Marilyn J. Siegel MD, Presenter: Research Consultant, Siemens AG Speakers Bureau, Siemens AG

David Bradley, Abstract Co-Author: Employee, Siemens AG

Bernhard Schmidt PhD, Abstract Co-Author: Employee, Siemens AG

Charles Floyd Hildebolt DDS, PhD, Abstract Co-Author: Nothing to Disclose

Sebastian Vogt PhD, Abstract Co-Author: Employee, Siemens AG

To evaluate radiation doses in CT as a function of object size and an automated tube voltage technique using different object sizes and shapes simulating pediatric patients.

CT scans were acquired on an AS+ (Siemens AG, Germany) which was equipped with a tool for automatic selection of tube voltage (CAREkV) based on the attenuation derived from the topogram. We used three anthropomorphic phantoms with long and short axes corresponding to a neonate, small child and small adult. All phantoms were scanned with and without automated mAs (CAREDose4D) and CAREkV using a standard contrast-enhanced abdominal/pelvis protocol (i.e., CTA protocol) using the 128x0.6mm collimation. For the scans without CAREkV, the reference standards were 120 kVp and 150 ref. mAs. For the scans with CAREkV, the system selected the best kV level, ranging from 70 kV to 140 kV. For both sets of scans, radiation doses (CTDIvol values) were measured. Image quality (contrast and pixel noise) also was evaluated for each by sampling regions of interest in the phantoms.

For constant mAs and varying voltage, dose increased from the large to the small phantom for all voltages (70 kV: 4.7 to 8.8 mGy, 80 kV: 7.5 to 13.1 mGy, 100 kV: 15.0 to 25.3 mGy, 120 kV: 22.8 to 39.0 mGy , 140 kV: 32.9 to 55,4 mGy). For all phantom sizes dose was substantially higher at higher kVs. When adapting just the tube current to phantom size using constant 120 kVp , dose was reduced for the large phantom by 44%, the medium phantom by 53% and the small phantom by 60%. When both tube current and tube voltage were automatically adjusted, the dose for CTA was reduced further. For the small, medium and large phantoms, the dose reduction were another 70%, 58%, and 44% respectively. For contrast-enhanced scans, image quality remained relatively constant but dose reduction was substantially lower compared to the CTA, regardless of phantom size.

Scans acquired with an automated technique  for kV reduction result in substantially lower doses with high image quality .

Use of automated kV has the potential to further reduce dose in pediatric contrast enhanced CT studies without loss of image quality.

Siegel, M, Bradley, D, Schmidt, B, Hildebolt, C, Vogt, S, Assessment of an Automatic Technique for Tube Voltage (kV) Adaptation to Reduce Dose to Pediatric Patients.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11012415.html