Boundary artifact due to truncation errors in MR imaging

A boundary artifact in MR images due to truncation of the infinite Fourier series necessary to encode tissue discontinuities was investigated by using doped water phantoms and normal volunteers. All images were obtained on 0.3-T permanent and 0.6-T superconducting MR imagers with varying phase and frequency sampling rates. The artifact appeared in both the phase and frequency encoding direction as parallel lines or ringing adjacent to borders or tissue discontinuities. This was unlike motion artifacts, which occur predominantly in the phase direction, and chemical shift misregistration errors, which are most pronounced in the frequency direction. Increasing the sampling frequency from 128 to 512 resulted in higher frequency ringing and more rapid drop-off in amplitude. Low-pass digital filtering also decreased the ringing at the expense of fine detail. The truncation of the infinite Fourier series necessary to encode edges to the 128-512 terms used for most MR imaging produces the artifact. It is important to recognize this common artifact and not mistake it for patient motion or disease.     

Hepatic abscess in liver transplantation. Accurate diagnosis and treatment

Serial HIDA scanning was performed on a patient following liver transplantation. During the patient's course he developed biliary obstruction that manifested as a photopenic region in the liver, on the HIDA scan which filled in on the delayed views. The patient subsequently developed a region in the superior portion of the right lobe of the liver that did not fill in with activity on delayed views. The patient was experiencing low-grade fevers and was clinically believed to have either an abscess or an episode of rejection. A gallium scan was performed revealing a photopenic defect in the same region as the HIDA. Because of the clinical suspicion of abscess, a percutaneous transhepatic drainage study was performed, revealing a large abscess cavity in the suspect area within the liver. Following the drainage the patient did well. This case illustrates the usefulness of serial HIDA scanning in patients who have received liver transplants. It also is important to note that the gallium scan was negative in this hepatic abscess. In the authors' opinions, the finding of an intrahepatic fluid collection in a septic patient that does not fill with activity on the HIDA study, should be considered the source of the infection, until proven otherwise, and should be drained regardless of the findings of other studies.     

Magnetic resonance imaging artifacts: mechanism and clinical significance

Many types of artifacts may occur in magnetic resonance imaging. These artifacts may be related to extrinsic factors such as patient motion or metallic artifacts; they may be due specifically to the MR system such as power gradient drop off and chemical shift artifacts; they may occur as a consequence of general image processing techniques, as in the case of truncation artifacts and aliasing. Change in patient position, pulse sequence, or other imaging variables may improve some artifacts. Although reduction of some artifacts may require a service engineer, the radiologist has the responsibility to recognize MR imaging problems. The radiologist's knowledge of MR imaging artifacts is important to the continued maintenance of high image quality and is essential if one is to avoid confusing artifactual appearances with pathology.     

A Proposed Model of Relapse Prevention for Adolescents Who Abuse Alcohol

Adolescents who abuse alcohol are being admitted to treatment centers in increasing numbers. However, relapse prevention, a critical aspect of recovery, rarely is addressed in this high-risk population. This article briefly reviews adolescent development, the current literature on adolescent drinking patterns and relapse, and analyzes current models of relapse prevention in adults. This information is then used to propose a relapse prevention model for adolescents.     

Nephrotoxicity of intravenous immunoglobulin

Individual case reports have documented nephrotoxicity of intravenous immunoglobulin (IVIG) preparations, but the true incidence of renal dysfunction is unknown and many data sheets do not include renal impairment as a side-effect of these preparations. We determined the incidence of renal impairment in an unselected cohort of patients receiving two different preparations of IVIG over 20 months, administering 287 courses of IVIG to 119 patients for a variety of indications, including thrombocytopenia, systemic lupus erythematosis, neuropathy, Guillain-Barre syndrome and infections. Two different preparations of IVIG were used, Vigam (BPL) and Sandoglobulin (Novartis), which differ in the concentration of sucrose added as a stabilizer. Eight patients showed deterioration in renal function (6.7%), and in two, no renal recovery occurred (1. 7%). There were no significant differences in the patient characteristics or dose or preparation of IVIG administered to those patients with or without changes in serum creatinine. There was no association between the amount of sucrose in the IVIG and development of renal failure. IVIG (regardless of the sucrose content) is associated with renal impairment which may be irreversible, with a maximum incidence of 6.7%. All patients should have their renal function monitored during the use of IVIG.     

Aortic dissection masquerading as systemic disease--the post-dissection syndrome

Three patients presented with a prolonged illness accompanied by fever, weight loss, high ESR, neutrophilia, abnormal liver function tests, urinary abnormalities and, in one case, splinter haemorrhages and impairment of renal function. Aortic dissection was diagnosed 3-12 weeks after the onset of the illness, and probably accounted for the entire syndrome. All abnormalities resolved spontaneously over the following months. There are few similar cases in the literature, and the syndrome could easily pass unrecognized. Aortic dissection should be considered as a possible cause of any systemic illness of sudden onset, but especially if there is an initial history of chest or abdominal pain, or evidence of previous hypertension or other risk factors.     

肌腱玻璃化法冷冻保存的体外实验

目的:目前临床上常用低温冷冻法来保存同种异体肌腱,但操作较复杂费时,并且所保存的肌腱活性较低而限制其应用。采用已筛选的玻璃化法冷冻保存鸡屈趾深肌腱,并将复温后的玻璃化肌腱进行体外检测,探索其作为肌腱移植材料的可行性。方法:实验于2003-11/2005-02在解放军总医院骨科研究所完成。①实验材料及分组:来亨鸡16只,雄性,体质量2.5kg左右,随机分为2组,玻璃化组为玻璃化肌腱,新鲜肌腱组为新鲜肌腱,每组8只。②实验过程:切取来亨鸡屈趾深肌腱,置入玻璃化液内快速投入液氮保存2周制备玻璃化肌腱。③实验评估:将2组肌腱在体外进行大体、组织学及超微结构观察,羟脯氨酸含量测定,生物力学性能检测,并对两组肌腱进行细胞培养与鉴定。结果:①玻璃化组肌腱的大体、组织学及超微结构与新鲜肌腱组相似,其细胞及细胞外结构得以良好保存。②应用碱解法测定玻璃化肌腱内的羟脯氨酸含量为69.27mg/g,与新鲜肌腱组间差异无统计学意义。③玻璃化组肌腱破裂强度为165.58MPa,弹性模量1.41GPa,与新鲜肌腱组的力学性能差异无统计学意义。④将玻璃化组肌腱进行细胞培养,细胞第8天自组织块长出,第21天后传代,培养3代后出现明显的退化现象,其生物学特性与新鲜肌腱组相似。⑤将两组肌腱培养的细胞分别进行免疫组织化学染色,经鉴定均为肌腱细胞。结论:玻璃化法保存的肌腱具有良好的细胞活性、细胞外结构及力学性能,其生物学及生物力学特性无明显变异。