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Abstract
Background Lung perfusion scan is widely undertaken as part of the assessment to select most affected lobes by emphysema prior to lung volume reduction (LVR) therapies by endo-bronchial valves, endo-bronchial coils and LVR surgery. More recently quantitative CT scans (QCT) have been introduced. QCTs quantify the degree of lung destruction by emphysema. To date there are no studies to evaluate whether lobar uptake of isotope by perfusion scan and areas of destruction on QCT’s are closely correlated.
Methods Patients referred for LVR therapies at our hospital underwent perfusion scans using single-photon emission computerised tomography (SPECT) scans. The degree of uptake of isotope in each lobe is visually scored from 0–10, 0 representing low lobar isotope uptake and 10 high uptake. The degree of lobar low attenuation area (emphysema) has been assessed by a QCT scan. This scan provided data on the proportion of each lobe with attenuation of −910 Hounsfield Units (HU) and −950 HU. Uptake on SPECT has been correlated with emphysema score on QCTs.
Results A total 47 patients are included (20 female). Their mean age 66.2 years, and mean FEV1 30% of predicted values. Analysis by QCT and SPECT is available on 235 lung lobes. For all lung lobes, mean low attenuation at −910 HU was 53.7% and at −950 HU of 36.9%. Median Score on SPECT was 5.3 points. A weak correlation between uptake score on SPECT and QCT scores; Spearman r=-0.33, p<0.0001 for emphysema area at −910 HU and r=-0.33, p<0.001 for emphysema area at −950 HU. Significant discordance is present between the two methods (graph.1) which could lead to either treating lobes with low perfusion but preserved lung tissue or not treating lobes with high perfusion but with significant emphysema.
Conclusion Despite the wide usage of perfusion scan to guide identification of lung lobes targeted for LVR, this study shows that this method needs to be interpreted with caution. QCT’s should be relied upon to choose lobes needing treatment. Longitudinal analysis is needed to evaluate the outcome of treatment when the treated lobe was selected according to low perfusion.