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Projection data from 83 patients undergoing unenhanced spiral head CT for suspected neurologic deficits were collected. A routine dose was obtained using 250 effective mAs and iterative reconstruction. Lower-dose configurations were reconstructed (25-effective mAs iterative reconstruction, 50-effective mAs filtered back-projection and iterative reconstruction, 100-effective mAs filtered back-projection and iterative reconstruction, 200-effective mAs filtered back-projection). Three neuroradiologists circled findings, indicating diagnosis, confidence, and image quality. The routine-dose jackknife alternative free-response receiver operating characteristic figure of merit was 0.87. Noninferiority was shown for 100-effective mAs iterative reconstruction and 200-effective mAs filtered back-projection, but not for100-effective mAs filtered back-projection. The authors conclude that substantial opportunity exists for dose reduction using spiral nonenhanced head CT and that the dose level might potentially be reduced to 40% of routine dose levels or a volume CT dose index of approximately 15mGy if slight decreases in performance are acceptable. The beneficial effect of iterative reconstrution was most pronounced at this 15-mGy dose level.

Brain MR imaging scans of National Aeronautics and Space Administration astronauts were retrospectively analyzed to quantify pre- to postflight changes in brain structure. Local structural changes were assessed using the Jacobian determinant. Structural changes were compared with clinical findings and cognitive and motor function. Long-duration spaceflights aboard the International Space Station, but not short-duration Space Shuttle flights, resulted in a significant increase in the percentage of total ventricular volume change (10.7% versus 0%). The percentage of total ventricular volume change was significantly associated with mission duration but negatively associated with age. Pre- to postflight structural changes of the left caudate correlated significantly with poor postural control, and the right primary motor area/midcingulate correlated significantly with a complex motor task completion time. These findings suggest that brain structural changes are associated with changes in cognitive and motor test scores and with the development of spaceflight-associated neuro-optic syndrome.