Carbon 11 radiolabeled inhaled Beta-2 agonist or corticosteroids, is it possible?
Positron emission tomography (PET) has been taken using $\ce{^{11}C}$- and $\ce{^{18}F}$-labelled reagents, although they are not $\beta_2$-agonists (Ref.1). The abstract states that:

Positron emission tomography (PET) provides three-dimensional images of the distributions of radionuclides that have been inhaled or injected into the lungs. By using radionuclides with short half-lives, the radiation exposure of the subject can be kept small. By following the evolution of the distributions of radionuclides in gases or compounds that participate in lung function, information about such diverse lung functions as regional ventilation, perfusion, shunt, gas fraction, capillary permeability, inflammation, and gene expression can be inferred. Thus PET has the potential to provide information about the links between cellular function and whole lung function in vivo. In this paper, recent advancements in PET methodology and techniques and information about lung function that have been obtained with these techniques are reviewed.

It is clear that unto 2007, there are no evidence for the use of radiolabeled $\beta_2$-agonist or corticosteroids for PET in literature. However, there are other radiolabeled reagents have been use for the imaging. For instance, the mixed-venous content is obtained by imaging the right heart during the infusion, and the alveolar concentration is obtained by imaging the lung, after the blood volume is subtracted from the image using a separate $\ce{^{11}C}$-labeled carbon monoxide ($\ce{^{11}CO}$) inhalation.
References:

R. Scott Harris, Daniel P. Schuster, &quot;Visualizing lung function with positron emission tomography,&quot; J. Appl. Physiol. 2007, 102(1), 448-458 (DOI: https://doi.org/10.1152/japplphysiol.00763.2006)(PDF).
C. G. Rhodes, S. O. Valind, L. H. Brudin, P. E. Wollmer, T. Jones, P. D. Buckingham, J. M. Hughes, &quot;Quantification of regional V/Q ratios in humans by use of PET. II. Procedure and normal values,&quot; J. Appl. Physiol. 1989, 66(4), 1905–1913 (DOI: https://doi.org/10.1152/jappl.1989.66.4.1905).