ABSTRACT
INTRODUCTION: To evaluate the image quality provided by MDCT scanners using an ACR phantom an to find out the relationship between CT parameters and physical quantities related to image quality. METHODS: A GE Lightspeed VCT and a GE Lightspeed Pro 16 are used. The ACR phantom consists of four modules for evaluating physical parameters. The image quality parameters, such as CT number, linearity, CNR, image uniformity, SNR and at least spatial resolution using MTF, by different sets of image acquisition protocols (IAPs) are characterized. The influences of the IAPs on the physical quantities are also discussed. RESULTS: The CT numbers behaved linearly relative to material density for all tube voltages. The impact of the tube current on the CT numbers is neglectable. However, the variation of the tube current reflects in the CT number uncertainties. The CNR are altered by changing the IAPs. 50% MTF decreases from 6.2 to 3.6 lp/cm and from 6.5 to 3.7 lp/cm using Lung and Soft kernel for the Lightspeed VCT and Lightspeed Pro 16 scanner, respectively. CONCLUSION: The dependence of the image quality parameters on reconstruction kernels, tube peak voltages, tube currents and the slice thicknesses has been discussed. The tube peak voltage has the most influence on the CT numbers. The results indicate that the reconstruction kernel has the main impact on the spatial resolution. The spatial resolution dependence on the tube voltages, tube currents and slice thicknesses can be ignored.
Subject(s)
Phantoms, Imaging/standards , Tomography Scanners, X-Ray Computed/standards , Tomography, X-Ray Computed/standards , Accreditation , Humans , Radiometry/instrumentationABSTRACT
OBJECTIVES: The authors had for aim to assess the local epidemiology, antibiotic resistance, and molecular typing of expanded spectrum betalactamase producing Klebsiella, Enterobacter, and Serratia (ESBL KES). MATERIALS AND METHODS: Two hundred and seven strains of the KES group were isolated in the microbiology laboratory of the Annaba Ibn Rochd hospital in 2009. The antibiotic resistance (diffusion method and MIC) was tested and ESBL detection was performed as recommended by the Clinical Laboratory Standard Institute (CLSI). The characterization of genes for resistance to ß-lactams (CTX-M-1, TEM, and SHV) and AmpC cephalosporinase (DHA-1) was performed by polymerase chain reaction. The epidemiological relationship among identified strains was analyzed by Pulsed Field Gel Electrophoresis (PFGE). Genetic transfers were performed by conjugation using sodium azide resistant Escherichia coli K(12)J(5) as recipient strain. RESULTS: The overall incidence of ESBL KES was 31.4% (65/207) distributed as follows: 17.4% of Klebsiella spp., 7.2% Enterobacter spp., and 6.8% Serratia marcescens. The ß-lactamase CTX-M 1 types were predominant (88%), followed by TEM (36.5%), and SHV (31.1%). Twenty-three strains expressed at least two bla genes. DHA-1 type cephalosporinase was found in 4 E. cloacae associated with CTX-M-1. Several epidemic clones were determined. Conjugation experiments showed that bla(CTX-M), bla(TEM), and bla(SHV) were carried by conjugative plasmids of high molecular weight (≥125kb). CONCLUSIONS: This study revealed a high frequency of ESBL KES with a predominance of CTX-M-1. This high rate of ESBLs could be due to a clonal spread and the emergence of new epidemic clones.
