Carotid Imaging. Dr Andrew Farrall. Consultant Neuroradiologist

Transcription

1 SSCA Andrew Farrall Carotid Imaging Dr Andrew Farrall Consultant Neuroradiologist SFC Brain Imaging Research Centre ( SINAPSE Collaboration ( Division of Clinical Neurosciences, Western General Hospital & The University of Edinburgh, Edinburgh EH4 2XU UK SINAPSE

2 Outline Why image? National guidelines NASCET & ECST Digital Subtraction Angiography (DSA) Carotid Doppler Ultrasound Magnetic Resonance Angiography (MRA) Computed Tomographic Angiography (CTA) Data collection

3 Carotid imaging Targeted primarily at minor stroke & TIA patients why?

4 Minor stroke or TIA After minor stroke or TIA there is a cumulative risk for severe, disabling stroke: % risk of stroke Minor stroke 15 TIA Days after initial event Coull et al. BMJ 2004(Feb). OXVASC Study

5 Minor stroke or TIA Within the first 2 weeks, most patients who are going to have a severe, disabling stroke will have it: % risk of stroke Minor stroke 15 13% TIA 10 8% weeks Days after initial event Coull et al. BMJ 2004(Feb). OXVASC Study

6 Minor stroke or TIA Within the first 2 weeks, most patients who are going to have a severe, disabling stroke will have it: % risk of stroke Minor stroke 15 13% TIA % 0 2 weeks Coull et al. BMJ 2004(Feb). OXVASC Study All patients with carotid stenosis > 70% NASCET (> 80% ECST) benefit from carotid endarterectomy i.e. risk of surgery is lower than the risk of having a severe, disabling stroke Days after initial event

7 Carotid Imaging National Guidelines Minor stroke & TIA patients All get medical therapy National Guidelines for Stroke 2 nd ed. 2004(July)

8 Carotid Imaging National Guidelines Minor stroke & TIA patients All get medical therapy If carotid territory & If disability not severe National Guidelines for Stroke 2 nd ed. 2004(July)

9 Carotid Imaging National Guidelines Minor stroke & TIA patients All get medical therapy If carotid territory & If disability not severe Consider endarterectomy All patients with carotid stenosis > 70% NASCET Selected patients with carotid stenosis > 50% NASCET National Guidelines for Stroke 2 nd ed. 2004(July)

10 Carotid Imaging National Guidelines Minor stroke & TIA patients All get medical therapy If carotid territory & If disability not severe Consider endarterectomy All patients with carotid stenosis > 70% NASCET Selected patients with carotid stenosis > 50% NASCET Only by a specialist surgeon Centres must routinely audit outcomes National Guidelines for Stroke 2 nd ed. 2004(July)

11 Carotid Imaging National Guidelines Minor stroke & TIA patients All get medical therapy If carotid territory & If disability not severe Consider endarterectomy All patients with carotid stenosis > 70% NASCET Selected patients with carotid stenosis > 50% NASCET Only by a specialist surgeon Centres must routinely audit outcomes Minor stroke: as soon as the patient is surgically fit TIA patients: < 2 weeks from the TIA National Guidelines for Stroke 2 nd ed. 2004(July)

12 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) 1 Angiography was used to determine stenosis 1. N Engl J Med. 1991;325:

13 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) 1 Angiography was used to determine stenosis 1. N Engl J Med. 1991;325:

14 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) 1 Angiography was used to determine stenosis Cannot see vessel walls 1. N Engl J Med. 1991;325:

15 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) 1 Angiography was used to determine stenosis Cannot see vessel walls 1. N Engl J Med. 1991;325:

16 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) 1 a ICA NASCET: (a s) / a ECA s Angiography was used to determine stenosis Cannot see vessel walls Compare stenotic diameter (s) to the next most normal arterial segment distally (a) CCA 1. N Engl J Med. 1991;325:

17 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) 1 a ICA NASCET: (a s) / a ECA CCA s Angiography was used to determine stenosis Cannot see vessel walls Compare stenotic diameter (s) to the next most normal arterial segment distally (a) Problems: Post stenotic collapse decreases a & therefore increases the stenosis measurement artificially May not be able to find next most normal level With Doppler, a may be out of visual range i.e. above the mandibular angle 1. N Engl J Med. 1991;325:

18 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) ECST (European Carotid Surgery Trial) 2 ECST: Angiography also used to determine stenosis 2. Lancet :

19 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) ECST (European Carotid Surgery Trial) 2 ECST: Angiography also used to determine stenosis Cannot see vessel walls; best estimate given 2. Lancet :

20 NASCET & ECST NASCET (North American Symptomatic Carotid Endarterectomy Trial) ECST (European Carotid Surgery Trial) 2 a ICA NASCET: (a s) / a s ECA b CCA ECST: (b s) / b Angiography also used to determine stenosis Cannot see vessel walls; best estimate given for b Problem: Estimation of where original vessel walls are Over estimation = stenosis appears tighter Under estimation = stenosis appears lower 2. Lancet :

21 NASCET versus ECST 3. Stroke :

22 NASCET versus ECST 80% ECST 70% NASCET 3. Stroke :

23 NASCET versus ECST 80% ECST 70% NASCET 3. Stroke :

24 NASCET versus ECST 80% ECST 70% NASCET 3. Stroke :

25 NASCET versus ECST ECST(%) = 0.6 x NASCET(%) + 40% 4. Eur J Vasc Endovasc Surg

26 Carotid Imaging National Guidelines NASCET (North American Symptomatic Carotid Endarterectomy Trial) ECST (European Carotid Surgery Trial) Severe stenosis i.e. ECST > 80% = NASCET > 70% Surgery reduced the relative risk of disabling stroke or death by 48% (95% CI 27-73%). Number needed to treat (NNT) to prevent one disabling stroke or death over 2 to 6 years follow-up was 15 (95% CI 10-31) Cina CS et al. Cochrane Review, Carotid endarterectomy for symptomatic carotid stenosis, 1999(March)

27 Carotid Imaging National Guidelines NASCET (North American Symptomatic Carotid Endarterectomy Trial) ECST (European Carotid Surgery Trial) Severe stenosis i.e. ECST > 80% = NASCET > 70% Surgery reduced the relative risk of disabling stroke or death by 48% (95% CI 27-73%). Number needed to treat (NNT) to prevent one disabling stroke or death over 2 to 6 years follow-up was 15 (95% CI 10-31) Less severe stenosis i.e. ECST 70 79% = NASCET 50-69% Relative risk reduction: 27% (95% CI 15-44%) Number needed to treat: 21 (95% CI ) Cina CS et al. Cochrane Review, Carotid endarterectomy for symptomatic carotid stenosis, 1999(March)

28 Carotid Imaging National Guidelines NASCET (North American Symptomatic Carotid Endarterectomy Trial) ECST (European Carotid Surgery Trial) Severe stenosis i.e. ECST > 80% = NASCET > 70% Surgery reduced the relative risk of disabling stroke or death by 48% (95% CI 27-73%). Number needed to treat (NNT) to prevent one disabling stroke or death over 2 to 6 years follow-up was 15 (95% CI 10-31) Less severe stenosis i.e. ECST 70 79% = NASCET 50-69% Relative risk reduction: 27% (95% CI 15-44%) Number needed to treat: 21 (95% CI ) Lesser degrees of stenosis: surgery caused harm Increased risk of disabling stroke or death: 20% (95% CI 0-44%) NNT to cause one disabling stroke or death: 45 (95% CI 22- ) 8 Cina CS et al. Cochrane Review, Carotid endarterectomy for symptomatic carotid stenosis, 1999(March)

29 Angiography versus ultrasound For both NASCET & ECST, gold standard was angiography Best measurement is based on 2D projection (i.e. may never have actually seen the tightest stenosis profile) Requires invasive injection of contrast material into femoral artery Radiation; sedation; anaesthetic Expensive (equipment including angiography suite, recovery suite; personnel nurse, radiographer, radiologist, Ultrasound introduced because it s non-invasive & rapid; Doppler became widely available shortly after 1991 Scope for identifying plaque, the vessel wall & stenosis visualisation is very different from angiography Can measure flow velocities (tighter stenosis = faster flow) which relate better to the 3D degree of stenosis Difficult to relate FLOW data back to NASCET / ECST measures

30 Doppler ultrasound 5. Radiographics :

31 Relating Doppler output to stenosis Joint Recommendations for Reporting Carotid Ultrasound Investigations in the United Kingdom 4 (a)peak systolic velocity in the internal carotid artery (ICAPSV); (b)peak Systolic Velocity Ratio (PSVR); and (c)peak systolic ICA to end-diastolic CCA ratio graded in deciles *Diagnostic confidence is gained where two or more of the measures are in agreement. 4. Eur J Vasc Endovasc Surg

32 Reporting Doppler ultrasound Joint Recommendations for Reporting Carotid Ultrasound Investigations in the United Kingdom 4 Tendency to report a 10% range of stenosis when > 50% NASCET Tendency may be to report > 70% NASCET or significant or 50%-69% 4. Eur J Vasc Endovasc Surg

33 Uncertainty in Doppler ultrasound Joint Recommendations for Reporting Carotid Ultrasound Investigations in the United Kingdom 4 (a)peak systolic velocity in the internal carotid artery (ICAPSV); (b)peak Systolic Velocity Ratio (PSVR); and (c)peak systolic ICA to end-diastolic CCA ratio graded in deciles *Diagnostic confidence is gained where two or more measures are in agreement. 4. Eur J Vasc Endovasc Surg

34 Doppler carotid assessment VELOCITY assessment!

35 Doppler carotid assessment VELOCITY assessment can also estimate ECST measure directly

36 Doppler carotid assessment VELOCITY assessment can also estimate ECST measure directly Stenosis assessment within 5% to 10% = confirmatory assessment Requires immediate access to repeated Doppler not available in most centres other techniques used for confirmation

37 Doppler carotid assessment VELOCITY assessment can also estimate ECST measure directly Stenosis assessment within 5% to 10% = confirmatory assessment Requires immediate access to repeated Doppler not available in most centres other techniques used for confirmation Tendancy may be to report second Doppler percentage stenosis and make comment about how it relates to first Doppler Tendancy may be to report second Doppler as confirmatory

38 MRA CE carotid assessment Most common confirmatory method is MRA (because this was available before CTA)

39 MRA CE carotid assessment Most common confirmatory method is MRA MRA stenosis measured similarly to DSA MRA allows 3D interrogation of stenosis i.e. measure most severe Same problems as with DSA assumptions of distal vessel diameter Also edge effects mean stenosis generally OVER estimated Tendancy may be to report MRA percentage stenosis and make comment about how it relates to first Doppler Tendancy may be to report second Doppler as confirmatory

40 MRA ToF carotid assessment Compare appearances of the same tight stenosis: Angiography (DSA) MR (2D ToF) MR (3D ToF) For ToF, also use NASCET method, but answer from each imaging technique on the SAME stenosis here will be different!

41 CTA carotid assessment What about CTA? Measure off raw images? off 2D projection? off 3D projection? Problems if plaque calcified cannot see lumen. AJNR : 13-19

42 SSCA FORM Carotid Intervention

43 SSCA FORM Carotid Intervention First assessment most likely to report a % stenosis Subsequent assessments may simply confirm significance and not actually report a % or state that the % stenosis is > 70% NASCET or between 50% and 69% NASCET Subsequent assessments if also reporting a % stenosis may do so to provide an indepent report and record of findings of that assessment, BUT are likely to go on and relate these findings to the first assessment and make some overall comment about significance of the findings Complex stenoses however may require subsequent evaluation before a relevant % stenosis can confidently be quoted

44 SSCA FORM Carotid Intervention 10% incremental range very likely to be reported as this is recommended Range may be reported as 50-69% NASCET or > 70% NASCET because ultiimately thresholds for triggering surgery are important The form allows specification of NASCET or ECST later; must be clear what the reporting protocol is at your centre, especially if not stated explicitly in the report!

45 SSCA FORM Carotid Intervention Velocities are always recorded somewhere. PACS systems mean the velocities are usually stored as part of the image record. The final REPORT is a summary document and therefore may never list the velocities, instead only giving the conversion to a % stenosis.

46 SSCA FORM Carotid Intervention Most likely description will be significant and should mean that the stenosis is of a degree that surgery is indicated. Significant therefore may mean > 70% NASCET (all patients go to CEA) Significant may also mean 50% - 69% NASCET (for patients who fit the relevant criteria for CEA when the stenosis is in this range)

47 SSCA FORM Carotid Intervention Information on both sides very important. A tight stenosis on the contralateral side may artifically increase velocity measurements on the relevant side.

48 SSCA FORM Carotid Intervention MRA ToF & MRA CE Usually both are performed; information almost never in the report Information will be embedded in the PACS images; may need radiographer / radiologist help to determine what was done

49 SSCA FORM Carotid Intervention Conventional angiography / Selected carotid angiography / Arch angiography I am unsure what is meant by conventional angiography (I assume this is catheter injected, digital subtraction angiography) DSA will usually include selected carotid DSA i.e. inject contrast directly into the CCA Where the CCA cannot be accessed to evaluate the bifurcation, arch angiography may be performed Arch angiography may be performed anyway to identify CCA stenosis Probably just need DSA selected carotid / DSA aortic arch

50 SSCA FORM Carotid Intervention Problem with form will occur if first carotid evaluation is inconclusive (cannot measure velocity accurately, plaque obscures lumen, physical patient constraints high bifurcations, motion / swallowing, previous neck surgery, etc.) First % stenosis may be derived from confirmatory imaging

51 SSCA FORM Observation summary 13. & 19 Clarify conventional angiography DSA? Clarify why need / if all conventional angiography carotid angiography and arch angiography are relevant / necessary 14, 15 & 16 Clarify what to do if first imaging evaluation does NOT result in a stenosis measurement OR does NOT give the final agreed stenosis (may need a check box to indicate the stenosis is derived at a later stage) 15c & 16c Clarify if velocity is a REQUIRED field versus ALTERNATE field if stenosis not given; what is the reason to have velocity? Often a range of velocities are given; need to be able to enter a range of PEAK systolic velocities

52 SSCA FORM Observation summary 17 NASCET is often the default measurement measure and will not be stated just assumed Probably need for force selection i.e. eliminate not stated What is meant by Common Carotid? 18 May need facility to enter % stenoses if confirmatory technique is the one used to make surgical decision

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54 Uncertainty in delays Practically, can we get patients to surgery within 2 weeks of insult? If not, what is the best imaging approach? % risk of stroke Minor stroke 15 13% TIA 10 8% weeks Coull et al. BMJ 2004(Feb). OXVASC Study Days after initial event 8

55 Carotid Imaging for Stenosis? Systematic review of literature to assess non-invasive test accuracy Incorporate: Individual patient data analysis Costs of tests, of treatments, of failing to prevent stroke Build model of process of care after TIA / minor stroke Test effect on life expectancy, QALYs, & net benefit of different noninvasive tests (alone / combined) instead of DSA 12 datasets; 1909 patients Wardlaw et al. in progress

56 Carotid Imaging for Stenosis? Systematic review of literature to assess non-invasive test accuracy Highest net benefit is for imaging as fast as possible If you can operate early i.e. < 30 days post insult: Speed is crucial High sensitivity is optimal Therefore US is best If surgery is delayed i.e. > 30 days post insult: Accuracy crucial High specificity is optimal DSA or equivalent (e.g. MRA-CE) essential Wardlaw et al. in progress

57 NASCET & ECST For both NASCET & ECST, gold standard was angiography best measurement is based on 2D projection! Ultrasound introduced because it s non-invasive & rapid; its scope for plaque, vessel wall & stenosis visualisation is different from angiography Velocities have been correlated to US measured stenosis & to the gold standards; this introduces error!! New techniques of CTA & MRA allow 3D rotation & evaluation; therefore it is not clear how tightest stenosis assessed with CTA or MRA relates to original 2D angiographic gold standard CTA problems include calcification in plaque difficult to distinguish from contrast material MRA ToF problems include flow artefact at tight stenoses rendering no signal with which to measure the stenosis