Asymptomatic carotid artery plaques: use of magnetic resonance imaging to characterize vulnerable plaques in 6 cases

BACKGROUND: Echography is a convenient and noninvasive method of characterizing carotid artery plaques. However, recent reports suggest that multisequential MR imaging may yield better data regarding the instability of asymptomatic carotid artery plaques. Therefore, the goal of the present study was to show the useful information for asymptomatic carotid artery plaque. METHODS: A total of 6 patients (5 men, 1 woman; age range, 62-76 years; mean age, 69.2 years) with carotid artery plaques, which were detected during medical check-up using carotid MR angiography and/or echography, underwent MR imaging. Two-dimensional TOF MR angiography, T1WI, and fat-suppressed, cardiac-gated, black-blood proton density image, and T2WI were obtained with a 1.5-T MR imager. All plaques underwent carotid endarterectomy and histological examination. RESULTS: The MR imaging demonstrated high signals in at least one modality in 4 of 7 plaques. In the remaining 3 patients, MR imaging detected partial-high signals, which corresponded to histologically confirmed partial lipid core or hemorrhagic components in the fibrous tissues The TOF MR imaging showed 2 cases of thin fibrous caps, and MR imaging also showed a large mural thrombus in 1 patient. CONCLUSIONS: Magnetic resonance imaging was useful in characterizing factors associated with plaque instability in patients with asymptomatic carotid artery plaques and may help guide therapeutic strategies for asymptomatic carotid artery plaques.     

Imaging vulnerable plaques by targeting inflammation in atherosclerosis using fluorescent-labeled dual-ligand microparticles of iron oxide and magnetic resonance imaging

Objective

Identification of patients with high-risk asymptomatic carotid plaques remains an elusive but essential step in stroke prevention. Inflammation is a key process in plaque destabilization and a prelude to clinical sequelae. There are currently no clinical imaging tools to assess the inflammatory activity within plaques. This study characterized inflammation in atherosclerosis using dual-targeted microparticles of iron oxide (DT-MPIO) as a magnetic resonance imaging (MRI) probe.

Unmasking complicated atherosclerotic plaques on carotid magnetic resonance angiography: a report of three cases

In stenotic lesions of the extracranial carotid arteries, the presence of intraplaque hemorrhage or thrombosed ulceration is considered to pose an additional risk. Although contrast-enhanced magnetic resonance angiography (MRA) is a powerful means for looking at the vascular lumen, it provides little information on the vessel wall, particularly when mask subtraction methods are used. We report three cases in which the maximal intensity projections obtained from gadolinium-enhanced MRA source images showed only internal carotid artery stenoses, whereas source images revealed a focal increased T1 signal in the wall of the internal carotid artery, representing either intraplaque hemorrhage or thrombosed ulceration. Hence, the physicians interpreting an MRA in an acute stroke patient should not limit themselves to the synthetic maximal intensity projections but should also always review the source partitions, which can contain information related to an acute intraplaque accident.     

In vivo elbow biomechanical analysis during flexion: three-dimensional motion analysis using magnetic resonance imaging

The purpose of this article is to evaluate in vivo 3-dimensional kinematics of the elbow joint during elbow flexion. We studied the ulnohumeral and radiohumeral joint noninvasively in 3 elbows in healthy volunteers using a markerless bone registration algorithm. Magnetic resonance images were acquired in 6 positions of elbow flexion. The inferred contact areas on the ulna against the trochlea tended to occur only on the medial facet of the trochlear notch in all of the elbow positions we tested. The inferred contact areas on the radial head against the capitellum occurred on the central depression of the radial head in all of the tested elbow positions except for 135 degrees flexion, where the anterior rim of the radial head articulates with the capitellum.     

Patients at high risk for upper tract urothelial cancer: evaluation of hydronephrosis using high resolution magnetic resonance urography

PURPOSE: We assessed the potential of magnetic resonance urography (MRU) in the evaluation of hydronephrosis not explained by standard investigation in patients at high risk for upper tract urothelial cancer. MATERIALS AND METHODS: A total of 23 consecutive patients in a specialist urological unit with unexplained hydronephrosis prospectively underwent MRU which comprised overview heavily T2-weighted MR urographic images followed by focused high resolution turbo spin echo T2-weighted sequences obtained in an axial and coronal oblique plane through the level of urinary obstruction. All were at high risk for urothelial cancer and had either contraindications to or problems with standard investigations including poor contrast excretion due to obstruction or renal failure, failed ureteral cannulation or contrast allergy. Clinical events and imaging followup, subsequent endoscopic/surgical findings and histopathology validated MR findings. RESULTS: In 23 patients with a high clinical suspicion of upper tract transitional cell tumors (TCC), 8 ureteral and 5 renal pelvic TCCs (2 bilateral) were diagnosed by MR, and confirmed histologically. In a further 5 patients benign causes for the hydronephrosis were found. No intrinsic or extrinsic pathology was demonstrable in 5 patients whose imaging findings were stable during 1 year of followup. CONCLUSIONS: MRU is a valuable noninvasive investigation for evaluating hydronephrosis in this group of patients with suspected urothelial cancer in which routine investigation had failed to provide clinically important information. Focused high resolution T2-weighted images were reliable in the diagnosis of ureteral and renal pelvic TCCs, and were valuable in excluding these and other mass lesions as the cause of hydronephrosis.     

In vivo three-dimensional wrist motion analysis using magnetic resonance imaging and volume-based registration.

This study represents a new attempt to non-invasively analyze three-dimensional motions of the wrist in vivo. A volume-based registration method using magnetic resonance imaging (MRI) was developed to avoid radiation exposure. The primary aim was to evaluate the accuracy of volume-based registration and compare it with surface-based registration. The secondary aim was to evaluate contributions of the scaphoid and lunate to global wrist motion during flexion-extension motion (FEM), radio-ulnar deviation (RUD) and radial-extension/ulnoflexion, "dart-throwing" motion (DTM) in the right wrists of 12 healthy volunteers. Volume-based registration displayed a mean rotation error of 1.29 degrees +/-1.03 degrees and a mean translation error of 0.21+/-0.25 mm and was significantly more accurate than surface-based registration in rotation. Different patterns of contribution of the scaphoid and lunate were identified for FEM, RUD, and DTM. The scaphoid contributes predominantly in the radiocarpal joint during FEM, in the midcarpal joint during RUD and almost equally between these joints during DTM. The lunate contributes almost equally in both joints during FEM and predominantly in the midcarpal joint during RUD and DTM.     

Biomechanical analysis of supra-acetabular insufficiency fracture using finite element analysis

Background

Supra-acetabular insufficiency fractures (SAIFs) occur in the upper acetabulum and are rare compared with insufficiency sacral, femoral head, or ischial fractures. However, SAIFs are known to occur in low grade trauma, and the underlying mechanism is still remained unclear.

In vivo myeloarchitectonic analysis of human striate and extrastriate cortex using magnetic resonance imaging.

A primary goal of investigations into the organization of human cerebral cortex is to determine the functional specificity of architectonic regions. This includes the correlation of neurobehavioral deficits with neuropathological data for clinical diagnosis and treatment, and the identification of active brain regions using functional neural imaging techniques, such as positron emission tomography, electroencephalographic and magnetoencephalographic (EEG and MEG) source localization algorithms, and direct cortical stimulation. Currently, the architectonic classification of a cortical region identified by these methods is inferred from the comparison of its cerebral topographic position to cytoarchitectonic brain atlases. However, substantial intersubject variability in the position of cytoarchitectonic regions with respect to cerebral topographic landmarks may lead to errors in this procedure. An alternative method is presented here, which uses magnetic resonance (MR) imaging to identify myeloarchitectonic regions of isocortex directly by estimating the relative concentration of myelin within cortical laminae. This high-resolution MR protocol is used to identify striate cortex (Brodmann's area 17) and extrastriate cortex in vivo. Correspondence of MR signal intensity with myeloarchitectonic data from a postmortem brain confirms this identification. As MR imaging technology improves, this noninvasive method has the potential to identify and discriminate among at least 50 cortical regions in the living human brain.     

High-resolution magnetic resonance imaging using gadolinium-based contrast agent for atherosclerotic carotid plaque

BACKGROUND: Early detection of vulnerable plaques at risk of causing thromboembolic events is very important, and many investigators report the usefulness of high-resolution MRI. The purpose of this study was to determine whether the detection of atherosclerotic carotid plaques can be enhanced after administration of contrast agents and, if so, to evaluate the potential for functional information. METHODS: We studied 9 patients (10 subjects) who underwent a high-resolution MRI examination using a gadolinium-based contrast agent before CEA. Pre- and postcontrast-enhanced T1-weighted images were reviewed, and their histopathologic characteristics evaluated in the corresponding tissue slices. RESULTS: Strong contrast enhancement patterns were found in 6 of 10 subjects. For 5 of 6 subjects, many microvessels with inflammatory cells or intraplaque hemorrhages were demonstrated in their corresponding tissue slices. Contrast enhancement patterns were noted to be focal, diffuse, and along the luminal surface or the vessel adventitial boundary. Moreover, some plaques were clearly demonstrated by using contrast agent, and others were clearly divided into fibrous and lipid regions. CONCLUSION: Gadolinium-based contrast agent can penetrate human atherosclerotic carotid plaques. The extent or size of neovascularization and the endothelial permeability are likely related to the mechanism of enhancement, and contrast-enhanced MRI may be essential for the identification of plaque neovascularization which is an important factor of vulnerable plaques. In addition to morphologic information, with the functional information provided using various contrast agents, we may expect a more correct diagnosis of carotid plaques at risk of causing thromboembolic events.     

Kinematics of the lumbar spine in trunk rotation: in vivo three-dimensional analysis using magnetic resonance imaging

In vivo three-dimensional (3D) kinematics of the lumbar spine has not been well evaluated by the conventional methods because of their methodological limitations, while 3D intervertebral motions have been quantitatively determined by cadaver studies. We thus developed a novel 3D analyzing system for the relative motions of individual vertebrae using 3D magnetic resonance imaging (MRI) and analyzed in vivo 3D intervertebral motions of the lumbar spine during trunk rotation. Ten healthy volunteers underwent 3D MRI of the lumbar spine in nine positions with 15° increments during trunk rotation (0°, 15°, 30°, 45°, and maximum). Relative motions of the lumbar spine were calculated by automatically superimposing a segmented 3D MRI of the vertebra in the neutral position over images of each position using the voxel-based registration method. These 3D motions were represented with 6 degrees of freedom by Euler angles and translations on the coordinate system. The mean axial rotation of ten healthy volunteers of each lumbar spinal segment in 45° trunk rotation to each side ranged from 1.2° to 1.7°. Coupled flexion with axial rotation was observed at the segments from L1/2 to L5/S1. Coupled lateral bending of the segments from L1/2 to L4/5 was in the opposite direction of the trunk rotation, while that of T12/L1 and L5/S1 was in the same direction. The direction of the coupled lateral bending in the present study was different from that in the previous cadaver study only at L4/5. This difference might result from the non-load state of the supine position in the current study and/or the non-physiological state in the cadaver study. Our system has two limitations: (1) the study was conducted with each volunteer in the supine position, and (2) because the rotation device regulated trunk rotation, trunk rotation might not have been physiological. In vivo 3D intervertebral motions of the lumbar spine during trunk rotation were evaluated using our novel motion analysis system. These data may be useful for the optimal orthopaedic management of lumbar spinal disorders. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

In vivo estimation of bone stiffness at the distal femur and proximal tibia using ultra-high-field 7-Tesla magnetic resonance imaging and micro-finite element analysis

The goal of this study was to demonstrate the feasibility of using 7-Tesla (7T) magnetic resonance imaging (MRI) and micro-finite element analysis (μFEA) to evaluate mechanical and structural properties of whole, cortical, and trabecular bone at the distal femur and proximal tibia in vivo. 14 healthy subjects were recruited (age 40.7 ± 15.7 years). The right knee was scanned on a 7T MRI scanner using a 28 channel-receive knee coil and a three-dimensional fast low-angle shot sequence (TR/TE 20 ms/5.02 ms, 0.234 mm × 0.234 mm × 1 mm, 80 axial images, 7 min 9 s). Bone was analyzed at the distal femoral metaphysis, femoral condyles, and tibial plateau. Whole, cortical, and trabecular bone stiffness was computed using μFEA. Bone volume fraction (BVF), bone areas, and cortical thickness were measured. Trabecular bone stiffness (933.7 ± 433.3 MPa) was greater than cortical bone stiffness (216 ± 152 MPa) at all three locations (P < 0.05). Across locations, there were no differences in bone stiffness (whole, cortical, or trabecular). Whole, cortical, and trabecular bone stiffness correlated with BVF (R ≥ 0.69, P < 0.05) and inversely correlated with corresponding whole, cortical, and trabecular areas (R ≤ −0.54, P < 0.05), but not with cortical thickness (R < −0.11, P > 0.05). Whole, cortical, and trabecular stiffness correlated with body mass index (R ≥ 0.62, P < 0.05). In conclusion, at the distal femur and proximal tibia, trabecular bone contributes 66–74% of whole bone stiffness. 7T MRI and μFEA may be used as a method to provide insight into how structural properties of cortical or trabecular bone affect bone mechanical competence in vivo.     

Optimisation of hip endoprosthesis election by using finite element analysis

The main aim of this study is to present an optimized method for election of hip endoprosthesis by using finite element analysis. MATERIAL AND METHODS: Four types of hip endoprosthesis with different design and fixation type were considered for this study. First step is three-dimensional reconstruction to one femur using CT sections; the second represent the hip endoprostheses components 3D reconstruction, virtual implantation of each endoprosthesis in femur, then finite element analysis. RESULTS: The calculated Von Mises stress as a result of finite element analysis indicates the optimum endoprosthesis by considering the stress on endoprosthetic nail and bone.     

Biochemical characterization of pediatric brain tumors by using in vivo and ex vivo magnetic resonance spectroscopy

OBJECT: Magnetic resonance (MR) spectroscopy provides biochemical information about tumors. The authors sought to determine the relationship between in vivo and ex vivo biochemical characterization of pediatric brain tumors by using MR spectroscopy. Their hypothesis was that ex vivo MR spectroscopy provides a link between in vivo MR spectroscopy and neuropathological analysis. METHODS: In vivo proton MR spectroscopy was performed before surgery in 11 patients with neuroepithelial tumors. During resection, a total of 40 tumor biopsy samples were obtained from within the volume of interest identified on in vivo MR spectroscopy and were frozen immediately in liquid nitrogen. High-Resolution Magic Angle Spinning (HRMAS) was used to perform ex vivo MR spectroscopy in these 40 tumor biopsy samples. Neuropathological analysis was performed using the same biopsy samples, and the tumors were classified as ependymoma, choroid plexus carcinoma, pineoblastoma (one each), and pilocytic astrocytoma, medullobastoma, low-grade glioma, and glioblastoma multiforme (two each). Ex vivo HRMAS MR spectroscopy improved line widths and line shapes in the spectra, compared with in vivo MR spectroscopy. Choline (Cho) detected in vivo corresponded to three different peaks ex vivo (glycerophosphocholine, phosphocholine [PCho], and Cho). Metabolite ratios from in vivo spectra correlated with ratios from ex vivo spectra (Pearson correlation coefficient range r = 0.72-0.91; p < or = 0.01). Metabolite ratios from ex vivo spectra, such as PCho/ total creatine (tCr) and lipid/tCr, correlated with the percentage of cancerous tissue and percentage of tumor necrosis, respectively (r = 0.84; p < 0.001). CONCLUSIONS: Agreement between in vivo and ex vivo MR spectroscopy indicates that ex vivo HRMAS MR spectroscopy can improve resolution of this modality and provide a link between in vivo MR spectroscopy and neuropathological analysis.     

磁共振技术行移植细胞在体示踪

目的寻找一种能够对移植细胞进行在体示踪方法,为细胞的迁移、分布及心功能改善机制的研究提供更多的信息。方法将超顺磁性氧化铁(SPIO)和骨髓间充质干细胞(MSCs)共同孵育培养36h。普鲁士蓝染色评价细胞的标记效率;MTT比色实验评价SPIO对细胞生长能力的影响;台盼蓝染色检验标记后细胞的活性;应用Costar Transwell方法评价铁离子对细胞迁移能力的影响;用细胞分化诱导液培养标记后的细胞评价其分化能力。将标记的细胞移植到中华小型猪心肌内。通过心脏MRI进行连续的在体示踪观察。细胞移植后不同时期取动物心脏切片进行普鲁士蓝染色观察移植细胞。结果MSCs经铁离子标记后,普鲁士蓝染色标记效率>95%,此试剂不影响细胞增殖,标记后98%的细胞保持活性,可继续培养、传代,迁移能力和分化能力未受影响。动态观察显示SPIO标记细胞在MRI影像上表现为低密度灶影或信号缺失,并且在移植后4周仍可显影。病理学检查可以看到移植细胞呈普鲁士蓝染色阳性,与影像学有很好的一致性。结论磁共振对比剂SPIO可以安全、有效的标记骨髓间充质细胞,并可通过心脏MRI进行持续的在体示踪。