The Catphan® 500 provides complete characterization of maximum imaging performance for axial and spiral CT scanners. The Catphan® 500 provides a comprehensive set of measurements to measure the maximum performance of your CT scanner’s sensitometry, uniformity, geometric and low-contrast sensitivity.

There are variations of the Catphan 500 phantom that are provided through Varian (CTP 504) and Elekta (CTP 503) . Please see Other Catphan Models for details.


  • CTP401
    sensitometry (linearity)
    scan slice geometry (slice width and slice sensitivity profile)
    pixel (matrix) size
    circular symmetry
    phantom position verification
    patient alignment system check
    scan incrementation

  • CTP528
    high resolution measurement - up to 21 line pairs per cm

  • CTP515
    low contrast sensitivity
    comparative subslice and supra-slice low contrast sensitivity

  • CTP486
    spatial uniformity
    noise (precision) of CT systems

To assist Catphan customers, The Phantom Laboratory has worked with Image Owl, Inc. to develop Catphan® QA, a web-based service for fully automated analysis of Catphan Phantom images. All currently manufactured Catphan models are supported.


The Catphan® 500 consists of 4 modules enclosed in a 20cm housing.

CTP401 Slice Geometry and Sensitometry Module:  Opposed 23 degree wire ramps are used to measure scan slice geometry, verify phantom position and check the patient alignment system and the scanner table incrementation. The shallow 23 degree angle allows for more precise measurement of slice thickness than the commonly used 45 degree ramps and the thin wires allow for accurate measurement of thin 1 and 2mm slices without streaking artifacts. Gantry angle (up to 10 degrees) can be determined by the ratio of the ramp lengths.

The module includes 4 sensitometry targets (Teflon, Acrylic, LDPE and Air)  to measure CT number linearity.

The module also contains five acrylic spheres to evaluate the scanner’s imaging of subslice spherical volumes. The diameters of the acrylic spheres are 2mm, 4mm, 6mm, 8mm, and 10mm.

Pixel size can be determined through measuring the number of pixels between the four holes (one with a teflon pin) located 50mm apart.

CTP528 High Resolution Module: This section has a 1 through 21 line pair per centimeter high resolution test gauge and two impulse sources (beads) which are cast into a uniform material. By minimizing the amount of high contrast material and employing a radial design, the CTP528 module eliminates streaking artifacts.

The spherical MTF beads can be used to obtain an accurate MTF curve characterization without tedious and time-consuming positioning inherent with MTF wires. The point source beads also eliminate the over-ranging problems and streaking artifacts that occur with MTF wires, because the bead density is volume averaged with the surrounding material.

CTP515 Low Contrast Module: The CTP515 consists of a series of cylindrical rods of various diameters and three contrast levels to measure low contrast performance. The 40mm-long rods provide consistent contrast values at all z-axis positions, thereby avoiding any volume-averaging errors as you scan through the section. The unique subslice test objects enable evaluation of the effectiveness of different scan protocols (pitch, slice width and reconstruction algorithms) in resolving subslice low contrast objects.

For selection of helical and multi-slice image protocols, unique subslice low contrast targets (truncated cylinders) have been included in this module. Comparing the images obtained by scanning the subslice targets with different imaging settings (slice width, pitch and reconstruction algorithms) provides valuable information to assist with the selection of optimal protocols for identifying small low contrast objects such as tumors.

All of the various samples and the background material have equivalent effective atomic numbers; only the density is varied to produce changes in the effective attenuation coefficients.

Subslice targets have a nominal 1.0% contrast and z-axis lengths of 3, 5, and 7mm. For each of these lengths, there are targets with diameters of 3, 5, 7 and 9mm.

CTP486 Uniformity Module: The image uniformity module is cast from a uniform material with a CT number designed to be within 2% (20H) of water’s density under standard scanning protocols. The typically recorded CT numbers range from 5H to 18H. This module is used for measurements of spatial uniformity, mean CT number and noise value.

Use of a solid material eliminates leaking or risk of damage from exposure to freezing temperatures. The CTP486 solid-image uniformity module provides consistent results, is much more convenient to use than modules using water-filled tanks, and eliminates variations due to different water sources. This solid material’s high radial and axial uniformity makes it an ideal substitute for water. It has been thoroughly tested over a wide variety of variables in the x, y and z planes and has proven stable in all applications.

For detailed phantom information please refer to the Catphan 500 manual.