Ultra-low-dose thoracic CT with model-based iterative reconstruction (MBIR) in cystic fibrosis patients undergoing treatment with cystic fibrosis transmembrane conductance regulators (CFTR)

F Moloney,R.G Kavanagh,N.J Ronan,T.M Grey,S Joyce,D.J Ryan,N Moore,O.J O'Connor,B.J Plant,M.M Maher

doi:10.1016/j.crad.2020.12.003

Abstract

To assess the utility of a volumetric low-dose computed tomography (CT) thorax (LDCTT) protocol at a dose equivalent to a posteroanterior (PA) and lateral chest radiograph for surveillance of cystic fibrosis (CF) patients. A prospective study was undertaken of 19 adult patients with CF that proceeded to LDCTT at 12 and 24 months following initiation of ivacaftor. A previously validated seven-section, low-dose axial CT protocol was used for the 12-month study. A volumetric LDCTT protocol was developed for the 24-month study and reconstructed with hybrid iterative reconstruction (LD-ASIR) and pure iterative reconstruction (model-based IR [LD-MBIR]). Radiation dose was recorded for each scan. Image quality was assessed quantitatively and qualitatively, and disease severity was assessed using a modified Bhalla score. Statistical analysis was performed and p-values of <0.05 were considered statistically significant. Volumetric LD-MBIR studies were acquired at a lower radiation dose than the seven-section studies (0.08±0.01 versus 0.10±0.02 mSv; p=0.02). LD-MBIR and seven-section ASIR images had significantly lower levels of image noise compared with LD-ASIR images (p<0.0001). Diagnostic acceptability scores and depiction of bronchovascular structures were found to be acceptable for axial and coronal LD-MBIR images. LD-MBIR images were superior to LD-ASIR images for all qualitative parameters assessed (p<0.0001). No significant change was observed in mean Bhalla score between 1-year and 2-year studies (p=0.84). The use of a volumetric LDCTT protocol (reconstructed with pure IR) enabled acquisition of diagnostic quality CT images, which were considered extremely useful for surveillance of CF patients, at a dose equivalent to a PA and lateral chest radiograph.

Highlights

Pulmonary disease is the primary cause of morbidity and mortality in patients with cystic fibrosis (CF).[1]
The major limitation to routine adoption of computed tomography (CT) for monitoring CF lung disease is the substantial radiation exposure associated with conventional chest CT compared with plain radiography (3.5 versus 0.02 mSv)
The unit has used this protocol on a routine basis to monitor pulmonary disease in CF patients in a study assessing the safety, efficacy, and tolerability of a range of CF transmembrane conductance regulator (CFTR) drugs including ivacaftor (Kalydeco).[8]

Summary

Introduction

Pulmonary disease is the primary cause of morbidity and mortality in patients with cystic fibrosis (CF).[1]. The major limitation to routine adoption of CT for monitoring CF lung disease is the substantial radiation exposure associated with conventional chest CT compared with plain radiography (3.5 versus 0.02 mSv). CFTR mutation frequencies are highly variable and demonstrate regional differences in prevalence.[14,15] This heterogeneity is thought to be explained by the ethnic or geographic origin of the parents and grandparents of the affected child.[14]

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Conclusion