization combined with exhaustive T1 synthetic contrasts

“…Since its inception in 2009, 1 the MP2RAGE sequence has been of great interest for the UHF MR community, thanks to its ability to provide uniform T 1 -weighted contrast. Over the years, numerous parameterizations, including FLAWS, have been proposed 17 and optimized, [18][19][20]25 to offer more clinically relevant contrasts from this sequence. In this work, T 1 -based synthetic imaging framework 26 was used to achieve this "single acquisition-multiple contrasts" objective, while also fundamentally changing the way the MP2RAGE sequence is parameterized.…”

“…20 As a consequence, there is not enough time to fit the RAGE trains between the two TIs for high-spatial-resolution FLAWS acquisitions (unless it is segmented, leading to even longer acquisition times). This limitation holds true even for the recently described FLAWS/MP2RAGE parameterizations, 25 which would also become unfeasible at a given high spatial resolution (i.e., < 0.65 mm 3 isotropic). With the proposed approach, this upper limit is removed, as a whole-brain (0.45 mm) 3 imaging was successfully performed in 20 min (Figure 4).…”

“…This implies that MP2RAGE and FLAWS contrasts (i.e., UNI, EDGE, FGATIR, MPRAGE, FLAWS MIN , and FLAWS HC&HCO ) cannot all be obtained in a single acquisition. A novel MP2RAGE optimization 25 using extended phase graph (EPG) has recently been proposed at 7 T by Dokumaci et al to simultaneously provide several key contrasts, such as UNI and FLAWS MIN , as well as T 1 mapping, in a single acquisition. However, this MP2RAGE parameterization choice came at the cost of inevitable tradeoffs, notably regarding achieved contrast‐to‐noise ratio (CNR), achievable spatial resolution, and visual outputs of clinical contrasts.…”