IPO - 4DMedical Limited, page-50

I’m not sure that everyone who bought 4DX actually knows what it sells.

At the moment the SaaS offering is new software to analyse existing CT scans. It is software that 4DX claim is better than existing and can look at lung ventilation - but only by inference.

Conclusion as to Substantial Equivalence
The XV Lung Ventilation Analysis Software application has the same intended use and similar target patient population, indications for use, principle of operation, and technical characteristics as the legally marketed Vitrea CT Lung Density Analysis Software from Vital Images (K151919). The subject Device and the Artis Q / Q.zen (K181407) share similar functionality of producing 3D data from cinefluorographs.Based on the close similarities between XV Lung Ventilation Analysis Software device and the predicates, the similar technological characteristics and as the proposed Device has no additional considerations impacting safety or effectiveness, it is believed the Vitrea CT Lung software is substantially equivalent to the subject Device
https://www.accessdata.fda.gov/cdrh_docs/pdf19/K193293.pdf