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348 results on '"Gati, Joseph S."'

38. Flexible retinotopy: motion-dependent position coding in the visual cortex

Author

Malick, Terrence, Goltz, Herbert C., Thomas, Christopher G., Gati, Joseph S., Menon, Ravi S., and Goodale, Melvyn A.

Subjects
Science and technology
Abstract

Although the visual cortex is organized retinotopically, it is not clear whether the cortical representation of position necessarily reflects perceived position. Using functional magnetic resonance imaging (fMRI), we show that the retinotopic representation of a stationary object in the cortex was systematically shifted when visual motion was present in the scene. Whereas the object could appear shifted in the direction of the visual motion, the representation of the object in the visual cortex was always shifted in the opposite direction. The results show that the representation of position in the primary visual cortex, as revealed by fMRI, can be dissociated from perceived location., When a stationary window or envelope is filled with a moving pattern, the position of the envelope can appear shifted in the direction of the internal motion (1, 2). The [...]

Published
2003

40. Integration of an RF coil and commercial field camera for ultrahigh‐field MRI.

Author

Gilbert, Kyle M., Dubovan, Paul I., Gati, Joseph S., Menon, Ravi S., and Baron, Corey A.

Subjects
CAMERAS, MAGNETIC resonance imaging
Abstract

Purpose: To develop an RF coil with an integrated commercial field camera for ultrahigh field (7T) neuroimaging. The RF coil would operate within a head‐only gradient coil and be subject to the corresponding design constraints. The RF coil can thereafter be used for subject‐specific correction of k‐space trajectories—notably in gradient‐sensitive sequences such as single‐shot spiral imaging. Methods: The transmit and receive performance was evaluated before and after the integration of field probes, whereas field probes were evaluated when in an optimal configuration external to the coil and after their integration. Diffusion‐weighted EPI and single‐shot spiral acquisitions were employed to evaluate the efficacy of correcting higher order field perturbations and the consequent effect on image quality. Results: Field probes had a negligible effect on RF‐coil performance, including the transmit efficiency, transmit uniformity, and mean SNR over the brain. Modest reductions in field‐probe signal lifetimes were observed, caused primarily by nonidealities in the gradient and shim fields of the head‐only gradient coil at the probe positions. The field‐monitoring system could correct up to second‐order field perturbations in single‐shot spiral imaging. Conclusion: The integrated RF coil and field camera was capable of concurrent‐field monitoring within a 7T head‐only scanner and facilitated the subsequent correction of k‐space trajectories during spiral imaging. [ABSTRACT FROM AUTHOR]

Published
2022
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