A transmit/receive radiofrequency array for imaging the carotid arteries at 7 Tesla: coil design and first in vivo results

  • Objective: To develop a transmit/receive radiofrequency (RF) array for magnetic resonance imaging (MRI) of the carotid arteries at 7 T. The prototype is characterized in numerical simulations and bench measurements, and the feasibility of plaque imaging at 7 T is demonstrated in first in vivo images. Materials and Methods: The RF phased array coil consists of 8 surface loop coils. To allow imaging of both sides of the neck, the RF array is divided into 2 coil clusters, each with 4 overlapping loop elements. For safety validation, numerical computations of the RF field distribution and the corresponding specific absorption rate were performed on the basis of a heterogeneous human body model. To validate the coil model, maps of the transmit B1+ field were compared between simulation and measurement. In vivo images of a healthy volunteer and a patient (ulcerating plaque and a 50% stenosis of the right internal carotid artery) were acquired using a 3-dimensional FLASH sequence with a high isotropic spatial resolution of 0.54 mm as well as using pulse-triggered proton density (PD)/T2-weighted turbo spin echo sequences. Results: Measurements of the S-parameters yielded a reflection and isolation of the coil elements of better than −18 and −13 dB, respectively. Measurements of the g-factor indicated good image quality for parallel imaging acceleration factors up to 2.4. A similar distribution and a very good match of the absolute values were found between the measured and simulated B1+ transmit RF field for the validation of the coil model. In vivo images revealed good signal excitation of both sides of the neck and a high vessel-to-background image contrast for the noncontrast-enhanced 3-dimensional FLASH sequence. Imaging at 7 T could depict the extent of stenosis, and revealed the disruption and ulcer of the plaque. Conclusions: This study demonstrates that 2 four-channel transmit/receive RF arrays for each side of the neck is a suitable concept for in vivo MRI of the carotid arteries at 7 Tesla. Further studies are needed to explore and exploit the full potential of 7 T high-field MRI for carotid atherosclerotic plaque imaging.

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Metadaten
Author:Oliver Kraff, Andreas Bitz, Tobias Breyer, Stefan Kruszona, Stefan Maderwald, Irina Brote, Elke R. Gizewski, Mark E. Ladd, Harald H. Quick
DOI:https://doi.org/10.1097/RLI.0b013e318206cee4
ISSN:1536-0210
Parent Title (English):Investigative Radiology
Publisher:Wolters Kluwer
Place of publication:Köln
Document Type:Article
Language:English
Year of Completion:2011
Volume:46
Issue:4
First Page:246
Last Page:254
Link:https://doi.org/10.1097/RLI.0b013e318206cee4
Zugriffsart:campus
Institutes:FH Aachen / Fachbereich Elektrotechnik und Informationstechnik
collections:Verlag / Wolters Kluwer