Introduction: T1-weighted variable-flip-angle 3D turbo spin-echo (TSE), has emerged as a vessel wall MRI technique promising for elucidating underlying intracranial vessel wall pathologies associated with stroke. Whole-brain 0.5-mm isotropic-resolution 3D TSE has recently been proposed at 3 Tesla. However, its scan time of 12 min renders it impractical for a clinical setting. This work aimed to design an expedited protocol and conduct a pilot study to demonstrate its potential for diagnosis of wall abnormalities.
Methods: To expedite the acquisition, one may exploit an elliptical data sampling strategy and prolonged echo train length (ETL). However, this would reduce image SNR and compromise vessel wall delineation. On the other hand, SNR is intimately related to refocusing flip angles that are calculated for a prescribed tissue with specific T1 and T2 values (denoted as simulation T1 and T2). In this work, the effects of simulation T2 and ETL on the SNR/CNR performance were first explored on 9 healthy subjects. An optimized imaging protocol was then determined from a narrowed range of choices on 7 healthy subjects and finally applied to a pilot study of 10 patients with known wall disease.
Results: Wall SNR, wall-CSF CNR, and white-gray matter CNR generally increased with simulation T2 and decreased with ETL. Optimization was focused on a narrowed range of protocol choices (ETL = 52; T2 = 140, 170, 200 ms) which enable a scan time of 8 min. ETL=52/T2=170ms was shown (Figure a.) to provide significantly higher (t-test) SNR/CNR performance than the original 12-min protocol (ETL=36/T2=100ms). With the 8-min protocol pre/post contrast, wall abnormalities (Figure b.) were correctly detected in all patients.
Conclusion: An 8-min whole-brain intracranial vessel wall imaging protocol is developed which has demonstrated the potential of accurately identifying various wall abnormalities. A large-scale trial on using the technique for diagnosis of stroke etiology is underway.