CT brain perfusion: A static phantom study of contrast‐to‐noise ratio and radiation dose

Computed tomography perfusion ( CTP ) is increasingly employed in the diagnosis and management of ischaemic stroke but radiation dose can be significant and optimising contrast‐to‐noise ratio ( CNR ) is challenging. This study aimed to quantify and optimise the balance between CNR as a surrogate for image quality and radiation dose. Methods A perspex head phantom with vials of dilute contrast agent was scanned using a Siemens Definition Flash 128‐slice scanner. The CTP protocol exposure parameters were adjusted over 70–120  kV p and 150–285  mA s. Measurements were obtained for the average dose per slice, Hounsfield Units ( HU ) for iodinated contrast agent, and the image noise for background regions of perspex. The CNR was measured as a function of the volumetric CT dose index ( CTDI vol) and kV p. Results A change from 120 to 80  kV p, achieved the same CNR with 60% reduction in dose. Alternatively, for the same dose, the change from 120 to 80  kV p improved CNR by +58%. A change from 80 to 70  kV p while operating at the same CNR , led to 13% reduction in dose. Alternatively, maintaining the same dose while changing from 80 to 70  kV p improved the CNR by +7%. Conclusion Lower beam energies achieved the same CNR with less dose, or improved CNR at the same dose. A reduction from 80  kV p to 70  kV p may be clinically useful to optimise CTP acquisitions.