Comparison of Lymphotropic Nanoparticle-Enhanced MRI Sequences in Patients with Various Primary Cancers

Abstract

This study was performed to empirically evaluate T2-weighted fast spin-echo, moderately T2*-weighted gradient-refocused echo (GRE), and heavily T2*-weighted GRE sequences to determine which sequence is the most effective for nodal characterization on lymphotropic nanoparticle-enhanced MRI (LNMRI). The study included 65 patients who had proven primary cancer and were scheduled for either surgical lymph node dissection or imaging-guided lymph node biopsy. All patients underwent LNMRI using T2-weighted fast spin-echo, moderately T2*-weighted GRE, and heavily T2*-weighted GRE sequences. Unequivocal correlation of histopathology and MRI could be made in 140 nodes and only these were included in the analysis. Two blinded reviewers performed qualitative analysis of the nodes. Alternative free-response receiver operating characteristic (ROC) curves with a continuous rating scale were plotted for each sequence for both reviewers and the diagnostic accuracy of fast spin-echo T2-weighted and GRE T2*-weighted images were compared by calculating the area under the curve (A(Z)). A two-tailed Student's t test was performed to test the significance (p < 0.05) of the differences between the ROC curves derived from the three sequences. Irrespective of reviewer experience, T2*-weighted sequences showed better nodal characterization when compared with T2-weighted sequences. For both reviewers, there was a statistically significant difference between the A(Z) for T2- and the two T2*-weighted sequences (p < 0.05). Neither reviewer showed a statistically significant difference between the two T2*-weighted sequences. GRE T2*-weighted sequences are superior for nodal characterization on LNMRI to fast spin-echo T2-weighted sequences. Imaging protocols for LNMRI should include fast spin-echo T2-weighted imaging for anatomic localization, but characterization of nodes should be based on their appearance on contrast-enhanced T2*-weighted images. The T2*-weighted images acquired with dual TE values, one of which is intermediate and the other longer, improve nodal characterization.