A volumetric MRI study of limbic structures in chronic schizophrenia--relationship to psychopathology.
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Adult↗
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Functional MRI-BOLD of brainstem structures during visually triggered migraine.
BACKGROUND: Previously, hyperoxia and blood volume increase were reported in the red nucleus and substantia nigra during spontaneous migraine with aura. OBJECTIVE: To further understand the pathophysiologic role of these centers, activation of brainstem structures was investigated in patients with visually triggered migraine. METHODS: Twenty-six patients with migraine (23 with aura and 3 without aura), and 10 normal control subjects were studied with blood oxygen level-dependent (BOLD) fMRI during repeated checkerboard visual stimulation. Three axial image sections, which covered the occipital cortex and brainstem, were acquired 224 times with a temporal resolution of 3.5 seconds. RESULTS: Repetitive visual stimulation triggered symptoms in 12 patients; four who had migraine with aura developed both visual symptoms and headaches, and six who had migraine with aura and two who had migraine without aura had headaches only. Four patients who had migraine with aura experienced the onset of their usual aura or onset of their typical headache either during the experiment or immediately after. In the remaining 10 patients with migraine, and all control subjects, visual stimulation failed to trigger symptoms at any time. In 75% of the patients who developed symptoms during stimulation, baseline T2*-weighted MR signal intensities increased in the red nucleus and substantia nigra before occipital cortex signal elevation or the onset of visually triggered symptoms. CONCLUSION: Activation (hyperoxia and blood volume increase) of the red nucleus and substantia nigra in association with visually triggered symptoms of migraine suggest that these brainstem structures are a part of a neuronal network activated during an attack.
Adult↗
Imaging microvascular structure with contrast enhanced MRI.
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Contrast Media↗
Challenges of imaging structure and function with MRI.
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Algorithms↗
[Examination of trabecular bone structures of the foot skeleton with MRI imaging].
AIMS: To assess trabecular density and structures at various cancellous bone sites in the foot using MR imaging. To compare the MRI findings with the bone mineral density (BMD) values obtained by quantitative computed tomography (QCT) in the lumbar vertebrae. MATERIALS AND METHODS: Bone mineral densities were measured by QCT in lumbar vertebrae 1 to 3 in ten patients with suspected osteoporosis. Sagittal images of the feet were obtained from these patients and also from seven healthy volunteers applying spin-echo and gradient-echo MR techniques. RESULTS: MR imaging revealed differences between patients with osteoporosis and individuals with healthy bones. Comparison of MR and BMD data revealed a significant dependence of MR data on the bone density measured by QCT (alpha < 0.05). In addition, a good correlation (r = 0.73) was found between the results of the different MRI techniques. CONCLUSIONS: The MR imaging techniques investigated offer an interesting tool for the non-invasive assessment of bony structures, at least at peripheral locations with yellow bone marrow. To enable reliable application in the clinical routine setting, additional studies are required to identify suitable standardized methods and establish normal ranges.
Adult↗
Fully automatic identification of AC and PC landmarks on brain MRI using scene analysis.
We describe a method for identification of brain structures from MRI data sets. The bulk of the paper concerns an automatic system for finding the anterior and posterior commissures [(AC) and (PC)] in the midsagittal plane. These landmarks are key for the definition of the Talairach space, commonly used in stereotactic neurosurgery, in the definition of common coordinate systems for the pooling of functional positron emission tomography (PET) images and for neuroanatomy studies. The process works according to a step-by-step procedure: it first analyzes the skull limits. A grey-level histogram is then calculated and allows an automated selection of thresholds. Then, the interhemispheric plane is detected. Following an advanced scene analysis in the midsagittal plane for anatomical structures, the AC and the PC are identified. Experimentally, with a set of 200 patients, the process never failed. Its performances and limits are comparable to that of neuroanatomy experts. Those results are due to a high degree of robustness at each step of the program.
Algorithms↗
Application of PET-MRI registration techniques to cat brain imaging.
UNLABELLED: In positron emission tomography (PET) studies of diseased animals, it is very useful to have accurate anatomical information as a reference. In human studies, anatomical information is usually obtained from magnetic resonance imaging (MRI) of the subject with retrospective registration of the subject's PET image to the MRI. A number of PET-MRI registration techniques are used for this purpose. However, the utility of these methods has not been tested for animals image registration. This paper studies the feasibility of applying two currently used human brain PET-MRI registration techniques to cat brain images. METHODS: Three cats were anesthetized with isoflurane gas, and PET images were acquired with H(2)(15)O, benzodiazepine receptor ligand 11C-flumazemil (FMZ), dopamine receptor ligand 11C-nemonapride (NEM) and fluorodeoxy glucose (18F-FDG). The four PET scans were acquired consecutively within the same day while the cat remained fixed in the scanner. We also obtained T1-weighted and T2-weighted MRI of the cats in a 4.7 T unit. The PET images were registered to MRI using two human brain registration techniques: a semi-automatic method (SAM), which is a two-step method based on the extraction of the midsagittal plane, and an automatic method (AMIR) method that minimizes PET pixel variance within spatially connected segments determined by MRI. RESULTS: T2-weighted MRI provided better structural information than T1 MRI. FMZ did, while FDG or H(2)O PET images did not, provide a structural outline of the brain. The FMZ PET image was registered to MRI satisfactorily using SAM. The striatum visualized in nemonapride PET image re-sliced with the same parameters matched the striatum identified in T2-weighted MRI. Registration by AMIR was successful by inspection for FMZ, FDG or H(2)O PET images in only one of the three cats. The registration error of SAM was estimated to be less than 2 mm or 2 degrees. CONCLUSION: A satisfactory registration of FMZ-PET to T2-weighted MRI of the cat brain was obtained by a two-step manual registration technique. This will enhance the usefulness of PET in the field of cerebral pathophysiology.
Animals↗
Thalamic activation during an attention-to-prepulse startle modification paradigm: a functional MRI study.
BACKGROUND: Prepulse inhibition (PPI) of the startle reflex reflects early stages of information processing and is modulated by selective attention. Animal models indicate medial frontal-thalamic circuitry is important in PPI modulation. We report data from the first functional magnetic resonance imaging (fMRI) study examining whether attending to or ignoring a prepulse differentially activates brain areas within this circuitry. METHODS: Ten healthy subjects received structural and functional MRI. During fMRI acquisition, subjects heard intermixed attended and ignored tones serving as prepulses to the startle stimulus. Regions of interest were traced on structural MRI and coregistered to fMRI images. RESULTS: Greater amplitude fMRI blood-oxygen-level-dependent response to attended than ignored PPI conditions occurred in the right thalamus, and bilaterally in the anterior and mediodorsal thalamic nuclei, whereas the startle-alone condition showed deactivation. In transitional medial cortex (Brodmann Area 32), which is involved in affective processing of noxious stimuli, the startle-alone condition elicited the greatest response, the attended-PPI condition showed the smallest response, and the ignored-PPI condition was intermediate. CONCLUSIONS: These findings extend animal models to humans by indicating thalamic involvement in the modulation of PPI. Further fMRI investigations may elucidate other key structures in the circuitry underlying normal and disordered modulation of PPI.
Adult↗
Quantitative MRI for the assessment of bone structure and function.
Osteoporosis is the most common degenerative disease in the elderly. It is characterized by low bone mass and structural deterioration of bone tissue, leading to morbidity and increased fracture risk in the hip, spine and wrist-all sites of predominantly trabecular bone. Bone densitometry, currently the standard methodology for diagnosis and treatment monitoring, has significant limitations in that it cannot provide information on the structural manifestations of the disease. Recent advances in imaging, in particular MRI, can now provide detailed insight into the architectural consequences of disease progression and regression in response to treatment. The focus of this review is on the emerging methodology of quantitative MRI for the assessment of structure and function of trabecular bone. During the past 10 years, various approaches have been explored for obtaining image-based quantitative information on trabecular architecture. Indirect methods that do not require resolution on the scale of individual trabeculae and therefore can be practiced at any skeletal location, make use of the induced magnetic fields in the intertrabecular space. These fields, which have their origin in the greater diamagnetism of bone relative to surrounding marrow, can be measured in various ways, most typically in the form of R2', the recoverable component of the total transverse relaxation rate. Alternatively, the trabecular network can be quantified by high-resolution MRI (micro-MRI), which requires resolution adequate to at least partially resolve individual trabeculae. Micro-MRI-based structure analysis is therefore technically demanding in terms of image acquisition and algorithms needed to extract the structural information under conditions of limited signal-to-noise ratio and resolution. Other requirements that must be met include motion correction and image registration, both critical for achieving the reproducibility needed in repeat studies. Key clinical applications targeted involve fracture risk prediction and evaluation of the effect of therapeutic intervention.
Animals↗
Searching the schizophrenic brain for temporal lobe deficits: a systematic review and meta-analysis.
BACKGROUND: Several empirical studies have found temporal lobe impairments in many patients with schizophrenia. The strength and consistency of this evidence, however, has not been evaluated and synthesized quantitatively. Hence, we ask to what extent are temporal cortices really defective in schizophrenia? METHODS: Meta-analytical methods were used to determine the magnitude of evidence in support of structural and physiological temporal-hippocampal system deficits in schizophrenia. We report effect sizes from studies since 1980 that used structural (CT, MRI) and functional (SPECT, PET) neuroimaging methods. RESULTS: Both structural and functional imaging literatures are distinguished by heterogeneity whereby most patients show normative temporal function and structure, a minority shows diminished values and some patients demonstrate augmented function and structure rather than a deficit. CONCLUSIONS: The findings are hard to incorporate within single disease models that propose major involvement of the temporal system in schizophrenia, at least at the degree of resolution obtained with current imaging technology.
Humans↗
Experimental and clinical evaluation of acromioclavicular joint structures with new scan orientations in MRI.
The objective of the study was to evaluate MRI for visualization of acromioclavicular (ac) joint structures in cadaveric shoulders, asymptomatic volunteers and symptomatic patients with trauma of the ac-joint. Three cadaveric shoulders were examined to find adequate planes and sequences for MRI. Afterwards, MR images were correlated to corresponding anatomical sections. Six asymptomatic volunteers and 13 patients were scanned in a 1.5 T Magnetom Vision with three sequences in the following planes: (1) parallel to the clavicle; (2) orthogonal to the ac joint, each time a fat-suppressed proton density-weighted + T2-sequence (TR/TE 4,000/15 ms) was performed; (3) parallel to the clavicle, T1-SE (TR/TE 817/20 ms). The parameters were: slice thickness 3 mm, field-of-view 180 mm, matrix 210x256 pixels. Standard of reference in the patients was clinical examination and conventional X-rays. Classification was by Rockwood grades I-VI. MRI allowed excellent visualization and diagnoses of ac-joint structures in volunteers and patients (n=6 normal, n=1 Rockwood I, n=5 Rockwood II, n=3 Rockwood III, n=4 Rockwood V). On MRI, in one lesion type II and III each, a lower lesion type was suspected clinically and by X-ray. In one patient additional information by MRI led to surgery. MRI allows excellent anatomical display of ac-joint structures and can give clinically relevant information on type and extension of ac-joint trauma, which may influence therapy.
Acromioclavicular Joint↗
Visualization and analysis of white matter structural asymmetry in diffusion tensor MRI data.
This work presents a method that permits the characterization, quantification, and 3D visualization of white matter structural information contained within diffusion tensor MR imaging (DT-MRI) data. In this method, regions within the brain are defined as possessing linear, planar, or spherical diffusion. Visualization of this diffusion metric data is realized by generating streamtube and streamsurface models to represent regions of linear and planar diffusion. Quantification of differences in diffusion anisotropy between different regions of interest (ROIs) is then achieved by analyzing 2D barycentric histograms created from the complete distribution of diffusion metric values measured in each region. In four healthy volunteers, there was only a small degree of asymmetry (epsilon) in the number of linear, planar, or spherical diffusion voxels between the right and left hemispheres (epsilon approximately equal to +/- 2%). However, in a patient with a metastatic brain lesion there was marked asymmetry in both linear (epsilon approximately -10%) and planar (epsilon approximately equal to 5%) diffusion between comparable ipsilateral and contralateral regions, with a significant reduction in the number of linear diffusion voxels and an increase in the number of planar diffusion voxels in the tumor-bearing hemisphere. These results demonstrate the potential of this approach to characterize brain structure in both healthy and diseased subjects.
Adenocarcinoma↗
A novel volumetric magnetic resonance imaging paradigm to study upper airway anatomy.
STUDY OBJECTIVES: We utilized novel three-dimensional volumetric analysis techniques with magnetic resonance imaging (MRI) to study the upper airway and surrounding soft-tissue structures. These MRI techniques allowed us to objectively quantify the volume of the tongue, soft palate, parapharyngeal fat pads, and lateral pharyngeal walls. DESIGN: We first validated our volumetric imaging techniques on a phantom and then demonstrated that our results were reliable and reproducible in normal subjects who did not lose weight. Finally, we studied 12 obese, nonapneic women during wakefulness before and after weight loss. We hypothesized that our novel magnetic-resonance computer-reconstruction techniques would allow us to detect small reductions in the volume of the tongue, soft palate, lateral pharyngeal walls, and parapharyngeal fat pads and increases in the volume of the upper airway with weight loss. SETTING: University medical center. PARTICIPANTS: Normal controls and 12 obese nonapneic women. INTERVENTIONS: Weight loss. MEASUREMENTS AND RESULTS: Following a mean 17.1+/-8.62 kg (17.3%) reduction in weight, upper airway volume increased (p = 0.06) in both the retropalatal and retroglossal regions. This increase in upper airway volume was mediated by significant reductions in the volume of the lateral pharyngeal wall (p = 0.0001) and parapharyngeal fat pads (p = 0.001). However, the volume of the tongue (p = 0.35) and soft palate (p = 0.39) were not reduced significantly with weight loss. CONCLUSIONS: These data indicate that volumetric MRI is a powerful tool to study anatomic changes in the upper airway and surrounding soft-tissue structures and is sensitive enough to detect changes in these structures.
Adipose Tissue↗
[Use of virtual reality for MRI data of complex vascular structures].
UNLABELLED: During the last years because of the progress in magnetic resonance imaging (MRI) magnetic resonance angiography (MRA) has become a serious alternative to conventional X-ray angiography. The potential of MRA in combination with methods for three-dimensional reconstruction will be presented and different methods for image post-processing are discussed based on a number of cases. The examinations were performed on a clinical 1.5 T magnetic resonance tomograph (Siemens Vision, Erlangen) using conventional MR angiography sequences. The different options of post-processing were carried out online on the console and offline using dedicated workstations (Siemens Virtuoso and CHILI). DISCUSSION: Complex post-processing procedures are applied to different areas like pulmonary vasculature, thoracic aorta, abdominal aorta, and renal transplant arteries. Different diagnostic values can be seen for the variety of three-dimensional reconstruction methods. According to our experience volume rendering has been selected as the method of choice due to the time needed for reconstruction and the information content of the resulting image.
Aortography↗
Three-dimensional deformation-based hippocampal surface anatomy, projected on MRI images.
The objectives of the present study were to illustrate three-dimensional hippocampal surface anatomy using deformation-based composite segmentations, superimposed on two-dimensional MRI (magnetic resonance images) in standard and oblique planes. The hippocampi from five normal volumetric MRI studies were segmented using a semiautomated, deformation-based technique. Segmentations were then processed to combine hippocampal surfaces, generating a composite (or average) deformation for each of the five left and five right hippocampi. Composite hippocampal surfaces were then projected on two-dimensional MRIs, with verification of projections using three-dimensional coordinate data. Composite hippocampal surfaces show anatomical details of hippocampal substructures, including the pes hippocampi, intralimbic gyrus, and uncinate gyrus. Projection on two-dimensional MRI helps to define hippocampal anatomy in relationship to surrounding structures. Composite images highlight specific features of normal hippocampal surface anatomy, and demonstrate the structural relationship of the hippocampus to surrounding structures on MRI.
Anatomy↗
Hadamard-based image decomposition and compression.
In this paper, we develop a general algorithm for decomposition and compression of grayscale images. The decomposition can be expressed as a functional relation between the original image and the Hadamard waveforms. The dynamic adaptive clustering procedure incorporates potential functions as a similarity measure for clustering as well as a reclustering phase. The latter is a multi-iteration, convergent procedure which divides the inputs into nonoverlapping clusters. These two techniques allow us to efficiently store and transmit a class of half-tone medical images such as magnetic resonance imaging (MRI) of the human brain. Due to the redundant image structure of MRI, obtained after the decomposition and clustering, almost half of the image can be omitted all together. Naturally, the compression rates for this specific type of grayscale image are increased greatly. A run-length coding is performed in order to compress further the retained information from the first two steps. Although all the techniques applied are simple, they represent an efficient way to compress grayscale images. The algorithm exhibits a performance which is competitive and often outperforming some of the methods reported in the literature.
Algorithms↗
Tumor-third ventricular relationships in supradiaphragmatic craniopharyngiomas: correlation of morphological, magnetic resonance imaging, and operative findings.
OBJECTIVE: To disclose the relationships of primarily supradiaphragmatic craniopharyngiomas with the third ventricular floor (3rdVF) by means of preoperative magnetic resonance imaging (MRI) and thus to select the surgical approach avoiding the hypothalamic structures. METHODS: MRI findings in 76 consecutive patients with craniopharyngiomas operated on between June 1991 and December 2002 were interpreted on the basis of the results of the authors' own previous microanatomic studies. The assumed tumor-3rdVF relationships were then correlated with the operative findings. MRI features characteristic for different topographical relationships were analyzed in 44 patients (18 children, 26 adults) with exclusively supradiaphragmatic tumors. RESULTS: In 14 of 15 patients with the tumor located below the 3rdVF (suprasellar extraventricular craniopharyngioma), the anterior communicating artery was displaced upward and indirectly indicated the position of the chiasm between the prechiasmatic and the retrochiasmatic tumor portions. Hydrocephalus was absent in 14 patients, including those with giant tumors. The anterior part of the third ventricular cavity was found in front of the level of the foramina of Monro in 6 patients. All 28 tumors growing partially inside and partially outside the third ventricular cavity (intraventricular and extraventricular craniopharyngioma) were retrochiasmatic. They caused severe or moderate hydrocephalus in 20 patients and mild hydrocephalus in 2. One purely intraventricular tumor caused severe hydrocephalus. CONCLUSION: The position of the optic chiasm and the size of the lateral ventricles on preoperative MRI enable us to determine the position of the 3rdVF or its remnants in relation to the supradiaphragmatic craniopharyngiomas and to select the proper surgical approach allowing exposure of the tumor while avoiding the hypothalamic structures.
Adolescent↗
[Magnetic resonance tomography examination of thoracolumbar spinal fractures after fixateur interne stabilization].
To analyse the possible injuries of vertebral segments, especially the disc, after unstable thoracolumbar fractures stabilised with AO internal fixator, we performed magnetic resonance imaging (MRI) of the traumatised region after implant removal. There were two aspects of disc degeneration (DD):(1) biochemical changes and (2) structural damage. MRI detects biochemical processes as one aspect of DD that is often small even in the presence of greater structural damage of the nucleus pulposus caused by fracture. None of the patients presented with structural failure of the anulus fibrosus, which is the essential structural component of the vertebral segments with regard to stability. We observed biochemical changes more often in the lower of the two fracture-adjacent discs and alterations of discal shape more often in the upper of the two, whereas loss of height concerned both discs to approximately the same degree. The supporters of upper-disc resection in thoracolumbar fractures justify their procedure among other things with the structural disc damage, such as alteration of shape and loss of height (altogether more frequent in the upper disc). Our observations that a disc with a structurally altered nucleus pulposus can be biochemically intact and can show an intact anulus fibrosus are arguments in favour of disc preservation. With regard to the upper disc, the widespread opinion that complete and regular disc damage requires a resection has to be revised. The question of whether the lower disc should be resected more often because of its greater biochemical changes cannot be answered by the present study alone. Besides the excellent static information in all anatomical structures of the vertebral column available by MRI, a repeat examination in a prone position yields dynamic information on the spinal cord in the case of suspected dorsal adhesions.
Adolescent↗