MRI of pneumonia in immunocompromised patients: Comparison with CT

PURPOSE Pneumonia is an important cause of mortality and morbidity in immunocompromised patients. Computed tomography (CT) is the most sensitive imaging modality for the diagnosis and surveillance of these patients. Since CT exposes the patient to ionizing radiation, we investigated the utility of magnetic resonance imaging (MRI) in the diagnosis and surveillance of immunocompromised patients with pneumonia. METHODS The study included 40 immunocompromised patients with pneumonia documented on CT. The patients were examined by MRI within 48 hours of CT examination. All images were obtained with three different sequences: balanced fast field echo, T1-weighted turbo spin-echo (TSE), and T2-weighted TSE. Lung abnormalities were evaluated using CT and MRI. RESULTS Infection was determined in 36 patients (90%), while the causative organism remained unknown in four patients (10%). In all the patients, the CT findings were consistent with infection, although three patients showed no abnormal findings on MRI. CT was superior to MRI in the detection of the tree-in-bud nodules, centrilobular nodules, and halo sign (P < 0.001, for all). A significant difference was observed between the MRI sequences and CT in terms of the number of detected nodules (P < 0.001). The nodule detection rate of MRI significantly increased in proportion to the size of the nodule (P < 0.001). All MRI sequences had almost perfect agreement with CT for the detection of consolidation (k=0.950, P < 0.001), patchy increased density (k=1, P < 0.001), pleural effusion (k=0.870, P < 0.001), pericardial effusion (k=1, P < 0.001), reverse halo sign, (k=1 P < 0.001), 10–20 mm, nodules (k=0.896, P < 0.001 for CT and B-FFE; k=0.948, P < 0.001 for CT and T1-or T2-weighted imaging) 10–20 mm, >20 mm nodules (k=0.844, P < 0.001). CONCLUSION Although CT is superior to MRI in the diagnosis of pneumonia in immunocompromised patients, MRI is an important imaging modality that can be used, particularly in the follow-up of these patients, thus decreasing to avoid ionizing radiation exposure.