It's hard to do. You don't have to own any equipment, but then your business is only as sound as your hospital contract. The new practices that I'm familiar with generally consisted of a handful of radiologists who were willing to provide on-site services to small, rural hospitals. Even then, there was always talk of consolidation, as is the trend in radiology.
I don't think I would want to own my own practice, because then I'd be more of a business person than a radiologist. I can also see problems with hiring quality people without giving them a stake. Or, put more clearly, I wouldn't want to work for an individual practice owner as an employee indefinitely. However, I could envision being in a small partnership, where the business side of things is shared but it's small enough that each individual really has a voice.
ETA: Outpatient imaging centers are also an option, but, as already mentioned, then there are issues of upfront capital. Nowadays, the profit margin on non-hospital-owned imaging centers is pretty thin, as I understand it.