Accuracy of MR angiography compared with radionuclide scanning in identifying the cause of pulmonary arterial hypertension.

OBJECTIVE: MR imaging has proven accurate in identifying patients with chronic thromboembolic pulmonary hypertension (CTEPH). However, we know of no attempt to distinguish patients with CTEPH from patients with other causes of pulmonary arterial hypertension (PAH). Primary pulmonary hypertension (PPH) is the disease most frequently confused with CTEPH. We examined patients with CTEPH or PPH and control subjects to identify MR imaging features that might distinguish CTEPH from PPH, to compare the accuracy of MR angiography (MRA) with that of radionuclide scanning, and to determine the cardiac and pulmonary vascular measurements in these groups. SUBJECTS AND METHODS: T1-weighted and two-dimensional multiplanar spoiled gradient-recalled scans were obtained in 30 patients with CTEPH who had undergone conventional pulmonary angiography, 10 patients with PPH, and 13 control subjects with no known vascular disease. Ventilation-perfusion scans were available in all patients with CTEPH and in six of the 10 patients with PPH. The MR scans were assessed independently by two radiologists who evaluated the appearance of segmental vessels and noted the presence of mosaic perfusion. Cardiac chambers and pulmonary vessels were measured on T1-weighted spin-echo scans. RESULTS: The two radiologists used MR angiograms to reliably distinguish between patients with CTEPH and those with PPH. The accuracy of MR angiograms matched that of ventilation-perfusion scans (92%). On T1-weighted scans, the two radiologists used cardiac and pulmonary vascular measurements to distinguish patients with PAH from control subjects but failed to distinguish between patients with CTEPH and those with PPH. CONCLUSION: MRA is useful in distinguishing patients with CTEPH from those with PPH. In this population, MRA had an accuracy that was identical to that of radionuclide scanning. Vascular and cardiac measurements made on MR scans reliably identified patients with PAH but did not distinguish between patients with CTEPH and those with PPH.

Technetium-99m labeled micro aerosol "Pertechnegas". A new agent for ventilation imaging in suspected pulmonary emboli.

In this preliminary study, four patients suspected of having pulmonary emboli underwent ventilation imaging after inhaling approximately 1 mCi (37 MBq) of Tc-99m Pertechnegas (micro aerosol carbon particles labeled with Tc-99m) in five breaths or less. Planar images in multiple projections were recorded for preset counts. A final posterior image was acquired to evaluate residual lung background activity. Immediately following ventilation imaging, perfusion imaging in the identical projections was performed using 4 mCi (148 MBq) of Tc-99m MAA. Two of the four patients demonstrated matched uniform ventilation and perfusion and two showed segmental ventilation-perfusion "mismatched" defects consistent with pulmonary emboli. In each case, residual Pertechnegas background lung activity (count rate) at the end of the last ventilation image was less than 10% of the initial Tc-99m MAA counts (count rate). The advantages of Pertechnegas, in comparison to aerosolized DTPA, include: less residual ventilation image activity superimposed on the MAA perfusion images, reduced demand for patient cooperation due to fewer required breaths (five or less), and lack of deposition of activity in the central airways. The authors conclude that Pertechnegas has properties that make it ideally suited for routine lung ventilation imaging.