In multi-inversion EPI (MI-EPI), each slice samples a distinct inversion time during each inversion recovery, providing an efficient method for estimating T1. MI-EPI is vulnerable to through-plane motion, which results in slices sampling a subset of the desired inversion times and wrong TIs will be attributed to the slices. This cannot be corrected retrospectively. We introduce prospective motion correction in MI-EPI using volumetric navigators (vNavs). vNavs are acquired at the beginning of the inversion recovery thus the effects of their excitation pulses must be modeled for T1 estimation. This provides improved T1 estimation accuracy in the presence of subject motion.
The quantification of the effects of low‐level radiation is based
mainly upon epidemiological studies. Recent reassessment of the data
from Japanese survivors of the effects of radiation from Second World
War bombing and from ankylosing spondylitis patients reveals an
increased risk of leukaemia from low level exposures. The implications
for the health of radiation workers and the management of the nuclear
power industry are important. There is controversy over possible
hormetic effects. A true hormetic effect has to be seen to affect the
whole person. Although there is evidence at the cellular level that
low‐level radiation may enhance the body′s immune system, this is not
sufficient to justify widespread scientific support. This is
particularly since the speculation on the effects of low‐level radiation
and the connection with the occurrence of leukaemia is creating concern.
The increases in the incidence of disease and the pattern of
distribution remain difficult to explain while the task of translating
the evidence from individual cases proves increasingly difficult in the
context of varied types of radiation and the properties of particular
radionuclides.
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