Association Between Flow Acceleration in the Carotid Artery and Intracranial Aneurysms.

OBJECTIVES: In physiologic pulsatile flow, velocity acceleration is an independent factor determining wall shear stress experienced by the vascular endothelium. The purpose of this study was to evaluate Doppler indices of systolic velocity acceleration in extracranial cerebral vessels and the occurrence of intracranial aneurysms. METHODS: We reviewed medical records and 3.0-T brain magnetic resonance imaging with 3-dimensional time-of-flight magnetic resonance angiography of 1323 adults who underwent health checkups from June 2006 to November 2011, in whom 53 intracranial aneurysms were identified in 45 patients. Doppler ultrasound parameters of the carotid and vertebral arteries were analyzed in these 45 patients with aneurysms and compared with another 45 control participants matched for age and sex. We defined the maximum systolic acceleration (ACCmax ) as the maximum slope of the early phase of systolic acceleration on the Doppler waveform and the maximum acceleration index (AImax ) as the ratio of the ACCmax and peak systolic velocity. RESULTS: The Doppler analysis showed a significantly increased AImax and ACCmax in the common carotid artery (CCA), internal carotid artery, and vertebral artery in the aneurysm group. A cutoff 13.89 s-1 for the AImax of the CCA had sensitivity of 80% with a negative predictive value of 99% for intracranial aneurysms. CONCLUSIONS: This study suggests that the AImax of the CCA with a cutoff of 13.89 s-1 may be an alternative to 3-dimensional time-of-flight magnetic resonance angiography or computed tomographic angiography as a screening tool for intracranial aneurysms. Further prospective studies are needed to validate the diagnostic performance and cost-effectiveness of these indices for screening.

The relationships between brain structural changes and perceived loneliness in older adults suffering from late-life depression.

OBJECTIVE: Late-life depression is a significant health risk factor for older adults, part of which is perceived loneliness. In this voxel-based morphometry study, we examined the relationships between perceived loneliness and depression recurrence. METHODS: Fifty-two older adults were recruited, and they were split into 3 groups: single episode, multiple episodes, or normal control groups, according to their clinical histories. RESULTS: This result suggests the level of functioning regarding the reward system may be negatively related to the number of depressive episodes. Taken together, the findings of this study offer important insight into the neural underpinnings of the course and chronicity of late-life depression.

Dual-phase 18F-florbetapir positron emission tomography in patients with primary progressive aphasia, Alzheimer's disease, and healthy controls: A preliminary study.

BACKGROUND/PURPOSE: To determine whether dual-phase 18F-florbetapir positron emission tomography imaging with perfusion-like and amyloid deposition information can distinguish among primary progressive aphasia (PPA), Alzheimer's disease (AD), and healthy controls (HCs). METHODS: Patients diagnosed with PPA, including four semantic dementia (SD) and two progressive nonfluent aphasia (PNFA), as well as one logopenic variant (LV) of PPA, were studied. All PPA patients, and age-/sex-matched patients with probable AD (n=8) and HCs (n=8) were subjected to dual-phase 18F-florbetapir imaging. Atlas-based quantitative volumes of interest (VOIs) analysis for six cortical areas and whole cerebellum was performed. The standardized uptake value ratios were calculated by normalizing the dual-phase-integrated activities of the six VOIs to whole cerebellum counts. RESULTS: Early phase 18F-florbetapir image showed significantly lower global perfusion index in six PPA patients as compared with HCs. According to VOI analysis, the hypoperfusion lesions were identified in the frontal, anterior cingulate, parietal, precuneus, and temporal regions. Similar findings were confirmed by voxel-base image comparison. 18F-florbetapir late-phase image showed significantly increased amyloid burden in the global cortex index and all six brain regions of eight AD and LV patients when compared with the other six PPA patients and eight HCs. There was no apparent uptake of amyloid tracer in both six PPA patients and eight HCs. CONCLUSION: Dual-phase 18F-florbetapir images of six PPA (SD and PNFA) patients showed hypoperfusion in the frontotemporal cortex, and little global amyloid uptake, which may be a distinct image pattern for differentiation among HC, AD, and PPA patients.

Alterations of diffusion tensor MRI parameters in the brains of patients with Parkinson's disease compared with normal brains: possible diagnostic use.

OBJECTIVES: To investigate the diagnostic performance of diffusion tensor imaging in patients with Parkinson's disease (PD). METHODS: We examined a total of 126 PD patients (68 males/58 females, mean age: 62.0 ±7.6 years) and 91 healthy controls (43 males/48 females, mean age: 59.8 ±7.2 years). Images were acquired on a 3 Tesla magnetic resonance scanner. The Camino software was used to normalize and parcellate diffusion-weighted images into 90 cerebral regions based on the automatic anatomical labelling template. The minimum, median, and maximum values of the mean/radial/axial diffusivity/fractional anisotropy were determined. The diagnostic performance was assessed by receiver operating characteristic analysis. The associations of imaging parameters with disease severity were tested using Pearson's correlation coefficients after adjustment for disease duration. RESULTS: Compared with healthy controls, PD patients showed increased diffusivity in multiple cortical regions that extended beyond the basal ganglia. An area under curve of 85 % was identified for the maximum values of mean diffusivity in the ipsilateral middle temporal gyrus. The most significant intergroup difference was 26.8 % for the ipsilateral inferior parietal gyrus. CONCLUSION: The measurement of water diffusion from the parcellated cortex may be clinically useful for the assessment of PD patients. KEY POINTS: • Increased diffusivity was identified in multiple cortical regions of Parkinson's disease patients. • The area under the receiver operating curve was 85 % in the middle temporal gyrus. • The ipsilateral inferior parietal gyrus showed the most significant change.

Neural correlates of motor recovery after robot-assisted stroke rehabilitation: a case series study.

Robot-assisted bilateral arm therapy (RBAT) has shown promising results in stroke rehabilitation; however, connectivity mapping of the sensorimotor networks after RBAT remains unclear. We used fMRI before and after RBAT and a dose-matched control intervention (DMCI) to explore the connectivity changes in 6 subacute stroke patients. Sensorimotor functions improved in the RBAT and DMCI groups after treatment. Enhanced activation changes were observed in bilateral primary motor cortex (M1) and bilateral supplementary motor area (SMA) after RBAT. Dynamic causal model analysis revealed that interhemispheric connections were enhanced in RBAT patients. These preliminary findings suggest that intracortical and intercortical coupling might underlie poststroke RBAT.

Human amygdala activation by the sound produced during dental treatment: A fMRI study.

During dental treatments, patients may experience negative emotions associated with the procedure. This study was conducted with the aim of using functional magnetic resonance imaging (fMRI) to visualize cerebral cortical stimulation among dental patients in response to auditory stimuli produced by ultrasonic scaling and power suction equipment. Subjects (n = 7) aged 23-35 years were recruited for this study. All were right-handed and underwent clinical pure-tone audiometry testing to reveal a normal hearing threshold below 20 dB hearing level (HL). As part of the study, subjects initially underwent a dental calculus removal treatment. During the treatment, subjects were exposed to ultrasonic auditory stimuli originating from the scaling handpiece and salivary suction instruments. After dental treatment, subjects were imaged with fMRI while being exposed to recordings of the noise from the same dental instrument so that cerebral cortical stimulation in response to aversive auditory stimulation could be observed. The independent sample confirmatory t-test was used. Subjects also showed stimulation in the amygdala and prefrontal cortex, indicating that the ultrasonic auditory stimuli elicited an unpleasant response in the subjects. Patients experienced unpleasant sensations caused by contact stimuli in the treatment procedure. In addition, this study has demonstrated that aversive auditory stimuli such as sounds from the ultrasonic scaling handpiece also cause aversive emotions. This study was indicated by observed stimulation of the auditory cortex as well as the amygdala, indicating that noise from the ultrasonic scaling handpiece was perceived as an aversive auditory stimulus by the subjects. Subjects can experience unpleasant sensations caused by the sounds from the ultrasonic scaling handpiece based on their auditory stimuli.

A simple method to improve the quality of diffusion-weighted magnetic resonance imaging with rapid histologic correlation in a murine model.

Diffusion-weighted magnetic resonance imaging (DW-MRI) has been used extensively in biomedical research. However, this technique has often suffered from distortion artifacts because of the magnetic field inhomogeneity surrounding the tissues. Histology is important for validating MRI interpretations, but correlating MRIs with tissue samples is challenging. Here we propose a method to improve DW-MRI and facilitate the matching between MRIs and tissue samples. A cryostat embedding medium, optimal cutting temperature (OCT) compound, was used to cover the examined target during the MRI studies. Frozen OCT compound could aid the examined target to be sectioned in parallel with the imaging plane. Phantom experiments demonstrated that embedding in OCT compound improved the magnetic field inhomogeneity while maintaining the apparent diffusion coefficient. Animal experiments revealed significantly reduced distortions in DW images in both the axial and coronal planes. The in vivo MRIs were easily matched with histologic specimens in a slice-to-slice fashion to examine the corresponding tissue microenvironment. This simple method might improve the quality of DW-MRI and provide histologic information for MRI to serve as an image biomarker.

Increased brain amyloid deposition in patients with a lifetime history of major depression: evidenced on 18F-florbetapir (AV-45/Amyvid) positron emission tomography.

PURPOSE: The literature suggests that a history of depression is associated with an increased risk of developing Alzheimer's disease (AD). The aim of this study was to examine brain amyloid accumulation in patients with lifetime major depression using (18)F-florbetapir (AV-45/Amyvid) PET imaging in comparison with that in nondepressed subjects. METHODS: The study groups comprised 25 depressed patients and 11 comparison subjects who did not meet the diagnostic criteria for AD or amnestic mild cognitive impairment. Vascular risk factors, homocysteine and apolipoprotein E (ApoE) genotype were also examined. The standard uptake value ratio (SUVR) of each volume of interest was analysed using whole the cerebellum as the reference region. RESULTS: Patients with a lifetime history of major depression had higher (18)F-florbetapir SUVRs in the precuneus (1.06 ± 0.08 vs. 1.00 ± 0.06, p = 0.045) and parietal region (1.05 ± 0.08 vs. 0.98 ± 0.07, p = 0.038) than the comparison subjects. Voxel-wise analysis revealed a significantly increased SUVR in depressed patients in the frontal, parietal, temporal and occipital areas (p < 0.01). There were no significant associations between global (18)F-florbetapir SUVRs and prior depression episodes, age at onset of depression, or time since onset of first depression. CONCLUSION: Increased (18)F-florbetapir binding values were found in patients with late-life major depression relative to comparison subjects in specific brain regions, despite no differences in age, sex, education, Mini Mental Status Examination score, vascular risk factor score, homocysteine and ApoE ε4 genotype between the two groups. A longitudinal follow-up study with a large sample size would be worthwhile.

A comparison of benign and inflammatory manifestations of Tolosa-Hunt syndrome.

BACKGROUND: Tolosa-Hunt syndrome (THS) manifests as a benign or an inflammatory type disease. The nosography differences between these types remain to be elucidated. We aimed to analyze and compare the clinical presentations of benign and inflammatory THS. METHODS: The ward patients who presented with THS from January 1990 to May 2011 were retrospectively reviewed. THS was diagnosed according to the recommendations of the International Headache Society. RESULTS: Of the 53 THS cases (49 patients), 30 (56.6%) were classified as benign and 23 (43.4%) as inflammatory THS. There were strong similarities between the groups in terms of clinical manifestations, laboratory findings, responses to glucocorticoid treatment, and outcomes. However, patients with inflammatory THS tended to be younger (mean age, 43.4 years; P 0.05) and have optic nerve dysfunction (56.5%; P 0.05) and longer disease duration (2.3 ± 1.0 months; P 0.05) compared to those with benign THS (mean age, 56.4 years; mean disease duration, 1.6 ± 0.7 months). The patients with additional involvement of both the optic nerve and the second division of the trigeminal nerve experienced a longer disease duration ( P 0.05). Additionally, patients with orbital pseudotumors had diplopia that responded poorly to treatment with glucocorticoids ( P 0.05). High-dose (>0.5 mg/kg/day) and low-dose (≤0.5 mg/kg/day) prednisolone were equally effective in relieving symptoms in both groups ( P > 0.05). CONCLUSION: Benign and inflammatory THS were highly similar in terms of nosography. The responses to glucocorticoid treatment were generally good except in patients with orbital pseudotumors.

Blind estimation of the arterial input function in dynamic contrast-enhanced MRI using purity maximization.

Uncertainty in arterial input function (AIF) estimation is one of the major errors in the quantification of dynamic contrast-enhanced MRI. A blind source separation algorithm was proposed to determine the AIF by selecting the voxel time course with maximum purity, which represents a minimal contamination from partial volume effects. Simulations were performed to assess the partial volume effect on the purity of AIF, the estimation accuracy of the AIF, and the influence of purity on the derived kinetic parameters. In vivo data were acquired from six patients with hypopharyngeal cancer and eight rats with brain tumor. Results showed that in simulation the AIF with the highest purity is closest to the true AIF. In patients, the manually selection had reduced purity, which could lead to underestimations of K(trans) and V(e) and an overestimation of V(p) when compared with those obtained by the proposed blind source separation algorithm. The derived kinetic parameters in the tumor were more susceptible to the changes in purity when compared with those in the muscle. The animal experiment demonstrated good reproducibility in blind source separation-AIF derived parameters. In conclusion, the blind source separation method is feasible and reproducible to identify the voxel with the tracer concentration time course closest to the true AIF.

Effect of growth hormone therapy on Taiwanese children with growth hormone deficiency.

BACKGROUND/PURPOSE: Human growth hormone (GH) has been successfully used in children with GH deficiency (GHD). However, there are few published data on the effect of GH in Taiwanese children with GHD. METHODS: We performed a retrospective cohort study to identify factors influencing the effect of GH therapy on ethnic Chinese children with GHD in Taiwan. Idiopathic GHD can be classified into isolated GHD (IGHD) and multiple pituitary hormone deficiency (MPHD). The study looked at the effect of GH on the auxological, biochemical, and imaging parameters of 51 patients (13 girls and 38 boys) in three different diagnostic groups: MPHD (n = 12), IGHD (n = 8), and transient GHD (TGHD; n = 31). TGHD is defined as a GH peak >10 µg/L in re-evaluation by two GH stimulation tests approximately 6 months after discontinuation of GH therapy. RESULTS: The height velocity for first-year GH therapy was 7.61 ± 1.46, 8.14 ± 1.92, and 9.99 ± 2.75 cm/y in the TGHD, IGHD, and MPHD groups, respectively. After post hoc comparison, the MPHD group had a significantly accelerated height velocity in the first year compared to the TGHD group. Correlation analysis showed that a change in height standard deviation score (SDS) in the first year had a significant negative correlation with the following variables: peak GH (r = -0.52, p < 0.001), pretreatment height SDS (r = -0.49, p < 0.001), and height-target height (Ht-TH) SDS (r = -0.49, p < 0.001). Change in height SDS in the first 2 years had a significantly negative correlation with peak GH (r = -0.51, p < 0.001), insulin-like growth factor-1 SDS (r = -0.35, p = 0.022), height SDS (r = -0.60, p < 0.001), difference between bone age and chronological age (r = -0.46, p = 0.001), and Ht-TH SDS (r = -0.50, p = 0.001). After using multiple linear regression, the pretreatment GH peak value was found to be significantly associated with height increments after 1 year of GH treatment (B = -0.07, p = 0.014). CONCLUSION: The administration of GH to children with GHD results in a pronounced acceleration in linear growth during the first year of treatment, especially in those with MPHD. The diagnosis of GHD requires comprehensive auxological, biochemical, and brain magnetic resonance imaging assessment. We also suggest that patients with GHD, specifically IGHD, must undergo a re-evaluation of GH secretion after completion of GH therapy.

Parkinson disease: diagnostic utility of diffusion kurtosis imaging.

PURPOSE: To examine the usefulness of diffusion kurtosis imaging for the diagnosis of Parkinson disease (PD). MATERIALS AND METHODS: Examinations were performed with the understanding and written consent of each subject, with local ethics committee approval, and in compliance with national legislation and Declaration of Helsinki guidelines. Diffusion-weighted magnetic resonance imaging was performed in 30 patients with idiopathic PD (mean age, 64.5 years ± 3.4 [standard deviation]) and 30 healthy subjects (mean age, 65.0 years ± 5.1). Mean kurtosis, fractional anisotropy, and mean, axial, and radial diffusivity of the basal ganglia were compared between the groups. Disease severity was assessed by using Hoehn and Yahr staging and the motor section of the Unified Parkinson's Disease Rating Scale (mean scores, 2.0 and 33.6, respectively). Receiver operating characteristic (ROC) analysis was used to compare the diagnostic accuracies of the indexes of interest. Pearson correlation coefficient analysis was used to correlate imaging findings with disease severity. RESULTS: Mean kurtosis in the putamen was higher in the PD group (0.93 ± 0.15) than in the control group (0.71 ± 0.09) (P < .000416). The area under the ROC curve (AUC) was 0.95 for both the ipsilateral putamen and the ipsilateral substantia nigra. The mean kurtosis for the ipsilateral substantia nigra had the best diagnostic performance (mean cutoff, 1.10; sensitivity, 0.92; specificity, 0.87). In contrast, AUCs for the tensor-derived indexes ranged between 0.43 (axial and radial diffusivity in substantia nigra) and 0.65 (fractional anisotropy in substantia nigra). CONCLUSION: Diffusion kurtosis imaging in the basal ganglia, as compared with conventional diffusion-tensor imaging, can improve the diagnosis of PD.

¹8F-FDG PET/CT and 3.0-T whole-body MRI for the detection of distant metastases and second primary tumours in patients with untreated oropharyngeal/hypopharyngeal carcinoma: a comparative study.

PURPOSE: The aim of this prospective study was to compare the diagnostic value of (18)F-FDG PET/CT and 3.0-T whole-body MRI (WB-MRI) for the assessment of distant metastases and second primary cancer (SPC) in patients with untreated oropharyngeal or hypopharyngeal squamous cell carcinoma (OHSCC). METHODS: A total of 103 patients were enrolled. All participants underwent 3.0-T WB-MRI and (18)F-FDG PET/CT. The diagnostic capabilities of the two imaging modalities were compared using the area under the receiver-operating-characteristic curve. Histology and follow-up data were used as the reference standard. RESULTS: Of the 103 patients, 18 (17.5%) were found to have either distant metastases or SPC. A total of 21 sites were involved. On a lesion-based analysis, (18)F-FDG PET/CT showed a trend toward a higher sensitivity than WB-MRI (81.0% vs. 61.9%, P = 0.125). The area under the curve (AUC) for PET/CT was also higher than for WB-MRI, although not significantly so (0.932 vs. 0.866, P = 0.189). On a patient-based analysis, the sensitivity of WB-MRI was lower than that of PET/CT (66.7% vs. 83.3%, P = 0.625). In terms of diagnostic capability, the AUC was higher for PET/CT than WB-MRI (0.886 vs. 0.813, P = 0.355). The maximal SUV of the regional lymph nodes (SUVn) above the median value (8.7 g/ml) was significantly associated with the occurrence of distant metastasis (P = 0.026). CONCLUSION: (18)F-FDG PET/CT showed a consistent trend toward higher sensitivity and diagnostic capability than 3.0-Tesla WB-MRI for the detection of distant metastases and SPCs in patients with untreated OHSCC. Our data also suggest that SUVn assessed by PET/CT can provide additional information for the prediction of distant metastases.

Validation of the jugular venous reflux animal model by three-dimensional time-of-flight MRA with a clinical scanner.

BACKGROUND AND PURPOSE: A rat model of jugular venous reflux (JVR) is widely used in studies of cerebral arteriovenous fistula, cerebral venous hypertension and chronic cerebral hypoperfusion. However, methods to validate the effectiveness of the operation are needed. METHODS: We performed neck 3-dimensional time-of-flight magnetic resonance angiography (MRA) with a clinical scanner in a rat model of JVR before and after the operation. High-resolution arterial angiography of the rat neck was acquired with maximum intensity projection. RESULTS: In the JVR model, the success of the operation was validated by enhanced venous structures on MRA. The angiogram also provided information on the height of JVR and the status of other neck vessels. CONCLUSIONS: In conclusion, neck 3-dimensional time-of-flight MRA is a useful noninvasive method for monitoring the blood flow in multiple cerebral vessels in this animal model. It also revealed the height of JVR, collateral development and changes in vessels over time in longitudinal studies. This information should be considered in the evaluation of the animal model.

Pretreatment evaluation of distant-site status in patients with nasopharyngeal carcinoma: accuracy of whole-body MRI at 3-Tesla and FDG-PET-CT.

We sought to prospectively evaluate the accuracy of 3.0-Tesla whole-body magnetic resonance imaging (WB-MRI) and integrated fluorodeoxyglucose (FDG) positron emission tomography (PET)/computed tomography (CT) (FDG-PETCT), and their combined interpretation for the assessment of distant-site status in 150 patients with untreated nasopharyngeal carcinoma (NPC). Eighteen (12%) patients were diagnosed as having distant malignancies (15 patients had distant metastases, and three distant synchronous tumours). On a patient-based analysis, WB-MRI and FDG-PET-CT showed similar sensitivity (77.8% vs 72.2%, P>0.999), specificity (98.5% vs 97.7%, P > 0.999) and diagnostic capability (0.905 vs 0.878, P = 0.669). Combined interpretation of WB-MRI and FDGPET-CT showed no significant benefit over either technique alone. In conclusion, 3.0-Tesla WB-MRI is a feasible, non-ionising technique that showed similar diagnostic capacity to FDG-PET-CT in assessing distant-site status in patients with untreated NPC and can be recommended as the first-line imaging technique for comprehensive evaluation of such patients.

The neural correlates of perceived energy levels in older adults with late-life depression.

Late-life depression is common among older adults. Although white-matter abnormality is highly implicated, the extent to which the corticospinal tract is associated with the pathophysiology of late-life depression is unclear. The current study aims to investigate the white-matter structural integrity of the corticospinal tract and determine its cognitive and functional correlates in older adults with late-life depression. Twenty-eight older adults with clinical depression and 23 healthy age-matched older adults participated in the study. The white matter volume and the white matter hyperintensities (WMHs) of the corticospinal tract, as well as the global WMHs, were measured. Psychomotor processing speed, severity of depression, perceived levels of energy and physical functioning were measured to examine the relationships among the correlates in the depressed participants. The right corticospinal tract volume was significantly higher in depressed older adults relative to healthy controls. Moreover, the right corticospinal tract volume was significantly associated with the overall severity of depression and accounted for 17% of its variance. It further attenuated the relationship between the severity of depression and perceived levels of energy. Our findings suggested that higher volume in the right corticospinal tract is implicated in LLD and may relate to lower perceived levels of energy experienced by older adults with depression.

Inflow effects on hemodynamic responses characterized by event-related fMRI using gradient-echo EPI sequences.

The purpose of this study is to determine whether blood inflow impacts the temporal behavior of BOLD-contrast fMRI signal changes in a typical event-related paradigm. The inflow contributions in the hemodynamic response to repeated single trials of short visual stimulation were assessed with a gradient-echo EPI sequence by altering the flip angle (FA) from 30 degrees to 90 degrees at a repetition time of 1 s. For each FA condition (30 degrees, 60 degrees, and 90 degrees), 30 trials were performed on 15 healthy volunteers on a 3T MRI scanner. Comparing the percent BOLD contrast, prominent inflow effects were found with statistical significance between the 90 degrees- and 30 degrees-FA conditions (0.73 +/- 0.15 versus 0.67 +/- 0.12%, p=0.028). BOLD responses with FA=30 degrees exhibited latencies significantly slower than those with FA=90 degrees (3.69 +/- 0.39 s versus 3.37 +/- 0.28 s, p=0.001). The falling time of the 30 degrees-FA responses was earlier but not statistically different from that of the 90 degrees-FA (8.17 +/- 1.04 s versus 8.03 +/- 1.15 s, p=0.3). Using a voxelwise analysis, the latency variations of the activated visual areas were determined at several contrast-to-noise ratio (CNR) levels (controlled by averaging different numbers of randomly selected trials). The latency variations from the 90 degrees-FA responses were greater at lower CNR but similar at higher CNR levels when comparing to the 30 degrees-FA ones. This study suggests that inflow effects contribute to the BOLD signal, resulting in hemodynamic response with shorter latency.

Hemorrhage detection during focused-ultrasound induced blood-brain-barrier opening by using susceptibility-weighted magnetic resonance imaging.

High-intensity focused ultrasound has been discovered to be able to locally and reversibly increase the permeability of the blood-brain barrier (BBB), which can be detected using magnetic resonance imaging (MRI). However, side effects such as microhemorrhage, erythrocyte extravasations or even extensive hemorrhage may also occur. Although current contrast-enhanced T1-weighted MRI can be used to detect the changes in BBB permeability, its efficacy in detecting tissue hemorrhage after focused-ultrasound sonication remains limited. The purpose of this study is to investigate the feasibility of magnetic resonance susceptibility-weighted imaging (MR-SWI) for identifying possible tissue hemorrhage associated with disruption of the BBB induced by focused ultrasound in a rat model. The brains of 42 Sprague-Dawley rats were subjected to 107 sonications, either unilaterally or bilaterally. Localized BBB opening was achieved by delivering burst-mode focused ultrasound energy into brain tissue in the presence of microbubbles. Rats were studied by T2-weighted and contrast-enhanced T1-weighted MRI techniques, as well as by SWI. Tissue changes were analyzed histologically and the extent of apoptosis was investigated with the terminal deoxynucleotidyl transferase biotin-dUTP nick-end labeling method. The results demonstrated that SWI is more sensitive than standard T2-weighted and contrast-enhanced T1-weighted MRI techniques in detecting hemorrhages after brain sonication. Longitudinal study showed that SWI is sensitive to the recovery process of the damage and, therefore, could provide important and complementary information to the conventional MR images. Potential applications such as drug delivery in the brain might be benefited.

Cortical reorganization for response regulation with unilateral thalamic stroke detected by functional MRI.

To understand neural reorganization of response regulation after stroke, a 54-year-old woman with a chronic left thalamic stroke performed a task requiring decisions about the directionality of an arrow during cerebral functional magnetic resonance imaging. Her performance was compared to 13 matched healthy control subjects. Her behavioral responses were slower but as accurate. Bilateral frontal activations were observed in the right medial frontal gyrus (BA 9), left superior frontal gyrus (BA 45), and left frontal rectus gyrus (BA 11). Activation in the right medial frontal gyrus, along with activity in close proximity to the anterior cingulate cortex, was observed, which may reflect reorganization of activity after the loss of function of the anterior cingulate cortex.

The effects of single-trial averaging on the temporal resolution of functional MRI.

Computer simulations and event-related functional MRI (ER-fMRI) experiments were performed to investigate the effects of single-trial averaging and the corresponding contrast-to-noise ratio (CNR) on the minimal resolvable hemodynamic timing difference between brain areas. Three ER-fMRI sessions with temporally delayed (250, 500 and 1,000 ms) visual stimulations between two hemifields, each with 70 repeated single trials, were examined on two subjects. From the computer simulation, the temporal resolution improved as the CNR increased, which reached 500 and 100 ms for CNRs of 1.55 and 6.44, respectively. In the ER-fMRI experiments, the measured CNR increased as more single trials were averaged. The detectability of temporal differences was positively correlated (P<.05) with the CNR in all sessions for one subject but only in the 1,000-ms session for the other subject. Temporal resolution of 1,000 ms was achieved when more than 10 trials were averaged. The 500- and 250-ms delays might be differentiable when more than 20 trials were averaged, but the results were subject-dependent. This study demonstrated that the CNR could be significantly improved by single-trial averaging, which led to an improved temporal resolution of ER-fMRI. Temporal resolution in the range of hundreds of milliseconds was subject-dependent, which might be attributed to the intrinsic spatial variations in the timing of the blood oxygenation level-dependent (BOLD) response.