Since the current emphasis of PAH therapeutics is to reverse the proliferative remodeling or regenerate the pulmonary circulation, molecular imaging end points will become increasingly relevant in the assessment of these patients. For example, promising vascular proapoptotic therapies, whether by drugs,3,5 or gene therapies,4 or cell-based regenerative approaches2 will require a means of anatomic and functional imaging of the pulmonary circulation. Some of these therapies2 have already entered clinical trials. The pulmonary circulation in PAH patients is difficult to be assessed with standard contrast angiography because of the complexity and high-risk nature of the required direct high-pressure injections. Simple injection of the relatively nontoxic gadolinium from a peripheral vein allows for beautiful imaging of the pulmonary circulation using MRI (Fig 1
, top, A). At the same time, preliminary protocols are being developed to image lung perfusion into the diseased lung in a manner similar to the commonly used single-photon emission CT-based coronary perfusion studies (Fig 1, top, A; and personal communication; Richard Thompson, PhD; November 2006). Such protocols allow for a quantitative analysis of lung perfusion, which if used “before and after” therapy, will allow both anatomic and perfusion/functional assessment of regenerative therapies. At the same time, more standard protocols can also be applied in order to estimate PA systolic and diastolic pressures, and measure RV mass and volume (Fig 1, center, B), RV perfusion, RV systolic function and, as the authors now show, diastolic function.