This paper reports, according to
MEPS, 644 imaging studies "per 1000 persons (all ages) in the U.S. population" in the year 1999. Today, there are 305,614,860 people in the US; at 1999 rates that's 196,815,970 imaging studies performed. If only
one half of one percent of that many people needed a study but couldn't have it (for a variety of very common reasons) that would be almost one million (984,080) people in the US alone.