Can CT scans accurately detect arteriosclerosis?

OnlyAfterLongEnough. Atherosclerosis, known to start ~age 7 on average, & microcalcifications (within artery wall smooth muscle cells just outside the plaque) can be seen with a microscope & ca+2 stains within early years but are too small to see with any current ct machines. These may become visible by the best ct machines by early 30's, 2 decades later but typically a decade before obvious clinical events & symptoms.
Yes. Especially if you are talking about the heart. A calcium score can be done to assess the degree. If you have some "soft plaque" in the heart arteries, that is not yet calcified, it can be missed, but in general the test is very good.
See below. A ct can be done without or with contrast. As stated in the answer above a noncontrast study can evaluate calcium deposit in the coronary arteries. A contrast enhanced ct study can show the degree of stenosis as compared to the normal portions of the arteries.