Imaging left ventricular tissue mechanics and hemodynamics during supine bicycle exercise using a combined tagging and phase-contrast MRI pulse sequence.

Imaging the left ventricular mechanical and hemodynamic response to the stress of exercise may offer early prognosis in select patients with cardiac disease. Here, we demonstrate the feasibility of obtaining simultaneous measurements of longitudinal strain and transvalvular blood velocity during supine bicycle exercise stress in a wide bore magnetic resonance scanner. Combining information from the two datasets, we observe that although the time to peak strain (33.28 ± 1.86 versus 25.7 ± 2.12 as % of R-R interval) and time to peak mitral inflow velocity (44.37 ± 5.21 versus 35.5 ± 4.19 as % of R-R interval) from R-wave of the QRS complex occurred earlier during stress, the time from peak strain to peak mitral inflow velocity was not statistically different (16.5 ± 3.23 versus 13.4 ± 3.06). Further, the percentage of longitudinal relaxation at peak mitral inflow velocity was higher during stress (63.5 ± 7.72 versus 84.32 ± 6.24). These results suggest that although diastole is shortened, early diastolic filling efficiency is augmented during exercise stress in normal volunteers in an effort to maintain stroke volume.

Prospective head-movement correction for high-resolution MRI using an in-bore optical tracking system.

In MRI of the human brain, subject motion is a major cause of magnetic resonance image quality degradation. To compensate for the effects of head motion during data acquisition, an in-bore optical motion tracking system is proposed. The system comprises two MR-compatible infrared cameras that are fixed on a holder right above and in front of the head coil. The resulting close proximity of the cameras to the object allows precise tracking of its movement. During image acquisition, the MRI scanner uses this tracking information to prospectively compensate for head motion by adjusting the gradient field direction and radio frequency (RF) phases and frequencies. Experiments performed on subjects demonstrate robust system performance with translation and rotation accuracies of 0.1 mm and 0.15 degrees, respectively.