Absorbed dose during helical CT acquisition: Influence of acquisition parameters

Purpose. European directive 97/43 specifies that the dose delivered to the patient during a radiological procedure should be estimated. In order to pr epare for implementation of this new regulation, we have studied the dose d elivered during spiral CT acquisition. Materials and methods. We have studied the influence of slice thickness, pi tch, tube voltage and intensity, and acquisition volume length. We present measurements for single and dual detector CT scanners. We used a pencil ion ization chamber to measure air kerma. We measured absorbed dose in water wi th a waterproof ionization chamber set in a semi-customized phantom filled with water. Chambers were set on the rotation axis of the CT scanners. We s tudied the dose outside the acquisition volume. Results. We quantified the influence of each parameter on the absorbed dose . We used our measurements to calculate the dose for different acquisition protocols. Also we evaluated the dose to organs distant from the acquisitio n area. Conclusion. This study is one step toward a systematic estimation of the do se delivered to patient during helical CT exams. To use these results in da ily practice, we have to develop software using our measurements.