Increasing slice overlap in PET/CT to more accurately prescribe scan range and reduce CT dose

Objectives In diagnostic CT a technologist is able to manipulate scan range by individual slices to achieve desired landmarks for scanning. In PET/CT however a technologist is confined to adjusting scan range by adding or subtracting full beds, approximately 40 slices with a traditional seven slice overlap in 3-D imaging. The goal of this abstract is to show that it is feasible to create a more customized prescription range by increasing slice overlap during the prescription without increasing the time of the scan. Also, we will show the CT dose benefits of this approach.

Methods By using a excel spreadsheet we analyzed the maximum increase in slice overlap before another bed would be needed by the formula: 40>(x-1) * (y-7). We then analyzed the potential CT dose savings for a traditional fixed tube current protocol by the equation: (x-1)(y-7)/(40x7). Where x is number of beds and y is the slice overlap. The equation of x-1 indicated the number of times we would account for slice overlap in a given scan. The equation y-7 indicated the number of slices increased in the slice overlap over our traditional 7 slices. 40x*7 indicates the number of slices that would be expected during a given exam with a seven slice overlap.

Results Our results show for our maximum number of beds (14) we can increase the slice overlap to nine without having to add another bed with a CT reduction of 4.6%. We also found we can increase our overlap to an extreme of 45 slices in two beds with a CT reduction of 46%. Slice overlap may be increased up to 27, 19, 15, 13, 13, 11, 11, 11, 9, 9, 9 for 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, and 13 beds respectively. Corresponding CT dose savings range from 31.5% for three beds with a slice overlap of 27 to 4.6% for 13 beds with a slice overlap of 9 in comparison to the same number of beds with a slice overlap of 7.

Conclusions Increasing slice overlap while prescribing CT scan range is an effective tool to allow for a more customized scan localization area while not increasing scan time and reducing radiation dose