Description ABSTRACT -- Computed tomography (CT) technology has changed considerably in recent years with the introduction of increasing numbers of
multiple detector arrays. There are several parameters specific to multi-detector computed tomography (MDCT) scanners that increase
or decrease patient dose systematically compared to older single detector computed tomography (SDCT) scanners. This document briefly
reviews the MDCT technology, radiation dose in MDCT, including differences from SDCT and factors that affect dose, radiation risks, and
the responsibilities for patient dose management. The document recommends that users need to understand the relationship between patient
dose and image quality and be aware that image quality in CT is often higher than that necessary for diagnostic confidence. Automatic
exposure control (AEC) does not totally free the operator from selection of scan parameters, and awareness of individual systems is important.
Scanning protocols cannot simply be transferred between scanners from different manufacturers and should be determined for each MDCT.
If the image quality is appropriately specified by the user, and suited to the clinical task, there will be a reduction in patient dose
for most patients. Understanding of some parameters is not intuitive and the selection of image quality parameter values in AEC systems
is not straightforward. Examples of some clinical situations have been included to demonstrate dose management e.g. CT examinations of
the chest, the heart for coronary calcium quantification and non-invasive coronary angiography, colonography, the urinary tract, children,
pregnant patients, trauma cases and CT guided interventions. CT is increasingly being used to replace conventional x-ray studies and
it is important that patient dose is given careful consideration, particularly with repeated or multiple examinations.
Contents 1.MDCT TECHNOLOGY
1.1.Background 1.2.Introduction to MDCT technology 1.3.Differences between SDCT and MDCT 1.4.Upcoming
developments 1.5.What is the motivation for this report?
2.RADIATION DOSE IN MDCT
2.1.Introduction 2.2.Are doses
in MDCT different and why? 2.3.What are the considerations for users switching over from SDCT to MDCT? 2.3.1.Factors that can
increase dose in MDCT 2.3.2.Factors that can decrease dose in MDCT 2.4.Dose surveys and diagnostic reference levels 2.5.Perspective
on radiation risks 2.5.1.Deterministic risk 2.5.2.Stochastic risk 2.6.Responsibilities for patient dose management
3.WHAT CONSIDERATIONS AND ACTIONS AFFECT PATIENT DOSE?
3.1.Compromise between dose and image quality 3.1.1.General
descriptors of image quality 3.1.2.Different imaging tasks require different levels of quality 3.2.Equipment and protocol issues
affecting patient dose 3.2.1.Overbeaming 3.2.2.Overranging 3.2.3.Image thickness 3.3.Operator choices that affect
patient dose 3.3.1.Scanner model and manufacturer 3.3.2.Tube current (mA) and tube current?exposure time product (mAs) 3.3.3.Image
quality selection paradigms 3.3.4.Temporal mA modulation 3.4.Tube voltage (kVp) 3.5.Pitch, beam collimation and slice width
3.6.Scan coverage and indication 3.7.System Software: Image reconstruction, noise reduction, and metal artefact reduction algorithms
3.8.Modification of scan acquisition and reconstruction parameters
4.DOSE MANAGEMENT IN CLINICAL PRACTICE
4.1.Justification
of examination 4.2.Training issues 4.3.Techniques and doses for particular CT examinations 4.3.1.Chest CT 4.3.2.CT for
coronary calcium quantification and non-invasive coronary angiography 4.3.3.CT colonography 4.3.4.CT for trauma 4.3.5.CT
of the urinary tract 4.3.6.CT-guided interventions 4.3.7.CT in children 4.3.8.CT of the pregnant patient 4.3.9 Future
directions
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