Impact of T2 decay on carotid artery wall thickness measurements

Abstract

Purpose To investigate the impact of T2 relaxation of the carotid wall on measurements of its thickness. Materials and Methods The common carotid artery wall was imaged using a spin echo sequence acquired at four echo times (17 ms to 68 ms) in 65 participants as part of VALIDATE study. Images were acquired transverse to the artery 1.5 cm proximal to the flow divider. Mean wall thickness, mean wall signal intensity, lumen area, and outer wall area were measured for each echo. Contours were also traced on the image from the fourth echo and then propagated to the images from the preceding echoes. This was repeated using the image from the first echo. Mean wall signal intensity measurements at the four echo times were fit to a mono-exponential decay curve to derive the mean T2 relaxation time for each set of contours. Results Mean wall thickness decreased with increasing echo time, with an average thickness reduction of 8.6% between images acquired at the first and last echo times (TE) (0.93 mm at TE 17 ms versus 0.85 mm at TE 68 ms, P < 0.001). Average T2 relaxation time of the carotid wall decreased by 3% when the smaller contours from the last echo were used, which excluded the outer-most layer (54.3 ± 7.6 ms versus 52.7 ± 6.6 ms, P = 0.03). Conclusion Carotid wall thickness measurements decrease with echo time as expected by the fast T2 relaxation time of the outer-most layer, namely the adventitia. A short echo time is needed for thickness measurements to include adventitia, which plays an important role in plaque development.

Carotid Artery Wall Thickness and Incident Cardiovascular Events: A Comparison between US and MRI in the Multi-Ethnic Study of Atherosclerosis (MESA)

“…Measurements of wall thickness by using MRI and US differ on wall boundary detection. IMT measurements by using US include the sum of the intima and media, whereas wall thickness measurements by using MRI also include adventitia in addition to intima and media (6,7). This is supported by our results that wall thickness measurements by using MRI were on average greater than were IMT by using US.…”

“…MRI can be used to image the entire wall circumference, in contrast to US measurements of IMT that are usually based solely on views of the far wall of the carotid artery (5,6). Additionally, MRI includes adventitia in the measurement of wall thickness, which might be important for defining vascular inflammation because it is the source of vasa vasorum (5,7).…”

Patterns and Implications of Intracranial Arterial Remodeling in Stroke Patients

“…A population-based study that includes solitary early and intermediate stages of atherosclerosis could provide more insight into the natural history of ICA remodeling. Finally, our BBMRI images of ICAD lesions lack histologic validation, although there is no reason to suspect that image interpretation would differ from carotid artery techniques 34 .…”

Segment-specific associations between local haemodynamic and imaging markers of early atherosclerosis at the carotid artery: an in vivo human study

“…At current resolutions, MRI is unable to discriminate the three vessel layers [43], and so our WT wall variable was only a surrogate for intimal thickening. Similarly, our CE wall variable was a surrogate for endothelial dysfunction, albeit a biologically plausible one, as previously outlined.…”