Meetings » 14th CTUG Meeting » Abstracts

New designed phantom to test CT ATCM systems

S Sookpeng, C J Martin and D J Gentle

Gartnavel Royal Hospital


Since the automatic tube current modulation (ATCM) system is now available on all CT scanners and used in majority of patient, failure to test them is to omit a major component of the image system. At the present time, there is not a standard phantom for the routine quality control of CT scanners ATCM operation. With the ATCM system, the tube current is modulated while scanning according to the patient size, shape and attenuation, although different CT manufacturers work on slightly different basis. The ideal phantom for testing these systems should be capable of evaluating how tube current and image quality as well as dose vary according to changes in patient size and shape. ImPACT developed a phantom for ATCM system assessment, that is a conical in shape, increasing in diameter in the x and y axis with the ratio of 3:2, which approximates to the Abdomen. The phantom has been used by several studies. However, phantoms of this type are expensive to manufacture.

For this study, two new designed phantoms have been developed. The concept of designing is to reflect the ATCM performance in varying dimension along the possible length and shape of the human body. The first phantom comprises of five elliptical sections of different dimensions. The advantage of a phantom of this type is that it is significantly less expensive to manufacture compared with the ImPACT phantom. There is, however, a limitation to the use of the phantom when testing the ATCM systems, as the abrupt change in attenuation provokes a typical ATCM response for some scanners. A second phantom has been developed from the results of the first which provides more effective of the ATCM system and a similar model may be suitable for use in our routine testing.

The study will show assessments of ATCM systems in terms of the dynamic changes in tube current and the image noise using new phantoms as well as evaluations of the new phantoms. The study was performed using three different CT scanner manufacturers; Toshiba, GE and Philips and the results were compared with ones obtained using the ImPACT phantom.

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