title: Ex vivo study of carotid endarterectomy specimens: quantitative relaxation times within atherosclerotic plaque tissues.
abstract: OBJECTIVE
  Previous studies reporting relaxation times within atherosclerotic plaque have typically used dedicated small-bore high-field systems and small sample sizes. This study reports quantitative T(1), T(2) and T(2) relaxation times within plaque tissue at 1.5 T using spatially co-matched histology to determine tissue constituents.
  
  
  METHODS
  Ten carotid endarterectomy specimens were removed from patients with advanced atherosclerosis. Imaging was performed on a 1.5-T whole-body scanner using a custom built 10-mm diameter receive-only solenoid coil. A protocol was defined to allow subsequent computation of T(1), T(2) and T(2) relaxation times using multi-flip angle spoiled gradient echo, multi-echo fast spin echo and multi-echo gradient echo sequences, respectively. The specimens were subsequently processed for histology and individually sectioned into 2-mm blocks to allow subsequent co-registration. Each imaging sequence was imported into in-house software and displayed alongside the digitized histology sections. Regions of interest were defined to demarcate fibrous cap, connective tissue and lipid/necrotic core at matched slice-locations. Relaxation times were calculated using Levenberg-Marquardt's least squares curve fitting algorithm. A linear-mixed effect model was applied to account for multiple measurements from the same patient and establish if there was a statistically significant difference between the plaque tissue constituents.
  
  
  RESULTS
  T(2) and T(2) relaxation times were statistically different between all plaque tissues (P=.026 and P=.002 respectively) [T(2): lipid/necrotic core was lower 47 ± 13.7 ms than connective tissue (67 ± 22.5 ms) and fibrous cap (60 ± 13.2 ms); T(2): fibrous cap was higher (48 ± 15.5 ms) than connective tissue (19 ± 10.6 ms) and lipid/necrotic core (24 ± 8.2 ms)]. T(1) relaxation times were not significantly different (P=.287) [T(1): Fibrous cap: 933 ± 271.9 ms; connective tissue (1002 ± 272.9 ms) and lipid/necrotic core (1044 ± 304.0 ms)]. We were unable to demarcate hemorrhage and calcium following histology processing.
  
  
  CONCLUSIONS
  This study demonstrates that there is a significant difference between qT(2) and qT(2) in plaque tissues types. Derivation of quantitative relaxation times shows promise for determining plaque tissue constituents.
authors.affiliation: Department of Radiology, Cambridge University Hospital NHS Foundation Trust, Cambridge, CB2 0QQ.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Degnan
authors.forename: Victoria E
authors.initials: VE
authors.lastname: Young
authors.forename: Tjun Y
authors.initials: TY
authors.lastname: Tang
authors.forename: Andrew B
authors.initials: AB
authors.lastname: Gill
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Graves
authors.forename: Jonathan H
authors.initials: JH
authors.lastname: Gillard
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Patterson
mesh_terms: D000368:Aged; D002339:Carotid Arteries / Q000473:pathology* / Q000601:surgery*; D016893:Carotid Stenosis / Q000473:pathology* / Q000601:surgery*; D016894:Endarterectomy, Carotid; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D066298:In Vitro Techniques; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008954:Models, Biological; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity