title: PAEDIATRIC NECK MULTIDETECTOR COMPUTED TOMOGRAPHY: THE EFFECT OF BISMUTH SHIELDING ON THYROID DOSE AND IMAGE QUALITY.
abstract: This study investigated the effect of bismuth shielding on thyroid dose and image quality in paediatric neck multidetector computed tomography (MDCT) performed with fixed tube current (FTC) and automatic exposure control (AEC). Four paediatric anthropomorphic phantoms representing the equivalent newborn, 1-, 5- and 10-y-old child were subjected to neck CT using a 16-slice MDCT system. Each scan was performed without and with single- and double-layered bismuth shield placed on the skin surface above the thyroid. Scans were repeated with cotton spacers of 1, 2 and 3 cm thick placed between the skin and shield, to study the effect of skin-to-shielding distance on image noise. Thyroid dose was measured with thermoluminescent dosemeters. The location of the thyroid within the phantom slices was determined by anthropometric data from patients' CT examinations whose body stature closely matched the phantoms. Effective dose (E) was estimated using the dose-length product (DLP) method. Image quality of resulted CT images was assessed through the image noise. Activation of AEC was found to decrease the thyroid dose by 46 % to the 10-y-old phantom subjected to neck CT. When FTC technique is used, single- and double-layered bismuth shielding was found to reduce the thyroid dose to the same phantom by 35 and 47 %, respectively. The corresponding reductions in AEC-activated scans were 60 and 66 %, respectively. Elevation of shields by 1-, 2- and 3-cm cotton spacers decreased the image noise by 69, 87 and 92 %, respectively, for single-layered FTC, without considerably affecting the thyroid dose. AEC was more effective in thyroid dose reduction than in-plane bismuth shields. Application of cotton spacers had no significant impact on thyroid dose, but significantly decreased the image noise.
authors.affiliation: Department of Medical Physics, Faculty of Medicine, University of Crete, P.O. Box 2208, 71003 Iraklion, Crete, Greece.
authors.forename: Stephen
authors.initials: S
authors.lastname: Inkoom
authors.affiliation: Department of Medical Physics, University Hospital of Heraklion, P. O. Box 1352, Heraklion 71110, Crete, Greece.
authors.forename: Antonios E
authors.initials: AE
authors.lastname: Papadakis
authors.affiliation: Department of Radiology, Faculty of Medicine, University of Crete, Iraklion 71003, Crete, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Raissaki
authors.affiliation: Department of Medical Physics, University Hospital of Heraklion, P. O. Box 1352, Heraklion 71110, Crete, Greece.
authors.forename: Kostas
authors.initials: K
authors.lastname: Perisinakis
authors.affiliation: School of Nuclear and Allied Sciences, University of Ghana, Atomic Campus, P. O. Box AE 1, Atomic, Accra, Ghana.
authors.forename: Cyril
authors.initials: C
authors.lastname: Schandorf
authors.affiliation: Department of Applied Physics, Faculty of Applied Sciences, University for Development Studies, Navrongo Campus, Navrongo, Ghana.
authors.forename: John J
authors.initials: JJ
authors.lastname: Fletcher
authors.affiliation: Department of Medical Physics, University Hospital of Heraklion, P. O. Box 1352, Heraklion 71110, Crete, Greece.
authors.forename: John
authors.initials: J
authors.lastname: Damilakis
mesh_terms: D001729:Bismuth; D002648:Child; D006801:Humans; D061330:Multidetector Computed Tomography; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011835:Radiation Protection; D013961:Thyroid Gland / Q000000981:diagnostic imaging*; D014057:Tomography, X-Ray Computed
chemical_list: D001729:Bismuth