I agree with thingmaker3's assessment. Is this a project that you are considering or are you simply curious about the feasibility of such an application of a television?
one simple application of such is monitoring an audio signal which functions as an audio-visual signal tracer. this circuit has to be in sync with the horizontal deflection frequency of the tv set.
You can do so with a PC and the software is Free, you need a video card that will put out standard composite video or SVideo and a TV than can accept those inputs. (or any of the bewildering variety of inputs on TVs now)
Yea I know but seriously it's the most economical way to do it. There are very expensive cards for PCs that will do hundreds of megahertz and those can be displayed on a TV as well.