Abstract
Magnetic resonance imaging (MRI) is a widely used method for non-invasive study of the structure and function of the human brain. Increasing magnetic field strengths enable higher resolution imaging; however, long scan times and high motion sensitivity mean that image quality is often limited by the involuntary motion of the subject. Prospective motion correction is a technique that addresses this problem by tracking head motion and continuously updating the imaging pulse sequence, locking the imaging volume position and orientation relative to the moving brain. The accuracy and precision of current MR-compatible tracking systems and navigator methods allows the quantification and correction of large-scale motion, but not the correction of very small involuntary movements in six degrees of freedom. In this work, we present an MR-compatible tracking system comprising a single camera and a single 15 mm marker that provides tracking precision in the order of 10 m and 0.01 degrees. We show preliminary results, which indicate that when used for prospective motion correction, the system enables improvement in image quality at both 3 T and 7 T, even in experienced and cooperative subjects trained to remain motionless during imaging. We also report direct observation and quantification of the mechanical ballistocardiogram (BCG) during simultaneous MR imaging. This is particularly apparent in the head-feet direction, with a peak-to-peak displacement of 140 m.
Highlights
Magnetic resonance imaging has become an indispensable tool for imaging of the human brain, both in patients for clinical diagnosis and in healthy volunteers for research purposes
There is a general trend to higher magnetic field strengths, which improves the image signal-to-noise ratio and allows higher nominal resolution [1]
The camera and lighting unit (CLU) is attached inside the scanner bore using adhesive strips, allowing a direct line of sight to the marker
Summary
Magnetic resonance imaging has become an indispensable tool for imaging of the human brain, both in patients for clinical diagnosis and in healthy volunteers for research purposes. There is a general trend to higher magnetic field strengths, which improves the image signal-to-noise ratio and allows higher nominal resolution [1]. With higher resolution imaging, the requirement for patients or subjects to remain motionless increases. This problem worsens with the longer scan durations required to achieve the highest resolutions. Large motion is typically observed in the youngest and oldest patients, rendering the images non-diagnostic. Even in cooperative volunteers, image quality can be degraded by small involuntary motion, such as that due to breathing, swallowing or the cardiac cycle
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