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DRIVE: shorter scan time, brighter fluid

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Janssen, Karen Philips Healthcare Philips Global

The 3D-TSE technique is used for producing high-resolution T2-weighted images. The technique has a higher signal-to-noise ratio and lower sensitivity for flow voids than multislice sequences. However, it has relatively long TRãs and thus relatively long scan times. DRIVE makes the powerful 3D-TSE method faster:

 

A DRIVE pulse helps fluids to relax faster,
so that the TR can be shortened, and scan time decreased.

 

Alternatively, as always in MRI, the increased speed can also be traded for better image quality in the same scan time.

 

Fluids have much longer T1 and T2 relaxation times than other tissues. For a high fluid signal and consistent contrast after each excitation, TR must be long enough to restore the fluidãs Mz magnetization. In 3D-TSE quite long repetition times are needed to maintain the high signal of fluids.

How DRIVE works

A DRIVE pulse is a driven equilibrium pulse. It consists of a -90ª RF pulse in combination with a gradient refocusing pulse and a spoiling gradient. The DRIVE pulse is given exactly at the time when an echo appears, because then all magnetization is in phase.

 

 

The -90ª RF pulse brings the still high magnetization back from the horizontal plane to the vertical axis. Therefore, the pulse rebuilds the vertical magnetization of the fluid much faster than without the DRIVE pulse. After the DRIVE pulse, only about 500 ms is needed until T1 relaxation of the fluid ¹ and the other tissues ¹ is complete and a subsequent excitation pulse can be applied.

Thus the TR is shortened by a factor of three to four, while fluids are still bright in the images.



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