title: Impact of T2 decay on carotid artery wall thickness measurements.
abstract: OBJECTIVE
  To investigate the impact of T2 relaxation of the carotid wall on measurements of its thickness.
  
  
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins Medical Institutions, Baltimore, Maryland 21287, USA.
authors.forename: Ye
authors.initials: Y
authors.lastname: Qiao
authors.forename: David A
authors.initials: DA
authors.lastname: Steinman
authors.forename: Maryam
authors.initials: M
authors.lastname: Etesami
authors.forename: Alex
authors.initials: A
authors.lastname: Martinez-Marquese
authors.forename: Edward G
authors.initials: EG
authors.lastname: Lakatta
authors.forename: Bruce A
authors.initials: BA
authors.lastname: Wasserman
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D017536:Carotid Artery, Common / Q000033:anatomy & histology*; D059168:Carotid Intima-Media Thickness; D005260:Female; D064368:Healthy Volunteers; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity