Detection of Subtle Asthma
The lung attenuation curve is a histogram that plots the frequency (number of pixels) versus X-ray attenuation (Hounsfield Units). Patients are imaged before and after a methacholine challenge. Pre- and post-challenge attenuation curves are plotted. An asthmatic patient shows a leftward shift of the LAC post-challenge that reflects air-trapping and a corresponding decrease in attenuation. A normal (non-asthmatic) patient will show no such shift. After the methacholine challenge patients are given a broncho-dilator which return the LAC to their original position.
The LAC technique has been used to evaluate the efficacy of drugs to treat asthma in randomized control trials.
Asthmatic Patient: image segmentation of the lung parenchyma and LACs for the right upper lobe - left shift of curve post-methacholine challenge.
Normal Patient: image segmentation of the lung parenchyma and LACs for the right upper lobe - no shift of curve.
