Adaptability index: quantifying CT tube current modulation performance from dose and quality informatics

Abstract

The balance between risk and benefit in modern CT scanners is governed by the automatic adaptation mechanisms that adjust x-ray flux for accommodating patient size to achieve certain image noise values. The effectiveness of this adaptation is an important aspect of CT performance and should ideally be characterized in the context of real patient cases. Objective of this study was to characterize CT performance with an index that includes image-noise and radiationdose across a clinical patient population.The study included 1526 examinations performed by three scanners, from two vendors, used for two clinical protocols (abdominopelvic and chest). The dose-patient size and noise-patient size dependencies were linearized, and a 3D-fit was performed for each protocol and each scanner with a planar function. In the fit residual plots the Root Mean Square Error (RMSE) values were estimated as a metric of CT adaptability across the patient population.The RMSE values were between 0.0344 HU 1/2 and 0.0215 HU 1/2: different scanners offer varying degrees of reproducibility of noise and dose across the population. This analysis could be performed with phantoms, but phantom data would only provide information concerning specific exposure parameters for a scan: instead, a general population comparison is a way to obtain new information related to the relevant clinical adaptability of scanner models.A theoretical relationship between image noise, CTDI vol and patient size was determined based on real patient data. This relationship may provide a new index related to the scanners' adaptability concerning image quality and radiation dose across a patient population.

Performance assessment of photon counting versus energy integrated CT: concordance of in vivo and phantom measurements

“…For the purpose of this study, only the four bigger sections were considered, representative of adult head and body anatomical regions. The phantom is made of virgin ultra-high molecular weight polyethylene (density 0.93 g/cm 3 ) and in each cylinder there is a uniform 3 cm axial section and a 3 cm axial section including five inserts surrogating air, bone, fat, iodine, and water composition (Figure 2).…”

“…However, phantoms generally cannot represent patient populations in terms of size. This limitation is critical especially in modern CT techniques, such as PCCT, that introduce non-linearity in the traditional relationship between image quality and patient body habitus established in energy-integrating CT (3). Studies showed that multi-sized phantoms can provide close prediction of image quality in clinical CT populations (4,5).…”