+ Advancements in Carotid Ultrasound Caitlin Gardiner

+ Limitations of Carotid Ultrasound Technical ability of the sonographer Extensive plaque (acoustic shadowing may hinder insonation distal to calcification) Significant narrowing of the underlying vessel may be present in the absence of a high velocity jet Only the cervical portion of the ICA can be evaluated (7) Patient anatomy A larger, thick neck A bifurcation at the level of the mandible Tortuous vessels

+ Accuracy of Carotid Sonography Detection Stenosis of the ICA 91-94% sensitivity and 85-99% specificity One study compared Carotid US with surgical findings and found PSV >440 cm/sec, EDV >155 cm/sec, or carotid index >10 indicated a residual lumen diameter of < 1.5 mm (specificity 100% and sensitivity of 58%, 63% and 30%, respectively). By combining these criteria, the sensitivity increased to 72% A PSV of >200 cm/sec combined with either an EDV >140 or a carotid index >4.5 has a sensitivity of 96% and a specificity of 61% (Suwanwela) Poor classification of plaque morphology and recognition of intraplaque hemorrhage

+ Ultrasound compared with other imaging modalities Magnetic resonance Angiography has a better discriminatory power compared with US in diagnosis 70-99% stenosis MRA is also more sensitive and specific than Digital Subtraction Angiography Both US and MRA are very accurate at detecting occlusion (6)

+ Advancements in Carotid Ultrasound Power Doppler Fibrous Cap Thickness Intimal Thickness Measurement Computer Aided Devices 3D ultrasound 4D Intra-Lumen Imaging Contrast Enhanced Ultrasound

+ Power Doppler Superior assessment of intensity More precisely reveal features of intrastenotic lumen, particularly in high grade stenosis Aid the differentiation between subtotal and total occlusion by demonstrating a trickle flow or ‘string sign’ (Tegeler)

+ Fibrous Cap Thickness High resolution evaluation of the mean thickness of the fibrous cap thickness (FCT) on the surface of atherosclerotic plaque. May assist in discriminating between symptomatic and asymptomatic plaques and atheroma stability. Measuring the FCT on ultrasound correlated well with histology, and intra-observer sonographer variability is small (3) Symptomatic patients demonstrate decreased FCT (3) Threshold of 0.65mm demonstrates a 75% positive predictor value and 88.2% negative-predicative value (9) Image B indicates concentric plaque with its fibrous cap identified as a hyperechoic rim on the intimal surface of the plaque. Image C and D are magnifications with automatically detected boundaries (red and green) to depict the cap thickness (Devuyst)

+ Intimal Thickness Measurement Identification of intima-media thickness to predict pre- clinical atherosclerotic changes and a vascular ischemic events in both the brain and heart. Aided by improvements of B-mode resolution, coded harmonics, reduction of acoustic shadowing and reverberation (9)

+ Computer Aided Devices Systems Computer Aided Devices are employed to objective classify carotid athermanous plaque and classify into symptomatic and asymptomatic classes Aims to eliminate the user discrepancies between sonographers Analyses US images obtained by a sonographer based on echogenicity, texture and morphology Below are examples of images obtained by sonographers, where the boundary of the sections have been determined by a vascular surgeon to be entered in to the CAD and undergo a series of algorithms. Accuracy, sensitivity and specificity of such study was determined at 82% (1)

+ 3D Ultrasound Evaluate plaque volume, measure shear stress, characterization of plaque motion and 4D color flow (9) Allows clearer visualization of the geometry Superior to 2D imaging in assessment of carotid plaque volume, surface morphology and plaque ulcers (5) Post-process 3D imaging techniques reduces user dependence

+ 4D intra-lumen Imaging Currently marketed by Phillips as ‘Fly Thru’ and referred to as ‘perspective imaging’ as it provided a different perspective similar to CT virtual colonoscopy and appears as an endoscopic procedure The system can either automatically navigate through a structure or the user can conduct a manual navigation Few studies to probe efficiency, particularly in carotid US, and in not widely in use (4)

+ Contrast Enhanced Ultrasound (CEUS) Ultrasound contrast agents (UCAs) are micron-sized, air filled spheres composed of a thin protein shell and readily diffusible. CEUS enhances vessel lumen and provides complete visualization of the carotid artery vasculature, luminal surfaces, near and far intimal thickness, adventitial and intraplaque angiogenesis. Improves artery wall thickness when findings are compared to histology. Particularly useful in assessing vasa vasorum (neovascularization). Vasa vasorum is a strong early predictor of symptomatic atherosclerosis, development of increased intimal thickness, intraplaque hemorrhage and lesion instability (2).

+ References Acharya RU, Faust O, Alvin APC et al, Symptomatic vs. Asymptomatic Plaque Classification in Carotid Ultrasound. J Med Syst 36(3): Coll B, Nambi V and Ferinstein SB, New Advances in Noninvasive Imaging of the Carotid Artery: CIMT, Contrast Enhanced Ultrasound, and Vasa Vasorum. Curr Cardiol Rep; 12: Devuyst G, Ruchat P, Karapanayiotides T et al. Ultrasound Measurement of the Fibrous Cap in Symptomatic and Asymptomatic Athermanous Carotid Plaques. Circulation; 111: Grant EG. Advanced Techniques in 4D Ultrasound: Fly Thru. Toshiba. Heliopoulos J, Vadikolias K and Piperidou C, Detection of carotid artery plaque ulceration using 3- dimension ultrasound. J Neuroimaging; 21(2): Nederkoorn PJ, van der Graaf Y, Hunink M, Duplex Ultrasound and magnetic resonance angiography compared with digital subtraction angiography in carotid artery stenosis: A systematic Review. Stroke; 34: Sidhu PS, Ultrasound of the carotid and vertebral arteries. British Medical Bulletin; 56(2): Suwanwela N, Can U, Furie KL et al, Carotid Doppler Ultrasound criterion for internal carotid artery stenosis based on residual lumen diameter calculated from en bloc carotid endarterectomy specimens. Stroke; 27: Tegeler CH, Ratanakorn D and Kim J, Advances in Carotid Ultrasound. Semin Cerebrovasc Dis Stroke; 5:74-82.