Characterization of Carotid Artery Plaque Components on Magnetic Resonance Imaging Using Signal Intensity of the Phantom as a Reference

Rationale and Objectives: To evaluate the properties of plaque by the use of magnetic resonance imaging (MRI), it is necessary to use amaterial with stable signal intensity (eg, muscle or submandibular gland) as a reference. However, there may be differences between individuals. Therefore, we used a small phantom set on the circumference of the neck as a reference. The signal intensity ratio (SIR) methods using the phantom as a reference were reviewed for discrimination of the properties of plaque in the carotid artery. Materials and Methods: Three phantoms (phantom 1: water; phantom 2: 5μmol gadopentetate dimeglumine; and phantom 3: 2.5μmol gadopentetate dimeglumine) were set around the neck. SIR was calculated for each region of interest and compared according to pathological grade. Results: The method using a phantom as a reference reduced the standard deviations of tissue ratios to 0.16 from 0.27 in comparison with the method using muscle and showed a close correlation with pathological grade. In addition, the agreement rates with pathological grade and grades from each SIR using signal intensity of the phantom as a reference were higher than using signal intensity of the muscle as a reference to 0.86 from 0.63 for two-dimensional images and to 0.86 from 0.71 for three-dimensional images. Conclusions: The method described here reduced error compared to the method using muscle as a reference, and the results were closely correlated with pathological grade.