Image Series Checks - Overview

1 Scan Protocol

The person who acquires the image series has the responsibility to review the images, and verify they meet the specifications listed on data sheets. Responsibilities also include means and standard deviation measurements, and keeping a record of failures that occur during the image series.

Unless otherwise stated, use the following scan parameters during the image series acquisition:

• Scan FOV equal to display FOV (Field of View)

• 512x512 matrix size

For means and standard deviations, 90% of the slices must pass. Any failure on a particular technique requires at least ten additional slices to evaluate effectively.

Systems with metal-free cradles have a phantom holder with a perpendicular adjustment (Z-axis) knob on it. Each time you change phantoms, make sure you use a bubble level, and the Z-axis knob on the phantom holder, to level the phantom.

2 Data Recording: Means and Standard Deviation

Any failure on a particular technique requires at least a ten additional slices to evaluate effectively. For means and standard deviations, 90% of the slices must pass.

• Record means to two decimal places, and round to the nearest one-tenth, (one decimal place) when you compare the resulting values to the spec.

• Record standard deviations to two decimal places, then round off to one decimal place, to compare it to the spec.

• Average standard deviations: Use two decimal places to average the values, then round off to one place.

Before you record the means and standard deviations, check the image data sheets to determine whether to average the means and standard deviations, or record them slice by slice. Make sure you record all the required image data on the HHS data sheets.

3 Term Definitions and Screens

Xc

Mean CT number for the specified center coordinates of the phantom image.

AvXc

Average Mean CT number for the center of the phantom image: Average the mean CT value for all specified center coordinates of all slices in an exam.

Xo

Mean CT number for the outside of the phantom image: Average the mean CT value for all specified outside coordinates of one slice.

AvXo

Average outside mean CT number for the number of slices in an exam.

AvSDc

Average image noise about the center image coordinate (measured as the standard deviation) of all slices in an exam.

AvSDo

Average image noise (standard deviation) for the outside of a phantom: Average of all outside coordinates of all the slices in an exam.