Comparison of pediatric temporal bone computed tomography at 100kVp with tin filtration versus conventional protocol

doi:10.21203/rs.3.rs-5280861/v1

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Comparison of pediatric temporal bone computed tomography at 100kVp with tin filtration versus conventional protocol

https://doi.org/10.21203/rs.3.rs-5280861/v1

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Background

Reducing the radiation dose of pediatric temporal bone computed tomography (CT) has always been a challenge.

Objective

To compare radiation doses and conspicuity of anatomic landmarks of the pediatric temporal bone between the CT protocol using spectral beam shaping at 100 kVp with a dedicated tin filter (Sn100 kVp) and the conventional protocol (100 kVp).

Matetials and Methods

: In total 100 children who had undergone head CT for diagnostic purposes and were found to have normal anatomical inner and middle ear structures were included in this study, of these, 50 children were examined with the Sn100kVp protocol and 50 with the conventional protocol. Subjective and objective image qualities, including visualization of temporal bone structures, image quality, image noise, and radiation doses, were compared between the two groups.

Results

The mean dose length product and effective dose (ED) of the Sn100 kVp scans (ED:0.03 ± 0.01 mSv) were significantly lower than those of the 100kVp scans ( ED: 0.50 ± 0.14 mSv, p < 0.001). The signal-to-noise ratio was slightly lower in the Sn100kVp scans than in the 100kVp scans, except for the squamous bone. However, the subjective evaluation of anatomic landmarks was not significantly different between the two groups, except for the labyrinth.

Conclusion

Temporal bone CT performed at 100 kVp with an additional tin fifilter for spectral shaping markedly reduced radiation dose and maintained good anatomic conspicuity in pediatric patients compared with conventional temporal bone CT .

Children

temporal bone CT

spectral shaping

Low dose

Middle ear mastoiditis, trauma, and congenital malformations of the inner and middle ear are common temporal bone lesions in children. Temporal bone computed tomography (CT) is a commonly used method for temporal bone imaging in children.However, children are more sensitive to the radiation dose than adults and are at high risk of prolonged exposure to ionizing radiation, therefore it is imperative to develop methods to reduce iatrogenic radiation exposure in children [1]. Some of the current technologies that can significantly reduce the radiation dose in pediatric patients include the use of automatic exposure control software, iterative reconstruction, noise reduction filters, and reduced tube currents [2–7]. However, most techniques for reducing radiation doses do not specifically target the radiation dose produced by low-energy photons. The third-generation dual-source CT systems were set up with a tin filter before the x-line tube to filter out low-energy photons, thereby improving the utilization rate of rays and achieve the purpose of reducing the radiation dose[8]. The objective of this study was to compare radiation doses and conspicuity of temporal anatomic landmarks,and explore the application of CT using spectral beam shaping at 100 kVp for low-dose scanning of pediatric temporal bone.

2.1. Patients

This study was approved by our institutional review board, The requirement for informed consent of patients was waived.

Out of the children who had undergone conventional CAREkV tube voltage from December 2021 to November 2022, 50 children (Mean age: 5.3 ± 3.82 years) showing normal anatomical inner and middle ear structures based on radiological reports and clinical evaluation were selected. From another set of children who had undergone temporal bone CT with a tube voltage of 100 kV (100kVp) with tin filter from December 2021 to November 2022, 50 children (Mean age: 5.68 ± 3.66 years) showing normal anatomical inner and middle ear structures were selected. Children with metal artifact dentures, cochlear implants, and orthodontic implants were excluded from both groups.

2.2. Scanning and reconstruction methods

All subjects underwent CT examination using a Siemens dual-source CT (Somatom Force; Siemens Healthineers, Germany).

The conventional protocol was performed with CARE Dose4D and CARE kV ( 114 reference mAs using automated tube current modulation;Ref kV 100) and the Sn100kVp performed with 200 mAs, Sn100 kVp.Other scanning parameters and recombination parameters were the same in both groups: rotation time, 1s; collimation, 128 × 0.6 mm; section thickness, 0.5mm; reconstruction increment, 0.5mm; pitch, 0.8; field of view, 80 mm; bone window Kernel, hr59. In both groups the advanced modeling iterative reconstruction algorithm(ADMIRE) was adopted with an intensity standard of 3.

2.3. Image quality analysis

The scanned images were transmitted to the dedicated workstation of Syngo.via (Siemens Healthineers, Germany), and only one side of the temporal bone was randomly selected for analysis. The number of left and right temporal bones in each group was roughly equal. A total of 100 temporal bones in the two groups were evaluated.

2.3.1. Objective evaluation of the image quality

The CT values and image noise (standard deviation of CT values) were calculated in four different regions of interest (ROIs), including the air in the external auditory canal, air in the mastoid antrum, soft tissue in the internal auditory canal, and squamous bone. To minimize measurement error,due efforts were made to avoid irrelevant structures and map as similar regions as possible at each position (Fig. 1). The mean attenuation and the noise of each ROI were recorded to calculate the signal-to-noise ratio (SNR).

2.3.2. Subjective evaluation of the image quality

The inner auditory canal, labyrinth, ossicles, and mastoid sinuses were assessed by two radiologists with more than 5 years of experience (Fig. 2). The rating scale was as follows [9]: 1 = Unidentifiable anatomy, 2 = Structure identifiable, but no details evaluable, 3 = anatomic structures fully evaluable in all parts, 4 = clear structure outline, 5 = very good delineation of structure. To minimize bias, the subjective evaluation of the images was performed 4 weeks after the objective evaluation.In addition,all personal information of patients and technical data were removed from the images, and the two protocols were randomly assigned to the two radiologists.

2.4. Radiation dose assessment

The CT dose index volume (CTDIvol) and dose-length product (DLP). The effective dose (ED) was calculated by multiplying the DLP with the Conversion factor k [10] (unit: msv /[mgycm]) proposed by the American College of Medical Physicists for different age groups. The values of k for the 0-0.5, 0.5-1, 1–5, 5-10and > 10 year age groups old are 0.013, 0.0085, 0.0057, 0.0042 and 0.0031, respectively.

2.5. Statistical analysis

Continuous variables (radiation dose, image value, noise, SNR) were expressed as mean ± standard deviation. Normally distributed continuous variables were compared between the two groups using the two independent sample t-test. Non-normally distributed continuous variables were compared using the Wilcoxon signed rank sum test. Overall subjective ratings of image quality did not conform to normal distribution and were tested with Wilcoxon signed rank sum test. Interobserver agreement and age distribution were evaluated using Cohen's kappa test [11]. All statistical analyses were conducted using SPSS 22.0 software. P values < 0.05 were considered indicative of statistical significance.

SD) measured in 4 different regions of interest (ROIS): external auditory canal(A) (area: 5.15mm², mean CT: -978HU, SD: 48HU),soft tissue in the internal auditory canal(B right circle) (area: 4.75mm², meanCT : 38HU, SD: 8HU), air in the mastoid antrum(B left circle) (area: 4.61mm², mean CT: -957, SD: 55HU), and squamous bone(C) (area: 2.57mm², mean CT value: 1438hu, SD: 113hu)

3.1. Comparison of the general data

There were no significant differences between the purified group and the conventional dose group with respect to sex and age.

3.2. Objective evaluation of the image quality

The SNRs of the different ROIs were significantly different between the two groups,except for the squamous bone (Table 1).

Table 1

Objective evaluation of the image quality(x⁻±s/M ± Q)
Structure	experimental group(n = 50)	Contrast group(n = 50)	P-value
the air in the external auditory canal
ROI(mm²)	5.06 ± 0.19	5.09 ± 0.12	0.178
SNR	17.96 ± 6.61	32.60 ± 10.75	0.000
soft tissue in the internal auditory canal
ROI(mm²)	5.95 ± 0.13	5.92 ± 0.23	0.48
SNR	0.46 ± 0.24	0.97 ± 0.77	0.000
air in the mastoid antrum
ROI(mm²)	5.05 ± 0.19	4.97 ± 0.18	0.472
SNR	16.38 ± 4.00	24.91 ± 7.20	0.000
squamous bone
ROI(mm²)	2.78 ± 0.44	2.89 ± 0.31	0.161
SNR	10.99 ± 4.63	13.63 ± 11.95	0.074

3.3. Subjective evaluation of the image quality

Interobserver agreement between the two image groups was tested using kappa test, The evaluations made by the two radiologists were almost completely consistent.There were no significant differences in the subjective scores of the two groups, except for the labyrinth (Fig. 2, Table 2).

Table 2

subjective evaluation of the image quality(M ± Q)
Structure	experimental group(n = 50)	Contrast group(n = 50)	P-value
inner auditory canal	4.00 ± 1.00	4.00 ± 1.00	0.31
labyrinth	3.00 ± 0.00	3.00 ± 1.00	0.007
ossicles	4.0 ± 1.00	4.00 ± 0.00	0.103
mastoid sinuses	4.00 ± 1.00	4.00 ± 0.00	0.059

3.4. Radiation dose assessment

The radiation dose of the energy spectral purification technology was significantly lower than that of the conventional scanning protocol (P < 0.05) (Fig. 2) which was aproximately 6.0% of the conventional measurement (Table 3).

Table 3

Radiation dose comparison(x⁻±s/M ± Q)
	experimental group(n = 50)	Contrast group(n = 50)	P-value
CTDIvol(mGy)	0.64	10.10 ± 1.88
DLP(mGy cm)	6.55 ± 0.73	98.10 ± 23.70	0.000
ED(mSv)	0.03 ± 0.01	0.50 ± 0.14	0.000

CT is one of the main temporal bone imaging examination methods.Recently, several methods have been introduced to reduce the radiation exposure of children undergoing temporal bone CT, such as reducing tube voltage and tube current, automatic tube voltage and tube current, and advanced iterative noise reduction algorithm, or a combination of these methods. Some methods have been shown to reduce the tube voltage and tube current to 100 kVp and 80 mAs, respectively, without compromising the image quality [12]. In the present study the radiation dose of CT technique using spectral beam shaping at 100 kVp in low-dose scanning was approximately 94% lower than that of conventional low-dose scanning. The X-ray tube of conventional low-dose group was filtered using copper and aluminum, whereas that of spectral beam shaping at 100 kVp group was filtered using Tin, tin has a high atomic number than copper and aluminum,and can filter out low-level rays while retaining high-level rays that are useful for imaging. Therefore, the radiation dose in the Sn100kVp group was lower than that in the conventional low-dose group [13–14].

In this study, the objective image quality of the spectral beam shaping at 100 kVp group was lower than that of the conventional low-dose group in each anatomical structure. This may be attributable to the higher average tube voltage of the conventional low-dose group than the spectral beam shaping at 100 kVp group, resulting in a higher ray penetration force and less noise. The subjective image quality was not significantly different between the two protocols in all anatomical structures, except for the labyrinth.This implies that, except for the labyrinth, the subjective conformance assessment was good in all anatomical structures. In this study,although the SNR of some structures of the temporal bone was sacrificed, the Sn100 energy spectrum purification technology greatly reduceed the radiation dose of temporal bone CT scanning while satisfying the diagnosability of subjective images. The third-generation dual-source CT spectral purification technology largely eliminates ineffective and low-energy photons, increasing the overall average energy [15]. In a study of CT scanning by 150 kVp with spectral beam shaping for adult temporal bone CT [16], the radiation dose was shown to decrease by 40% compared with the traditional conditions, and the diagnostic quality of the temporal bone images was equal to that of the conventional dose group. In the present study, considering the greater sensitivity of children to radiation, we chose a lower tube voltage than that used for adult temporal bone study, which greatly reduced the radiation dose compared with the conventional group.The technology still met most of the subjective image diagnostic criteria, indicating its certain application value for temporal bone CT scanning in children. In the adult study of Wang Qingyun et al. [16], the SNRs of the the air in the external auditory canal and air in the mastoid antrum did not differ from the conventional dose group;however, only in the air in the mastoid antrum in this study the objective image quality in the child group study was lower compared to the adult group. This is likely attributable to the following reasons: the tube voltage used for children was lower than that of adults, and the temporal bone density of children is lower than that of adults, resulting in a higher SNR than that in adults.

This study had some limitations. First, the sample size was small,and the study population exclusively comprised children with normal temporal bones.Second,the study did not distinguish the imaging parameters of children of different ages in detail.Third,the tube voltage used was 100 kV, which was relatively low.

In conclusion, low-dose CT using spectral beam shaping at 100 kVp can significantly reduce the radiation dose while ensuring the subjective image quality of images of inner auditory canal, ossicles, and mastoid sinuses. This technique can help reduce the radiation dose in children, especially for ray-sensitive organs, such as the lens and thyroid.This protocol can be applied for screening and review of non-inner ear deformity lesions, such as traumatic injury and otitis media in children.

Author Contribution

Y.W. conceived the study. Y.W. collated the data, and performed the statistical analysis. Y.W. wrote the main manuscript text and prepared all figures . All authors reviewed and approved the fnal the manuscript.

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No competing interests reported.

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You are reading this latest preprint version

Comparison of pediatric temporal bone computed tomography at 100kVp with tin filtration versus conventional protocol

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials and methods

2.1. Patients

2.2. Scanning and reconstruction methods

2.3. Image quality analysis

2.3.1. Objective evaluation of the image quality

2.3.2. Subjective evaluation of the image quality

2.4. Radiation dose assessment

2.5. Statistical analysis

3. Results

3.1. Comparison of the general data

3.2. Objective evaluation of the image quality

3.3. Subjective evaluation of the image quality

3.4. Radiation dose assessment

4. Discussion

5. Conclussion

Declarations

Author Contribution

References

Additional Declarations

Supplementary Files

Status:

Version 1