Validation study of a pulsed arterial spin labeling technique by comparison to perfusion computed tomography.

Abnormalities in cerebral blood flow (CBF) are believed to play a significant role in the development of major neonatal neuropathologies. One approach that would appear ideal for measuring CBF in this fragile age group is arterial spin labeling (ASL) since ASL techniques are noninvasive and quantitative. The purpose of this study was to assess the accuracy of a pulsed ASL method implemented on a 3-T scanner dedicated to neonatal imaging. Cerebral blood flow was measured in nine neonatal piglets, the ASL-CBF measurements were acquired at two inversion times (TI) (1,200 and 1,700 ms), and CBF was measured by perfusion computed tomography (pCT) for validation. Perfusion CT also provided images of cerebral blood volume, which were used to identify large blood vessels, and contrast arrival time, which were used to assess differences in arterial transit times between gray and white matter. Good agreement was found between gray matter CBF values from pCT (76+/-1 ml/min per 100 g) and ASL at TI=1,700 ms (73+/-1 ml/min per 100 g). At TI=1,200 ms, ASL overestimated CBF (91+/-2 ml/min per 100 g), which was attributed to substantial intravascular signal. No significant differences in white matter CBF from pCT and ASL were observed (average CBF=60+/-1 ml/min per 100 g), nor was there any difference in contrast arrival times for gray and white matter (0.95+/-0.04 and 0.99+/-0.03 s, respectively), which suggests that the arterial transit times for ASL were the same in this animal model. This study verified the accuracy of the implemented ASL technique and showed the value of using pCT to study other factors that can affect ASL-CBF measurements.

Light alters nociceptive effects of magnetic field shielding.

Orientation and nociception (pain sensitivity) are affected by exposure to geomagnetic or low frequency (<1,000 Hz) magnetic fields of approximately the earth's field strength, i.e., 50 microT. However, these effects are often dependent on the simultaneous presence of visible light. Recently, it was shown that nociception was affected in mice acutely exposed to an electromagnetic-shielded environment in the dark (<0.05 W/m(2)) during the mid-light phase of the diurnal cycle. Here, we report for the first time that if mice are exposed to magnetic shielding in the presence of visible light (0.6 W/m(2), 400-750 nm) that most of the effects of shielding are eliminated. This simple experimental protocol may be useful in investigating the role that light plays in the detection of ambient electromagnetic fields.