Cirs ATS539 - Dead Zone Assessment

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DEAD ZONE ASSESSMENT
The dead zone is the distance from the front face of the transducer to the rst
identiable echo at the phantom/patient interface. In the region of the dead zone no
clinical data can be collected. The dead zone occurs because an imaging sys-
tem cannot send and receive data at the same time. The depth of the dead zone
depends upon the frequency and performance of the transducer and the pulsing/
receiving section of the system.
The depth of the dead zone may be measured as follows:
1. Place the phantom on a clean, at surface with scanning surface #1
positioned for use.
5. Freeze the image and obtain a hard copy.
6. Examine the image to determine the rst and last target in each size group
displayed. Record the range of depths visualized for each group. Due to the
conguration of the sound beam small targets in the near eld may not be
imaged.
7. All ndings should be documented on the quality assurance record.
Results:
The targets should appear circular with sharp clearly dened edges, indicating an
abrupt transition from the echogenic to the anechoic region. The targets are an-
echoic and should be free of any internal echoes or ll-in. However, the presence of
internal system noise may manifest itself by producing an observable shade of gray
within the target area.
The specic values determined, while signicant in their own right, are somewhat
less important than stability over time. Performing this test on a routine basis at the
same instrument settings should produce the same results. Any changes should be
investigated.