Characterization of solitary pulmonary nodules using double phase Tc-99m methoxyisobutylisonitrile scan: Comparison of visual and quantitative analyses

Background: We assessed the diagnostic usefulness of Tc-99m methoxyisobutylisonitrile (MIBI) single photon emission computed tomography (SPECT) for the evaluation of solitary pulmonary nodule (SPN).

Methods: Thirty-five patients (17 malignant and 18 benign) were recruited. Double phase Tc-99m MIBI SPECT was performed 10 min and then 2 h after an injection of 925 MBq of Tc-99m MIBI. Visual interpretation grades of the Tc-99m MIBI scan were used for the determination of SPN characteristics. Receiver-operator curve analyses were performed for the optimal cut-off values of visual and quantitative indices for differentiation of benign and malignant SPN.

Results: The optimal visual grades were grade 4 and 5. When 3+ was used as the cut-off value for the detection of malignant SPN, the sensitivity and specificity of Tc-99m SPECT were 47.1% and 88.9%, respectively. The area under curve (AUC) was 0.758. The optimal planar lesions to non-lesion (L/N) ratios were 2.3 for the early image and 1.6 for the delayed image. The optimal SPECT L/N ratios were 3.1 for the early and 1.6 for the delayed image. The SPECT early L/N was superior to other quantitative indices and visual analysis.

Conclusion: This study shows that Tc-99m MIBI SPECT is a useful non-invasive method for the evaluation of SPN.