MRI of anterior cruciate ligament repair with patellar and hamstring tendon autografts

OBJECTIVE

Several MRI sequences were used to evaluate the 2-year postoperative appearance of asymptomatic knee with a torn anterior cruciate ligament (ACL) reconstructed with bone-patellar tendon-bone (BTB) and semitendinosus and gracilis (STG) tendon autografts.

DESIGN AND PATIENTS

Two groups with successful repair of ACL tear with BTB (n = 10) or STG (n = 10) autografts were imaged at 1.5 T with sagittal and oblique coronal proton density-, T2-weighted and sagittal STIR sequences and plain and contrast-enhanced oblique coronal T1-weighted sequences. The appearance of the graft and periligamentous tissues was evaluated.

RESULTS

In all 20 cases, the ACL graft showed homogeneous, low signal intensity with periligamentous streaks of intermediate signal intensity on T2-weighted images. In 10 cases, localised areas of intermediate signal intensity were seen in the intra-articular segment of the graft on proton density- and T1-weighted images. The graft itself did not show enhancement in either of the two groups, but mild to moderate periligamentous enhancement was detected in 10 cases.

CONCLUSION

The MRI appearance of ACL autograft is variable on proton density- and T -weighted images. Periligamentous tissue showing contrast enhancement is a typical MRI finding after clinically successful ACL reconstruction.

Evolution of MR contrast enhancement patterns during the first week after acute ischemic stroke

BACKGROUND AND PURPOSE

Intravascular and parenchymal enhancement have been detected with contrast-enhanced T1-weighted MR imaging in patients with ischemic stroke. Diffusion-weighted MR imaging depicts infarct within minutes after the onset of symptoms. The aims of this study were to study the different MR enhancement findings during the first week after stroke and to ascertain whether the presence of intravascular enhancement over a larger area than the infarct on diffusion-weighted images on day 1 is able to predict substantial infarct growth during the first week.

METHODS

Forty-eight patients were imaged on the first and second days and again 1 week after the onset of ischemic stroke. T1-weighted spin-echo imaging was performed before and after a 0.2 mmol/kg bolus of gadolinium chelate. Diffusion-weighted imaging was performed at the same slice positions. Enhancement findings were categorized as intravascular and parenchymal, with further categorization of parenchymal enhancement as cortical, subcortical, and deep; these findings were then compared with diffusion-weighted imaging findings.

RESULTS

Intravascular enhancement in the infarcted area was detected on day 1 in 78% of the cases, on day 2 in 78% of the cases, and at 1 week in 30% of the cases. Parenchymal enhancement was detected in 26%, 56%, and 100% of the cases, respectively. Intravascular enhancement over a larger area than the infarct on diffusion-weighted images on day 1 was not associated with the extent of infarct growth.

CONCLUSION

Detection of different patterns of contrast enhancement can help in determining the age of infarct. Parenchymal enhancement may be intense and can cause diagnostic uncertainty in cases in which the clinical history is obscure.

Combined perfusion- and diffusion-weighted MR imaging in acute ischemic stroke during the 1st week: a longitudinal study

PURPOSE

To compare findings with different magnetic resonance (MR) perfusion maps in acute ischemic stroke.

MATERIALS AND METHODS

Combined diffusion-weighted (DW) and perfusion-weighted (PW) MR imaging was performed in 49 patients with acute (<24 hours) stroke, on the 1st and 2nd days and 1 week after stroke. Volumes of hypoperfused tissue on maps of relative cerebral blood volume (rCBV), relative cerebral blood flow (rCBF), and mean transit time (MTT) were compared with the volume of infarcted tissue at DW imaging.

RESULTS

The mean infarct volume increased from 41 to 65 cm(3) between the 1st and 2nd days (P: <.001; n = 49). On the 1st day, all perfusion maps on average showed hypoperfusion lesions larger than the infarct at DW imaging (P: <.001; n = 49). MTT maps showed significantly (P: <.001) larger hypoperfusion lesions than did rCBF maps, which showed significantly (P: <.001) larger hypoperfusion lesions than did rCBV maps. The sizes of the initial perfusion-diffusion mismatches correlated significantly with the extent of infarct growth (0.479 < r < 0.657; P: </=.001). The hypoperfusion volume on the initial rCBV maps correlated best with the final infarct size at 1 week (r = 0.891; P: <.001).

CONCLUSION

Combined DW and PW imaging is a powerful tool in evaluating the hemodynamics of acute ischemic stroke.

Multimodality MR imaging assessment of myocardial viability: combination of first-pass and late contrast enhancement to wall motion dynamics and comparison with FDG PET-initial experience

PURPOSE

To combine three magnetic resonance (MR) imaging modalities-dobutamine stress cine, first pass, and late contrast material-enhanced T1-weighted imaging-and to compare the results with 2-[fluorine 18]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in the assessment of unviable myocardium in coronary artery disease.

MATERIALS AND METHODS

Ten patients with multivessel coronary artery disease underwent MR imaging before and 6 months after bypass surgery. Left ventricular cine MR imaging was performed at rest and during dobutamine infusion. Inversion-recovery gradient-echo images were obtained to study myocardial contrast enhancement at first pass and 5 minutes later. FDG PET was performed with orally administered acipimox before surgery.

RESULTS

With dobutamine cine MR imaging, unviable myocardium was detected with a sensitivity of 79% and a specificity of 93%; postoperative wall thickening was the standard. First-pass analysis increased these values to 97% and 96%; analysis of late enhancement with T1-weighted imaging, to 62% and 98%. FDG PET had a sensitivity of 81% and a specificity of 86%.

CONCLUSION

The combination of first-pass enhancement analysis and wall motion assessment with stress significantly increases the specificity of MR imaging in the detection of unviable sectors.

MRI correlates of dementia after first clinical ischemic stroke

BACKGROUND AND PURPOSE

Dementia after first clinical stroke frequently has been found, but the clinical and radiological correlates have not been fully detailed. We examined magnetic resonance imaging (MRI) correlates of dementia in a large well-defined series of patients with first clinical ischemic stroke.

METHODS

Detailed medical, neurological and neuropsychological examination was conducted 3 months after ischemic stroke for 273 patients with first clinical stroke from a consecutive series of 486 patients aged 55-85 years. MRI of the head categorised infarcts (type, site, side, number, volume), extent of white matter lesions (WMLs) and degree of atrophy. The DSM-III definition for dementia was used.

RESULTS

Dementia was diagnosed in 79 (28.9%) of the patients with first clinical stroke. Volumes, numbers, distinct sites of infarcts, extent of WMLs and degree of atrophy were different for the demented and nondemented subjects. Logistic regression analysis showed that the correlates of dementia included the combination of infarct features (volume of infarcts in left-sided anterior corona radiata; OR 1.86), extent of WMLs (OR 1. 37), medial temporal lobe atrophy (OR 3.4) and host factors (low education; OR 1.11). The additive effect of having more than one correlate was detected (OR 2.53).

CONCLUSIONS

Dementia occurring after first clinical stroke is frequent and not solely due to a single stroke, but contain a combination of infarcts features, extent of WMLs, medial temporal lobe atrophy and host factors reflecting more than one underlying pathology.

How complex interactions of ischemic brain infarcts, white matter lesions, and atrophy relate to poststroke dementia

BACKGROUND

Cerebrovascular disease is a major factor related to cognitive impairment. However, behavioral correlates of ischemic brain lesions are insufficiently characterized.

OBJECTIVE

To examine magnetic resonance imaging correlates of dementia in a large, well-defined series of patients with ischemic stroke.

METHODS

Detailed medical, neurological, and neuropsychological examinations were conducted 3 months after ischemic stroke for 337 of 486 consecutive patients aged 55 to 85 years. Infarcts (type, site, side, number, and volume), extent of white matter lesions (WMLs), and degree of atrophy were categorized according to magnetic resonance images of the head. The definition for dementia of the Diagnostic and Statistical Manual of Mental Disorders, Third Edition (DSM-III) was used.

RESULTS

Dementia was diagnosed in 107 (31.8%) of the patients and stroke-related dementia in 87 (25.8%). Volumes, numbers, distinct sites of infarcts, extent of WMLs, and degree of atrophy were different for the demented and nondemented subjects. Particularly, volumes of infarcts in any (right- or left-sided) superior middle cerebral artery territory (27.3 vs 13.7 cm(3), P =. 002) and left thalamocortical connection (14.8 vs 4.0 cm(3), P =. 002) differentiated the 2 groups. Logistic regression analysis showed that the correlates of any dementia included the combination of infarct features (volume of infarcts in any superior middle cerebral artery: odds ratio [OR], 1.11; frequency of left-sided infarcts: OR, 1.21), extent of WMLs (OR, 1.3), medial temporal lobe atrophy (OR, 2.1), and host factors (education; OR, 0.91). In the patients with stroke-related dementia, the main correlate was volume of infarcts in the left anterior corona radiata (OR, 1.68).

CONCLUSION

Correlates of poststroke dementia do not include merely 1 feature but a combination of infarct features, extent of WMLs, medial temporal lobe atrophy, and host features.

Working memory of auditory localization

To investigate brain mechanisms of sound location memory, we studied the distribution of brain activation with functional magnetic resonance imaging (fMRI) in subjects performing an audiospatial n-back task with three memory load levels. Working memory processing of audiospatial information activated areas in the superior, middle and inferior frontal gyri, and in the posterior parietal and middle temporal cortices. In a control experiment, fMRI during audio- and visuospatial 2-back task performances revealed only few differentially activated subregions between the two tasks. These results demonstrate that working memory processing of auditory locations involves a distributed network of brain areas and suggest that mnemonic processing of audio- and visuospatial information is directed along a common neural pathway in the posterior parietal and prefrontal cortices.

MR imaging of overuse injuries of the Achilles tendon

OBJECTIVE

This study was conducted to illustrate and classify the abnormalities found on high-resolution MR imaging of symptomatic Achilles tendons in athletic adult patients.

SUBJECTS AND METHODS

One hundred patients with 118 painful Achilles tendons were imaged with a 1.5-T magnet. The tendon, peritendinous tissues, tendon insertion, and musculotendinous junction were examined on MR imaging. Twenty-eight patients underwent surgery, and histopathologic samples were taken in 13. Long-term follow-up was performed, on average, 3.4 years after MR imaging.

RESULTS

Of 118 painful Achilles tendons, abnormalities were detected in 111. These were in the tendon (n = 90), surrounding structures, or both. Fifty-four tendons had a focal area of increased intratendinous signal, best detected on axial high-resolution T1-weighted gradient-echo MR imaging. Histopathology confirmed abnormal tendon structure. Of the 21 surgically proven foci of tendinosis, 20 were revealed on MR imaging. At the level of the insertion, changes were found in the tendon in 15%, in the retrocalcaneal bursa in 19%, and in the calcaneal bone marrow in 8% of the studies. Abnormalities in peritendinous soft tissues were detected in 67%. More than one type of abnormality was found in 64% of the studies.

CONCLUSION

Lesions in the Achilles tendon and in the peritendinous structures can have similar clinical presentation. MR imaging detects and characterizes these changes. A more specific diagnosis and prognosis can be made with the use of MR imaging than with clinical examination alone.

Hippocampus and entorhinal cortex in frontotemporal dementia and Alzheimer's disease: a morphometric MRI study

BACKGROUND

Magnetic resonance imaging (MRI) of hippocampal atrophy is a sensitive but not specific method to support the clinical diagnosis of early Alzheimer's disease (AD). We recently described our findings that atrophy of the entorhinal cortex (ERC) in frontotemporal dementia (FTD) is equal to that found in AD but that hippocampal atrophy in FTD is less than that found in AD. The MRI volumes of these structures provide a topographic representation of the region of interest. We hypothesized that two different dementias with distinct histopathologic and clinical features might, in addition to quantitative patterns, display topographically different patterns of atrophy.

METHODS

We adopted a morphometric approach to monitor the pattern of atrophy of the hippocampus and the ERC by computing two-dimensional profiles from MRI volumes of the structures in control subjects and patients with FTD and AD.

RESULTS

Compared with control subjects, atrophy of the hippocampus in patients with AD was diffuse. In patients with FTD, atrophy of the hippocampus was localized predominantly in the anterior hippocampus, suggesting a different pattern of hippocampal atrophy in FTD compared with AD. The amount and pattern of atrophy of the entorhinal cortex was virtually equal in both demented groups.

CONCLUSIONS

This study provides novel data on the nature of medial temporal lobe atrophy in FTD. Morphometric MRI may be a useful technique for characterizing different patterns of atrophy in primary degenerative dementias in vivo.

High microvascular blood volume is associated with high glucose uptake and tumor angiogenesis in human gliomas

The purpose of this investigation was to elucidate the association between microvascular blood volume and glucose uptake and to link these measures with tumor angiogenesis. We demonstrate a regionally specific correlation between tumor relative microvascular blood volume (CBV), determined in vivo with functional magnetic resonance imaging techniques, and tumor glucose uptake determined with fluorodeoxyglucose positron emission tomography. Regions of maximum glucose uptake were well matched with maximum CBV across all patients (n = 21; r = 0.572; P = 0.023). High-grade gliomas showed significantly elevated CBV and glucose uptake compared with low-grade gliomas, (P = 0.009 and 0.008, respectively). Correlations between CBV and glucose uptake were then determined on a voxel-by-voxel basis within each patient's glioma. Correlation indices varied widely, but in 16 of 21 cases of human glioma, CBV and glucose uptake were correlated (r > 0.150). These measures were well correlated in all cases when comparing healthy brain tissue in these same patients. Tumor vascularity, as determined immunohistochemically and morphometrically on clinical samples, revealed statistically significant relationships with functional imaging characteristics in vivo. Regional heterogeneities in glucose uptake were well matched with functional magnetic resonance imaging CBV maps. Our findings support the concept that there is an association of microvascular density and tumor energy metabolism in most human gliomas. In addition, the findings are likely to have important clinical applications in the initial evaluation, treatment, and longitudinal monitoring of patients with malignant gliomas.

Cerebral hemodynamics in human acute ischemic stroke: a study with diffusion- and perfusion-weighted magnetic resonance imaging and SPECT

Nineteen patients with acute ischemic stroke (<24 hours) underwent diffusion-weighted and perfusion-weighted (PWI) magnetic resonance imaging at the acute stage and 1 week later. Eleven patients also underwent technetium-99m ethyl cysteinate dimer single-photon emission computed tomography (SPECT) at the acute stage. Relative (ischemic vs. contralateral control) cerebral blood flow (relCBF), relative cerebral blood volume, and relative mean transit time were measured in the ischemic core, in the area of infarct growth, and in the eventually viable ischemic tissue on PWI maps. The relCBF was also measured from SPECT. There was a curvilinear relationship between the relCBF measured from PWI and SPECT (r = 0.854; P < 0.001). The tissue proceeding to infarction during the follow-up had significantly lower initial CBF and cerebral blood volume values on PWI maps (P < 0.001) than the eventually viable ischemic tissue had. The best value for discriminating the area of infarct growth from the eventually viable ischemic tissue was 48% for PWI relCBF and 87% for PWI relative cerebral blood volume. Combined diffusion and perfusion-weighted imaging enables one to detect hemodynamically different subregions inside the initial perfusion abnormality. Tissue survival may be different in these subregions and may be predicted.

A volumetric MRI study of the hippocampus in type 1 and 2 alcoholism

In recent years, magnetic resonance imaging (MRI) of the hippocampus has been extensively studied on neurological and psychiatric disorders. Particularly in studies on schizophrenia and mood disorders, findings regarding the hippocampal involvement have been most controversial. Previously, minor volume loss of the hippocampus in alcoholism, a major comorbidity alongside psychiatric disorders, has been reported but no data exist on the hippocampal volumes in subtypes of alcoholism. In this study, MRI was used to measure volumes of the hippocampus in late-onset type 1 alcoholics and early-onset type 2 alcoholics. The type 2 alcoholic subjects were also violent offenders with antisocial personality disorder, derived from a forensic psychiatric sample. All were non-psychotic and legally competent. Normal volunteers, representing a wide age range, served as a controls group. Compared to the controls, the right, but not left, hippocampi were significantly smaller in both alcoholic groups. While there was no correlation between the hippocampal volumes with age in the control subjects, there was tendency towards decreased volumes with aging and also with the duration of alcoholism in the type 1 alcoholic subjects. Surprisingly, there was a significant positive correlation between the right hippocampal volume and age in the type 2 alcoholics. This study provides further in vivo evidence that type 1 alcoholism, in general, is associated with a minor loss in hippocampal volume. It is suggested that type 2 alcoholism, in general, similarly displays a minor decrease in hippocampal volume, but this decrease is unevenly distributed within the type 2 category, being weighted towards the younger subjects. These effects suggest differences between the two alcoholic groups, and raise the possibility that the observed effects within the type 2 category are due to other factors than the cumulative acquired effects related to alcohol abuse, such as primary personality psychopathology.

Combined SPECT and diffusion-weighted MRI as a predictor of infarct growth in acute ischemic stroke

In acute ischemic stroke, the infarcted core is surrounded by a zone of tissue that has decreased perfusion. Some of this tissue may be salvaged by prompt, effective treatment. Diffusion-weighted MRI is sensitive in detecting the infarcted tissue, whereas SPECT also detects the hypoperfused tissue around the infarcted core. We studied the potential of combined diffusion-weighted MRI and SPECT to predict infarct growth and clinical outcome in patients not receiving thrombolytic treatment.

METHODS

Sixteen patients with acute stroke were examined consecutively with diffusion-weighted MRI and 99mTc-ethyl cysteinate dimer (99mTc-ECD) SPECT within 24 h of the onset of symptoms. Follow-up diffusion-weighted MRI was performed on the second day and after 1 wk. The volumes of infarcted and hypoperfused brain tissue were measured from diffusion-weighted MRI and SPECT, respectively. The volume difference between the hypoperfused and infarcted tissue on the first day was compared with the possible increase in infarct volume during the follow-up. Each patient's neurologic status was assessed with the National Institutes of Health Stroke Scale (NIHSS).

RESULTS

The volume of infarcted tissue increased from 48 +/- 54 cm3 (mean +/- SD) on the first day to 88 +/- 93 cm3 on the second day (P = 0.001) and to 110 +/- 121 cm3 at 1 wk (P = 0.001). The volume of hypoperfused tissue on the first day was significantly greater than the infarct volume (102 +/- 135 cm3; P = 0.001). The volume difference between the hypoperfused and infarcted tissue on the first day correlated significantly with the infarct growth between the first day and 1 wk (r = 0.71; P < 0.01). Between the first day and 1 wk, the increase of the infarct volume correlated significantly with the change in the NIHSS (r = 0.54; P < 0.05).

CONCLUSION

A large hypoperfusion zone around the infarct core in the acute phase of ischemic stroke predicts the infarct growth during the first week, and this correlates significantly with the change in the neurologic status of the patient. Combined diffusion-weighted MRI and SPECT performed within 24 h after the onset of symptoms can be useful in the evaluation of acute stroke to predict infarct growth.

Verbal fluency activates the left medial temporal lobe: a functional magnetic resonance imaging study

Verbal fluency tests (VFTs) are suggested to assess frontal lobe function. This view is supported by functional imaging studies that report left frontal activation during VFTs. VFTs require retrieval of semantically associated words from long-term memory storage. The neural networks that participate in this process, however, are largely unknown. These neural networks are of interest, given that patients with early Alzheimer's disease, typically without frontal pathology, are often impaired in VFTs. In the present study, functional magnetic resonance imaging was performed to determine brain activation areas during VFTs in young subjects. In the activation task, category fluency was contrasted with orderly listing of numbers. As judged from using this comparison, there was activation in the left medial temporal lobe, in the inferior frontal and retrosplenial cortices bilaterally, and in the left superior parietal lobule. Left medial temporal lobe activation was present in 13 of the 14 study subjects either in the hippocampal formation (11 of 14) or in the posterior parahippocampal gyrus (12 of 14). These results suggest that the medial temporal lobe is required for the process of retrieval by category. Functional magnetic resonance imaging combined with a category fluency task may provide a new method to study patients with early Alzheimer's disease.

Specific changes in somatosensory evoked magnetic fields during recovery from sensorimotor stroke

We studied recovery-induced changes in the responsiveness of the primary somatosensory cortex in stroke patients with sensory and/or motor symptoms. Somatosensory evoked magnetic fields, in response to median nerve stimulation, were recorded in 14 patients with their first symptomatic unilateral stroke 1 to 15 days from the first symptoms and again 2 to 3 months later. Neuronal activity at the contralateral primary somatosensory cortex was modeled with equivalent current dipoles at the peak latencies of the first two cortical deflections at about 20 msec (N1m) and at 28 to 91 msec (P1m). Twenty-three age-matched healthy volunteers, 9 of whom were tested also in serial recordings, served as control subjects. At follow-up, 6 patients showed a significant increase of P1m amplitude, whereas N1m increased only in 1. Clinical improvement of two-point discrimination ability, but not of other basic somatosensory skills, was significantly correlated with the increase of P1m. We conclude that the recovery of discriminative touch after stroke is paralleled by the growth of the P1m somatosensory evoked magnetic field deflection, and we propose that this may reflect re-establishment of lateral inhibitory functions at the primary somatosensory cortex.

MRI pontine hyperintensity after supratentorial ischemic stroke relates to poor clinical outcome

BACKGROUND AND PURPOSE

MRI studies in patients with atherosclerosis often reveal ill-defined hyperintensity in the pons on T2-weighted images. This pontine hyperintensity (PHI) does not fulfill the criteria of a brain infarct, and its clinical relevance is not established. We examined the frequency, as well as the radiological and clinical correlates, of PHI in poststroke patients.

METHODS

Three hundred nineteen patients were studied 3 months after supratentorial ischemic stroke with the use of 1.0-T MRI. Brain infarcts, atrophy, white matter hyperintensities, and PHI were registered. The clinical outcome was assessed 3 and 15 months after the stroke.

RESULTS

Of the patients, 152 (47.6%) had PHI. The risk factors for stroke did not differ in patients without or with PHI. PHI was related to a higher frequency (P=0.002) and larger volume (P<0.001) of supratentorial brain infarcts, to parietal (P=0.020) and temporal (P=0.002) atrophy, to central atrophy (P< or =0.040), and to white matter hyperintensity grade (P<0.001). Brain infarcts that affected the corpus striatum (putamen, caudate, and pallidum) (P< or =0. 011) or pyramidal tract (P<0.001) were more frequent in patients with PHI. The 3- and 15-month outcomes were worse in patients with PHI (P< or =0.004). The total volume of brain infarcts (OR 1.22), mean atrophy (OR 3.59), and PHI (OR 3.76) were independent correlates of a poor 15-month outcome.

CONCLUSIONS

PHI after supratentorial ischemic stroke deserves attention because it relates to poor clinical outcome.

Clinical and radiological determinants of prestroke cognitive decline in a stroke cohort

OBJECTIVES

Stroke seems to be related to dementia more often than previously assumed and vascular factors are also related to Alzheimer's disease. The pathophysiology of poststroke dementia includes ischaemic changes in the brain, a combination of degenerative and vascular changes, and changes only related to Alzheimer's disease. Some cognitive decline recognised after a stroke may be due to pre-existing cognitive decline. The aim of this study was to determine the clinical and radiological determinants of prestroke cognitive decline.

METHODS

The study group comprised 337 of 486 consecutive patients aged 55 to 85 years who 3 months after ischaemic stroke completed a comprehensive neuropsychological test battery; structured medical, neurological, and mental status examination; interview of a knowledgeable informant containing structured questions on abnormality in the cognitive functions; assessment of social functions before the index stroke; and MRI.

RESULTS

Frequency of prestroke cognitive decline including that of dementia was 9.2% (31/337). The patients with prestroke cognitive decline were older, more often had less than 6 years of education, and had history of previous stroke. Vascular risk factors did not differ significantly between these two groups. White matter changes (p=0.004), cortical entorhinal, hippocampal, and medial temporal atrophy (p<0.001), cortical frontal atrophy (p=0.008); and any central atrophy (p<0.01), but not the frequencies or volumes of old, silent, or all infarcts on MRI differentiated those with and without prestroke cognitive decline. The correlates of prestroke cognitive decline in logistic regression analysis were medial temporal cortical atrophy (odds ratio (OR) 7.5, 95% confidence interval (95%CI) 3.2-18.2), history of previous ischaemic stroke (OR 4.4, 95% CI 1.8-10.6), and education (OR 0.9, 95% CI 0.8-0.9).

CONCLUSIONS

History of previous stroke, but not volumes or frequencies was found to correlate with prestroke cognitive decline. Other associating factors were rather those usually associated with degenerative dementia: white matter changes and cerebral atrophy; and in multiple models medial temporal cortical atrophy and education. The possible overlap between two or more underlying diseases must be remembered in diagnosis and treatment of patients with vascular cognitive impairment.

Spatiotemporal activity of a cortical network for processing visual motion revealed by MEG and fMRI

A sudden change in the direction of motion is a particularly salient and relevant feature of visual information. Extensive research has identified cortical areas responsive to visual motion and characterized their sensitivity to different features of motion, such as directional specificity. However, relatively little is known about responses to sudden changes in direction. Electrophysiological data from animals and functional imaging data from humans suggest a number of brain areas responsive to motion, presumably working as a network. Temporal patterns of activity allow the same network to process information in different ways. The present study in humans sought to determine which motion-sensitive areas are involved in processing changes in the direction of motion and to characterize the temporal patterns of processing within this network of brain regions. To accomplish this, we used both magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). The fMRI data were used as supplementary information in the localization of MEG sources. The change in the direction of visual motion was found to activate a number of areas, each displaying a different temporal behavior. The fMRI revealed motion-related activity in areas MT+ (the human homologue of monkey middle temporal area and possibly also other motion sensitive areas next to MT), a region near the posterior end of the superior temporal sulcus (pSTS), V3A, and V1/V2. The MEG data suggested additional frontal sources. An equivalent dipole model for the generators of MEG signals indicated activity in MT+, starting at 130 ms and peaking at 170 ms after the reversal of the direction of motion, and then again at approximately 260 ms. Frontal activity began 0-20 ms later than in MT+, and peaked approximately 180 ms. Both pSTS and FEF+ showed long-duration activity continuing over the latency range of 200-400 ms. MEG responses in the region of V3A and V1/V2 were relatively small, and peaked at longer latencies than the initial peak in MT+. These data revealed characteristic patterns of activity in this cortical network for processing sudden changes in the direction of visual motion.

Bone tunnel enlargement after anterior cruciate ligament reconstruction with the hamstring autograft and endobutton fixation technique. A clinical, radiographic and magnetic resonance imaging study with 2 years follow-up

The aim of this study was to describe the contrast-enhanced magnetic resonance imaging (MRI) appearance of bone tunnel enlargement detected on radiography after anterior cruciate ligament (ACL) reconstruction with semitendinosus and gracilis tendon endobutton (STG-endobutton) fixation technique. Fourteen patients with a STG-endobutton ACL reconstruction were examined 3 months (n = 1), 1 year (n = 1) and 2 years (n = 12) postoperatively. An age- and sex-matched group with a bone-patellar tendon-bone (BTB) autograft ACL reconstruction with similar follow-up was taken as control. Data on clinical examination, laxity and isokinetic muscle torque measurements, anteroposterior and lateral view radiography were obtained, and knee scores (Lysholm and Tegner) were collected. Contrast-enhanced MRI was performed in the STG-endobutton group with a 1.5-T imager. There were no statistical differences between the groups with respect to clinical findings, stability tests, or knee scores. In the STG-endobutton group the average femoral and tibial bone tunnel diameter detected on anteroposterior view radiography had increased at 2-year follow-up by 33% and 23%, respectively. On MRI the ligamentous graft itself was not enhanced by the contrast medium whereas periligamentous tissue within and around the STG graft bundles showed mild contrast enhancement. In conclusion, the MRI results suggest that enhancing periligamentous tissue accumulated in and around the STG graft associated with the tunnel expansion. In spite of the significant bone tunnel enlargement observed on the follow-up radiography the STG-endobutton knees were stable and the patients satisfied.

Magnetic resonance imaging white matter hyperintensities and mechanism of ischemic stroke

BACKGROUND AND PURPOSE

We sought to determine the relations between infarct subtype and white matter hyperintensities (WMHIs) on MRI.

MATERIALS AND METHODS

We studied 395 ischemic stroke patients with 1. 0-T MRI. The number of lacunar, border-zone, and cortical infarcts was registered. WMHIs were analyzed in 6 areas. Univariate and multivariate statistical analyses were used to find the risk factors for different infarct subtypes and to study the connections between WMHIs and brain infarcts.

RESULTS

Lacunar infarcts were associated with hypertension (odds ratio [OR], 1.79; 95% CI, 1.17 to 2.73), alcohol consumption (OR, 1.96; 95% CI, 1.17 to 3.28), and age (OR, 1. 03; 95% CI, 1.00 to 1.06). Border-zone infarcts were associated with carotid atherosclerosis (OR, 2.20; 95% CI, 1.15 to 4.19). Atrial fibrillation (OR, 3.02; 95% CI, 1.66 to 5.50) and carotid atherosclerosis (OR, 1.94; 95% CI, 1.12 to 3.36) were independent positive predictors, and history of hyperlipidemia (OR, 0.44; 95% CI, 0.26 to 0.75) and migraine (OR, 0.48; 95% CI, 0.25 to 0.93) were negative predictors for cortical infarcts. Patients with lacunar infarcts had more severe WMHIs than patients with nonlacunar infarcts in all WM areas (P</=0.001). Patients with border-zone infarcts showed severe periventricular lesions (P=0.002), especially around posterior horns (P=0.003). The extent of WMHIs in patients with cortical infarcts did not differ from that in those without cortical infarcts.

CONCLUSIONS

Various infarct subtypes have different risk profiles. The association between lacunar infarcts and WMHIs supports the concept of small-vessel disease underlying these 2 phenomena. The connection between border-zone infarcts and periventricular WMHIs again raises the question of the disputed periventricular vascular border zone.

The prevalence and distribution of white-matter changes on different MRI pulse sequences in a post-stroke cohort

No uniform criteria currently exist for rating white-matter (WM) high-signal foci on MRI. Ratings are based on descriptive terms, different pulse sequences and different WM areas. Reports on the prevalence and clinical correlates of high-signal foci have been contradictory. We wanted to examine the contribution of the pulse sequence and WM area on rating WM changes. We analysed WM changes separately on T2-, protondensity (PD)- and T1-weighted images in periventricular, subcortical, watershed area and deep WM. The difference between T2- and PD-weighted images was significant for frontal caps, counting small foci or analysing subcortical changes. T1-weighted images showed significantly less change, but the number of foci detected was greater than previously thought. The prevalence of WM high-signal foci was greatest in the watershed zone and smallest in the subcortical area. There was a significant correlation between foci in different areas.

3D spin-lock imaging of human gliomas

We investigated whether the simultaneous use of paramagnetic contrast medium and 3D on-resonance spin lock (SL) imaging could improve the contrast of enhancing brain tumors at 0.1 T. A phantom containing serial concentrations of gadopentetate dimeglumine (Gd-DTPA) in cross-linked bovine serum albumin (BSA) was imaged. Eleven patients with histologically verified glioma were also studied. T1-weighted 3D gradient echo images with and without SL pulse were acquired before and after a Gd-DTPA injection. SL effect, contrast, and contrast-to-noise ratio (CNR) were calculated for each patient. In the glioma patients, the SL effect was significantly smaller in the tumor than in the white and gray matter both before (p = 0.001, p = 0.025, respectively), and after contrast medium injection (p < 0.001, p < 0.001, respectively). On post-contrast images, SL imaging significantly improved tumor contrast (p = 0.001) whereas tumor CNR decreased slightly (p = 0.024). The combined use of SL imaging and paramagnetic Gd-DTPA contrast agent offers a modality for improving tumor contrast in magnetic resonance imaging (MRI) of enhancing brain tumors. 3D gradient echo SL imaging has also shown potential to increase tissue characterization properties of MR imaging of human gliomas.

Selective interference reveals dissociation between memory for location and colour

The aim was to study whether there is indication of a dissociation in processing of visuospatial and colour information in working memory in humans. Experimental subjects performed visuospatial and colour n-back tasks with and without visuospatial and colour distractive stimuli presented in the middle of the delay period to specifically affect mnemonic processing of task-related information. In the high memory-load condition, the visuospatial, but not the colour, task was selectively disrupted by visuospatial but not colour distractors. When subvocal rehearsal of the memoranda in the colour task was prevented by articulatory suppression; colour task performance was also selectively disrupted by distractors qualitatively similar to the memoranda. The results support the suggestion that visual working memory for location is processed separate from that for colour.

High-resolution MR imaging of the asymptomatic Achilles tendon: new observations

OBJECTIVE

Our aim was to describe the normal appearance of the Achilles tendon and peritendinous tissues in asymptomatic active volunteers using high-resolution MR imaging.

MATERIALS AND METHODS

One hundred clinically asymptomatic Achilles tendons were imaged at 1.5 T with axial high-resolution T1-weighted gradient-echo (fast low-angle shot [FLASH]) and short inversion time inversion recovery (STIR) sequences. The tendons, peritendinous tissues, tendon insertions, and musculotendinous junctions were separately evaluated by two observers.

RESULTS

The average anteroposterior diameter (+/-SD) of the asymptomatic Achilles tendons was 5.2+/-0.73 mm. The anterior margin was flat or concave in all, except for 10 tendons that showed mild convexity. A wave-like bulge, which shifted from lateral to medial in the craniocaudal direction, was detected in the anterior margin of 56 tendons. The signal intensity was heterogeneous in 45 tendons. In these tendons, distal stripes or punctate foci were seen. A small (3 mm) intermediate intensity intratendinous region thought to represent tendon degeneration was detected in four cases on FLASH images. The retrocalcaneal bursae contained a prominent fluid collection in 15 cases. The paratenon was visualized in all cases on both FLASH and STIR images.

CONCLUSION

High-resolution MR imaging depicts the Achilles tendon and peritendinous soft tissues in great detail. The normal anatomy of the asymptomatic Achilles tendon is variable. We postulate that the variability may be a potential source of diagnostic misinterpretation.

Combined diffusion and perfusion MRI with correlation to single-photon emission CT in acute ischemic stroke. Ischemic penumbra predicts infarct growth

BACKGROUND AND PURPOSE

More effective imaging methods are needed to overcome the limitations of CT in the investigation of treatments for acute ischemic stroke. Diffusion-weighted MRI (DWI) is sensitive in detecting infarcted brain tissue, whereas perfusion-weighted MRI (PWI) can detect brain perfusion in the same imaging session. Combining these methods may help in identifying the ischemic penumbra, which is an important concept in the hemodynamics of acute stroke. The purpose of this study was to determine whether combined DWI and PWI in acute (<24 hours) ischemic stroke can predict infarct growth and final size.

METHODS

Forty-six patients with acute ischemic stroke underwent DWI and PWI on days 1, 2, and 8. No patient received thrombolysis. Twenty-three patients underwent single-photon emission CT in the acute phase. Lesion volumes were measured from DWI, SPECT, and maps of relative cerebral blood flow calculated from PWI.

RESULTS

The mean volume of infarcted tissue detected by DWI increased from 46.1 to 75.6 cm(3) between days 1 and 2 (P<0.001; n=46) and to 78.5 cm(3) after 1 week (P<0.001; n=42). The perfusion-diffusion mismatch correlated with infarct growth (r=0. 699, P<0.001). The volume of hypoperfusion on the initial PWI correlated with final infarct size (r=0.827, P<0.001). The hypoperfusion volumes detected by PWI and SPECT correlated significantly (r=0.824, P<0.001).

CONCLUSIONS

Combined DWI and PWI can predict infarct enlargement in acute stroke. PWI can detect hypoperfused brain tissue in good agreement with SPECT in acute stroke.

Activation of multiple cortical areas in response to somatosensory stimulation: combined magnetoencephalographic and functional magnetic resonance imaging

We combined information from functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) to assess which cortical areas and in which temporal order show macroscopic activation after right median nerve stimulation. Five healthy subjects were studied with the two imaging modalities, which both revealed significant activation in the contra- and ipsilateral primary somatosensory cortex (SI), the contra- and ipsilateral opercular areas, the walls of the contralateral postcentral sulcus (PoCS), and the contralateral supplementary motor area (SMA). In fMRI, two separate foci of activation in the opercular cortex were discerned, one posteriorly in the parietal operculum (PO), and one anteriorly near the insula or frontal operculum (anterior operculum, AO). The activation sites from fMRI were used to constrain the solution of the inverse problem of MEG, which allowed us to construct a model of the temporal sequence of activation of the different sites. According to this model, the mean onset latency for significant activation at the contralateral SI was 20 msec (range, 17-22 msec), followed by activation of PoCS at 23 msec (range, 21-25 msec). The contralateral PO was activated at 26 msec (range, 19-32 msec) and AO at 33 msec (range, 22-51 msec). The contralateral SMA became active at 36 msec (range, 24-48 msec). The ipsilateral SI, PO, and AO became activated at 54-67 msec. We conclude that fMRI provides a useful means to constrain the inverse problem of MEG, allowing the construction of spatiotemporal models of cortical activation, which may have significant implications for the understanding of cortical network functioning.

MRI enhancement and microvascular density in gliomas. Correlation with tumor cell proliferation

RATIONALE AND OBJECTIVES

Angiogenesis and proliferation activity are important indicators of tumor behavior in human gliomas. The authors studied how tumor enhancement in MR imaging and intratumoral vascular density were correlated with cell proliferation in cerebral gliomas.

METHODS

The authors studied retrospectively 62 cerebral gliomas. Patients were examined before surgery with contrast-enhanced MR imaging. Microvessel density and the cell proliferation rate of tumor specimens were measured immunohistochemically using factor VIII and MIB-1 antibodies. Contrast enhancement of the tumors was evaluated by two radiologists.

RESULTS

Contrast enhancement was observed in 45 tumors and was correlated with histologic cell proliferation (P = 0.0007) and microvessel density (P = 0.01). There was also a correlation between tumor vascular density and the cell proliferation rate (r = 0.51, P < 0.0001). Histologic tumor grade was associated with vascular density (P = 0.001).

CONCLUSIONS

Lesion enhancement on preoperative contrast-enhanced MR imaging correlates with vascularity and proliferation activity of gliomas. The additional correlation between tumor vascularity and proliferation suggests that intratumoral microvessel density could be useful in estimating tumor proliferation.

Somatosensory evoked magnetic fields from the primary somatosensory cortex (SI) in acute stroke

We recorded somatosensory evoked magnetic fields (SEFs) to median nerve stimulation from 15 patients in the acute stage (1-15 days from the onset of the symptoms) of their first-ever unilateral stroke involving sensorimotor cortical and/or subcortical structures in the territory of the middle cerebral artery (MCA). Neuronal activity corresponding to the peaks of the N20m, P35m and P60m SEF deflections from the contralateral primary somatosensory cortex (SI) was modelled with equivalent current dipoles (ECDs), the locations and strengths of which were compared with those of an age-matched normal population. Four patients with pure motor stroke had symmetric SEFs. In one of the 4 patients with pure sensory stroke, and in 5 of the 7 patients with sensorimotor paresis, the SEFs were markedly attenuated or missing. All except one patient with abnormal SEFs had deficient two-point discrimination ability; especially the attenuation of N20m was more clearly correlated with two-point discrimination than with joint-position or vibration senses. Of the different SEF deflections, P35m and P60m were slightly more sensitive indicators of abnormality than N20m, the former being affected in two patients with symmetric N20m. Three patients with pure sensory stroke and lesions in the opercular cortex had normal SEFs from SI. We conclude that the SEF deflections N20m, P35m and P60m from SI are related to cutaneous sensation, in particular discriminative to touch. The results also demonstrate that basic somatosensory perception can be affected by lesions in the opercular cortex in patients with functionally intact SI.

Prognostic value of vascular density and cell proliferation in breast cancer patients

We measured microvessel density and cell proliferation index in 84 breast cancers using survival analysis to find out their prognostic value. Immunohistochemistry was applied using antibody to factor VIII-related antigen as a marker for microvessels and MIB-1 antibody to stain proliferating cells. We were not able to show any difference in survival with a mean follow-up of 10.3 years between patients with high and low microvessel count or cell proliferation index. Vascular density did not correlate with the cell proliferation rate (p = 0.4). However, patient age correlated negatively with the cell proliferation index of the tumor (p = 0.0009). There was no significant difference both in microvessel count and in cell proliferation between patients with lymph node metastasis and node negative patients. This result questions the usefulness of vascular density and cell proliferation rate as prognostic markers in breast cancer.

111In-labelled bleomycin complex for the differentiation of high- and low-grade gliomas

The aim of this study was to evaluate 111In-labelled bleomycin complex (111In-BLMC) SPET in the differentiation of high- and low-grade gliomas. Nineteen glioma patients, 14 with high-grade and five with low-grade tumours, were studied 1, 4 and 24 h after the injection of 111In-BLMC. In the high-grade glioma group, there was significant uptake of 111In-BLMC in 12 patients and no uptake in two patients based on the visual classification of SPET images at 4 and 24 h. In the low-grade glioma group, one patient had low uptake at 4 and 24 h, but the other four patients showed no visible uptake. The mean tumour to extracerebral circulation activity ratio (T/Cr) at 4 h was 0.13 +/- 0.10 (n = 5) in low-grade gliomas and 1.7 +/- 1.0 (n = 14) in high-grade gliomas. At 24 h the T/Cr ratios were 0.56 +/- 0.21 and 3.4 +/- 1.7, respectively. The mean tumour to contralateral normal brain activity ratios (T/Br) were 5.0 +/- 3.9 (4 h) and 3.0 +/- 2.8 (24 h) in low-grade gliomas, and 37.2 +/- 37.3 (4 h) and 8.3 +/- 8.2 (24 h) in high-grade gliomas. These higher T/Br ratios did not, however, result in improved differentiation between the two groups of gliomas; at 4 h the T/Cr and T/Br ratios were of equal value, as two high-grade gliomas would have been misclassified as low-grade, but at 24 h the T/Br ratio resulted in more misclassifications. Our results show that 111In-BLMC can be used in the differentiation of high- and low-grade gliomas and that the selection of the reference area for calculating tumour to non-tumour ratios is important.

Activation of multiple cortical areas in response to somatosensory stimulation: combined magnetoencephalographic and functional magnetic resonance imaging

We combined information from functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) to assess which cortical areas and in which temporal order show macroscopic activation after right median nerve stimulation. Five healthy subjects were studied with the two imaging modalities, which both revealed significant activation in the contra- and ipsilateral primary somatosensory cortex (SI), the contra- and ipsilateral opercular areas, the walls of the contralateral postcentral sulcus (PoCS), and the contralateral supplementary motor area (SMA). In fMRI, two separate foci of activation in the opercular cortex were discerned, one posteriorly in the parietal operculum (PO), and one anteriorly near the insula or frontal operculum (anterior operculum, AO). The activation sites from fMRI were used to constrain the solution of the inverse problem of MEG, which allowed us to construct a model of the temporal sequence of activation of the different sites. According to this model, the mean onset latency for significant activation at the contralateral SI was 20 msec (range, 17-22 msec), followed by activation of PoCS at 23 msec (range, 21-25 msec). The contralateral PO was activated at 26 msec (range, 19-32 msec) and AO at 33 msec (range, 22-51 msec). The contralateral SMA became active at 36 msec (range, 24-48 msec). The ipsilateral SI, PO, and AO became activated at 54-67 msec. We conclude that fMRI provides a useful means to constrain the inverse problem of MEG, allowing the construction of spatiotemporal models of cortical activation, which may have significant implications for the understanding of cortical network functioning.

MR imaging in pelvic inflammatory disease: comparison with laparoscopy and US

PURPOSE

To assess the value of magnetic resonance (MR) imaging in the diagnosis of pelvic inflammatory disease (PID) and to compare MR imaging with transvaginal ultrasonography (US) and laparoscopy.

MATERIALS AND METHODS

Thirty consecutive patients hospitalized because they were clinically suspected of having PID underwent transvaginal US and T1-weighted spin-echo, T2-weighted turbo spin-echo, and inversion-recovery MR imaging at 1.5 T. All patients underwent laparoscopy after MR imaging.

RESULTS

PID was laparoscopically proved in 21 (70%) patients. The MR imaging diagnosis agreed with that obtained with laparoscopy in 20 (95%) of the 21 patients with PID. The imaging findings for PID were as follows: fluid-filled tube, pyosalpinx, tubo-ovarian abscess, or polycystic-like ovaries and free pelvic fluid. Findings at transvaginal US agreed with those at laparoscopy in 17 (81%) of the 21 patients with PID. The sensitivity of MR imaging in the diagnosis of PID was 95%, the specificity was 89%, and the overall accuracy was 93%. For transvaginal US, the corresponding values were 81%, 78%, and 80%.

CONCLUSION

MR imaging is more accurate than transvaginal US in the diagnosis of PID and provides information about the differential diagnosis of PID. MR imaging may reduce the need for diagnostic laparoscopy.

On- and off-resonance spin-lock MR imaging of normal human brain at 0.1 T: possibilities to modify image contrast

The aim of the present investigation was to determine spin lock (SL) relaxation parameters for the normal brain tissues and thus, to provide basis for optimizing the imaging contrast at 0.1 T. 68 healthy volunteers were included. On-resonance spin lock relaxation time (T1rho) and off-resonance spin lock relaxation parameters (T1rho(off), Me/Mo), MT parameters (T1sat, Ms/Mo), and T1, T2 were determined for the cortical gray matter, and for the frontal and parietal white matters. The T1rho for the frontal and parietal white matters ranged from 110 to 133 ms and from 122 to 155 ms with locking field strengths from 50 microT to 250 microT, respectively. Accordingly, the values for the gray matter ranged from 127 to 155 ms. With a locking field strength of 50 microT, T1rho(off) for the frontal and parietal white matters were from 114 to 217 ms and from 126 to 219 ms, and for the gray matter from 136 to 267 ms with the angle between the effective magnetic field (B(eff)) and the z-axis (theta) ranging from 60 degrees to 15 degrees, respectively. The T1rho of the white and gray matters increased significantly with increasing locking field amplitude (p < 0.001). The T1rho(off) decreased significantly with increasing theta (p < 0.001). T1rho and T1rho(off) with theta > or = 30 degrees were statistically significantly shorter in the frontal than in the parietal white matters (p < 0.05). The duration, amplitude and theta of the locking pulse provide additional parameters to optimize contrast in brain SL imaging.

Kinetics of 111In-labeled bleomycin in patients with brain tumors: compartmental vs. non-compartmental models

The kinetics of an indium-111 labeled bleomycin complex (111In-BLMC) after rapid intravenous injection in patients with brain tumors was quantified by using compartmental and non-compartmental models. The models were applied to data obtained from 10 glioma, one meningioma, and one adenocarcinoma brain metastasis patients. Blood and urine samples from all the patients and tumor samples from three patients were collected. The mean transit time of 111In-BLMC in the plasma pool was 14 +/- 7 min without and 1.8 +/- 0.6 h when accounting for recirculation, and 13 +/- 4 h in the total body pool. The mean plasma clearance of 111In-BLMC was 0.3 +/- 0.1 m/blood/min and the mean half-life in urine was 3.5 +/- 0.6 h. The mean transfer coefficients for the open three-compartmental model were: excretion from plasma = 0.02 +/- 0.01, from depot to plasma = (12 +/- 9)*10(-4), from plasma to depot = 0.01 +/- 0.01, from tumor to plasma = 0.39 +/- 0.19 and from plasma to tumor = 1.11 +/- 0.57, all in units minute-1. The mean turnover time from the tumor was 4.5 +/- 2.7 min and from the depot 20 +/- 8 h. It is concluded that both compartmental and non-compartmental models are sufficient to describe the kinetics of indium-111 labeled bleomycin complex. The non-compartmental model is more practical and to some extent more efficient in describing the in vivo behaviors of 111In-BLMC than the compartmental model. The compartmental model used provides estimates of both extraction and excretion from the plasma and tumor.

Distribution of cortical activation during visuospatial n-back tasks as revealed by functional magnetic resonance imaging

Human neuroimaging studies conducted during visuospatial working memory tasks have inconsistently detected activation in the prefrontal cortical areas depending presumably on the type of memory and control tasks employed. We used functional magnetic resonance imaging to study brain activation related to the performance of a visuospatial n-back task with different memory loads (0-back, 1-back and 2-back tasks). Comparison of the 2-back versus 0-back tasks revealed consistent, bilateral activation in the medial frontal gyrus (MFG), superior frontal sulcus and adjacent cortical tissue (SFS/SFG) in all subjects and in six out of seven subjects in the intraparietal sulcus (IPS). Activation was also detected in the inferior frontal gyrus, medially in the superior frontal gyrus, precentral gyrus, superior and inferior parietal lobuli, occipital visual association areas, anterior and posterior cingulate areas and in the insula. Comparison between the 1-back versus 0-back tasks revealed activation only in a few brain areas. Activation in the MFG, SFS/SFG and IPS appeared dependent on memory load. The results suggest that the performance of a visuospatial working memory task engages a network of distributed brain areas and that areas in the dorsal visual pathway are engaged in mnemonic processing of visuospatial information.

Face-selective processing in human extrastriate cortex around 120 ms after stimulus onset revealed by magneto- and electroencephalography

Quick recognition of faces is crucial to a variety of human interactions, and highly specialized pathways may be involved in the processing of faces. To reveal selectivity to faces in early cortical processing, whole-scalp magnetoencephalography (MEG) and electroencephalography (EEG) were used to record event-related responses to faces and degraded faces and their inverted counterparts. We observed increases in the peak latency and amplitude of the early 120-ms component (P120) for the inverted faces. These effects were enhanced for the 1 70-ms component (N170). For the degraded counterparts, a significant effect of the inversion was observed only for the N170, which was strongly delayed. Source modelling suggested that the early response originated at the posterior occipital areas whereas the later response was generated anterior and lateral to this location. We conclude that under sufficiently good conditions face-selective activity may be taking place during the P120.

The effect of paramagnetic contrast media on T1 relaxation times in brain tumors

PURPOSE

To study T1 relaxation times in brain tumors before and after paramagnetic contrast medium injection.

MATERIAL AND METHODS

Seventeen patients with a known or suspected brain tumor were studied with an echo planar inversion recovery imaging sequence using 10 different inversion times. Double injections of Gd chelate (0.1 mmol/kg + 0.2 mmol/kg) were administered in 5 patients, and a single 0.2-mmol/kg dose in 12 patients.

RESULTS

After the 0.2-mmol/kg dose, T1 decreased from 1121 +/- 130 ms to 987 +/- 103 ms in gray matter (p < 0.001), and from 666 +/- 29 ms to 646 +/- 27 ms in white matter (p < 0.001). Tumor T1 shortened from 1515 +/- 319 ms to 717 +/- 383 ms. After the 0.1-mmol/kg dose (n = 5), tumor T1 decreased from 1116 +/- 261 ms to 793 +/- 202 ms and after the additional 0.2-mmol/kg dose it decreased further to 526 +/- 141 ms.

CONCLUSION

Postcontrast T1 relaxation times in tumors showed considerable variation and remained, on average, relatively long compared to white matter. This should be taken into account when deciding which pulse sequences, imaging parameters, and contrast agent doses are optimal for brain tumor imaging.

Determination of T1rho values for head and neck tissues at 0.1 T: a comparison to T1 and T2 relaxation times

In order to optimize head and neck magnetic resonance (MR) imaging with the spin-lock (SL) technique, the T1rho relaxation times for normal tissues were determined. Furthermore, T1rho was compared to T1 and T2 relaxation times. Ten healthy volunteers were studied with a 0.1 T clinical MR imager. T1rho values were determined by first measuring the tissue signal intensities with different locking pulse durations (TL), and then by fitting the signal intensity values to the equation with the least-squares method. The T1rho relaxation times were shortest for the muscle and tongue, intermediate for lymphatic and parotid gland tissue and longest for fat. T1rho demonstrated statistically significant differences (p < 0.05) between all tissues, except between muscle and tongue. T1rho values measured at locking field strength (B1L) of 35 microT were close to T2 values, the only exception being fat tissue, which showed T1rho values much longer than T2 values. Determination of tissue relaxation times may be utilized to optimize image contrast, and also to achieve better tissue discrimination potential, by choosing appropriate imaging parameters for the head and neck spin-lock sequences.

Reversal of cerebral asymmetry in schizophrenia measured with magnetoencephalography

It has been suggested that schizophrenic patients fail to develop left-hemisphere dominance because of an early disturbance in neuronal development. This hypothesis has been supported by some post-mortem. CT and magnetic resonance imaging (MRI) studies, while other in-vivo studies have given contradicting results. We used 122-channel whole-head magnetoencephalography and MRI to locate the sources of auditory evoked responses in 19 schizophrenic patients and in 20 healthy controls. Auditory evoked responses were detected in all subjects. The left-right hemisphere asymmetry of cerebral sources for auditory evoked responses was markedly dispersed among patients when compared with controls. The source locations for left auditory cortex were clearly anterior with respect to the right hemisphere in 32% of the patients, while the corresponding prevalence of this abnormal asymmetry was 0% in controls (p = 0.008. Fisher's exact test). The reversed asymmetry appeared to be associated with a shorter anterior-posterior distance between the auditory cortex and the anterior tip of the temporal lobe in the left side when compared with the right side. The reversed asymmetry was associated with higher PANSS general psychopathological score, and especially with higher guilt feelings and motor retardation scores. The large 2.5-fold standard deviation in the inter-hemispheric anterior posterior difference in the location of the auditory cortex among patients (p 0.001 for the difference in the magnitude of variance between controls and patients) clearly reflects the dispersion of the left right asymmetry into both direction, and three of the patients with 'normal asymmetry' had a greater left-right asymmetry than any of the controls. Markedly greater reversal of hemispheric asymmetry among patients implies that regulation of the development of brain asymmetry is disturbed among schizophrenic patients. Abnormality in the cerebral asymmetry may be a crucial factor in the development of schizophrenic disorder in a substantial proportion of patients. The results suggest that the reversed asymmetry is associated with the higher severity of general psychopathological symptoms.

Neuronal responses to magnetic stimulation reveal cortical reactivity and connectivity

Motor and visual cortices of normal volunteers were activated by transcranial magnetic stimulation. The electrical brain activity resulting from the brief electromagnetic pulse was recorded with high-resolution electroencephalography (HR-EEG) and located using inversion algorithms. The stimulation of the left sensorimotor hand area elicited an immediate response at the stimulated site. The activation had spread to adjacent ipsilateral motor areas within 5-10 ms and to homologous regions in the opposite hemisphere within 20 ms. Similar activation patterns were generated by magnetic stimulation of the visual cortex. This new non-invasive method provides direct information about cortical reactivity and area-to-area neuronal connections.

Multislice MRI in assessment of myocardial perfusion in patients with single-vessel proximal left anterior descending coronary artery disease before and after revascularization

BACKGROUND

Our purpose was to use multislice MRI for detection of reversible myocardial ischemia and assessment of the effect of revascularization on tissue perfusion in patients with coronary artery disease.

METHODS AND RESULTS

Eleven patients with single-vessel proximal left anterior descending coronary artery disease were studied with MRI and thallium scintigraphy before and 3 months after revascularization. All patients had a reversible perfusion defect by scintigraphy before treatment. With a 1.5-T MR imager, IR-prepared turboflash images were acquired in three left ventricular short-axis planes during 0.05 mmol/kg Gd-DTPA bolus at rest and with dipyridamole-induced stress. Before treatment, stress increased enhancement slope in normal (6.4+/-4.4 to 7.4+/-5.0 s(-1), P<.04) and decreased it in underperfused (5.4+/-3.7 to 2.6+/-1.4 s(-1), P<.02) regions, resulting in a contrast-to-noise ratio of 6.87+/-3.09 in underperfused myocardium. Revascularization normalized enhancement patterns of the formerly underperfused myocardium and decreased defect size both in scintigraphy (66+/-53 degrees to 8+/-12 degrees, P<.001) and MRI sections (49+/-41 degrees to 9+/-8 degrees, P<.001). Agreement of 85% in detection and correlation of 0.86 (SEE, 21 degrees, P<.001) in sizing perfusion defects was found between MRI and scintigraphy.

CONCLUSIONS

Multislice contrast-enhanced MRI can be used to detect myocardial perfusion defects in patients with coronary artery disease and in assessment of the effect of treatment on myocardial perfusion.

Somatosensory evoked magnetic fields to median nerve stimulation: interhemispheric differences in a normal population

The objective of the present study was to evaluate the normal interhemispheric variability of the locations and activation strengths of the somatosensory cortices. Somatosensory evoked magnetic fields (SEFs) were recorded with a 122-channel magnetometer in 23 healthy subjects (mean age 57 years) to stimulation of left and right median nerves. Equivalent current dipole (ECD) strengths and locations were determined for the main SEF deflections at the contralateral primary sensorimotor (SMI) and secondary somatosensory (SIIc) cortices. In a Cartesian co-ordinate system, defined by the preauricular points and the nasion, the SMI sources were slightly but significantly more laterally and anteriorly located in the right than in the left hemisphere. No systematic co-ordinate asymmetries were found for the SIIc sources. In individual subjects, the interhemispheric differences in the ECD co-ordinates averaged less than 6 mm at both SMI and SIIc. The group means of the source strengths did not differ between the hemispheres, but individual differences were on average 20% for the SMI and 65% for the SIIc sources. We conclude that at the individual level, the median nerve SEFs from SMI can be used to detect abnormally large interhemispheric asymmetries of source locations in the centimetre scale.

MR imaging of biodegradable polylevolactide osteosynthesis devices in the ankle

OBJECTIVE

To assess the feasibility of magnetic resonance (MR) imaging in the postoperative follow-up after internal fracture fixation using biodegradable polylevolactide (PLLA) plugs and to investigate the MR characteristics of these devices.

STUDY DESIGN AND METHODS

MR findings in ten patients with displaced malleolar fractures treated by internal fixation using absorbable PLLA plugs were evaluated after three different postoperative periods. The average postoperative follow-up time was thirty months for four patients, forty-two months for another four patients, and fifty-one months for the remaining two patients.

RESULTS

On T1-weighted coronal images, the geometry of the PLLA plug was clearly visible in all cases, without signs of fatigue failure or absorption. The host-to-tissue area between the deployed two fins of the plug showed higher signal intensity than the surrounding cancellous bone on fat-saturated proton density (PD) and turbo inversion recovery (tIR) images. This area had signal intensity similar to articular cartilage on T1-weighted coronal images. In none of the cases could any fluid accumulation be seen around the plug. In all ten cases, a thin rim with signal intensity similar to the area between the deployed fins was detected around the PLLA plug on fat-saturated axial PD images. On fat-saturated T2 and tIR sequences, this rim was less clearly detectable in all cases. No differences in the signal intensity or geometry of the PLLA plug on the MR images emerged between the three patient groups with mean follow-ups of thirty, forty-two, and fifty-one months. No artifacts produced by the implants were seen on any of the MR images. A biopsy specimen obtained at a reoperation necessary seventeen months postoperatively showed no signs of degradation of the PLLA plug.

CONCLUSIONS

MR imaging can visualize PLLA implants within bone. It also shows, without artifacts, the tissue interaction between the artificial biodegradable material and bone tissue in humans.