Can CT co-registration improve the accuracy of segmental localisation on V/Q SPECT?

  • Dr Denis Gradinscak, Royal North Shore Hospital Sydney, Australia
  • A/Prof Paul Roach, Royal North Shore Hospital Sydney, Australia
  • Dr Geoff Schembri, Royal North Shore Hospital Sydney, Australia
  • Ms Elizabeth Bailey, Royal North Shore Hospital Sydney, Australia

    • Objective: To determine the accuracy of anatomical localisation of mismatched perfusion defects on V/Q SPECT using CT.

    Methods: 30 patients with suspected pulmonary emboli (PE) and positive SPECT VQ scans who also underwent CTPA within 48 hours were included. Perfusion defects on SPECT were localised by 2 experienced Nuclear Medicine physicians to pulmonary segments using a normal lung tomographic segmental lung chart as a guide. Perfusion SPECT and the CTPA were fused on a HERMES workstation and the CT data used to determine the accuracy of their anatomical localisation of perfusion defects in each patient.

    Results: A total 96 mismatched perfusion defects were reported. Using CTPA fusion, anatomical localisation on SPECT alone was concordant with the individual patient’s anatomy on CTPA in 78/96 (81%) cases. 18/96 (19%) perfusion defects localised to discordant pulmonary segments on CTPA. Discrepancies were most commonly seen in the mid-zone segments of each lung (R lung - middle lobe, posterior segment RUL, L lung - lingula) and were most noticeable in patients with evidence of lower lobe volume loss on CT.

    Conclusion: The addition of CT improves anatomical localisation of perfusion abnormalities on V/Q SPECT particularly in patients with lower lobe parenchymal abnormalities associated with volume loss on CT. The most frequent added benefit of CT for anatomical localisation was in the mid-zones of the lungs.