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เอกสำรประกอบกำรบรรยำยวันที่ 16 ห้อง 1 เวลำ 10.30-11.00Carotid Artery Stenosis นำำมำจำกบำงส่วนของบทควำมโดย : Lennard A Nadalo, MD, Clinical Professor, Department of Radiology, University of Texas Southwestern MedicalSchool; Consulting Staff, Envision Imaging of Allen and Radiological Consultants Association บรรยำยโดย รศ. นพ. พิพัฒน์ เชี่ยววิทย์ ภำควิชำรังสีวิทยำ คณะแพทยศำสตร์ศิริรำชพยำบำลBackgroundStroke (brain attack) represents one of the most seriouscauses of mortality and morbidity throughout the world.Each year, 150,000 patients die as a direct result of acerebrovascular accident (CVA), while 600,000 patientsexperience the morbidity of aphasia, blindness, orparalysis. Among patients with stroke, extracranialcarotid disease represents the cause of approximatelyone half of cases. The goals of carotid imaging can bedescribed as early detection, clinical staging, surgicalroad mapping, and postoperative therapeuticsurveillance.Imaging helps in detecting associated conditions early.Coronary artery disease, peripheral arterial stenosis, andhypertension are associated with an increased incidenceof carotid arterial stenosis. Carotid arterial screeningremains controversial. Good evidence supportsevaluation for carotid stenosis prior to coronary arterialbypass surgery.Detection of a carotid bruit is a common physicalexamination finding that may lead to a referral forcarotid duplex sonography. The correlation between a 1

carotid bruit and a hemodynamically important carotidstenosis is reported to be between 10-20%. A cardiacmurmur may be transmitted to the neck. Stiff, calcified,or torturous vessels may generate a bruit in the absenceof stenosisClinical DetailsRisk factors for carotid artery disease are similar to thosefor coronary artery disease, ie, atherosclerosis of themain arteries that carry the oxygen-rich blood to theheart (coronary arteries). Therefore, people with onecondition often also have the other. Risk factors for both(as shown by a coronary risk profile) that can bemodified include smoking, lack of regular exercise,eating a high-fat high-cholesterol diet, obesity (>20%over an individuals ideal weight), uncontrolled diabetes,uncontrolled hypertension, uncontrolled stress andanger, high low-density lipoprotein (bad cholesterol)levels, and low high-density lipoprotein (goodcholesterol) levels.Risk factors that cannot be modified include (1) sex, ie,men are more likely to have a stroke and survive,women are more likely to die as a result of stroke; (2)advanced age, ie, cardiovascular diseases tend to affectolder people more than younger people; and (3)ethnicity, ie, African Americans have a higher risk of highblood pressure than others.TIA is a warning sign of a future stroke. An estimated25% of patients with TIA develop a stroke within thenext 2 years. Symptoms of a TIA include weakness,numbness or tingling on one side of the body, confusion,trouble with speaking, difficulty understanding speech,vertigo, and severe headache. TIAs also may cause avariety of visual symptoms that include partial loss ofvision or complete blindness, double vision, abnormal 2

eye movements, blurred vision, and a gray shading orfogging within the field of vision.Medical treatment for mild to moderate carotid stenosisis most appropriate. Treatment is directed towardreducing the progression of the atherosclerotic diseaseprocess by lowering serum cholesterol levels, controllinghypertension, and by the administration of a medicationsuch as aspirin, which decreases the likelihood of plateletor small clot embolization.Carotid endarterectomy of asymptomatic carotid stenosisis most commonly limited to lesions with a 70% orgreater degree of stenosis. Asymptomatic carotidstenosis may be detected by the auscultation of acervical (neck) bruit or other screening method.Symptomatic carotid stenosis (SCS) is characterized byan associated stroke, TIA, transient monocular (1 eye)blindness, or other objective symptom or sign of anipsilateral cerebral vascular event. Treatment for mostSCS is surgical.More recently, carotid stenosis has been successfullymanaged by means of endovascular carotid stentplacement. The selection of a specific clinical treatmentis based upon the degree of stenosis, the condition ofthe arterial vessels proximal to the carotid stenosis, andthe availability of specific treatment options.Preferred ExaminationA complete medical history should be taken first. On thebasis of risk factors and the family history and currentsymptoms, selecting a screening examination such asduplex carotid sonography, CT angiography (CTA), ormagnetic resonance angiography (MRA) of the carotidartery may be appropriateAfter obtaining the medical history, carotid dupleximaging is performed most commonly in patients withmoderate risk factors. In the authors practice, duplex 3

sonography is the initial triage examination for patientswith an asymptomatic bruit, known asymptomaticcarotid vascular disease, and in patients with a completestroke without prior history of carotid stenosis.In symptomatic patients and in most who present withabnormal carotid sonographic findings, another imagingtest is performed. MRA or CTA offer full depiction of thecervical and cerebral portions of the CCA and ICA. Inmost cases, a diagnostic evaluation for cerebral vasculardisease can be performed by using either MRA or CTA.The immediate availability of CTA in many criticalhospitals on a 24-hour basis makes CTA attractive in thecare of patients who present after hours in theemergency department.In the selection of patients for acute treatment forcerebral ischemia, axial CT images should be reviewedby using the criteria of less than one-third involvementof the middle cerebral distribution or by using theAlberta Stroke Program Early CT Score (ASPECTS). Therole of cervical-cerebral angiography is evolving as lessinvasive alternative tests have become available. Manyexperienced vascular surgeons are more comfortablewith cervical-cerebral catheter angiography than withother studies. In the authors practice, clinicians performcarotid angiography routinely, and cerebral angiographyor digital subtraction angiography (DSA) is reserved forpatients who are likely candidates for surgery or forpatients who may benefit from angiographically basedcarotid intervention.Limitations of TechniquesAlthough carotid duplex imaging offers an excellentmeans of initial evaluation of the extracranial cerebralvessels, the presence of dense calcifications in thecarotid plaque tends to make the study less accurateBecause carotid duplex imaging does not help inassessing the intracranial portion of the carotid artery, 4

tandem lesions of the ICA may be missed. In a similarmanner, proximal stenosis of the innominate artery andthe left carotid artery cannot be evaluated near theorigins from the aortic arch.MRA is contraindicated in patients who have cardiacpacemakers or cerebral aneurysm clips or in those whohave undergone certain other medical procedures. Inaddition, MRA is highly motion sensitive. Many patientsrequire sedation. Because of artifacts related to the MRAimage, the degree of stenosis may be overestimated.CTA requires iodinated contrast agents to be injected ata relatively high flow rate. Patients with renal diseasemay not tolerate intravenous contrast agents. Motionartifacts remain a problem if the examination isperformed by using older CT equipmentCerebral angiography also involves the injection ofiodinated contrast agents. The overall contrast dose issimilar to that required for CTA. The performance ofcatheter-based cervical-cerebral angiography depends onthe skill and experience of the angiographer. Overallmajor morbidity rates are 0.1-1%. Injury may occur inthe form of iatrogenic stroke or bleeding around thecatheter introduction site. Angiograms do not providemuch information concerning the nature of the plaquelesion. Cerebral angiography is the most costly means ofcarotid stenosis evaluation. If cases are selectedcarefully, the overall risk of diagnostic angiographytogether with the morbidity related to carotid surgery isless than the risk of stroke for the untreated patient 5

More detail about modalities for carotid arteryevaluation :- 1. RADIOGRAPHFindingsStandard radiographs may demonstrate calcification inthe carotid vessels in the neck; however, only largecalcified plaques are demonstrated on radiographs. Ingeneral, the information provided by radiographs of theneck or skull is not clinically helpful except to alert theclinical physician that the patient may be at risk forcarotid stenosis.Degree of ConfidenceIn general, calcification in a plaque indicates a chronicdisease pattern. The absence of calcification onradiographs of the neck or lateral aspect of the skulldoes not exclude significant extracranial carotid disease.False Positives/NegativesCalcification in the carotid bulb is not fully correlatedwith significant carotid arterial stenosis. High-gradestenosis of the proximal carotid artery may occur in theabsence of calcifications, and dense carotid calcificationmay be seen in the absence of a high-grade carotidstenosis. 2. CT SCANFindingsAxial CT images of the cerebral circulation provide bothan accurate means of assessing stenosis and carotidplaque. Although early attempts to apply CT in theevaluation of the carotid artery were limited bymovement artifacts and thick scanning sections, current 6

multisection CT scanners allow for the acquisition of thin(eg, 1.0-2.0 mm) axial images within a brief time (asingle breath hold). Intravenous contrast material mustbe injected rapidly enough (3-4 mL/s for a total volumeof 120-150 mL of 300-320 mg/mL nonionic contrastagent) to achieve a contrast density of at least 150 HUor in the innominate and carotid inflow to continuingdistally into the intracranial carotid artery. Imagingbegins just before the contrast density peaks in thecarotid artery.Initially, all images should be reviewed in the axial plane.Multiplanar and curved multiplanar reformatted imagesare often helpful. The intraluminal diameter should bemeasured by using an electronic workstation withelectronic calipers. If the image of the carotid artery isenlarged before measurement, error is reduced.Measurements are made across the lumen through thenarrowest portion of the proximal ICA and across thearea of the ICA that is above the stenosis and is believedto be normal. The degree of stenosis is calculatedaccording to criteria developed by the North AmericanSymptomatic Carotid Endarterectomy Trial (NASCET) andis reported as a percentage of stenosis.Carotid ulcerationAnother mechanism related to cerebral infarction isembolization from the heart or great vessels. Except toacknowledge the need to evaluate some patients afterMI by using echocardiography, the heart as a source ofcerebral emboli is beyond the scope of consideration forthis article. The carotid arteries may be a source ofcerebral emboli via release of the contents of the plaque,via turbulence or clot formation on the ulcerated surface.Carotid ulcers are best demonstrated by using the higherresolution of catheter angiography; however, the use ofmultisection CTA increases the likelihood of carotid ulceridentification. Larger deeper ulcers are successfullydepicted with most CTA techniques .Carotid plaque 7

Dense calcifications in the carotid artery limit theaccuracy of measurements of the degree of stenosisacross the plaque if maximum intensity projection (MIP)or shaded-surface display imaging is used. After firstattempting to measure the degree of stenosis by usingaxial images, curved multiplanar reformatted imagesobtained through the lumen help show the stenosis.Certain workstation techniques can be applied that canimage reverse the pixels above 300 HU. Image inversionsubtracts calcified plaque from the image, which tends toresult in a clearer image of the contrast agent–filledcarotid lumen. Occasionally, contrast may be seenentering the subintimal area of the plaque. Complex anddissected carotid plaques may be detected in thismanner.Carotid thrombosisCare must be exercised in cases of carotid thrombosis.Very slow flow rates may be missed if the timing of theintravenous contrast agent bolus or the peak density ofthe contrast material is less than optimal. Comparison of3-dimensional (3D) volume images should always bemade to axial images . The intracranial collateralizationpattern helps make the diagnosis of thrombosis andoffers important clinical information.Tumors of the cervical region may surround the CCA orthe ICAs. One of the advantages of cross-sectionalimaging, such as CTA, is the identification of the tissuesthat surround the carotid and vertebral arteries.Degree of ConfidenceCarotid CTA represents a reliable means of estimatingthe degree of stenosis in both extracranial andintracranial vessels. Limitations in the degree of 8

confidence are related to technical factors. Currentmultisection CT scanners allow for the acquisition of upto 16 sections for each gantry rotation. Each rotationmay require as little as 0.4 seconds. Axial collimation forcervical-cerebral CTA is performed by using a collimationof 0.75 mm with a reconstruction of 1.5 mm for eachaxial image.Axial images, multiplanar reformatted images, and 3Dvolume MIP and volume-model images contribute to thesensitivity and accuracy of multisection CTA. By usingavailable multisection CT scanners, extracranial carotidstenosis can be diagnosed to a degree of accuracy equalto or exceeding that of catheter-based angiography. CToffers an excellent means of detecting a tumor thatmight surround the carotid artery in the neck.When the carotid artery is imaged by using CTA, artifactsinclude motion, poor cardiac function, and dense carotidcalcification. Overall accuracy for carotid CTA exceeds95%. Intracranial CTA with a multisection scannerreportedly helps in identifying intracranial carotidstenosis with a sensitivity of greater than 98%, aspecificity of 99%, and an accuracy of greater than 98%.Multisection CT scanners have been introduced thatacquire 8 scans with each gantry rotation. With thisnewest technology, CTA represents the best overallmeans with which to investigate carotid stenosis in a lessinvasive and more cost-effective manner.False Positives/NegativesFalse-positive results of carotid CTA are related tomotion artifacts. Sudden movement, breathing, orswallowing by the patient during scanning may result ina misregistration of the axial images on 3D ormultiplanar reformatted images. In such cases, onlymeasurements taken from the axial images should beconsidered. 9

False-negative results may occur if the vessels of thecarotid bulb are very dilated and torturous.Superimposed jugular veins and arteries may hide astenosis. A careful review of axial images, together withcarefully performed curved multiplanar reformattedimages through the carotid lumen, demonstrate thestenotic area in most patients. 3. MRIFindingsMRA usually is performed by using 2 primary methods,ie, time-of-flight and ultrashort T1-weighted imaging.Time-of-flight imaging is performed without intravenouscontrast agent by using a spoiled gradient-echosequence. The images are displayed with a MIP protocolin multiple projections. Contrast-enhanced MRA isperformed by using a timed and rapid injection of agadolinium-based contrast, such as gadoliniumdimeglumine. Because the volume of contrast agent islimited to 15-20 mL in most cases, timing of the contrastagent bolus and good venous access are essential. Theimages are obtained by using a short recovery time (TR),short echo time (TE), and T1-weighted technique(TR/TE/flip angle, 4.9/2.4/35°). The images aredisplayed in multiple projections by using an MIPtechnique.A 3D time-of-flight image of the carotid artery or acontrast-enhanced short-TE short-TR image isinterpreted in much the same manner as CTAs or carotidangiograms of the same area. The stenotic area of theICA should be evaluated according to the NASCETcriteria. Because of the effects of turbulence, 3D time-of-flight imaging tends to cause overestimation of high-grade stenoses. In some cases, an area of discontinuitymay be generated in the area of the stenosis. Thisresults from turbulent blood flow patterns at the point ofa high-grade stenosis and within very stenotic longerstenoses.The results of contrast-enhanced MRA are closelycorrelated with angiographic and operative findings. 10

Gadolinium-based contrast agent has the effect ofshortening the T1 qualities of the blood flowing throughthe stenosis. Residual lumen is displayed with high signalintensity. High-grade stenosis tends to remain anattenuated but visible lumen. Results of contrast-enhanced MRA are usually better than those of 3D time-of-flight imaging.Recent advances in contrast-enhanced MRA allow forimproved imaging speed without the need for temporalinterpolation. Time-resolved contrast-enhanced carotidMRA with a sensitivity-encoding (SENSE) reconstructiontechnique enables visualization of the carotid arterywithout superimposed venous structures.The early identification of stroke in the vasculardistribution of a related carotid stenosis helps in focusingon an ipsilateral carotid lesion. T1-weighted diffusion-based imaging effectively depicts focal cerebral ischemia,and the finding is often correlated with a proximalcarotid stenosis. In other cases, intracranial MRAdemonstrates no flow pattern, confirming carotidthrombosis.Gadolinium-based contrast agents (gadopentetatedimeglumine [Magnevist], gadobenate dimeglumine[MultiHance], gadodiamide [Omniscan],gadoversetamide [OptiMARK], gadoteridol [ProHance])have recently been linked to the development ofnephrogenic systemic fibrosis (NSF) or nephrogenicfibrosing dermopathy (NFD). For more information, seethe eMedicine topic Nephrogenic Fibrosing Dermopathy.The disease has occurred in patients with moderate toend-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans.As of late December 2006, the FDA had received reportsof 90 such cases of NSF/NFD . Worldwide, over 200cases have been reported, according to the FDA.NSF/NFD is a debilitating and sometimes fatal disease.Characteristics include red or dark patches on the skin;burning, itching, swelling, hardening, and tightening ofthe skin; yellow spots on the whites of the eyes; jointstiffness with trouble moving or straightening the arms, 11

hands, legs, or feet; pain deep in the hip bones or ribs;and muscle weakness. For more information, see theFDA Public Health Advisory or Medscape.Degree of ConfidenceBoth systematic and random errors affect the results ofcerebrovascular MRA. Systematic errors are primarily theresult of artifacts and are related to 3D time-of-flightimaging. Areas within the carotid artery that generateturbulence may develop a recirculating pattern of bloodflow. In the returning blood flow, the lumen is recordedas artifactually narrowed. Short-segment occlusions maybe suggested in patients with very high-grade stenosis(>85% stenosis). Time-of-flight MRA results should bereported in a manner similar to those of carotid duplexsonography. Although measurements obtained by usingthe NASCET criteria should be attempted, thesignificance of the recorded stenosis should be reportedwith caution.Random errors may occur when measurements of theinternal lumen are made mechanically. Measuring fromenlarged images reduces the relative degree of randomerror. MRA results obtained by using a very short-TR,short-TE, gadolinium-enhanced, timed bolus techniquecan be interpreted in much the same manner as those ofcarotid angiography and CTA. Intracranial MRA has asensitivity of 92-95%, a specificity of 91%, and anoverall accuracy of 91% in the detection of intracranialcarotid stenosis.False Positives/NegativesCertain variations of the CCA may be difficult to interpretby using MRA findings. Narrow bands of intimalthickening may result in a high degree of stenosis;however, the central luminal narrowing is difficult todemonstrate on MRA examination. The proximal ICAmay become folded or kinked. Such a kink generatesturbulence just beyond the fold. A short-segmentpseudo-occlusion may be seen on a time-of-flight study.The ectatic appearance of fibromuscular hyperplasia may 12

be difficult to resolve by using time-of-flight imagingalone.The spasm of migraine can simulate carotid dissectionon MRA studies performed during an acute migraineevent. Assessment of the proximal carotid artery near itsorigin from the aortic arch requires a good contrastbolus, breath-holding and, in general, good cooperationon the part of the patient.False-negative carotid MRA results are primarily theresult of limitations of resolution. Small surface ulcersmay not be resolved on MRA images. At other times,deeper ulcers may contain blood clots, which reduce theapparent size of some ulcers.4. ULTRASOUNDFindingsB-mode ultrasonographyThe earliest manifestation of carotid vascular disease ischaracterized by increased arterial intimal-medialthickness. The normal range for combined intimal-medialthickness of the CCA has been reported to vary with age,up to a maximum thickness of 0.8 mm. Incrementalincreased thickening of the carotid intima is associatedwith increased risk of cerebral ischemic events, coronaryischemia, and first-time MI. Treatment with lipid-lowering drugs has been shown to decrease the intimal 13

thickness of the carotid artery. Decrease in the thicknessof the intima of the CCA has been correlated directlywith successful treatment with drugs that lower serumlow-density lipoprotein levels.The sonographic characteristics of symptomatic andasymptomatic carotid plaques are different. Symptomaticplaques are more likely to be hypoechoic and highlystenotic while asymptomatic plaques are hyperechoicand moderately stenotic. Evaluation of the surface of theplaque has not been demonstrated to be a satisfactoryindex of plaque instability.After carotid endarterectomy, intimal thickness varies inthe surgical site. The thickness of the neointima hasbeen correlated with carotid wall stiffness and restenosisafter carotid surgery. Comparison of current carotidsonographic velocities to those obtained before carotidendarterectomy is important. In general, the velocity offlow should become reduced with successful surgery.However, velocities may remain elevated after surgerydue to scar formation, which results in carotid wallstiffness. Restenosis may occur as a result of surgery orgeneralized atherosclerotic vascular disease.Doppler ultrasonographyDoppler ultrasonography is the primary noninvasive testfor evaluating carotid stenosis. Primary examination ofthe carotid plaque is somewhat subjective because termssuch as soft plaque or irregular surface are often used todescribe the primary sonographic images. The degree ofstenosis is better measured on the basis of thewaveform and spectral analysis of the CCA and its majorbranches, especially the ICA.As an example, consider the following case history. A 70-year-old man presented with a suspected stroke.Symptoms included right-sided hemiparesis anddysphasia. Duplex ultrasound findings revealed asignificant stenosis of the proximal left ICA . The imageshowed mostly soft echogenic plaque protruding fromthe posterior aspect of the bulb and origin of the ICA. Afairly narrow residual lumen remained. Spectral Doppler 14

imaging confirmed the high-grade stenosis, with peaksystolic velocity of 325 cm/s and diastolic velocity of 105cm/s. In the authors laboratory, a diastolic cutoff of90cm/s is used to distinguish 60-79% from 80-99%lesions in patients such as this man.Note the blunted flow in the distal ICA compatible withthe high-grade proximal obstruction. The CCA showsnarrowing of approximately 40%. The opposite ICA wasonly mildly narrowed and demonstrated normal findingson spectral Doppler examination. The patient underwentcarotid angiography. Angiographic findings helpedconfirm an 80% ICA stenosis. The patient was eventuallytreated with carotid endarterectomy. Follow-up studiesin the authors laboratory (not shown) demonstrated afully patent ICA. Some residual hemiparesis hasremained on the right side, but the patient is muchimproved from his status after the initial stroke.Many published lists exist of carotid flow velocities,which are associated with a graduated degree ofstenosis. A listing of flow velocity/carotid stenosis criteriaused in the authors department is shown in the Tablebelow.Carotid Stenosis Criteria Peak SystolicSteno Velocity (cm/ Peak End Peak Systolicsis Diastolic s) Velocity (cm/s) Velocity Ratio <50 <150 <50 <2.0 50-59 150-200 50-70 2.0-2.5 60-69 200-250 50-70 2.5-3.0 70-79 250-325 70-90 3.0-3.5 80-89 325-400 70-100 3.5-4.0 90-99 >400 >100 >4.0Occlusi Not applicable Not applicable Not applicableon 15

Doppler ultrasonographic findings associated withstenosis include the following: • Ipsilateral CCA-to-ICA flow ratios may not be valid in the setting of contralateral ICA occlusion. • CCA waveforms may have a high-resistance configuration in ipsilateral ICA lesions. • ICA waveforms may have a high-resistance configuration in ipsilateral distal ICA lesions. • ICA waveforms may be dampened in ipsilateral CCA lesions. • Long-segment ICA stenosis may not have high end- diastolic velocity. • Velocities supersede imaging in grading stenosis. • Imaging can be used to downgrade stenosis in the setting of turbulence caused by kinking.In addition to the typical evaluation of the flow rate inthe proximal ICA, it has been shown that the flowdirectly within the ophthalmic artery is highly specific forsevere carotid stenosis.Transcranial Doppler ultrasonographyTranscranial Doppler imaging is both sensitive andspecific in the detection of intracranial ICA stenosis thatis hemodynamically significant. By using a mean flowvelocity of 100 cm/s, transcranial Doppler images help inidentifying most intracranial stenotic lesions, with goodspecificity.Degree of ConfidenceThe success of duplex sonography depends on carefultechnique. Results vary somewhat among laboratories.The authors practice has chosen to base its results on acomposite mix of the published results comparing thedegree of proven stenosis versus flow velocity and ICA-to-CCA velocity ratios. Results should be reported in thecontext of established criteria as a percentage ofstenosis. The Table, above, represents the criteria used 16

in the authors practice. The results should be confirmedwith carotid CTA or carotid MRA before surgery.Discovery of a reversed direction of flow in theophthalmic artery is closely associated with high-gradeipsilateral ICA stenosis, with a sensitivity of 55%, aspecificity of 100%, a negative predictive value of 82%,and a positive predictive value of 100%.Transcranial duplex sonography with a threshold of 100cm/s helps in identifying hemodynamically significantlesions, with a sensitivity of 93.9% and a specificity of91.2%.False Positives/NegativesUse of duplex sonography is not valid in the setting ofcontralateral ICA occlusion. CCA waveforms may have ahigh-resistance configuration with ipsilateral ICA lesions.ICA waveforms may have a high-resistance configurationwith ipsilateral distal ICA lesions. ICA waveforms may bedampened with ipsilateral CCA lesions. Long-segmentICA stenosis may not have high end-diastolic velocity.Velocities supersede imaging in grading stenosis.Imaging can be used to downgrade stenosis in thesetting of turbulence caused by kinking.After carotid surgery, recorded flow velocities may beelevated more than those recorded during preoperativeexaminations. Comparison of the results of the currentexamination to those of a prior study is essential. 5. NUCLEAR MEDICINEFindingsSingle photon emission CT (SPECT) and positronemission tomography (PET) of the brain maydemonstrate areas of cerebral ischemia versus areas ofcomplete cerebral infarction. However, these studiesprovide only indirect imaging information related tocarotid stenosis. By using a dynamic imaging method, anassessment of the inflow of technetium Tc 99m 17

hexamethylpropylamine oxime (HMPAO) can be used toestimate the hemispheric cerebral blood flow. If such anassay is combined with a provocative challenge withacetazolamide, it is possible to differentiate patients withmigraine from patients with an irreversible cerebralischemia.Degree of ConfidenceSPECT and PET of the brain both demonstrate cerebralinfarction, which may indicate a related carotid stenosis.An acetazolamide challenge can successfully differentiatecertain subclasses of cerebral ischemic syndromes, butall such studies provide indirect evidence of carotidstenosis.False Positives/NegativesFalse-positive results may occur as a result of confusionin the findings between an infarct of the brain and a low-grade brain neoplasm or abscess. In the evaluation ofstroke, false-negative findings may occur in small areasof infarction, which may be below the resolution of anuclear examination. Comparison with other studies(such as CT or MRI), which have higher resolution, isrecommended. 6. ANGIOGRAPHYFindingsCarotid angiography via a catheter injection of contrastagent is considered the standard of diagnostic imagingof the cervical and intracranial carotid arteries againstwhich other techniques are often judged . The NASCETstudy was based on images created during catheterangiography. The diameters of stenosis can be measureddirectly. Luminal diameter ratios can be expressed. Allcontrast-enhanced angiographic studies depend on theradiographic density of iodinated contrast agentcompared with normal blood and the density of the wallof the carotid artery . Lesions may be smooth, irregular,or focal, or they may involve a long segment . 18

Angiographic techniqueIn the authors institution, all cervical-cerebralangiography is performed by using the Seldingertechnique. The procedure initially involves entering thelumen of the artery of access with a needle. The femoralartery is used as access in most cases, while the axillaryarteries may be entered as an alternative. A heparin-coated guide wire is passed through the hub of theneedle into the lumen of the artery. Often a J-shapedguide wire is used initially to avoid intimal trauma. A 4Fpigtail catheter is generally introduced over theguidewire into the ascending aortic arch. Nonioniccontrast (320 mg/mL of organically bound iodine) isinjected at a rate of 20-25 mL for a total volume of40-50 mL. The left anterior oblique projection is mostcommon. If imaging is performed by using a digitallysubtracted technique, less contrast material is needed.After the shape, smoothness, and patency of theproximal right CCA, the right subclavian artery, the leftCCA, and the left subclavian artery are inspected, acatheter is selected to assist in the selectivecatheterization of the right CCA, the left CCA, and eitheror both of the vertebral arteries. A 0.035-in guidewirewith a soft, straight tip is used to exchange the pigtailcatheter for either a simple angle-tip catheter (eg, onewith an HN1 shape) or one with a more complex hook orshort-radius, curved shape.The guidewire chosen for the exchange may have avariable degree of flexibility in the distal severalcentimeters near the tip. With the guidewire leading intothe proximal right and left CCA origins, the cerebral-shaped catheter is positioned in the CCAs below thecarotid bulb. Vertebral injections are performed with thecatheter in the vertebral artery near the origin of thevertebral artery to avoid spasm. After a small testinjection is disinterred to verify the location and securityof the catheter tip position, each of the carotid arterialcirculations is studied. Images in a 30° ipsilateral leftanterior oblique or right anterior oblique projection areobtained to clearly outline the carotid bifurcations. In 19

some cases, the lateral and the anterior projections areneeded.DSA performed by using a C-arm imager permits anoptimal degree of rotation based on the patientsanatomic form. Imaging should include the intracranialcarotid circulation in most cases. Selectivecatheterization of 1 or both vertebral arteries should beperformed if clinically indicated in patients with vertebralbasilar symptoms.Each injection of contrast agent into the CCA is given ata rate of 6-7 mL/s for a total volume of 10-12 mLdepending on the estimated flow rate in the CCA.Selective vertebral artery angiography is generallyperformed by using an injection rate of 4-5 mL/s for atotal volume of 6-8 mL. Somewhat less contrast agent isneeded if DSA imaging techniques are applied.The degree to which intracranial arteries beyond theICA-MCA trifurcation must be studied should be basedon an understanding of the patients clinical presentationand symptoms. Collateral circulation is best understoodby having full visualization of the intracranial circulationas well as the aortic arch and cervical carotidcirculations.Measurements and other findingsThe most common method used to expressmeasurements of the carotid artery is the NASCETcriteria, which state that a percentage of stenosis isexpressed as a factor of 100, ie, the diameter of thenormal ICA located above the carotid bulb divided by thediameter of the proximal ICA at the narrowest point .Special consideration must be given for critical degreesof stenosis, often termed the string sign The presence ofcontrast agent in a markedly restricted lumen may be anindication of a critical proximal focal stenosis or longersegmental narrowing. Depiction of residual intracranialarterial flow helps establish patency.Other findings noted on carotid angiography includecalcification, ulceration, fibromuscular hyperplasia, 20

carotid kinking or folding, focal thrombus formation , andintimal dissection. The plaque may become complicatedby marked intimal thickening or subintimal hemorrhage .After a carotid thrombosis form, extensivecollateralization patterns may be demonstrated , orpartial recanalization may occur, resulting in a complexpattern of alternating narrowing and dilatation .Degree of ConfidenceFindings on catheter-contrast angiography of the carotidartery are accurate if measurements and calculation ofthe degree of stenosis are made carefully by using anenlarged image. Both systematic and random errors mayoccur during stenosis measurement. The calculation ofthe degree of stenosis should be based on the NASCETcriteria if possible. Catheter-based angiographic studiesremain the most accurate means of assessment of thedegree of carotid stenosis.False Positives/NegativesFalse-positive examinations may occur if injection of thecontrast agent is not timed properly, resulting in awashed-out appearance on the image. If subtractedimages are developed, overlying metal or densecalcifications result in shadowing of some of the plaque-artery lumen, making an accurate measurement of theresidual lumen difficult. Movement, coughing, and thepresence of metal artifacts may prevent an accurateexamination. Rapid injection may cause a standing waveto form, which may appear similar to fibromuscularhyperplasia.False-negative results may occur if a nonselectiveangiographic technique is used . Superimposition ofother arterial and venous structures may preventadequate depiction or measurement of the stenosis.Despite technical limitations, catheter-based angiographyremains the criterion standard against which otherimaging techniques are compared. 21

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