Parallel transmit improves 7T MRI adult epilepsy pre-surgical evaluation
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Objective
To implement parallel transmit (pTx) 7T MRI in the pre-surgical evaluation of patients with drug resistant focal epilepsy, and to compare quality and diagnostic yield to conventional single transmit (specifically, circularly polarised, CP) 7T MRI.
Methods
We implemented a comparative protocol comprising both pTx and CP 7T MRI in consecutive adult candidates for epilepsy surgery who had negative or equivocal 3T MRI imaging. Here we report the outcomes from the first 31 patients.
We acquired pTx and CP T 1 , T 2 , FLAIR and EDGE images, all in the same 3D 0.8mm isotropic space. 2D high-resolution T 2 and T 2 *-weighted sequences were acquired only in CP mode due to current technological limitations.
Two neuroradiologists, a neurologist and a neurosurgeon made independent, blinded quality and preference ratings of pTx vs CP images. Quantitative methods were used to assess signal dropout.
Results
Blinded comparison confirmed significantly better overall quality of pTx FLAIR images (F(2,184)=13.7, p=2.88×10 -6 ), while pTx MP2RAGE images were subjectively non-inferior and had improved temporal lobe coverage with quantitatively less signal drop-out.
7T-pTx revealed previously-unseen structural lesions in 9 patients (29%), confirmed 3T-equivocal lesions in 4 patients (13%), and disproved 3T-equivocal lesions in 4 patients (13%).
Lesions were better visualised on pTx than CP in 57% of cases, and never better visualised on CP.
Clinical management was altered by pTx-7T in 18 cases (58%). 9 cases were offered surgical resection and 1 LITT. 3 cases were removed from the surgical pathway because of bilateral or extensive lesions. 5 cases were offered sEEG with better targeting (in 3 because the 7T lesion was deemed equivocal by the MDT, and in 2 because the lesion was extensive).
Significance
Parallel transmit 7T MRI is implementable in a clinical pathway, is superior to single transmit 7T MRI, and changed management in 58% of patients scanned.
Key points
We scanned 31 patients with parallel transmit and conventional 7T MRI, finding previously-unreported structural lesions in 9 patients (29% of cases).
In 13% of cases pTx 7T MRI showed that an equivocal lesion at 3T MRI was likely significant.
In 13% of cases pTx 7T MRI showed that an equivocal lesion at 3T MRI could be disregarded.
Both qualitative and quantitative quality assessments indicate superiority of pTx images over CP.
Future clinical implementations of 7T MRI for epilepsy should utilise parallel transmit where possible.
