Radiographics : a review publication of the Radiological Society of North America, Inc
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Use of diagnostic imaging studies for evaluation of pregnant patients with medical conditions not related to pregnancy poses a persistent and recurring dilemma. Although a theoretical risk of carcinogenesis exists, there are no known risks for development of congenital malformations or mental retardation in a fetus exposed to ionizing radiation at the levels typically used for diagnostic imaging. An understanding of the effects of ionizing radiation on the fetus at different gestational stages and the estimated exposure dose received by the fetus from various imaging modalities facilitates appropriate choices for diagnostic imaging of pregnant patients with nonobstetric conditions. ⋯ Imaging algorithms based on a review of the current literature have been developed for specific nonobstetric conditions: pulmonary embolism, acute appendicitis, urolithiasis, biliary disease, and trauma. Imaging modalities that do not use ionizing radiation (ie, ultrasonography and magnetic resonance imaging) are preferred for pregnant patients. If ionizing radiation is used, one must adhere to the principle of using a dose that is as low as reasonably achievable after a discussion of risks versus benefits with the patient.
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Stabilization and fusion of the lumbar spine may be performed by using various anterior and posterior surgical techniques and a wide range of devices, including screws, spinal wires, artificial ligaments, vertebral cages, and artificial disks. Because spinal procedures are increasingly common, such devices are seen more and more often in everyday radiologic practice. ⋯ Computed tomography and magnetic resonance (MR) imaging may be useful alternatives, but MR imaging of the postoperative spine is vulnerable to metal-induced artifacts. For an accurate postoperative assessment of spinal instrumentation and of any complications, it is important that radiologists be familiar with the normal imaging appearances of the lumbar spine after stabilization, fusion, and disk replacement with various techniques and devices.
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Fungal sinusitis was once considered a rare disorder but is now reported with increasing frequency throughout the world. The classification of fungal sinusitis has evolved in the past two decades, and this entity is now thought to comprise five subtypes. Acute invasive fungal sinusitis, chronic invasive fungal sinusitis, and chronic granulomatous invasive fungal sinusitis make up the invasive group, whereas noninvasive fungal sinusitis is composed of allergic fungal sinusitis and fungus ball (fungal mycetoma). ⋯ The treatment strategies for the subtypes are also different, as are their prognoses. An understanding of the different types of fungal sinusitis and knowledge of their particular radiologic features allow the radiologist to play a crucial role in alerting the clinician to use appropriate diagnostic techniques for confirmation. Prompt diagnosis and initiation of appropriate therapy are essential to avoid a protracted or fatal outcome.
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The development of high-field-strength magnetic resonance (MR) imaging systems has been driven in part by expected improvements in signal-to-noise ratio, contrast-to-noise ratio, spatial-temporal resolution trade-off, and spectral resolution. However, the transition from 1.5- to 3.0-T MR imaging is not straightforward. Compared with body imaging at lower field strength, body imaging at 3.0 T results in altered relaxation times, augmented and new artifacts, changes in chemical shift effects, and a dramatic increase in power deposition, all of which must be accounted for when developing imaging protocols. ⋯ Techniques to reduce total body heating are demanded by the physics governing the specific absorption rate. Furthermore, the siting and maintenance of 3.0-T MR imaging systems are complicated by additional safety hazards unique to high-field-strength magnets. These aspects of 3.0-T body imaging represent current challenges and opportunities for radiology practice.
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Magnetic resonance (MR) imaging at 3.0 T offers an improved signal-to-noise ratio compared with that at 1.5 T. However, the physics of high field strength also brings disadvantages, such as increases in the specific absorption rate, in magnetic field inhomogeneity effects, and in susceptibility artifacts. ⋯ Such modifications may include a decrease in the flip angle used for refocusing pulses and an increase in the repetition time for T1-weighted acquisitions. In addition, parallel imaging and other techniques (hyper-echo sequences, transition between pseudo steady states) may be used to maintain a high signal-to-noise ratio while decreasing acquisition time and minimizing the occurrence of artifacts on abdominal MR images.