PURPOSE: To determine optimal pitch and slice thickness when detecting small hepatoma by spiral CT. MATERIAL AND METHODS: Three types of artificial liver phantom of 45, 65, and 85 HU using agarose and three types ofartifical nodules of cheese with 95 HU of CT attenuation (5, 10 and 15mm in diameter) were prepared. After thethree types of phantom were embedded with three kinds of artificial nodules of different sizes, nine types ofphantom were made. In addition, four more 10-HU artificial liver phantoms embedded with 5-mm nodules were made.After the phantoms were scanned by spiral CT at different slice thicknesses (5, 8 and 10mm) and different pitches(1.0, 1.25, 1.5 and 2.0), nodule detection rates were determined ; these rates were, in addition, determined afteroverlapping reconstruction and changes in CT attenuation according to pitch. RESULT: Regardless of size, pitchand slice thickness, all nodules with more than 30 HU difference between the embedded nodule and artificial liverphantom were detected. The detection rate of 5mm nodules with a density difference of 10 HU decreased at a pitchof 2.0 and at 10mm slice thickness. After overlapping reconstruction, detection rates increased and there were noCT attenuation differences according to pitch. CONCLUSION: Eight-mm slice thickness is preferred and for thedetection of a nodule by spiral CT, pitch should not be greater than 1.5. After overlapping reconstruction,additional nodules were detected.