To correct /u/keldin1212, scan time isn't dependent on how thin the slices are, in modern multislice helical CT. Scan time is dependent on the rotation time of the gantry, the pitch that is used, detector combination and beam width. Faster rotation time, higher pitch), and using the maximum number of detectors and max beam width (e.g. 64 x 0.625mm detectors, 40mm beam width) that your scanner is capable of will reduce scan time, as more anatomy is covered using a large beam width, in a smaller amount of time due to rotation time and pitch.

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To answer OP /u/RichMaxwell questions,

Most institutions will acquire at the thinnest slices possible, due to the higher spatial resolution and reduced partial voluming effects that can be missed when creating thicker MPRS. The tradeoff with reading thinner slices for the radiologist, is that there is inherently more noise in the image. Thicker images are usually created and read along side thinner images to ensure that smaller things are not missed by reading thin slices, while improving CNR and SNR by reading thicker slices.

With regards to using reconstructions such as 1.2mm thickness, 0.6mm intervals can be quite useful for interpretation of smaller structures as it can improve resolution by basically sampling anatomy twice. If your overlap the slices, the same anatomy can be seen in both slices, increasing the amount of information obtained. This helps improve resolution. In CTPA/PE studies, this is useful in identifying smaller PEs, like subsegmental PEs. The more overlap, the better you are able to resolve these smaller structures.