University of Oulu

Kivistö, S., Kotiaho, A., Henner, A., Nevala, T., Niinimäki, J., Nieminen, M.T. and Hanni, M. (2020), Air gap technique is recommended in axiolateral hip radiographs. J Appl Clin Med Phys, 21: 210-217.

Air gap technique is recommended in axiolateral hip radiographs

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Author: Kivistö, Susanne1; Kotiaho, Antti1,2,3; Henner, Anja4;
Organizations: 1Department of Diagnostic Radiology, Oulu University Hospital, Oulu, Finland
2Research Unit of Medical Imaging, Physics and Technology, University of Oulu, Oulu, Finland
3Medical Research Center, University of Oulu and Oulu University Hospital, Oulu, Finland
4Oulu University of Applied Sciences, Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.9 MB)
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Language: English
Published: John Wiley & Sons, 2020
Publish Date: 2021-01-21


Purpose: To investigate the replacement of conventional grid by air gap in axiolateral hip radiographs. The optimal air gap distance was studied with respect to radiation dose and image quality using phantom images, as well as 26 patient axiolateral hip radiographs.

Methods: The CDRAD phantom, along with polymethylmethacrylate slabs with thicknesses of 10.0, 14.6, and 20.0 cm was employed. The inverse image quality index and dose area product (DAP), as well as their combination, so called figure‐of‐merit (FOM) parameter, were evaluated for these images, with air gaps from 20 to 50 cm in increments of 10 cm. Images were compared to those acquired using a conventional grid utilized in hip radiography. Radiation dose was measured and kept constant at the surface of the detector by using a reference dosimeter. Verbal consent was asked from 26 patients to participate to the study. Air gap distances from 20 to 50 cm and tube current‐time products from 8 to 50 mAs were employed. Exposure index, DAP, as well as patient height and weight were recorded. Two radiologists evaluated the image quality of 26 hip axiolateral projection images on a 3‐point nondiagnostic — good/sufficiently good — too good scale. Source‐to‐image distance of 200 cm and peak tube voltage of 90 kVp were used in both studies.

Results and conclusion: Based on the phantom study, it is possible to reduce radiation dose by replacing conventional grid with air gap without compromising image quality. The optimal air gap distance appears to be 30 cm, based on the FOM analysis. Patient study corroborates this observation, as sufficiently good image quality was found in 24 of 26 patient radiographs, with 7 of 26 images obtained with 30 cm air gap. Thus, air gap method, with an air gap distance of 30 cm, is recommended in axiolateral hip radiography.

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Series: Journal of applied clinical medical physics
ISSN: 1526-9914
ISSN-E: 1526-9914
ISSN-L: 1526-9914
Volume: 21
Issue: 10
Pages: 210 - 217
DOI: 10.1002/acm2.13021
Type of Publication: A1 Journal article – refereed
Field of Science: 3125 Otorhinolaryngology, ophthalmology
Copyright information: © 2020 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.