5. Measurements with the Barracuda System
CT
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Barracuda & QABrowser Reference Manual
5.8.3 CT Scan Time (Exposure Time)
You must use a CT chamber when measuring the exposure time or scan time. You can
follow the point #1 to #11 in the description of how to measure CTDI to measure the
scan time. Read previous topic CT Dose and CT Dose Index (CTDI) to get a detailed
description. Of course is the CT phantom not required if only the scan time is of
interest.
5.8.4 CT mAs
How to measure mAs is described in the topic mAs Measurement .
5.8.5 Parameters for CT Scanner Models
The Barracuda kV CT calibrations are specified as follows:
C1 = W/3.0 mm Al
C2 = W/3.0 mm Al + 0.25 Cu (optional)
C3 = W/3 mm Al + 1.2 mm Ti (optional) (for Siemens Somatom Definition 32 and
similar)
With the calibration C1 the total filtration can be measured and the Barracuda
automatically corrects the kV value accordingly. It is optional to set a known total
filtration instead, see the table below. To achieve optimal measurements of the total
filtration, first perform a measurement at a low kV, preferable 80-100 kV. The
measured total filtration is displayed on the screen. Press "Keep" to store the value
and carry on with measurements. Now you can be certain to have a correct total
filtration and kV-value throughout the measurements. Further information about the
total filtration can be found in section HVL & Total Filtration or in the Application
Note 1-AN-52020-14 from RTI Electronics AB, see your product CD or www.rti.se.
Essential for correct measurements are correct settings of the CT. The book "Radiation
Exposure in Computed Tomography" by H.D. Nagel, contains useful information about
how correct settings are done on different types of CT scanners. A computer
application CT-Expo based on the book may also be of great help. CT-Expo is an MS
Excel application written in Visual Basic used to calculate patient dose values resulting
from CT examinations. The program is applicable for all existing scanner models and
can be of assistance to make correct settings.
References
1.
Nagel, H. D. Radiation Exposure in Computed Tomography. Fundamentals, Influencing
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