A practical method to standardise and optimise the Philips DoseRight 2.0 CT automatic exposure control system

Abstract

Given the increasing use of computed tomography (CT) in the UK over the last 30 years, it is essential to ensure that all imaging protocols are optimised to keep radiation doses as low as reasonably practicable, consistent with the intended clinical task. However, the complexity of modern CT equipment can make this task difficult to achieve in practice. Recent results of local patient dose audits have shown discrepancies between two Philips CT scanners that use the DoseRight 2.0 automatic exposure control (AEC) system in the 'automatic' mode of operation. The use of this system can result in drifting dose and image quality performance over time as it is designed to evolve based on operator technique. The purpose of this study was to develop a practical technique for configuring examination protocols on four CT scanners that use the DoseRight 2.0 AEC system in the 'manual' mode of operation. This method used a uniform phantom to generate reference images which form the basis for how the AEC system calculates exposure factors for any given patient. The results of this study have demonstrated excellent agreement in the configuration of the CT scanners in terms of average patient dose and image quality when using this technique. This work highlights the importance of CT protocol harmonisation in a modern Radiology department to ensure both consistent image quality and radiation dose. Following this study, the average radiation dose for a range of CT examinations has been reduced without any negative impact on clinical image quality.

Best practice for the nuclear medicine technologist in CT-based attenuation correction and calcium score for nuclear cardiology

“…The software determines a reduction of the tube current relative for the low-density regions. The ATCM system is constantly updated and the machine adjusts the perceived image quality from the changes of the milliamperes per slice done by the NMT, who may override the milliamperes per slice suggested by the software (Wood et al 2015 ).…”

A routine quality assurance test for CT automatic exposure control systems

“…In automatic, or learning, mode when the operator overrides the mAs suggested by the AEC system, the scanner adjusts the size of the built‐in reference phantom which it uses for patient size calculation (24) . In manual mode, the AEC system uses a built‐in 33 cm diameter phantom whereas, in automatic mode, since the size of the reference phantom can change over time, the apparent size of a fixed sized standard phantom changes over time, thus causing the scanner to vary the dose given under AEC control.…”

Design and use of a phantom for testing and comparing the performance of computed tomography automatic tube current modulation systems

“…There have been a variety of approaches to the design of phantoms for testing ATCM systems with custom -made models with a range of shapes, sizes, and eccentricities [15][16][17][18][19][20][21][22][23][24]. Early designs used a series of separate ellipsoid-shaped phantoms, often fitting inside each other or around a 160 mm CTDI head phantom, to evaluate current modulation in the x-y plane during a series of scans [15].…”

“…Early designs used a series of separate ellipsoid-shaped phantoms, often fitting inside each other or around a 160 mm CTDI head phantom, to evaluate current modulation in the x-y plane during a series of scans [15]. Following this, phantoms in the shape of truncated cones with diameters varying continuously along their lengths were employed to provide information on overall ATCM performance [16][17][18]. For example, ImPACT (UK) developed a conical elliptical phantom 300 mm long with cross -sectional dimensions in the ratio of 3:2, increasing from 61 mm × 41 mm to 429 mm × 286 mm [16], and a phantom constructed from a series of elliptical polymethlymethacrylate slabs each 25 mm thick with dimensions decreasing from 175 mm to 429 mm has been manufactured by Leeds Test Objects (Boroughbridge, UK) [18].…”

“…Following this, phantoms in the shape of truncated cones with diameters varying continuously along their lengths were employed to provide information on overall ATCM performance [16][17][18]. For example, ImPACT (UK) developed a conical elliptical phantom 300 mm long with cross -sectional dimensions in the ratio of 3:2, increasing from 61 mm × 41 mm to 429 mm × 286 mm [16], and a phantom constructed from a series of elliptical polymethlymethacrylate slabs each 25 mm thick with dimensions decreasing from 175 mm to 429 mm has been manufactured by Leeds Test Objects (Boroughbridge, UK) [18]. These phantoms demonstrate the modulation with body size, but since there is no region of constant diameter, the tube current changes continuously so it is not possible to quantify performance through assessments of dose or image quality for particular body sizes, or analyse ATCM operation in more detail.…”