Page 122 - Assessing right ventricular function and the pulmonary circulation in pulmonary hypertension Onno Anthonius Spruijt

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failing RV in relation to perfusion, metabolism and power output. For instance, in another study by Wong et al. it was shown that oxygen efficiency was reduced in more advanced right heart failure [77], indicating that mitochondrial dysfunction might play a role. Potential tracers of interest are [18F]-RGD to assess changes in angiogenesis [78] and [11C]-hydroxyephedrine [11C]-HED) and [11C]- CGP-12177 to assess changes in beta-adrenergic receptor density [79, 80] due to sympathetic nerve overactivity in PH.
A future application of nuclear imaging techniques in the field of PH is the use of tracers and radioligands to image the abnormal pulmonary vascular bed. Due to the large space of air and the double circulation of the lung (pulmonary and bronchial) methodological problems need to be solved before reliable answers can be provided and understand the current controversies in literature. For instance, Marsboom et al. found an increased [18F]-FDG uptake in the lungs of patients with PH, giving evidence for the so called glycolytic shift in the pulmonary vasculature [81]. However, Ruiter et al. corrected [18F]-FDG uptake for the decreased perfusion and could not observe this phenomenon [82]. The most interesting development is to image the pathobiology and site of action of drugs and by that guide treatment decisions and monitoring. An example of such a ligand is [11C]RAL-01PDE, a potential phosphodieseterase 5 (PDE5) ligand [83]. In a study by Jacobsen et al. it was shown that this ligand binds to the binding site of PDE5 on the myocardium and lung [83]. The results of this study showed that this ligand has the potential to quantify PDE5 expression in the lung of PAH patients and by that guide therapeutic decisions. A potential tracer to image the increased proliferation of endothelial cells and smooth muscle cells in the small pulmonary arteries is [18F]-fluorothymidine ([18F-FLT) [84], which has yet to be tested in PH.
Conclusions
Both MRI and nuclear imaging techniques are promising emerging techniques in the field of PH. MRI offers not only the possibility to measure accurately RV structure and function and its relation with changes in the pulmonary vasculature, but also provides information on morphological changes of the RV wall and coronary flow. In addition, although the role of MRI is not yet defined, the advantage of MRI to monitor PAH patients is presently well recognized by many clinicians [85]. Although nuclear imaging techniques have not been frequently applied to study RV failure, lessons learned from the LV, especially with respect to perfusion and metabolism, show that this modality can play an important role in the near future.