Helical CT scan has been acknowledged to be a very useful scanning mode. Normally, the speed of bed movement per
rotation (pitch) for a helical CT is fixed to meet the requirement of CT scanning speed. To reduce system cost, single
slice helical CT (SSHCT) is often chosen in many applications. It is interesting and useful in real life to answer the
question that how to design the detector to obtain optimal performance of a SSHCT in a detection task. In this work, we
applied ROC study for the optimization of detector thickness along the direction of rotation axis for our SSHCT.
Numerical simulations followed by human observer studies are done in this investigation. Compound Gaussian noises
are modeled in our numerical simulations for objects both with and without lesions. An analytical FBP reconstruction
method with rebinning is used for noisy data reconstruction. It can be seen in the reconstructions that thin detectors lead
to artifacts, and that thick detectors lead to lesion blurring and lower contrast. All these impact on lesion detection in the
practical imaging applications. According to our ROC tests done on images from five choices of detector thickness,
optimal performance is obtained when choosing detector thickness being around 1~1.25 times of the helical pitch.
Moreover, we find that, under different noise level, the optimal point is about the same.
Some other figures of merit including SNR and HTC are also calculated and examined in this work. The results relates
well with the results of AUCs. It shows that, they could serve very well as the indicators for system optimization when
few non-linear physical effect and reconstruction processing are involved.