Initial radiation dose reduction studies in cervical spine multidetector CT

Abstract

Feasibility studies were performed to evaluate the potential for dose reduction when investigating cervical spine trauma using multidetector CT (MDCT), without reducing fracture detectability. The studies utilised both in vitro phantom work and low-dose (LD) clinical images from archive. Test phantoms were constructed using dry human cervical vertebrae suspended inside tissue equivalent material. Vertebrae were modified with fine osteotomies to simulate fracture lines. A LightSpeed VCT 64-slice scanner (GE Healthcare Medical Systems, Milwaukee, WI) was employed to scan the phantom using a series of tube current (mA) settings and constant tube voltage (kVp). The phantom was also scanned using the manufacturer’s programme for automatic tube current modulation (TCM). The recommended TCM tube current table ranges were found to be set to high values (120–600 mA); therefore further modified TCM exposures were made with lower minimum value of 50 mA. Images were assessed under standard clinical review conditions. Low-dose CT series from clinical PET/CT examinations on clinical archive were also evaluated to explore their suitability to visualise cortices and other bony characteristics. Preliminary indications are that image assessments of critical bony features can be achieved with a high degree of confidence when the radiation dose is reduced by a factor of two. Dose Length Product (DLP), was used for relative comparisons between examinations. Using the standard TCM’s DLP as the reference value, bony features were visualised suitably using 60–80 mA and a tube current of 60 mA would lead to a halving of the total DLP to 130 mGy cm. Just reducing the lower limit of the TCM selection range to 50 mA led to a more than 58% reduction in DLP. Our study demonstrates that there is potential for radiation dose reduction during routine clinical imaging for cervical spine trauma and provides supporting evidence for a clinical study.