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

Abstract

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. 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 70-120kVp and 150-285mAs. 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 (CTDIvol) and kVp. A change from 120 to 80kVp, achieved the same CNR with 60% reduction in dose. Alternatively, for the same dose, the change from 120 to 80kVp improved CNR by +58%. A change from 80 to 70kVp while operating at the same CNR, led to 13% reduction in dose. Alternatively, maintaining the same dose while changing from 80 to 70kVp improved the CNR by +7%. Lower beam energies achieved the same CNR with less dose, or improved CNR at the same dose. A reduction from 80kVp to 70kVp may be clinically useful to optimise CTP acquisitions.