Published ahead of print on September 3, 2008
doi: 10.3174/ajnr.A1252
3D Time-Resolved MR Angiography (MRA) of the Carotid Arteries with Time-Resolved Imaging with Stochastic Trajectories: Comparison with 3D Contrast-Enhanced Bolus-Chase MRA and 3D Time-Of-Flight MRA
R.P. Lima,
M. Shapiroa,
E.Y. Wanga,
M. Lawc,
J.S. Babba,
L.E. Rueffa,
J.S. Jacoba,
S. Kima,
R.H. Carsona,c,
T.P. Mulhollanda,
G. Laubb and
E.M. Hechta
a Department of Radiology, NYU Langone Medical Center, New York, NY
b Department of Siemens Medical Solutions, Malvern, Pa
c Department of Mount Sinai Medical Center, New York, NY
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Fig 1. Diagram detailing the k-space trajectory used with the TWIST sequence, with a continuous sampling profile. Sampling commences 1) at the outer edge of the center region (A) of k-space, kc and moves toward the center of k-space; 2) spirals back to kc; 3) traverses a trajectory through the periphery (B) of k-space, moving out to the outer edge of k-space, kmax and then 4) back to kc. 5) The cycle continues with the next iteration. The difference between iterations are the points of k-space sampled in B (points sampled for steps 7–9 differ from those sampled from 3–5). Therefore A is fully sampled with every iteration, but B requires 2 iterations in this schematic to be fully sampled, with subsequent gain in temporal resolution compared with conventional sampling of all points in k-space with each iteration. Filling of k-space is demonstrated at time points 1–9 at the bottom of the figure, with complete filling of k-space at time point 9.
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Fig 2. A 36-year-old woman (patient 13) presenting with right hemiparesis and left anterior circulation infarct diagnosed at brain MR imaging. A, TOF MIP (left anterior oblique projection) demonstrates tapering of the left ICA at the distal bulb level consistent with dissection (arrow). B, TWIST subtracted consecutive sagittal MIP images also demonstrate left ICA dissection (arrow), with delayed filling of the left carotid bulb in contrast to the right. Subsequent consecutive images (not shown) failed to show filling of the left ICA distal to the carotid bulb, and the left middle cerebral artery never opacified. C, Left anterior oblique subtraction MIP images from the TWIST (left) and HR (right) sequences demonstrate proximal left cervical ICA dissection (arrowhead). The HR sequence ia degraded by motion artifact and high-concentration contrast agent within the central veins (arrow).
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Fig 3. TOF MIP image (A), TWIST arterial phase subtracted MIP image (B), and HR MRA subtracted MIP image (C) demonstrate ulcerated plaque of the left ICA in an 80-year-old man (patient 4), causing mild (46%) stenosis (arrows). The degree of stenosis was overestimated by both readers using the TOF technique (73% and 65% for readers 1 and 2, respectively) and was accurately categorized for TWIST MRA (31% and 47%) and HR MRA (32% and 35%). TOF stenosis overestimation was attributed to in-plane saturation effects, because the proximal ICA is approaching the axial imaging plane in its orientation. Note the clear arterial phase image obtained by using the TWIST technique and the presence of venous contamination on the HR image.
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Fig 4. A 29-year-old woman (patient 2) presenting with neck pain. A, TWIST inverted MIP subtraction images in the coronal plane demonstrate the delayed appearance of a narrowed distal left cervical ICA (arrow), following the appearance of the intracranial left ICA and circle of Willis. B, TWIST (left) and HR inverted subtracted MIP image (right) in the left anterior oblique plane demonstrate an abnormal tapered appearance to the distal cervical left ICA (arrows). C, DSA images confirm a dissection of the distal left cervical ICA (arrow), reflected by delayed filling of the proximal left ICA in comparison with the left external carotid artery, best seen in the internal maxillary artery (arrowhead).
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