It is unquestionable that doctors generally, and radiologists specifically, will be effected by the ACA going forward. But the question here is what the net effect will be. What makes this difficult to really answer is that there are a number of provisions that come into play, and some can be deemed negative while others are positive. No one knows for sure what the ultimate net effect will be, but we can try by looking at a few to get an idea of what the bottom line might be.
1) A decrease in insurance payments made for imaging.
According to How Healthcare Reform Is Affecting Radiology, slide 11 (and others), there is a decrease in pay for various imaging work of up to 50%, both directly for procedures such as an MRI and in a policy that groups together certain procedures that were performed at the same time into one single payable service.
The stated goal of this is that these sorts of common expenses are much more expensive in the US than other comparable countries, and the rationale that two sets of images done during one visit to one patient should not cost the same as if they were done at entirely different times, etc.
Rationale aside, one could easily consider this a negative for radiological businesses, but radiologists are largely salaried staff and are not paid per procedure or even per hour. But the economic value provided by radiologists is reduced, so this could provide a negative pressure on pay.
One of the reasons this is a concern for some radiologists is that that they are already very highly paid positions (both in general and compared to general care doctors), with salaries in the US ranging from $160,000-500,000+ per year, and a very high predicted job growth rate in the coming years. Glassdoor Survey of Salaries. One can thus reason that if anyone is going to be targeted for a pay cut, radiologists could be at the front of that line.
2) A major increase in potential demand for healthcare
On the other hand, the major increases in healthcare coverage that are a central goal of the ACA are likely to provide far more demand (paying customers) looking for healthcare. Those who were previously unable to pay for services performed in an emergency care environment would now be covered, which is another positive effect.
This could be viewed as a mixed impact, however, as many/most medical professionals are salaried now and would be called upon to work more. The increase in demand for nurses and doctors would provide an upwards pressure on salary and increased bargaining power.
It seems odd to claim that an increased demand for ones services is harmful. If you are already highly paid and work long hours, I suppose you could reasonably think that there is no benefit to you directly of having more people waiting in line for your services. But it would provide more opportunities for people seeking to be radiologists and provide additional justification for pay 2-4 times higher than other medical doctors.
3) An increase in pay for some physicians and regional incentives
According to the National Physicians Alliance (and many other sources) there will be a 10% boost in payments for primary care services, a 10% boost for surgeons and other personnel working in under-served communities, an increase in Medicaid payments so they match Medicare payments, and incentives/pay/loan forgiveness for working in under-served communities.
As far as the claim that there will be less flexibility to choose where to work, I can only assume this is what is being referenced - but to claim reduced flexibility when payments/incentives are offered to work in rural and under-served areas seems like a backwards way to look at things. If there is a shortage of doctors this should tend to increase the flexibility of choosing where one lives and works.
4) Insurance stability, availability, limit elimination
The ACA will be removing lifetime/yearly limits on healthcare coverage, make insurance companies unable to drop people who are getting ill, etc. This effects physicians, too, as they need insurance too. It also means doctors don't suddenly lose patients because of bureaucratic nonsense.
5) Digital medical records requirements
This is billed as an upside, but I heard an NPR report the other day (sorry, no citation - radio program) that many older private practice physicians say that the cost of going digital is just too expensive and they're just going to work until the penalties are too much and then they'll retire from their practice.
The cost of systems and converting records is considerable, and for small practices the advantages of digital patient records are vastly reduced while the out of pocket costs are still high. For some doctors this is a negative, though for many its a benefit. YMMV
This is just a natural downside, as if nothing else the ACA signals changes in physician pay, work environments, insurance, and a real or perceived move towards a pay-for-performance or packaged-payment system. People naturally fear change, and this can be perfectly rational. Who trusts the government not to screw things up, really? But the present system is untenable, so it is inevitable and scary.
So as you can see, even this partial treatment reveals the situation is mixed. Some physicians will make more money, find more flexibility, more bargaining power, and have better work environments. Upcoming physicians may find better pay, modernized systems, and more opportunities and options to pay for their (already prohibitively expensive) education. Older physicians, and those in highly paid specialties (such as radiology), may find the ACA costs them more than it helps them.
It is important to remember that the Affordable Care Act is a monolithic piece of legislation, and as such it inevitable contains pros and cons for everyone involved. How you judge the net result depends on who you are, how well the current system suits you, and how a variety of provisions and interpreted and implemented in the future. The NPA link provided earlier has many additional readings/links/citations that may provide further reading.
TL;DR: Some physicians love Obamacare, some hate it, some are ambivalent, and some have such a mixed bag that its hard to evaluate whether its ultimately good or bad. And for some, only time will tell.