Magnetic Resonance Imaging for Monitoring of Hepatic Disease Induced by Ebola Virus: a Nonhuman Primate Proof-of-Concept Study.

Severe liver impairment is a well-known hallmark of Ebola virus disease (EVD). However, the role of hepatic involvement in EVD progression is understudied. Medical imaging in established animal models of EVD (e.g., nonhuman primates [NHPs]) can be a strong complement to traditional assays to better investigate this pathophysiological process in vivo and noninvasively. In this proof-of-concept study, we used longitudinal multiparametric magnetic resonance imaging (MRI) to characterize liver morphology and function in nine rhesus monkeys after exposure to Ebola virus (EBOV). Starting 5 days postexposure, MRI assessments of liver appearance, morphology, and size were consistently compatible with the presence of hepatic edema, inflammation, and congestion, leading to significant hepatomegaly at necropsy. MRI performed after injection of a hepatobiliary contrast agent demonstrated decreased liver signal on the day of euthanasia, suggesting progressive hepatocellular dysfunction and hepatic secretory impairment associated with EBOV infection. Importantly, MRI-assessed deterioration of biliary function was acute and progressed faster than changes in serum bilirubin concentrations. These findings suggest that longitudinal quantitative in vivo imaging may be a useful addition to standard biological assays to gain additional knowledge about organ pathophysiology in animal models of EVD. IMPORTANCE Severe liver impairment is a well-known hallmark of Ebola virus disease (EVD), but the contribution of hepatic pathophysiology to EVD progression is not fully understood. Noninvasive medical imaging of liver structure and function in well-established animal models of disease may shed light on this important aspect of EVD. In this proof-of-concept study, we used longitudinal magnetic resonance imaging (MRI) to characterize liver abnormalities and dysfunction in rhesus monkeys exposed to Ebola virus. The results indicate that in vivo MRI may be used as a noninvasive readout of organ pathophysiology in EVD and may be used in future animal studies to further characterize organ-specific damage of this condition, in addition to standard biological assays.

Acute Late-Stage Myocarditis in the Crab-Eating Macaque Model of Hemorrhagic Smallpox.

Hemorrhagic smallpox, caused by variola virus (VARV), was a rare but nearly 100% lethal human disease manifestation. Hemorrhagic smallpox is frequently characterized by secondary bacterial infection, coagulopathy, and myocardial and subendocardial hemorrhages. Previous experiments have demonstrated that intravenous (IV) cowpox virus (CPXV) exposure of macaques mimics human hemorrhagic smallpox. The goal of this experiment was to further understand the onset, nature, and severity of cardiac pathology and how it may contribute to disease. The findings support an acute late-stage myocarditis with lymphohistiocytic infiltrates in the CPXV model of hemorrhagic smallpox.

The Human Sodium Iodide Symporter as a Reporter Gene for Studying Middle East Respiratory Syndrome Coronavirus Pathogenesis.

Single photon emission computed tomography (SPECT) is frequently used in oncology and cardiology to evaluate disease progression and/or treatment efficacy. Such technology allows for real-time evaluation of disease progression and when applied to studying infectious diseases may provide insight into pathogenesis. Insertion of a SPECT-compatible reporter gene into a virus may provide insight into mechanisms of pathogenesis and viral tropism. The human sodium iodide symporter (hNIS), a SPECT and positron emission tomography reporter gene, was inserted into Middle East respiratory syndrome coronavirus (MERS-CoV), a recently emerged virus that can cause severe respiratory disease and death in afflicted humans to obtain a quantifiable and sensitive marker for viral replication to further MERS-CoV animal model development. The recombinant virus was evaluated for fitness, stability, and reporter gene functionality. The recombinant and parental viruses demonstrated equal fitness in terms of peak titer and replication kinetics, were stable for up to six in vitro passages, and were functional. Further in vivo evaluation indicated variable stability, but resolution limits hampered in vivo functional evaluation. These data support the further development of hNIS for monitoring infection in animal models of viral disease.IMPORTANCE Advanced medical imaging such as single photon emission computed tomography with computed tomography (SPECT/CT) enhances fields such as oncology and cardiology. Application of SPECT/CT, magnetic resonance imaging, and positron emission tomography to infectious disease may enhance pathogenesis studies and provide alternate biomarkers of disease progression. The experiments described in this article focus on insertion of a SPECT/CT-compatible reporter gene into MERS-CoV to demonstrate that a functional SPECT/CT reporter gene can be inserted into a virus.

[18F]-Fluorodeoxyglucose Uptake in Lymphoid Tissue Serves as a Predictor of Disease Outcome in the Nonhuman Primate Model of Monkeypox Virus Infection.

Real-time bioimaging of infectious disease processes may aid countermeasure development and lead to an improved understanding of pathogenesis. However, few studies have identified biomarkers for monitoring infections using in vivo imaging. Previously, we demonstrated that positron emission tomography/computed tomography (PET/CT) imaging with [18F]-fluorodeoxyglucose (FDG) can monitor monkeypox disease progression in vivo in nonhuman primates (NHPs). In this study, we investigated [18F]-FDG-PET/CT imaging of immune processes in lymphoid tissues to identify patterns of inflammation in the monkepox NHP model and to determine the value of [18F]-FDG-PET/CT as a biomarker for disease and treatment outcomes. Quantitative analysis of [18F]-FDG-PET/CT images revealed differences between moribund and surviving animals at two sites vital to the immune response to viral infections, bone marrow and lymph nodes (LNs). Moribund NHPs demonstrated increased [18F]-FDG uptake in bone marrow 4 days postinfection compared to surviving NHPs. In surviving, treated NHPs, increase in LN volume correlated with [18F]-FDG uptake and peaked 10 days postinfection, while minimal lymphadenopathy and higher glycolytic activity were observed in moribund NHPs early in infection. Imaging data were supported by standard virology, pathology, and immunology findings. Even with the limited number of subjects, imaging was able to differentiate the difference between disease outcomes, warranting additional studies to demonstrate whether [18F]-FDG-PET/CT can identify other, subtler effects. Visualizing altered metabolic activity at sites involved in the immune response by [18F]-FDG-PET/CT imaging is a powerful tool for identifying key disease-specific time points and locations that are most relevant for pathogenesis and treatment.IMPORTANCE Positron emission tomography and computed tomography (PET/CT) imaging is a universal tool in oncology and neuroscience. The application of this technology to infectious diseases is far less developed. We used PET/CT imaging with [18F]-labeled fluorodeoxyglucose ([18F]-FDG) in monkeys after monkeypox virus exposure to monitor the immune response in lymphoid tissues. In lymph nodes of surviving monkeys, changes in [18F]-FDG uptake positively correlated with enlargement of the lymph nodes and peaked on day 10 postinfection. In contrast, the bone marrow and lymph nodes of nonsurvivors showed increased [18F]-FDG uptake by day 4 postinfection with minimal lymph node enlargement, indicating that elevated cell metabolic activity early after infection is predictive of disease outcome. [18F]-FDG-PET/CT imaging can provide real-time snapshots of metabolic activity changes in response to viral infections and identify key time points and locations most relevant for monitoring the development of pathogenesis and for potential treatment to be effective.

Modeling [(18)F]-FDG lymphoid tissue kinetics to characterize nonhuman primate immune response to Middle East respiratory syndrome-coronavirus aerosol challenge.

BACKGROUND: The pathogenesis and immune response to Middle East respiratory syndrome (MERS) caused by a recently discovered coronavirus, MERS-CoV, have not been fully characterized because a suitable animal model is currently not available. (18)F-Fluorodeoxyglucose ([(18)F]-FDG)-positron emission tomography/computed tomography (PET/CT) as a longitudinal noninvasive approach can be beneficial in providing biomarkers for host immune response. [(18)F]-FDG uptake is increased in activated immune cells in response to virus entry and can be localized by PET imaging. We used [(18)F]-FDG-PET/CT to investigate the host response developing in nonhuman primates after MERS-CoV exposure and applied kinetic modeling to monitor the influx rate constant (K i ) in responsive lymphoid tissue. METHODS: Multiple [(18)F]-FDG-PET and CT images were acquired on a PET/CT clinical scanner modified to operate in a biosafety level 4 environment prior to and up to 29 days after MERS-CoV aerosol exposure. Time activity curves of various lymphoid tissues were reconstructed to follow the [(18)F]-FDG uptake for approximately 60 min (3,600 s). Image-derived input function was used to calculate K i for lymphoid tissues by Patlak plot. RESULTS: Two-way repeated measures analysis of variance revealed alterations in K i that was associated with the time point (p < 0.001) after virus exposure and the location of lymphoid tissue (p = 0.0004). As revealed by a statistically significant interaction (p < 0.0001) between these two factors, the pattern of K i changes over time differed between three locations but not between subjects. A distinguished pattern of statistically significant elevation in K i was observed in mediastinal lymph nodes (LNs) that correlated to K i changes in axillary LNs. Changes in LNs K i were concurrent with elevations of monocytes in peripheral blood. CONCLUSIONS: [(18)F]-FDG-PET is able to detect subtle changes in host immune response to contain a subclinical virus infection. Full quantitative analysis is the preferred approach rather than semiquantitative analysis using standardized uptake value for detection of the immune response to the virus.

Improving the use of principal component analysis to reduce physiological noise and motion artifacts to increase the sensitivity of task-based fMRI.

BACKGROUND: Functional magnetic resonance imaging (fMRI) time series are subject to corruption by many noise sources, especially physiological noise and motion. Researchers have developed many methods to reduce physiological noise, including RETROICOR, which retroactively removes cardiac and respiratory waveforms collected during the scan, and CompCor, which applies principal components analysis (PCA) to remove physiological noise components without any physiological monitoring during the scan. NEW METHOD: We developed four variants of the CompCor method. The optimized CompCor method applies PCA to time series in a noise mask, but orthogonalizes each component to the BOLD response waveform and uses an algorithm to determine a favorable number of components to use as "nuisance regressors." Whole brain component correction (WCompCor) is similar, except that it applies PCA to time-series throughout the whole brain. Low-pass component correction (LCompCor) identifies low-pass filtered components throughout the brain, while high-pass component correction (HCompCor) identifies high-pass filtered components. COMPARISON WITH EXISTING METHOD: We compared the new methods with the original CompCor method by examining the resulting functional contrast-to-noise ratio (CNR), sensitivity, and specificity. RESULTS: (1) The optimized CompCor method increased the CNR and sensitivity compared to the original CompCor method and (2) the application of WCompCor yielded the best improvement in the CNR and sensitivity. CONCLUSIONS: The sensitivity of the optimized CompCor, WCompCor, and LCompCor methods exceeded that of the original CompCor method. However, regressing noise signals showed a paradoxical consequence of reducing specificity for all noise reduction methods attempted.

Segmentation based denoising of PET images: an iterative approach via regional means and affinity propagation.

Delineation and noise removal play a significant role in clinical quantification of PET images. Conventionally, these two tasks are considered independent, however, denoising can improve the performance of boundary delineation by enhancing SNR while preserving the structural continuity of local regions. On the other hand, we postulate that segmentation can help denoising process by constraining the smoothing criteria locally. Herein, we present a novel iterative approach for simultaneous PET image denoising and segmentation. The proposed algorithm uses generalized Anscombe transformation priori to non-local means based noise removal scheme and affinity propagation based delineation. For nonlocal means denoising, we propose a new regional means approach where we automatically and efficiently extract the appropriate subset of the image voxels by incorporating the class information from affinity propagation based segmentation. PET images after denoising are further utilized for refinement of the segmentation in an iterative manner. Qualitative and quantitative results demonstrate that the proposed framework successfully removes the noise from PET images while preserving the structures, and improves the segmentation accuracy.

Combination of multichannel single-voxel MRS signals using generalized least squares.

PURPOSE: To propose using the generalized least square (GLS) algorithm for combining multichannel single-voxel magnetic resonance spectroscopy (MRS) signals. MATERIALS AND METHODS: Phantom and in vivo brain MRS experiments on a 7 T scanner equipped with a 32-channel receiver coil, as well as Monte Carlo simulations, were performed to compare the coefficient of variation (CV) of the GLS method with those of two recently reported spectral combination methods. RESULTS: Compared to the two existing methods, the GLS method significantly reduced CV values for the simulation, phantom, and in vivo experiments. CONCLUSION: The GLS method can lead to improved precision of peak quantification.

Hydrogen-1 MR spectroscopy for measurement and diagnosis of hepatic steatosis.

OBJECTIVE: Hydrogen-1 MR spectroscopy ((1)H-MRS) is gaining acceptance as a noninvasive technique for assessment of hepatic steatosis, and the findings have been found to correlate closely with histopathologic grade. The aims of this study were to validate (1)H-MRS performed with a 3-T MRI system for quantifying hepatic steatosis and to determine threshold values of (1)H-MRS proton density fat fraction corresponding to standard histopathologic grade in patients undergoing diagnostic liver biopsy. SUBJECTS AND METHODS: We conducted a prospective cross-sectional liver MRS study with 52 subjects undergoing diagnostic liver biopsy. The diagnostic accuracy of (1)H-MRS was evaluated with receiver operating characteristic curves. RESULTS: The diagnostic accuracy of (1)H-MRS for hepatic steatosis was high with an area under the receiver operating characteristic curve of 0.94 (95% CI, 0.88-1.0). Results were similar for three (1)H-MRS measurements obtained at different locations in the liver, for two independent pathologists, and whether fibrosis was present or absent. One third of participants had elevated transaminase concentrations of unknown cause, and (1)H-MRS estimates of steatosis had perfect agreement with histopathologic grade in this group. Calculated (1)H-MRS proton density fat fraction thresholds for histologic grades were less than 17% for grade 0 or trace steatosis, 17-38.6% for grade 1, and greater than 38.6% for grade 2 or higher. CONCLUSION: Hydrogen-1 MR spectroscopy is an effective, noninvasive technique that can be used to diagnose and quantify hepatic steatosis. Hydrogen-1 MR spectroscopy thresholds corresponded with histopathologic grades and may be useful in the workup of patients with elevated transaminase concentrations.

Usefulness of [18F]-DA and [18F]-DOPA for PET imaging in a mouse model of pheochromocytoma.

PURPOSE: To evaluate the usefulness of [(18)F]-6-fluorodopamine ([(18)F]-DA) and [(18)F]-L-6-fluoro-3,4-dihydroxyphenylalanine ([(18)F]-DOPA) positron emission tomography (PET) in the detection of subcutaneous (s.c.) and metastatic pheochromocytoma in mice; to assess the expression of the norepinephrine transporter (NET) and vesicular monoamine transporters 1 and 2 (VMAT1 and VMAT2), all important for [(18)F]-DA and [(18)F]-DOPA uptake. Furthermore, to compare tumor detection by micro-computed tomography (microCT) to magnetic resonance imaging (MRI) in individual mouse. METHODS: SUV(max) values were calculated from [(18)F]-DA and [(18)F]-DOPA PET, tumor-to-liver ratios (TLR) were obtained and expression of NET, VMAT1 and VMAT2 was evaluated. RESULTS: [(18)F]-DA detected less metastatic lesions compared to [(18)F]-DOPA. TLR values for liver metastases were 2.26-2.71 for [(18)F]-DOPA and 1.83-2.83 for [(18)F]-DA. A limited uptake of [(18)F]-DA was found in s.c. tumors (TLR = 0.22-0.27) compared to [(18)F]-DOPA (TLR = 1.56-2.24). Overall, NET and VMAT2 were expressed in all organ and s.c. tumors. However, s.c. tumors lacked expression of VMAT1. We confirmed [(18)F]-DA's high affinity for the NET for its uptake and VMAT1 and VMAT2 for its storage and retention in pheochromocytoma cell vesicles. In contrast, [(18)F]-DOPA was found to utilize only VMAT2. CONCLUSION: MRI was superior in the detection of all organ tumors compared to microCT and PET. [(18)F]-DOPA had overall better sensitivity than [(18)F]-DA for the detection of metastases. Subcutaneous tumors were localized only with [(18)F]-DOPA, a finding that may reflect differences in expression of VMAT1 and VMAT2, perhaps similar to some patients with pheochromocytoma where [(18)F]-DOPA provides better visualization of lesions than [(18)F]-DA.

Head-repositioning does not reduce the reproducibility of fMRI activation in a block-design motor task.

It is hypothesized that, based upon partial volume effects and spatial non-uniformities of the scanning environment, repositioning a subject's head inside the head coil between separate functional MRI scans will reduce the reproducibility of fMRI activation compared to a series of functional runs where the subject's head remains in the same position. Nine subjects underwent fMRI scanning where they performed a sequential, oppositional finger-tapping task. The first five runs were conducted with the subject's head remaining stable inside the head coil. Following this, four more runs were collected after the subject removed and replaced his/her head inside the head coil before each run. The coefficient of variation was calculated for four metrics: the distance from the anterior commisure to the center of mass of sensorimotor activation, maximum t-statistic, activation volume, and average percent signal change. These values were compared for five head-stabilization runs and five head-repositioning runs. Voxelwise intraclass correlation coefficients were also calculated to assess the spatial distribution of sources of variance. Interestingly, head repositioning was not seen to significantly affect the reproducibility of fMRI activation (p<0.05). In addition, the threshold level affected the reproducibility of activation volume and percent signal change.

Formulation and characterisation of magnetic resonance imageable thermally sensitive liposomes for use with magnetic resonance-guided high intensity focused ultrasound.

PURPOSE: Objectives of this study were to: 1) develop iLTSL, a low temperature sensitive liposome co-loaded with an MRI contrast agent (ProHance® Gd-HP-DO3A) and doxorubicin, 2) characterise doxorubicin and Gd-HP-DO3A release from iLTSL and 3) investigate the ability of magnetic resonance-guided high intensity focused ultrasound (MR-HIFU) to induce and monitor iLTSL content release in phantoms and in vivo. METHODS: iLTSL was passively loaded with Gd-HP-DO3A and actively loaded with doxorubicin. Doxorubicin and Gd-HP-DO3A release was quantified by fluorescence and spectroscopic techniques, respectively. Release with MR-HIFU was examined in tissue-mimicking phantoms containing iLTSL and in a VX2 rabbit tumour model. RESULTS: iLTSL demonstrated consistent size and doxorubicin release kinetics after storage at 4°C for 7 days. Release of doxorubicin and Gd-HP-DO3A from iLTSL was minimal at 37°C but fast when heated to 41.3°C. The magnitude of release was not significantly different between doxorubicin and Gd-HP-DO3A over 10 min in HEPES buffer and plasma at 37°, 40° and 41.3°C (p > 0.05). Relaxivity of iLTSL increased significantly (p < 0.0001) from 1.95 ± 0.05 to 4.01 ± 0.1 mMs⁻¹ when heated above the transition temperature. Signal increase corresponded spatially and temporally to MR-HIFU-heated locations in phantoms. Signal increase was also observed in vivo after iLTSL injection and after each 10-min heating (41°C), with greatest increase in the heated tumour region. CONCLUSION: An MR imageable liposome formulation co-loaded with doxorubicin and an MR contrast agent was developed. Stability, imageability, and MR-HIFU monitoring and control of content release suggest that MR-HIFU combined with iLTSL may enable real-time monitoring and spatial control of content release.

Increased uptake of [¹²³I]meta-iodobenzylguanidine, [¹8F]fluorodopamine, and [³H]norepinephrine in mouse pheochromocytoma cells and tumors after treatment with the histone deacetylase inhibitors.

[¹³¹I]meta-iodobenzylguanidine ([¹³¹I]MIBG) is the most commonly used treatment for metastatic pheochromocytoma and paraganglioma. It enters the chromaffin cells via the membrane norepinephrine transporter; however, its success has been modest. We studied the ability of histone deacetylase (HDAC) inhibitors to enhance [¹²³I]MIBG uptake by tumors in a mouse metastatic pheochromocytoma model. HDAC inhibitors are known to arrest growth, induce differentiation and apoptosis in various cancer cells, and further inhibit tumor growth. We report the in vitro and in vivo effects of two HDAC inhibitors, romidepsin and trichostatin A, on the uptake of [(3)H]norepinephrine, [¹²³I]MIBG, and [(18)F]fluorodopamine in a mouse model of metastatic pheochromocytoma. The effects of both inhibitors on norepinephrine transporter activity were assessed in mouse pheochromocytoma (MPC) cells by using the transporter-blocking agent desipramine and the vesicular-blocking agent reserpine. HDAC inhibitors increased [(3)H]norepinephrine, [¹²³I]MIBG, and [(18)F]fluorodopamine uptake through the norepinephrine transporter in MPC cells. In vivo, inhibitor treatment resulted in significantly increased uptake of [(18)F]fluorodopamine positron emission tomography (PET) in pheochromocytoma liver metastases (19.1 ± 3.2% injected dose per gram of tumor (%ID/g) compared to liver metastases in pretreatment scans 5.9 ± 0.6%; P<0.001). Biodistribution analysis after inhibitors treatment confirmed the PET results. The uptake of [(123)I]MIBG was significantly increased in liver metastases 9.5 ± 1.1% compared to 3.19 ± 0.4% in untreated control liver metastases (P<0.05). We found that HDAC inhibitors caused an increase in the amount of norepinephrine transporter expressed in tumors. HDAC inhibitors may enhance the therapeutic efficacy of [(131)I]MIBG treatment in patients with advanced malignant pheochromocytoma and paraganglioma.

Template-based B1 inhomogeneity correction in 3T MRI brain studies.

Low noise, high resolution, fast and accurate T1 maps from MRI images of the brain can be performed using a dual flip angle method. However, B1 field inhomogeneity, which is particularly problematic at high field strengths (e.g., 3T), limits the ability of the scanner to deliver the prescribed flip angle, introducing errors into the T1 maps that limit the accuracy of quantitative analyses based on those maps. A dual repetition time method was used for acquiring a B1 map to correct that inhomogeneity. Additional inaccuracies due to misregistration of the acquired T1-weighted images were corrected by rigid registration, and the effects of misalignment on the T1 maps were compared to those of B1 inhomogeneity in 19 normal subjects. However, since B1 map acquisition takes up precious scanning time and most retrospective studies do not have B1 map, we designed a template-based correction strategy. B1 maps from different subjects were aligned using a twelve-parameter affine registration. Recomputed T1 maps showed an important improvement with respect to the noncorrected maps: histograms of all corrected maps exhibited two peaks corresponding to white and gray matter tissues, while unimodal histograms were observed in all uncorrected maps because of the inhomogeneity. A method to detect the best nonsubject-specific B1 correction based on a set of features was designed. The optimum set of weighting factors for those features was computed. The best available B1 correction was detected in almost all subjects while corrections comparable to the T1 map corrected using the B1 map from the same subject were detected in the others.

The role of dynamic contrast-enhanced MRI in cancer diagnosis and treatment.

Angiogenesis is a key step in the pathophysiology of tumor growth and metastatic spread. Recently, dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) has emerged as a method for assessing angiogenesis both during the initial diagnosis and for follow up of anti-angiogenic therapies. In this review, we discuss the technical aspects of implementing DCE-MRI in clinical practice with emphasis on acquisition methods and analytic techniques.

Reliability of fiber tracking measurements in diffusion tensor imaging for longitudinal study.

UNLABELLED: The statistical reliability of diffusion property measurements was evaluated in ten healthy subjects using deterministic fiber tracking to localize tracts affected in motor neuron disease: corticospinal tract (CST), uncinate fasciculus (UNC), and the corpus callosum in its entirety (CC), and its genu (GE), motor (CCM), and splenium (SP) fibers separately. Measurements of fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (lambda(1)), transverse diffusivity (lambda( perpendicular)), and volume of voxels containing fibers (VV) were obtained within each tract. To assess intra-rater and inter-rater reliability, two raters carried out fiber tracking five times on each scan. Scan-rescan and longitudinal reliability were assessed in a subset of four subjects who had six scans, with two sets of three scans separated by 1 year. The statistical reliability of repeated measurements was evaluated using intraclass correlation coefficients (ICC) and coefficients of variation (CV). Spatial agreement of tract shape was assessed using the kappa (kappa) statistic. RESULTS: Repeated same-scan fiber tracking evaluations showed good geometric alignment (intra-rater kappa >0.90, inter-rater kappa >0.76) and reliable diffusion property measurements (intra-rater ICC >0.92, inter-rater ICC >0.77). FA, MD, and lambda( perpendicular) were highly reliable with repeated scans on different days, up to a year apart (ICC >0.8). VV also exhibited good reliability, but with higher CVs. We were unable to demonstrate reproducibility of lambda(1). Longitudinal reliability after one year was improved by averaging measurements from multiple scans at each time point. Fiber tracking provides a reliable tool for the longitudinal evaluation of white matter diffusion properties.

Measurement of glutathione in normal volunteers and stroke patients at 3T using J-difference spectroscopy with minimized subtraction errors.

PURPOSE: To develop and optimize a (1)H magnetic resonance spectroscopy (MRS) method for measuring brain glutathione (GSH) levels. MATERIALS AND METHODS: Phantom experiments and density operator simulations were performed to determine the optimal TE for measuring GSH at 3T using J-difference spectral editing. In vivo data collected from 11 normal volunteers (43 measurements) and five stroke patients (10 measurements) were processed using a new spectral alignment method (adaptive spectral registration). RESULTS: In phantom experiments and density operator simulations where relaxation effects were ignored, close to maximum GSH signal (2.95 ppm) was obtained at TE approximately 131 msec with minimum N-acetyl-aspartate (NAA) signal interference. Using adaptive spectral registration, GSH levels in healthy volunteers were found to be 1.20 +/- 0.14 mM (mean +/- standard deviation [SD]). GSH levels in stroke patients were found to be 1.19 +/- 0.24 mM in lesion and 1.25 +/- 0.19 mM in contralateral normal tissue. In comparison, the SDs were significantly larger when only the NAA singlet (2.01 ppm) was used as a navigator for spectral alignment. CONCLUSION: Spectral editing using J-differences is a reliable method for measuring GSH levels in volunteers and stroke patients.

Noninvasive monitoring of a murine model of metastatic pheochromocytoma: a comparison of contrast-enhanced microCT and nonenhanced MRI.

PURPOSE: To compare contrast-enhanced micro-computed tomography (microCT) and nonenhanced respiratory-triggered magnetic resonance imaging (MRI) in an animal model of metastatic pheochromocytoma. Animal models are becoming important in the study of cancer treatment and imaging is useful in minimizing the number of animals needed and reducing costs associated with autopsies. However, the choice of imaging modality is still evolving. MATERIALS AND METHODS: Adult female nude mice were injected by tail vein with a mouse pheochromocytoma (MPC) cell line (MPC 4/30PRR) to create a metastatic model. After optimizing imaging techniques, eight mice were imaged with both respiratory triggered MRI and microCT and the findings were verified histologically. RESULTS: MicroCT and MRI were approximately equal in their ability to detect hepatic metastases at a size threshold of 350 microm. In the lungs, MRI was more sensitive than microCT, detecting lesions 0.6 mm in diameter versus 1 mm for microCT. Additionally, MRI was more sensitive for lesions in the kidneys, bone, ovaries, and adrenal glands. MRI demonstrated a higher contrast-to-noise ratio (CNR) than microCT. CONCLUSION: In addition to the advantage of not exposing the animal to ionizing radiation, MRI provided a more complete assessment of the extent of metastases in this model compared to microCT.

Normal regional fractional anisotropy and apparent diffusion coefficient of the brain measured on a 3 T MR scanner.

INTRODUCTION: We aim to establish norms of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in 20 different regions of the brain in healthy human volunteers. METHODS: Thirty-one individuals were examined for ADC and FA in 20 regions of the brain using a single-shot, spin echo, echo planar diffusion tensor imaging sequence with 32 directions at 3 T. FA and ADC maps were computed using the Philips PRIDE tool, and regions of interest were drawn at 20 different locations in the brain. Relationships of FA and ADC with age and gender were explored. RESULTS: We found a negative correlation between age and FA in the inferior fronto-occipital fasciculus and forceps minor. There were no gender differences. The cerebral peduncle, the middle cerebellum, and cingulum had the highest variation in FA, while fornix, optic radiation, and optic tract had the highest variation in ADC. CONCLUSION: We provide a table of normative FA and ADC measurements in 20 brain regions of potential clinical relevance to the diagnosis and monitoring of specific neurological diseases.

Automatic determination of arterial input function for dynamic contrast enhanced MRI in tumor assessment.

Dynamic Contrast Enhanced MRI (DCE-MRI) is today one of the most popular methods for tumor assessment. Several pharmacokinetic models have been proposed to analyze DCE-MRI. Most of them depend on an accurate arterial input function (AIF). We propose an automatic and versatile method to determine the AIF. The method has two stages, detection and segmentation, incorporating knowledge about artery structure, fluid kinetics, and the dynamic temporal property of DCE-MRI. We have applied our method in DCE-MRIs of four different body parts: breast, brain, liver and prostate. The results show that we achieve average 89.5% success rate for 40 cases. The pharmacokinetic parameters computed from the automatic AIF are highly agreeable with those from a manually derived AIF (R2 = 0.89, P (T <=t) = 0.19) and a semiautomatic AIF (R2 = 0.98, P(T <=t) = 0.01).