In vitro analysis of carotid lesions using a preliminary microwave sensor to detect vulnerable plaques: Correlation with histology, Duplex ultrasound examination, and computed tomography scanner: The Imaging and Microwave Phenotyping Assessment of Carotid stenosis Threat (IMPACT) study

Abstract

Objective: Progress in best medical treatment have made identification of best candidates for carotid surgery more difficult. New diagnostic modalities could be helpful in this perspective. Microwaves (MWs) can quantify dielectric properties (complex relative permittivity) of biological tissues and MW technology has emerged as a promising field of research for distinguishing abnormal tissues from healthy ones. We here evaluated the ability of a dedicated MW sensor developed in our laboratory to identify vulnerable carotid lesions.

Methods: We included 50 carotid lesions in this study. The plaques were analyzed and classified preoperatively by ultrasound (US) examination, computed tomography angiography and tested postoperatively using a MW sensor. Histopathological analysis was used as a gold standard to separate vulnerable plaques (VPs) from nonvulnerable plaques (NVPs).

Results: VPs were more frequently types 2 or 3 plaques (on US examination), had a greater proportion of low (<60 Hounsfield unit) and moderate (60-130 Hounsfield unit) attenuation components (computed tomography angiography) and displayed higher dielectric constant values (MW) than NVPs, which had an opposite profile. NVPs were more frequently asymptomatic plaques compared with VPs (P = .035). Multivariate analysis showed that US examination and MW identified VPs with a sensitivity of 77% and a specificity of 76% (cutoff value, -0.045; area under the curve, 0.848; P < .0001).

Conclusions: We found that the presence of types 2 to 3 (on US examination) and high dielectric constant plaques in vitro was highly indicative of a VP based on histological analysis. Further studies are needed to determine the potential of MW to identify the most dangerous asymptomatic carotid lesions.

Keywords: Carotid plaque stability; Duplex US; Microwave; Risk assessment; Stroke.

Fig 1

Representative illustration of multimodal assessment of vulnerable plaques (VPs) (A-D) and nonvulnerable plaques (NVPs) (E-H). The VP in (A) shows similar findings between the in vivo examination of duplex ultrasound (DUS) examination and computed tomography (CT) scan (B, C), respectively, and the histological analysis in (D). Similarly, the NVP in (E) displays comparable findings between the in vivo assessment of DUS examination and CT scan (F, G), respectively, and the histological analysis in (H).

Fig 2

Statistical analysis of the relationship between histology and duplex ultrasound (DUS) examination. The degree of calcification was higher (A) and the lipid-rich necrotic core (LRNC) amount lower (C) in type 4/5 plaques based on the Grey-Weale updated scale classification. No significant difference was noted in terms of fibrosis (B). Receiving operating characteristic (ROC) curve analysis found that a cutoff of 17% of necrosis (sensitivity, 70%; specificity, 70%; P = .003) and 4.2% of calcification (sensitivity, 65%; specificity, 70%; P = .021) distinguished type 2/3 from type 4/5 plaques (A-C).

Fig 3

Association between computed tomography (CT) scan and duplex ultrasound (DUS) examination. Box plot analysis of Hounsfield unit (HU) groups vs Gray-Weale scale groups in DUS examination showing no significant association between CT scan results and DUS analysis.

Fig 4

Microwave (MW) and multimodal assessment of carotid vulnerable plaques (VPs). Whisker chart and receiving operating characteristic (ROC) curve statistical analysis of the constant dielectric vs echogenicity types (A and a) and multimodal prognostic score aiming at predicting the vulnerability of carotid plaques (B, b and table). The constant dielectric significantly decreased from type 2 to type 5 plaques (P = .004) (area under the curve [AUC], 0.76; cutoff value, 18.75; sensitivity, 73%; specificity, 80%; P = .00). Constant dielectric c (P = .033) combined with type 2/3 plaque on duplex ultrasound (DUS) examination (P = .011) are predictive of VPs: score = 1.760 + (–0.062 × constant dielectric) + (−3.367 × Gray-Weale scale classification 23 or 45) (cutoff value, –0.045; AUC, 0.848; sensitivity, 77%; specificity, 76%; P < .0001).

Supplementary Fig 1

Supplementary Fig 2