99mTc-MAA/81mKr dual isotope ventilation-perfusion ratio distribution after unilateral lung transplantation

Aim: Dual isotope planar lung scintigraphy (DIPLS) realized with 99mTc-macroaggregated albumin (99mTc-MAA) and 81mKr is a useful tool for the characterization of lung ventilation-perfusion ratio (VA/Q) distribution. Previous studies have shown a relative mismatch in ventilation and perfusion in both the transplanted and native lungs after unilateral lung transplantation (ULT). The aim of our study was to describe and evaluate the significance of quantitative variables derived from DIPLS VA/Q distribution histograms after ULT. Material and Methods: 14 patients (6 women and 8 men; mean age 56 y; range 45-69 y) who underwent ULT (10 right, 4 left) for emphysema (n=5), lymphangiomyomatosis (n=5) and pulmonary fibrosis (n=4) were studied. Arterial blood gases, 99mTc-MAA/81mKr DIPLS, and forced expiratory volume in the first second (FEV1) were measured in all patients. Lung regions of interest were drawn manually on posterior view of the ventilation-perfusion scans and a corresponding VA/Q functional image reflecting a pixel-by-pixel VA/Q ratio was computed. VA/Q lung distribution histograms were computed by plotting the percentage of overall perfusion counts against VA/Q on a log scale abscissa for both the native and the transplanted lungs and the corresponding standard deviations were calculated from the % perfusion-VA/Q distribution histograms (sdP for both lung, TsdP for the transplanted lung and NsdP for the native lung). The mode of the transplanted (Mt) and native (Mn) lungs %perfusion-VA/Q distributions and the relative perfusion of the transplanted lung (RP) were also computed. Results: The RP values were 89%±9% with a range of 75-99%. Bimodal distribution of %perfusion-VA/Q distribution was encountered in 12/14 patients and the mode of these VA/Q distribution histograms were higher in native lung than in transplanted lung (1.86±0.65 versus 0.76±0.12, p<0.0001). The difference Mn-Mt showed significant correlation with sdP (r=0.913, p<0.001) and NsdP (r=0.769, p=0.001) but no significant correlation with TsdP (r=0.311, p>0.05). Significant correlation with arterial PO2 was encountered with TsdP (r=-0.708, p=0.005) but not with the other parameters (sdP, NsdP, Mn, Mt, RP). As opposed to the other parameters, TsdP tended to be correlated to FEV1 (r=-0.51, p=0.06). Conclusion: TsdP reflects ventilation-perfusion inequality of lung transplant. It is correlated with arterial PO2 and tends to be correlated with FEV1. The other parameters (sdP, NsdP) reflecting DIPLS VA/Q distribution heterogeneity are correlated to the difference between Mn and Mt and reflect the high VA/Q ratio observed in native lung after ULT