Objective methods to determine minimal required Kv and mAs for DSCT cardiac
The following question has been asked by Y.S.Lee, Singapore:
Objective methods to determine minimal required Kv and mAs for DSCT cardiac: For DS cardiac CT, the optimal Kv and mAs used by radiographers at time can be suboptimum depending on their experiences. Using BMI method, can at time be inconvenient.What objective methods to determine the minimal required Kv and mAs but at the same time also ensured acceptable images and minimal possible radiation dose to the patient are used in your institution?
Dear Dr Lee,
thank you for your important question regarding the optimal kV and mAs settings required for cardiac DSCT.
You are absolutely right in stating that the optimal, i.e. minimal settings resulting in the lowest required radiation dose for the patient have not been evaluated and largely depend on the individual experience of different users, partly adapting the default settings from the vendor.
We have tested different protocols regarding both subjective and objective image quality parameters and can recommend the following approach:
- ECG-pulsing with adaptation of the pulsing window to the individual heart rate is mandatory in each DSCT exam (see Leschka et al., Invest Radiol 2007).
- In patients with a BMI below 25, the tube voltage can be set to 100 kV, without loss of image quality (spiral data acquisition).
- In these patients, lowering of the tube current time product to 250 mAs can be also done while maintaining a diagnostic image quality (spiral data acquisition).
- In patients with an BMI > 25, the tube voltage should be set at 120 mV and the tube current time product to 330-370 mAs (spiral data acquisition).
- Consider the use of the step-and-shoot technique in patients having a low (eg < 65-70 bpm) and regular heart rate.
- When using the step-and-shoot technique in patients with a BMI < 25, the tube voltage can be lowered to 100 kV.
- Consider the use of attenuation-based tube current modulation in all step-and-shoot CT examinations.
- It is obvious that the use of the BMI may result in a wrong estimation of the true attenuation of the thorax of the individual patient. However, the same can be true when only using the body weight but not taking into account the entire body constitution.
Thank your for your question.
Best regards, Hatem Alkadhi
