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Three‐dimensional time‐of‐flight MR angiography with a specialized gradient head coil
Author(s) -
Tkach Jean A.,
Ruggieri Paul M.,
Dillinger John J.,
Ross Jeffrey S.,
Modic Michael T.,
Masaryk Thomas J.
Publication year - 1993
Publication title -
journal of magnetic resonance imaging
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.563
H-Index - 160
eISSN - 1522-2586
pISSN - 1053-1807
DOI - 10.1002/jmri.1880030212
Subject(s) - pulsatile flow , stenosis , electromagnetic coil , imaging phantom , magnetic resonance angiography , angiography , signal (programming language) , nuclear magnetic resonance , flip angle , amplitude , nuclear medicine , magnetic resonance imaging , physics , radiology , medicine , computer science , optics , cardiology , quantum mechanics , programming language
A gradient head coil has been developed, incorporating two independent gradients within the conventional body coil of the magnetic resonance (MR) system, with reduced rise times (200 μsec) and maximum amplitudes of 37 and 18 mT/m in the z and y directions, respectively. This gradient coil was systematically evaluated by testing two‐dimensional (2D) and three‐dimensional (3D) time‐of‐flight (TOF) MR angiography sequences applied to a pulsatile flow phantom simulating a carotid stenosis and the intracranial vasculature. When standard 2D and 3D TOF MR angiography techniques were used to image the carotid stenosis model, dramatic signal loss in the stenotic segment and a large flow void distal to the stenosis were seen. The shorter (3.8 msec) absolute echo times (TEs) achievable with the gradient coil in 3D sequences substantially reduced the phase dispersion and associated signal loss in the region of stenosis. Shorter TEs alone (3.2 msec) did not minimize signal loss, and firstorder flow compensation in the read and section‐select directions provided further improvements (despite slightly longer TEs). Reduction of TEs in 2D sequences yielded relatively poor results regardless of the refocusing scheme or TE. This study confirms the predicted benefits of a dedicated coil with improved gradient capabilities for 3D MR angiography. The study suggests the limitations of 2D TOF MR angiography in the evaluation of severe stenoses.