Low-dose temporal bone CT in infants and young children: effective dose and image quality

Abstract

Background and purpose: The temporal bone is ideal for low-dose CT because of its intrinsic high contrast. The aim of this study was to retrospectively evaluate image quality and radiation doses of a new low-dose versus a standard high-dose pediatric temporal bone CT protocol and to review dosimetric data from the literature.

Materials and methods: Image quality and radiation doses were compared for 38 low-dose (80 kV/90-110 mAs) and 16 high-dose (140 kV/170 mAs) temporal bone CT scans of infants to 5-year-old children. The CT visualization quality of 23 middle and inner ear structures was subjectively graded by 3 neuroradiologists and 3 otologists by using a 5-point scale with scores 1-2 indicating insufficient and scores 3-5 indicating sufficient image quality. Effective doses of local and literature-derived protocols were calculated from dosimetric data by using NRPB-SR250 software.

Results: Insufficient image-quality scores were more frequent in low-dose scans versus high-dose scans, but the difference was only statistically significant for otologists (6.0% versus 3.4%, P = .004) and not for neuroradiologists (1.2% versus 0.7%, P = .84). Image quality was critical for small structures (such as the stapes or lamella at the internal auditory canal fundus). Effective doses were 0.25-0.3 mSv for low-dose scans, 1.4-1.8 mSv for high-dose scans, and 0.9-2.6 mSv for literature-derived protocols.

Conclusions: The image quality of the new low-dose protocol remains diagnostic for assessing middle and inner ear anatomy despite a 3- to 8-fold dose reduction over previous and literature-derived protocols. However, image quality of small structures is critical and may be perceived as insufficient.

Fig 1.

A and B, The relative frequencies of scores 1–5 are shown for the neuroradiologists (A) and the otologists (B) and for high-dose and low-dose CT. C, The pooled insufficient scores are shown for the neuroradiologists and the otologists for high-dose versus low-dose CT.

Fig 2.

Axial CT section of the right temporal bone obtained with a CTDI_vol of 63 mGy (A) (14-month-old patient; DLP, 223 mGy cm; estimated D_eff, 1.4 mSv) and with the low-dose protocol (B) (16-month-old child; CTDI_vol, 10.8 mGy; DLP, 46.9 mGy cm; estimated D_eff, 0.35 mSv). Critical structures like the modiolus and the thin bony lamella separating the internal auditory canal from the cochlea (1) and the spiral osseous lamina (2) are delineated well despite the higher image noise.

Fig 3.

The same patients as in Fig 2. Oblique axial image, reformatted in the stapes main plane, a high-dose scan (A) versus a low-dose scan (B). The posterior stapes crus (1) and the incudostapedial articulation (2) are identifiable on both scans.