This help page gives information on the data and graphical displays in each section of the report.

**Please Note:** For more information on the calculations and physics background for each section of the report, please view the corresponding help page in the "Physics Background" section of this help pages.

# Positional Information

Positional information is given for the following Catphan® models: 500, 503, 504, 600, 700

## Center of Phantom

The center of the phantom described is the pixel coordinate in the center of the phantom (in pixels).

## Rotation

Degrees of phantom rotation around the z-axis.

## Tilt

Degrees of phantom rotation around the x-axis.

## Yaw

Degrees of phantom rotation around the y-axis.

# Low Contrast

Low contrast information is given for the following Catphan® models: 500, 504, 600, 700

## Contrast Detail Plot

The contrast detail plot corresponds to the contrast detail values. The plot is calculated using the formula *contrast = constant/diameter. *The Image Owl algorithm computes the y-axis (contrast) values for every diameter rod (x-axis).

## Contrast Detail Values

Low contrast values are based on three factors: nominal contrast, estimation of noise, and a detection level.

The nominal contrast is the difference in CT number between the background (HU_bg) and the target (HU_target). (HU_target - HU_bg)/10HU = %contrast To estimate the noise, two rows (inner and outer) of circles are generated for each target size (mm) and a standard deviation is calculated from the mean HUs for each circle.The detection level is a perceptibility factor, the Image Owl algorithms use 4, times the SD for each target size.

More information on low contrast calcuation can be found in the Low Contrast page of the Physics Background section of these help pages.

# Sensitometry

Sensitometry information is given for the following Catphan® models: 500, 503, 504, 600, 700

## Linearity Plot

The CT linearity measurements come from a representative slice. The representative slice is the slice closest to the median of the estimated effective energy. The CT measurements from this representative slice are then used for the plotted points in the graph below. This plot is the optimal linear fit of measured CT numbers vs. attenuation coefficient from the linear attenuation coefficienct table values.

*The "Table Values" can be found in the linear attenuation coefficient table in the Sensitometry Physics Help section. *

#### Sensitometry Header Information

The data displayed from the DICOM header is information significant to sensitometry analysis.

## Measured CT Numbers

The CT number measurements for the individual materials are from the representative slice closest to the median of the estimated effective energy. Approximate expected CT numbers for each target material can be found in the linear attenuation coefficient table in the Sensitometry Physics Help Section.

## Contrast Scale

The contrast scale is the calculated slope of the linearity plot.

## Residual Plot

The residuals are calculated from linearity plots for each tabular energy value. The residuals are the distances of the measured values from the line in the linearity plot. From this residual plot the estimated effective energy is derived as the minimum point on the plot.

## Sensitometry Plot

The sensitometry plot calculates the effective energy (keV) of the scan by plotting the measured CT number and the table values at each keV for the materials. The estimated effective energy value shown is obtained from the minimum residual from the linear fit of measured CT values vs. attenuation coefficient. The graph on the left displays the measured and table values for each material found. The graph on the right displays only the measured and table value of air.

*The "Table Values" can be found in the linear attenuation coefficient table in the Sensitometry Physics Help section.*

## Effective Energy

The effective energy is obtained from the minimum point, or best fit, on the residual plot.

# Spatial Linearity

Spatial Linearity information is given for the following Catphan® models: 500, 503, 504, 600, 700

The spatial linerarity is the reported estimated pixel spacing. The distance between the spatial targets is measured (the small teflon and air plugs) and from the known distance the real pixel spacing is calculated.

# Slice Thickness

Slice thickness information from the wire is given for the following Catphan® models: 500, 503, 504, 600, 700

Slice thickness information from the bead ramps is given for the following Catphan® models: 600, 700

## Slice Thickness - Wire Ramps

To calculate slice thickness from the wire ramp, a Gaussian fit to the wire is made and then the FWHM is found and multiplied by tan23º (or 0.42).

## Slice Thickness - Coarse Bead Ramps

A profile line through the beads is used to calculate slice thickness. In this profile there will be peaks at each of the bead locations and these will be separated by 0.25mm from each other. Thus for example, for the 1.0mm slice width we measure about four bead spacings at the Full Width at Half Maximum (FWHM). Multiplying the four bead spacings times the y axis increment 0.25mm per bead yields a 1mm slice width.

## Slice Thickness - Fine Bead Ramps

The method for calculating slice thickness with the fine and coarse bead ramps is the same. It is suggested that in thinner slices, measurements be taken from the fine bead ramps for better measurement precision.

# Uniformity

Uniformity information is given for the following Catphan® models: 500, 503, 504, 600, 700

## Vertical Profile and Corresponding Fitted Curve

The profile plotted below is a line profile from a vertical line across the uniformity module. The points on the plot are an average over 5 columns of pixels. The plot is then smoothed further to reduce noise before the fitted curve is completed.

## Horizontal Profile and Corresponding Fitted Curve

The profile plotted below is a line profile from a horizontal line across the uniformity module. The points on the plot are an average over 5 rows of pixels. The plot is then smoothed further to reduce noise before the fitted curve is completed.

## Uniformity Index (Vertical/Horizontal)

To calculate the uniformity index for the horizontal and vertical profiles, the maximum and minimum y-axis CT values (HU) from the fitted curve are entered into the following equation: 1 - (CTmax-CTmin) / (CTmax+CTmin)

The closer a value is to "1", the more uniform the image.

## Mean CT Value - Center Region

The mean CT number value in the center region of interest (ROI) is used as a reference for other uniformity caluclations and can be viewed in the "Noise and Mean Values Plot".

## Noise and Mean Values Plot

In this plot, the mean CT number (HU value) for each region of interest (ROI) is displayed as the blue column. The noise, displayed as the red column, is the standard deviation of HU values within each ROI. The upper and lower limits, indicated by the green horizontal lines, are +/- 4HU from the mean HU value of the center ROI as required by the IEC standards.

## Absolute Difference from Center in Regions of Interest

The absolute difference in mean CT number from the center ROI is calculated for each ROI.

## Noise

Noise is calculated as the standard deviation of CT numbers from a center ROI that encompasses 40% of the uniformity module.

# Modulation Transfer Function(MTF)

MTF information is given for the following Catphan® models: 500, 503, 504, 600, 700

## MTF Plot from Wire

The MTF plot displays the measured points, critical frequencies (50, 10, 5, and 2%), and MTF curve from the line spread function (LSF) data from the wire. The Nyquist frequency, which is the sampling threshold, is also displayed.

## Critical Frequency - Wire

The critical frequency for 50, 10, 5, and 2% of the MTF is displayed for data from the wire.

## Line Spread Function (LSF) Plot from Wire

The line spread function (LSF) is derived by averaging the pixel intesities, the point spread function (PSF) values, surrounding the wire. The x and y-axis PSF values are averaged and symmetrized, and then both directions are averaged to create the LSF plot.

## MTF Plot from Beads

The MTF plot displays the measured points, critical frequencies (50, 10, 5, and 2%), and MTF curve from the line spread function (LSF) data from the bead or beads if both upper and lower beads are found. The Nyquist frequency, which is the sampling threshold, is also displayed.

## Critical Frequency - Beads

The critical frequency for 50, 10, 5, and 2% of the MTF is displayed for data from the found bead(s).

## Line Spread Function (LSF) Plot from Beads

The line spread function (LSF) is derived by averaging the pixel intesities, the point spread function (PSF) values, surrounding the bead(s). The x and y-axis PSF values are averaged and symmetrized, and then both directions are averaged to create the LSF plot.

# Wave

Wave insert information is given for the following Catphan® models: 700

The wave insert was developed to sample the 3D resolution properties of a CT image, including in–plane (x,y) and z-axis information. The key development is to incorporate a z axis aspect of a more traditional step (bar) phantom. The phantom is amenable to mathematical analysis of the x, y, and z axis resolution properties separately and combined. A periodic pattern of a pair of opposed (30°) angled ramps is embedded in a phantom and is configured to produce a waveform profile across the CT image.

## Harmonics Plot from Ramps

This graph plots the measured harmonics and the theoretical ideal square wave harmonics. With thinner slices and better in-plane resolution, the measured values get closer to the ideal square wave. Below you will see a plot of a scan with 5mm slice thickness followed by a plot with 0.5mm slice thickness.

## Intensity Profile from Ramps

This graph plots the pixel intensities through the wave insert. This profile gives rise to the harmonics through the Fourier transform. Again, below are profiles with 5mm and 0.5mm slice thickness.

5mm Slice Thickness:

## Amplitudes for Odd Harmonics

This shows measured amplitude values for the odd harmonics for the wave ramps.

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