Korean J Radiol.  2018 Aug;19(4):809-817. 10.3348/kjr.2018.19.4.809.

Comparison of Filtered Back Projection, Hybrid Iterative Reconstruction, Model-Based Iterative Reconstruction, and Virtual Monoenergetic Reconstruction Images at Both Low- and Standard-Dose Settings in Measurement of Emphysema Volume and Airway Wall Thickness: A CT Phantom Study

• Kim C
• Lee KY
• Shin C
• Kang EY
• Oh YW
• Ha M
• Ko CS
• Cha J

• KMID: 2413711
• DOI: http://doi.org/10.3348/kjr.2018.19.4.809

Abstract

OBJECTIVE
To evaluate the accuracy of emphysema volume (EV) and airway measurements (AMs) produced by various iterative reconstruction (IR) algorithms and virtual monoenergetic images (VME) at both low- and standard-dose settings.
MATERIALS AND METHODS
Computed tomography (CT) images were obtained on phantom at both low- (30 mAs at 120 kVp) and standard-doses (100 mAs at 120 kVp). Each CT scan was reconstructed using filtered back projection, hybrid IR (iDose4; Philips Healthcare), model-based IR (IMR-R1, IMR-ST1, IMR-SP1; Philips Healthcare), and VME at 70 keV (VME70). The EV of each air column and wall area percentage (WA%) of each airway tube were measured in all algorithms. Absolute percentage measurement errors of EV (APEvol) and AM (APEWA%) were then calculated.
RESULTS
Emphysema volume was most accurately measured in IMR-R1 (APEvol in low-dose, 0.053 ± 0.002; APEvol in standard-dose, 0.047 ± 0.003; all p < 0.001) and AM was the most accurate in IMR-SP1 on both low- and standard-doses CT (APEWA% in low-dose, 0.067 ± 0.002; APEWA% in standard-dose, 0.06 ± 0.003; all p < 0.001). There were no significant differences in the APEvol of IMR-R1 between low- and standard-doses (all p > 0.05). VME70 showed a significantly higher APEvol than iDose4, IMR-R1, and IMR-ST1 (all p < 0.004). VME70 also showed a significantly higher APEWA% compared with the other algorithms (all p < 0.001).
CONCLUSION
IMR was the most accurate technique for measurement of both EV and airway wall thickness. However, VME70 did not show a significantly better accuracy compared with other algorithms.

Keyword

Computed tomography; Model-based iterative reconstruction; Virtual monoenergetic image; Emphysema volume; Airway wall thickness

MeSH Terms

Emphysema*
Tomography, X-Ray Computed

Figure

• 

  Fig. 1 Illustration and CT images of CTP674 lung phantom (The Phantom Laboratory).A. Illustration of CTP674 lung phantom. Nine air columns with three different diameters and volumes were chosen for EV measurements (E1–E9), and three polycarbonate tubes (airway tubes) with different wall thicknesses and angles were analyzed for airway wall measurements (A1–A3). Two airway tubes (A1 and A2) were placed at different angle of 30° from z-axis of CT couch. B. CT scans with various algorithms at low-dose setting. C. CT scans with various algorithms at standard-dose setting. CT = computed tomography, EV = emphysema volume, FBP = filtered back projection, IMR-R1 = MIR with image definition of body routine level 1, IMR-SP1 = MIR with image definition of sharp plus level, IMR-ST1 = MIR with image definition of body soft tissue level 1, MIR = model-based iterative reconstruction, VME70 = standard virtual monoenergetic dataset at 70 keV

• 

  Fig. 2 APEvol of across all air columns (all of 5-, 10-, and 30-mm air columns) on (A) low-dose CT and (B) standard-dose CT.Mean APEvol in all air columns was lowest in IMR-R1 in both low-dose and standard-dose settings. APE = absolute percentage measurement error, APEvol = APE of EV

• 

  Fig. 3 APEvol of each column (each 5-, 10-, and 30-mm) on (A) low-dose CT and (B) standard-dose CT.Mean APEvol in all air columns was lowest in IMR-R1 in both low-dose and standard-dose settings. Mean APEvol decreased as volume of air columns increased.

• 

  Fig. 4 Mean APEvol in each air column on (A) low-dose CT and (B) standard-dose CT.Significant differences in APEvol from IMR-R1 are marked with an asterisk (*).

• 

  Fig. 5 APEWA% of across all airway tubes (all of A1, A2, and A3 airway tubes) on (A) low-dose CT and (B) standard-dose CT.Mean APEWA% of across all airway tubes was lowest in IMR-SP1 in both low-dose and standard-dose settings. Mean APEWA% decreased as WA% increased. APEWA% = absolute percentage measurement error of wall area percentage, WA% = wall area percentage

• 

  Fig. 6 Absolute percentage measurement error of each airway tube (each A1, A2, and A3 airway tube) on (A) low-dose CT and (B) standard-dose CT.Mean APEWA% decreased as WA% increased.

• 

  Fig. 7 Mean APEWA% in each airway tube on (A) low-dose and (B) standard-dose CT.Significant differences in APEWA% from IMR-SP1 are marked with asterisk (*).

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