Page 120 - Assessing right ventricular function and the pulmonary circulation in pulmonary hypertension Onno Anthonius Spruijt

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MRI based dynamic pulmonary perfusion imaging is a technique visualizing the passage of an contrast bolus of an MRI-contrast agent through the lungs in a 3-dimensional way, enabling the visualization of sub-segmental perfusion defects in chronic thromboembolic PAH [63, 64]. In addition, post-processing of the perfusion images makes it possible to derive quantitative data from the dynamic perfusion scan such as pulmonary blood volume, flow and transit time defined as the time required for the contrast to transit through the lungs [65]. Although it has been shown that all of these MRI derived parameters are directly related to hemodynamic parameters such as pulmonary artery pressure and cardiac output, accurate calculation of the main determinant of the pulmonary vascular bed, the pulmonary vascular resistance, is not yet possible [66, 67].
Nuclear imaging techniques
Nuclear techniques can be used for imaging the lung and the heart. The application of lung perfusion scintigraphy in the diagnosis of chronic thromboembolic pulmonary hypertension is well established and its role is further discussed in chapter 13. A refinement of perfusion scintigraphy is single photon emission computed tomography (SPECT). This technique enables the reconstruction of perfusion images in a way similar to the reconstruction of CT images, further improving the diagnostic accuracy of perfusion scintigraphy [68].
The role of nuclear techniques in the diagnosis of RV failure is less well established despite the fact that these techniques play a pivotal role in the diagnosis of left heart disease. In the past, ventricular angiography was frequently used to assess RV volumes and function. Several approaches have been described to measure RV volumes, including SPECT equilibrium radionuclide angiography [69, 70]. Despite the fact that these approaches provide reliable data on RV volumes, its role is limited and has been replaced by echocardiography, magnetic resonance imaging and computed tomography. Recent insights obtained by nuclear imaging techniques are that the metabolic function of the RV is altered in PAH. Several studies showed that in PH the uptake of free fatty acids is decreased whereas the uptake of glucose is increased [71, 72]. In healthy subjects glucose uptake in the RV can barely be seen using fluoro-18-deoxyglucose ([18F]-FDG) positron emission tomography (PET). Figure 6 shows an example of glucose consumption measured by [18F]-FDG PET in the RV in a patient with severe PAH. This image shows that glucose uptake of the RV exceeds glucose uptake of the LV. Kluge et al. found that glucose uptake in the RV is closely related to RV function as measured by echocardiography indicating that a failing RV switches from free fatty acids metabolism to glucose metabolism [73]. In a study by Oikawa et al. it was shown that glucose uptake in the RV can