Lung MRI at 1.5 and 3 tesla

Objectives: To compare the image quality and lesion contrast of lung MRI using 5 different pulse sequences at 1.5 T and 3 T. Materials and Methods: Lung MRI was performed at 1.5 T and 3 T using 5 pulse sequences which have been previously proposed for lung MRI: 3D volumetric interpolated breath-hold examination (VIBE), true fast imaging with steady-state precession (TrueFISP), half-Fourier single-shot turbo spin-echo (HASTE), short tau inversion recovery (STIR), T-2-weighted turbo spin-echo (TSE). In addition to 4 healthy volunteers, 5 porcine lungs were examined in a dedicated chest phantom. Lung pathology (nodules and infiltrates) was simulated in the phantom by intrapulmonary and intrabronchial injections of agarose. CT was performed in the phantom for correlation. Image quality of the sequences was ranked in a side-by-side comparison by 3 blinded radiologists regarding the delineation of pulmonary and mediastinal anatomy, conspicuity of pulmonary nodules and infiltrates, and presence of artifacts. The contrast of nodules and infiltrates (C-NODULES and C-INFILTRATES) defined by the ratio of the signal intensities of the lesion and adjacent normal lung parenchyma was determined. Results: There were no relevant differences regarding the preference for the individual sequences between both field strengths. TSE was the preferred sequence for the visualization of the mediastinum at both field strengths. For the visualization of lung parenchyma the observers preferred TrueFISP in volunteers and TSE in the phantom studies. At both field strengths VIBE achieved the best rating for the depiction of nodules, whereas HASTE was rated best for the delineation of infiltrates. TrueFISP had the fewest artifacts in volunteers, whereas STIR showed the fewest artifacts in the phantom. For all but the TrueFISP sequence the lesion contrast increased from 1.5 T to 3 T. At both field strengths VIBE showed the highest C-NODULES (6.6 and 7.1) and HASTE the highest C-INFILTRATES (6.1 and 6.3). Conclusion: The imaging characteristics of different pulse sequences used for lung MRI do not substantially differ between 1.5 T and 3 T. A higher lesion contrast can be expected at 3 T.