Intravascular Ultrasound Imaging of Pulmonary Arteries: Validation of Pulmonary IVUS Imaging
Using a disposable 6F 20 MHz ultrasound probe in isolated pulmonary artery segments of dogs, it has been shown that IVUS-derived measurements of pulmonary artery area, diameter, and wall thickness correlated very well with anatomic measurements in vitro (Fig 1). In this preliminary study, pulmonary IVUS images in humans were also obtained and provided detailed examinations of the changes in pulmonary artery vessel shape and pulsatility from the proximal to the distal pulmonary artery. An example of a normal human pulmonary artery using 20 MHz IVUS at end-diastole and end-systole is shown in Figure 2.
The unique features of pulmonary IVUS described above have been used for diagnostic, interventional, and pathophysiologic assessments in pulmonary vascular diseases (Table 1).
Acute Pulmonary Thromboembolic Disease: Recent experimental and clinical studies have delineated the ability of pulmonary IVUS to diagnose acute pulmonary embolus. Kumar et al injected 2-day-old radiopaque thrombi into the jugular vein of dogs and showed that IVUS was able to identify the location of the pulmonary embolus. In this study, pulmonary emboli were identifiable as bright granular echoes and easily distinguishable from the normal vessel wall. Mechanical disruption of the embolus was also performed in this study, and subsequent destruction of thrombus was verified by IVUS. Tap-son et al also showed in dogs that pulmonary IVUS was a safe, highly sensitive technique for diagnosing experimental pulmonary emboli. asthma inhaler
Hermiller et al showed in humans that a large acute pulmonary embolus appears as soft echoes within the lumen of an otherwise normal-appearing artery. These investigators also used IVUS (4.8F 20 MHz) to show dissolution of the embolus after intra-pulmonary administration of thrombolytic therapy. Gorge et al3a also showed that pulmonary intravascular ultrasound could rapidly make the diagnosis of small and large pulmonary emboli, as well as visualize the success of thrombolysis. These preliminary clinical studies suggest that IVUS of the pulmonary artery may be a useful method of rapidly diagnosing pulmonary emboli in critically ill patients who are too unstable for pulmonary angiography. The technique can be rapidly performed in the ICU or emergency department using an internal jugular venous approach with time periods reported to be as short as 10 min.
Figure 1. A comparison of in vitro IVUS measurements with anatomic measurements or luminal area (left), luminal diameter (middle), and vessel wall thickness (right). Reproduced with permission, from reference 12.
Figure 2. IVUS image of a pulmonary artery from a normal patient. The end-diastolic (EDA) and end-systolic (ESA) areas have been planimetered. Note the thin intimal surface and vessel pulsatility. Reproduced with permission, from reference 17.
Table 1—Clinical Applications of Pulmonary IVUS
|Acute Pulmonary Embolism|
|Chronic Pulmonary Embolism|
|Vessel Wall Abnormalities|
|Guidance During Therapy|
|Assessment of pulmonary artery angioplasty results|
|Assessment of response to pharmacologic therapy|
|Assessment of Pathophysiology|
|Primary and secondary pulmonary hypertension|
|Pulmonary artery endothelial function|