Quantitative Assessment of Regional Alveolar Ventilation and Gas Volume Using 13N-N2 Washout and PET

Quantitative Assessment of Regional Alveolar Ventilation and Gas Volume Using ¹³N-N₂ Washout and PET

Jean-Christophe Richard, MD, PhD¹^,2, Marc Janier, MD, PhD³^,4, Franck Lavenne³, Christian Tourvieille³, Didier Le Bars, PharmD, PhD³, Nicolas Costes³, Gerard Gimenez, PhD³ and Claude Guerin, MD, PhD¹^,2

¹ Service de Réanimation Médicale et d’Assistance Respiratoire, Lyon, France
² Equipe d’Accueil Universitaire, Lyon, France
³ Hôpital Neuro-Cardiologique, Centre d’Exploration et de Recherche Médicales par Emission de Positons, Lyon, France
⁴ Hôpital Neuro-Cardiologique, Centre de Recherche et d’Application en Traitement de l’Image et du Signal (Unité Mixte de Recherche, Centre National de la Recherche Scientifique), Batiment Centre d’Etudes et de Recherche Médicales par Émission de Positons, Lyon, France

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FIGURE 1. Experimental setup to deliver ¹³N-N₂ to lungs. C_input is tracer concentration measured at equilibrium at the Y piece level.

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FIGURE 2. Generation of a pulmonary time–activity curve from the multiple-image dataset during washout in 1 pig. Regions of interest (ROIs) are drawn on multiple transverse slices of the first PET image obtained during washout (0–5 s) of ¹³N-N₂. These ROIs are then superimposed on subsequent frames. For clarity, only one ROI and one of the multiple thoracic slices are displayed on 5 of 37 time points.

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FIGURE 3. Parametric images of thorax density obtained in control pig (A) and in pig with lung injury (B). Slices are displayed according to radiologic convention. In each pig, only 12 of 19 planes are displayed for clarity.

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FIGURE 4. First frame of ¹³N-N₂ washout obtained in control pig (A) and in pig with lung injury (B). Slices are displayed according to radiologic convention. In each pig, only 12 of 19 planes are displayed for clarity.

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FIGURE 5. Examples of curve fitting using monocompartmental model (A) and bicompartmental model (C) for the same representative ROI in a control pig. ${circ}$ , Time–activity curve data points obtained with PET. Continuous lines are fitted data using monocompartmental or bicompartmental model. (B) and (D) Corresponding plots of residuals over time. (E) Extra sum of square analysis for nested models as a way to compare relevance of models.

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FIGURE 6. (A) Relationship between regional alveolar gas volume measured from transmission (VA_T_rans) and emission scans (VA_emission). Each symbol is the regional value of VA in one lung ROI in a given experimental condition in 1 animal. The total number of ROIs amounts to 749. Solid and dashed lines are regression line and line of identity, respectively. (B) Bland–Altman representation (23) of relationship shown in A. Solid and dashed lines represent mean and mean ± SD, respectively.

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FIGURE 7. Relationships between preset minute-ventilation and alveolar ventilation (VA_emission, A) or specific ventilation ( $V$ A_emission/VA_emission, B) assessed with PET in control pigs (•) and pigs with lung injury ( ${circ}$ ). For each pig, VA_emission and $V$ A_emission/VA_emission were measured regionally using modeling in each ROI. Regional values of VA_emission were summed to obtain global ventilation expressed as mean ± SD for each experimental group (A). Median values of regional $V$ A_emission/VA_emission were calculated for each animal and data were finally expressed as mean ± SD for each experimental group (B). Bars are SDs. Solid and dotted lines are regression lines for control and oleic acid groups, respectively.