Incremental benefit of maximum-intensity-projection images on observer detection of small pulmonary nodules revealed by multidetector CT

OBJECTIVE. Our purpose was to assess the incremental effect of maximum-intensity-projection (MIP) image processing on the ability of various observers to detect small (<1 cm in diameter) central and peripheral lung nodules revealed by multidetector CT. MATERIALS AND METHODS. We retrospectively identified 25 patients with metastatic disease, each having from two to nine nodules that were 3-9 mm in diameter. Two senior and three junior reviewers interpreted all images on a workstation. The observers first reviewed axial images (3.75-mm collimation, 3-mm reconstruction interval, multidetector acquisition) in cine and sequential fashion and recorded the size, lobe, and central or peripheral (within 1 cm of the edge of lung) location of each nodule. MIP images (10-mm slab, 8-mm interval) were then reviewed, and additional nodules detected were recorded. Final counts were established by consensus. RESULTS. The reviewers found 122 nodules (71 peripheral, 51 central) in the 25 patients. The addition of MIP slabs significantly enhanced reviewer detection of central nodules (p < 0.001) and junior reviewer detection of peripheral nodules (p < 0.001). MIP slabs also reduced the effects of reviewer experience, particularly for peripheral nodules. CONCLUSION. MIP processing reduces the number of overlooked small nodules, particularly in the central lung. Observer nodule detection remains imperfect even when lesions are clearly depicted on images.