The correction of puncture point error in CT-guided puncturing biopsy: study of the methods

Objective: To discuss the method of correcting the puncture point error in performing CT-guided puncturing biopsy. Methods: CT-guided puncture biopsy was performed in 201 cases on a GE Prospeed F II CT scanner. In order to easily understand the function relationship between bed coordinates and scan section coordinates, the gantry slant angles of 0°(n = 30), 5°(n = 50), 10°(n = 80) and 20°(n = 41) were used separately. Skin-marker was stuck on the skin to indicate the puncture point. CT-guided puncture/biopsy was carried out in all patients. CT scanning was repeated to adjust the puncture point error, and the actual error was estimated by water phantom experiment method. Results: A function relationship existed between bed coordinates and scan section coordinates. When the gantry position had no angle, the function formula was: T_WM = S190 + M. When the gantry had some angle, the function formula was: T_WM = S190/Cosθ + M. The function formula between the error value X and the gantry angle was: T_WM = ∣190(1/Cosθ-1)∣. The error values obtained from function method were completely in agreement with the values determined by repeated CT scanning. Conclusion: Function method can precisely calculate the bed coordinates of target layer and quickly adjust the error of CT-guided puncture point. If these function formulas can be built in the scanner's software and worked automatically to adjust the error when the gantry is in angled state, the operation time as well as the radiation dose will be reduced. (authors)