Transit of blood flow through the human left ventricle mapped by cardiovascular magnetic resonance.

BACKGROUND: The transit of blood through the beating heart is a basic aspect of cardiovascular physiology which remains incompletely studied. Quantification of the components of multidirectional flow in the normal left ventricle (LV) is lacking, making it difficult to put the changes observed with LV dysfunction and cardiac surgery into context. METHODS: Three dimensional, three directional, time resolved magnetic resonance phase-contrast velocity mapping was performed at 1.5 Tesla in 17 normal subjects, 6 female, aged 44+/-14 years (mean+/-SD). We visualized and measured the relative volumes of LV flow components and the diastolic changes in inflowing kinetic energy (KE). Of total diastolic inflow volume, 44+/-11% followed a direct, albeit curved route to systolic ejection (videos 1 and 2), in contrast to 11% in a subject with mildly dilated cardiomyopathy (DCM), who was included for preliminary comparison (video 3). In normals, 16+/-8% of the KE of inflow was conserved to the end of diastole, compared with 5% in the DCM patient. Blood following the direct route lost or transferred less of its KE during diastole than blood that was retained until the next beat (1.6+/-1.0 millijoules vs 8.2+/-1.9 millijoules, p<0.05); whereas, in the DCM patient, the reduction in KE of retained inflow was 18-fold greater than that of the blood tracing the direct route. CONCLUSION: Multidimensional flow mapping can measure the paths, compartmentalization and kinetic energy changes of blood flowing into the LV, demonstrating differences of KE loss between compartments, and potentially between the flows in normal and dilated left ventricles.     

Determination of normal gender-specific left atrial dimensions by cardiovascular magnetic resonance imaging.

BACKGROUND: Because cardiovascular magnetic resonance imaging (CMR) is becoming increasingly available in clinical practice, there is a need to establish normal values for left atrial dimensions as determined by this method to allow accurate assessment of cardiac dimensions and to provide standardization for follow up studies. For clinical purpose measurements of the left atrial end diastolic diameter (LAEDD) are most appropriate to assess left atrial size. We aimed to establish normal values for LAEDD using CMR and a fast gradient-echo sequence with steady-state free precession (SSFP). METHODS: A total of 111 healthy subjects (52 women and 59 men, mean age 51.5 +/- 14.5 years) were examined by CMR. Images were acquired using SSFP in the horizontal (HLA) and vertical (VLA) long axis planes and the left ventricular outflow tract plane (LVOT) to measure the LAEDD. RESULTS: Age between men and women was not different (p = 0.7050). CMR yielded the following normal ranges for LAEDD: HLA 4.5 +/- 0.4 cm for men and 4.2 +/- 0.5 for women, VLA 4.5 +/- 0.5 cm for men and 4.2 +/- 0.4 for women, and LVOT 2.8 +/- 0.3 cm for men and 2.8 +/- 0.4 for women. LAEDD were significantly larger in HLA and VLA than in LVOT (p < or = 0.0001). There was no significant difference in the measurements between HLA and VLA (p = 0.4617). Gender-related differences for LAEDD were found in HLA (p = 0.0087) and VLA (p = 0.0015) but not in LVOT (p = 0.5281). LAEDD were not found to be age-related (p > or = 0.0994). CONCLUSIONS: LAEDD differ significantly according to the image plane. We provide reference values for CMR using prospective triggering in the evaluation of left atrial diameters to identify patients with enlarged left atria and for follow-up studies.     

Quantitative cardiovascular magnetic resonance for molecular imaging

Cardiovascular magnetic resonance (CMR) molecular imaging aims to identify and map the expression of important biomarkers on a cellular scale utilizing contrast agents that are specifically targeted to the biochemical signatures of disease and are capable of generating sufficient image contrast. In some cases, the contrast agents may be designed to carry a drug payload or to be sensitive to important physiological factors, such as pH, temperature or oxygenation. In this review, examples will be presented that utilize a number of different molecular imaging quantification techniques, including measuring signal changes, calculating the area of contrast enhancement, mapping relaxation time changes or direct detection of contrast agents through multi-nuclear imaging or spectroscopy. The clinical application of CMR molecular imaging could offer far reaching benefits to patient populations, including early detection of therapeutic response, localizing ruptured atherosclerotic plaques, stratifying patients based on biochemical disease markers, tissue-specific drug delivery, confirmation and quantification of end-organ drug uptake, and noninvasive monitoring of disease recurrence. Eventually, such agents may play a leading role in reducing the human burden of cardiovascular disease, by providing early diagnosis, noninvasive monitoring and effective therapy with reduced side effects.     

Cine and tagged magnetic resonance imaging in short-term stunned versus necrotic myocardium

We investigated the potential of Cine and 2D Tagged Cardiac Magnetic Resonance (CMR) Imaging to distinguish stunned from necrotic left ventricular (LV) myocardium in the early postischemic phase in an open-chest animal model (N=12). Reversible and permanent occlusion of the LAD coronary artery resulted in global LV dysfunction in both groups without significant differences. LAD perfused segments revealed significant higher values for end systolic wall thickening (ESWT) and percentual systolic wall thickening in animals with stunned myocardium. Analysis of strain parameters showed significant regional differences (maximal principal strain ₁, deviation angle ) between postischemic and remote myocardium within both groups, however results were not significantly different comparing animals with stunned myocardium to animals with myocardial necrosis. In conclusion, at rest neither global LV functional nor regional strain parameters derived from Cine and 2D Tagged CMR Imaging can distinguish animals with short-term stunned myocardium from respective animals with necrotic myocardium. Diagnostic value of ESWT is limited due to the spatial resolution of the gradient-echo sequence used.Supported by a grant from the Interdisciplinary Center of Clinical Research (IZKF; B1, BMBF-01KS 9604).     

Cine and tagged cardiovascular magnetic resonance imaging in normal rat at 1.5 T: a rest and stress study

Background

The purpose of this study was to measure regional contractile function in the normal rat using cardiac cine and tagged cardiovascular magnetic resonance (CMR) during incremental low doses of dobutamine and at rest.

Methods

Five rats were investigated for invasive left ventricle pressure measurements and five additional rats were imaged on a clinical 1.5 T MR system using a cine sequence (11–20 phases per cycle, 0.28/0.28/2 mm) and a C-SPAMM tag sequence (18–25 phases per cycle, 0.63/1.79/3 mm, tag spacing 1.25 mm). For each slice, wall thickening (WT) and circumferential strains (CS) were calculated at rest and at stress (2.5, 5 and 10 μg/min/kg of dobutamine).

Results

Good cine and tagged images were obtained in all the rats even at higher heart rate (300–440 bpm). Ejection fraction and left ventricular (LV) end-systolic volume showed significant changes after each dobutamine perfusion dose (p < 0.001). Tagged CMR had the capacity to resolve the CS transmural gradient and showed a significant increase of both WT and CS at stress compared to rest. Intra and interobserver study showed less variability for the tagged technique. In rats in which a LV catheter was placed, dobutamine produced a significant increase of heart rate, LV dP/dtmax and LV pressure significantly already at the lowest infusion dose.

Conclusion

Robust cardiac cine and tagging CMR measurements can be obtained in the rat under incremental dobutamine stress using a clinical 1.5 T MR scanner.     

Regional differences in shape and load in normal and diseased hearts studied by three dimensional tagged magnetic resonance imaging

Objectives: We aimed to characterize regional geometry in relation to load in two groups of patients with hypertrophic cardiomyopathy (HCM) and right ventricular pressure overload (RVPO) in relation to a group of subjects with normal left ventricular (LV) function. Background: Both these diseases are associated with marked changes in LV shape and function, which have not been studied with detailed three dimensional tools. Methods: Three dimensional (3D) tagged magnetic resonance imaging (MRI) was used to characterize the 3D geometry and regional stresses of the left ventricles in patients with HCM and RVPO. Curvatures, stresses, wall thickness, and endocardial motion were calculated from surface and volume elements. Results: Hearts with RVPO exhibited more circumferential and meridional flattening of the septum than normal and HCM hearts. The stress indices were lowest in the HCM hearts, compared to normal and RVPO hearts, due to the larger thicknesses. There was a more significant difference between lateral wall motion and other regional wall motions in the HCM and RVPO hearts as compared to normal hearts. Conclusions: It is suggested that curvature and stress mapping by 3D tagged MRI can be used as an important clinical tool for characterizing and distinguishing between healthy and diseased hearts. The results provided here validated previous knowledge on HCM and RVPO known from planary imaging methods.     

正常人脑弥散定量研究

目的确立标准化的正常人脑各部位ADC参考值,探讨ADC值与脑内不同结构部位的关系.方法选择健康男女各30名,所有对象进行MR检查,包括常规MRI和EPI弥散加权成像,弥散敏感系数分别为b=0,b=1000 s/mm2;测定双侧半球的34个感兴趣区的平均ADC值.结果灰质的平均ADCAv最高(0.80±0.05)×10-3mm2/s,其次是白质的平均ADCAv(0.77±0.05)×10-3mm2/s,丘脑的平均ADCAv(0.75±0.07)×10-3mm2/s,基底节的平均ADCAv最低(0.73±0.06)×10-3mm2/s.双侧半球相同部位之间经配对t检验,双侧脑室间平均ADCAv存在差异(P＜0.05),其余结构之间差异无显著性意义(P＞0.05).结论正常人脑各部位ADC值的定量研究为弥散成像的临床应用提供了依据和指导.     

左心耳多模态磁共振成像研究进展

左心耳(left atrial appendage,LAA)是左心房的重要附属结构,对其结构和功能的评价在房颤治疗、相关介入手术中至关重要。多模态磁共振成像可以清晰地显示LAA结构并可定量测量其功能指标,其在评估LAA结构和功能方面的应用日益广泛。现将近年来多模态MRI在LAA扫描技术、LAA结构及功能的定量研究、LAA血栓检测及相关危险因素评价、LAA介入治疗的相关评估等方面予以综述。     

磁共振扩散峰度成像在人体肾脏的应用

目的探讨磁共振扩散峰度成像(diffusion kurtosis imaging,DKI)在人体肾脏应用的可行性。材料与方法收集2016年3月至2017年2月在我院招募的健康男性志愿者35例,最终纳入30例。采用3.0 T MR进行双侧肾脏冠状位扫描,扫描序列包括:T1WI、T2WI与DKI序列;DKI采用三个不同b值(0、500s/mm2、1000 s/mm2)和30个扩散敏感梯度方向。采用配对t检验对肾皮质、髓质DKI参数进行组间比较。结果正常人左、右两侧肾皮质、髓质DKI均无统计学差异(P>0.05)。正常人肾脏皮质峰度参数值MK值、Ka值及Kr值均高于髓质(P<0.05);皮质的扩散参数FA值、Da值明显低于髓质,MD值、Dr值高于髓质(P<0.05)。结论肾脏的DKI成像不仅能够反映肾皮质、髓质水分子扩散状态差异,而且其特有的峰度参数值还能够提供更多关于肾皮质、髓质微结构的信息。     

Wavelets and functional magnetic resonance imaging of the human brain

The discrete wavelet transform (DWT) is widely used for multiresolution analysis and decorrelation or "whitening" of nonstationary time series and spatial processes. Wavelets are naturally appropriate for analysis of biological data, such as functional magnetic resonance images of the human brain, which often demonstrate scale invariant or fractal properties. We provide a brief formal introduction to key properties of the DWT and review the growing literature on its application to fMRI. We focus on three applications in particular: (i) wavelet coefficient resampling or "wavestrapping" of 1-D time series, 2- to 3-D spatial maps and 4-D spatiotemporal processes; (ii) wavelet-based estimators for signal and noise parameters of time series regression models assuming the errors are fractional Gaussian noise (fGn); and (iii) wavelet shrinkage in frequentist and Bayesian frameworks to support multiresolution hypothesis testing on spatially extended statistic maps. We conclude that the wavelet domain is a rich source of new concepts and techniques to enhance the power of statistical analysis of human fMRI data.     

Multi-projection magnetic resonance inverse imaging of the human visuomotor system

Using highly parallel radiofrequency (RF) detection, magnetic resonance inverse imaging (InI) can achieve 100 ms temporal resolution with whole brain coverage. This is achieved by trading off partition encoding steps and thus spatial resolution for a higher acquisition rate. The reduced spatial information is estimated by solving under-determined inverse problems using RF coil sensitivity information. Here we propose multi projection inverse imaging (mInI) to combine different projection images to improve the spatial resolution of InI. Specifically, coronal, sagittal, and transverse projection images were acquired from different runs of the fMRI acquisitions using a 32-channel head coil array. Simulations show that mInI improves the quality of the instantaneous image reconstruction significantly. Going from one projection to three projections, the spatial resolution quantified by the full width at half maximum of the point-spread function (PSF) is improved from 2.6 pixels to 1.4 pixels (4 mm nominal resolution per pixel). Considering the shape of the PSF, the effective spatial resolution is improved from 16.9 pixels to 4.7 pixels. In vivo fMRI experiments using a two-choice reaction time tasks show visual and sensorimotor cortical activities spatially consistent with typical EPI data, yet mInI offers 100 ms temporal resolution with the whole brain coverage. The mInI data with three projections revealed that the sensorimotor cortex was activated 700 ms after the visual cortex. mInI can be applied to BOLD-contrast fMRI experiments to characterize the dynamics of the activated brain areas with a high spatiotemporal resolution.     

Normal human left and right ventricular and left atrial dimensions using steady state free precession magnetic resonance imaging.

PURPOSE: The aim of this project was to establish a database of left and right ventricular and left atrial dimensions in healthy volunteers using steady-state free precession cardiac magnetic resonance imaging, the clinical technique of choice, across a wide age range. METHODS: 108 healthy volunteers (63 male, 45 female) underwent cardiac magnetic resonance imaging using steady-state free precession sequences. Manual analysis was performed by 2 experienced observers. RESULTS: Left and right ventricular volumes and left ventricular mass were larger in males than females: LV end-diastolic volume 160 +/- 29 mL vs. 135 +/- 26 mL, LV end-systolic volume 50 +/- 16 mL vs. 42 +/- 12 mL; RV end-diastolic volume 190 +/- 33 mL vs. 148 +/- 35 mL, RV end-systolic volume 78 +/- 20 mL vs. 56 +/- 18 mL (p < .05 for all). Normalization of values to body surface area removed the statistical differences for LV volumes, but not for LV mass or RV volumes. With increased age, males showed a significant decrease in volume and mass indices for both ventricles, while female values remained unchanged. Compared to females, males had significantly larger maximal left atrial volumes (103 +/- 30 mL vs. 89 +/- 21 mL, p = .01) and left atrial stroke volumes (58 +/- 23 mL vs. 48 +/- 15 mL, p = .01). There was no difference in left atrial ejection fraction between the sexes. CONCLUSION: We have produced a large database of age-related normal ranges for left and right ventricular function and left atrial function in males and females. This will allow accurate interpretation of clinical and research datasets.     

Quantitative susceptibility-weighted imaging in amyotrophic lateral sclerosis with 3.0 T magnetic resonance imaging

ObjectiveTo evaluate alterations in phase-shift values in the gray matter of patients with amyotrophic lateral sclerosis (ALS) using susceptibility-weighted imaging (SWI).MethodsTwenty patients with definite or probable ALS and 19 age- and sex-matched healthy controls were enrolled. SWI was performed using a 3.0 T magnetic resonance imaging scanner. Phase-shift values were measured in corrected phase images using regions of interest, which were placed on the bilateral precentral gyrus, frontal cortex, caudate nucleus, globus pallidus, and putamen.ResultsPhase-shift values of the precentral gyrus were significantly lower in ALS patients (−0.176 ± 0.050) than in the control group (−0.119 ± 0.016) on SWI. The average phase-shift values of the frontal cortex, caudate nucleus, globus pallidus, and putamen in ALS patients (−0.089 ± 0.023, −0.065 ± 0.016, −0.336 ± 0.191, and −0.227 ± 0.101, respectively) were not significantly different from those in the healthy controls (−0.885 ± 0.015, −0.079 ± 0.018, −0.329 ± 0.136, and −0.229 ± 0.083, respectively).ConclusionsCompared with healthy controls, ALS patients had a lower phase-shift value in the precentral gyrus, which may be related to abnormal iron overload. Thus, SWI is a potential method for identifying ALS patients.     

磁共振扩散张量成像在正常脑老化研究中的应用

脑老化指随着年龄增长,大脑组织结构、功能、形态逐渐出现衰退的现象,其中认知功能减退是脑老化的重要标志,脑白质的退行性改变可能是造成脑老化的重要因素。DTI及其图像处理技术能够无创显示活体人脑组织微观结构,有利于分析脑老化过程及脑老化相关疾病。本文对DTI技术在正常脑老化中的研究现状及进展做一综述。