WACS 57th Annual Scientific Conference, Ougadougou, Burkina Faso 26th February – 4th March 2017.
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Overscanning, overranging and overbeaming in CT: their practical effects on patients' radiation doses and how to prevent them - Experience from Nnewi, Nigeria 1Eze Kenneth C
Department of Radiology,
Faculty Medicine, Nnamdi Azikiwe University, Awka (Nnewi Campus),
Departments of Radiology, Nnamdi Azikiwe University Teaching hospital (NAUTH), Nnewi, Anambra State, Nigeria.
Correspondence to Dr KC Eze, Email = ezechallenge@yahoo.co.uk
Background
Overscanning is the exposure of tissues beyond the boundaries of volume of anatomy to be imaged. Overhanging is the significant extension of the planned scan length at both ends of the imaged volume that occurs in helical CT. Overbeaming is the extension of primary x-ray beam outside the width of detectors required to construct the CT image. Overscanning and overranging are associated with scanning protocols while overbeaming is inherent in CT scanner design. All these adversely affects patients doses.
Objectives
To highlight the effects of overscanning, overranging and overbeaming in patients’ radiation doses and how to prevent them.
Methodologies
A total of 200 CT scan studies done over 12 months period were reviewed to find out the presence of over scanning on the images and thus unnecessary increase in patients radiation doses. The types of 30 CT scanners in government hospitals in Nigeria were reviewed to find out the presence of overbeaming and overranging in the models and thus their affectation of patients’ radiation doses.
Result There is universal presence of overscanning in all the completed CT studies but the overscan length was variable. Over 90% of CT scanners used in Nigeria exhibit overranging and overbeaming being made of earlier helical CT models. Their presence results in an increase in patient’s radiation doses in up to 30% or more.
Conclusion Knowledge of overscanning, overranging and overbeaming is vital because their presence tend to cancel the advantages of other strategies put in place to reduce radiation dose in T studies
Key words:Morning glory syndrome, Optic disc excavation, Poor vision, Nigerian male.
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