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Controlled Clinical Trial
. 2005 Dec;12(12):1521-6.
doi: 10.1016/j.acra.2005.08.009.

High-resolution black-blood MRI of the carotid vessel wall using phased-array coils at 1.5 and 3 Tesla

Seshasailaja Anumula  1 , Hee Kwon Song, Alexander C Wright, Felix W Wehrli
Affiliations
Controlled Clinical Trial

High-resolution black-blood MRI of the carotid vessel wall using phased-array coils at 1.5 and 3 Tesla

Seshasailaja Anumula et al. Acad Radiol. 2005 Dec.

Abstract

Rationale and objectives: The aim of this report is to investigate the magnetic field dependence of the signal-to-noise ratio (SNR) for carotid vessel wall magnetic resonance imaging using phased-array (PA) surface coils by comparing images obtained at 1.5 and 3 Tesla (T) and determine the extent to which the improved SNR at the higher field can be traded for improved spatial resolution.

Materials and methods: Two pairs of dual-element PA coils were constructed for operation at the two field strengths. The individual elements of each PA were matched to 50 Omega impedance on the neck and tuned at the respective frequencies. The coils were evaluated on a cylindrical phantom positioned with its axis parallel to the main field and the coils placed on either side of the phantom parallel to the sagittal plane. In vivo magnetic resonance images of the carotid arteries were obtained in five subjects at both field strengths with a fast spin-echo double-inversion black-blood pulse sequence with fat saturation. SNR was measured at both field strengths by using standard techniques.

Results: At a depth corresponding to the average location of the carotid arteries in the study subjects, mean phantom SNR for the two coils was higher at 3 T by a factor of 2.5. The greater than linear increase is caused by only partial coil loading of these relatively small coils. The practically achievable average SNR gain in vivo was 2.1. The lower in vivo SNR gain is attributed to a reduction in T2 and prolongation of T1 at the higher field strength and, to a lesser extent, the requirement for a decreased refocusing pulse flip angle to operate within specific absorption rate limits. The superior SNR at 3 T appears to provide considerably improved vessel-wall delineation.

Conclusions: Carotid artery vessel-wall magnetic resonance imaging using PA surface coils provides a considerable increase in SNR when field strength is increased from 1.5 to 3 T. This increase can be traded for enhanced in-plane resolution.

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Figures

FIGURE 1
FIGURE 1
Dual-element phased-array surface coil, representing half of a bilateral pair, custom-built for imaging the carotid vessel wall, with decoupling circuits indicated.
FIGURE 2
FIGURE 2
a) Cylindrical phantom with the coils on either side showing the axis along which the signal profile was obtained. b) SNR profile along the axis shown in a).
FIGURE 3
FIGURE 3
Axial images of the carotid arteries at approximately 0.8cm distal to the right carotid bifurcation in one subject showing the improved SNR at a) 3 T compared to b) 1.5 T. (FOV = 12 cm x 12 cm; matrix size = 256 x 256; Pixel size = 0.47 x 0.47 mm2). The typical signal measurements in the adjacent muscles are shown by the ROIs. c) Measurement of noise level by increasing FOV (24 cm x 12cm) to allow measurement in a region devoid of phase-encoding ghosting (Matrix 512 x 256). Noise is estimated as mean of signal from 4 ROIs in the image background.
FIGURE 4
FIGURE 4
Effect of reduced pixel size in magnified carotid artery in three subjects below (top row), at (center row), and above (bottom row) the bifurcation: a) 3 T, pixel size 0.47 x 0.47 mm2; b) 3 T, pixel size 0.31 x 0.31 mm2; c) 1.5 T, pixel size same as in b).
See this image and copyright information in PMC

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