Intravascular Ultrasound Imaging of Pulmonary Arteries: Computed Tomography
Computed tomography (CT) and MR imaging provide anatomic detail in pulmonary artery disease that cannot be obtained from pulmonary angiography. In pulmonary atresia, MR imaging has shown the presence or absence of pulmonary arteries in regions that are not accessible to catheters. In a small study of 21 patients with pulmonary embolism, high resolution CT scanning was shown to be better than angiography in assessing proximal thrombi, examining pulmonary arteries distal to thrombi, and detecting pulmonary infarction. Cine MR imaging has also been clinically applied in infants to define accurately the placement of pulmonary artery banding. Cardiac and respiratory motion, as well as pulmonary artery pulsatility, limit the application of these imaging techniques in assessing intraluminal abnormalities. Recently, MR angiography has been able to compensate for cardiac motion by using electrocardiographic gating and phase velocity mapping techniques which also may be able to quantify pulmonary blood flow. Fast gradient echo-images may be able to semi-quantify the severity of pulmonary hypertension in a wide variety of pulmonary vascular diseases
Transesophageal echocardiography has been used to image proximal pulmonary arteries in central pulmonary artery thromboemboli. Wittlich et al showed that transesophageal echocardiography is more than 95% sensitive and more than 85% specific for detecting central pulmonary thromboemboli. read only
With the advent of multiplane transesophageal echocardiography, more distal portions of the right and left pulmonary arteries can now be visualized with good resolution.
Direct animal and human pulmonary artery imaging has also been performed with a small caliber fiberoptic angioscope. The angioscope is typically advanced with the aid of a balloon tip on the scope, or the scope is passed through the central lumen of a balloon-tipped guide catheter. Intraluminal visualization requires balloon inflation and interruption of blood flow.