Evaluation of a limited three-slice head CT protocol for monitoring patients with ventriculoperitoneal shunts

OBJECTIVE: Patients with a ventriculoperitoneal shunt for the management of hydrocephalus often undergo multiple head CT examinations for assessment of shunt malfunction. The purpose of this study was to evaluate whether a limited three-slice CT protocol would consistently provide adequate information for the diagnosis of shunt malfunction with a decrease in effective dose. MATERIALS AND METHODS: The study group included 231 unenhanced head CT examinations performed on 128 patients with shunts for hydrocephalus. The original contiguous CT images were reviewed retrospectively. A theoretic limited three-slice study was then created from the original complete CT study and separately reviewed. This limited three-slice study was created by using the lateral topographic image to select three axial locations as follows: midpoint between foramen magnum and vertex, top of the mastoid air cells, and orbital roof. The limited study was graded for parameters of image adequacy with the original full protocol study as the reference standard. RESULTS: Twenty-four of the 231 (10.4%) full studies had findings consistent with shunt failure; all 231 studies would have been correctly categorized with the limited three-slice protocol. The sensitivity of three-slice CT for identifying the ventricular system was 91.6% and for identifying the catheter tip, 93.5%. Limited-slice CT examination would have resulted in greater than 90% mean dose reduction in both adult and pediatric populations. CONCLUSION: Unenhanced head CT with a limited-slice protocol provides adequate diagnostic information for the diagnosis of shunt malfunction with a greater than 90% reduction in effective dose

Comparison of simulated cone beam computed tomography to conventional helical computed tomography for imaging of rhinosinusitis

OBJECTIVES/HYPOTHESIS: Cone beam computed tomography (CBCT) has emerged as a low radiation dose alternative to traditional computed tomography (CT) to evaluate the paranasal sinuses. The purpose of our study was to determine how often clinically important findings would be missed if CBCT was used routinely for sinus imaging. STUDY DESIGN: Retrospective review. METHODS: We evaluated all maxillofacial CT scans performed for sinusitis over a 1-year period. The original multidetector CT (MDCT) images were reviewed retrospectively. A theoretical CBCT was then created from the original study utilizing only the bone algorithm images and separately reviewed. We calculated the proportion of abnormal findings that were identified on the MDCT but would have been missed by the theoretical CBCT, and reviewed the medical record to determine which potentially missed findings would have changed management. Radiation dose from the MDCT scanners was calculated and compared to published dose estimates for the paranasal sinuses on CBCT. RESULTS: Maxillofacial CTs from 361 consecutive patients were included, of which 12 (3.3%) demonstrated findings that would have been missed on the theoretical CBCT. Of those, four (1.1%) would have resulted in a change in management. Effective radiation dose for our scanners ranged from 0.67 mSv to 2.15 mSv, compared to a published estimated dose of 0.2 mSV for CBCT. CONCLUSIONS: In the majority of patients undergoing simulated CBCT for evaluation of sinusitis, incidental findings of soft-tissue disease were rare. With appropriate selection of patients, CBCT can offer substantial radiation dose reduction and may provide a viable alternative to standard MDCT sinus imaging protocols