Article 1 is about certain for profit hospitals setting quotas on the number of patients doctors admitted to the hospital, and giving kickbacks to doctors for ordering tests (which is illegal).

Article 2 is addressing a cancer treatment, not diagnostic tests. And has one quote by a doctor concerned about oncologists being pressured to use proton therapy. No mention of quotas.

Article 3 is about the proliferation of advanced diagnostic imaging (MRI, CT, etc) in private clinics and the concerns about over utilization of these diagnostic tests as well as potential conflicts of interest with doctors having a financial stake in the tests they're ordering. These are both real problems in the US medical system. However, no mention of US hospitals placing quotas on diagnostic tests ordered by doctors on their staff.

Is it possible these types of quotas have occurred? Sure. But is this typical practice in the US? No.