All imaging was performed using a commercially available 3 Tesla MRI system (TIM Trio, Siemens Healthcare, Erlangen, Germany). The volunteers were laid in the supine position and placed head first in the scanner. External vibrations were induced in the abdominal aorta using a pneumatic driver system by placing the passive driver just inferior to the xiphisternum as shown in figure 1 (3 (link)). The pneumatic driver system consists of two parts; an acoustic speaker also known as active driver, and a passive driver. The active driver is placed outside the scan room. The passive driver and active driver are connected through a plastic tube to send the 60Hz vibrations into the abdominal aorta as shown in figure 1 .
Gradient recalled echo MRE (23 ) and phase contrast (PC)-MRI (24 ,25 (link)) sequences were performed to obtain wave and velocity data on the same sagittal slice of the aorta. The imaging parameters for MRE included: TE/TR = 21.3/25 ms, acquisition matrix = 128×64, FOV = 40 cm, slice thickness = 5 mm, flip angle = 16°, temporal resolution = 25ms, GRAPPA acceleration factor = 2 with 24 reference lines collected in the same scan and a MEG of 60Hz was applied separately in the x, y, and z direction. 4 MRE time offsets were collected to obtain the propagating waves in the aorta during a breathhold of 11 sec. The imaging parameters for the PC-MRI included: TE/TR = 2.1 /9.1 ms, venc = 150 cm/s, acquisition matrix = 192×144, FOV = 30×40 cm2, slice thickness = 5 mm, flip angle = 15°, number of cardiac phases = 128, GRAPPA acceleration factor = 2 with 24 reference lines collected in the same scan, number of averages = 2 and lines per segment = 15. PC-MRI images were acquired using retrospective gating under free breathing.
A T1-weighted–Sampling Perfection with Application of optimized Contrasts using different flip angle Evolution (T1w-SPACE) sequence (26 (link)) was performed to obtain high spatial resolution images to determine diameter and thickness of the abdominal aorta. The acquisition parameters for the T1w-SPACE included: TE/TR = 21/600 ms, echo spacing = 3.4 ms, FOV = 27.1×32 cm2, slice thickness = 1.1mm, acquisition matrix = 246×304, GRAPPA acceleration factor = 2 with 24 reference lines collected. The images were acquired using cardiac triggering and respiratory navigated acquisition. The heart rate during the above acquisitions for all the volunteers was in the range of 52-96 bpm.
Gradient recalled echo MRE (23 ) and phase contrast (PC)-MRI (24 ,25 (link)) sequences were performed to obtain wave and velocity data on the same sagittal slice of the aorta. The imaging parameters for MRE included: TE/TR = 21.3/25 ms, acquisition matrix = 128×64, FOV = 40 cm, slice thickness = 5 mm, flip angle = 16°, temporal resolution = 25ms, GRAPPA acceleration factor = 2 with 24 reference lines collected in the same scan and a MEG of 60Hz was applied separately in the x, y, and z direction. 4 MRE time offsets were collected to obtain the propagating waves in the aorta during a breathhold of 11 sec. The imaging parameters for the PC-MRI included: TE/TR = 2.1 /9.1 ms, venc = 150 cm/s, acquisition matrix = 192×144, FOV = 30×40 cm2, slice thickness = 5 mm, flip angle = 15°, number of cardiac phases = 128, GRAPPA acceleration factor = 2 with 24 reference lines collected in the same scan, number of averages = 2 and lines per segment = 15. PC-MRI images were acquired using retrospective gating under free breathing.
A T1-weighted–Sampling Perfection with Application of optimized Contrasts using different flip angle Evolution (T1w-SPACE) sequence (26 (link)) was performed to obtain high spatial resolution images to determine diameter and thickness of the abdominal aorta. The acquisition parameters for the T1w-SPACE included: TE/TR = 21/600 ms, echo spacing = 3.4 ms, FOV = 27.1×32 cm2, slice thickness = 1.1mm, acquisition matrix = 246×304, GRAPPA acceleration factor = 2 with 24 reference lines collected. The images were acquired using cardiac triggering and respiratory navigated acquisition. The heart rate during the above acquisitions for all the volunteers was in the range of 52-96 bpm.
