Head-neck RF coil with local field control for comprehensive high-resolution 7T neuro MRI exams

Massachusetts General Hospital, Boston MA

Investigators

Abstract

Project Summary/Abstract Many diseases of the central nervous system (CNS: brain and spine) involve not only the neocortex but also lower regions such as the cerebellum, brainstem, and cervical spine as well as vessels and nerves in the skull base and neck. Diagnosis and tracking with MRI exams therefore requires full head-neck coverage, for example in multiple sclerosis for visualizing demylinating lesions spanning from brain down to c-spine as well as for surgical planning involving tumors in the skull face or face. For depicting subtle lesions and small structures such as nerves and vessels, ultra-high field (7 Tesla) MRI provides superior image resolution and enhanced soft tissue contrast as compared to conventional 3T imaging. Unfortunately, comprehensive neurological exams covering the head and neck are not possible at present day due to the limited anatomical coverage of standard radiofrequency (RF) head coils as well as artifacts arising from RF and magnetostatic (B0) fields with the body. To overcome these limitations, this BPI project will forge a partnership between a leading academic imaging center and the world’s preeminent UHF MRI vendor. Together, we will create a head-neck imaging system that enables, for the first time, comprehensive neuro exams at 7T. To achieve this, we design and build a 16-ch Tx/64-ch Rx coil with field coverage extending down to C6 that fits 95% of the patient population comfortably and is optimized to balance Tx, Rx, and B0 shimming requirements. We apply the state-of-the-art Siemens pTx framework to design “universal” RF pulses that robust excitation, inversion, and refocusing over the whole head and neck. Moreover, we design an optimized B0 shim array to efficiently null spatiotemporal DB0 fields over the head and neck, bringing them down to typical 3T levels. To track motion and temporal B0 fluctuations in real-time, we use ~200 ms accelerated volumetric navigators (vNAVs) us to stabilize the B0 field using real-time shim updating.