Changes in neuronal activation in patients with bipolar disorder during performance of a working memory task

OBJECTIVES

Several lines of evidence suggest that deficits in cognition persist in bipolar patients during periods of euthymia. Working memory impairment has been observed in euthymic bipolar patients and noted to be a significant source of functional deficits in psychiatric disorders. Functional changes associated with these cognitive deficits however, remain poorly understood. We hypothesized that patients with bipolar disorder would demonstrate changes in neuronal activation in specific regions forming part of the working memory network.

METHODS

Fifteen euthymic bipolar patients and fifteen age- and gender-matched healthy controls were recruited. Subjects participated in fMRI scans during which a two-back working memory task alternated with a zero-back control/attention task using a block-design paradigm. Groups were analyzed separately, and intergroup comparisons were made using an exploratory, voxel-by-voxel analysis.

RESULTS

Bipolar patients performed more poorly on the cognitive tasks than did healthy controls (F = 3.77, p = 0.04). After covarying for task performance and reaction time, bipolar patients demonstrated significantly greater activation than healthy subjects in several regions including the fronto-polar prefrontal cortex, temporal cortex, basal ganglia, thalamus, and posterior parietal cortex. No areas showed a significant decrease in activation, compared with healthy controls.

CONCLUSIONS

Our findings suggest that decreased working memory performance in bipolar patients reflects specific neurofunctional deficits. These deficits may represent primary areas of neuropathology or be secondary to neuropathology elsewhere in the working memory network. Continued research utilizing other imaging modalities may further clarify the underlying neuropathology involved in these cognitive deficits.

Functional magnetic resonance imaging: contemporary and future use

PURPOSE OF REVIEW

Functional magnetic resonance imaging is a relatively new neuroimaging technique that is being used in both research and clinical applications. Increasing work has been done to elucidate the auditory cortex.

RECENT FINDINGS

Current studies focus on enhancing the sensitivity of functional magnetic resonance imaging in studying the auditory cortex and subcortical pathways in response to tonal stimulation, to evaluate the integrity of the auditory cortex before cochlear implantation, and as a screening tool for hearing impairment in the young child.

SUMMARY

Recent work has been encouraging: silent functional magnetic resonance imaging techniques allow for better evaluation of the auditory cortex with less confounding scanner noises. Functional magnetic resonance imaging can be safely and reproducibly performed in hearing-impaired children and in the preoperative evaluation of candidates for cochlear implantation.

A STAP algorithm approach to fMRI: a simulation study

PURPOSE

To adapt the space-time adaptive processing (STAP) algorithm, previously developed in the field of sensor array processing and applied to radar signal processing, for use in construction of brain activation maps in functional magnetic resonance imaging (fMRI).

MATERIALS AND METHODS

STAP is a two-dimensional filter in which both the spatial and temporal responses are controlled adaptively. It processes space-time data as a complete spatiotemporal set. Unlike presently used fMRI techniques, STAP locates activated regions both spatially and in frequency.

RESULTS

Computer simulations incorporating actual MRI noise indicate that STAP exhibits a high degree of accuracy in detecting the small signal intensity changes inherent in fMRI.

CONCLUSION

Because STAP processes space-time data as a single data matrix, it exhibits potential over currently available fMRI methods in providing a measure of the full spatiotemporal extent of a task-related activity.

Comparison of three methods for generating group statistical inferences from independent component analysis of functional magnetic resonance imaging data

PURPOSE

To evaluate the relative effectiveness of three previously proposed methods of performing group independent component analysis (ICA) of functional magnetic resonance imaging (fMRI) data.

MATERIALS AND METHODS

Data were generated via computer simulation. Components were added to a varying number of subjects between 1 and 20, and intersubject variability was simulated for both the added sources and their associated time courses. Three methods of group ICA analyses were performed: across-subject averaging, subject-wise concatenation, and row-wise concatenation (e.g., across time courses).

RESULTS

Concatenating across subjects provided the best overall performance in terms of accurate estimation of the sources and associated time courses. Averaging across subjects provided accurate estimation (R > 0.9) of the time courses when the sources were present in a sufficient fraction (about 15%) of 100 subjects. Concatenating across time courses was shown not to be a feasible method when unique sources were added to the data from each subject, simulating the effects of motion and susceptibility artifacts.

CONCLUSION

Subject-wise concatenation should be used when computationally feasible. For studies involving a large number of subjects, across-subject averaging provides an acceptable alternative and reduces the computational load.

A preliminary FMRI study of sustained attention in euthymic, unmedicated bipolar disorder

The symptoms of bipolar disorder suggest dysfunction of anterior limbic networks that modulate emotional behavior and that reciprocally interact with dorsal attentional systems. Bipolar patients maintain a constant vulnerability to mood episodes even during euthymia, when symptoms are minimal. Consequently, we predicted that, compared with healthy subjects, bipolar patients would exhibit abnormal activation of regions of the anterior limbic network with corresponding abnormal activation of other cortical areas involved in attentional processing. In all, 10 unmedicated euthymic bipolar patients and 10 group-matched healthy subjects were studied with fMRI while performing the Continuous Performance Task-Identical Pairs version (CPT-IP). fMRI scans were obtained on a 3.0 T Bruker system using an echo planar imaging (EPI) pulse sequence, while subjects performed the CPT-IP and a control condition to contrast group differences in regional brain activation. The euthymic bipolar and healthy subjects performed similarly on the CPT-IP, yet showed significantly different patterns of brain activation. Specifically, bipolar patients exhibited increased activation of limbic, paralimbic, and ventrolateral prefrontal areas, as well as visual associational cortices. Healthy subjects exhibited relatively increased activation in fusiform gyrus and medial prefrontal cortex. In conclusion, these differences suggest that bipolar patients exhibit overactivation of anterior limbic areas with corresponding abnormal activation in visual associational cortical areas, permitting successful performance of an attentional task. Since the differences occurred in euthymia, they may represent trait, rather than state, abnormalities of brain function in bipolar disorder.

Event-related fMRI technique for auditory processing with hemodynamics unrelated to acoustic gradient noise

Acoustic noise from the imaging gradients presents a major difficulty in functional MRI (fMRI) studies of auditory cortical function. For studies involving hearing-impaired pediatric subjects, the auditory stimuli should be presented during completely silent gradient intervals. In addition, the scan time is limited by constraints involving subject motion and subject compliance. A novel event-related method for conducting fMRI studies of auditory function is proposed. Auditory stimuli are presented during completely silent gradient intervals, but using a variable TR. A general nonlinear model (GNLM) is proposed as a postprocessing methodology for the data. The technique increases the flexibility of the experimental design, with minimal loss of sensitivity compared to standard fMRI acquisition techniques, and may therefore be useful for fMRI studies of auditory function in hearing-impaired pediatric subjects.

Abnormal frontal white matter tracts in bipolar disorder: a diffusion tensor imaging study

OBJECTIVES

Prefrontal white matter has been hypothesized to be integral to the pathophysiology of bipolar disorder. Recent morphometric studies however, have not observed changes in white matter in bipolar patients. We hypothesized that changes in prefrontal function in bipolar disorder, widely reported in the literature, may be related to a loss of white matter tract integrity with a resultant dysconnectivity syndrome. In this study we utilized diffusion tensor imaging (DTI) to examine prefrontal white matter in patients with bipolar disorder.

METHODS

Nine patients with bipolar disorder and nine healthy controls were recruited. DTI and localizing anatomic data were acquired, and regions of interest (ROIs) identified in the prefrontal white matter at 15, 20, 25, and 30 mm superior to the anterior commissure (AC). Fractional anisotropy (FA) and trace apparent diffusion coefficient (TADC) were compared by ROI between study groups.

RESULTS

The FA of ROIs 25 and 30 mm above the AC was significantly reduced in patients with bipolar disorder; FA of all ROIs showed high-medium to large effect sizes. No significant group differences were identified in TADC.

CONCLUSIONS

Our findings suggest that a loss of bundle coherence is present in prefrontal white matter. This loss of coherence may contribute to prefrontal cortical pathology in patients with bipolar disorder.

Voxel-based morphometry in adolescents with bipolar disorder: first results

Bipolar disorder is an increasingly recognized cause of significant morbidity in the pediatric age group. However, there is still a large degree of uncertainty regarding the underlying neurobiological deficits. In this preliminary study, we performed automated volumetric studies and whole-brain voxel-based morphometry (VBM) on gray matter. Imaging data from 10 adolescents with bipolar disorder were compared with data from 52 age- and gender-matched healthy controls. Previously defined brain parcellations and optimized VBM protocols were used, based on custom-made pediatric reference data. An additional, exploratory whole-brain comparison was also implemented. The volumetric region-of-interest study revealed significantly greater gray matter volume in central gray matter structures bilaterally (including the basal ganglia and the thalamus) and the left temporal lobe in the bipolar group. VBM confirmed bilaterally larger basal ganglia. Localized gray matter deficits in bipolar subjects were found in the medial temporal lobe, orbito-frontal cortex, and the anterior cingulate, confirming and extending earlier studies.

High-resolution functional MRI at 3T in healthy and epilepsy subjects: hippocampal activation with picture encoding task

Functional MRI (fMRI) studies of memory with coarse resolution of 4 x 4 x 5 mm often fail to demonstrate blood oxygenation level-dependent (BOLD) activation in the hippocampal formation. This failure occurs when nonactivating white matter is averaged with the signal from hippocampal gray matter, attenuating the total BOLD signal from a single voxel due to the "partial volume effect." In this study, we evaluated the suitability of high-resolution fMRI at 3T (voxel size 2 x 2 x 3 mm) for improved visualization of hippocampal activation during memory encoding in 21 healthy and 6 epilepsy subjects. We used a picture encoding task (block design) that involved memorization of indoor and outdoor scenes along with an appropriate resting task. Region-of-interest (ROI) analysis was performed; laterality indices (LIs) were calculated based on hippocampal ROIs (hROIs) or on global medial temporal ROIs (mtROIs). In 19 healthy subjects, robust bilateral BOLD signal changes within both ROIs were noted. The mean LI+/-SD for the hROIs is -0.12+/-0.06 and that for the medial temporal ROIs -0.12+/-0.05, with correlation between the LIs (r = 0.59, P = 0.009). Good concordance was noted between the surgical outcome and memory lateralization with the fMRI task employed in this study. The preliminary results are encouraging, and with continuing improvements in MRI scanner technology, we expect fMRI of the hippocampal formation at higher resolution to be possible and preferable. Furthermore, these results suggest that a larger study to test the utility of high-resolution fMRI in epilepsy presurgical evaluation is needed.

The effect of musical training on the neural correlates of math processing: a functional magnetic resonance imaging study in humans

The neural correlates of the previously hypothesized link between formal musical training and mathematics performance are investigated using functional magnetic resonance imaging (fMRI). FMRI was performed on fifteen normal adults, seven with musical training since early childhood, and eight without, while they mentally added and subtracted fractions. Musical training was associated with increased activation in the left fusiform gyrus and prefrontal cortex, and decreased activation in visual association areas and the left inferior parietal lobule during the mathematical task. We hypothesize that the correlation between musical training and math proficiency may be associated with improved working memory performance and an increased abstract representation of numerical quantities.

Variability of gray and white matter during normal development: a voxel-based MRI analysis

This study was aimed at investigating regional and local variability of brain tissue during normal human brain development. We investigated high-resolution MR-imaging data using SPM99 (Wellcome Department, University College London, UK). A pixel-wise variation coefficient of gray and white matter was calculated to visualize local variability. Data from 200 normal children (5-18 years) were analyzed. We found a profound interaction between variability of brain structures and normal development in both gray and white matter. Variability in gray and white matter shows regionally specific, age-related variations, possibly offering a new tool for the assessment of subtle brain abnormalities. Our results emphasize the necessity to take this variability into account when planning pediatric neuroimaging studies.

Normative pediatric brain data for spatial normalization and segmentation differs from standard adult data

Spatial normalization and morphological studies of pediatric brain imaging data based on adult reference data may not be appropriate due to the developmental differences between the two populations. In this study, we set out to create pediatric templates and a priori brain tissue data from a large collection of normal, healthy children to compare it to standard adult data available within a widely used imaging software solution (SPM99, WDOCN, London, UK). Employing four different processing strategies, we found considerable differences between our pediatric data and the adult data. We conclude that caution should be used when analyzing pediatric brain data using adult a priori information. To assess the effects of using pediatric a priori brain information, the data obtained in this study is available to the scientific community from our website (www.irc.cchmc.org).

The effect of musical training on music processing: a functional magnetic resonance imaging study in humans

Previous studies have demonstrated changes in neuronal activity in trained musicians relative to controls while performing various music processing tasks. In this study the neural correlates of the effect of music training on two aspects of music processing, melody and harmony, are investigated using functional magnetic resonance imaging (fMRI). Fifteen subjects, seven with continuous musical training from early childhood to adulthood and eight without, underwent a passive fMRI listening paradigm designed to test the effects of melodic and harmonic processing. Melodic processing activated the most anterior part of the superior temporal gyrus for both musicians and non-musicians, while harmonic processing activated different visual association areas for musicians relative to non-musicians. The inferior parietal lobules were recruited only by musicians for both tasks. We conclude that musical training results in the recruitment of different neural networks for these aspects of music processing.

Bright spots: correlations of gray matter volume with IQ in a normal pediatric population

The localization of brain areas related to cognitive functions has yet to be thoroughly explored in children. We therefore set out to apply volumetric, voxel-based, and structural connectivity analyses to magnetic resonance images from a large sample of healthy children. We could confirm a strong correlation of whole-brain gray matter volume and the individual intelligence quotient; however, this correlation only developed with age in our sample, in that it was not present in the younger children. With the application of an optimized protocol for voxel-based morphometry, the anterior cingulate was shown to be directly correlated with a measure of human intelligence. Furthermore, an analysis of structural connectivity identified gray matter volume in several distinct brain areas to be related to cognitive functions. The implications of our findings for normal development, pathological processes, and our understanding of cognition are discussed and related to previous findings.

Functional magnetic resonance imaging in pediatrics

Functional magnetic resonance imaging (fMRI) allows non-invasive assessment of human brain function in vivo by detecting blood flow differences. In this review, we want to illustrate the background and different aspects of performing functional magnetic resonance imaging (fMRI) in the pediatric age group. An overview over current and future applications of fMRI will be given, and typical problems, pitfalls, and benefits of doing fMRI in the pediatric age group are discussed. We conclude that fMRI can successfully be applied in children and holds great promise for both research and clinical purposes.

Using a phantom to compare MR techniques for determining the ratio of intraabdominal to subcutaneous adipose tissue

OBJECTIVE

Patients who have a greater distribution of intraabdominal adipose tissue as compared with subcutaneous adipose tissue and an increased ratio of intraabdominal adipose tissue to subcutaneous adipose tissue are at greater risk for developing cardiovascular disease and type 2 diabetes mellitus. In previous MR investigations, researchers have used conventional T1-weighted spin-echo images to determine the ratio of intraabdominal adipose tissue to subcutaneous adipose tissue. However, no investigation, to our knowledge, has been performed to determine the accuracy of using different MR sequences to estimate adipose distribution. The purpose of our investigation was to compare MR imaging and segmentation techniques in calculating the ratio of intraabdominal to subcutaneous adipose tissue using an adiposity phantom.

MATERIALS AND METHODS

A phantom was created to simulate the distribution of subcutaneous and intraabdominal fat (with known volumes). Axial MR images were obtained twice through the phantom using a 5-mm slice thickness and zero gap for the following T1-weighted sequences: spin-echo, fast Dixon, and three-dimensional (3D) spoiled gradient-echo. An in-house computer software program was then used to segment the volumes of fat and calculate the volume of intraabdominal adipose tissue and subcutaneous adipose tissue and the ratio of intraabdominal to subcutaneous adipose tissue. Each imaging data set was segmented three times, so six sets of data were yielded for each imaging technique. The percentage predicted of the true volume was calculated for each MR imaging technique for each fat variable. The mean percentages for each variable were then compared using one-factor analysis of variance to determine whether differences exist among the three MR techniques.

RESULTS

The three MR imaging techniques had statistically significant different means for the predicted true volume of two variables: volume of subcutaneous adipose tissue (p < 0.001) and volume of intraabdominal adipose tissue (p = 0.0426). Estimates based on fast Dixon images were closest to the true volumes for all the variables. All MR imaging techniques performed similarly in estimating the ratio of intraabdominal adipose tissue to subcutaneous adipose tissue (p = 0.9117). The acquisition time for the 3D spoiled gradient-echo images was 10-22 times faster than for the other sequences.

CONCLUSION

Conventional T1-weighted spin-echo MR imaging, the current sequence used in practice for measuring visceral adiposity, may not be the optimal MR sequence for this purpose. We found that the T1-weighted fast Dixon sequence was the most accurate at estimating all fat volumes. The T1-weighted 3D spoiled gradient-echo sequence generated similar ratios of intraabdominal to subcutaneous adipose tissue in a fraction of the acquisition time.

Fast high-resolution 3D segmented echo planar imaging for dose mapping using a superheated emulsion chamber

The superheated emulsion chamber (SEC) consists of superheated droplets of halocarbons in an aqueous gel. The gel resides in a pressure chamber. Brachytherapy sources can be implanted in the SEC for radiation dosimetry studies. Upon irradiation by ionizing radiation, the metastable droplets vaporize to form microbubbles. MRI can be used to determine the distribution of bubbles following irradiation of the SEC. In order to generate sufficient statistical accuracy in the determination of dose distributions around brachytherapy sources, it is necessary to use hundreds of irradiation cycles. Susceptibility-weighted images provide contrast between the gel and the vapor microbubbles. This article describes a 3D, blipped, double-sampled, segmented echo-planar imaging technique for rapidly imaging the SEC at 650 microm isotropic 3D resolution in about 2 min. This method was used with a pressure cycling SEC to acquire hundreds of images in several hours. Results are presented showing the 2D dose distribution generated by an (125)I source as measured in the SEC using this new imaging method.

Language processing during natural sleep in a 6-year-old boy, as assessed with functional MR imaging

Functional MR imaging for language lateralization was performed in a 6-year-old child before neurosurgical intervention. A passive story-listening task was used; this revealed a bilateral language network. The task was repeated during the same session when the child had fallen asleep and surprisingly yielded strong activation in similar language areas. Our findings suggest that language processing does occur during natural sleep, even in young children. This potentially allows for an assessment of language functions, even in sleeping children.

Practical aspects of conducting large-scale functional magnetic resonance imaging studies in children

The potential benefits of functional magnetic resonance imaging (MRI) for the investigation of normal development have been limited by difficulties in its use with children. We describe the practical aspects, including failure rates, involved in conducting large-scale functional MRI studies with normal children. Two hundred and nine healthy children between the ages of 5 and 18 years participated in a functional MRI study of language development. Reliable activation maps were obtained across the age range. Younger children had significantly higher failure rates than older children and adolescents. It is concluded that it is feasible to conduct large-scale functional MRI studies of children as young as 5 years old. These findings can be used by other research groups to guide study design and plans for recruitment of young subjects.

Assessment of spatial normalization of whole-brain magnetic resonance images in children

Commonly used frameworks for spatial normalization of brain imaging data (e.g., Talairach-space) are based on one or more adult brains. As pediatric brains are different in size and shape from adult brains and continue to develop through childhood, we aimed to assess the influence of age on various spatial normalization parameters. One hundred forty-eight healthy children aged 5-18 years were included in this study. The linear scaling parameters and the deformations from the non-linear spatial normalization to both a standard adult and a custom pediatric template were analyzed within SPM99. The effect of using a brain mask on the linear and of using different levels of constraint on the non-linear spatial normalization was assessed. Of the linear scaling factors, only the X-dimension (left-right) showed a significant age-correlation when based on brain tissue, whereas the overall scaling was not correlated with age. When based on the whole head, a very strong age-effect can be found in all dimensions. Non-linear deformations also show localized correlations with age, most pronounced in parietal and frontal areas. The total amount of volume change is significantly lower when using a pediatric template. It is also substantially influenced by the degree of regularization that is exerted on the spatial normalization parameters. Our results suggest that in the cortical areas showing a strong correlation of deformation with age, caution should be used in assigning imaging results in children to a specific morphological structure. Also, to minimize the amount of deformation during non-linear spatial normalization, a pediatric template should be used. Further implications of our findings on developmental neuroimaging studies are discussed.

Correlation of white matter diffusivity and anisotropy with age during childhood and adolescence: a cross-sectional diffusion-tensor MR imaging study

PURPOSE

To evaluate differences in white matter diffusion properties as a function of age in healthy children and adolescents.

MATERIALS AND METHODS

Echo-planar diffusion-tensor magnetic resonance (MR) imaging was performed in 33 healthy subjects aged 5-18 years who were recruited from a functional imaging study of normal language development. Results of neurologic, psychologic, and structural MR imaging examinations were within the normal range for all subjects. The trace of the apparent diffusion coefficient and fractional anisotropy in white matter were correlated as a function of age by using Spearman rank correlation.

RESULTS

Statistically significant negative correlation of the trace of the apparent diffusion coefficient with age was found throughout the white matter. Significant positive correlation of fractional anisotropy with age was found in the internal capsule, corticospinal tract, left arcuate fasciculus, and right inferior longitudinal fasciculus.

CONCLUSION

Diffusion-tensor MR imaging results indicate that white matter maturation assessed at different ages involves increases in both white matter density and organization during childhood and adolescence. The trace of the apparent diffusion coefficient and fractional anisotropy may reflect different physiologic processes in healthy children and adolescents.

Age-related changes in regional activation during working memory in young adults: an fMRI study

Several lines of evidence suggest that working memory diminishes with advancing age, with concomitant functional changes in associated neuronal activation in frontal cortical regions and hippocampi. No studies to date, however, have investigated age-related changes in neuronal activation in these regions during performance of a working memory task in younger subjects without working memory deficits. In this study, we utilized fMRI to examine changes in brain activation with increasing age in specific regions-of-interest. Eleven healthy subjects performed a "two-back" working memory task and a matched "zero-back" attention task during fMRI. There was no association between age and performance on either task. Left hippocampal activation significantly correlated with age (P = 0.01) and right hippocampal activation showed an association with age (P = 0.09). This study demonstrates that increasing age is associated with increased activation of hippocampus even in young patients without evidence of working memory deficits and suggests that functional changes may precede overt evidence of working memory deficits.

Changes in neuronal activation with increasing attention demand in healthy volunteers: an fMRI study

Several lines of evidence suggest that structures involved in mediating attention differentially respond to increasing processing demand. Investigation of differences in neuronal activation, however, has been complicated by methodological inconsistencies and concomitant discrepancies in degree of difficulty and subject effort between disparate tasks. In this study, we utilized fMRI to compare neural activation patterns associated with two related attention tasks associated with different degrees of processing load while controlling for degree of performance difficulty. Healthy volunteers performed two continuous performance tasks, utilizing an identical pairs paradigm (CPT-IP) and a matched simple number recognition paradigm with degraded stimuli (CPT-DS) during a single fMRI scan. Degree of stimulus resolution degradation in the latter CPT was designed to equalize degree of performance difficulty between the two tasks. CPT-IP and CPT-DS were both associated with activation of frontal, limbic, subcortical, and sensory integratory structures. CPT-IP administration was associated with significantly greater activation of left dorsolateral prefrontal cortex, bilateral posterior temporal cortex, bilateral putamen, and thalamus. This study demonstrates both that differing attention tasks are associated with a high degree of functional overlap and that increasing processing demand is associated with increased activation of specific portions of attentional networks.

Changes in neuronal activation with increasing attention demand in healthy volunteers: an fMRI study

Several lines of evidence suggest that structures involved in mediating attention differentially respond to increasing processing demand. Investigation of differences in neuronal activation, however, has been complicated by methodological inconsistencies and concomitant discrepancies in degree of difficulty and subject effort between disparate tasks. In this study, we utilized fMRI to compare neural activation patterns associated with two related attention tasks associated with different degrees of processing load while controlling for degree of performance difficulty. Healthy volunteers performed two continuous performance tasks, utilizing an identical pairs paradigm (CPT-IP) and a matched simple number recognition paradigm with degraded stimuli (CPT-DS) during a single fMRI scan. Degree of stimulus resolution degradation in the latter CPT was designed to equalize degree of performance difficulty between the two tasks. CPT-IP and CPT-DS were both associated with activation of frontal, limbic, subcortical, and sensory integratory structures. CPT-IP administration was associated with significantly greater activation of left dorsolateral prefrontal cortex, bilateral posterior temporal cortex, bilateral putamen, and thalamus. This study demonstrates both that differing attention tasks are associated with a high degree of functional overlap and that increasing processing demand is associated with increased activation of specific portions of attentional networks.

MR imaging of murine arthritis using ultrasmall superparamagnetic iron oxide particles

The objective of this work was to determine the ability of magnetic resonance (MR) imaging with ultrasmall superparamagnetic iron oxide (USPIO) particles to provide quantitative measures of inflammation in autoimmune arthritis. Mice were injected intravenously or intra-articularly with USPIO followed by magnetic resonance and histological assessment of the knee joint. Comparisons were made between MR microimages and histology in naïve mice and mice with collagen-induced arthritis.Following intravenous administration, accumulation of USPIO was observed in the popliteal lymph nodes, but not the joint. Administration of USPIO intra-articularly resulted in signal loss in the joint. The MR signal intensity could be quantified and correlated with iron staining in the synovial lining. A marked increase in USPIO uptake and a corresponding decrease in signal intensity were observed in arthritic, compared to naïve mice. Areas of focal signal loss corresponded to foci of iron staining by histology. These studies may provide a basis for the clinical application of USPIO in arthritis for assessing disease severity and monitoring response to therapy.