Pulmonary Functional Imaging: Part 2—State-of-the-Art Clinical Applications and Opportunities for Improved Patient Care

Abstract

P ulmonary functional imaging may be defined as the regional quantification of lung function by using primarily CT, MRI, and nuclear medicine techniques. The distribution of pulmonary physiologic parameters including ventilation, perfusion, gas exchange, and biomechanics can be mapped and measured noninvasively throughout the entire lungs. This regional and localized information is inaccessible by using conventional pulmonary function tests. Moreover, techniques such as hyperpolarized (HP) helium 3 ( 3 He) and xenon 129 ( 129 Xe) gas MRI are able to probe lung physiologic structure and microstructure down to the level of the alveolar-capillary units (1-3). This is beyond the spatial resolution of modern clinical CT scanners.Our review aims to provide an overview of the current status of pulmonary functional imaging. The technical and physiologic underpinnings of these pulmonary functional imaging methods were discussed in part 1 of this review (4). Here in part 2, we focus on current and emerging clinical applications. Both the multiple opportunities and the challenges in the clinical translation and deployment of pulmonary functional imaging in routine clinical practice are presented. Several approaches to facilitating clinical adoption are suggested. With continued progress in this active field, pulmonary functional imaging is anticipated to have an increasing role in our understanding of pulmonary disease and in the imaging evaluation of patients with lung disorders as illustrated in the clinical disorders discussed. OpportunitiesBecause virtually all lung disorders are heterogeneously distributed in the lungs, the regional and spatially localized information provided by using pulmonary functional imaging provides clinically relevant information beyond that of conventional pulmonary function tests. The latter, including spirometry, diffusing capacity for carbon monoxide, and body plethysmography, measure total lung function without spatial localization. Furthermore, pulmonary functional imaging methods such as HP gas MRI with 3 He and 129 Xe can probe function and microstructure at the level of the alveolar-capillary interface (1-3,5-7), as discussed in part 1 (4). This is the site of gas exchange, the fundamental and vital function of the lungs. The alveolar-capillary units are beyond the anatomic resolution of current clinical scanners such as high-spatial-resolution CT. The functional and microstructural abnormalities depicted at pulmonary functional imaging may occur early in the evolution of lung Pulmonary functional imaging may be defined as the regional quantification of lung function by using primarily CT, MRI, and nuclear medicine techniques. The distribution of pulmonary physiologic parameters, including ventilation, perfusion, gas exchange, and biomechanics, can be noninvasively mapped and measured throughout the lungs. This information is not accessible by using conventional pulmonary function tests, which measure total lung function without viewing the regional distribution. The latter is importan...

Statistical evaluation of the effectiveness of dual amplitude-gated stereotactic body radiotherapy using fiducial markers and lung volume

“…Notably, the correlation coefficient of the optimal fiducial marker was 0.99, and the median correlation coefficient of the volume of both lungs was slightly inferior at 0.94. This may be attributable to differences in the end-expiratory phase due to lung function between ipsilateral and contralateral lungs and changes in respiratory volume due to 4DCT from the waveform represented by the body surface marker [1] , [15] . The correlation between the lung tumor and fiducial markers was low, with approximately 30 % of the fiducial markers obtained by comparison between lung tumor and lung volume.…”

“…In addition, the motion amplitude difference obtained by varying the normalized setting of 50 % phase was 0.8 mm, and the maximum difference was 3.3 mm for the included patients. These motion amplitude differences are attributable to individual differences as well as to differences in movements between the body surface infrared marker and the actual lung volume, delayed transmission of respiratory information, and other causes [15] . When performing dual amplitude-gated SBRT using lung volumes and fiducial markers, phase shifts should be considered on a case-by-case basis.…”

Quantitative assessment of ventilation-perfusion relationships with gallium-68 positron emission tomography/computed tomography imaging in lung cancer patients

“…Given the basic physiologic principle that gas exchange is the primary function of the lungs and previous work demonstrating an association between D LCO and toxicity [23] , [24] , [25] , [26] , V/Q imaging may serve as a better imaging biomarker for planning and improve toxicity prediction compared to imaging of ventilation or perfusion alone. Furthermore, V/Q imaging offers opportunities for applications in pulmonary medicine, such as early detection and phenotyping of COPD [27] , assessment of severity of infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and response to therapy [28] .…”

Total Lung and Lobar Quantitative Assessment Based on Paired Inspiratory–Expiratory Chest CT in Healthy Adults: Correlation with Pulmonary Ventilatory Function

“…In the past few decades, the most clinically used methods for pulmonary functional imaging have been nuclear medicine methods with gaseous radionuclides [15]. With the advancement of CT equipment and supporting software, CT images can not only provide qualitative information for routine subjective diagnosis, but also provide rich quantitative information from axial two-dimensional to three-dimensional structure, which can broaden the view for pulmonary function evaluation [16,17]. There have been studies of quantitative CT on assessment of air trapping in small airway diseases, as well as for assessing COPD phenotype [6,18,19].…”