title: Noninvasive characterization of carotid plaque strain.
abstract: Current risk stratification of internal carotid artery plaques based on diameter-reducing percentage stenosis may be unreliable because ischemic stroke results from plaque disruption with atheroembolization. Biomechanical forces acting on the plaque may render it vulnerable to rupture. The feasibility of ultrasound-based quantification of plaque displacement and strain induced by hemodynamic forces and their relationship to high-risk plaques have not been determined. We studied the feasibility and reliability of carotid plaque strain measurement from clinical B-mode ultrasound images and the relationship of strain to high-risk plaque morphology.
  
  
  
  We analyzed carotid ultrasound B-mode cine loops obtained in patients with asymptomatic ≥50% stenosis during routine clinical scanning. Optical flow methods were used to quantify plaque motion and shear strain during the cardiac cycle. The magnitude (maximum absolute shear strain rate [MASSR]) and variability (entropy of shear strain rate [ESSR] and variance of shear strain rate [VSSR]) of strain were combined into a composite shear strain index (SSI), which was assessed for interscan repeatability and correlated with plaque echolucency.
  
  
  
  Nineteen patients (mean age, 70 years) constituting 36 plaques underwent imaging; 37% of patients (n = 7) showed high strain (SSI ≥0.5; MASSR, 2.2; ESSR, 39.7; VSSR, 0.03) in their plaques; the remaining clustered into a low-strain group (SSI <0.5; MASSR, 0.58; ESSR, 21.2; VSSR, 0.002). The area of echolucent morphology was greater in high-strain plaques vs low-strain plaques (28% vs 17%; P = .018). Strain measurements showed low variability on Bland-Altman plots with cluster assignment agreement of 76% on repeated scanning. Two patients developed a stroke during 2 years of follow-up; both demonstrated high SSI (≥0.5) at baseline.
  
  
  
  Carotid plaque strain is reliably computed from routine B-mode imaging using clinical ultrasound machines. High plaque strain correlates with known high-risk echolucent morphology. Strain measurement can complement identification of patients at high risk for plaque disruption and stroke.
authors.affiliation: Department of Bioengineering, George Mason University, Fairfax, Va; Center for Vascular Diagnostics, Division of Vascular Surgery, University of Maryland School of Medicine, Baltimore, Md.
authors.forename: Amir A
authors.initials: AA
authors.lastname: Khan
authors.affiliation: Department of Bioengineering, George Mason University, Fairfax, Va.
authors.forename: Siddhartha
authors.initials: S
authors.lastname: Sikdar
authors.affiliation: Department of Surgery, University of Washington, Seattle, Wash.
authors.forename: Thomas
authors.initials: T
authors.lastname: Hatsukami
authors.affiliation: Department of Bioengineering, George Mason University, Fairfax, Va.
authors.forename: Juan
authors.initials: J
authors.lastname: Cebral
authors.affiliation: Department of Cardiology, Baptist Health Lexington, Lexington, Ky.
authors.forename: Michael
authors.initials: M
authors.lastname: Jones
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, Minn.
authors.forename: John
authors.initials: J
authors.lastname: Huston
authors.affiliation: Department of Biostatistics, UAB School of Public Health, Birmingham, Ala.
authors.forename: George
authors.initials: G
authors.lastname: Howard
authors.affiliation: Center for Vascular Diagnostics, Division of Vascular Surgery, University of Maryland School of Medicine, Baltimore, Md. Electronic address: blal@smail.umaryland.edu.
authors.forename: Brajesh K
authors.initials: BK
authors.lastname: Lal
mesh_terms: D000368:Aged; D002343:Carotid Artery, Internal / Q000000981:diagnostic imaging* / Q000503:physiopathology; D016893:Carotid Stenosis / Q000150:complications / Q000000981:diagnostic imaging* / Q000503:physiopathology; D005240:Feasibility Studies; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008396:Maryland; D008875:Middle Aged; D058226:Plaque, Atherosclerotic; D011237:Predictive Value of Tests; D011379:Prognosis; D011446:Prospective Studies; D012039:Regional Blood Flow; D015203:Reproducibility of Results; D012307:Risk Factors; D012720:Severity of Illness Index; D013314:Stress, Mechanical; D020521:Stroke / Q000209:etiology / Q000503:physiopathology; D014463:Ultrasonography / Q000379:methods*