Contemporary SPECT/CT V/Q scanning: protocols, pearls and pitfalls

Lung scintigraphy has withstood the test of time having been in use for over 60 years. It has evolved today to a tomographic modality with optimal radiopharmaceuticals for both ventilation (V) and perfusion (Q) imaging using technetium-99m radiolabeled agents. In addition to the SPECT imaging of V and Q, today's multimodality imaging devices can add low-dose CT to provide anatomical correlation further improving the sensitivity and, in particular, specificity of lung scanning for pulmonary embolism (PE). Lung scanning has moved beyond just imaging for PE now to assessing regional lung function and the matching between ventilation and perfusion for optimal gas exchange. This helps guide decisions regarding surgical and similar interventions. The enhanced capability afforded by SPECT/CT imaging of regional ventilation and perfusion also brings some attendant challenges such as apparent artefacts due to ventilation patterns that exceed normal perfusion at the borders of the lungs. However, with appropriate experience, the lung scan can now produce an answer on the diagnosis of PE in better than 95% of cases with few indeterminate reports.