Cine magnetic resonance microscopy of the rat heart using cardiorespiratory-synchronous projection reconstruction

PURPOSE: To tailor a cardiac magnetic resonance (MR) microscopy technique for the rat that combines improvements in pulse sequence design and physiologic control to acquire high-resolution images of cardiac structure and function. MATERIALS AND METHODS: Projection reconstruction (PR) was compared to conventional Cartesian techniques in point-spread function simulations and experimental studies to evaluate its artifact sensitivity. Female Sprague-Dawley rats were imaged at 2.0 T using PR with direct encoding of the free induction decay. Specialized physiologic support and monitoring equipment ensured consistency of biological motion and permitted synchronization of imaging with the cardiac and respiratory cycles. RESULTS: The reduced artifact sensitivity of PR offered improved delineation of cardiac and pulmonary structures. Ventilatory synchronization further increased the signal-to-noise ratio by reducing inter-view variability. High-quality short-axis and long-axis cine images of the rat heart were acquired with 10-msec temporal resolution and microscopic spatial resolution down to 175 microm x 175 microm x 1 mm. CONCLUSION: Integrating careful biological control with an optimized pulse sequence significantly limits both the source and impact of image artifacts. This work represents a novel integration of techniques designed to support measurement of cardiac morphology and function in rodent models of cardiovascular disease.     

Vulnerabilities of ventral mesencephalic neurons projecting to the nucleus accumbens following infusions of 6-hydroxydopamine into the medial forebrain bundle in the rat

The terminal arbors of dopaminergic projections in the nucleus accumbens (Acb) core degenerate more rapidly, completely and permanently in a variety of neurotoxic circumstances than do those in the medial shell. It is unknown if this always reflects purely losses of the distal parts of axons from the core (as proposed in methamphetamine intoxication), or whether, in some circumstances, the disproportionate loss of core axons may also stem from an intrinsic vulnerability to degeneration of core-projecting neuronal perikarya. Experiments described here addressed this issue in the following manner. Three days after Fluoro-Gold (FG), a retrogradely transported tracer, had been iontophoresed selectively into the core or medial shell of male Sprague-Dawley rats, each received an infusion of saline vehicle containing or lacking 6-hydroxydopamine (6-OHDA) in the ipsilateral medial forebrain bundle (MFB). Twenty-one days later the brains were processed to exhibit ventral mesencephalic neurons containing FG. Application of an unbiased sampling method revealed substantially greater losses of FG labeled neurons relative to controls in rats that had received 6-OHDA lesions and deposition of FG in the Acb core as compared to the medial shell. Of the few core-projecting neurons that remained in the ventral mesencephalon after these lesions, 54% did not co-localize tyrosine hydroxylase immunoreactivity (TH-ir) and, thus, were not expected to degenerate. The capacity to selectively remove core-projecting dopaminergic neurons may be useful in the determination of molecular correlates of vulnerability and resistance to neurotoxicity and to possibly test the role of the core in reinforcement paradigms.     

Fiber order of the normal and regenerated optic tract of the frog (Rana pipiens)

In the normal frog, axons from the peripheral retina arising at the temporal pole course superficially in the middle stream of the diencephalic optic tract. Axons from the nasal pole course in two streams running in the opposite margins of the tract, dorsonasal axons ventrally, ventronasal axons dorsally. Axons from the dorsal and ventral poles of the retina occupy the intervals between the aforementioned middle and marginal streams. Axons from more central regions of the retina tend to occupy deeper levels of the optic tract. The regenerated optic tract does not regain its normal organization, e.g., axons of peripheral nasal origin are spread out widely over the entire width of the tract. However, axons from the temporal pole of the retina do return approximately to their original location in the middle stream. The concentration of temporal axons in the middle stream of the optic tract after regeneration may now be understood in terms of the expression pattern of the ephrin-A class of receptor tyrosine kinase ligands in the cellular matrix of the optic tract. The ephrin-As, which have a repellent effect on growing temporal retinal axons, are concentrated in and along the margins of the diencephalic optic tract and essentially absent from its middle stream. It is proposed here that peripheral temporal axons may be forced into this middle region by their avoidance of the higher levels of ephrin-A expression in the tract margins. In contrast, the growth pattern of regenerating peripheral nasal axons would not be affected by the ephrin-A gradient in the optic tract.     

Optimization of the projection screen in a display system for minimal access surgery

Background: The operative image for minimal access surgery currently is displayed on a monitor located outside the sterile field. It is ergonomically advantageous to locate the image adjacent to the surgeons hands by projection onto a sterile screen, but there has been no research into the optimal screen material. Methods: Several screen materials were compared for image resolution, brightness, variation of brightness with viewing angle, and image artifact. Results: Glossy materials perform poorly, whereas finely grained surfaces improve image clarity. Excessive roughness and incomplete opacity limit the image resolution. Conventional screen fabrics are unsuitable in this application. Ambient lighting and projector brightness affect image contrast, but a correct choice of material can address this. Practical issues such as moisture absorbency and ease of sterilization are considered. Conclusions: Potential screen materials were rejected because of excessive glare, poor resolution, and image artifact. Finely textured surfaces (e.g., polystyrene sheeting) provide an acceptable screen.     

Dynamic contrast enhancement of paragangliomas of the head and neck: evaluation with time-resolved 2D MR projection angiography

Our objective was to evaluate tumor hemodynamics of paragangliomas of the head and neck. A 2D magnetic resonance projection angiography (MRPA) protocol was developed. Six patients with histologically proven paragangliomas were included in the study. The sequence protocol and data post-processing procedure were optimized in view of a high temporal resolution and maximum contrast-to-noise ratio. Image-time series of two freely orientated slabs could be obtained. Correlation analysis was performed to generate selective arterial and venous weighted angiographic images. Glomus tumors showed a rapid and intense homogeneous enhancement following the intravenous administration of contrast material. The smallest tumors investigated measured 10 mm and could be visualized clearly. Time-resolved analysis of the tumor enhancement revealed an early bolus arrival within the vascular bed of the tumor and prolonged incomplete washout indicating blood pooling. The dynamic contrast enhancement of glomus tumors can be evaluated non-invasively with MRPA providing a high temporal resolution and high image quality. The characteristic contrast enhancement of glomus tumors can be helpful in the diagnostic workup of lesions that may mimic glomus tumors.     

The coding of odour-intensity in the honeybee antennal lobe: local computation optimizes odour representation

We investigated strategies involved in odour intensity coding by the primary olfactory centre of insects, the antennal lobe (AL), the structural and functional analogue of the olfactory bulb. Using calcium imaging in the honeybee, we simultaneously measured the projection neuron output responses and a compound signal dominated by receptor neuron input in identified olfactory glomeruli to odours spanning seven log units of concentration. A comparison of the two processing levels indicates that the intercellular computation within the AL modulates and contrast-enhances the primary olfactory signals. As a result the AL network optimizes the olfactory code: odour representation is improved at lower concentrations, the relative activity of olfactory glomeruli allows encoding odour quality over up to four log-unit concentrations, and odour-intensity is reliably represented in the overall excitation across AL.     

Brain targeting and glomerulus formation of two olfactory neuron populations expressing related receptor types

Olfactory sensory neurons expressing different members of the mOR37 odourant receptor subfamily send their axons to distinct glomeruli located in the immediate vicinity in the olfactory bulb [Strotmann, J., Conzelmann, S., Beck, A., Feinstein, P., Breer, H. & Mombaerts, P. (2000) J. Neurosci., 20, 6927-6938]. In this study, the potential of transgenic mouse lines was used to explore the onset of receptor expression, the outgrowth of axons as well as the glomerulus formation for two neuron populations expressing different mOR37 subtypes. The data indicate a synchronous time course of these features for both neuron populations. From E15 until the day of birth, the axons of the two mOR37 populations terminate in a common, small area of the presumptive olfactory bulb. During a short postnatal phase, the two axon populations segregate into distinct, protoglomerular structures; some aberrant fibers can still be observed during this period.     

胸部螺旋CT最大密度投影重建的参数优化

目的探讨胸部螺旋CT最大密度投影(MIP)重建合理的扫描和重建参数。方法6例煤工的尸检离体肺脏制成充气固定肺标本,分别行不同参数组合的螺旋CT扫描,包括层厚1.5mm,2mm,4mm及8mm,重建间隔1mm,3mm,5mm;曝光量150mA,100mA;螺距1.5;滤过算法包括标准、锐利和平滑3种。每组图像均行MIP重建,重建厚度为12.5mm～13mm,比较不同参数MIP重建图像对支气管血管束的显示。结果a)曝光量对MIP重建图像的影响甚微,150mA、100mA两组剂量MIP无显著性差异(P>0.05);b)重建算法对MIP重建无显著影响。c)扫描层厚影响MIP图像,以薄层(1.5mm)扫描重建为最佳,1.5mm、2mm、4mm层厚MIP图像之间无显著性差异(P>0.05),8mm层厚与前4者MIP图像有显著性差异(P<0.01)。d)重建间隔影响MIP重建效果,8mm层厚扫描,1mm和5mm重建间隔重建图像MIP之间有显著性差异(P<0.05)。结论影响MIP重建的参数主要为扫描层厚和重建间隔,薄层扫描可获得理想的MIP图像,随层厚的增加,减小重建间隔有利于获得理想的MIP图像。建议以中等层厚(4mm)扫描,小重建间隔(1.5mm,2mm)行MIP重建。     

Incidence trends and projections for childhood cancer in Ontario

Studies of cancer incidence patterns and trends can provide useful measures of health burden and possible disease etiology, which can aid the planning of cancer care services. This report aims to characterize trends in incidence of childhood cancer, and to assess the implications of these trends by generating incidence projections to 2015. Cancer incidence data were obtained from the database of the Pediatric Oncology Group of Ontario (POGO), which has registered all cancer cases in Ontario since 1985. Annual incidence rates were calculated with census-based population estimates for the 1986-2001 period. Poisson regression models were used to analyze trends, and to calculate projected numbers of cases up to the year 2015. From 1986 to 2001, 5,163 cancer cases occurred among children aged 0-14. Leukemia, CNS tumors and lymphomas were the most common cancers. The number of incident cases increased by 14%, from 296 in 1986 to 336 in 2001. For all cancers, average annual age-standardized rates increased from 147 per million in 1991 to 157 per million in 2001. Over the next 15 years, the 0-14 year population is expected to decrease from 2.28 million in 2000 to 2.13 million in 2015. A marginally statistically significant trend in incidence was projected for all cancers combined (0.5% increase per year p < 0.10) and a statistically significant increase for lymphomas, (1.2% per year 95% CI = 0.0-3.9%). During this period, the number of cases of leukemia and CNS tumors is expected to remain relatively stable. The number of cases of all cancers is expected to increase by 8%, from the average of 320 in 1995 to approximately 347 in 2015. Understanding of these projections will facilitate health care resource planning.     

颈椎关节突关节摄影位置的研究

目的研究一种能够显示颈椎上、下关节突及关节突关节的最佳摄影位置。方法测量63例正常人颈椎关节突关节(第3~7颈椎)CT横断扫描片(920个有效数据),在颈椎关节突关节CT片上做椎体前后缘中点连线的延长线和颈椎上关节突关节面两端点连线的延长线,两直线相交所形成的夹角即人体矢状面与颈椎关节突关节的角度,称颈椎关节突关节角。结果颈椎关节突关节角为70°~75,°经统计学处理,颈椎的关节突关节在不同性别、不同椎体、不同侧别之间无明显差异。在摄影时,使人体冠状面与胶片成70°~75°摄片,此时关节突关节与胶片垂直,与中心线平行,可得到清晰的关节突关节影像,此摄影位置称颈椎关节突关节位。结论颈椎关节突关节位能清晰显示颈椎上、下关节突及关节突关节间隙。