The measurement of R2, and R2′ in HIV-infected patients using the prime sequence as a measure of brain iron deposition

Brain iron deposition was assessed at 1.5 T in the caudate nucleus, globus pallidus and frontal and parietooccipital white matter in 28 human immunodeficiency virus (HIV)-infected patients and 15 control subjects with a new Partially Refocussed Interleaved Multi-Echo sequence by measuring 1/T₂, 1/T₂^* and 1/T2′ (i.e., R₂, and R₂′). There were significant differences in the R₂ and of the caudate nucleus (p < 0.0001 and p < 0.05) and the R₂, and R₂′ of the globus pallidus (p < 0.001, p < 0.005 and p < 0.05) in HIV-infected patients compared to control subjects. There was a trend for higher values of R₂, and R₂′ in the globus pallidus and caudate nucleus in HIV-infected patients with later stage HIV disease. These results suggest that there is greater iron deposition in the basal ganglia of HIV-infected patients compared with control subjects, with a predilection for the globus pallidus. The relationship between iron deposition in the brain and various parameters of severity of HIV infection remains uncertain.     

The aqueduct echo method applied to brain stem tumours

Echoencephalography of the posterior fossa was performed in nine cases of brain stem lesion. In all instances a dorsal displacement of the cerebral aqueduct was disclosed by means of the aqueduct echo method. The quantitative displacement was expressed by the A:B ratio method and found to agree well with calculations from corresponding pneumoencephalography.     

Analysis of input functions from different arterial branches with gamma variate functions and cluster analysis for quantitative blood volume measurements

Regional cerebral blood volume (rCBV) provides valuable information about the nature and progress of diseases of the central nervous system. While relative rCBV maps can be derived directly from dynamic susceptibility contrast data, the arterial input function (AIF) has to be measured for absolute rCBV quantification. For determination of the AIF pixels located completely within a feeding artery must be selected. However, by using a region-of-interest (ROI) based selection some confounding effects can occur, especially if single shot echo planar imaging (EPI) with low spatial resolution is used. In this study we analyzed the influence of partial volume effects and spatial misregistration due to frequency shifts induced by paramagnetic contrast agents. We analyzed AIFs from the internal carotid artery (ICA), the vertebral artery (VA) and the middle cerebral artery (MCA) using gamma variate function based parameterization. The concentration time curves (CTC) of several pixels which were selected on the basis of strong signal drop appeared distorted during the bolus passage. Moreover, the amplitudes of input functions derived from the MCA were smaller by a factor of three as compared to those of the ICA and VA. Simulations revealed that these effects can be attributed to a spatial shift of the vessel along phase-encoding direction during the passage of the bolus. We therefore developed a procedure for a pixel selection based on cluster analysis which classifies pixels according to the parameters of the fitted gamma variate functions. This approach accounted for misregistration of the vessel and yielded very consistent results for a group of normal subjects.     

The accuracy of whole brain N-acetylaspartate quantification

A non-localizing pulse sequence to quantify the total amount of N-acetylaspartate (NAA) in the whole brain (WBNAA) was introduced recently [Magn. Reson. Med. 40, 684–689 (1998)]. However, it is known that regional magnetic field inhomogeneities, ΔB₀s, arising from susceptibility differences at tissue interfaces, shift and broaden local resonances to outside the integration window, leading to an underestimation of the true amount of NAA in the entire brain. To quantify the upper limit of this loss, the whole-head proton MR spectrum (¹H-MRS) of the water was integrated over the same frequency width as the NAA. The ratio of this area/total-water-line was 75 ± 5% in 5 volunteers. The procedure was repeated with the brain-only water peak, obtained by summing signals only from voxels within that organ from a three-dimensional chemical-shift-imaging (3D CSI) set. It indicated that <10% of the water signal loss occurred in the brain. Therefore, by analogy, WBNAA accounts for >90% of that metabolite.     

急性肺栓塞患者血浆脑钠肽与右心功能的关系及其预后评估价值

目的研究血浆脑钠肽（BNP）与急性肺栓塞（APE）患者右心室功能不全（RVD）的关系及其预后评估价值。方法采用酶联免疫法测定44例APE患者血浆BNP水平,同时根据超声心动图检查分为RVD组和无RVD组。观察两组间血浆BNP水平差异及血浆BNP水平与不良事件发生率的关系。结果 APE患者RVD组BNP水平[（2352.5±1987.8）pg/ml]高于无RVD组[（349.9±299.4）pg/ml]（P＜0.01）;低BNP者不良事件发生率（10.0％）低于高BNP者（69.2％）,差异有统计学意义（P＜0.05）;低BNP者1年生存率高于高BNP者（χ2=6.554,P＜0.05）。结论 BNP可作为反应APE患者RVD的有效手段,对预测患者不良事件及预后有重要作用。     

双源CT4D-CTA联合灌注成像在急性脑缺血性疾病中的应用价值

目的：探讨双源CT 4维血管造影（4D- CTA）及灌注成像（CTPI）在急性脑缺血性疾病中的应用价值。方法对30例临床拟诊为急性脑缺血性疾病的患者于发病2-24h内行头颅CT平扫和全脑CTPI检查,获得脑血流量、脑血容量、平均通过时间、达峰时间等参数图,同时获得4D- CTA图像;于发病的1-3d后行MRI检查,分析CT平扫、CTPI、4D- CTA、MRI表现。结果 CT平扫发现12例有16个缺血病灶,CTPI发现26例32个缺血病灶,MRI发现25例28个缺血病灶,4D- CTA显示有20例责任血管有不同程度的狭窄或闭塞。结论双源CT 4D- CTA联合灌注成像能为急性脑缺血患者提供全面、详细的影像学信息,对急性缺血性脑梗死的早期诊断和治疗有重要价值。     

The rapid and automatic combination of proton MRSI data using multi-channel coils without water suppression

The use of multi-channel coils can efficiently increase the signal-to-noise ratio (SNR) of magnetic resonance spectroscopy data if the signals from multiple channels are optimally combined. Combining multi-channel signals requires proper alignment of the phases of the signals from each of the elements of the coil and then accurately weighting the summation of those signals. We present a procedure for acquiring proton magnetic resonance spectroscopic imaging (MRSI) data using an eight-channel coil without water suppression and a rapid and robust method that uses unsuppressed water signal as a reference both for aligning the phases and for weighting the summation of signals that originate in the multiple coil elements. We use both computer simulation and in vivo proton MRSI data to demonstrate the advantages of our method for optimizing the SNR of the combined signal compared with the SNRs of signals that were acquired either using a standard volume head coil or using an eight-channel coil with a metabolite signal as the reference for combination.     

PDE-based spatial smoothing: a practical demonstration of impacts on MRI brain extraction, tissue segmentation and registration

Spatial smoothing is typically used to denoise magnetic resonance imaging (MRI) data. Gaussian smoothing kernels, associated with heat equations or isotropic diffusion (ISD), are widely adopted for this purpose because of their easy implementation and efficient computation, but despite these advantages, Gaussian smoothing kernels blur the edges, curvature and texture of images. To overcome these issues, researchers have proposed anisotropic diffusion (ASD) and non-local means [i.e., diffusion (NLD)] kernels. However, these new filtering paradigms are rarely applied to MRI analyses. In the current study, using real degraded MRI data, we demonstrated the effect of denoising using ISD, ASD and NLD kernels. Furthermore, we evaluated their impact on three common preprocessing steps of MRI data analysis: brain extraction, segmentation and registration. Results suggest that NLD-based spatial smoothing is most effective at improving the quality of MRI data preprocessing and thus should become the new standard method of smoothing in MRI data processing.     

Convertible pneumatic actuator for magnetic resonance elastography of the brain

Here we present a novel pneumatic actuator design for brain magnetic resonance elastography (MRE). Magnetic resonance elastography is a phase contrast technique capable of tracing strain wave propagation and utilizing this information for the calculation of mechanical properties of materials and living tissues. In MRE experiments, the acoustic waves are generated in a synchronized way with respect to image acquisition, using various types of mechanical actuators. The unique feature of the design is its simplicity and flexibility, which allows reconfiguration of the actuator for different applications ranging from in vivo brain MRE to experiments with phantoms. Phantom and in vivo data are presented to demonstrate actuator performance.     

DTI-based segmentation and quantification of human brain lateral ventricular CSF volumetry and mean diffusivity: Validation,age, gender effects and biophysical implications

The human brain lateral ventricular (LV) cerebrospinal fluid (CSF) volume has been used as a neuroimaging marker of brain changes in health and disease. The LV CSF diffusivity may offer a useful quality assurance measure and become a potential noninvasive marker of deep brain temperature. In this work we sought to validate a method for human brain lateral ventricular (LV) cerebrospinal fluid (CSF) using diffusion tensor imaging (DTI) contrast to provide LV volume and corresponding DTI metrics. We compared LV volume obtained using DTI with that obtained using validated segmentations of the LV on T1-weighted data. DTI and T1-weighted data were acquired at 3 T on 49 healthy males and 56 age-matched females aged 18–59 years. We showed histogram distributions of LV DTI metrics to establish quality assurance measures. We also analyzed the age and gender effects of LV volume and diffusivity. LV volumes estimated using both T1-weighted and DTI correlated strongly in males and females (ICC = 0.99; median Dice index ~ 80%). The LV-to-intracranial volume percentage increased significantly with age only in males, using the DTI-based approach (r = 0.39; p = 0.005). LV CSF Mean diffusivity was greater in males than females ((~ 1.2%; p = 0.03). Mean diffusivity of lateral ventricular CSF decreased significantly with age in healthy adults (r = − 0.30; p = 0.02). Our results highlight the importance of age and gender-based analyses and the potential of LV diffusivity measures as a quantitative marker.