Abstract
Scintigraphic pulmonary studies are designed to demonstrate patterns of ventilation and perfusion. It is crucial to make an image of both ventilation and perfusion for a proper diagnostic interpretation of any disorder. In pulmonary embolism, there are areas with absent perfusion and preserved ventilation. Pulmonary embolism is diagnosed when there is more than one sub-segment showing a ventilation/perfusion mismatch, representing an anatomic lung unit. Ventilation/perfusion single-photon emission computed tomography (V/P SPECT) is recommended as the first-choice imaging technique for the diagnosis of acute pulmonary embolism and is the golden standard for the diagnosis of chronic pulmonary embolism. Antigravitational perfusion distribution from posterior to anterior region indicates pulmonary congestion (heart failure). As ventilation is usually less affected, the typical pattern is a non-segmental ventilation/perfusion mismatch in dorsal regions of the lung. Some other diseases cause declines in both ventilation and perfusion resulting in a “matched” functional defect. Acute pneumonia causes frequently reverse mismatches. Later in the progress of the pneumonia matched defects may be seen. Using Technegas for the ventilation study over radiolabeled liquid aerosols enable grading of airway obstruction in chronic obstructive pulmonary disease. Areas of absent/decreased ventilation with usually less pronounced perfusion defects (reverse mismatch) are typical for the damage of lung parenchyma (emphysema).
Minimizing radiation exposure without sacrificing image quality and diagnostic accuracy are essentials for an imaging test that follows good clinical practice. An optimal combination of radiopharmaceuticals, nuclide activities and acquisition times for ventilation and perfusion, collimators, and imaging matrix yield an adequate ventilation perfusion SPECT study in approximately 20 minutes of imaging time. Ventilation/perfusion SPECT is using a holistic interpretation strategy based on all relevant information about the patient and all ventilation/perfusion patterns. The method allows quantification of lung function and measurement of the extent of functional deteriorations that have impact on the diagnostics and treatment.
Following the recent European Association of Nuclear Medicine guideline of ventilation/perfusion SPECT allows diagnostics of comorbidities such as obstructive lung disease, pulmonary congestion, and pneumonia separately or simultaneously with pulmonary embolism.