A numerical approach to non-circular birdcage RF coil optimization: verification with a fourth-order coil.

It is demonstrated that birdcage resonators, satisfying conditions of quadrature operation and radiofrequency field homogeneity, can be realized in practice on formers of non-circular cross section described by an equation of the form (x/a)n + (y/b)n = 1 where a and b are constants and n > or = 2 is an integer. Using a ladder network analogous to that of a conventional circular birdcage, optimization algorithms were employed to determine the elemental current distribution on the non-circular cylindrical surfaces. A comparison of circular, elliptical, symmetric and asymmetric fourth-order (n = 4) section birdcage current distributions is presented. A short, asymmetric fourth-order cage was constructed and tested experimentally at 3 T and compared with a conventional circular-section head coil.     

Management of Coronary Artery Aneurysms

Aneurysmal dilation of coronary arteries is observed in up to 5% of patients undergoing coronary angiography. Due to their poorly elucidated underlying mechanisms, their variable presentations, and the lack of largescale outcome data on their various treatment modalities, coronary artery aneurysms and coronary ectasia pose a challenge to the managing clinician. This paper aims to provide a succinct review of aneurysmal coronary disease, with a special emphasis on the challenges associated with its interventional treatment.     

Newly designed “pieced” stent in a rabbit model of benign esophageal stricture

AIM: To investigate a newly designed stent and its dilatation effect in a rabbit model of benign esophageal stricture.METHODS: Thirty-four New Zealand white rabbits underwent a corrosive injury in the middle esophagus for esophageal stricture formation. Thirty rabbits with a successful formation of esophageal strictures were randomly allocated into two groups. The control group (n = 15) was implanted with a conventional stent, and the study group (n = 15) was implanted with a detachable “pieced” stent. The study stent (30 mm in length, 10 mm in diameter) was composed of three covered metallic pieces connected by surgical suture lines. The stent was collapsed by pulling the suture lines out of the mesh. Two weeks after stricture formation, endoscopic placement of a conventional stent or the new stent was performed. Endoscopic extraction was carried out four weeks later. The extraction rate, ease of extraction, migration, complications, and survival were evaluated.RESULTS: Stent migration occurred in 3/15 (20%) animals in the control group and 2/15 (13%) animals in the study group; the difference between the two groups was not statistically significant. At the end of four weeks, the remaining stents were successfully extracted with the endoscope in 100% (11/11) of the animals in the study group, and 60% (6/10) of the animals in the control group; this difference was statistically significant (P < 0.05). There was no difference in the mean number of follow-up days between the control and study groups (25.33 vs 25.85). Minor bleeding was reported in five cases in the study group and four in the control group. There were no severe complications directly associated with stent implantation or extraction in either of the two groups.CONCLUSION: In this experimental protocol of benign esophageal strictures, the novel “pieced” stent demonstrated a superior removal rate with a similar migration rate compared to a conventional stent.     

儿童期颅内动脉瘤的诊断及治疗

目的 描述儿童颅内动脉瘤的临床特点,评价不同治疗方法对儿童颅内动脉瘤的疗效和安伞性.方法 总结北京天坛医院1990年1月至2008年12月诊治的23例儿童颅内动脉瘤病例的临床资料,其中男16例,女7例,年龄3～15例.观察手术组16例和电解可脱性微弹簧栓塞术(GDC),5例的疗效.全部病例中有2例未做进一步的治疗.结果 手术治疗组中15例恢复良好,1例死亡;GDC治疗组中1例栓塞成功,术后恢复良好;2例栓塞治疗后动脉瘤有残留,1例行动脉瘤孤立切除术,术后死亡.1例行瘤颈夹闭动脉瘤切除术,恢复良好;2例介入治疗后动脉瘤再通,其中1例二次行栓塞治疗后再通,经手术切除动脉瘤后恢复良好.结论 显微手术治疗儿童颅内动脉瘤是安全有效的,GDC对急性出血的儿童颅内动脉瘤的治疗也是安全的,但需长期随访观察其疗效,如有动脉瘤残留或再通者,建议行显微手术治疗.     

Selective endovascular treatment of a traumatic basilar aneurysm after endoscopic third ventriculostomy

A 4-year-old girl suffered intraventricular and subarachnoid hemorrhage during endoscopic third ventriculostomy. Cerebral angiography revealed a traumatic basilar aneurysm secondary to basilar artery injury. The aneurysm was treated with selective endovascular embolization using Guglielmi detachable coils. We review some therapeutic features of traumatic basilar aneurysms after endoscopic third ventriculostomy and describe the feasibility of endovascular selective therapy to manage these lesions successfully.     

Intraocular metastases: differential diagnosis from uveal melanomas with high-resolution MRI using a surface coil

Magnetic resonance imaging with dedicated surface coils plays a pivotal role in differential diagnosis and staging of intraocular tumors. The purpose of this study was to establish MRI criteria for the differential diagnosis of uveal melanomas and intraocular metastases. In a prospective study 44 eyes in 36 patients with intraocular metastases and 200 patients with uveal melanomas were investigated with MRI using a 1.5-T scanner and a 5-cm surface coil. Both quantitative and qualitative evaluation of the resulting images was performed. The MR signal intensities typically expected for metastases (slightly hyperintense on non-contrast T1-weighted images and hypointense on T2-weighted images compared to the vitreous body) were seen in only 23.1%. The typical melanoma signal of either moderate or strong hyperintensity on T1-weighted images and hypointensity on T2-weighted images was seen in 69.4% of the proven melanomas. Contrast enhancement was observed in both metastases and melanomas. Morphological differences between metastases and melanomas were detected in tumor size, shape, position, frequency of retinal detachment, and homogeneity of the tumor. Differentiation between intraocular metastases and uveal melanoma is limited by overlap of signal intensities. Some improvement is achieved with morphologic criteria.