Tube current modulation
Method 1: use one or more SPRs to assess attenuation along patient length
- vary overall mA according to patient size
- vary mA slice by slice during scan (e.g. GE’s Auto mA)
Method 2: use feedback mechanism
- adjust mA based on signal to detectors during previous rotation (e.g. Siemens CARE Dose, Philips DoseRight)
Advantages
- lower dose (e.g. mean mAs reduction of 28% with CARE Dose)
- image quality is constant, with fewer artefacts
- tube heat capacity conserved