To investigate dose reduction and comparability of standard dose CT vs Ultra low dose CT in evaluating pulmonary emphysema

Highlights

• ULD CT is a comparable protocol in assessment of emphysema severity relative to standard CT.

• 95% reduction compared to standard dose.

• Thoracic CT provides a more detailed assessment of the phenotype and severity of COPD.

• ULD CT could be safely used in clinical practice to more effectively target therapies to individual patients.

Abstract

Objectives

The aim of this study was to investigate the extent of dose reduction and comparability of standard dose CT vs Ultra low dose CT in evaluating pulmonary emphysema.

Methods

Forty-nine patients with emphysema were recruited from a tertiary referral respiratory clinic. Each patient had a non-contrast Standard Dose (SD) and Ultra Low Dose (ULD) thoracic CT. The images were reconstructed using contemporary iterative reconstruction with a standard lung kernel. Lung volumes and emphysema severity was calculated using a commercially available automated densitometry segmentation package. The effective dose was calculated for both CT protocols.

Results

Automated densitometry calculated the total lung volume and percentage lung area of emphysema. The findings were highly comparable between ULD and SD protocols. A strong correlation was seen between ULD and SD images in measurement of total lung volume (R = 0.925, p < 0.001) and percentage lung involvement by densitometry (R = 0.940, p < 0.001). There is a 95% dose reduction with the ULD protocol, the mean effective dose is 0.12 ± 0.09 mSv versus 2.33 ± 1.54 mSv for the SD protocol.

Conclusions

ULD thoracic CT is a comparable protocol for the assessment of emphysema severity relative to standard dose CT. ULD CT is performed at a 95% dose reduction compared to SD CT.

Introduction

Emphysema, both in isolation and as a part of Chronic Obstructive Pulmonary Disease (COPD), is a major global health problem with an overall estimated worldwide prevalence of 7.6% [1]. Early diagnosis can facilitate identification of the disease phenotype and severity guiding treatment and management [2]. Diagnosis currently is spirometry based. There tends to be a big discordance between symptoms, spirometry and CT morphology of emphysema. GOLD staging is the classic method of defining disease severity, however; patients with the same GOLD stage may have differing disease phenotypes and therefore require more alternative treatment. Radiology provides a clear and detailed account of the phenotype and severity of disease and therefore in conjunction with spirometry is optimal for the quantification and description of the COPD. CT is non-invasive and provides detailed evaluation of the morphology of the emphysema and its distribution. CT can also detect other causes for symptoms such as; shortness of breath, cough or haemoptysis. In our CT protocol we included calculations of densitometry and lung volumes, contributing added value to the evaluation of symptoms and treatment planning. Most patients benefit from medical therapy such as; bronchodilators, glucocorticoids and antibiotics for acute exacerbations while a smaller subgroup will benefit from more invasive lung volume reduction procedures [3]. CT guides cardiothoracic planning in this latter group.

This study demonstrates the added value of CT in the assessment of COPD and employs an ULD technique comparable to that of a combined dose from a PA and Lateral chest radiograph.