Justin Bennion Solomon MSc, Presenter: Nothing to Disclose

Daniel Jack Frush BS, Abstract Co-Author: Nothing to Disclose

Baiyu Chen, Abstract Co-Author: Nothing to Disclose

Juan Carlos Ramirez Giraldo PhD, Abstract Co-Author: Employee, Siemens AG

Ehsan Samei PhD, Abstract Co-Author: Research Grant, Siemens AG Research Grant, General Electric Company Research Grant, Carestream Health, Inc

To assess the impact of tube current modulation (TCM) on detectability as a function of patient size using phantom measurements.

The task-based Mercury 3.0 phantom, composed of cylindrical sections of 12, 18, 23, 30 and 37cm diameters, and connected through tapered sections, was imaged on a modern dual-source CT scanner (Flash, Siemens) using fixed tube current-time product (fixed mAs) and TCM. An abdominal protocol was used with 120 kVp and pitch = 1.0 with comparable radiation output (CTDIvol) values. Image series were reconstructed using filtered back projection at 0.6 mm. The task transfer function (TTF), the noise power spectrum (NPS), and the detectability index (d’) for a 10 mm- 50 HU designer lesion were estimated as a function of phantom size. The results were compared in terms of the impact of TCM on detectability and phantom-size relationship.

For both TCM and fixed tube-current scans, d’ decreased with increasing phantom size. However, the magnitude of detectability change was reduced with the use of TCM. For TCM scans, d’ decreased on average by 75%, when comparing the largest and smallest phantom sections. For fixed mAs scans, d’ decreased on average by 90%.

TCM reduces the degradation of image quality with phantom size, but it does not eliminate that dependency. The data can be used to design and optimize CT protocols as a function of patient size.

The use of the tube current modulation can lead to an improvement in image quality consistency across patient sizes. However, larger patients still have a lower level of image quality.

Solomon, J, Frush, D, Chen, B, Ramirez Giraldo, J, Samei, E, Impact of Tube Current Modulation on Lesion Detectability as a Function of Patient Size.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14045684.html