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Clinical Portfolio-Carotid UltrasoundThere are numerous reasons why a patient may present to the imaging department for a carotid ultrasound. These include but are not limited to; recent T.I.A, progression of a known stenosis, post endartarectomy assessment, family history and query dissection. Our role as a sonographer is to assess for the presence, extent, location and degree of stenosis along with any other pathology that we may detect. While there is still some debate regarding the accuracy of sonography, the morphology of the plaque detected should be assessed with attention made to calcification and evidence of ulcer formation (1). Once it has been confirmed that it is the appropriate patient through full name and date of birth being checked with the patient then I introduce myself to the patient and show them to the ultrasound room. The procedure is then explained to the patient and once verbal consent is obtained the patient is asked to lie supine with their neck exposed, chin extended and turned to the side opposite to that being examined. A towel is then tucked under the edge of their clothing to keep the warmed gel of their clothing. On the Phillips iu22 the L9-3 and L12-5 probes are used, depending upon patient body habitus, on the carotid preset.The carotid artery is initially surveyed in the transverse plane from the origin through the bulb and the visible extent of the internal and external carotid arteries. The initial survey allows us to assess the patient’s individual anatomy and gives us an impression of the disease extent. During the initial survey note is also made for any Sonographic evidence of lymphadenopathy, carotid dissection, thyroid lesion and sub-mandibular gland mass. If any of these are noted then appropriate images are obtained to document the pathology. In the case of carotid dissection/aneurysm, jugular thrombosis or suspicious neck mass the radiologist would be informed so as appropriate clinical management can be arranged.As per department protocol grey scale images are obtained in the longitudinal plane. Diagram one indicates the approximate levels at which images are recorded.Diagram 1Triplex images are then obtained at the above levels with additional images recorded along the course of the I.C.A./Vertebral, subclavian and innominate artery if we are examining the right side of the neck. With velocity scale and color gain set so as to accurately represent arterial flow without bleeding into the adjacent carotid sheath. See figure 2.Image 1 Image 2Image 3 Image 4Figure 2Image 5 Image 6Image 7 Image 8Color assessment is then performed in the transverse plane from the carotid origin extending distally as far as technically possible.This is done so as to assess for the presence of plaque which can be almost isoechoic with blood (2). Some manufactures have had an option called B-Flow which when selected allows for visualization of blood flow. This option may also be of benefit in detecting very soft plaque.Any areas of stenosis identified are imaged in the transverse plane with color Doppler on and the degree of stenosis documented. The degree of stenosis is assessed based on velocity profile changes and percentage diameter reduction changes. It is the protocol in my department to characterize less than 50% stenosis by percentage diameter reduction given the minimal velocity changes. While greater than 50% diameter reduction is estimated based on velocity profile changes. With attention paid to systolic and diastolic velocities, ratio changes in velocities, spectral broadening and the charasteric sound of a high grade stenosis. Velocity based estimation of stenotic severity is based on NASCET criteria (3).While sonography has been shown to have similar sensitivity and specificity, in experienced hands, to other imaging modalities in assessing carotid artery stenosis (4). The limitations inherent to sonography in assessing heavily calcified and technically difficult patients’ needs to be recognized and quantified in the sonographers report when appropriate. While typically the external carotid artery is smaller, more anterior and lateral relative to the internal carotid artery the appropriate designation of internal and external carotid artery needs to be confirmed. This is done through identification of an arterial branch (superior thyroid) originating from the E.C.A, sound, waveform profile and temporal “tapping” of the E.C.A. While it is acknowledged that waveform, sound and temporal tapping (as the I.C.A waveform can be affected by tapping as well although not to the same extent as the E.C.A) are not definitive ways to differentiate E.C.A and I.C.A they certainly assist us. Assessment of the ophthalmic artery can also be of benefit due to the decrease in P.S.V and even reversed flow being present in this vessel in the presence of significant I.C.A stenosis/occlusion (4).Figure 3 Figure 4Images nine and ten demonstrate the superior thyroid originating from the E.C.A and temporal tapping of the E.C.A.Image 9 Image 10Images eleven and twelve depict a transverse view of an artery with no plaque compared with a vessel containing atheromatus change.Image 11 Image 12When assessing carotid arteries for disease presence and severity it is important that the grey scale, color and pulse wave information are all consistent with each other. If this is not the case the examination is not complete until the discrepancies are resolved. In this case the Doppler waveforms obtained in the I.C.A are consistent with the grey scale images and percentage diameter reduction noted in image 12. That is the pulse wave Doppler image five depicting a clean acoustic window with no spectral broadening and a normal peak systolic velocity are all consistent with a less than 50% stenosis.Plaque morphology is essentially homogenous with no Sonographic evidence of calcification or ulcer formation.It should be noted that while in many cases carotid sonography is not an emergency examination if a high grade stenosis, in our department greater than 90%, is noted then the radiologist should be informed so appropriate medical/surgical intervention can be arranged.Image critique indicates that the pulse wave gain was too high on image seven resulting in more pronounced spectral broadening than was real. This is especially relevant in carotid Doppler assessment as spectral broadening can indicate stenosis. It may also just mean that the vessel was quite deep and Doppler gain had to be increased in order to obtain any reading. Also the Doppler scale for image seven was too high which may result in low flow not being displayed.References1/ Acharya UR, Sree SV, Krishnan MM, Molinari F, Saba L, Ho SY, Ahuja AT, Ho SC, Nicolaides A; Atherosclerotic risk stratification strategy for carotid arteries using texture-based features: J Ultrasound Med Biol. 2012 Jun;38(6):899-915.S.2/ Ultrasonic Characterization of Carotid Plaques Andrew N. Nicolaides, Maura Griffin, Stavros K. Kakkos, George Geroulakos, Efthyvoulos Kyriacou, Niki Georgiou; Noninvasive Cerebrovascular Diagnosis: 2010, pp 97-118.3/ Overview of the Principal Results and Secondary Analyses from the European and North American Randomised Trials ofEndarterectomy for Symptomatic Carotid Stenosis; A. R. Naylor, P. M. Rothwell and P. R. F. Bell: Eur J Vasc Endovasc Surg 26, 115-129 (2003).4/ The importance of ophthalmic artery hemodynamics in patients with atheromatous carotid artery disease; Drakou AA, Koutsiaris AG, Tachmitzi SV, Roussas N, Tsironi E, Giannoukas AD: Int Angiol. 2011 Dec;30(6):547-54. Review. ................
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