Lung scintigraphy: Use of different interpretative criteria in patients with low pretest probability for pulmonary embolism

Objectives To investigate the usefulness of different interpretative criteria used in lung scintigraphy in patients with low pretest probability for PE.

Methods In the study were included 62 patients (33 M and 29 F) with low pretest probability for PE (according to Wells’ criteria) in whom ventitilation/perfusion (V/Q) scintigraphy was performed in year 2010. All patients had a chest radiograph performed before V/Q scintigraphy. Mean age of patients was 70. Final diagnosis of PE was a composite based on clinical decision of the attending physician and evaluation of a 6-12 months follow-up period. V/Q scintigraphy: Technegas was used for ventilation studies and 150 MBq of 99mTc-MAA for perfusion studies. Ventilation and perfusion scintigrams were done in at least posterior, anterior, left and right posterior oblique projection. Diagnostic criteria: Modified PIOPED II, PISAPED and 0.5 segment mismatch (SM) criteria were used for scan interpretation. In 0.5 SM criteria we did a little change compared to modified PIOPED II criteria. The only change was that one mismatched defect bigger than 0,5 segment represented nondiagnostic result instead of 1-3 small segmental defects as it is in modified PIOPED II criteria.

Results Results of lung scintigraphy using different interpretative criteria are presented in the table. PE was confirmed as the final diagnosis in 2 patients and it was correctly diagnosed with all three interpretative criteria. PISAPED criteria had also 3 false positive results. There were no false negative results in our study. The percentage of nondiagnostic results is the smallest if 0.5 SM criteria were used.

Conclusions We recommend the use of 0.5 SM interpretative criteria if V/Q scintigraphy is done in patients with low pretest probability for PE. Lung perfusion scintigrapy in combination with PISAPED interpretative criteria are inappropriate for use in patients with low pretest probability for PE.