Low-dose spiral-CT

Purpose: To examine the clinical use of a reduced dose in high-resolution spiral-CT (HR-SCT) in combination with a multiplanar volume reconstruction technique (MPVR) to decrease image noise. Material and methods: Facial bones, skull and extremities of 33 patients with different pathological findings were examined with spiral-CT using a slice thickness of 1 mm (pitch 1.7-2.0), a tube amperage of 40 mA and tube voltages of 80 or 120 kV. Additionally: 2-D, 3-D, and MPVR image reconstructions were performed. MPVR takes advantage of displaying planar volumes of variable thickness. Results: Increased image noise was negligible if high contrast structures like bones were examined. However, very small bony structures like the stapes of the middle ear were not seen. Soft tissues could also be imaged by using the MPVR-technique. This technique did reduce image noise while at the same time partial volume averaging was increased. The skin entrance dose per investigation did not exceed 3 mGy, which is based on twelve dose measurements in two patients. Conclusion: It is feasible to perform HR-SCT with secondary reconstructions of facial bones, skull and extremities using reduced skin entrance doses by 10 to 20 fold to below 3 mGy. With the exception of imaging very small structures, sufficient image quality can be accomplished in routine examinations without relevant diagnostic compromise.