Dual dynamic contrast-enhanced MR imaging.

A method was devised for obtaining dynamic contrast-enhanced T1-weighted and relaxation rate (delta R2*) images simultaneously to evaluate regional hemodynamics of the brain tumors. On a 1.5-T MR system, dual dynamic contrast-enhanced images were obtained using a gradient echo (dual echo fast field echo) pulse sequence with the keyhole technique to improve temporal and spatial resolution during a rapid bolus injection of gadopentetate dimeglumine. The dynamic T1 contrast images were obtained from the first echo: moreover. integral delta R2*dt values were calculated from the first and the second echo images. The dynamic T1 contrast images provided information about characteristic enhancement pattern (vascularization and disruption of blood-brain barrier), and the integral delta R2*dt values provided a map of regional blood pool in tumor site, peritumoral edema, and other surrounding regions of the brain. The ability to obtain dynamic contrast-enhanced T1 contrast and delta R2* imaging at the same time allows optimization of the advantages of each and thereby more information about the microvascular circulation of the brain lesions.

Fast RARE MR imaging with variable flip angle excitation.

A method was developed for performing T1-weighted magnetic resonance imaging with the rapid acquisition with relaxation enhancement (RARE) sequence by altering the excitation flip angle. This method was called variable flip angle turbo spin-echo (VF-TSE) imaging. When the effective echo time corresponds to the first echo, the resolution worsens as the echo train length becomes longer. For this reason, the echo train length was set at three, the repetition time (TR) was shortened (100- 200 msec) to decrease imaging time, and the initial flip angle was adjusted (120 degrees-140 degrees) to improve image quality. Another advantage of this method is that the initial flip angle can be reduced to below 90 degrees when a longer TR is needed. Measured signal intensities for VF-TSE imaging matched theoretic predictions. VF-TSE imaging yielded high contrast-to-noise and signal-to-noise ratios without sacrificing resolution. The VF-TSE technique was useful for breath-hold, three-dimensional, and cardiac synchronization imaging.