Effects of transducer position on backscattered intensity in coronary arteries

Acute myocardial infarction is a frequent cause of sudden death, and is typically initiated by the rupture of coronary artery plaques. The likelihood and severity of rupture are influenced by the plaque structures and components. Radiofrequency (RF) intravascular ultrasound (US) (IVUS-RF) measurements extend current IVUS imaging techniques and may eventually enable the in vivo identification of these features. However, IVUS-RF measurements are affected by the transducer’s instantaneous position in the vessel. Specifically, backscattered intensity (BI) decreases as either the distance between the tissue and the transducer increases, or as the beam’s angle of incidence on the tissue increases. IVUS-RF data were acquired from seven disease-free coronary arteries in vitro. The 0-dB level for BI was defined as the peak intensity of the reflection from a stainless-steel flat reflector at each distance. The baseline BI measured in adventitial tissue was −32.5 dB (at 0 degrees, 0 mm) with angle and distance dependencies of −0.172 dB/° and −3.37 dB/mm. In contrast, the BI from combined intima and media was −38.2 dB with dependencies of −0.111 dB/° and −4.46 dB/mm ( p < 0.05 for all three parameters). Acknowledging and compensating for these effects may allow IVUS-RF to develop into a rapidly deployable tool for the clinical detection of vulnerable plaques and to monitor coronary artery disease progression and regression. (E-mail: ivus@crci.stanford.edu)