Perhaps you should try some spelling variations:
complexity approximation » complex approximation, complexity applications, completeness approximation
approximation based » approximation a
based extensions » based extension, base extension, brand extensions
array imaging » arrays imaging, airway imaging, ray imaging
array using » arrays using

You may be able to get more results by adjusting your search query.

• Performing a fuzzy search may retrieve terms with similar spellings: complexity approximation based extensions ((array imaging) or (((array using) or (array format))))~.
• If you are trying to use Boolean operators, they must be ALL CAPS: complexity approximation based extensions ((array imaging) OR (((array using) OR (array format)))).
• Adding a wildcard symbol may retrieve word variants: complexity approximation based extensions ((array imaging) or (((array using) or (array format))))*.