The High Risk Versus the Population Approach to Prevention

<p>(Figure: John Emberson)</p

Ultrasonography of the Carotid Artery to Measure the IMT

<div><p>This figure provides a framework for understanding the multiple, quantitative calculations undertaken for each patient's carotid ultrasound scan. Two images of carotid artery without plaques (left) and two with plaques (right) are shown at the top. ROI indicates the region of interest in which thickness measurements are made. These were obtained from a single patient. Schematics for each image are provided below the video images. The grey lines indicate the measured IMT within the defined region of interest. Regarding the plaques (PL₁ and PL₂), M indicates maximum plaque thickness, and L indicates minimum lumen diameter at the site of maximum plaque thickness. Percent diameter stenosis is calculated as [M/(M + L)] × 100%. The graph (bottom) indicates length in millimeters on the x-axis and thickness in millimeters on the y-axis. The areas from the far wall of the left (L) and right (R) common carotid arteries are measured in all patients. AIMT designates the average IMT derived from the left and right measurements. PL₁ and PL₂ are the lesion lengths of the respective plaques, and M₁ and M₂ are the respective maximal thicknesses. APT₁ and APT₂ designate the respective average lesion thicknesses for each plaque. The total area is given by the sum of all the areas shown on the graph in units of square millimeters. The average total thickness (ATT) is given by the total area divided by the total length shown on the x-axis. PL_n on the x-axis is intended to indicate that the calculations are undertaken using these concepts, irrespective of the number of plaques identified in a given study.</p> <p>(Figure from [<a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.0020098#pmed-0020098-b28" target="_blank">28</a>] with permission of all four authors.)</p></div