Effect of artifacts due to flowing blood on the reproducibility of phase-contrast measurements of myocardial motion

The reproducibility of myocardial motion trajectories calculated from cine phase-contrast (PC) velocity data is reduced by artifacts due to the inconsistent motion of intracardiac blood. Spatial presaturation reduces these artifacts but requires a longer sequence TR, with a potentially negative effect on trajectory accuracy and reproducibility. We investigated the effect of spatial presaturation on trajectory reproducibility. A midventricular transaxial slice was imaged in five normal volunteers. The same slice was imaged three times each with sequences using spatial presaturation or not. Because the most serious artifacts originate in the heart chambers and propagate in the phase-encoded direction, myocardial regions that were in line with the heart chambers (in the phase-encode direction) had the highest artifact level in the scans without spatial presaturation. The reproducibility of trajectories for regions placed in these areas (the anterior wall, septum and posterior wall in the transaxial scans with phase encoding in the anterior-posterior direction) improved by a factor of two when presaturation was used (P < .001). In areas that were not in line with the heart chambers (eg, the anterior aspect of the lateral wall in the transaxial scans), the effect of presaturation was not significant. These results correlate well with the measured reduction in artifact level. The reproducibility of myocardial motion trajectories over large areas of the heart is improved to approximately 1 mm when presaturation is used. Therefore, use of presaturation is recommended for myocardial motion studies using cine PC velocity data.     

电动秋千的研制及其在前庭功能研究中的应用

本文介绍了带转椅的电动秋千的研制及其使用,包括其工作原理、结构与控制系统的设计、主要技术性能及其在前庭功能与空间运动病研究中的应用。多年的实验证明,这台电动秋千设计合理,技术指标先进,使用性能良好,是研究前庭功能和空间运动病的实用设备。     

Artifacts due to stimulus correlated motion in functional imaging of the brain

To assess the effect of stimulus correlated motion on the appearance of functional magnetic resonance images, conventional visual and motor protocols were each performed by four normal volunteers and an image co-registration technique was used to retrospectively monitor subject motion. In three studies synthetic data sets were constructed from single baseline images using the positional information obtained from the co-registration procedure. Cumulative difference images were then created from both the synthetic and functional image sets. Stimulus correlated motion was detected in all eight studies and the synthetic cumulative difference images showed striking similarities to the equivalent functional images in each case.     

高血胆固醇症病人体内铁贮水平与心肌灌注 左心室功能的相关研究

目的评价血清铁参数与高血胆固醇症(HCL)病人心肌灌注、室壁运动异常及血管造影显示的冠状动脉疾病(CAD)程度的相互关系.方法选择38名具有高血胆固醇症(LDL-C＞3.38mmol/L)从未治疗过的男性病人(平均年龄59±6岁)作为HCL组和32名年龄匹配而胆固醇水平正常(NCL)的男性为NCL组,进行冠状动脉造影并在10d内行SPECT检查,应用99mTc-甲氧基异丙基异氰(MIBI)进行静息/负荷门控断层心肌灌注显像、室壁运动功能图像分析;同时测定血清铁参数、血脂及常规血液学参数.结果在HCL组发现血清铁蛋白(SF)与心肌灌注系数(r=0.70,P＜0.01),可逆系数(r=0.66,P＜0.01)和室壁运动系数(r=0.53,P＜0.05)之间呈显著性相关;而总铁结合力与灌注系数之间呈一弱(负)相关(r=-0.52,P＜0.05).在NCL组铁参数与灌注系数及室壁运动系数之间无显著性相关.多元回归分析证实血清铁蛋白水平是决定HCL病人中心肌灌注的独立因素(β=0.55,P＞0.05).铁参数与两组通过冠状动脉造影(CAG)进行评分所定义的CAD程度无关.结论体内铁贮水平升高与HCL病人心肌灌注和功能异常的严重性和程度有着密切的关系,但与CAD的造影显示的病变范围无关.血清铁蛋白水平增高,可增加铁介导的氧化应力和LDL过氧化作用,导致HCL相关的血管内皮功能紊乱并进一步损伤心肌灌注和室壁运动功能.     

兔膝关节持续被动活动对前交叉韧带重建术后切口局部组织血氧饱和度的影响

目的 探讨膝关节持续被动活动（continuous passive motion, CPM）对兔前交叉韧带重建术后切口局部组织血氧饱和度的影响. 方法 20 只八月龄雄性新西兰大白兔右侧后肢膝关节行自体双股半腱肌腱移植重建前交叉韧带手术,术后随机分为2组：自由活动组（n＝10）和CPM组（n＝10）.自由活动组笼内自由活动;CPM组应用兔膝关节持续被动活动器运动.术后第2天,近红外光技术装置ODISseyTM 局部组织血氧监护仪测量每一来回（屈曲30°～110°）不同CPM速度（分别为2.35°/s、3.2°/s 、8°/s）时的切口局部组织血氧饱和度（tissue oxygen saturation ,StO2）变化,选择最好的CPM范围和速度.分别在术前和术后第2、4、6、8、10、14天观察膝关节CPM不同角度时切口局部组织StO2的变化. 结果 与自由活动组相比,3种速度的CPM在不同屈曲角度下均保持较高的StO2,且有显著性差异（P＜0.05）,不同CPM速度之间StO2有显著性差异（P＜0.05）.每一来回（屈曲30°～110°）运动速度为3.2°/s时保持最高的StO2.在术前和术后第2、4、6、8、10、14天等各时间点,膝关节屈曲30°、60°、90°、110°时StO2均无显著性差异（P＞0.05）,不同的时间点（术前和术后第2、4、6、8、10、14天）切口的StO2差别均有显著统计学意义（P＜0.05）.术后第2～4天最低,然后逐渐上升.术后第2周拆线后,切口愈合良好,没有感染、血肿和切口裂开. 结论 兔膝前交叉韧带重建术后第2天开始进行膝关节CPM（屈曲30°～110°）,可增加切口局部组织血氧饱和度,以3.2°/s的CPM速度最佳.     

Three-dimensional magnetic resonance myocardial motion tracking from a single image plane.

Three-dimensional imaging for the quantification of myocardial motion is a key step in the evaluation of cardiac disease. A tagged magnetic resonance imaging method that automatically tracks myocardial displacement in three dimensions is presented. Unlike other techniques, this method tracks both in-plane and through-plane motion from a single image plane without affecting the duration of image acquisition. A small z-encoding gradient is subsequently added to the refocusing lobe of the slice-selection gradient pulse in a slice following CSPAMM acquisition. An opposite polarity z-encoding gradient is added to the orthogonal tag direction. The additional z-gradients encode the instantaneous through plane position of the slice. The vertical and horizontal tags are used to resolve in-plane motion, while the added z-gradients is used to resolve through-plane motion. Postprocessing automatically decodes the acquired data and tracks the three-dimensional displacement of every material point within the image plane for each cine frame. Experiments include both a phantom and in vivo human validation. These studies demonstrate that the simultaneous extraction of both in-plane and through-plane displacements and pathlines from tagged images is achievable. This capability should open up new avenues for the automatic quantification of cardiac motion and strain for scientific and clinical purposes.     

头低位模拟失重状态对前庭功能的影响

为研究头低位模拟失重对运动病症状、垂直视动眼震（ＶＯＫＮ）及体液重新分配的影响，在头低位－１０°的模拟失重状态下，采用大视野的垂直视动刺激，观察１８名正常人的运动病症状、ＶＯＫＮ、激素（ＡＶＰ、ＶＩＰ、ＣＯＲＴ、ＡＬＤＯ）的反应特点。结果表明，头低位－１０°状态下的大视野垂直视动刺激可以诱发出明显的运动病症状，头低位－１０°的垂直视动刺激比坐位更容易诱发运动病。坐位状态ＶＯＫＮ慢相速度有明显的方向性不对称，敏感组ＶＯＫＮ方向性不对称有显著差异（Ｐ＜０．０５）。头低位－１０°时ＶＯＫＮ的不对称现象不明显，向下方向运动的ＶＯＫＮ慢相速度显著增加。分析指出，头低位－１０°状态下垂直视动刺激比坐位和秋千刺激的贡献率大。尿中ＣＯＲＴ（皮质醇）在秋千和头低位的垂直视动刺激前后有显著性增加。提示：大视野的垂直视动刺激与头低位－１０°两种刺激的结合可能成为预测空间运动病的方法之一．     

Partial k-space reconstruction in single-shot diffusion-weighted echo-planar imaging.

Partial k-space sampling is frequently used in single-shot diffusion-weighted echo-planar imaging (DW-EPI) to reduce the TE and thereby improve the SNR. However, it increases the sensitivity of the technique to bulk rotational motion, which introduces a phase gradient across the tissue that shifts the echo in k-space. If the echo is displaced into the high spatial frequencies, conventional homodyne reconstruction fails, causing intensity oscillations across the image. Zero-padding, on the other hand, compromises the image resolution and may cause truncation artifacts. We present an adaptive version of the homodyne algorithm that detects the location of the echo in k-space and adjusts the center and width of the homodyne filters accordingly. The adaptive algorithm produces artifact-free images when the echo is shifted into the high positive k-space range, and reduces to the standard homodyne algorithm in the absence of bulk motion.     

Quantification of in-plane motion of the coronary arteries during the cardiac cycle: Implications for acquisition window duration for MR flow quantification

Motion of the coronary arteries during the heart cycle can result in image blurring and inaccurate flow quantification by MR. This condition applies particularly for longer acquisition windows that are typical of breath-hold coronary flow measurements. To determine the sensitivity of the technique to in-plane motion of different coronary arteries, the temporal variation in coronary position was measured in a plane perpendicular to the proximal portion of the vessel. The results indicated the presence of substantial displacement of the coronary arteries within the cardiac cycle, with a magnitude of motion approximately twice as large for the right as for the left coronary arteries. An estimation of the resulting vessel blurring was calculated, showing that the duration of the acquisition window for high spatial resolution coronary flow acquisitions should be less than 25 to 120 msec, depending on the specific coronary artery studied. In addition, these data specify optimal acquisition window placement for high resolution coronary angiography.     

A framework for automatic analysis of the dynamic behaviour of coronary angiograms

A framework for coronary vessels analysis in digital subtracted angiograms is described. This method combines the motion estimation with the frame-to-frame structure detection in a natural way such that they act interactively. The first step consists of the extraction of the vessel centrelines in one image and their organization into meaningful constituents or branches of the coronary arterial tree. The motion is then estimated along the centrelines through a gradient based method. These motion estimates supply an initial positioning of an active contour model (or snake) in the next image. This model adapts itself by changing its shape to accurately fit onto the new centrelines. This process is then reiterated on the subsequent images to depict the dynamic behaviour of all the relevant branches. The main interests of this scheme are: (1) the active models operate locally so a fast detection of the vessels can be performed; (2) the centrelines extraction is fully guided by the confluence of the motion estimation and the contour model; (3) both morphological and kinetic features are provided on a quantitative basis.