Acoustic Radiation Force Impulse (ARFI) Ultrasound for Noninvasive, Diagnostic Atherosclerosis Imaging; Independent Scientist: ARFI and RWI Ultrasound for Improved Atherosclerosis Imaging

The purpose of this study is to evaluate Acoustic Radiation Force Impulse (ARFI) ultrasound imaging for describing the composition and structure of atherosclerotic plaques. The surgical atherosclerotic plaques of 16 patient volunteers undergoing clinically indicated carotid endarterectomy (surgical removal of plaque from the carotid artery) will be imaged preoperatively by ARFI. ARFI imaging will occur during the volunteers' preoperative workup visits (inpatient or outpatient), in the surgical holding area (inpatient or outpatient), or at the patient bedside (inpatient). Then, the routinely excised plaque specimens will be sent for histopathological processing to determine plaque composition and structure. The histopathological data will be used to validate ARFI imaging performance for plaque material and structural characterization. This will end the participant's involvement in the study.

There are two experimental components to this study beyond what is standard practice for carotid endarterectomy patients: 1) preoperative ARFI ultrasound imaging of ipsilateral (surgical) carotid arteries, and 2) submission of sections of the carotid plaque excised intraoperatively to the UNC Hospitals clinical laboratories for immunohistochemical analysis.

This study will commence with ARFI ultrasound imaging at the time of the patient volunteer's preoperative workup for carotid endarterectomy surgery (outpatients and inpatients), while the patient is in the holding area for surgery (outpatients and inpatients), or at the patient bedside (inpatients). If the patient volunteer is an outpatient, ARFI ultrasound imaging will be performed up to two weeks prior to surgery. Preoperative ARFI ultrasound imaging will be performed in addition to the patient volunteer's routine preoperative duplex ultrasound and any other exams used to determine if carotid endarterectomy is clinically indicated.

ARFI ultrasound is a noninvasive diagnostic imaging technology performed using commercially available clinical ultrasound imaging equipment - the Siemens SONOLINE or Acuson Antares imaging systems equipped for research purposes and VF10-5 or VF7-3 linear array transducers (Siemens Medical Solutions, USA Inc. Ultrasound Division). ARFI imaging will be carried out by a professional sonographer trained in peripheral vascular ultrasound and faculty (Caterina Gallippi, Ph.D., Associate Professor, study PI) and/or graduate student research assistants in the UNC-CH Joint Department of Biomedical Engineering. The sonographer will acquire ARFI ultrasound data with matched B-Mode (for anatomical reference) in ipsilateral (surgical) carotid arteries of patient volunteers. Patient volunteers will be asked to lie on an examination table (outpatients) or to remain in their hospital beds (inpatients). The head of the exam table/bed may be raised to an approximate 45 degree angle to best visualize the carotid arteries with ultrasound imaging.

Once the patient volunteer is positioned, ultrasound gel will be applied to the patient volunteer's neck. The ultrasound imaging transducer will then be placed on top of the gel. Once the carotid artery is located, ARFI ultrasound imaging will begin. In the ipsilateral (surgical) carotid artery, the imaging field of view will be centered on the carotid plaque, with axial focal depth directed to the position of the near or far wall containing the thickest portion of the plaque. Data acquisitions will be gated to diastole. Two repeated acquisitions will be acquired for each of four ARFI imaging sequences. The position of landmarks such as arterial branch points and morphological features such as arterial wall thickness will be recorded for spatial registration to duplex ultrasound and histology.