Lung imaging in asthmatic patients: the picture is clearer

Abstract

Imaging of the lungs in patients with asthma has evolved dramatically over the last decade with sophisticated techniques, such as computed tomography, magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography. New insights into current and future modalities for imaging in asthmatic patients and their application are discussed to potentially shed a clearer picture of the underlying pathophysiology of asthma, especially severe asthma, and the proposed clinical utility of imaging in patients with this common disease.

Figure 1. Quantitative CT of airways in asthma

MDCT analysis was performed using the Pulmonary Workstation software (VIDA) and a screen capture of the cross-sectional MDCT image is demonstrated across three segmental pathways (in blue) in the right and left lung.

Figure 2. Quantitative CT of lungs in asthma

Quantitative CT allows accurate assessment of air trapping in asthma: non-severe (upper row) and severe asthma (lower row). Trapped air defined as voxels within the lung field falling below -856 HU are demonstrated by sphericals proportional to area of air trapping (volume rendered view) in the right panels. Each lobe is color-coded. Corresponding CT sagittal views are shown in the left panels. For non-severe asthmatic (upper row) the percent air trapping values (below –856 HU) are: RUL 3%, RML 17%, RLL 0.5% and LUL 6%, LLL 8%. For severe asthmatic (lower row) the percent air trapping (below –856 HU) is: RUL 28%, RML 60%, RLL 29% and LUL 25%, LLL 27%.

Figure 3. Three-dimensional and cross-sectional quantitative CT of the airway and lungs in asthma

Quantitative rendering of airway tree in 3D with RB1 segmental pathway highlighted with numerical quantitative airway dimensions (upper image), and in cross-section with airway boundaries outlined in red (lower image).

Figure 4. MR of lungs in health and asthma

Examples of conventional proton MR images paired with corresponding slices from HP He MR images in a healthy normal subject without ventilation defects (a and b) and a healthy normal subject with ventilation defects (c and d, arrows). HP He MR images in a patient with mild-moderate persistent asthma (e) and severe asthma (f). Note the greater central extent of the defects more typical of severe asthma (f, arrowheads).

Figure 5. Functional MR in asthma

Three dimensional dynamic HP He MRI showing gas wash-in (a), breath-hold (b), and forced expiration (c and d) at a 0.5 second frame rate for a patient with moderate persistent asthma demonstrating hetereogeneous gas distribution (b) with gas trapping in the lower right and, most prominently, in the lower left lung (c and d, arrows). (e) Kinetics of wash-in and wash-out derived from regions of interest in the right upper lobe (dotted) and left upper lobe (solid) can be used to quantify regional spirometry.

Figure 6. PET imaging of the lungs

Fluorodeoxyglucose (FDG) PET/CT images depicting standardized uptake value (SUV) parametric maps overlain on CT images for a subject with mild persistent asthma during a respiratory tract infection. Areas of uptake on both (a) sagittal and (b) axial slices indicate mediastinal lymph node inflammation (black arrowheads), and selected peripheral areas of localized airway inflammation (white arrows in b).

Figure 7. Air trapping and severe exacerbations

The presence of air trapping is associated with severe asthma and severe exacerbations of asthma (Reproduced with permission from Ref.).