Thyroid shields versus z-axis automatic tube current modulation for dose reduction at neck CT.

Abstract

PurposeTo assess the effectiveness of in-plane bismuth thyroid shields and a z-axis automatic tube current modulation (ATCM) technique with respect to dose reduction and image noise in the thyroid and other regional tissues during neck computed tomography (CT).Materials and methodsBecause this was a phantom study, neither institutional review board approval nor HIPAA compliance was required. A female phantom, thyroid shields, and an eight-section CT scanner were used. Radiation dose was measured by using thermoluminescent dosimetry (TLD) chips placed in the phantom's thyroid, cervical bone marrow, and soft tissues. Scans were performed by using fixed tube current and a z-axis ATCM technique with and without shields. Image noise was quantified as the standard deviation of the attenuation value (in Hounsfield units) on CT images.ResultsThyroid dose was 76.9 mGy with an unshielded fixed tube current technique. Use of shields and ATCM reduced this dose to 44.7 mGy (42% reduction, P Conclusionz-Axis ATCM is more effective than shields at reducing thyroid radiation dose during neck CT. Shields combined with ATCM slightly further reduces dose; however, this is associated with higher image noise.