Automatic Tube Current Modulation (ATCM) is used with modern CT scanners to optimize patient dose while maintaining acceptable image quality. The effectiveness of ATCM varies both with different imaging protocols and between different manufacturers.

The CT228 ATCM Phantom, developed in cooperation with researchers from the Karolinska Institute, assists CT operators in characterizing ATCM performance.

The phantom is cast in a single piece from rugged Catphan® Uniformity Material allowing the signal noise to be measured in three different sized oval sections to demonstrate how well the ATCM compensates for variations in torso sizes and anatomical transitions. The phantom also helps assess the effects of variations in patient alignment.

The 65cm long phantom consists of 3 ellipsoidal sections. Each ellipsoid is 15 cm in length with a 3:2 ratio; 25:16.7 cm, 30:20 cm and 35:23.3 cm sizes.  Smooth transitions are provided between the sections and the ends are rounded.  The phantom has 1.6mm diameter teflon markers on the side and top to assist with aligning the phantom.

The phantom is designed to be scanned with a projection radiograph (SPR) used by ATCM algorithms to estimate patient attenuation. Various scan parameters or phantom repositioning may be applied to assess the effects of changing parameters or patient positioning errors. The resulting CT image set can be assessed against a reference scan to calculate the normalized root mean square error (NRMSE) of tube current curves and to provide visual evaluation of tube current fluctuation curves and image noise.

To better understand the full effects of different imaging parameters the Catphan® phantoms can be used for a comprehensive image performance evaluation.