定量磁共振成像在关节软骨中的应用研究进展

在临床上,关节软骨损伤是一种常见病,其发生发展可由外伤、骨性关节炎(osteoarthritis, OA)以及剥脱性骨软骨炎等原因造成,而且这种损坏发生后很难修复。关节软骨损伤主要表现为关节疼痛及功能障碍,关节软骨的损伤以及退变都不同程度地发生在老年人及长期剧烈运动的人群中。关节镜检查被认为是诊断关节软骨病变的金标准。但由于其有创检查的性质,对检查者的技术水平要求很高,且无法深入了解软骨的内部情况。定量磁共振成像(quantitative magnetic resonance imaging, qMRI)既可显示软骨形态学变化,又可以定量评估软骨的生化成分,由于该技术具有无创、良好的软组织分辨力、多参数、多平面成像的优势,它能以非侵入性的定量测量来敏感地监测软骨的微细变化,提供可靠和可重复的成像生物标志物。

Correlations of transcranial sonography of substantia nigra characteristics with MRI iron deposition on substantia nigra in patients with Parkinson disease

Objective To explore the correlations of transcranial sonography of substantia nigra(SN-TCS)characteristics with MRI iron deposition on substantia nigra in patients with Parkinson disease(PD).Methods Data of SN-TCS and craniocerebral MRI in 120 PD patients were retrospectively analyzed.The patients were divided into iron deposition positive group(positive group,n=46)and iron deposition negative group(negative group,n=74)according to quantitative susceptibility mapping(QSM)value.Then parameters of SN-TCS and MRI were compared between groups(both P<0.05),and correlation analysis were also performed.Results The proportion of high echo positive,strong echo area and QSM value of substantia nigra,as well as of hyper-substantia nigra area/midbrain area(S/M)in positive group were all higher than those in negative group(all P<0.001).No significant difference of midbrain area was found between groups(P>0.05).Strong echo area of substantia nigra and S/M based on SN-TCS were both low-medium positively correlated with substantia nigra QSM value showed on MRI(r=0.497,0.529,both P<0.001).Conclusion SN-TCS characteristics of PD patients were correlated with MRI iron deposition on substantia nigra,among which strong echo area and S/M were valuable for evaluating iron deposition on substantia nigra.

Isotropic volumetric MRI for displaying cranial perineural spread of cranial nerve in nasopharyngeal carcinoma

Objective To observe the value of isotropic volumetric MRI for displaying perineural spread(PNS)of cranial nerve(CN)in nasopharyngeal carcinoma.Methods Eighty-seven patients with pathologically proven nasopharyngeal carcinoma were prospectively enrolled.MR scanning,including three-dimensional liver acquisition with volume acceleration-flexible(3D LAVA_Flex)image,T2WI with fat suppression(T2WI-FS),T1WI,contrast enhancement(CE)T1WI-FS of nasopharynx and neck region were performed.The displaying rates of CN PNS were evaluated and compared between 3D LAVA_Flex and T2WI-FS,T1WI,CE-T1WI-FS at patient level,CN group level and neural level,respectively.Results The displaying rate of CN PNS in all 87 nasopharyngeal carcinoma patients by 3D LAVA_Flex sequence was 49.43%(43/87),higher than that of conventional MRI(30/87,34.48%,P=0.001).Among 59 patients with advanced nasopharyngeal carcinoma diagnosed with conventional sequences,the displaying rate of CN PNS was 71.19%(42/59)by 3D LAVA-Flex sequence,higher than that of conventional MRI(30/59,50.85%,P=0.001).At both patient level and posterior CN level,significant differences of the displaying rate of CN PNS were found between 3D LAVA-Flex sequence and T2WI-FS,T1WI,CE-T1WI-FS,while at CN level,the displaying rates of mandibular nerve PNS,CNⅨ—ⅪPNS in jugular foramen(P<0.05)and CNⅨ—ⅫPNS in carotid space of 3D LAVA_Flex sequence were all significantly higher than that of T2WI-FS,T1WI and CE-T1WI-FS(all P<0.05),of PNS of CNⅢ—Ⅴin cavernous sinus were higher than that of T2WI-FS(P<0.05),while of PNS of hypoglossal nerve were significantly higher than that of T2WI-FS and T1WI(both P<0.05).Conclusion 3D LAVA_Flex sequence could be used to effectively display CN PNS of nasopharyngeal carcinoma.

Preliminary clinical application of total free-breathing cardiac MR examination

Objective To observe the clinical application value of total free-breathing cardiac MR(CMR)examination preliminarily.Methods Two patients who underwent CMR scanning under free-breathing state,including cine,motion correction T1 and T2 mapping,blood flow imaging,and late gadolinium enhancement scanning were retrospectively enrolled,and the qualities of the above images were evaluated and compared with that of conventional CMR images under breath-holding state.Results No significant difference of imaging quality was found between total free-breathing and conventional breath-holding CMR.The differences of left ventricular ejection fraction,cardiac output,left ventricular end-diastolic volume index and left ventricular mass measured based on CMR images under different breath conditions were limited.Conclusion Total free-breathing CMR was feasible in clinical practice,which could provide"one-stop"evaluation of cardiac structure,function and myocardial histological characteristics,hence having promising clinical prospects.

Intravoxel incoherent motion and dynamic contrast-enhanced MRI for assessing abnormalities of brucellosis spondylitis without conventional MRI changes

Objective To observe the value of intravoxel incoherent motion(IVIM)and dynamic contrast-enhanced MRI(DCE-MRI)for assessing abnormalities of brucellosis spondylitis(BS)without conventional MRI changes.Methods Data of 36 brucellosis patients with definite spinal lesions displayed on conventional MRI(BS 1 group),14 cases without brucellosis infection nor abnormal spinal signals on MRI(control group)and 36 brucellosis patients without definite spinal lesions on conventional MRI(BS 2 group)were retrospectively analyzed.The values of IVIM parameters,including perfusion fraction(f),pure water diffusion coefficient(D)and pseudo-diffusion coefficient(D*),also of DCE-MRI parameters,including time-intensity curve(TIC)type,volume transport constant(K trans),the rate constant(K ep)and volume fraction of extravascular extracellular space per unit tissue volume(V e)were compared among groups.Univariate and multivariate logistic regression were used to screen independent factors for discriminating BS 1 and BS 2.Receiver operating characteristic curves were drawn,and the areas under the curve(AUC)were calculated to evaluate the efficiency of the above parameters for discriminating BS 1 and BS 2.Results Among IVIM parameters,compared with control group,D*values decreased but D values increased in BS 1 group,while D*values increased in BS 2 group(all adjusted P<0.05).Compared with BS 2 group,BS 1 group had higher values of f and D and lower D*(all adjusted P<0.05).In BS 1 group,the TIC types were predominantly typeⅠ(23/36,63.89%),which were wholly or predominantly typeⅢin BS 2 group and control group,and of the former was significantly different with latter 2(both adjusted P<0.05).Compared with control group,K trans increased progressively in both BS 1 and BS 2 groups(both adjusted P<0.05).BS 1 group had lower K ep and higher V e than BS 2 and control groups(all adjusted P<0.05).Among univariate logistic regression models,the model including only f had lower capability for discriminating BS 1 and BS 2(AUC=0.759)than those including D,K trans and V e(AUC=0.951,0.833,0.894,all P<0.05).No significant different was found among multivariate logistic regression model including f and D,model including K trans and V e nor model including all above parameters(all P>0.05).Conclusion Both IVIM and DCE-MRI could be used to evaluate BS abnormality without conventional MRI changes.

Differentiating consistency of meningioma based on grey-level histogram analysis of T2WI

Objective To observe the value of grey-level histogram analysis based on T2WI for differentiating consistency of meningioma.Methods Data of 109 patients with meningioma were retrospectively analyzed.The patients were divided into hard group(n=71)and soft group(n=38)according to the consistency of tumors.Tumor ROI was outlined on axial T2WI showing the largest tumor section,gray levels were extracted and histogram analysis was performed.The value of each histogram parameter were compared between groups.Then receiver operating characteristic curve was drawn,and the area under the curve(AUC)was calculated to evaluate the efficiency for differentiating soft and hard meningioma.Results P 1,P 10,P 50,P 90,P 99 and the mean grey levels on T2WI in soft group were all higher than those in hard group(all P<0.05),while the variance,the kurtosis and the skewness were not significantly different between groups(all P>0.05).The differentiating efficiency of P 1,P 10,P 50,P 90,P 99 and the mean grey levels on T2WI were all fine,with AUC of 0.774 to 0.833,and no significant difference was found(all P>0.05).Conclusion Parameters of grey-level histogram analysis such as P 1,P 10,P 50,P 90,P 99 and the mean values based on T2WI were all valuable for differentiating soft and hard meningioma.

Research progresses of artificial intelligence in MRI of lumbar degenerative diseases

The incidence of lumbar degenerative diseases is increasing year by year,and MRI is often used in clinical diagnosis.In recent years,artificial intelligence(AI)has rapidly developed in medical field and can be used for image segmentation and auxiliary diagnosis of lumbar degenerative diseases.The research progresses of AI in MRI of lumbar degenerative diseases were reviewed in this article.

Long TR three-dimensional inversion recovery sequence with real reconstruction(3D real IR)for quantifying inner ear endolymphatic hydrops

Objective To observe the value of long TR three-dimensional inversion recovery sequence with real reconstruction(3D real IR)for quantifying inner ear endolymphatic hydrops(EH).Methods Totally 46 Ménière's disease(MD)patients and 21 healthy volunteers were prospectively enrolled.MR scanning for inner ear based on 3D real IR and 3D fluid attenuated inversion recovery(3D FLAIR)sequence 4—6 h after administration of contrast agents were performed.The imaging qualities were scored and compared between groups.The endolymphatic space area and the membranous labyrinth area of cochlea and vestibule,as well as endolymph/membranous labyrinth area percentage were calculated,the present or not of EH and the grade of EH were evaluated.EH inner ears of MD patients were enrolled in EH group,while inner ears of healthy volunteers were taken as controls(control group).The endolymphatic space area,membranous labyrinth area and endolymph/membranous labyrinth area percentage of cochlea and vestibule were compared between groups.The receiver operating characteristic(ROC)curve was drawn to calculate the diagnostic efficacy of the above indexes.Results Cochlear and/or vestibular EH were detected in 56 ears,including cochlear EH in 52 ears and vestibular EH in 45 ears among 46 MD patients(EH group),but not in 42 ears in control group.The subjective quality scores of 3D real IR images were higher than those of 3D-FLAIR(both P<0.05).Quantitative analysis based on 3D real IR images revealed that,compared with control group,significantly larger endolymph areas and endolymph/membranous labyrinth area percentages in both cochlea and vestibule were found in EH group(all P<0.001).The area under the curve(AUC)of cochlear or vestibular endolymph/membranous labyrinth area percentage for identifying inner ear EH was 0.999 and 0.985,respectively.Taken 13.64%and 24.13%as the critical value of cochlear or vestibular endolymph,the specificity was 100%and 92.86%,respectively,and the sensitivity was 96.43%and 96.43%,respectively.Conclusion MR long TR 3D real IR was helpful to quantifying inner ear EH.

Research progresses of resting-state functional MRI in mild cognitive impairment and Alzheimer's disease

Alzheimer's disease(AD)is a prevalent neurodegenerative disease characterized by cognitive decline in the early stage.Mild cognitive impairment(MCI)is considered as an intermediate stage between normal aging and AD.In recent years,studies related to resting-state functional MRI(rs-fMRI)indicated that the occurrence and development process of MCI and AD might be closely linked to spontaneous brain activity and alterations in functional connectivity among brain regions,and rs-fMRI could provide important reference for specific diagnosis and early treatment of MCI and AD.The research progresses of rs-fMRI for MCI and AD were reviewed in this article.

Pore structure and liquid flow velocity distribution in water-saturated porous media probed by MRI

Magnetic resonance imaging （MRI） was used to probe the structure and flow velocity within the interparticle space of a packed bed of agar beads under water-saturated condition. The images of the velocity field at three different flow rates were obtained. To determine the pore-parameter of the porous media, the internal structure of the bed was also obtained using image processing technique. The results show that the porosity of the sample is 31.28% and the fitting curve for the distribution of pore equivalent diameter follows Gaussian distribution. The velocity profiles do shift as the flow rate varies and the solution flow through the void space is not a homogeneous flow in any pores. The velocity distributions within the pore are roughly parabolic with the local maximum being near the center. About half of the velocity components are in the class of 0-1 cm/s. The frequency of lower velocity components is lower at higher flow rate, but to higher velocity components, it is just the opposite.

MOTOR CORTEX NETWORKS IN STROKE PATIENTS DURING RECOVERY WITH fMRI

To investigate changes of functional activation areas of the cerebral cortex and the connectivity of motor cortex networks （MCNs） in stroke patients during the recovery, five patients with the infarct in their left hemispheres are recruited. Functional magnetic resonance imaging （fMRI） is performed in the second, fourth, eighth, and sixteenth weeks after the stroke. Images are analyzed using the professional software SPM5 to obtain the bilateral activation of the motor cortex in left and right handgrip tests. MCN data are extracted from the active areas, and the structural and functional characteristic parameters are computed to indicate the connectivity of the network. Results show that the ipsilesional hemisphere recruits more areas with less active extent during the handgrip test, compared with the contralesional hemisphere. MCN shows a higher overall degree of statistical independence and more statistical dependence among motor areas with the gradual recovery. It can help physicians understand the recovery mechanism.

Effects of microcystin-LR on hippocampal N-acetylaspartate and neurobehaviors in rats

The effects of low-doses of microcystin-leucinearginine （ MC-LR ） exposure on neurobehaviors and N-acetylaspartate （NAA） expression in the hippocampus of rats were investigated. After male Sprague-Dawley （SD） rats were treated intra-gastrically with different doses of MC-LR for 90 d, the locomotor activity, spatial learning and memory function were evaluated in the rats after treatment using open field tests and Morris water maze tests. The results show that MC-LR exposure can lead to impairment of the spatial learning capacity and locomotor activity in rats at the dose of 2. 00 p,g/kg. The levels of NAA in the hippocampus were measured by magnetic resonance spectroscopy （MRI）. A significant decrease of NAA/Cr ratio （ P 〈 0. 05） was observed in the hippocampous. This study indicates that intra-gastrical exposure to low-doses of MC-LR has adverse effects on neuronal behavior and NAA levels in the hippocampous.

Clinical application of magnetic resonance neurography in peripheral nerve disorders

Recent advances in the technology of magnetic resonance （MR） imaging （MRI） have made the diagnostic evaluations for peripheral nerve disorders shift from the clinical and physiological examination to the anatomical study. As a sensitive noninvasive tool, MR neurography could directly display high-resolution longitudinal and cross-sectional images of peripheral nerves, including nerve compression, nerve inflammation, nerve trauma, nerve recovery, and systemic neuropathies, thereby the morphology of intraneural and extraneural lesions can be visualized. Thus neurologists, as well as specialist radiologists, should be highly familiar with the various new types of image findings in this steadily advancing field. The purpose of this review is to overview how to evaluate peripheral nerve problems with MR neurogra- phy and its current limitations and advances in experimental MR research. The techniques for peripheral nerve MR neurography will also be discussed.

EFFECT OF POSITIVE-INDEFINITE MATRIX ON MAGNETIC RESONANCE DIFFUSION TENSOR-DERIVED PARAMETERS

To evaluate the effect of the positive-indefinite matrix on the diffusion tensor-derived parameters, a modified algorithm is proposed for calculating these parameters. Magnetic resonance （MR） diffusion tensor images of five healthy volunteers are collected. The diffusion sensitive gradient magnetic fields are applied along 25 directions and the diffusion weighting value is 1 000 s/mm^2. Many positive-indefinite diffusion tensors can be found in the white matter area, such as the genu and the splenium of corpus callosum. Due to the positive-indefinite matrix, the mean diffusivity （MD） and the fractional anisotropy （FA） are under-estimated and over-estimated by using the conventional algorithm. Thus, the conventional algorithm is modified by using the absolute values of all eigenvalues. Results show that both the robustness and the reliability for deriving these parameters are improved by the modified algorithm.

Folate-conjugated Fe_3O_4 nanoparticles for in vivo tumor labeling

Highly biocompatible superparamagnetic Fe3O4 nanoparticles were synthesized by amide of folic acid （FA） ligands and the NH2-group onto the surface of Fe3O4 nanoparticles. The as-synthesized folate-conjugated Fe3O4 nanoparticles were characterized by X-ray diffraction diffractometer, transmission electron microscope, FT-IR spectrometer, vibrating sample magnetometer, and dynamic light scattering instrument. The in vivo labeling effect of folate-conjugated Fe3O4 nanoparticles on the hepatoma cells was investigated in tumor-bearing rat. The results demonstrate that the as-prepared nanoparticles have cubic structure of Fe3O4 with a particle size of about 8 nm and hydrated diameter of 25.7 nm at a saturation magnetization of 51 A·m2/kg. These nanoparticles possess good physiological stability, low cytotoxicity on human skin fibroblasts and negligible effect on Wistar rats at the concentration as high as 3 mg/kg body mass. The folate-conjugated Fe3O4 nanoparticles could be effectively mediated into the human hepatoma Bel 7402 cells through the binding of folate and folic acid receptor, enhancing the signal contrast of tumor tissue and surrounding normal tissue in MRI imaging. It is in favor of the tumor cells labeling, tracing, magnetic resonance imaging （MRI） target detection and magnetic hyperthermia.

Ghost artifact removal in EPI using projection in hybrid-space

Ghost artifacts occur in magnetic resonance imaging （MRI） reconstruction because odd and even echoes have different phase offsets. A method based on the projection in hybrid-space is described to remove ghost artifacts. First, the projection of the even and odd lines along phase-encoding direction in hybrid-space was used to estimate the phase difference between odd and even echoes. Secondly, we fit the phase difference and used it to correct the phase of even or odd echoes. Finally, the corrected image was obtained by performing the inverse Fourier transform along phase-encoding direction in hybrid-space. The experimental results show that linear and nonlinear differences can be corrected and the intensity of ghost artifacts is significantly reduced. The effectiveness of the proposed method is demonstrated in ghost artifact removal.

ARTIFACT CORRECTION OF RIGID TRANSLATIONAL MOTION IN MRI

During the process of magnetic resonance imaging （MRI）, the patient motion causes phase errors in collected signals and induces motion artifacts in the reconstructed image. Severe artifacts interfere with the focus location. Because the genetic algorithm （GA） has characteristics of parallel, random and adaptive stochastic searching, a correction method of motion artifacts is presented based on the algorithm. The method can correct the phase error in K-space signals step by step. Experiments show that the motion artifacts in MRI can be effectively suppressed by using the method.

Magnetic Resonance Imaging Findings of Temporal Lobe Radiation Encephalopathy in Nasopharyngeal Carcinoma

Objective： To observe the magnetic resonance imaging （MRI） morphological features of radiation encephalopathy （REP） in nasopharyngeal carcinoma （NPC） and investigate their diagnostic value. Methods： The MRI data of 160 lesions from 104 NPC patients with the diagnosis of temporal lobe REP were retrospectively analyzed. The MRI was performed after radiation therapy of NPC with an interval ranged from 8 months to 13 years. The imaging sequences included T1-weighted imaging and T2-weighted imaging. Additionally T1-weighted imaging with injection of the contrast agent of Gd-DTPA was performed in 111 lesions and fluid attenuated inversion recovery （FLAIR） was performed on 37 lesions, and among them, 2 cases were subjected to MR perfusion weighted imaging （PWI）. Results： Unilateral temporal lobe was involved in 48 cases of REP, bilateral temporal lobe in 56 cases of REP respectively, with a total of 160 lesions. The REP in the white matter displayed hyper-intensity signal on T2-weighted imaging which could be homogenous, whereas areas with heterogeneous hypo-intensity signal could be seen in 59 of them otherwise with hyper-intensity signal, and 91 lesions of white matter were associated with gray matter lesions with an appearance of hypo-intensity signal on T1-weighted imaging and hyper-intensity signal on T2-weighted imaging. In 111 lesions with the Gd-DTPA enhanced T1-weigthed imaging, 91 showed the enhancement of brain parenchyma. Hemorrhage and hemosiderosis occurred in 5 lesions of REP. Conclusion： REP in NPC has a multiplicity of the imaging features on MRI, in addition to the common involvement of white matter, including other relatively frequent findings, such as the involvement of gray matter, hemorrhage, hemosiderosis and blood-brain barrier destruction, those could be clearly revealed on MRI.