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Objective: The aim of the present study was to evaluate the metallic artifacts in MRI of the orthopedic patients after removal of metallic implants., Subjects and Methods: From March to August 2009, 40 orthopedic patients operated for removal of orthopedic metallic implants were studied by post-operative MRI from the site of removal of implants. A grading scale of 0-3 was assigned for artifact in MR images whereby 0 was considered no artifact; and I-III were considered mild, moderate, and severe metallic artifacts, respectively. These grading records were correlated with other variables including the type, size, number, and composition of metallic devices; and the site and duration of orthopedic devices stay in the body., Results: Metallic susceptibly artifacts were detected in MRI of 18 of 40 cases (45%). Screws and pins in removed hardware were the most important factors for causing artifacts in MRI. The artifacts were found more frequently in the patients who had more screws and pins in the removed implants. Gender, age, site of implantation of the device, length of the hardware, composition of the metallic implants (stainless steel versus titanium), and duration of implantation of the hardware exerted no effect in producing metallic artifacts after removal of implants. Short TE sequences of MRI (such as T1 weighted) showed fewer artifacts., Conclusion: Susceptibility of metallic artifacts is a frequent phenomenon in MRI of patients upon removal of metallic orthopedic implants., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Rationale and Objective: Small AP diameter of L5 can mimic spondylolisthesis in lumbosacral MRI. The aim of the present study was to evaluate the prevalence of small L5 mimicking spondylolisthesis in lumbosacral MRI of the patients referred to an imaging center by any symptoms. Association between small anteroposterior diameter of L5 and presence and absence of unilateral or bilateral spondylolysis at L5 were also evaluated., Materials and Methods: 2000 lumbosacral MRI of the patients referred to an imaging center for any reasons were evaluated. The posterior step of L5 was measured and the cases with posterior step of more than 2 mm were selected. These cases were evaluated for presence or absence of spondylolysis., Results: Small anteroposterior diameters of L5 were detected in 38 cases (2%), mimicking the spondylolisthesis in lumbosacral MRI. The prevalence of small L5 in lumbosacral MRI of the patients referred by any symptoms was about 2%. In these selected cases, 6 (15.8%) show unilateral spondylolysis and 5 (13.1%) show bilateral spondylolysis., Conclusion: Pseudospondylolisthesis secondary to small AP diameter of L5 has prevalence of about 2% in lumbosacral MRI of cases referred for any reasons and can be overlooked in reporting of LS MRI. There was an association between small anteroposterior diameter of L5 and presence of spondylolysis at L5., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)