TY  - JOUR
A1  - Kraff, Oliver
A1  - Bitz, Andreas
A1  - Breyer, Tobias
A1  - Kruszona, Stefan
A1  - Maderwald, Stefan
A1  - Brote, Irina
A1  - Gizewski, Elke R.
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
T1  - A transmit/receive radiofrequency array for imaging the carotid arteries at 7 Tesla: coil design and first in vivo results
JF  - Investigative Radiology
N2  - 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.
Y1  - 2011
U6  - http://dx.doi.org/10.1097/RLI.0b013e318206cee4
SN  - 1536-0210
VL  - 46
IS  - 4
SP  - 246
EP  - 254
PB  - Wolters Kluwer
CY  - Köln
ER  - 
TY  - JOUR
A1  - Kraff, Oliver
A1  - Bitz, Andreas
A1  - Kruszona, Stefan
A1  - Orzada, Stephan
A1  - Schaefer, Lena C.
A1  - Theysohn, Jens M.
A1  - Maderwald, Stefan
A1  - Ladd, Mark E.
A1  - Quick, Harald H.
T1  - An eight-channel phased array RF coil for spine MR imaging at 7 T
JF  - Investigative Radiology
Y1  - 2009
U6  - http://dx.doi.org/10.1097/RLI.0b013e3181b24ab7
SN  - 1536-0210
VL  - 44
IS  - 11
SP  - 734
EP  - 740
PB  - Lippincott Williams & Wilkins
ER  -