Implementation of mixed bandwidth MRI pulse sequences using a single analog lowpass filter.

In many MR imaging situations, such as when imaging certain areas of the brain, substantial increases in the signal-to-noise and contrast-to-noise ratios can be achieved by extending the duration of the data sampling period, or equivalently stated, by reducing the bandwidth of the data acquisition. This technique is particularly applicable for the clinically useful long TR double spin-echo sequence for improving the signal-to-noise and contrast-to-noise ratios for the long TE second echo image. Such a sequence would employ a relatively short data sampling period (wide bandwidth) for the short TE first echo, and a relatively long data sampling period (narrow bandwidth) for the long TE second echo. Implementing such a sequence which uses two data acquisitions of different bandwidths within one sequence repetition can present certain technical problems. In this communication, we describe a method to implement such a mixed bandwidth pulse sequence on a standard commercial whole-body imager without the need for additional software or hardware. This sequence is now in routine clinical use at our institution.