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Association of Focal Radiation Dose Adjusted on Cross Sections with Subsolid Nodule Visibility and Quantification on Computed Tomography Images Using AIDR 3D

Posted Aug 31, 2018 Updated Apr 10, 2023
By Yukihiro Nagatani MD , Hiroshi Moriya MD PhD , Satoshi Noma MD , Shigetaka Sato MD , Shinsuke Tsukagoshi PhD , Tsuneo Yamashiro MD , Mitsuhiro Koyama MD PhD , Noriyuki Tomiyama MD PhD , Yoshiharu Ono MD PhD , Sadayuki Murayama MD PhD , Kiyoshi Murata MD PhD
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Rationale and Objectives

The objectives of this study were to compare the visibility and quantification of subsolid nodules (SSNs) on computed tomography (CT) using adaptive iterative dose reduction using three-dimensional processing between 7 and 42 mAs and to assess the association of size-specific dose estimate (SSDE) with relative measured value change between 7 and 84 mAs (RMVC 7–84 ) and relative measured value change between 42 and 84 mAs (RMVC 42–84 ).

Materials and Methods

As a Japanese multicenter research project (Area-detector Computed Tomography for the Investigation of Thoracic Diseases [ACTIve] study), 50 subjects underwent chest CT with 120 kV, 0.35 second per location and three tube currents: 240 mA (84 mAs), 120 mA (42 mAs), and 20 mA (7 mAs). Axial CT images were reconstructed using adaptive iterative dose reduction using three-dimensional processing. SSN visibility was assessed with three grades (1, obscure, to 3, definitely visible) using CT at 84 mAs as reference standard and compared between 7 and 42 mAs using t test. Dimension, mean CT density, and particular SSDE to the nodular center of 71 SSNs and volume of 58 SSNs (diameter >5 mm) were measured. Measured values (MVs) were compared using Wilcoxon signed-rank tests among CTs at three doses. Pearson correlation analyses were performed to assess the association of SSDE with RMVC 7–84 : 100 × (MV at 7 mAs − MV at 84 mAs)/MV at 84 mAs and RMVC 42–84 .

Results

SSN visibilities were similar between 7 and 42 mAs (2.76 ± 0.45 vs 2.78 ± 0.40) ( P = .67). For larger SSNs (>8 mm), MVs were similar among CTs at three doses ( P > .05). For smaller SSNs (<8 mm), dimensions and volumes on CT at 7 mAs were larger and the mean CT density was smaller than 42 and 84 mAs, and SSDE had mild negative correlations with RMVC 7–84 ( P < .05).

Conclusions

Comparable quantification was demonstrated irrespective of doses for larger SSNs. For smaller SSNs, nodular exaggerating effect associated with decreased SSDE on CT at 7 mAs compared to 84 mAs could result in comparable visibilities to CT at 42 mAs.

Introduction

Persistent subsolid nodules (SSNs) are often an early sign of lung cancer , and pure ground-glass nodules should be followed up at 6–12 months to confirm their persistence and every 2 years until 5 years; part-solid nodules should be followed up at 3–6 months to confirm their persistence and annually for 5 years, if unchanged and solid component size remain less than 6 mm by chest computed tomography (CT) from their initial detections in cases with a diameter of 6 mm or more according to the latest management guidelines by the Fleischner Society . Dependable quantitative assessment of changes in SSN volume or density on CT images supports the feasibility of subjective visual inspection of changes in SSN size, which is typically applicable in routine clinical settings, and could be useful to determine an appropriate choice of treatment . The accuracy of the volume measurement of lung nodules, including SSNs, is influenced by some mutually related factors, such as characteristics of the nodular margin, algorithm of the measurement tool, data acquisition, and reconstruction parameters . Among these factors, radiation dose has a considerable effect on SSN quantification and should be as low as possible for CT to be applicable as the follow-up tool in terms of the exaggerating influence of radiation dose on carcinogenesis probability .

In combination with an iterative reconstruction (IR) algorithm, ultra–low-dose CT (0.16–0.29 mSv) has recently demonstrated comparable detection performance of lung nodules to low-dose computed tomography (LDCT) (0.92–1.74 mSv) regardless of the different IR techniques developed by different manufacturers . Furthermore, in addition to lung nodule detectability, simulated SSNs placed in an anthropomorphic phantom have been shown to be measured on ultra–low-dose CT images obtained with an IR algorithm as reliably as on LDCT images obtained with an IR algorithm despite the different acquisition and reconstruction techniques . However, simulated nodules in an anthropomorphic phantom lack the diversity and complexity of clinical nodules and background lung fields modified by dependent effects and respiratory levels. In contrast, the size-specific dose estimate (SSDE) corresponding to an individual image plane has been recently introduced as one of the more practicable dose adjustments on body cross sections , and SSDEs in the transaxial plane, including SSNs, can vary among nodular locations even in an individual patient and have an association with SSN detection performance.

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Materials and Methods

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Patients’ Populations

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Image Data Acquisition and Reconstruction

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Subsolid Nodule Visibility Evaluation

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Measurement of the Dimension, Density, and Volume of Subsolid Nodules

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Association of SSDE with Relative Measured Value Change and Image Noise

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Statistical Analyses

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Results

Radiation Dose and Total Lung Volume Measurement

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Subsolid Nodule Visibility

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TABLE 1

Comparison in SSN Visibility Between 42 and 7 mAs with Reference to 84 mAs

Number 42 mAs 7 mAs_P_ Value Total SSNs (5 mm ≤ LD) 71 2.78 ± 0.40 2.66 ± 0.45 .658 Smaller SSNs (5 mm ≤ LD ≤ 8 mm) 31 2.66 ± 0.45 2.67 ± 0.48 .856 Larger SSNs (8 mm ≤ LD) 40 2.88 ± 0.33 2.83 ± 0.41 .323

LD, longest diameter; SSN, subsolid nodule.

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Measurement of the Dimension, Density, and Volume of Subsolid Nodules

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TABLE 2

Bland-Altman Plots for Interobserver Variation in the Measured Values for SSN Dimension, Mean Density, and Volume

SSN Dimension (mm 2 ) Difference in the Measured Value Slope of the Regression Line with the Mean Value Distribution Mean 95% Level of Confidence LOA_r_ Value_P_ Value 84 mAs 3.5 −50.4 to 57.3 −39.1 to 55.4 0.049 .682 42 mAs 3.4 −57.3 to 64.1 −44.6 to 62.1 0.084 .485 7 mAs 3.3 −62.6 to 69.2 −48.7 to 67.2 0.132 .272

SSN Volume (mm 3 ) Difference in the Measured Value Slope of the Regression Line with the Mean Value Distribution Mean 95% Level of Confidence LOA_r_ Value_P_ Value 84 mAs 12.2 −252.8 to 277.3 −191.3 to 270.3 0.079 .510 42 mAs 17.0 −289.9 to 323.8 −218.7 to 314.6 0.021 .860 7 mAs 9.2 −308.6 to 327.0 −234.8 to 321.3 0.207 .084

SSN Mean CT Density (HU) Difference in the Measured Value Slope of the Regression Line with the Mean Value Distribution Mean 95% Level of Confidence MDC_r_ Value_P_ Value 84 mAs −1.1 −67.6 to 65.3 66.5 0.023 .667 42 mAs 0.9 −69.1 to 71.1 70.1 −0.246 .063 7 mAs 1.3 −71.7 to 74.3 73.0 −0.036 .788

CT, computed tomography; LOA, limit of agreement; MDC, minimal detectable change; SSN, subsolid nodule.

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Figure 1, Transaxial images including the center of a pure ground-glass nodule at the right lower lobe in a 64-year-old woman with a body mass index of 21.2. The size-specific dose estimate in this cross section was 0.684 mGy. The measured values of nodular dimension on CT with AIDR 3D at 84 mAs (a) , 42 mAs (b) , and 7 mAs (c) were 35.5, 41.0, and 51.8 mm 2 , respectively. RMVC 42–84 and RMVC 7–84 were 15.4% and 45.6%. The measured values of nodular mean density on CT with AIDR 3D at 84, 42, and 7 mAs were −701.1, −702.5, and −716.5 HU, respectively. RMVC 42–84 and RMVC 7–84 were 0.2% and 2.2%. The measured values of nodular volume on CT with AIDR 3D at 84, 42, and 7 mAs were 143.9, 188.6, and 196.2 mm 3 , respectively. RMVC 42–84 and RMVC 7–84 were 31.1% and 36.3%. AIDR 3D, adaptive iterative dose reduction using three-dimensional processing; CT, computed tomography; RMVC 7–84 , relative measured value change between 7 and 84 mAs; RMVC 42–84 , relative measured value change between 42 and 84 mAs.

TABLE 3

Comparison of SSN Dimensions Among 84, 42, and 7 mAs

Number 84 mAs (mm 2 ) 42 mAs (mm 2 ) 7 mAs (mm 2 )P Value Total SSNs (5 mm ≤ LD) 71 80.3 ± 67.5 80.3 ± 67.5 84.7 ± 68.8 .001 \* Smaller SSNs (5 mm ≤ LD ≤ 8 mm) 31 31.9 ± 8.6 33.9 ± 10.1 37.0 ± 10.8 <.001 † Larger SSNs (8 mm ≤ LD) 40 117.7 ± 69.6 116.4 ± 68.9 121.8 ± 72.0 .088

LD, longest diameter; SSN, subsolid nodule.

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Figure 2, Transaxial images including the center of a part-solid nodule at the left upper lobe in an 80-year-old woman with a body mass index of 25.6. The size-specific dose estimate in this cross section was 0.736 mGy. The measured values of nodular dimension on CT with AIDR 3D at 84 mAs (a) , 42 mAs (b) , and 7 mAs (c) were 208.8, 203.1, and 207.8 mm 2 , respectively. RMVC 42–84 and RMVC 7–84 were −2.7% and −0.5%. The measured values of nodular mean density on CT with AIDR 3D at 84, 42, and 7 mAs were −681.5, −656.1, and −669.6 HU, respectively. RMVC 42–84 and RMVC 7–84 were −3.7% and −1.7%. The measured values of nodular volume on CT with AIDR 3D at 84, 42, and 7 mAs were 1481.7, 1351.8, and 1471.6 mm 3 , respectively. RMVC 42–84 and RMVC 7–84 were −8.7% and −0.6%. AIDR 3D, adaptive iterative dose reduction using three-dimensional processing; CT, computed tomography; RMVC 7–84 , relative measured value change between 7 and 84 mAs; RMVC 42–84 , relative measured value change between 42 and 84 mAs.

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TABLE 4

Comparison of SSN Mean Densities Among 84, 42, and 7 mAs

Number 84 mAs (HU) 42 mAs (HU) 7 mAs (HU)P Value Total SSNs (5 mm ≤ LD) 71 −613.2 ± 117.1 −618.1 ± 115.7 −626.8 ± 107.3 .089 Smaller SSNs (5 mm ≤ LD ≤ 8 mm) 31 −635.6 ± 115.7 −634.2 ± 123.2 −651.8 ± 101.6 .050 \* Larger SSNs (8 mm ≤ LD) 40 −595.9 ± 116.7 −605.7 ± 108.2 −607.4 ± 108.9 .294

LD, longest diameter; SSN, subsolid nodule.

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TABLE 5

Comparison in SSN Volumes Among 84, 42, and 7 mAs

Number 84 mAs (mm 3 ) 42 mAs (mm 3 ) 7 mAs (mm 3 )P Value Total SSNs (5 mm ≤ LD) 58 536.0 ± 672.6 530.6 ± 628.8 565.9 ± 676.1 .001 \* Smaller SSNs (5 mm ≤ LD ≤ 8 mm) 31 139.3 ± 67.4 146.6 ± 70.0 164.0 ± 80.7 <.001 † Larger SSNs (8 mm ≤ LD) 27 991.5 ± 763.9 971.5 ± 695.3 1027.2 ± 762.3 .097

LD, longest diameter; SSN, subsolid nodule.

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Association of SSDE with Relative Measured Value Change and Image Noise

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Figure 3, Scatter plots of RMVC 42–84 (%) are shown in the nodular dimension with SSDE on computed tomography with adaptive iterative dose reduction using three-dimensional processing at 42 mAs for 31 subsolid nodules with the longest diameter of less than 8 mm (a) and 40 subsolid nodules with the longest diameter of 8 mm or more (b) , and of RMVC 7–84 (%) in the nodular dimension with SSDE on computed tomography with adaptive iterative dose reduction using three-dimensional processing at 7 mAs for 31 subsolid nodules with the longest diameter of less than 8 mm (c) and 40 subsolid nodules with the longest diameter of 8 mm or more (d) . RMVC 7–84 , relative measured value change between 7 and 84 mAs; RMVC 42–84 , relative measured value change between 42 and 84 mAs; SSDE, size-specific dose estimate.

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Figure 4, Scatter plots of RMVC 42–84 (%) are shown in the nodular mean CT density with SSDE on CT with AIDR 3D at 42 mAs for 31 subsolid nodules with the longest diameter of less than 8 mm (a) and 40 subsolid nodules with the longest diameter of 8 mm or more (b) , and of RMVC 7–84 (%) in the nodular dimension with SSDE on CT with AIDR 3D at 7 mAs for 31 subsolid nodules with the longest diameter of less than 8 mm (c) and 40 subsolid nodules with the longest diameter of 8 mm or more (d) . CT, computed tomography; RMVC 7–84 , relative measured value change between 7 and 84 mAs; RMVC 42–84 , relative measured value change between 42 and 84 mAs; SSDE, size-specific dose estimate.

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Figure 5, Scatter plots of RMVC 42–84 (%) are shown in the nodular volume with SSDE on computed tomography with AIDR 3D at 42 mAs for 31 subsolid nodules with the longest diameter of less than 8 mm (a) and 27 subsolid nodules with the longest diameter of 8 mm or more (b) , and of RMVC 7–84 (%) in the nodular dimension with SSDE on computed tomography with AIDR 3D at 7 mAs for 31 subsolid nodules with the longest diameter of less than 8 mm (c) and 27 subsolid nodules with the longest diameter of 8 mm or more (d) . RMVC 7–84 , relative measured value change between 7 and 84 mAs; RMVC 42–84 , relative measured value change between 42 and 84 mAs; SSDE, size-specific dose estimate.

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Discussion

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The Extent of Patients’ Overlap Between This Study and Our Previous Ones

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The ACTIve Study Group

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Academic Radiology, Volume 25, Issue 9
Journals General Radiology
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