Coronary intravascular ultrasound: a closer view

Intravascular ultrasound (IVUS) is an invasive tomographic imaging modality, providing images of coronary arteries and other blood vessels. Over the last 20 years IVUS has evolved into an excellent adjunct to coronary angiography. Although coronary angiography continues to be the standard tool to assess the coronary artery lumen, angiography does not supply direct information about the plaque and vessel wall. IVUS provides complementary diagnostic information about the artery wall which cannot be obtained by angiography alone. IVUS systems contain a special transducer mounted catheter and an electronics console to reconstruct the image. The ultrasound signal is produced in the transducer by passing an electrical current through the piezoelectric (pressure-electric) crystalline material (usually ceramic) that expands and contracts when electrically excited. After reflection from tissue, part of the ultrasound energy returns to the transducer and is converted into the image. High ultrasound frequencies (20–40 MHz) are employed resulting in an axial resolution in the range of 80–150 μm and lateral resolution of 200–250 μm.1 ### Catheter technology Currently available monorail rapid exchange intracoronary ultrasound catheters have an outer diameter of between 2.6–3.5 French (0.87–1.17 mm diameter) which can be advanced through a 6 French guide catheter. Two transducer designs are commonly used: the mechanically rotating transducer and the electronically switched phased array system. Mechanical systems consist of a drive cable to rotate a single transducer at the catheter tip at 1800 rpm (30 revolutions per second), sweeping an ultrasound beam perpendicular to the catheter. At approximately 1° increments, the transducer sends and receives ultrasound signals. In mechanical catheter systems, the imaging transducer is inside a protective sheath, through which the imaging catheter is advanced and pulled back. Electronic systems , also referred to as the solid state IVUS system, have multiple transducer elements (up to 64) arranged in an annular array rather than a single rotating transducer. The transducers …