Impacts of Phantom Off-Center Positioning on CT Numbers and Dose Index CTDIv: An Evaluation of Two CT Scanners from GE.

Xiaoming Zheng,Lachlan Gutsche,Johanna Stanton,Yazan Al-Hayek,Kelsey Jensen,Wiam Elshami

doi:10.3390/jimaging7110235

Xiaoming Zheng, Lachlan Gutsche + Show 4 more

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https://doi.org/10.3390/jimaging7110235

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Abstract

The purpose of this work is to evaluate the impacts of body off-center positioning on CT numbers and dose index CTDIv of two scanners from GE. HD750 and APEX scanners were used to acquire a PBU60 phantom of Kagaku and a 062M phantom of CIRS respectively. CT images were acquired at various off-center positions under automatic tube current modulation using various peak voltages. CTDIv were recorded for each of the acquisitions. An abdomen section of the PBU60 phantom was used for CT number analysis and tissue inserts of the 062M phantom were filled with water balloons to mimic the human abdomen. CT numbers of central regions of interests were averaged using the Fiji software. As phantoms were lifted above the iso-center, both CTDIv and CT numbers were increased for the HD750 scanner whilst they were approximately constant for the APEX scanner. The measured sizes of anterior-posterior projection images were also increased for both scanners whilst the sizes of lateral projection images were increased for the HD750 scanner but decreased for the APEX scanner. Off-center correction algorithms were implemented in the APEX scanner. Matching the X-ray projection center with the system’s iso-center could improve the accuracy of CT imaging.

Highlights

Patient vertical off-center positioning is common in clinical CT imaging [1,2]
Correction algorithms for patient off-center positioning have been implemented in the Revolution APEX scanner of General Electric (GE)
LAT localizers in Automatic tube current modulation (ATCM) if this option is available in Siemens CT scanners

Summary

Introduction

Patient vertical off-center positioning is common in clinical CT imaging [1,2]. It can cause an increased surface dose to patients [1] and varied CT numbers at different locations within the bodies of patients [2]. Computer software may be used to automatically adjust patient’s positions during CT scans [3,4] or auto couch height position compensation can be applied to correct for the mis-positioning and reduce radiation doses to patients [5]. Not all CT scanners currently being used in clinical practice have off-center correction algorithms implemented [8,9]. Radiologic technologists can only guess if an off-center correction algorithm is implemented in a clinical scanner. The correction algorithms themselves are proprietary information of the manufacturers [5,9]

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