Head motion detection using FID navigators.

This work explores a concept for motion detection in brain MR examinations using high channel-count RF coil arrays. It applies ultrashort (<100 μsec) free induction decay signals, making use of the knowledge that motion induces variations in these signals when compared to a reference free induction decay signal. As a proof-of-concept, the method was implemented in a standard structural MRI sequence. The stability of the free induction decay-signal was verified in phantom experiments. Human experiments demonstrated that the observed variations in the navigator data provide a sensitive measure for detection of relevant and common subject motion patterns. The proposed methodology provides a means to monitor subject motion throughout a MRI scan while causing little or no impact on the sequence timing and image contrast. It could hence complement available motion detection and correction methods, thus further reducing motion sensitivity in MR applications.

Accuracy and Precision of Head Motion Information in Multi-Channel Free Induction Decay Navigators for Magnetic Resonance Imaging.

Free induction decay (FID) navigators were found to qualitatively detect rigid-body head movements, yet it is unknown to what extent they can provide quantitative motion estimates. Here, we acquired FID navigators at different sampling rates and simultaneously measured head movements using a highly accurate optical motion tracking system. This strategy allowed us to estimate the accuracy and precision of FID navigators for quantification of rigid-body head movements. Five subjects were scanned with a 32-channel head coil array on a clinical 3T MR scanner during several resting and guided head movement periods. For each subject we trained a linear regression model based on FID navigator and optical motion tracking signals. FID-based motion model accuracy and precision was evaluated using cross-validation. FID-based prediction of rigid-body head motion was found to be with a mean translational and rotational error of 0.14±0.21 mm and 0.08±0.13(°) , respectively. Robust model training with sub-millimeter and sub-degree accuracy could be achieved using 100 data points with motion magnitudes of ±2 mm and ±1(°) for translation and rotation. The obtained linear models appeared to be subject-specific as inter-subject application of a "universal" FID-based motion model resulted in poor prediction accuracy. The results show that substantial rigid-body motion information is encoded in FID navigator signal time courses. Although, the applied method currently requires the simultaneous acquisition of FID signals and optical tracking data, the findings suggest that multi-channel FID navigators have a potential to complement existing tracking technologies for accurate rigid-body motion detection and correction in MRI.

Prospective motion correction with FID-triggered image navigators

In this work, we propose a method for prospective motion correction in MRI using a novel image navigator module, which is triggered by a free induction decay (FID) navigator. Only when motion occurs, the image navigator is run and new positional information is obtained through image registration. The image navigator was specifically designed to match the impact on the magnetization and the acoustic noise of the host sequence. This detection-correction scheme was implemented for an MP-RAGE sequence and 5 healthy volunteers were scanned at 3T while performing various head movements. The correction performance was demonstrated through automated brain segmentation and an image quality index whose results are sensitive to motion artifacts.

The golden book of the Dutch navigators,

Title within ornamental border.

Stars for navigators and polaris tables for the year 1910. (Appendix to the American nautical almanac for the year 1910)

Mode of access: Internet.

Vikings of the Pacific; the adventures of the explorers who came from the West, eastward; Bering, the Dane; the outlaw hunters of Russia; Benyowsky, the Polish pirate; Cook and Vancouver, the English navigators; Gray of Boston, the discoverer of the Columbia; Drake, Ledyard, and other soldiers of fortune on the west coast of America.

"The contents of this volume appeared serially in Leslie's monthly, Outing, and Harper's magazine." - Foreword.

The Colombian navigator, or, Sailing directory for the American coasts and the West-Indies ... composed ... from many valuable documents and surveys, especially those of Capt. Andr. Livingston, of the Spanish navigators, and the American pilots, of Messrs. Des Barres, Holland ... /

Catalog of charts available from R.H. Laurie at end of work, dated 1825.

The last voyage of Capt. Sir John Ross ... to the Arctic regions for the discovery of a north west passage : performed in the years 1829-30-31-32 and 33 : to which is prefixed an abridgement of the former voyages of Captns. Ross, Parry & other celebrated navigators to the northern latitudes : compiled from authentic information and original documents transmitted by an officer attached to the last expedition ; illustrated by engravings from drawings taken on the spot /

"On the position of the north magnetic pole. (Supplement)": 44 p. at end.

An historical and descriptive account of China; its ancient and modern history, language, literature, religion, government, industry, manners, and social state; intercourse with Europe from the earliest ages; missions and embassies to the imperial court; British and foreign commerce; directions to navigators; state of mathematics and astronomy; survey of its geography, geology, botany, and zoology.

Added t.p., illustrated.

Navigators handbook,

"Lithoprinted."

Retrospective correction of involuntary microscopic head movement using highly accelerated fat image navigators (3D FatNavs) at 7T.

PURPOSE: The goal of the present study was to use a three-dimensional (3D) gradient echo volume in combination with a fat-selective excitation as a 3D motion navigator (3D FatNav) for retrospective correction of microscopic head motion during high-resolution 3D structural scans of extended duration. The fat excitation leads to a 3D image that is itself sparse, allowing high parallel imaging acceleration factors - with the additional advantage of a minimal disturbance of the water signal used for the host sequence. METHODS: A 3D FatNav was inserted into two structural protocols: an inversion-prepared gradient echo at 0.33 × 0.33 × 1.00 mm resolution and a turbo spin echo at 600 μm isotropic resolution. RESULTS: Motion estimation was possible with high precision, allowing retrospective motion correction to yield clear improvements in image quality, especially in the conspicuity of very small blood vessels. CONCLUSION: The highly accelerated 3D FatNav allowed motion correction with noticeable improvements in image quality, even for head motion which was small compared with the voxel dimensions of the host sequence. Magn Reson Med 75:1030-1039, 2016. © 2015 Wiley Periodicals, Inc.

A invocação de Nossa Senhora dos Navegantes em Cascais

A invocação de Nossa Senhora dos Navegantes esteve na base da ordenação heráldica da Casa dos Pescadores de Cascais. Analisado o culto dos homens do mar daquela vila pode-se questionar a opção iconográfica instituída.

The scramble for the seas : the ballad evidence of Sir Andrew Barton

The presence and importance of the sea as a factor that has helped shape the history of England since at least the Roman invasions of 55-54 BC (less successful, incidentally, than most of Caesar’s other military ventures ...) need no particular urging or demonstration. Nonetheless, a bird’s-eye view would necessarily survey the waves of invasions and settlements that, one after the other, came dashing over the centuries upon England’s shores; not to mention the requested invasion of 1688, Angles and Saxons, Scandinavians, Normans, they all crossed the whale’s path and cast anchor in England’s green and pleasant land. In the course of this retrospective voyage through the oceans of History, one would inevitably stop at the so-called ‘Discoveries’ of the 15th-16th centuries, meet their navigators, sailors and pirates extolled by Richard Hakluyt (1553?-1616), face an anonymous crowd of merchants and witness the huge expansion of trade, largely to the benefit of the ‘discovering’ countries as prescribed by the economic Gospel Adam Smith (1723-90) would later baptize as “mercantilism”.

O "ser português" e o "outro": Revisitar a história de Portugal no diálogo com a civilização chinesa - O caso Tomás Pereira

Tese de Doutoramento em Ciências da Cultura - Especialidade em Culturas do Extremo Oriente