Eye-lens bismuth shielding in paediatric head CT: artefact evaluation and reduction.
BACKGROUND
CT scans of the brain, sinuses and petrous bones performed as the initial imaging test for a variety of indications have the potential to expose the eye-lens, considered among the most radiosensitive human tissues, to a radiation dose. There are several studies in adults discussing the reduction of orbital dose resulting from the use of commercially available bismuth-impregnated latex shields during CT examinations of the head.


OBJECTIVE
To evaluate bismuth shielding-induced artefacts and to provide suggestions for optimal eye-lens shielding in paediatric head CT.


METHODS
A bismuth shield was placed over the eyelids of 60 consecutive children undergoing head CT. Images were assessed for the presence and severity of artefacts with regard to eye-shield distance and shield wrinkling. An anthropomorphic paediatric phantom and thermoluminescence dosimeters (TLDs) were used to study the effect of eye lens-to-shield distance on shielding efficiency.


RESULTS
Shields were tolerated by 56/60 children. Artefacts were absent in 45% of scans. Artefacts on orbits, not affecting and affecting orbit evaluation were noted in 39% and 14% of scans, respectively. Diagnostically insignificant artefacts on intracranial structures were noted in 1 case (2%) with shield misplacement. Mean eye-lens-to-shield distance was 8.8 mm in scans without artefacts, and 4.3 mm and 2.2 mm in scans with unimportant and diagnostically important artefacts, respectively. Artefacts occurred in 8 out of 9 cases with shield wrinkling. Dose reduction remained unchanged for different shield-to-eye distances.


CONCLUSIONS
Bismuth shielding-related artefacts occurring in paediatric head CT are frequent, superficial and diagnostically insignificant when brain pathology is assessed. Shields should be placed 1 cm above the eyes when orbital pathology is addressed. Shield wrinkling should be avoided.
Raissaki
Maria
M
Department of Radiology, University Hospital of Heraklion, University of Crete, Faculty of Medicine, Stavrakia, Voutes, PO Box 2208, 71003 Heraklion, Crete, Greece. mraissaki@yahoo.gr
Perisinakis
Kostas
K
Damilakis
John
J
Gourtsoyiannis
Nicholas
N
D016477:Artifacts; D001729:Bismuth; D002648:Child; D002675:Child, Preschool; D005260:Female; D006257:Head / Q000000981:diagnostic imaging*; D006801:Humans; D007908:Lens, Crystalline; D008297:Male; D009915:Orbit / Q000000981:diagnostic imaging*; D011829:Radiation Dosage; D011835:Radiation Protection / Q000295:instrumentation*; D011856:Radiographic Image Enhancement / Q000295:instrumentation* / Q000379:methods; D011874:Radiometry; D014057:Tomography, X-Ray Computed
D001729:Bismuth