Objective: Our objective was to train machine-learning algorithms on hyperpolarized 3He magnetic resonance imaging (MRI) datasets to generate models of accelerated lung function decline in participants with chronic obstructive pulmonary disease (COPD). We hypothesized that hyperpolarized gas MRI ventilation, machine-learning and multivariate modelling could be combined to explain clinically relevant changes in forced expiratory volume in 1 sec (FEV1) over a relatively short, three year time period. Methods: Hyperpolarized 3He MRI was acquired using a coronal Cartesian FGRE sequence with a partial echo and segmented using a k-means cluster algorithm. A maximum entropy mask was used to generate a region of interest for texture feature extraction using a custom-built algorithm and PyRadiomics platform. Forward logistic-regression and principal-component-analysis were used for feature selection. Ensemble-based and single machine-learning classifiers were utilized; accuracies were evaluated using a confusion-matrix and area under the curve (AUC) of a sensitivityspecificity plot. Results: We evaluated 42 COPD patients with three year follow-up data, 27 of whom (9 Females/18 Males, 66±7 years) reported negligible changes in FEV1 and 15 participants (5 Females/10 Males, 71±8 years) reported worsening FEV1 greater than -5%pred, 30±8 months later. We generated a predictive model to explain FEV1 decline using bagged-trees trained on four texture features which correlated with FEV1 and FEV1/FVC (r=0.2-0.5; p<0.05) and yielded a classification accuracy of 85%. Conclusion: For the first time, we have employed hyperpolarized 3He MRI ventilation texture features and machine learning to identify COPD patients with accelerated decline in FEV1 with 84% accuracy.
Objective: Hyperpolarized noble gas magnetic resonance imaging (MRI) provides valuable insights on lung function, and yet is not widely available, whereas thoracic x-ray computed tomography (CT) protocols are nearly universally accessible. Our aim was to develop a texture analysis pipeline to train and test machine learning classifiers, predicting MRI-based ventilation metrics from single-volume thoracic CT in patients with chronic obstructive pulmonary disease (COPD). Methods: MR ventilation maps were generated and registered to thoracic CT datasets. Images were segmented into volumes of interest (15x15x15mm), resulting in approximately 6,000 volumes-of-interest per subject participant. 85 firstorder and texture features were calculated to describe each volume, including a new texture feature based on the size and occurrence of CT clusters (we called the cluster volume matrix), which is similar to run-length-matrix. A Logistic Regression, Linear Support Vector Machine and Quadratic Support Vector Machine were trained using 5-fold crossvalidation on a cohort of seven subjects. The highest performing classification model was then applied to a test cohort of three subjects. Results: There was qualitative spatial agreement for the experimental MRI ventilation maps and the CT-predicted functional maps. The training set was classified with 71% accuracy, while the test set was classified with 66% accuracy and area under the curve (AUC) = 0.72. Conclusions: This proof-of-concept study demonstrated feasibility in a small group of patients with moderate classification accuracy. Novel insights will be used to optimize this approach with future application to a larger heterogeneous patient cohort.
Objective: Our aim was to develop and evaluate multi-parametric response maps derived from pulmonary x-ray computed tomography (CT), 1H and hyperpolarized 3He static ventilation and diffusion-weighted magnetic resonance imaging (MRI). These maps were generated to phenotype patients with chronic obstructive pulmonary disease (COPD) based on the presence of airways disease, air trapping, emphysema, alveolar distension, and ventilation defects. Methods: To generate thoracic imaging multi-parametric response maps (mPRM), multispectral 1H, 3He and CT images were segmented and co-registered. 1H and 3He MR images were segmented using a semi-automated segmentation algorithm, the diffusion weighted MR images were segmented using a threshold-based algorithm and CT images were segmented using Pulmonary Workstation 2.0 (VIDA Diagnostics, Coralville, IA). The volume-matched segmented 1H/3He maps were registered using landmark rigid registration. The 3He maps/the diffusion weighted images were registered using an intensity-based rigid registration. CT-to-MRI co-registration was achieved using modality-independent neighborhood descriptor (MIND) deformable registration; inspiratory and expiratory CT were co-registered using an affine registration with a deformable step provided by the NiftyReg toolkit. The co-registered thoracic maps were used to generate multiparametric maps. Results: mPRM maps were generated for six different voxel classifications with increasing disease abnormality/severity as follows: 1) ventilated voxels with >-856HU/>-950HU and normal apparent diffusion coefficient (ADC) values, 2) ventilated voxels with <-856HU/<-950HU and abnormal ADC values, 3) ventilated voxels with >-856HU/>-950HU and normal ADC values, 4) ventilated voxels with <-856HU/<-950HU and abnormal ADC values, 5) unventilated voxels with >-856HU/>-950HU, and, 6) unventilated voxels with <-856HU/<-950HU. Conclusion: mPRM measurements were automated in a dedicated pipeline for MRI and CT measurements to phenotype COPD patients.
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