Intravascular Ultrasound Imaging of Pulmonary Arteries: Pulmonary IVUS Instrumentation
This technique has been used to examine 1.0- to 4.5-mm diameter pulmonary arteries in humans with chronic lung disease. It has also accurately detected acute pulmonary emboli in dogs. It has been used clinically in patients suspected of having chronic pulmonary emboli where the angiogram is not conclusive. In these cases, angio-scopy has been useful in excluding other pulmonary vascular disorders, which may mimic thromboemboli, eg, plaque, and has also been used in determining operability. review
IVUS of the pulmonary artery is a new catheter-based imaging modality with high resolution and real time imaging capabilities. Its advantages over other imaging techniques include significantly better resolution of the pulmonary vessel lumen and wall, detailed description of both proximal and distal pulmonary arterial anatomy, real time imaging of the pulmonary artery throughout the cardiac cycle, and the ability to rapidly assess the effect of mechanical and pharmacologic interventions. Unlike angio-scopy, it is capable of imaging through blood and can describe disease within the vessel wall.
Currently available intravascular ultrasound imaging devices consist of a mechanical or phased array catheter (3.5-9F) capable of imaging at frequencies ranging from 10 to 40 MHz. Axial resolution with these catheters, therefore, ranges from 150 to 300 fim depending on the transmitted frequency and lateral resolution within the focal point of the transducer is about 150 fim. The catheters can be advanced into the pulmonary artery fluoroscopically using an 0.014-inch guide wire. In some cases, a long sheath that is normally used for transeptal catheterization (Mullins sheath) or endomyocardial biopsy may be necessary to assist in guiding the catheter to a select region in the pulmonary vasculature.
Imaging consoles display ultrasound images at between 15 to 30 frames/s. This is an important feature because it allows the clinician to characterize changes in pulmonary vascular diameter and area throughout the cardiac cycle. This is especially important in the determination of pulmonary artery stiffness.