Emphysema quantification using chest CT: influence of radiation dose reduction and reconstruction technique

Annemarie M Den Harder,Julien Milles,Tim Leiner,Arnold M R Schilham,Erwin De Boer,Ricardo P J Budde,Martin J Willemink,Pim A De Jong,Martijn F Boomsma,Suzanne J Lagerweij

doi:10.1186/s41747-018-0064-3

Annemarie M Den Harder, Julien Milles + Show 8 more

Open Access

https://doi.org/10.1186/s41747-018-0064-3

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Abstract

BackgroundComputed tomography (CT) emphysema quantification is affected by both radiation dose (i.e. image noise) and reconstruction technique. At reduced dose, filtered back projection (FBP) results in an overestimation of the amount of emphysema due to higher noise levels, while the use of iterative reconstruction (IR) can result in an underestimation due to reduced noise. The objective of this study was to determine the influence of dose reduction and hybrid IR (HIR) or model-based IR (MIR) on CT emphysema quantification.MethodsTwenty-two patients underwent inspiratory chest CT scan at routine radiation dose and at 45%, 60% and 75% reduced radiation dose. Acquisitions were reconstructed with FBP, HIR and MIR. Emphysema was quantified using the 15th percentile of the attenuation curve and the percentage of voxels below -950 HU. To determine whether the use of a different percentile or HU threshold is more accurate at reduced dose levels and with IR, additional measurements were performed using different percentiles and HU thresholds to determine the optimal combination.ResultsDose reduction resulted in a significant overestimation of emphysema, while HIR and MIR resulted in an underestimation. Lower HU thresholds with FBP at reduced dose and higher HU thresholds with HIR and MIR resulted in emphysema percentages comparable to the reference. The 15th percentile quantification method showed similar results as the HU threshold method.ConclusionsThis within-patients study showed that CT emphysema quantification is significantly affected by dose reduction and IR. This can potentially be solved by adapting commonly used thresholds.

Highlights

Computed tomography (CT) emphysema quantification is affected by both radiation dose and reconstruction technique
Emphysema is traditionally a pathology-based diagnosis [4, 5], CT densitometry of the lungs has demonstrated it to be associated with airflow obstruction, forced expiratory volume in 1 s and severity according to the Global initiative for chronic Obstructive Lung Disease (GOLD) criteria [6,7,8]
Images were reconstructed at a slice thickness of 2 mm with filtered back projection (FBP), hybrid iterative reconstruction (IR) (HIR; iDose level 4, Philips Healthcare, Best, The Netherlands) and model-based IR (MIR; IMR level 2, Philips Healthcare, Best, The Netherlands)

Summary

Introduction

Computed tomography (CT) emphysema quantification is affected by both radiation dose (i.e. image noise) and reconstruction technique. Additional quantification of emphysema on screening CT acquisitions will likely gain importance. This additional information may contribute to optimisation of the benefits and cost-effectiveness of CT screening [3]. Emphysema is traditionally a pathology-based diagnosis [4, 5], CT densitometry of the lungs has demonstrated it to be associated with airflow obstruction, forced expiratory volume in 1 s and severity according to the Global initiative for chronic Obstructive Lung Disease (GOLD) criteria [6,7,8]. CT, on the other hand, provides in vivo information about pathological changes and allows for differentiation between airway obstruction and emphysematous destruction [10]

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