基于FFT频域积累的非接触生命参数信号检测

目的：提高非接触生命参数检测系统信噪比。方法：采用两种基于FFT的频域积累检测方法，利用Matlab软件环境编写算法，进行仿真实验与实际信号处理。结果：该方法提高了非接触检测系统信号的信噪比，能够在强噪声背景下检测出生命参数信号。结论：该方法适用于低信噪比下的微弱信号提取，在本系统中得到了较好应用。     

Arterial spin labeling: Clinical applications

Arterial spin labeling (ASL) is a magnetic resonance imaging perfusion technique that enables quantification of cerebral blood flow (CBF) without the use of intravenous gadolinium contrast. An understanding of the technical basis of ASL and physiologic variations in perfusion are important for recognizing normal variants and artifacts. Pathologic variations in perfusion can be seen in a number of disorders including acute and chronic ischemia, vasculopathy, vascular malformations, tumors, trauma, infection/inflammation, epilepsy and dementia.     

Increasing spatial coverage for high‐resolution functional MRI

For high‐resolution functional MRI (fMRI) studies, one of the major challenges is limited spatial coverage, which results because of the tradeoffs between temporal resolution and covering more k‐space. Given the same temporal resolution, fewer slices can be collected for high‐resolution fMRI. If the number of slices is not large enough to cover all regions of interest, additional scans may become necessary, which increases both the total scan time and the complexity of interpreting data. In this work, we propose a method that combines the undersampled 3D stack‐of‐spirals acquisition method with the UNFOLD technique to significantly increase the spatial coverage for high‐resolution fMRI. Undersampling allows more slices to be fit into a given temporal resolution. The signal‐to‐noise ratio (SNR) drop associated with undersampling can be compensated by the increase in the excited volume in 3D acquisitions. Theoretical analysis shows that although there is a negligible increase in temporal coherence due to spectral filtering in the UNFOLD technique, twice the spatial coverage can be achieved given the same total scan time and similar quality of activation maps, which was confirmed by experiments on normal subjects. Magn Reson Med, 2009. © 2008 Wiley‐Liss, Inc.     

Mechanically adjustable coil array for wrist MRI

In this work, the concept of mechanically adjustable MR receiver coil arrays is proposed and implemented for the specific case of human wrist imaging. An eight‐channel wrist array for proton MRI at 3 Tesla was constructed and evaluated. The array adjusts to the individual anatomy by a mechanism that fits a configuration of flexible coil elements closely around the wrist. With such adjustability, it is challenging to ensure robust electrical behavior and signal‐to‐noise (SNR) performance. These requirements are met by preamplifier decoupling and a suitable matching strategy based on π networks that render the coil responses robust against changes in tuning, loading and mutual coupling. The robustness of the resulting SNR yield was studied by varying the effective coil matching over a wide range in a phantom imaging experiment. While SNR variation of up to 25% was observed at the surface of the phantom the SNR was essentially constant in the critical center region. A second SNR study in wrist phantoms of different sizes confirmed the benefits of bringing the coil elements very close, up to 3 mm, to the individual target volume. These findings were supported by initial in vivo imaging, exploiting high‐sensitivity detection for highly resolved structural imaging. Magn Reson Med 61:429–438, 2009. © 2009 Wiley‐Liss, Inc.     

消除ECG信号噪声的信号平均方法的探讨

本文讨论了信号平均法去除噪声的基本原理，针对带有随机噪声的ECG信号，利用UW Digiscope程序进行了实验仿真，结果表明，该方法可以在不失真的前提下通过多次叠加提高信噪比，从而分离出目标信号，抑制了噪声。     

Performance of a 200-MHz cryogenic RF probe designed for MRI and MRS of the murine brain.

A cryogenic 200-MHz RF transmit/receive probe (CryoProbe) made of copper and designed for murine brain studies is described. The probe operates at 30K and its performance was compared to a home-made surface coil of equal dimensions and a mouse head volume resonator, both operating at room temperature (RT). Since for small volumes of tissue interrogated (<5 mL) sample noise and thermal noise of the receiver are of comparable magnitude, considerable noise reduction can be achieved by cooling of the receiver system, e.g., using cold helium gas. The effect of temperature lowering on the signal-to-noise ratio (SNR) was assessed in phantom and in vivo murine brain studies using conventional MRI sequences (spin and gradient echo) and single voxel MR spectroscopy. Consistent sensitivity increases were observed for the CryoProbe. SNR increases by a factor>or=2 for the phantom experiments and by factors of 1.8 to 1.9 for in vivo experiments when compared to the RT surface coil for both MRI and MRS experiments. These results are in good agreement with estimated SNR gains for a circular surface coil probe cooled to 30K. The use of a cryogenic probe represents an economically attractive option to enhance the sensitivity in small animal MRI/MRS.     

Application of refocused steady-state free-precession methods at 1.5 and 3 T to in vivo high-resolution MRI of trabecular bone: simulations and experiments

PURPOSE: To evaluate the potential of fully-balanced steady-state free-precession (SSFP) sequences in in vivo high-resolution (HR) MRI of trabecular bone at field strengths of 1.5 and 3 T by simulation and experimental methods. MATERIALS AND METHODS: Using simulation studies, refocused SSFP acquisition was optimized for our imaging purposes with a focus on signal-to-noise ratio (SNR) and SNR efficiency. The signal behavior in trabecular bone was estimated using a magnetostatic model of the trabecular bone and marrow. Eight normal volunteers were imaged at the proximal femur, calcaneus, and the distal tibia on a GE Signa scanner at 1.5 and at 3 T with an optimized single-acquisition SSFP sequence (three-dimensional FIESTA) and an optimized multiple-acquisition SSFP sequence (three-dimensional FIESTA-c). Images were also acquired with a fast gradient echo (FGRE) sequence for evaluation of the SNR performance of SSFP methods. RESULTS: Refocused SSFP images outperformed FGRE acquisitions in both SNR and SNR efficiency at both field strengths. At 3 T, susceptibility effects were visible in FIESTA and FGRE images and much reduced in FIESTA-c images. The magnitude of SNR boost at 3 T was closely predicted by simulations. CONCLUSION: Single-acquisition SSFP (at 1.5 T) and multiple-acquisition SSFP (at 3 T) hold great potential for HR-MRI of trabecular bone.     

MR信噪比一幅图像测量方法与两幅图像测量方法对照研究

目的对比分析MR信噪比一幅图像测量方法和两幅图像测量方法的差异与关系.方法利用Magphan体模的均匀模块在8台不同场强、不同厂家的MRI设备上进行实验.利用一幅图像测量方法和两幅图像测量方法得到信噪比结果.计算不同测量方法的重复性(Rp1和Rp2)及两幅图像测量方法的信噪比与一幅图像测量方法的信噪比的比值(R).结果8台设备的检测结果为:Rp1在77.65%～98.78%之间;Rp2均大于99.00%;R值在0.39到9.50之间.结论利用两幅图像测量方法得到信噪比的重复性较好,在MR系统稳定性较好的条件下,能够真实反映MR系统信噪比.但是在进行MR系统性能检测过程中,应结合两幅图像测量方法和一幅图像测量方法对信噪比进行评价,利用Rp1、Rp2和R给出信噪比检测结论,与其他性能参数相结合可对MR系统其他性能进行评价,如主磁场均匀性、主磁场稳定性、射频场与梯度场的性能,使检测结果能够更准确地反映MRI设备的质量状况.     

Role of the ventromedial nucleus of the thalamus in motor behaviour—II. Effects of lesions

Rotational behaviour was initiated in naive rats by injecting muscimol into one substantia nigra pars reticulata, or in unilaterally 6-hydroxydopamine-treated rats with systemic or intracaudate apomorphine. Electrolytic or kainic acid lesions were made in one or both ventromedial nuclei of the thalamus and their effects on the components of circling studied. A unilateral ventromedial electrolesion imposed a weak ipsilateral posture and occasionally elicited weak ipsiversive circling acutely, but not chronically. Challenging these rats with a large subcutaneous dose of apomorphine invariably provoked ipsiversive circling, however old was the lesion. Bilateral electrolesions caused slight hypoactivity. Kainic acid treatments of one or both ventromedial thalami produced uncontrolled hypermotility initially, with subsequent loss of ventromedial neurones and recovery of normal motor behaviour. No form of ventromedial lesion affected the incidence of stereotypy. Acute (but not chronic) contralateral or ipsilateral ventromedial electrolesions, or both, slowed muscimol and apomorphine-induced circling (often in different ways) through complex changes in posture and/or locomotor drive. Animals lesioned during the course of a circling episode often showed the biggest changes in circling to begin with, only to recover minutes later. Rapidly circling rats were sometimes more readily inhibited than slowly circling rats. Toxin injury of the ventromedial nucleus appeared to suppress muscimol and not apomorphine circling. Any ventromedial lesion (electrical or chemical, acute or chronic), if positioned opposite a contraversive circling stimulus, intensified the associated posture. Ipsilateral lesions tended to abolish posture altogether or, like bilateral treatments, to suppress locomotion. Sham operations had none of these effects. Acute electrical lesions and drug-induced inhibition of one or both ventromedial thalami were more or less identical in their effects on rat circling behaviour, save that bilateral muscimol injection caused profound catalepsy while lesions did not.

It is suggested that the ventromedial thalamus is more concerned with the registration of striatal dopamine-mediated behaviours in drug-stimulated than in spontaneously behaving rats, and that other output pathways may rapidly compensate for any impairment of function in the ventromedial nuclei.