Project Summary Cystic brosis is a genetic lung disease marked by progressive decline in lung structure and function. Use of the gold standards of CT scans and pulmonary function tests (PFT's) to assess lung structure and function, respectively, are hindered by the ionizing radiation applied to the patient in CT scanning, and the inability of very young patients to perform PFTs. The goal of this research is to determine whether electrical impedance tomography (EIT) can provide sensitive measures of changes in lung structure and function in CF patients of all ages. To test this hypothesis we will study the ability of EIT images and derived measures to detect structural changes through a 3 year longitudinal study and changes pre and post-treatment for an acute PE. This project is part of a long term goal to develop an EIT system for imaging patients with chronic lung disease. EIT is a noninvasive, non-ionizing functional imaging technique in which images are formed from voltages measured on electrodes on the body arising from imperceptilbe applied currents. Since EIT is a safe and portable technology with no damaging side e ects, it can be used as needed. This research builds on the results of a previous grant in which a strong correlation was demonstrated between EIT-derived measures of pulmonary function and PFT output measures in CF patients, and the ability to identify air trapping was demonstrated. In this work, novel EIT hardware and algorithms will be developed to obtain 3-D reconstructions with current patterns that provide the highest signal-to-noise ratio (SNR) on all electrodes. The design and validation of this improved high performance EIT system is the rst speci c aim. The second speci c aim is to develop algorithms in 3-D for the computation of regional aeration and ventilation perfusion ratio (V/Q) maps in 3-D, and for the identi cation and quanti cation of regions of air trapping and consolidation. The third aim is to determine the ability of EIT to identify functional and structural physiological changes that occur with disease progression through a clinical study with the following subaims: to determine whether EIT can serve as a selective alternative for CT to identify regions of air trapping and consolidation, whether EIT can provide clinically useful information about response to treatment for an acute PE, and whether EIT can provide longitudinal information about structural changes in the lung. 1