Low-dose high-resolution CT of the petrous bone

Purpose: To show that CT of the petrous bone can be realized using a low-do se technique. Material and methods: A high-contrast phantom was scanned with 1.5 mm slice thickness and 60-510 mAs using the reconstruction algorithms standard, bon e and edge. In 50 patients, the petrous bone was examined using the standar d protocol at 510 mAS. Additionally, selected slices were made at 120 or 21 0 mAs. The resolution of relevant structures was compared. Phantom studies were repeated on a second CT-device; images of patients scanned with 80 mAs were analyzed in regard to resolution of osseous details. Results: With the first: CT-device structures of the phantom up to 0.5 mm w ere depicted using 510 mAs and the edge kernel. With 120 mAs and the bone k ernel structures of 0.6 mm could be distinguished. Although the same resolu tion was achieved with 60 mAs and the edge kernel, patient examinations sho wed a profound image noise. The results achieved with 120 mAs and the bone algorithm, however, were equal to that of 510 mAs. With the second device t he same image quality was realized with only 80 mAs. Conclusion: CT-examinations of the petrous bone can be effected without los s of diagnostic information using only 15 % of the radiation dose used for a standard brain examination.