Smiths Medical Pneupac babyPAC 100, Руководство пользователя

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504-2056A 50
the field and trial disconnections and high airway pressures were always correctly indicated.
A small reduction in the set level of the inflation pressure relief valve was observed, the
maximum change being about 12% in the 3 Tesla field, but in normal use this valve will be
set with sufficient margin for this change not to affect the ventilation. Similarly the inflation
manometer deviated by up to 3 x100Pa (3cmH
2
O) at the position of maximum field
gradient. Neither of these deviations was evident at the intended position of use – outside the
bore of the magnet.
(iv) Imaging Tests
Imaging tests were performed using the body gradient set with either head or body RF coils
(transmit and receive). A tissue mimetic phantom was placed inside the head RF coil to
simulate a person’s head. This consisted of a Perspex cylinder filled with a copper sulphate
and salt solution to mimic the electrical properties of the head.
(v) Effect of switching gradients
A standard echo planar pulse sequence was run whilst the paraPAC ventilator was at the
position of maximum gradient switching (1m from the magnetic isocentre). This sequence
was chosen for its high switching rates and values. The maximum gradient value used at
this position was +/- 13.3mT (566396Hz) (EPI alternates from high positive gradient to high
negative gradient in 452
μ
s) giving a switching rate of 29.43T/s (1253Hz/
μ
s). This process
is repeated after 214
μ
s with the polarity switching again. This was run continuously whilst
observing the ventilator. No effect due to magnetic field switching could be detected.
(vi) Effect of RF fields
A standard inversion recovery spin echo sequence was run with the paraPAC ventilator at
the edge of the RF coil. This sequence was chosen because of its high RF load (0.4W/kg for
the head coil and 0.82W/kg for the body coil). No effects were seen resulting from
interaction of the system RF with the ventilator.
(vii) Image quality
A standard spin echo sequence (employing both transverse and coronal views), used for
daily quality assurance, was used to test for any RF interference due to RF emissions from
the paraPAC ventilator. No spikes in the images were observed, indicating no RF
interference. Placing the ventilator control module next to the phantom’s edge did, as would
be expected, cause a magnetic susceptibility artifact due to the presence of the metallic
contents near the imaging volume. When the control module was situated at the base of the
head cradle, 21cm away from the phantom’s edge, no RF interference or susceptibility
artifact was observed.