Comparison of mip and vr with average at various slab thickness in mdct for detecting pulmonary nodules

Introduction: Lung cancer found to be the most common cause of death worldwide. Early detection of pulmonary nodules can improve the survival rate of the patients suffering from lung cancer. In case of patients with known pulmonary metastasis, infection, other diseases the presence of bilateral pulmonary nodules is an indicative of metastasis. Objective: to compare the detection rate of pulmonary nodules in MIP and VR and to find out best slab thickness. Materials and methods: 15 patients referred for HRCT who had < 20 nodules in each lung on source (1mm) images and who did not have any evidence of fibrosis in lungs were included. The source images were reconstructed into MIP and VR (slab thickness: 4, 7 and 11 mm; Interval: 3.5mm). Two radiologists independently evaluated different thickness of MIP and VR in separate sittings and documented the number of nodules with size and density of each nodule. Difference between the number of nodules detected on MIP and VR at various thickness was assessed using Wilcoxon sign rank test and p values were calculated to assess the significance. Results: Both readers detected more nodules on VR as compared to MIP (Total nodules on VR: 493, Total nodules on MIP: 467) with p- value being 0.262, indicating that there was no statistical significant difference between both techniques. Slab thickness of 11mm was best for nodule detection on MIP (p value: 0.027); however, there was no statistically significant difference between 7 mm and 11 mm thickness on VR (p: 0.3). 11 mm MIP was also better than the other thickness in detection of low density nodules (p: 0.039); but there was no significant difference in the detection of high density nodules (p: 0.131). Conclusion: MIP and VR were equally accurate in detecting lung nodules. 11mm MIP detected significantly more number of nodules than 7 mm, but both thickness were equally accurate on VR.