Imaging of the CIMT (carotid artery intima-media thickness) should be performed with a linear array transducer with the highest possible operating frequency allowing visualization of the posterior carotid artery wall. Typical transducer frequencies range between 7 Mhz to 15 Mhz. The carotid artery should be scanned from the proximal common carotid artery (CCA) through the carotid bulb as well as the internal and external carotid arteries in both the transverse and longitudinal planes documenting any atherosclerotic plaque or change in carotid artery wall dimensions. Color and pulsed Doppler waveforms should be documented with peak systolic velocities measured at any levels of stenosis as well as the proximal common carotid artery (CCA), distal CCA, Carotid bulb, Proximal and distal internal carotid artery (ICA), and the external carotid artery (ECA). Measurements of the CIMT should be calculated in the long axis of the artery at the level of the distal common carotid artery at least 10 millimeters proximal to the end of the common carotid artery. Measurements should be obtained on the posterior wall of the artery in a region free from any atherosclerotic plaque with the posterior wall as parallel as possible to the transducer surface (perpendicular to the ultrasound beam) for an optimal angle of isonation as close to 90 degrees as possible. While there are many protocols and opinions on where to make the calculation, the most widely used and reliable location is the posterior wall of the common carotid artery. Acquiring multiple images and measurements in this region is acceptable to confirm the consistency and accuracy of the measurement.
Figure 1: (a). Diagram of the common carotid, carotid bulb, internal and external carotid arteries. (b). Diagram of the arterial wall carotid artery intima-media thickness
Figure 2: 2D sonographic image of the distal common carotid artery showing some thickening of the anterior intima media at the origin of the carotid bulb.CIMT measurements of multiple areas can be performed in a screening or research setting. The posterior and anterior wall of the distal common carotid, carotid bulb, and proximal internal carotid artery can be evaluated, and measurements taken in this region. Calculations obtained on the anterior wall of the carotid artery can be difficult to measure accurately due to reverberation artifacts. This artifact is common in the anterior region and can cause overestimation of the arterial wall with both manual and automatic measurement tools.
Fig 3: Image of the distal common carotid artery with automated CIMT calculation sample boxes placed in the appropriate location on the anterior and posterior carotid walls 10 mm proximal to the carotid bulb
Fig 4: Image of the distal common carotid artery with automated CIMT calculation sample boxes placed in the wrong location too close to the carotid bulb. The appropriate location should be 10 mm proximal to the carotid bulb.