WORLD OF MEDICINE Gamma Finder, Инструкция по эксплуатации

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Purpose
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8 Purpose
8.1 Counting Time
The gate time of the count defines the time base of the
count value formation. The default gate time of 500 milli-
seconds is a suitable default which means that the position
and angle of the GAMMA FINDER® III must be kept constant
for at least 500 milliseconds for an accurate count.
8.2 Distance to Activity Center
The counting rate is inversely proportional to the square of
the distance to the measured source. Therefore, the
GAMMA FINDER® III should be moved as close as possible to
the assumed center of activity.
8.3 Spatial Resolution
The site-dependent maximum counting rate serves to local-
ize the center of activity. This counting rate, however, also
depends on the angle of the GAMMA FINDER® III to the cen-
ter of activity. Superimposition of both dependencies may
lead to the incorrect localization of the maximum activity.
Therefore, it is recommended within a series of measure-
ments to change the position with a constant angle or the
angle with a constant position. It is recommended to train
this technique using experiments on models. Only with the
W.O.M. WORLD OF MEDICINE GmbH sleeve can the position
of the GAMMA FINDER® III tip to the tissue be properly as-
sessed. Universal covers are not customfitted to this specific
device and the bulkiness occurring in some areas reduces
the effective spatial resolution.
8.4 Counting Rates Corruption
Especially with breast cancer sentinel node detection pro-
cedures, the lymph nodes to be localized are frequently loc-
ated in close proximity of the injection site while the activity
absorbed by the lymph node is about 2 to 3 times less than
the activity of the injection site. Therefore, lymph node
activity is best determined by guiding the GAMMA FINDER®
III so that the injection site activity is not within the range of
sensitivity of the GAMMA FINDER® III and is completely
shielded by the collimator.