Xenon133 scintigraphy

Asthma exacerbation is characterized by a bronchial obstruction that unequally affects airways and leads to uneven ventilation which can be imaged by Xenon scintigraphy.

Principle

After intravenous injection, the Xenon 133 is eliminated to the alveolar space with the first respiratory cycle, then emptied to the lower airways. Successive recordings of chest radioactivity allow visualization of the tracer in the vascular then alveolar spaces before its emptying via the bronchial tractus.

3D-maps of blood distribution and of alveolar ventilation can be acquired by using a grid (approx. 1000 areas).

Examples

Xenon scintigraphy in a healthy subject (posterior views) :

	Vascular time (blood flow distribution)   Almost equal distribution of tracer within both lungs (45 and 55%). Preferential fixation around the hila.
	Alveolar time (residual activity 1 second after alveolo-capillar transfer) 95% of tracer was eliminated from the lungs, Homogeneous emptying of the different regions, Even distribution of VA.

Asthmatic subject
Alveolar time scans before (on left) and after (on right) bronchodilatator inhalation (ipratropium bromide) (posterior views):

Bronchospasm before inhalation : Marked heterogeneity of alveolar emptying depending on unevenness of bronchial obstruction which mainly involves upper left and lower right areas of the lungs.	After inhalation : Improved overall emptying , VA evens up.

Absence of marked modifications in blood flow distribution confirms unevenness of VA/Q distribution during asthma attacks which is responsible for capnographic deformations.