Korean J Radiol.  2016 Dec;17(6):950-960. 10.3348/kjr.2016.17.6.950.

The Impact of Iterative Reconstruction in Low-Dose Computed Tomography on the Evaluation of Diffuse Interstitial Lung Disease

• Lim HJ
• Chung MJ
• Shin KE
• Hwang HS
• Lee KS

• KMID: 2466292
• DOI: http://doi.org/10.3348/kjr.2016.17.6.950

Abstract

OBJECTIVE
To evaluate the impact of iterative reconstruction (IR) on the assessment of diffuse interstitial lung disease (DILD) using CT.
MATERIALS AND METHODS
An American College of Radiology (ACR) phantom (module 4 to assess spatial resolution) was scanned with 10-100 effective mAs at 120 kVp. The images were reconstructed using filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), with blending ratios of 0%, 30%, 70% and 100%, and model-based iterative reconstruction (MBIR), and their spatial resolution was objectively assessed by the line pair structure method. The patient study was based on retrospective interpretation of prospectively acquired data, and it was approved by the institutional review board. Chest CT scans of 23 patients (mean age 64 years) were performed at 120 kVp using 1) standard dose protocol applying 142-275 mA with dose modulation (high-resolution computed tomography [HRCT]) and 2) low-dose protocol applying 20 mA (low dose CT, LDCT). HRCT images were reconstructed with FBP, and LDCT images were reconstructed using FBP, ASIR, and MBIR. Matching images were randomized and independently reviewed by chest radiologists. Subjective assessment of disease presence and radiological diagnosis was made on a 10-point scale. In addition, semi-quantitative results were compared for the extent of abnormalities estimated to the nearest 5% of parenchymal involvement.
RESULTS
In the phantom study, ASIR was comparable to FBP in terms of spatial resolution. However, for MBIR, the spatial resolution was greatly decreased under 10 mA. In the patient study, the detection of the presence of disease was not significantly different. The values for area under the curve for detection of DILD by HRCT, FBP, ASIR, and MBIR were as follows: 0.978, 0.979, 0.972, and 0.963. LDCT images reconstructed with FBP, ASIR, and MBIR tended to underestimate reticular or honeycombing opacities (-2.8%, -4.1%, and -5.3%, respectively) and overestimate ground glass opacities (+4.6%, +8.9%, and +8.5%, respectively) compared to the HRCT images. However, the reconstruction methods did not differ with respect to radiologic diagnosis.
CONCLUSION
The diagnostic performance of LDCT with MBIR was similar to that of HRCT in typical DILD cases. However, caution should be exercised when comparing disease extent, especially in follow-up studies with IR.

Keyword

Model-based iterative reconstruction; Adaptive statistical iterative reconstruction; Computed tomography; Spatial resolution; Interstitial lung disease

MeSH Terms

Aged
Algorithms
Female
Humans
Lung Diseases, Interstitial/*diagnosis/diagnostic imaging
Male
Middle Aged
Models, Biological
Radiation Dosage
Radiographic Image Interpretation, Computer-Assisted/*methods
Retrospective Studies
Tomography, X-Ray Computed

Figure

• 

  Fig. 1 Example results of phantom study with model-based iterative reconstruction (MBIR) are shown (A, scanned under 120 kVp, 10 mA); B (120 kVp, 50 mA).(A) shows significant decrease in difference between maximal and minimum values (NB[i]–NA[i]) in higher spatial resolution phantom images (7 lp/cm) at lower dose (120 kVp, 10 mA) compared with (B) (120 kVp, 50 mA). (C) shows changes in numerator value when using same radiation dose and reconstruction method. MBIR images obtained at 10 mA demonstrated significant decrease in numerator value for bar resolution pattern with 7 lp/cm. ASIR = adaptive statistical iterative reconstruction, FBP = filtered back projection, HU = Hounsfield unit

• 

  Fig. 2 Bland-Altman plots for each of four observers illustrating differences in measurement of disease extent based on FBP, ASIR, and MBIR images.With MBIR images, observers overestimated extent of GGO and underestimated extent of reticular opacity. However, there were no significant differences in evaluation of extent of consolidation (data not shown). ASIR = adaptive statistical iterative reconstruction, FBP = filtered back projection, GGO = ground glass opacity, MBIR = model-based iterative reconstruction

• 

  Fig. 3 Computed tomography (CT) images from a 69-year-old man with biopsy-proven usual interstitial pneumonia.A. Standard-dose HRCT image with FBP reconstruction. B-D. Exact same level images from raw data of low-dose CT reconstructed with (B) FBP, (C) ASIR, and (D) MBIR. Blurring phenomenon due to effect of MBIR, not due to respiratory artifact is shown in (D). ASIR = adaptive statistical iterative reconstruction, FBP = filtered back projection, HRCT = high resolution computed tomography, MBIR = model-based iterative reconstruction

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