Tesla MR Scanner Research Articles

Altered Cerebrovenous Drainage in Patients With Migraine as Assessed by Phase-Contrast Magnetic Resonance Imaging

We aimed to assess whether migraine is associated with changes in the distribution of the venous drainage through primary and secondary pathways by using phase-contrast magnetic resonance imaging (MRI). We examined 26 patients (37.3 ± 13.9 years) with recurring migraine headaches and 26 age- and gender-matched controls with no neurologic disease (37.3 ± 13.7 years) on a 3 Tesla MR scanner. A 2D time-of-flight MR-venography of the upper neck region was performed to visualize the venous vasculature. Cine-phase contrast scans with high-velocity encoding were employed to quantify arterial inflow and flow in the primary venous channels (right and left jugular veins), whereas scans with low-velocity encoding were employed to quantify flow in the secondary venous channels (epidural, vertebral, and deep cervical veins). Patients with migraine showed (i) a higher prevalence of dense secondary extracranial venous networks (15 vs. 2, P = 0.00002) and (ii) a significantly larger percentage of venous outflow through secondary channels (10.5% vs. 5.5%; of total cerebral blood flow, P = 0.02). This mainly included drainage through epidural, vertebral, and deep cervical veins. Migraine patients showed a significantly larger percentage of venous outflow through secondary channels. The mechanism of this alteration remains to be elucidated. Potential mechanisms include repeated release of vasoactive substances or growth factors.

Grasping-Related Functional Magnetic Resonance Imaging Brain Responses in the Macaque Monkey

Research in recent decades has suggested the existence of a dedicated brain network devoted to the organization and execution of grasping, one of the most important and skilled movements of primates. Grasping an object requires the transformation of intrinsic object properties such as size, orientation, and shape into an appropriate motor scheme shaping the hand. Although electrophysiological recordings in the monkey model have proven invaluable for gaining insights into the neuronal substrate underlying this complex behavior, knowledge concerning the existence and organization of a similar system in the human brain is derived mainly from imaging studies. Here, we present for the first time functional magnetic resonance imaging (fMRI) of brain activity while macaque monkeys performed reaching and grasping movements in a 3 tesla MR scanner. Grasping in the dark (compared with reaching) yielded significant activations in anterior intraparietal area and ventral premotor area F5, in addition to area PFG in the rostral inferior parietal lobule, somatosensory areas (SI, SII, area 5), and the hand field of F1. Whole-brain macaque fMRI motor studies will be instrumental in establishing possible homologies concerning grasping organization in the human and monkey brains, bridging the gap between human imaging and monkey electrophysiology.

SU‐E‐T‐281: Quantitative Evaluation of the MRI Image Distortion in Gamma Knife Radiosurgery

Purpose: To quantify the spatial distortion of the MRI images in the Elekta Leksell GammaPlan version 9 planning system using different registration methods. Methods: The RPC SRS phantom was imaged using a GE Signa HDxt 1.5Tesla MR scanner and a GE LightSpeed VCT CT scanner. Both the T1 weighted MRI images and the fast imaging employing steady state acquisition (FIESTA) MRI images were acquired, along with the axial and helical CT images. The skull shell and the target in the phantom were contoured in all the four series of images acquired. The MRI images were registered in the planning system in three different ways: 1) using the fiduciary marks in the imaging box; 2) using a global co‐registration with FOV just covering skull shell; 3) using a local co‐registration to max 8.5cm FOV at image center. The target positions in all the four series of images were compared using the software tool in the planning system. Results: The target positions as obtained from the helical and the axial CT images agree within 0.1mm. For the registration method the fiduciary marks, the T1 weighted MRI images are shifted from the CT images 0.9mm in the anterior‐posterior direction, and 0.5mm in both the superior‐inferior and the left‐right directions. The corresponding displacements for the FIESTA images are 0.6mm, 0.5mm and 0.5mm respectively. The shifts of the target positions are significantly reduced in the global co‐registration approach, and all less than 0.2mm in the local co‐registration approach. Conclusions: MRI image distortion in GammaPlan version 9 is in the sub‐millimeter range for the central region of the MRI image. The spatial distortion in the FIESTA images is smaller than that in the T1 weighted images. Co‐registration to the central region of images can reduce MRI imaging distortion effect significantly.

Diagnostic value of apparent diffusion coefficient calculated with diffusion-weighted MRI for quantification of liver fibrosis

Aim of the workTo evaluate the diagnostic values of the hepatic ADC calculated with diffusion-weighted MRI for quantification of the hepatic fibrosis in patients with chronic viral hepatitis. Subjects and methodsThirty-eight chronic viral hepatitis C patients with similar control group were examined by 1.5 Tesla MR scanner with diffusion gradient encoding in three orthogonal directions at b values of (300, 500, 700, and 1000s/mm2). They were correlated to biopsy finding and graded according to Ishak scoring system. Hepatic ADC values were measured for both patients and control groups. ResultsThe best correlation between ADC values and biopsy were seen at b values 300, 700, and 1000s/mm2, which showed high sensitivity, specificity, positive, and negative predictive values, with lesser correlation were obtained at b values of 500s/mm2. Cut off values between different grades of fibrosis were calculated and presented in the text. ConclusionADC measured with DWI is a reliable non-invasive technique for quantification of liver fibrosis, and could replace liver biopsy in certain cases.

MR enterography in the investigation of abdominal pain

IntroductionMagnetic Resonance Enterography (MRE) has an established role in the management of patients with small bowel Crohn's disease1 and has the advantages of diagnosing extra-enteric lesions which may be clinically...

White matter anatomy of the human deep brain revisited with high resolution DTI fibre tracking

Background and PurposeDeep white matter (WM) fascicles play a major, yet poorly understood, role in the overall connectivity of human brain. Better knowledge of their anatomy is requisite to understand the clinical correlates of their lesions and develop targeted treatments. We investigated whether MR-based diffusion tensor imaging (DTI) and fibre tracking could reveal in vivo, in explicit details, the 3D WM architecture within the subthalamic region and the internal capsule. MethodsHigh-resolution DTI images were acquired on six healthy volunteers on a three Tesla MR scanner. We studied using single-subject analysis WM fascicles within the subthalamic region and the internal capsule, as follows: DTI deterministic fibre tracking (FT) of fascicles; embedding fascicles in the volume-rendered brain coupled with a triplanar view; rigorous anatomic labelling of each fascicle according to classical knowledge as described by pioneer neuroanatomists. Deterministic FT effects were taken into account. ResultsWe charted most of WM fascicles of the deep brain, in particular large and complex fascicles such as the basal forebrain bundle and the ansa lenticularis. A topographic classification of subthalamic fascicles was proposed into three groups: the cerebellorubral, the reticulo-dorsal and the tegmento-peripheral one. ConclusionsBeyond to demonstrate the feasibility of imaging the deepest WM fascicles in vivo, our results pave the way for a better understanding of the brain connectivity and for developing targeted neuromodulation.

Evaluation of hippocampal volume based on MR imaging in patients with bipolar affective disorder applying manual and automatic segmentation techniques

To compare the hippocampal volumes in patients with bipolar disorder (BD) and healthy controls, obtained by applying different segmentation methods (manual, Freesurfer [FS], and FSL). The study included 27 patients with BD and 40 healthy controls. T1-weighted images in the sagittal plane were acquired on a 3 Tesla (T) MR scanner. Hippocampal volumetry was performed using one manual and two automated methods (FS and FSL). One-way repeated analysis of variance was applied to test the differences in hippocampal volumes using the three segmentation methods. To evaluate the agreement among the three tested volumetric segmentation methods the intraclass correlation coefficients (ICCs) were calculated. Hippocampal volumes obtained from all methods were significantly different (P < 0.05) in BD patients after intracranial volume correction, indicating a reduction in volume, unless from the manual method of the left hippocampal volume. The ICCs of the hippocampal volume between the manual method and FS were 0.846 (right) and 0.859 (left), and between the manual method and FSL were 0.746 (right) and 0.654 (left). Both manual and automatic segmentation methods detected reductions in the hippocampal volumes in BD patients. Automated segmentation methods are a robust and reproducible option for assessing hippocampal volume.

Correlates of Aortic Pulse wave velocity measured by cardiac MRI

Methods 223 consenting nondiabetic, normotensive volunteers without clinical cardiovascular disease or echocardiographic abnormalities (124 females, 116 hyperlipidemic (42 treated), age: 58.6+/-14.9yrs, BMI: 24.8+/-3.3 (24 with BMI>28) were studied. CMR studies were performed on a 1.5 Tesla MR scanner (Siemens, Germany) using a phased array surface-coil and a spine-coil array. PWV was assessed using breath-held through-plane phase-contrast gradient echo imaging of the ascending and descending aorta at the pulmonary artery level with a VENC of 1.5 m/sec, temporal resolution of 24 frames per second and slice thickness of 6mm. Aortic images were manually contoured using QFlow (Medis, Leiden, the Netherlands) and PWV determined by the ratio of the distance between the ascending and descending aortic plane along a candy-cane view over the time of pressure pulse travel in between. Pearson and Spearman correlation coefficients were used to examine associations between PWV and age, CCTscore, blood pressure (BP), rate pressure product(RPP), lipid levels, and cardiac function.

Cardiac MRI to investigate myocardial scar and coronary venous anatomy using a slow infusion of dimeglumine gadobenate in patients undergoing assessment for cardiac resynchronization therapy

To evaluate a cardiac MR (CMR) examination with slow infusion of a high-relaxivity contrast agent to visualize coronary venous anatomy (CVA) and myocardial scar in heart failure patients awaiting cardiac resynchronization therapy (CRT). Fourteen patients awaiting CRT (seven ischemic cardiomyopathy (ICM) and seven non-ICM) and two with normal LV function underwent CMR on a 1.5 Tesla (T) MR scanner. Dimeglumine-gadobenate was slowly infused. Bolus arrival in the LV was measured by a dynamic electrocardiogram (ECG) -triggered inversion recovery (IR) scan subsequent to starting an ECG-triggered respiratory-navigated three-dimensional (3D) SSFP MR scan with IR preparation to acquire systolic whole-heart anatomy for vein visualization. Delayed contrast-enhanced MR scan was performed to assess myocardial scar. CVA obtained by CMR was compared with X-ray venography in 11 patients. CVA and scar were segmented and registered for visual inspection. For all subjects, there was excellent visualization of the CVA. All ICM and one non-ICM patient showed scar. There was excellent correlation between veins seen by CMR and venography. We have demonstrated that slow infusion protocol of dimeglumine-gadobenate can be used to assess both CVA and myocardial scar in a single MR examination. Furthermore, an image overlay technique has been used to show the relationship of scar to the CVA.

Cardiac Iron Overload Assessed by T2* Magnetic Resonance (CMR) In Thalassemia Major Patients Treated with Different Iron Chelators

AbstractAbstract 4275 Introduction.Although iron chelation therapy has markedly improved the survival, heart failure due to myocardial iron overload still remains the leading cause of morbidity and mortality in adult thalassemia major (TM) patients. T2* cardiovascular magnetic resonance (CMR) is a non invasive technique that provides rapid and direct assessment of myocardial iron content and its usefulness in monitoring iron chelation has been proved (Wood et al, Circulation 2009). AIM OF THE STUDY. To evaluate the efficacy of different iron-chelation therapies on removal of cardiac iron content assessed by CMR in adult TM patients. PATIENTS AND METHODS. Sixty-seven TM patients (27 males/40 women, mean age 35 ± 6 yrs) treated with different iron chelators underwent repeated cardiac CMR to assess myocardial iron load. Myocardial T2* was assessed at baseline (t0), after 6–14 months (t1) (according to clinical conditions and to T2* at baseline), and as second control (t2) after a mean of 32±7 months from baseline. CMR was performed at Cardiology and CMR Department “A. De Gasperis” at Niguarda Ca' Granda Hospital in Milan, using a 1.5 Tesla MR scanner (Avanto Siemens, Erlangen). Normal cardiac T2* was defined > 20 ms; T2* < 10 ms indicated severe cardiac siderosis and T2* between 10 and 20 ms moderate-to-mild cardiac siderosis. Each patient has to be chelated with the same iron chelation therapy at least for 1 year before the baseline CMR evaluation. Patients were divided based on chelation therapy in 4 groups: group A (n=36, 53.7 %) patients chelated with deferasirox (DFX, mean actual dose 27±7 mg/Kg/die), group B (n=15, 22.4 %) deferoxamine (DFO, actual mean dose 48±9 mg/kg for a median of 6 days/week), group C (n=12, 17,9 %) DFO (mean actual dose 46±7 mg/kg for a median of 4 days/week) plus deferiprone (DFP, mean actual dose 73±7 mg/kg/day) and group D (n=4,6 %) only DFP (mean actual dose 75±0 mg/kg/day). Statistical analysis was performed using a paired Student's t-test. RESULTS. Overall, the pre-transfusional mean hemoglobin (Hb) was 9.7±0.5 g/dl, the median ferritin value was 913 ng/ml (range 229–5934 ng/ml) and the mean iron intake was 0.41±0.12 mg/Kg/day. In the overall population, the baseline myocardial T2* was < 10 ms in 8 patients (11.9 %), between 10 and 20 ms in 22 patients (32.8 %) and ≥ 20 ms in 37 patients (55.2 %). At baseline evaluation, T2* < 10 ms was detected only in 1 patient (1/36: 2.77 %) in group A, in 4 patients (4/15: 26.6 %) in group B and in 3 patients (3/12: 25 %) in group C. In group D all patients showed a myocardial T2* above 20 ms at baseline. Progressive changes in T2* values were observed at t1 and t2 for all the groups. Ten patients (10/36: 27.8 %) in group A, 3 patients (3/15: 20 %) in group B, 3 patients (3/12: 25%) in group C, respectively, moved from an abnormal T2* (< 20 ms) to normal values, in 32±7 months (Table 1). T2* values at t2 improved significantly compared to baseline (p=0.0006) in patients treated with DFX (group A). In patients treated with combination therapy (DFO and DFP), T2* increased more rapidly in those with severe siderosis (T2* < 10 ms) (p=0.006). No significant changes in left ventricular ejection fraction (LVEF) values were observed in all groups of patients: only patients in group A with baseline cardiac T2* between 10 and 20 ms showed a slight improvement in LVEF (p=0.049). No statistically significant reduction in ferritin levels were associated with ameliorating myocardial T2* values. DISCUSSION AND CONCLUSIONS. Our data showed that compliance to chelation therapy at proper doses significantly improve myocardial T2* over 3-year treatment period. Continued treatment with deferasirox significantly increase myocardial T2* over time, showing its efficacy to remove iron from the heart. DFO and DFP combination therapy seems to ameliorate cardiac T2* more rapidly only in patients with T2* < 10 ms at baseline.Table 1t0t1t2GROUP An.T2*(ms)n.T2*(ms)n.T2*(ms)T2* < 10 ms18.70–0–T2* 10–20 ms1315.3 ± 2.9125.8 ± 2.8415.8 ± 1.9T* > 20 ms2232.3 ± 6.52434.6 ± 6.83233.8 ± 8.0GROUP BT2* < 10 ms48.5 ± 1.137.2 ± 1.70–T2* 10–20 ms414.1 ± 3.8613.5 ± 3.1512.3 ± 1.5T* > 20 ms731.5 ± 7.8632.9 ± 10.01030.4 ± 9.8GROUP CT2* < 10 ms35.9 ± 1.337.9 ± 1.226.9 ± 0.6T2* 10–20 ms513.7 ± 3.0513.4 ± 1.9316.9 ± 3.3T* > 20 ms438.4 ± 17.0438.0 ± 10.7739.8 ± 6.4 Disclosures:No relevant conflicts of interest to declare.

Individual voxel‐based analysis of brain magnetization transfer maps shows great variability of gray matter injury in the first stage of multiple sclerosis

In multiple sclerosis (MS), it seems likely that the variability of the long-term disability might be partly due to the variability of the early gray matter (GM) injury. In the present study, we assessed the variability of GM injury in early MS, using a method designed to determine individual pathological GM patterns. Eighteen patients presenting with a clinically isolated syndrome and 24 healthy matched control subjects were included in this study. Patients were explored using a 1.5 Tesla MR scanner (Magnetom Vision Plus; Siemens). Brain MR protocol included magnetization transfer ratio imaging (MTR). Statistical mapping analyses were performed to compare each subject's GM MTR maps with those of the whole group of control subjects (SPM5). The statistical threshold was taken to be the maximum P value showing no significant cluster when any control individual was compared with the whole control population. GM abnormalities were observed in 83% of the patients, ranging in size from 0.3 to 125 cm(3). Among the patients with GM abnormalities, 87% had abnormalities located in the temporal cortex, 80% in the frontal cortex, 80% in the limbic cortex, 73% in the posterior fossa, 53% in the deep GM, 47% in the parietal cortex, and 47% in the occipital cortex. Individual statistical mapping of MTR data, which gives a quantitative assessment of individual GM lesions, demonstrates great variability of grey matter injury in the first stage of multiple sclerosis.

Two‐dimensional MR spectroscopy of minimal hepatic encephalopathy and neuropsychological correlates in vivo

To evaluate regional cerebral metabolic and structural changes in patients with minimal hepatic encephalopathy (MHE) using two-dimensional (2D) MR spectroscopy (MRS) and T( (1) )-weighted MRI, to correlate the observed MR changes with neuropsychological (NP) test scores, and to compare the diagnostic accuracy of MRI, 2D MRS, and NP tests in discriminating between patients and healthy subjects. Thirty-three MHE patients and 30 healthy controls were investigated. The 2D localized correlated spectroscopy (L-COSY) was performed in the frontal and occipital brain on a 1.5 Tesla (T) MR scanner. The NP test battery included 15 tests, grouped into 6 cognitive domains. Globus pallidus signal intensities were calculated from T(1)-weighted images. The 2D MRS showed significant differences in ratios of the following metabolite(s) peaks with respect to creatine (Cr): decreased myo-inositol (mI), choline (Ch), mICh, and increased (glutamate plus glutamine) (Glx) in patients compared with healthy subjects in both occipital and frontal lobes. Frontal lobe taurine also showed a decline in patients. The NP test results revealed declines in cognitive speed, motor function, executive function, and global cognitive status. Significant correlations were found between the altered metabolites and NP tests. Alteration in the mICh/Cr ratio was noted as a powerful discriminant between healthy subjects and the patients. The study demonstrates that relative metabolite levels determined by 2D MRS, in particular mICh/Cr, provide the best diagnostic prediction for MHE. The results suggest that depletions of myo-inositol, choline and taurine with respect to creatine correlate with measures of neuropsychological impairment.

Meta-analysis of the diagnostic performance of stress perfusion cardiovascular magnetic resonance for detection of coronary artery disease.

AimEvaluation of the diagnostic accuracy of stress perfusion cardiovascular magnetic resonance for the diagnosis of significant obstructive coronary artery disease (CAD) through meta-analysis of the available data.MethodologyOriginal articles in any language published before July 2009 were selected from available databases (MEDLINE, Cochrane Library and BioMedCentral) using the combined search terms of magnetic resonance, perfusion, and coronary angiography; with the exploded term coronary artery disease. Statistical analysis was only performed on studies that: (1) used a [greater than or equal to] 1.5 Tesla MR scanner; (2) employed invasive coronary angiography as the reference standard for diagnosing significant obstructive CAD, defined as a [greater than or equal to] 50% diameter stenosis; and (3) provided sufficient data to permit analysis.ResultsFrom the 263 citations identified, 55 relevant original articles were selected. Only 35 fulfilled all of the inclusion criteria, and of these 26 presented data on patient-based analysis. The overall patient-based analysis demonstrated a sensitivity of 89% (95% CI: 88-91%), and a specificity of 80% (95% CI: 78-83%). Adenosine stress perfusion CMR had better sensitivity than with dipyridamole (90% (88-92%) versus 86% (80-90%), P = 0.022), and a tendency to a better specificity (81% (78-84%) versus 77% (71-82%), P = 0.065).ConclusionStress perfusion CMR is highly sensitive for detection of CAD but its specificity remains moderate.

Comparison of two different injection rates of gadoxetic acid for arterial phase MRI of the liver

To compare two different injection rates for gadoxetic acid-enhanced hepatic arterial phase images on hepatic dynamic MRI. Hepatic arterial phase images were obtained after an intravenous bolus injection of gadoxetic acid at a rate of 1 mL/second in 62 patients and 2 mL/second in 64 patients on a 3 Tesla MR scanner using a test-bolus injection method. The signal-to-noise ratios (SNR) of the liver, portal vein, hepatic vein, aorta, spleen and pancreas were measured. The contrast-to-noise ratio (CNR) of hypervascular hepatic tumors was calculated. Two radiologists independently scored items to evaluate image quality of hepatic arterial phase and detected hypervascular hepatocellular carcinoma (HCC). The SNR of the aorta on the arterial phase images was significantly higher in the 1 mL/second group (235.43 +/- 82.59) than in the 2 mL/second group (190.94 +/- 96.90, P < 0.05). The SNRs of the liver, spleen and pancreas, the CNRs of hypervascular hepatic tumors, the detection rate of hypervascular HCC and subjective ratings for the optimal arterial enhancement were comparable between the two groups. Injection rates of 2 mL/second and 1 mL/second provided comparable image qualities on arterial phase images of hepatic dynamic MRI using gadoxetic acid.

Material Orientation Artifact Studies in Magnetic Resonance Imaging

With the increased interest of MRI guided interventional procedures in modern medical treatments, image distortion and artifact formation based on material selection and orientation within the MRI scanner are central concerns for precise object localization. The goal of this study was to illustrate the artifact behavior of materials with various magnetic susceptibilities and radio frequency conductivity values corresponding to object orientation relative to the primary magnetic field. To test the effects of orientation on image distortion and image artifacts, 0.125 inch cylindrical test samples of various materials were imaged using a clinical Siemens 3 Tesla MR scanner. Modern medical instrumentation and surgical utensils are typically made from highly paramagnetic materials (e.g., titanium, nitinol, or stainless steel) which also have high RF conductivities. The combination of these two material properties cause both primary magnetic field (B0) and RF field (B1) inhomogeneities which lead to local image distortions. A change in the local magnetic field induces errors within the slice selection gradient, as the precessional frequency of the proton nuclei in the desired region of interest will not correspond to the exact spatial location on the object and will excite a broader region due to the RF conductivity of the material. Conversely to more traditional surgical materials, diamagnetic materials (e.g., bismuth, pyrolytic carbon, water, most plastics) are free from the susceptibility artifacts due to B0 inhomogeneities and thus offer a level of MR compatibility that traditional materials cannot. A specific testing phantom was built to fit a clinical wrist coil. The phantom consisted of an aqueous solution of gadolinium and copper sulfate to increase image contrast and a rotatable turret post for sample positioning. The particular materials studied were chosen to demonstrate the wide variation in both magnetic susceptibility values and RF conductivities (e.g., 6A1-4V titanium, 316L stainless steel, carbon fiber, 6061 T6 aluminum, brass, copper, beryllium copper). ImageJ software measured the overall pixel area and major dimension of each MR image artifact at 0, 45, and 90 degree orientations of each test sample relative to B0. The results of the measurements indicated measurable increases in signal are of the paramagnetic and highly conductive test specimens orientated orthogonal to the primary magnetic field. For instance, two common medical grade materials such as 316L stainless steel and 6Al-4V titanium resulted in artifact area increases of 770±10% and 234±10%, respectively, relative to the actual cross sectional area of the sample. Conversely, the more diamagnetic materials, carbon fiber and beryllium copper demonstrated increased artifact areas of 8±10% and 12±10%, respectively. Errors in artifact area percentage growth measurement are primarily attributed to manual image segmentation and variation in coil positioning within the MRI bore. The results indicate that MR image artifact size and object distortion characteristics can be influenced by both material selection and object orientation relative to the primary magnetic field. In the interest of accurate navigation of image guided equipment and devices, interventional devices should be tested for image distortion in multiple orientations. This work is supported by MIMTeC, a National Science Foundation Industry University Collaborative Research Center and by NIH Grant P30 NS057091.

Magnetic resonance imaging and biological properties of pancreatic islets labeled with iron oxide nanoparticles

This study was undertaken to investigate the in vitro effect of islet labeling with iron oxide nanoparticles for MRI on islet viability, insulin secretion, and gene expression. Isolated rat islets were labeled with Resovist (25-200 microg Fe/mL, a clinically approved MRI contrast agent) in the presence or absence of poly-l-Lysine (PLL, 1.5 microg/mL) for 48 h. The iron content of labeled islets was found to increase in a dose-dependent manner. More than 90% of the islets were labeled with 100 microg Fe/mL. We confirmed the localizations of iron oxide nanoparticles within islet beta-cells by insulin immunostaining. As the concentration of Resovist increased, T(2) values as determined by T(2)-weighted MRI on a 1.5 Tesla MR scanner decreased. Labeling of 100 islets in a medium containing 100 microg Fe/mL of Resovist in the absence of PLL provided sufficient contrast for islet visualization on T(2)-weighted MRI. MTT assays showed that the viability of labeled islets was not different from that of unlabeled islets. No statistical difference was observed between labeled (2.91 +/- 0.36) and unlabeled islets (2.83 +/- 0.61) in terms of the ability to secrete insulin, as determined by the glucose stimulation index. We also evaluated the effect of iron oxide incorporation on the gene expressions in islet cells using RT-PCR (reverse transcriptase PCR). Insulin expression in labeled islets was significantly elevated (1.83 +/- 0.25 fold vs. unlabeled; p = 0.005), but not the expression of somatostatin (1.39 +/- 0.18 fold vs. unlabeled; p = 0.085) or glucagons (1.28 +/- 0.13 fold vs. unlabeled; p = 0.09). Expression of an important transcription factor for insulin gene transcription, BETA2 (beta-cell E-box trans-activator), was increased in labeled islets (1.67 +/- 0.15 fold vs. unlabeled; p = 0.029). The findings of this study indicate that Resovist provides a satisfactory means to image islets and has no deleterious effect on islet function or gene expression.

Muscle Phosphocreatine Kinetics In Children And Adults During High-intensity Exercise

PURPOSE: To compare the age and sex differences in the kinetic response of muscle PCr during high-intensity exercise in children and adults. METHODS: Eleven adults (6 men 25 ± 5 y and 5 women 23 ± 3 y) and 11 children (6 boys 13 ± 0.2 y and 5 girls 13 ±1.3 y) exercised using their right leg on a quadriceps ergometer within a 1.5 Tesla MR scanner. Following habituation, each participant completed an incremental test to exhaustion. After a minimum 48 hours recovery, participants completed two to four constant work rate bouts on separate days. Exercise bouts consisted of 2 min rest and 7 min exercise, at an intensity equivalent to 20% of the difference between the workload at the intracellular Pi/PCr threshold and the maximal workload. 31P spectra were collected every 6 s using a 6 cm surface coil positioned beneath the right quadriceps muscle. The breakdown of muscle PCr at the onset of exercise was modelled using a single-exponential function until the onset of the PCr slow component (SC). This point was identified using an iterative fitting window - where the time constant diverged from a plateau, a PCr SC was deemed to emerge. Data are reported as mean ± standard deviation and 95% confidence intervals (CI) are presented. A two by two factorial ANOVA was utilised to determine group differences. RESULTS: No significant interaction effect was found for the fundamental time constant (boys: 31 ± 10, CI 5; girls: 31 ± 10, CI 6; men: 44 ± 20, CI 6; women: 29 ± 14 s, CI 6 s; P=0.26), or the fundamental amplitude (boys: -39 ± 10; girls: -42 ± 9; men: -36 ± 9; women: -48 ± 9%; P=0.23), or the SC PCr (as a % of the difference between the fundamental amplitude and end exercise PCr) which was similar across groups (boys: 6 ± 1; girls: 13 ± 8; men: 8 ± 5; women: 8 ± 6% P=0.15). The end-exercise PCr revealed a significant sex difference (P=0.03) but no significant age or interaction effect (boys: 55 ± 10; girls: 46 ± 14; men: 56 ± 11; women: 44 ± 8%). There was no significant difference between age (P=0.22) or sex (P=0.13) for the PCr cost of contraction at end-exercise (boys: 1.7 ± 0.5; girls: 1.3 ± 0.5; men: 1.4 ± 0.4; women: 1.2 ± 0.2 mM·W-1P=0.13). CONCLUSION: The kinetics of muscle PCr during high intensity exercise are similar in 13 y old children and adults, suggesting the phosphate-linked control of oxidative metabolism, at least during high-intensity exercise, is adult like by this age.

Comparative velocity investigations in cerebral arteries and aneurysms: 3D phase‐contrast MR angiography, laser Doppler velocimetry and computational fluid dynamics

In western populations, cerebral aneurysms develop in approximately 4% of humans and they involve the risk of rupture. Blood flow patterns are of interest for understanding the pathogenesis of the lesions and may eventually contribute to deciding on the most efficient treatment procedure for a specific patient. Velocity mapping with phase-contrast magnetic resonance angiography (PC-MRA) is a non-invasive method for performing in vivo measurements on blood velocity. Several hemodynamic properties can either be derived directly from these measurements or a flow field with all its parameters can be simulated on the basis of the measurements. For both approaches, the accuracy of the PC-MRA data and subsequent modeling must be validated. Therefore, a realistic transient flow field in a well-defined patient-specific silicone phantom was investigated. Velocity investigations with PC-MRA in a 3 Tesla MR scanner, laser Doppler velocimetry (LDV) and computational fluid dynamics (CFD) were performed in the same model under equal flow conditions and compared to each other. The results showed that PC-MRA was qualitatively similar to LDV and CFD, but showed notable quantitative differences, while LDV and CFD agreed well. The accuracy of velocity quantification by PC-MRA was best in straight artery regions with the measurement plane being perpendicular to the primary flow direction. The accuracy decreased in regions with disturbed flow and in cases where the measurement plane was not perpendicular to the primary flow. Due to these findings, it is appropriate to use PC-MRA as the inlet and outlet conditions for numerical simulations to calculate velocities and shear stresses in disturbed regions like aneurysms, rather than derive these values directly from the full PC-MRA measured velocity field.

In vivo quantification of intracerebral GABA by single-voxel 1H-MRS—How reproducible are the results?

Gamma aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the human brain. It plays a decisive role in a variety of nervous system disorders, such as anxiety disorders, epilepsy, schizophrenia, insomnia, and many others. The reproducibility of GABA quantification results obtained with a single-voxel spectroscopy J-difference editing sequence with Point Resolved Spectroscopy localization (MEGA-PRESS) was determined on a 3.0 Tesla MR scanner in healthy adults. Eleven volunteers were measured in long- and short-term intervals. Intra- and inter-subject reproducibility were evaluated. Internal referencing of GABA+ to total creatine (tCr) and water (H 2O), as well as two different post-processing methods for the evaluation (signal integration and time-domain fitting) were compared. In all subjects lower coefficient of variation and therefore higher reproducibility can be observed for fitting compared to integration. The GABA+/tCr ratio performs better than the GABA+/H 2O ratio or GABA+ without internal referencing for both fitting and integration (GABA+/tCr: 13.3% and 17.0%; GABA+/H 2O: 15.0% and 17.8%; GABA+: 19.2% and 21.7%). Four-day measurements on three subjects showed higher intra- than inter-subject reproducibility (GABA+/tCr ∼10–12%). With a coefficient of variation of about 13% for inter-subject and 10–12% for intra-subject variability of GABA+/tCr, this technique seems to be a precise tool that can detect GABA confidently. The results of this study show the reproducibility limitations of GABA quantification in vivo, which are necessary for further clinical studies.

Quantitative T2 mapping during follow‐up after matrix‐associated autologous chondrocyte transplantation (MACT): Full‐thickness and zonal evaluation to visualize the maturation of cartilage repair tissue

The purpose of this article was to evaluate the potential of in vivo zonal T2-mapping as a noninvasive tool in the longitudinal visualization of cartilage repair tissue maturation after matrix-associated autologous chondrocyte transplantation (MACT). Fifteen patients were treated with MACT and evaluated cross-sectionally, with a baseline MRI at a follow-up of 19.7 +/- 12.1 months after cartilage transplantation surgery of the knee. In the same 15 patients, 12 months later (31.7 +/- 12.0 months after surgery), a longitudinal 1-year follow-up MRI was obtained. MRI was performed on a 3 Tesla MR scanner; morphological evaluation was performed using a double-echo steady-state sequence; T2 maps were calculated from a multiecho, spin-echo sequence. Quantitative mean (full-thickness) and zonal (deep and superficial) T2 values were calculated in the cartilage repair area and in control cartilage sites. A statistical analysis of variance was performed. Full-tickness T2 values showed no significant difference between sites of healthy cartilage and cartilage repair tissue (p < 0.05). Using zonal T2 evaluation, healthy cartilage showed a significant increase from the deep to superficial cartilage layers (p < 0.05). Cartilage repair tissue after MACT showed no significant zonal increase from deep to superficial cartilage areas during baseline MRI (p > 0.05); however, during the 1-year follow-up, a significant zonal stratification could be observed (p < 0.05). Morphological evaluation showed no significant difference between the baseline and the 1-year follow-up MRI. T2 mapping seems to be more sensitive in revealing changes in the repair tissue compared to morphological MRI. In vivo zonal T2 assessment may be sensitive enough to characterize the maturation of cartilage repair tissue.