Low-dose nonenhanced head CT protocol for follow-up evaluation of children with ventriculoperitoneal shunt: reduction of radiation and effect on image quality

Abstract

Background and purpose: Children with a shunt for hydrocephalus often undergo multiple follow-up head CT scans, increasing the risk for long-term effects of ionizing radiation. The purpose of our study was to evaluate if an unenhanced low-dose head CT could consistently provide acceptable image quality and diagnostic information.

Materials and methods: Ninety-two children (mean age, 9 years; range, 8 months to 21 years; 45 boys and 47 girls) with a shunt for hydrocephalus and no clinical evidence of shunt malfunction who were referred for a follow-up nonenhanced head CT were included in the study. All studies were performed on a 4-section multidetector CT. Two CT studies were selected retrospectively for each patient, 1 performed at standard dose (220 mA) and 1 at low dose (80 mAs). Two radiologists independently evaluated and graded both standard-dose and low-dose studies for various image quality parameters. Attenuation and noise levels were measured, and gray-white differentiation and contrast-to-noise ratio (CNR) were calculated.

Results: Low-dose CT resulted in 63% mean dose reduction. All low-dose CT scans were diagnostically acceptable. Image quality parameters were significantly lower at low dose (P = .0001) except for the parameters for streak artifacts (P = .46) and need for further imaging (P = .47), which were higher. Mean noise levels were significantly higher (P = .001) in low-dose studies, whereas CNR was significantly higher in standard dose CT (P = .001). A moderate to perfect agreement was noted between the 2 readers with regard to image quality assessment (65%-99%).

Conclusion: Low-dose nonenhanced head CT consistently provides diagnostically acceptable images with relevant diagnostic information in children with VP shunts resulting in substantial dose savings.

Fig 1.

Diagnostic acceptability of low-dose CT studies. Standard-dose (A) and low-dose (B) head CT studies were obtained in a 16-year-old male adolescent at an interval of 8 months and were rated as good (grade 4) by both readers.

Fig 2.

A,B, Attenuation characteristics of standard-dose and low-dose head CT studies in a 7-year-old girl with a shunt for hydrocephalus. (A) Transverse standard-dose supraventricular CT image with sample ROIs (white circles) showed GM and WM attenuations of 31.6 HU and 25.6 HU, respectively, with noise (SD, HU within ROI) levels of 1.6 HU and 1.8 HU. Low-dose image (B) showed no significant change in attenuation (30.6 HU and 26.8 HU) despite increased noise levels (4.3 HU and 2.8 HU). CNR of standard-dose CT (1.88) was significantly higher (P < .01) than that of low-dose CT (0.47). However, both readers ranked standard-dose (grade 4) and low-dose (grade 3) studies as diagnostically acceptable.