Feasibility of quantitative evaluation of hemodynamics using SPECT/CT in patients with chronic thromboembolic pulmonary hypertension

Abstract Background A ventilation/perfusion (V/Q) lung scan is recommended in the diagnostic work-up of patients with newly diagnosed pulmonary hypertension to rule out chronic thromboembolic pulmonary hypertension (CTEPH). V/Q single-photon emission computed tomography (SPECT) is considered the method of choice for diagnosis in CTEPH because it allows more precise evaluation than planar imaging. However, the evaluation of lung perfusion using V/Q SPECT imaging remains mainly a qualitative evaluation, and no quantitative method has been established. We hypothesized that the standardized uptake value (SUV) technique in Positron Emission Tomography (PET)-CT, a nuclear imaging technique well suited for quantitative of tumor biology, could be applied to quantitative assessment of lung perfusion. Purpose The purpose of this study was to evaluate the correlation between pulmonary perfusion distribution and hemodynamic data in Tc-labeled large-assembly albumin (99mTc-MAA) SPECT images in order to determine the feasibility of SPECT/CT for quantitative assessment of lung perfusion. Methods Twenty-five patients with CTEPH who underwent BPA and received SPECT-CT were included. Since the injected 99mTc-MAA selectively accumulates only in the lungs, SUV normalization was conducted using each patient’s lung volume, calculated by SPECT/CT and defined as SUV lung volume (LV) . The percentage of lung volume below each SUVLV value in total lung volume on SPECT/CT was examined before BPA, after two procedures of BPA, and six months after a series of BPA, and the correlations with hemodynamic parameters on right heart catheterization at each time point were evaluated. Results The Percent lung volume below SUVLV of 0.7 in total lung volume before BPA, after two procedures of BPA, and six months after a series of BPA had the strongest correlation with mean pulmonary artery pressure (mPAP) (rs; 0.727, p<0.001, Figure 1). The percent lung volume below SUVLV of 0.7 decreased with the BPA procedure in each patient with CTEPH (Figure 2). Furthermore, receiver operating characteristic analysis revealed that a threshold for the percent lung volume below SUVLV of 0.7 of 50.3% or greater could identify mPAP greater than 21 mmHg for right heart catheterization (area under the curve = 0.86, 95% CI 0.78-0.94, p<0.001). Conclusion Percent lung volume below SUVLV of 0.7 in total lung volume using SPECT/CT might reflect the severity of hemodynamics in patients with CTEPH. This method would be feasible for quantitative assessment of lung perfusion, even inter-patient and intra-patient.Figure 1Figure 2