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At least 451 records · Page 25Linked to original sources
PubMed1996

[Postoperative MRI morphology of the anterior cruciate ligament after primary ligament suture or ligament-plasty. A prospective study of 50 patients].

AIM: Identification of typical postoperative change after anterior cruciate ligament reconstruction (sutures, tendon grafts) and comparison with clinical tests and ultrasound. PATIENTS AND METHODS: 50 patients with anterior cruciate ligament ruptures were examinated with MRI (1.0 T, surface coil, sagittal T1-3DFT-Fast and sagittal spin-echo), US and clinical function tests (Lachmann, pivot-shift, anterior drawer test). RESULTS: In 19 of 21 patients with continuous low-intensity ligament structures in the MRI, knee stability was very good or good in the clinical tests and US. In 17 of 20 patients with a diagnosis of partial rupture at MRI, we also found a stable knee. 5 of 7 patients with the MRI-signs of ligament rupture showed knee stability at US and clinical tests. Furthermore, at MRI we found minor effusions in 10 patients, meniscus tears in 8 patients and ligament impingement in 2 patients. CONCLUSION: MRI is a valuable method for evaluating and assessing anterior ligament reconstructions. We found a good correlation between the continuous low-intensity ligaments at MRI and knee-stability. In contrast there is a bad correlation between discontinuous ligament structures at MRI and clinical stability of the knee. MRI seems to provide more information than US and clinical tests (for example: minor effusion, meniscus tears, ligament impingement, bone lesions).

Anterior Cruciate Ligament↗
PubMedDate not supplied

Neuroimaging in epilepsy.

Neuroimaging techniques have improved the understanding, diagnosis, and management of epilepsy. By providing excellent structural information, MRI is the technique of choice in evaluating patients with epilepsy. Functional imaging techniques, including MR spectroscopy, functional MRI, positron emission tomography, and single photon emission CT, permit noninvasive assessment of the epileptic substrate, its functional status, and neuroreceptors. The MRI-based techniques will potentially assume a greater role in the cost-effective workup of the patient. Currently, newer techniques such as magnetoencephalography, magnetic source imaging, and optical imaging are research tools.

Brain↗
PubMed2006

MP-SAGE: A new MP-RAGE sequence with enhanced SNR and CNR for brain imaging utilizing square-spiral phase encoding and variable flip angles.

The magnetization-prepared rapid gradient-echo (MP-RAGE) sequence is well known and widely used for high-resolution, structural brain MRI. Here we present a new version, termed magnetization-prepared spiral acquisition gradient-echo (MP-SAGE), that employs interleaved square-spiral phase-encoding (PE) to take advantage of the 3D nature of the sequence. Resolution loss caused by point-spread function (PSF) blurring is circumvented by the use of variable flip angle (VFA) radiofrequency (RF) pulses. The pulse train is calculated by means of an accurate new signal evolution theory that is derived from the extended phase graph (EPG) description. Phantom results show excellent agreement between theory and experiment for substances with relaxation times similar to those of human brain tissue. Both phantom and in vivo results show a strong enhancement of SNR and CNR compared to the standard MP-RAGE in high-resolution MRI. The benefits for brain tissue segmentation using images obtained with MP-SAGE are shown.

Algorithms↗
PubMed1999

Asymmetric MRI magnet design using a hybrid numerical method.

This paper describes a hybrid numerical method for the design of asymmetric magnetic resonance imaging magnet systems. The problem is formulated as a field synthesis and the desired current density on the surface of a cylinder is first calculated by solving a Fredholm equation of the first kind. Nonlinear optimization methods are then invoked to fit practical magnet coils to the desired current density. The field calculations are performed using a semi-analytical method. A new type of asymmetric magnet is proposed in this work. The asymmetric MRI magnet allows the diameter spherical imaging volume to be positioned close to one end of the magnet. The main advantages of making the magnet asymmetric include the potential to reduce the perception of claustrophobia for the patient, better access to the patient by attending physicians, and the potential for reduced peripheral nerve stimulation due to the gradient coil configuration. The results highlight that the method can be used to obtain an asymmetric MRI magnet structure and a very homogeneous magnetic field over the central imaging volume in clinical systems of approximately 1.2 m in length. Unshielded designs are the focus of this work. This method is flexible and may be applied to magnets of other geometries.

Algorithms↗
PubMed1993

VirR and Mry are homologous trans-acting regulators of M protein and C5a peptidase expression in group A streptococci.

Transcription of the group A streptococcal M12 protein gene (emm12) and the C5a peptidase gene (scpA), which encodes an inhibitor of complement-mediated chemotaxis, was previously shown to depend on a third genetic locus, designated virR. A 1.6 kb region of DNA which is 200 bp upstream of emm12 and is thought to contain the virR locus, was sequenced. An open reading frame which overlaps deletion mutations that define virR was identified. The sequence of the encoded VirR protein, which was deduced to contain 499 amino acids, is characteristic of cytoplasmic proteins. Comparison of the VirR protein to a variety of DNA binding proteins, such as lambda Cro, revealed a DNA binding motif. VirR was also compared to the M6 positive regulator, mry, and found to be 98% homologous. The predicted virR promoter is preceded by two sets of inverted repeats, in contrast to mry which is preceded by one repeat. Introduction of virR on the shuttle vector pAM401 into a strain of group A Streptococcus with a deletion in the chromosomal virR gene demonstrated that the VirR protein activated transcription of both emm12 and scpA genes in trans. Analysis of RNA by Northern blot using virR-specific probes identified two virR transcripts, a 1.6 kb transcript which corresponds to the predicted size of the gene, and a second transcript, 3.5 kb, which also overlaps virR. These results demonstrate that virR and mry are structurally and functionally very similar and show that the former is a trans activator of both M protein and C5a peptidase synthesis.

Adhesins, Bacterial↗
PubMed2001

MRI assessment of normal ligamentous structures in the craniovertebral junction.

We have established an imaging protocol in order to characterise the normal ligamentous structures in the craniovertebral junction. Thirty volunteers without a history of car accident or head or neck trauma underwent MR imaging with 2-mm-thick proton-density-weighted sections in three orthogonal planes. The alar ligaments were clearly seen in every case and had three different configurations in cross-section: round, ovoid or wing-like. A broadening from lateral to medial in the coronal plane was observed in all cases. The transverse ligament was clearly demonstrated in 26 out of 30 cases. The ligament was flattened where it arched across the dens. Towards the insertions the ligament twisted into an oblique-horizontal orientation. The lower tectorial membrane had a median portion merging with the dura, and a lateral portion separated from it. Between the dens and clivus this membrane either merged totally with dura or was partly separated from it by a thin layer of fat. The posterior atlanto-occipital membrane was clearly demonstrated. It either merged with the dura or was partly or totally separated from it by a fat layer. The anterior atlanto-occipital membrane was inconsistently seen and could not be evaluated. Our refined MR protocol improves the visualisation of the craniovertebral ligamentous structures, and may in the future give new insight into post-traumatic neck disorders up to now poorly understood.

Adult↗
PubMed2002

Multimodal target point assessment for stereotactic biopsy in children with diffuse bithalamic astrocytomas.

INTRODUCTION: Diffuse glial tumors with bithalamic involvement are rare in children. Diagnostic assessment can be difficult as the radiological findings can be unspecific. MATERIALS AND METHODS: In order to enhance the diagnostic yield metabolic imaging with MRS and PET using FET ( O-(2-[(18)F]fluoroethyl)- L-tyrosine) was performed in two children (2 and 10 years of age). Co-registered images were used for image-guided biopsy, which was planned with neuronavigation and stereotaxy simultaneously. RESULTS: Biopsies from the right thalamus were planned, but locations were changed in both cases after metabolic imaging was available. MRS (thalamic voxel) was typical for a glial tumor in one child. In the older girl FET-PET revealed an unexpected lesion in the left cerebellar hemisphere, with a tumor-to-cortex ratio of 3.8, as against 1.7 in the thalamus. Accordingly, a stereotactic biopsy specimen was taken from the left cerebellar hemisphere, and a final diagnosis of anaplastic astrocytoma was made. The other patient showed a higher uptake (tumor-to-cortex ratio 1.6) in the left dorsal thalamus, compared with bilateral homogeneous hyperintensity of the thalamus structures on MRI. Stereotactic biopsy revealed a low-grade diffuse astrocytoma. CONCLUSION: Stereotactic biopsy using metabolic imaging and image fusion can enhance the diagnostic yield in cases of diffuse pediatric gliomas disclosing unexpected 'hot spots'.

Astrocytoma↗
PubMedDate not supplied

MRA-guided stereotactic radiation treatment planning for cerebral angiomas.

Stereotactic neurosurgical interventions are characterized by a high risk of rupturing intracranial vessels or damaging vital brain structures. By MRI and MRA, the anatomic information necessary for stereotactic treatment planning may be assessed with a single modality as a high-resolution digital image volume. The adequacy of MR as a modality for stereotactic guidance is demonstrated by the example of the radiosurgical treatment of cerebral angiomas. An optimized acquisition protocol, a stereotactic apparatus, a distortion correction and minimization method, and a 3D treatment planning workstation are elements of a proposed preoperative approach which in a clinical study met with good acceptance.

Algorithms↗
PubMed2005

Long-term effects of repetitive transcranial magnetic stimulation (rTMS) in patients with chronic tinnitus.

OBJECTIVES: The pathophysiologic mechanisms of idiopathic tinnitus remain unclear. Recent studies demonstrated focal brain activation in the auditory cortex of patients with chronic tinnitus. Low-frequency repetitive transcranial magnetic stimulation (rTMS) is able to reduce cortical hyperexcitability. STUDY DESIGN: Fusing of the individual PET-scan with the structural MRI-scan (T1, MPRAGE) allowed us to identify exactly the area of increased metabolic activity in the auditory cortex of patients with chronic tinnitus. With the use of a neuronavigational system, this target area was exactly stimulated by the figure 8-shaped magnetic coil. In a prospective study, rTMS (110% motor threshold; 1 Hz; 2000 stimuli/day over 5 days) was performed using a placebo controlled cross-over design. Patients were blinded regarding the stimulus condition. For the sham stimulation a specific sham-coil system was used. Fourteen patients were followed for 6 months. Treatment outcome was assessed with a specific tinnitus questionnaire (Goebel and Hiller). SETTING: Tertiary referral medical center. RESULTS: Increased metabolic activation in the auditory cortex was verified in all patients. After 5 days of verum rTMS, a highly significant improvement of the tinnitus score was found whereas the sham treatment did not show any significant changes. The treatment outcome after 6 months still demonstrated significant reduction of tinnitus score. CONCLUSION: These preliminary results demonstrate that neuronavigated rTMS offers new possibilities in the understanding and treatment of chronic tinnitus.

Adult↗
PubMed2000

An MRI study of temporal lobe structures in men with bipolar disorder or schizophrenia.

BACKGROUND: Hippocampal atrophy has been described in postmortem and magnetic resonance imaging studies of schizophrenia. The specificity of this finding to schizophrenia remains to be determined. The neuropathology of bipolar disorder is understudied, and temporal lobe structures have only recently been evaluated. METHODS: Twenty-four bipolar, 20 schizophrenic, and 18 normal comparison subjects were evaluated using magnetic resonance brain imaging. Image data were acquired using a three-dimensional spoiled GRASS sequence, and brain images were reformatted in three planes. Temporal lobe structures including the amygdala, hippocampus, parahippocampus, and total temporal lobe were measured to obtain volumes for each structure in the three subject groups. Severity of symptoms in both patient groups was assessed at the time the magnetic resonance images were obtained. RESULTS: Hippocampal volumes were significantly smaller in the schizophrenic group than in both bipolar and normal comparison subjects. Further, amygdala volumes were significantly larger in the bipolar group than in both schizophrenic and normal comparison subjects. CONCLUSIONS: The results suggest differences in affected limbic structures in patients with schizophrenia and bipolar disorder. These specific neuroanatomic abnormalities may shed light on the underlying pathophysiology and presentation of the two disorders.

Adolescent↗
PubMed1996

Spinal chondroma of the lumbar tract: case report.

BACKGROUND: Cartilage-forming tumors are benign cartilaginous tumors that rarely affect the spinal canal: they account for 2% of all spinal tumors and 2.6% of all benign bone tumors. Pathologically, they may be classified as chondromas, osteochondromas, chondroblastomas, and chondromyxoid fibromas. This oncotype may remain asymptomatic (it is confined within the vertebral structure) or may present as a hard paravertebral swelling (it invades the paravertebral structures) or more rarely, with a slowly-developing neurologic syndrome (it extends into the vertebral canal). METHODS: Thirty-one cases have been reported (including our case) of benign cartilage-forming tumors localized in the lumbar column. Only three cases of chondroma of the lumbar spine presented with lumbar radicular pain. We report a fourth case and review clinical and radiologic characteristics of these lesions. RESULTS: Eleven out of the 31 cases were diagnosed as chondromas, 17 as osteochondromas, while in three cases the histopathologic diagnosis was not reported. Seventeen cases originated from the neural arch, seven from the vertebral body, two from the spinous process, and in five cases the exact localization was not reported. This tumor is more frequent in males (21 cases out of 31), than in females (five cases); in five cases the sex was not reported. Mean duration of symptoms was 23 +/- 5.1 months (range: 1-96); chondromas have a short clinical history before diagnosis (13.8 +/- 3.4 months) compared to osteochondromas (28.6 +/- 7.6). Clinical presentation with local swelling is reported in 10 cases, in 10 cases local pain without radicular irradiation, in six cases lumbar pain with sciatica, in two cases signs and symptoms of cord compression, one case of cauda syndrome, while in four cases no clinical details are reported. Among the six cases presenting with sciatica, four were chondromas (in all cases the L4 level was involved), and one osteochondroma, while in one case the histopathologic diagnosis was not reported. CONCLUSION: Computed tomography is important and indispensable for preoperative diagnosis, giving a precise indication of tumor extent and location and its relationship to the adjacent structures; while MRI is helpful in detecting patterns related to histologic malignancy. It is important to examine the whole tumor histologically because it is known that there may be small areas that show signs of malignancy; thus is more likely in chondromas than osteochondromas.

Adult↗
PubMed2001

Corpus callosum area and functioning in schizophrenic patients with auditory--verbal hallucinations.

Auditory--verbal hallucinations (AVH) are a characteristic feature of schizophrenia. Patients with AVHs have been found to differ from non-hallucinating patients in volumes of certain asymmetrical brain structures on MRI, and on certain neuropsychological measures. There is also evidence of corpus callosum (CC) abnormalities in schizophrenia, and it has been proposed that abnormalities of inter-hemispheric transmission may underlie hallucinations and other symptoms. The aim of this study was to examine whether patients with AVHs have smaller corpora callosa than those without AVH, and whether CC size is related to performance on neuropsychological tests of functional cerebral asymmetry. Seventy-one DSM-IV male schizophrenics were recruited on the basis of their hallucination history plus 33 matched normal controls. Twenty-nine patients had no history of AVH, and 42 had a strong history of AVH. The mid-sagittal surface area and longitudinal length of the CC were measured from T(1)-weighted spin echo images. Callosal area was divided into four sections. There were no significant differences in any of the measurements between the two patient groups, or between patients with schizophrenia and controls. There was no association between CC measures and handedness, or performance on dichotic listening or finger tapping tasks. The results of this study do not lend support for there being a major morphological abnormality of the corpus callosum in schizophrenic patients, or for a specific relationship to AVH. However, a significant association between CC area and overall grey and white matter volumes was noted in the hallucinating patients and, to a lesser extent, in the non-hallucinators, which may point to differing influences on brain development or degeneration in such patients compared with normal controls.

Adolescent↗
PubMed2002

Neuroanatomic characterization of schizoaffective disorder using MRI: a pilot study.

For over 50 years, there has been uncertainty in the conceptual understanding and neuropathogenesis of the diagnosis of schizoaffective disorder (SCA). In order to better characterize SCA, we performed a quantitative assessment of MRI neuroanatomical structures in patients with SCA (n = 12), compared to patients with bipolar disorder (BPD) (n = 12) and healthy volunteers (HV) (n = 12). Patients diagnosed with SCA exhibited regional abnormalities on the striatum that resemble those seen in BPD. This study suggests that SCA has some neuroanatomical characteristics similar to BPD.

Adult↗
PubMed2004

Distortion of normal pituitary structures in sellar pathologies on MRI.

OBJECTIVE: This study was undertaken to assess the displacement patterns and shifts of the normal pituitary gland in sellar pathologies on MRI and to determine if the position of the bright spot (BS) represents a predicting factor for the position of the residual adenohypophysis (RAH) in pathological conditions. METHODS: In a control group of 102 patients without any pituitary pathology, the presence of the BS was evaluated. In 100 patients with intra- or suprasellar pathologies, presence and respective topography of BS and RAH were scrutinized on MRI, according to lesion type, size, endocrine status and intra-operative findings in the surgical group. RESULTS: The BS was visible in 91.2% of 102 cases in the control group, as compared to 75 of the 100 patients with sellar lesions. Location of RAH was identified in 58% of the patients, and RAH enhanced more than the lesion in all cases after contrast infusion. The RAH was identified in 65.3% of the 75 "BS positive" patients, as compared to 36% of the 25 "BS negative". The normal residual gland was visualized intra-operatively in 63.5% of the 52 operated patients: in 37 "BS positive" patients, it was visualized intra-operatively in 81.1% and in 28 "RAH positive" patients, it was identified in 82.1%. CONCLUSIONS: The BS can be identified in the majority and RAH in more than half of the cases with pituitary lesions on MRI. Positions of both the BS and RAH help predict the location of the normal residual gland during surgery and, therefore, may contribute to preserving the pituitary function.

Anatomy, Regional↗
PubMed1997

Hormones, radiosurgery and virtual reality: new aspects of meningioma management.

The understanding and management of meningiomas is changing significantly today. One of the most striking features of their pathophysiology is their predominance in women. In a series of 517 patients with meningiomas seen by the Brain Tumor Group at Brigham and Women's Hospital, the female:male ratio was 24:1. The progesterone receptor appears to be the major candidate to explain this difference. Although meningioma cells variably express receptors for estrogen, androgen, platelet-derived growth factor, epidermal growth factor, and somatostatin, these molecules do not explain the differences because they are not differentially expressed or are not activated. Progesterone receptor can be shown to be expressed in 81% of women and 40% of men with meningiomas; it can also be shown to be activated by transfecting a construct with the progesterone responsive element and a reporter in it and using the cell's own receptors to activate this construct. Surgery remains the mainstay of meningioma management. At the Brigham and Women's Hospital three-dimensional reconstruction techniques have markedly improved the ability to visualize the tumor as well as its relation to vascular structures. With MRI reconstruction, it is possible to know the tumor's relation to the sagittal and other sinuses, to identify feeders and proximity to major arteries, and to establish its location and relation to cortex by frameless stereotaxis. These techniques can be used in a virtual reality format are some of the most powerful in neurosurgery both for teaching and for the surgical procedure itself. External beam radiation has been shown by others to be an effective adjunctive treatment to prevent meningioma recurrence. Recently, linear accelerator radiosurgery and stereotactic radiotherapy have changed the pattern of radiation at our institution. In a series of 56 skull base meningiomas, for example, 95% were controlled (i.e., showed no growth) over a four year period. Fractionated focal radiation potentially offers the same control rate with fewer complications. With increasing understanding and treatment possibilities, meningiomas remain one of the most intriguing and challenging tumors in the nervous system.

Female↗
PubMed2001

Combination of 3D MRI and connectivity analysis in structural evaluation of cancellous bone in rat proximal femur.

Three dimensional (3-D) magnetic resonance (MR) microimaging combined with connectivity analysis was tested in the study of the structure of cancellous bone. MR microimaging was performed in vitro with an average resolution of 20*20*35 microm. A 3-D connectivity analysis was used to model the trabecular bone as a network consisting of nodes and struts. Size distribution curves of these two structural elements and the interconnectivity of nodes was used to estimate the cancellous structure. The analysis suggested the occurrence of two simultaneous network structures in cancellous bone differed by the size of details. The degradative effect of ostcopenia is found to be slightly different in these two subsystems. Interconnectivity is seen to increase with the size of a node and the expected loss of connectivity due to ostcopenia is observed. The method described offers a new way in the topological estimation of interconnected medium.

Journal Article↗
PubMed1997

Graphical 3D medical image registration and quantification.

We present a graphical three-dimensional method that facilitates image registration and fusion, and provides quantitative geometric and volume information. In particular it enhances the use of functional (radiopharmaceutical) imaging (SPECT, PET) which, though a powerful clinical tool, has the disadvantage of low spatial resolution and ill-defined boundaries. Registration between functional images and structural images (MRI, CT) can augment the anatomical context of these functional images.

Abdominal Neoplasms↗