Paranazal Sinüs Bilgisayarlı Tomografi Tetkiklerinde Yüksek Pitch Kullanımının Radyasyon Dozu Üzerine Etkisi

Abstract

The aim of this study is to assess the effects of high pitch on radiation dose reduction and image quality of paranasal sinus CT examinations. The skulls from 13 cadavers were examined with a standard low-pitch protocol and different high-pitch (pitch:3) protocols on a 64-detector first generation dual tube CT (Definition, Siemens Medical Systems; Erlangen, Germany). On standard paranasal sinus CT protocol, tube voltage and tube current were 120 kV/80 mAs and pitch value was 1.2. High-pitch paranasal sinus CT protocols were conducted using various tube voltages and tube current preferences (120 kV/80 mAs, 100 kV/50 mAs, 80 kV/50 mAs,120 kV/20 mAs, 100 kV/20 mAs, and 80 kV, 100 kV, 120 kV with automatic tube current modulation set as active). Assessments were performed by use of qualitative (semi-quantitative scoring systems for diagnostic qualities of 2 and 3 planes images and osseous anatomic structures) and quantitative (radiation dose, objective noise, signal, signal/noise ratio) metrics. CTDIvol and DLP values, automatically calculated by computer and presented on dose reports for each examination, were corrected according to appropriate phantom. Effective dose was calculated by using conversion coefficients given by AAPM at Report no:204. Comparisons and statistical analyses were made by using weighted kappa test, Wilcoxon test and Friedman test. Based on the level of objective noise, diagnostic qualites, signal to noise ratios, the ten protocols were grouped in three subgroups. Standard protocol, 120 kV/80mAs and 120 kV/50 mAs high-pitch protocols were included in the group which had the best diagnostic imaging qualities. Ideal imaging of osseous anatomic structures was performed with 50 mAs tube current at minimum and the 120 kV/50 mAs high-pitch protocol was equivalent to the standard protocol. The second best group in terms of good diagnostic image quality, were 100 kV/50 mAs, 80 kV/50 mAs, 120 kV/20 mAs and 120 kV CARE 50 high-pitch protocols. Under appropriate clinical indications, these protocols can provide sufficient diagnostic scans. Imaging paranasal sinuses with high-pitch using first generation dual source CT, provides similar diagnostic image quality but increases radiation dose, probably because of the absence of noise-reducing-filters. There is no relation between radiation dose and pitch on DSCT in paranasal sinus imaging.