|ECR 2018 / C-0409||
|Simultaneous Acquisition of MR Elastography and Two-point Dixon Imaging|
Methods and materials
One of the authors has reported that a conventional gradientecho-type multiecho sequence can be used for simple-MRE sequence as a substitute for the dedicated MRE sequence. You can the simple-MRE on all conventional MR imager as long as you have access to a gradientecho-type multiecho sequence (Fig. 1). The multiple symmetrical gradientechoes in the simple-MRE are acquired by symmetrical bipolar readout gradient lobes. This readout gradient lobes have a function similar to motion encoding gradient (MEG-like effect).
The magnitude image of the 1st echo has the smallest MEG-like effect, but provides the best anatomical structure image because the 1st echo signal has the highest SNR, and it is less affected by magnetic susceptibility artifacts. Therefore, we applied the 1st echo images to Dixon method. The MR phase images of 2nd echo were used for MRE (Fig. 2). The TE of in-phase and opposed-phase imaging were different, which causes vibration phase mismatch (dθ). This dθ was corrected by vibration waveform generator (Fig. 3).
Trzasko et al. (2015) reported a new sequence that combines a dedicated MRE (built-in MEG) and Dixon method. In our study, we combined a Dixon method with the simple-MRE.
All MRE experiments were performed on a conventional MR imager (Achieva 3.0 T; Philips Healthcare, Best, The Netherlands). For acquisition parameters, see Table 1. A self-made waveform generation system (LabVIEW, USB-6221; National Instruments, TX, USA) was used to generate the vibration waveform. This system is capable of generating sinusoidal waveforms with arbitrary frequencies and phases. Power amplifier (XTi 1000; Crown, IN, USA) and a pneumatic pressure generator (Subwoofer TIT320C-4 12”; Dayton Audio, OH, USA) units were used to supply vibrations to a vibration pad. The vibration pad was printed by using a three-dimensional (3D) printer (3D touch; 3D system, SC, USA) in order to adapt to various points on the body shapes. All volunteer studies was being approved by Tokyo Metropolitan University Ethical Review Board (13001).
Thematically related posters
ECR 2018 / C-2384
Ultrasound evaluation of the mandibular condyle cartilage thickness and its influence on the temporomandibular joint and masseter muscle