Quantification of Atheromatous Stenosis in the Extracranial
Internal Carotid Artery

J. M. de Bray, B. Glatt;
For the International Consensus Conference, Paris, December 2-3, 1994
Cerebrovasc Dis 1995; 5: 414-426

Abstract

An international consensus meeting to determine criteria for the quantification of stenosis of the extracranial internal carotid artery was held in Paris on December 2 and 3, 1994. A review of the literature and expert analysis of validity and reproducibility led to the following recommandations:Intra-arterial X-ray angiography: At present, two main methods of quantifications are being evaluated, the distal and the local method, the former being the better validated. The latter method, on the other hand, is better able to represent moderate lesions at the level of the carotid bulb. Therefore, it is suggested that a ratio between the stenosis and the common carotid artery should also be established. X-ray angiography prior to carotid endarterectomy can be avoided if ultrasound and MR angiography concur in identifying severe stenosis provided that intracranial vessels are without relevant disease.
Ultrasound Doppler duplex methods can quantify the degree of extracranial carotid artery stenosis in terms of both diameter reduction according to the criteria established by recent surgical studies (NASCET - distal degree of stenosis - and ECST - local degree of stenosis - as well as residual area in cross-sections. The latter is more suiteable since hemodynamic effect, local increase of velocity, and pressure drop are taken into consideration. Technical requirements (carrier frequency 4-5 MHz, Doppler angle inferior to 60°ree;, sample volume > 5 mm) call for a combination of three validated criteria.
Maximum Doppler shift/flow velocities measured at the narrowest point of the stenosis and the degree of poststenotic flow disturbances should be examined. In systole, a value of 4 kHz (120 cm/s) (f0 = 4 MHz), identifies most stenoses > 50% in local diameter reduction and as in end-diastole, a value of 4.5 kHz (135 cm/s) identifies stenoses of >80%.
Carotid ratio: The systolic velocity ratio should be recorded between the site of the stenosis and the common carotid artery obtained 3 cm below the bifurcation. This limits the influence of general hemodynamic factors unrelated to the stenosis such as the cardiac output. A threshold value of > 1.5 determines stenoses of > 50% and a threshold value of > 4, stenosis of >70%.
Area ratio: The ratio between the total arterial lumen in cross-section and the minimal residual lumen should be determined by echotomography and additional color Doppler flow imaging. In addition there are indirect criteria, such as asymmetry of pulsatility of the common carotid artery and middle cerebral artery signals as well as inverted flow of the ophthalmic artery which distinguish moderate from high-degree stenoses (>80% diameter reduction).
Magnetic resonance angiography (MRA): With this method, a diameter ratio using the distal degree of stenosis is recommended with data obtained from transverse source images in addition to transverse T1 sequences. MRA is a complement to ultrasonic methods, particularly in cases of calcified stenoses and for the analysis of intracranial vessels.

Consensus Concerning the Morphology and the Risk of Carotid Plaques

J.M. de Bray, J.M. Baud, M. Dauzat,
on behalf of the Consensus Conference, Paris, December 13-14, 1996
Cerebrovasc Dis 1997;7:289-296

Abstract

An international consensus meeting to determine criteria for the characterization of extracranial carotid artery stenosis was held in Paris on December 13 th and 14 th 1996. Recommendations are the following if the degree of the stenosis and the precise location of the stenosis are well defined:
Ultrasonic Doppler Duplex methods describe the composition and the surface topography of carotid plaques. Echogenicity (from anechoic to hyperechoic), surface (from smooth to cavitated) and texture (from homogeneous to heterogeneous) are the features to be estimated as plaque thickness and length. Echogenicity is standardized against blood (anechoic), mastoid muscle (isoechogenic) or bone (hyperechogenic cervical vertebrae). Luminal surface is classified in 3 classes: regular, irregular (0,4 to 2 mm depth) and ulcerated (> 2 mm depth with a well defined back wall at its base and a color Doppler injection). Texture is a function of pixle size and, in a given region of interest, reflects the variability of the grey scale values. Recommended technical requirements are frequency - and amplitude modulated Color Doppler flow imaging, carrier frequency > 5 MHz capable of insonating up to 4 cm and retrievable documentation of relevant findings.
Computed Tomographic Angiography permits 3D rendering of the size and extent of the plaque and allows to recognize calcifications, deposits, plaque isodense to muscle and ulcers > 2 mm in size.
Angiography may identify gross calcifications and large ulcers defined in 2 classes: 1 - large (2 mm depth by 2 mm width), 2 - complex with multiple craters.
Magnetic Resonance Imaging with or without angiography may play a role in the future. "In vitro" studies show that MR can demonstrate plaque components such as fibrosis, calcification, hermorrhage and necrotic core, but current technical limitations related to resolution and motion artifacts prevent this from being implemented "in vivo".
Pathological studies require "en bloc" surgery. Component areas should be calculated from their length and width and ulcerations measured from their width.
The risk of cerebrovascular ischemia is clearly related to the degree of stenosis. Factors of individual importance for higher risk include in descending importance: evidence of progression, surface ulceration and low echogenicity. Texture is still under investigation as a prognostic factor.

Consensus opinion on diagnosis of cerebral circulatory arrest using
Doppler-sonography: Task Force Group on cerebral death of the
Neurosonology Research Group of the
World Federation of Neurology

Ducrocq X, Hassler W, Moritake K, Newell DW, von Reutern GM,
Shiogai T, Smith RR
J Neurol Sci 1998;159:145-150

BACKGROUND AND PURPOSE:

Oscillating flow or systolic spikes are typical Doppler-sonographic flow signals found in the presence of cerebral circulatory arrest, which if irreversible, results in brain death. The Neurosonology Research Group (NSRG) of the World Federation of Neurology (WFN) created a Task Force Group in order to evaluate the role of Doppler-sonography as a confirmatory test for determining brain death.

METHODS:

The available evidence from the literature has been reviewed and discussed by a group of experts, the members of the Task Force Group on cerebral death of the NSRG.

RESULTS AND CONCLUSIONS:

Extra- and intracranial Doppler-sonography is a useful confirmatory test to establish irreversibility of cerebral circulatory arrest as optional part of a brain death protocol. Doppler-sonography is of special value when the therapeutic use of sedative drugs renders electroencephalography unreliable. Doppler-sonographic criteria are defined and guidelines for the use of Doppler-sonography in this setting are presented.

Transcranial Doppler ultrasonography: Year 2000 update.

Babikian VL; Feldmann E; Wechsler LR; Newell DW; Gomez CR; Bogdahn U;
Caplan LR; Spencer MP; Tegeler C; Ringelstein EB; Alexandrov AV
J Neuroimaging 2000;10:101-115

In this update, the main clinical applications of transcranial Doppler ultrasonography are reassessed. A specific format for technology assessment, personal experience, and an extensive review of the literature form the basis of the evaluation. The document is approved by the American Society of Neuroimaging and the Neurosonology Research Group of the World Federation of Neurology.