PubMed · 7969995
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T Lempert. 1994. Horizontal benign positional vertigo.. https://doi.org/10.1212/wnl.44.11.2213-a
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Interpolation between slices is necessary whenever reslicing a volume of data into a different coordinate frame. This may be done to view the data from different perspectives, to align data from different sessions, or to remove the effects of head movement in functional imaging studies. In this paper, issues surrounding slice-selection in two-dimensional imaging are examined in the context of through-plane interpolation and a spectral framework is introduced to describe the sources of error when interpolating between slices. This framework suggests that there is a trade-off between precision in localization, which requires high spatial frequencies, and interpolation, which requires a narrow spectrum of spatial frequencies. An analysis of the sources of error has lead to several approaches to reducing interpolation error including elimination of interslice gaps or making slices overlap, use of a slice profile with a narrower spatial frequency bandwidth such as a Gaussian profile, and use of high-order interpolation. The simulation and experimental data demonstrate significant reductions in interpolation error for these approaches.
We investigated the contribution of somatosensory and vestibular inputs in the detection of the direction of linear whole-body displacement (1.5 m) at low levels of linear acceleration (peak acceleration 0.2 m/s2), in normal subjects. Subjects sat on a mobile robot wearing opaque goggles and headphones. They indicated the direction of motion by using a laser pointer held by the right hand at the level of the chin. Adaptation to a long-lasting static head turn (45 degrees to the right) was used to modify the perceived head orientation relative to the trunk. After about 15 min the head and trunk were perceived to be aligned with each other. After adaptation subjects pointed in the same direction as in the control condition in spite of the change in the perception of the head orientation. Because space orientated reactions to vestibular stimuli were previously shown to be coded in the perceived head reference frame, these results indicate that somatosensory cues are also integrated in the perception of linear motion. Unexpectedly, after adaptation, trunk and head perceived orientations were attracted toward the direction of the imposed motion. This suggests that the internal representation of body configuration depends also upon available cues from the extrapersonal space.
CT is a high-dose examination and possibly the dominant contributor to dose from diagnostic radiology. Estimates of organ doses are obtained from Monte Carlo calculations and used to quantify radiation risk. To ensure the validity of using Monte Carlo calculations to estimate actual dose, measurements must be compared with calculations. We have measured doses to CT head and chest dosimetry phantoms and compared them with Monte Carlo (EGS4) calculated doses in voxel-based computational models of the phantoms. The simulation used an x-ray spectrum calculated from the specified values of the scanner's x-ray tube parameters. The scanner's beam-shaping filter was included in the modelling. Measured and calculated doses to both the head and chest phantoms agreed to within 7%. The inclusion of Rayleigh scattering in the calculations has a significant effect if only one slice is scanned but not if multiple slices are scanned.