Assessment of Hyperpolarized Gas Ventilation Defect Percentage via User-defined Defect Thresholds

Motivation: A common endpoint of Hyperpolarized Gas MRI (HPG) is the ventilation defect percentage (VDP), but the signal threshold which defines ventilation defects differs among published techniques. Goal(s): Allow a human reader to manually choose a threshold which best identifies ventilation defects and assess the method which best represents the selection. Approach: A custom GUI program was developed and 65 HPG cases were evaluated by multiple readers. The selected threshold values were compared with those of commonly used techniques. Results: The reader thresholds were often lower than those of published techniques for lower-VDP cases and higher in higher-VDP cases. Impact: Single-threshold VDP methods are often discordant with human reader selection of defect thresholds. The extent to which defect mis-labeling is acceptable differs substantially between researchers and radiologists. Defect maps should always be evaluated visually and mis-labeled voxels corrected if necessary.