Kullervo H. Hynynen PhD, Abstract Co-Author: Nothing to Disclose

Nathan Judson McDannold PhD, Presenter: Nothing to Disclose

To explore the feasibility of performing ultrasound imaging in an MRI scanner to obtain truly simultaneous MR and ultrasound images. This could be useful for comparing the two imaging modalities and to potentially provide additional diagnostic information in one exam.

A custom MRI compatible diagnostic ultrasound transducer (center frequency=5 MHz, bandwidth approximately 50%) was placed in a mechanical positioning device in a 1.5 T MRI scanner. The transducer was excited with an RF pulse, and the signal generated by the ultrasound echoes in the transducer were amplified, digitized and stored in computer memory. This was done at each image location of the transducer while moving the transducer during MR imaging. The RF information was used to form B-scan ultrasound images. Images of in vivo brain were performed. Fast Spin Echo T2-weighted images (TR/TE =2500/80) were performed along the scan path of the ultrasound transducer. In vivo brain imaging was performed using a rabbit model that had a piece of skull bone removed few months earlier while replacing the skin over the dura. This allowed the ultrasound to propagate into the brain. This model was used since it provides good anatomical detail to compare the imaging methods.

The ultrasound set-up did not distort the MR images. Ultrasound imaging during MR imaging produced some increase in noise (SNR in the brain decreased by approximately 25%). The MR imaging did not distort the ultrasound images, and similar image quality was obtained with and without the MR imaging. The MR and ultrasound images correlated well.

This study demonstrates that ultrasound and MR imaging can be performed simultaneously in vivo. The addition of the noise in the MR image did not have a fatal impact on the image quality, however, it should be possible to eliminate it completely by better filtering and timing procedures. Simultaneous ultrasound imaging may offer additional diagnostic information and will provide a means to perfectly correlate diagnostic ultrasound and MR imaging findings. Based on the results, it should be feasible to develop a low cost ultrasound imaging device that can be used during routine ultrasound imaging.

Hynynen, K, McDannold, N, Simultaneous MR and Ultrasound Imaging.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4419134.html