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Updating of MRI gradients using a infrared tracking system to compensate motion artifacts

: Dold, C.; Zaitsev, M.; Speck, O.; Firle, E.; Hennig, J.; Sakas, G.

International Society for Magnetic Resonance in Medicine -ISMRM-:
ISMRM Twelfth Scientific Meeting 2004. Proceedings. CD-ROM
Kyoto, 2004
ISSN: 1545-4436
International Society for Magnetic Resonance in Medicine (Scientific Meeting) <12, 2004, Kyoto, Japan>
Fraunhofer IGD ()
magnetic resonance imaging; MRI; diagnostic imaging; tracking

Functional MRI (fMRI) is a non-invasive imaging technique that is used to investigate cerebral function. Patient motion remains a significant problem in many MRI applications, including fMRI, cardiac and abdominal imaging, and conventional long TR acquisitions. Many techniques are available to reduce or to compensate for bulk motion effects, such as physiological gating, phase-encode reordering, fiducial markers, fast acquisitions, image volume registration, or alternative data acquisitions strategies such as projection reconstruction, spiral and PROPELLER. Navigator echoes are used to measure motion with one or more degrees of freedom; the motion is then compensated for either retrospectively or prospectively.
Implementing a similar technique in MRI presents additional challenges. Foremost the tracking system and the MRI system have to be compatible. High magnetic fields >= 1.5 Tesla in magnetic resonance imaging systems require that the tracking camera system be positioned a sufficient distance from the MRI system to ensure proper function and safety. Functional MRI also proves challenging because of the high spatial accuracy (RMS <0,3mm) required by the complete measurement chain with a small latency time (<30ms) of the tracking system. The coordinate system of a MRI scanner is controlled using magnetic field gradients and frequencies in the sequence. Determining a precise relationship between the spatial varying magnetic field gradients and the spatial tracking information is necessary to compensate for motion artifacts.