Ultra-low-dose chest computed tomography for interstitial lung disease using model-based iterative reconstruction with or without the lung setting

Akinori Hata, Masahiro Yanagawa, Osamu Honda, Tomo Miyata, Noriyuki Tomiyama, Akinori Hata, Masahiro Yanagawa, Osamu Honda, Tomo Miyata, Noriyuki Tomiyama

Abstract

The aim of this study was to assess the effects of reconstruction on the image quality and quantitative analysis for interstitial lung disease (ILD) using filtered back projection (FBP) and model-based iterative reconstruction (MBIR) with the lung setting and the conventional setting on ultra-low-dose computed tomography (CT).Fifty-two patients with known ILD were prospectively enrolled and underwent CT at an ultra-low dose (0.18 ± 0.02 mSv) and a standard dose (7.01 ± 2.66 mSv). Ultra-low-dose CT was reconstructed using FBP (uFBP) and MBIR with the lung setting (uMBIR-Lung) and the conventional setting (uMBIR-Stnd). Standard-dose CT was reconstructed using FBP (sFBP). Three radiologists subjectively evaluated the images on a 3-point scale (1 = worst, 3 = best). For objective image quality analysis, regions of interest were placed in the lung parenchyma and the axillary fat, and standard deviation (SD), signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) were evaluated. For 32 patients with clinically diagnosed idiopathic interstitial pneumonia, quantitative measurements including total lung volume (TLV) and the percentage of ILD volume (%ILDV) were obtained. The medians of 3 radiologists' scores were analyzed using the Wilcoxon signed-rank test and the objective noise was analyzed using the paired t test. The Bonferroni correction was used for multiple comparisons. The quantitative measurements were analyzed using the Bland-Altman method.uMBIR-Lung scored better than uMBIR-Stnd and worse than sFBP (P < .001), except for noise and streak artifact in subjective analysis. The SD decreased significantly in the order of uMBIR-Stnd, uMBIR-Lung, sFBP, and uFBP (P < .001). The SNR and CNR increased significantly in the order of uMBIR-Stnd, uMBIR-Lung, sFBP, and uFBP (P < .001). For TLV, there was no significant bias between ultra-low-dose MBIRs and sFBP (P > .3). For %ILDV, there was no significant bias between uMBIR-Lung and sFBP (p = 0.8), but uMBIR-Stnd showed significantly lower %ILDV than sFBP (P = .013).uMBIR-Lung provided more appropriate image quality than uMBIR-Stnd. Although inferior to standard-dose CT for image quality, uMBIR-Lung showed equivalent CT quantitative measurements to standard-dose CT.

Conflict of interest statement

N.T. received a research grant from GE Healthcare for this study. A.H., M.Y., O.H., and T.M. have no conflicts of interest related to this study.

The authors report no conflicts of interest.

Figures

Figure 1
Figure 1
Flowchart of enrolled patients and our procedure.
Figure 2
Figure 2
A 72-year-old woman with collagen vascular diseases (systemic sclerosis and polymyositis). Body mass index was 19.2 kg/m2. Axial images at the carina level reconstructed using FBP on standard-dose CT (A), FBP on ultra-low-dose CT (B), MBIR with the lung setting (C), and MBIR with the conventional setting (D). Ground-glass opacity (arrowheads) is depicted more clearly on MBIR with the lung setting compared with the conventional setting, but they are slightly blurred compared with FBP on standard-dose CT. The border between the lung and chest wall (black arrows) is blurred on MBIR with the conventional setting. The noise of MBIR with the conventional setting is less than that with the lung setting. FBP on ultra-low-dose CT shows poor image quality with much noise and streak artifact. CT = computed tomography, FBP = filtered back projection, MBIR = model-based iterative reconstruction.
Figure 3
Figure 3
A 66-year-old man with idiopathic interstitial pneumonia (usual interstitial pneumonia pattern). Body mass index was 22.2 kg/m2. Axial images using FBP on standard-dose CT (A), FBP on ultra-low-dose CT (B), MBIR with the lung setting (C), and MBIR with the conventional setting (D). Bronchiectasis (black arrows), reticulation (arrowheads), and small vessels (white arrows) are depicted more clearly on MBIR with the lung setting than with the conventional setting. They are depicted similarly using FBP on standard-dose CT and MBIR with the lung setting. CT = computed tomography, FBP = filtered back projection, MBIR = model-based iterative reconstruction.
Figure 4
Figure 4
A 73-year-old woman with idiopathic interstitial pneumonia (usual interstitial pneumonia pattern). Body mass index was 19.7 kg/m2. Axial images using FBP on standard-dose CT (A), FBP on ultra-low-dose CT (B), MBIR with the lung setting (C), and MBIR with the conventional setting (D). Small honeycombing is detectable on the FBP image on standard-dose CT, but it is difficult to see on ultra-low-dose CT images (arrows). CT = computed tomography, FBP = filtered back projection, MBIR = model-based iterative reconstruction.
Figure 5
Figure 5
Bland-Altman plots of TLV (A and B) and %ILDV (C and D) comparing MBIRs on ultra-low-dose CT with FBP on standard-dose CT. MBIR with lung setting (a and c) and MBIR with conventional setting (b and d). Solid thin line indicates mean difference (bias). Top and bottom dashed lines correspond to upper and lower margins of limits of agreement. Linear regression lines are indicated as solid bold lines; y = 0.004 x − 0.046, R2 = 0.001, and P = .86 for (A); y = −0.002 x − 0.009, R2 < 0.001, and P = 0.94 for (B); y = −0.031 x + 0.3, R2 = 0.01, and P = .58 for (C); y = −0.1.11 x + 0.5, R2 = 0.10, and P = 0.08 for (D). CT = computed tomography, FBP = filtered back projection, ILDV = the percentage of interstitial lung disease volume, MBIR = model-based iterative reconstruction, TLV = total lung volume%.

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