Topics covered in this article include:

Introduction

IBA CT-IQ is a CT phantom for conducting acceptance and constancy tests in accordance with IEC 61223-3-5 and the AAPM guidelines, ensuring reliable and accurate result. Its versatile design allows for precise alignment for measurements both on and off the CT table, providing the necessary flexibility to suit a range of testing scenarios.

Measurement Summary

The analysis provides the following results:

Sensitometry Target Values
Geometry: Geometric Accuracy (by Segment)
Geometry: Geometric Mean Distances
Geometry: Slice Thickness and Detail Plot
Uniformity: Abs. Max. Deviation from Center ROI
High Contrast/Resolution: Line spread function (LSF) from wire
High Contrast/Resolution: Modulation transfer function (MTF) from wire
High Contrast/Resolution: Critical Frequency (Wire)
High Contrast/Resolution: CNR ROI Detail
High Contrast/Resolution: Contrast to Noise Ratio (the contrast-to-noise ratio between the PTFE object and PMMA background)
High Contrast/Resolution: Noise
Low Contrast: Smallest Detected Target
Low Contrast: Statistics
Low Contrast: Constant Contrast vs LC Target Diameter

The measurements are completely automated, requiring the user only to drag and drop the image set into the web-based software interface. A detailed report is created.

Instructions

The test requires a full contiguous scan of the phantom and each slice must be a separate DICOM file. The files must contain "iba_ct_iq" somewhere in the file name or that "IBA CT IQ" is selected in the Type drop down as shown below:

When imaging QA tests are added to templates an upload control will appear in the scheduled QA's data entry screen allowing the user to upload images for automated analysis.

To add files to the upload queue simply drag them from a Windows Explorer folder to the drag and drop folder and release them. Alternatively, by clicking on the Add Files button to the lower right of the control a windows file selection dialog will open and files can be selected for upload. Under either method, multiple files may be selected for upload at once.

If the automatically upload checkbox is checked (the default) then file uploading will start immediately as files are added.

If the automatically upload button is turned to off the file upload process must be started manually clicking the Start upload button on the lower right of the control. To clear the upload queue click the Clear button.

Once file series have been uploaded they will be displayed below the upload control. To remove a series from the queue click the Cancel button beside the series. To start processing click the Start Processing button. A description for the image series can be added at this point. Click the Edit button next to the series. Type a description for the series into the text box that appears below Description and either click Save or press the enter key. The description can also be edited after the images have been processed. Descriptions will appear in the report with the analysis of the series.

While files are being processed users may perform other tasks such as data entry.

Image Acquisition Suggestions

Reference the latest manufacturer's guidance for phantom placement and scan acquisition parameters. The image set should include a full, contiguous scan of the phantom.

Detailed Discussion of Measurements

Sensitometry

The CT IQ analysis detects and measures the mean and standard deviation of each material in the phantom in a 200mm2 circular ROI centered on the sensitometry targets. For PMMA (the module's body material), an ROI is taken at the center of the phantom.

Geometry

Geometric Accuracy

The geometric accuracy module has two sets of four rods arranged in squares with a 45-degree rotation between the sets.

The thicker rods (5mm) are designated with the letters A, B, C, and D. The thinner rods are designated by the numbers 1 through 4. The nominal distance between the rods in each square is 100mm. The actual distance is measured and compared to the nominal distance for each side of the two sets.

The mean distances for each set are reported, and the Mean Absolute Deviation of both sets' sides is reported.

Slice Thickness

There are four slice-thickness ramps in the geometric module. A FWHM measurement is taken for each slice thickness ramp. If the ratio of the nominal slice thickness to the axial pixel spacing is less than 2.5, a composite image of three slices is produced to improve the signal for a more accurate measurement. The final measurement is scaled to a single slice.

The slice thickness is measured for each ramp. The mean of all four ramps is compared to the nominal thickness from the DICOM header, and an absolute and percentage deviation is reported.

Uniformity

The uniformity module measures the mean and standard deviations of 50mm2 ROI’s located in the center of the phantom ad at the four cardinal angles towards the edges of the phantom. Each edge ROI’s mean value is compared against the center ROI. The ROI with the maximum deviation is identified.

High Resolution

The high-resolution module produces MTF, and line spread function measurements from 0.25mm stainless steel wire. Contrast-to-noise measurements are also made on the PTFE/PMMA interface.

Resolution

An MTF and LSF plots are displayed along with MTFs at critical frequencies.

CNR Measurements

CNR measurements are taken between the PTFE and PMMA (background) areas.

Low Contrast

The low-contrast objects are detected and measured in each of the 1%, 0.6%, and 0.3% nominal contrast series.

The smallest diameter object that can be discerned against the background is reported for each series.

Contrast-to-noise measurements are made of the detected targets, whereas a background ROI is taken 18mm closer to the phantom center at the same angle as the target.

The constant contrast (contrast% x target diameter (mm)) is plotted for each of the three series