KEYWORDS: Lung, Point clouds, Image segmentation, Education and training, Data modeling, Magnetic resonance imaging, Computed tomography, Performance modeling, Databases, Spirometry
This paper addresses the problem of lung lobe partitioning in ultra-short time echo (UTE) MRI acquisitions, which are recently used for lung ventilation assessment with MRI spirometry. Because of the low image contrast, which does not enable the lung fissures display, the developed approach relies only on the vascular structures which still can be segmented from these images. The vascular network is segmented in lobes in order to generate reference clusters used for lung space partitioning. A point cloud representing the unstructured points of the vascular medial axis is partitioned in five lobes exploiting the PointNet++ framework. The PointNet++ model is trained on data extracted from CT acquisitions and labeled using the airway and vascular trees connectivity. The airway tree lobes will define the lung lobar regions, which are propagated on the vessel structure to achieve the complete vascular labeling. A separate model is trained for the right and left lungs in order to alleviate for limited input point cloud size imposed by the model architecture and reach a high precision in classification. The trained model is applied to UTE-MRI data to generate, for a given subject, a point cloud reference that will be used for vascular lobes clustering, which will be then exploited for lung space partitioning in lobes. The approach was quantitatively evaluated on 10 CT volumes from LUNA16 dataset and qualitatively tested on additional 25 CT and 15 UTE-MRI datasets. The analysis of CT data results shows pertinent lung partitioning with respect to the lung fissures, even if a precise fissure localization is not achieved. Such result is however expected, since no information related to the lung fissure is exploited in our method because this would not be applicable to UTE-MRI data. Nevertheless, the proposed partitioning respects the vascular lobes and, to the best of our knowledge, is novel for lung MRI sequences making it possible the regional investigation of ventilation parameters in MRI spirometry. The method can be further on extended for lung fissure matching in CT data by integrating new constraints related to fissure detection.
Fibrosing idiopathic interstitial pneumonia (fIIP) is a subclass of interstitial lung diseases, which leads to fibrosis in a continuous and irreversible process of lung function decay. Patients with fIIP require regular quantitative follow-up with CT and several image biomarkers have already been proposed to grade the pathology severity and try to predict the evolution. Among them, we cite the spatial extent of the diseased lung parenchyma and airway and vascular remodeling markers. COVID-19 (Cov-19) presents several similarities with fIIP and this condition is moreover suspected to evolve to fIIP in 10-30% of severe cases. Note also that the main difference between Cov-19 and fIIP is the presence of peripheral ground glass opacities and less or no amount of fibrosis in the lung, as well as the absence of airway remodeling. This paper proposes a preliminary study to investigate how existing image markers for fIIP may apply to Cov-19 phenotyping, namely texture classification and vascular remodeling. In addition, since for some patients, the fIIP/Cov-19 follow-up protocol imposes CT acquisitions at both full inspiration and full expiration, this information could also be exploited to extract additional knowledge for each individual case. We hypothesize that taking into account the two respiratory phases to analyze breathing parameters through interpolation and registration might contribute to a better phenotyping of the pathology. This preliminary study, conducted on a reduced number of patients (eight Cov-19 of different severity degrees, two fIIP patients and one control), shows a great potential of the selected CT image markers.
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