I think there has been some confusion in the above posts about some definitions, and some comparing of apples and oranges.
So the original question was "when must a pilot fly a procedure turn as depicted?"
Well, let's talk about what is usually depicted with some examples, and what you are required to fly.
In the U.S., you will most commonly see a "barb" depicted. This is the normal "procedure turn". If you see a "barb" then you can do any of the course reversal maneuvers described in AIM. The 45/180, the 80-260, the racetrack pattern (or holding-type pattern), or the teardrop pattern.
Here's an example:
http://204.108.4.16/d-tpp/0612/00387I33.PDF
Sometimes, instead of a procedure turn, there will be a depicted routing to the final, and this is what is usually meant by "procedure track". It's just some kind of an instrument routing from the IAF to the FAF. Usually they are some kind of radial, some kind of DME arc, or some combination of the two. In these cases, you must fly the track exactly as it is depicted, from the IAF, unless you are being vectored to final.
Here's an example. This one has to places to start from (2 IAF's), KOZEY or WEKPA.
http://204.108.4.16/d-tpp/0612/00274T15.PDF
The procedure track is the same idea as the "NoPT routing" but I think that the words "NoPT" are only displayed if the plate shows both a procedure turn and a procedure track on the same plate. Here's an example of that from Golden Triangle Regional. Notice that there is a barb depicted, but there are also two procedure tracks that get you to final also. If you fly the procedure track from NEZDE or NEYMU, then you don't do the procedure turn at ARTES.
http://204.108.4.16/d-tpp/0612/05855VDGE.PDF
Also common is the holding in lieu of Procedure turn, or HILO. In a HILO, you are expected to fly the course reversal like a holding pattern. So that means that you can still do a teardrop, because you can enter a holding pattern with a teardrop entry, but you can't do a 45/180 or an 80-260. Here's an example of a HILO.
http://204.108.4.16/d-tpp/0612/00372VG32.PDF
There are also some approaches built in the U.S. that don't have a barb, but are depicted as a teardrop. I couldn't find an example of one, though, but if you fly that one you have to fly it as a tear drop only. Just think of it as a "procedure track" in the shape of a teardrop, rather than as a procedure turn, per se.
Now keep in mind that these are all U.S. procedures. If you are flying in the ICAO (international) environment, everything changes. Those procedures are built as a 45/180 only, or an 80-260 only, or a racetrack, or a teardrop. For ICAO, you have to fly the procedure exactly as it's depicted.
Ready for a funky one? Check this one out:
http://204.108.4.16/d-tpp/0612/00354HI21.PDF
The FBO at Roswell, NM nicknamed it the widow-maker, based on the number of failed IFR checkrides that it caused. They used to sell T-shirts with a picture of the plate on it.
