Identification of vulnerable carotid plaque with histologically validated CT-derived plaque maps

Abstract

Objectives: Ruptured carotid plaque causes stroke, but differentiating rupture-prone necrotic core from fibrous tissue with CT is limited by overlap of X-ray attenuation. We investigated the ability of CT-derived plaque maps created from ratios of plaque/contrast attenuation to identify histologically proven vulnerable plaques.

Methods: Seventy patients underwent carotid CT angiography and carotid endarterectomy. A derivation cohort of 20 patients had CT images matched with histology and carotid plaque components attenuation defined. In a validation cohort of 50 patients, CT-derived plaque maps were compared in 43 symptomatic vs 40 asymptomatic carotid plaques and accuracy detecting vulnerable plaques calculated.

Results: In 250 plaque areas co-registered with histology, the median attenuation (HU) of necrotic core 43(26-63), fibrous plaque 127(110-162) and calcified plaque 964 (816-1207) created significantly different ratios of plaque/contrast attenuation. CT-derived plaque maps revealed symptomatic plaques had larger necrotic core than asymptomatic (13.5%(5.9-33.3) vs 7.4%(2.3-14.3), p = 0.004) with large necrotic core predicting symptoms (area under ROC curve 0.68, p = 0.004). Twenty-four of 47 carotid plaques were histologically classified as most vulnerable (Starry-Type VI). Plaque maps revealed Type VI plaques had a greater necrotic core volume than Type IV/V plaques and a necrotic core/fibrous plaque ratio >0.5 distinguished Type VI plaques with sensitivity 75.0% (55.1-88.0) and specificity of 39.1% (22.2-59.2).

Conclusions: Carotid plaque components can be differentiated by CT using a ratio of plaque/contrast attenuation. CT-derived plaque map volumes of necrotic core help distinguished the most vulnerable plaques.

Advances in knowledge: CT-derived plaque maps based on plaque/contrast attenuation may provide new markers of carotid plaque vulnerability.

Figure 1.

Co-registration of computed tomography (CT) with histology and attenuation sampling. (a) Eversion carotid endarterectomy sample removed “en-bloc”. (b) Plaque components pre-classified using histology (Ca – calcified plaque, Lu – lumen and NC – necrotic core). (c) Attenuation sampling of luminal contrast distal and proximal to plaque. (d) Co-registered CT cross-sectional image. (e) Attenuation sampling from regions of interest in necrotic core.

Figure 2.

Curved multiplanar reforms of carotid artery plaque with cross-section level of arrow (inserts) of: (a) Ulcerated plaque, (b) Napkin-ring plaque and (c) Low attenuation plaque.

Figure 3.

Conventional multiplanar reformat and CT Plaque Map analysis of (a) and (b) predominantly fibrous plaque, (c) and (d) calcified plaque and (E) and (F) necrotic core. With fibrous plaque colored blue, calcified plaque white, necrotic core red and lumen green.

Figure 4.

Box and whisker plot showing (a) attenuation values of carotid plaque components and (b) plaque/contrast attenuation ratios of carotid plaque components.

Figure 5.

Receiver operating characteristic curve for necrotic core percentage in symptomatic carotid plaque.