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Positron Emission Tomography Imaging of Regional Pulmonary Perfusion and Ventilation

Department of Anesthesia and Critical Care, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts

Correspondence and request for reprints should be addressed to Guido Musch, M.D., Department of Anesthesia and Critical Care, CLN 309, Massachusetts General Hospital, 55 Fruit Street, Boston, MA 02114. E-mail: gmusch{at}partners.org

ABSTRACT

Positron emission tomography (PET) imaging is a noninvasive, quantitative method to assess pulmonary perfusion and ventilation in vivo. The core of this article focuses on the use of [¹³N]nitrogen (¹³N₂) and PET to assess regional gas exchange. Regional perfusion and shunt can be measured with the ¹³N₂–saline bolus infusion technique. A bolus of ¹³N₂, dissolved in saline solution, is injected intravenously at the start of a brief apnea, while the tracer kinetics in the lung is measured by a sequence of PET frames. Because of its low solubility in blood, virtually all ¹³N₂ delivered to aerated lung regions diffuses into the alveolar airspace, where it accumulates in proportion to regional perfusion during the apnea. In contrast, lung regions that are perfused but are not aerated and do not exchange gas (i.e., "shunting" units) do not retain ¹³N₂ during apnea and the tracer concentration drops after the initial peak. Accurate estimates of regional perfusion and regional shunt can be derived by applying a mathematical model to the pulmonary kinetics of a ¹³N₂–saline bolus. When breathing is resumed, specific alveolar ventilation can be calculated from the tracer washout rate, because ¹³N₂ is eliminated almost exclusively by ventilation. Because of the rapid elimination of the tracer, ¹³N₂ infusion scans can be followed by ¹³N₂ inhalation scans that allow determination of regional gas fraction. This article describes insights into the pathophysiology of acute lung injury, pulmonary embolism, and asthma that have been gained by PET imaging of regional gas exchange.

Key Words: adult respiratory distress syndrome • asthma • emission-computed tomography • nitrogen isotopes • pulmonary embolism • pulmonary gas exchange

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Proceedings of the American Thoracic Society 2005 2: 499-516. [Full Text]  

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