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1.
J Cereb Blood Flow Metab ; 40(3): 539-551, 2020 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-30732551

RESUMO

Recent clinical trials of new revascularization therapies in acute ischemic stroke have highlighted the importance of physiological imaging to identify optimal treatments for patients. Oxygen extraction fraction (OEF) is a hallmark of at-risk tissue in stroke, and can be quantified from the susceptibility effect of deoxyhemoglobin molecules in venous blood on MRI phase scans. We measured OEF within cerebral veins using advanced quantitative susceptibility mapping (QSM) MRI reconstructions in 20 acute stroke patients. Absolute OEF was elevated in the affected (29.3 ± 3.4%) versus the contralateral hemisphere (25.5 ± 3.1%) of patients with large diffusion-perfusion lesion mismatch (P = 0.032). In these patients, OEF negatively correlated with relative CBF measured by dynamic susceptibility contrast MRI (P = 0.004), suggesting compensation for reduced flow. Patients with perfusion-diffusion match or no hypo-perfusion showed less OEF difference between hemispheres. Nine patients received longitudinal assessment and showed OEF ratio (affected to contralateral) of 1.2 ± 0.1 at baseline that normalized (decreased) to 1.0 ± 0.1 at follow-up three days later (P = 0.03). Our feasibility study demonstrates that QSM MRI can non-invasively quantify OEF in stroke patients, relates to perfusion status, and is sensitive to OEF changes over time. Clinical trial registration: Longitudinal MRI examinations of patients with brain ischemia and blood brain barrier permeability; clinicaltrials.org : NCT02077582.

3.
Eur J Nucl Med Mol Imaging ; 46(12): 2452-2463, 2019 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-31385012

RESUMO

PURPOSE: The acute effect of loading on bone tissue and physiology can offer important information with regard to joint function in diseases such as osteoarthritis. Imaging studies using [18F]-sodium fluoride ([18F]NaF) have found changes in tracer kinetics in animals after subjecting bones to strain, indicating an acute physiological response. The aim of this study is to measure acute changes in NaF uptake in human bone due to exercise-induced loading. METHODS: Twelve healthy subjects underwent two consecutive 50-min [18F]NaF PET/MRI examinations of the knees, one baseline followed by one post-exercise scan. Quantification of tracer kinetics was performed using an image-derived input function from the popliteal artery. For both scans, kinetic parameters of KiNLR, K1, k2, k3, and blood volume were mapped parametrically using nonlinear regression with the Hawkins model. The kinetic parameters along with mean SUV and SUVmax were compared between the pre- and post-exercise examinations. Differences in response to exercise were analysed between bone tissue types (subchondral, cortical, and trabecular bone) and between regional subsections of knee subchondral bone. RESULTS: Exercise induced a significant (p < <0.001) increase in [18F]NaF uptake in all bone tissues in both knees, with mean SUV increases ranging from 47% in trabecular bone tissue to 131% in subchondral bone tissue. Kinetic parameters involving vascularization (K1 and blood volume) increased, whereas the NaF extraction fraction [k3/(k2 + k3)] was reduced. CONCLUSIONS: Bone loading induces an acute response in bone physiology as quantified by [18F]NaF PET kinetics. Dynamic imaging after bone loading using [18F]NaF PET is a promising diagnostic tool in bone physiology and imaging of biomechanics.

4.
Brain Struct Funct ; 224(7): 2467-2485, 2019 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-31278570

RESUMO

The vascular organization of the human brain can determine neurological and neurophysiological functions, yet thus far it has not been comprehensively mapped. Aging and diseases such as dementia are known to be associated with changes to the vasculature and normative data could help detect these vascular changes in neuroimaging studies. Furthermore, given the well-known impact of venous vessels on the blood oxygen level dependent (BOLD) signal, information about the common location of veins could help detect biases in existing datasets. In this work, a quantitative atlas of the venous vasculature using quantitative susceptibility maps (QSM) acquired with a 0.6-mm isotropic resolution is presented. The Venous Neuroanatomy (VENAT) atlas was created from 5 repeated 7 Tesla MRI measurements in young and healthy volunteers (n = 20, 10 females, mean age = 25.1 ± 2.5 years) using a two-step registration method on 3D segmentations of the venous vasculature. This cerebral vein atlas includes the average vessel location, diameter (mean: 0.84 ± 0.33 mm) and curvature (0.11 ± 0.05 mm-1) from all participants and provides an in vivo measure of the angio-architectonic organization of the human brain and its variability. This atlas can be used as a basis to understand changes in the vasculature during aging and neurodegeneration, as well as vascular and physiological effects in neuroimaging.


Assuntos
Mapeamento Encefálico , Encéfalo/irrigação sanguínea , Neuroimagem , Veias/fisiologia , Adulto , Mapeamento Encefálico/métodos , Feminino , Humanos , Processamento de Imagem Assistida por Computador/métodos , Imagem por Ressonância Magnética/métodos , Masculino , Veias/patologia
5.
Clin Nucl Med ; 44(5): 377-385, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30888996

RESUMO

PURPOSE: [F]-sodium fluoride ([F]NaF) is a well-established bone-seeking agent that has shown promise to assess bone turnover in a variety of disorders, but its distribution in healthy knee joints has not been explored. This study aimed to investigate parametric values for [F]NaF uptake in various bone tissues types of the knee and their spatial distributions. METHODS: Twelve healthy subjects were hand-injected with 92.5 MBq of [F]NaF and scanned on a 3-T PET/MRI system. Listmode PET data for both knees were acquired for 50 minutes from injection simultaneously with MRI Dixon and angiography data. The image-derived input function was determined from the popliteal artery. Using the Hawkins model, Patlak analysis was performed to obtain Ki (Ki) values and nonlinear regression analysis to obtain Ki, K1, k3/(k2 + k3), and blood volume. Comparisons for the measured kinetic parameters, SUV, and SUVmax were made between tissue types (subchondral, cortical, and trabecular bone) and between regional subsections of subchondral bone. RESULTS: Cortical bone had the highest [F]NaF uptake differing significantly in all measured parameters when compared with trabecular bone and significantly higher SUVmax and K1 than subchondral bone. Subchondral bone also had significantly higher SUV, SUVmax, and Ki than trabecular bone tissue. Regional differences were observed in K1 and k3/(k2 + k3) values. CONCLUSIONS: Quantitative [F]NaF PET is sensitive to variations in bone vascularization and metabolism in the knee joint.


Assuntos
Fluoretos/farmacocinética , Joelho/diagnóstico por imagem , Tomografia por Emissão de Pósitrons/métodos , Compostos Radiofarmacêuticos/farmacocinética , Adulto , Feminino , Voluntários Saudáveis , Humanos , Imagem por Ressonância Magnética , Masculino , Imagem Multimodal , Tomografia por Emissão de Pósitrons/normas , Reprodutibilidade dos Testes
6.
Stroke ; 50(2): 373-380, 2019 02.
Artigo em Inglês | MEDLINE | ID: mdl-30636572

RESUMO

Background and Purpose- Noninvasive imaging of brain perfusion has the potential to elucidate pathophysiological mechanisms underlying Moyamoya disease and enable clinical imaging of cerebral blood flow (CBF) to select revascularization therapies for patients. We used hybrid positron emission tomography (PET)/magnetic resonance imaging (MRI) technology to characterize the distribution of hypoperfusion in Moyamoya disease and its relationship to vessel stenosis severity, through comparisons with a normative perfusion database of healthy controls. Methods- To image CBF, we acquired [15O]-water PET as a reference and simultaneously acquired arterial spin labeling (ASL) MRI scans in 20 Moyamoya patients and 15 age-matched, healthy controls on a PET/MRI scanner. The ASL MRI scans included a standard single-delay ASL scan with postlabel delay of 2.0 s and a multidelay scan with 5 postlabel delays (0.7-3.0s) to estimate and account for arterial transit time in CBF quantification. The percent volume of hypoperfusion in patients (determined as the fifth percentile of CBF values in the healthy control database) was the outcome measure in a logistic regression model that included stenosis grade and location. Results- Logistic regression showed that anterior ( P<0.0001) and middle cerebral artery territory regions ( P=0.003) in Moyamoya patients were susceptible to hypoperfusion, whereas posterior regions were not. Cortical regions supplied by arteries with stenosis on MR angiography showed more hypoperfusion than normal arteries ( P=0.001), but the extent of hypoperfusion was not different between mild-moderate versus severe stenosis. Multidelay ASL did not perform differently from [15O]-water PET in detecting perfusion abnormalities, but standard ASL overestimated the extent of hypoperfusion in patients ( P=0.003). Conclusions- This simultaneous PET/MRI study supports the use of multidelay ASL MRI in clinical evaluation of Moyamoya disease in settings where nuclear medicine imaging is not available and application of a normative perfusion database to automatically identify abnormal CBF in patients.


Assuntos
Bases de Dados Factuais , Imagem por Ressonância Magnética , Artéria Cerebral Média , Doença de Moyamoya , Tomografia por Emissão de Pósitrons , Adolescente , Adulto , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Artéria Cerebral Média/diagnóstico por imagem , Artéria Cerebral Média/fisiopatologia , Doença de Moyamoya/diagnóstico por imagem , Doença de Moyamoya/fisiopatologia , Marcadores de Spin
7.
J Magn Reson Imaging ; 47(4): 1119-1132, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-28792653

RESUMO

PURPOSE: To compare performance of sequential and Hadamard-encoded pseudocontinuous arterial spin labeling (PCASL). MATERIALS AND METHODS: Monte Carlo simulations and in vivo experiments were performed in 10 healthy subjects. Field strength and sequence: 5-delay sequential (5-del. Seq.), 7-delay Hadamard-encoded (7-del. Had.), and a single-delay (1-del.) PCASL, without and with vascular crushing at 3.0T. The errors and variations of cerebral blood flow (CBF) and arterial transit time (ATT) from simulations and the CBF and ATT estimates and variations in gray matter (GM) with different ATT ranges were compared. Pairwise t-tests with Bonferroni correction were used. RESULTS: The simulations and in vivo experiments showed that 1-del. PCASL underestimated GM CBF due to insufficient postlabeling delay (PLD) (37.2 ± 8.1 vs. 47.3 ± 8.5 and 47.3 ± 9.0 ml/100g/min, P ≤ 6.5 × 10-6 ), while 5-del. Seq. and 7-del. Had. yielded comparable GM CBF (P ≥ 0.49). 5-del. Seq. was more reproducible for CBF (P = 4.7 × 10-4 ), while 7-del. Had. was more reproducible for ATT (P = 0.033). 5-del. Seq. was more prone to intravascular artifacts and yielded lower GM ATTs compared to 7-del. Had. without crushing (1.13 ± 0.18 vs. 1.23 ± 0.13 seconds, P = 2.3 × 10-3 ), but they gave comparable ATTs with crushing (P = 0.12). ATTs measured with crushing were longer than those without crushing (P ≤ 6.7 × 10-4 ), but CBF was not affected (P ≥ 0.16). CONCLUSION: The theoretical signal-to-noise ratio (SNR) gain through Hadamard encoding was confirmed experimentally. For 1-del., a PLD of 1.8 seconds is recommended for healthy subjects. With current parameters, 5-del. Seq. was more reproducible for CBF, and 7-del. Had. for ATT. Vascular crushing may help reduce variations in multidelay experiments without compromising tissue CBF or ATT measurements. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:1119-1132.


Assuntos
Circulação Cerebrovascular/fisiologia , Imagem por Ressonância Magnética/métodos , Processamento de Sinais Assistido por Computador , Adulto , Velocidade do Fluxo Sanguíneo/fisiologia , Simulação por Computador , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Valores de Referência , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Marcadores de Spin
8.
J Cereb Blood Flow Metab ; 38(9): 1391-1417, 2018 09.
Artigo em Inglês | MEDLINE | ID: mdl-28816594

RESUMO

Cerebrovascular disease (CVD) remains a leading cause of death and the leading cause of adult disability in most developed countries. This work summarizes state-of-the-art, and possible future, diagnostic and evaluation approaches in multiple stages of CVD, including (i) visualization of sub-clinical disease processes, (ii) acute stroke theranostics, and (iii) characterization of post-stroke recovery mechanisms. Underlying pathophysiology as it relates to large vessel steno-occlusive disease and the impact of this macrovascular disease on tissue-level viability, hemodynamics (cerebral blood flow, cerebral blood volume, and mean transit time), and metabolism (cerebral metabolic rate of oxygen consumption and pH) are also discussed in the context of emerging neuroimaging protocols with sensitivity to these factors. The overall purpose is to highlight advancements in stroke care and diagnostics and to provide a general overview of emerging research topics that have potential for reducing morbidity in multiple areas of CVD.


Assuntos
Transtornos Cerebrovasculares/diagnóstico , Transtornos Cerebrovasculares/fisiopatologia , Humanos
9.
Stroke ; 48(9): 2441-2449, 2017 09.
Artigo em Inglês | MEDLINE | ID: mdl-28765286

RESUMO

BACKGROUND AND PURPOSE: Arterial spin labeling (ASL) MRI is a promising, noninvasive technique to image cerebral blood flow (CBF) but is difficult to use in cerebrovascular patients with abnormal, long arterial transit times through collateral pathways. To be clinically adopted, ASL must first be optimized and validated against a reference standard in these challenging patient cases. METHODS: We compared standard-delay ASL (post-label delay=2.025 seconds), multidelay ASL (post-label delay=0.7-3.0 seconds), and long-label long-delay ASL acquisitions (post-label delay=4.0 seconds) against simultaneous [15O]-positron emission tomography (PET) CBF maps in 15 Moyamoya patients on a hybrid PET/MRI scanner. Dynamic susceptibility contrast was performed in each patient to identify areas of mild, moderate, and severe time-to-maximum (Tmax) delays. Relative CBF measurements by each ASL scan in 20 cortical regions were compared with the PET reference standard, and correlations were calculated for areas with moderate and severe Tmax delays. RESULTS: Standard-delay ASL underestimated relative CBF by 20% in areas of severe Tmax delays, particularly in anterior and middle territories commonly affected by Moyamoya disease (P<0.001). Arterial transit times correction by multidelay acquisitions led to improved consistency with PET, but still underestimated CBF in the presence of long transit delays (P=0.02). Long-label long-delay ASL scans showed the strongest correlation relative to PET, and there was no difference in mean relative CBF between the modalities, even in areas of severe delays. CONCLUSIONS: Post-label delay times of ≥4 seconds are needed and may be combined with multidelay strategies for robust ASL assessment of CBF in Moyamoya disease.


Assuntos
Encéfalo/diagnóstico por imagem , Circulação Cerebrovascular , Doença de Moyamoya/diagnóstico por imagem , Adolescente , Adulto , Encéfalo/irrigação sanguínea , Circulação Colateral , Feminino , Humanos , Imagem por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Imagem Multimodal , Radioisótopos de Oxigênio , Tomografia por Emissão de Pósitrons , Marcadores de Spin
10.
Front Neurosci ; 11: 89, 2017.
Artigo em Inglês | MEDLINE | ID: mdl-28289372

RESUMO

Purpose: Quantitative susceptibility mapping (QSM) enables cerebral venous characterization and physiological measurements, such as oxygen extraction fraction (OEF). The exquisite sensitivity of QSM to deoxygenated blood makes it possible to image small veins; however partial volume effects must be addressed for accurate quantification. We present a new method, Iterative Cylindrical Fitting (ICF), to estimate voxel-based partial volume effects for susceptibility maps and use it to improve OEF quantification of small veins with diameters between 1.5 and 4 voxels. Materials and Methods: Simulated QSM maps were generated to assess the performance of the ICF method over a range of vein geometries with varying echo times and noise levels. The ICF method was also applied to in vivo human brain data to assess the feasibility and behavior of OEF measurements compared to the maximum intensity voxel (MIV) method. Results: Improved quantification of OEF measurements was achieved for vessels with contrast to noise greater than 3.0 and vein radii greater than 0.75 voxels. The ICF method produced improved quantitative accuracy of OEF measurement compared to the MIV approach (mean OEF error 7.7 vs. 12.4%). The ICF method provided estimates of vein radius (mean error <27%) and partial volume maps (root mean-squared error <13%). In vivo results demonstrated consistent estimates of OEF along vein segments. Conclusion: OEF quantification in small veins (1.5-4 voxels in diameter) had lower error when using partial volume estimates from the ICF method.

11.
Magn Reson Med ; 77(4): 1713-1727, 2017 04.
Artigo em Inglês | MEDLINE | ID: mdl-27059521

RESUMO

PURPOSE: Susceptibility-based blood oxygenation measurements in small vessels of the brain derive from gradient echo (GRE) phase and can provide localized assessment of brain function and pathology. However, when vessel diameter becomes smaller than the acquisition voxel size, partial volume effects compromise these measurements. The purpose of this study was to develop a technique to improve the reliability of vessel oxygenation estimates in the presence of partial volume effects. METHODS: Intravoxel susceptibility variations are present when a vessel and parenchyma experience partial volume effects, modifying the voxel's GRE phase signal and attenuating the GRE magnitude signal. Using joint utilization of magnitude and phase (JUMP), both vessel susceptibility and voxel partial volume fraction can be estimated, providing measurements of venous oxygen saturation ( Yv) in straight, nearly vertical vessels that have improved robustness to partial volume effects. RESULTS: JUMP was demonstrated by estimating vessel Yv in numerical and in vivo experiments. Deviations from ground truth of Yv measurements in vessels tilted up to 30° from B0 were reduced by over 50% when using JUMP compared with phase-only techniques. CONCLUSION: JUMP exploits both magnitude and phase data in GRE imaging to mitigate partial volume effects in estimation of vessel oxygenation. Magn Reson Med 77:1713-1727, 2017. © 2016 International Society for Magnetic Resonance in Medicine.


Assuntos
Artefatos , Aumento da Imagem/métodos , Angiografia por Ressonância Magnética/métodos , Imagem Multimodal/métodos , Oximetria/métodos , Processamento de Sinais Assistido por Computador , Algoritmos , Feminino , Humanos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Aprendizado de Máquina , Masculino , Análise Numérica Assistida por Computador , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
12.
NMR Biomed ; 30(4)2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-26918319

RESUMO

The magnetism of hemoglobin - being paramagnetic in its deoxy and diamagnetic in its oxy state - offers unique opportunities to probe oxygen metabolism in blood and tissues. The magnetic susceptibility χ of blood scales linearly with blood oxygen saturation, which can be obtained by measuring the magnetic field ΔB of the intravascular MR signal relative to tissue. In contrast to χ, the induced field ΔB is non-local. Therefore, to obtain the intravascular susceptibility Δχ relative to adjoining tissue from the measured ΔB demands solution of an inverse problem. Fortunately, for ellipsoidal structures, to which a straight, cylindrically shaped blood vessel segment conforms, the solution is trivial. The article reviews the principle of MR susceptometry-based blood oximetry. It then discusses applications for quantification of whole-brain oxygen extraction - typically on the basis of a measurement in the superior sagittal sinus - and, in conjunction with total cerebral blood flow, the cerebral metabolic rate of oxygen (CMRO2 ). By simultaneously measuring flow and venous oxygen saturation (SvO2 ) a temporal resolution of a few seconds can be achieved, allowing the study of the response to non-steady-state challenges such as volitional apnea. Extensions to regional measurements in smaller cerebral veins are also possible, as well as voxelwise quantification of venous blood saturation in cerebral veins accomplished by quantitative susceptibility mapping (QSM) techniques. Applications of susceptometry-based oximetry to studies of metabolic and degenerative disorders of the brain are reviewed. Lastly, the technique is shown to be applicable to other organ systems such as the extremities using SvO2 as a dynamic tracer to monitor the kinetics of the microvascular response to induced ischemia. Copyright © 2016 John Wiley & Sons, Ltd.


Assuntos
Encéfalo/metabolismo , Interpretação de Imagem Assistida por Computador/métodos , Imagem por Ressonância Magnética/métodos , Imagem Molecular/métodos , Oximetria/métodos , Oxigênio/metabolismo , Animais , Humanos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Distribuição Tecidual
13.
J Magn Reson Imaging ; 45(6): 1736-1745, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-27796082

RESUMO

PURPOSE: To evaluate positron emission tomography / magnetic resonance imaging (PET/MRI) knee imaging to detect and characterize osseous metabolic abnormalities and correlate PET radiotracer uptake with osseous abnormalities and cartilage degeneration observed on MRI. MATERIALS AND METHODS: Both knees of 22 subjects with knee pain or injury were scanned at one timepoint, without gadolinium, on a hybrid 3.0T PET-MRI system following injection of 18 F-fluoride or 18 F-fluorodeoxyglucose (FDG). A musculoskeletal radiologist identified volumes of interest (VOIs) around bone abnormalities on MR images and scored bone marrow lesions (BMLs) and osteophytes using a MOAKS scoring system. Cartilage appearance adjacent to bone abnormalities was graded with MRI-modified Outerbridge classifications. On PET standardized uptake values (SUV) maps, VOIs with SUV greater than 5 times the SUV in normal-appearing bone were identified as high-uptake VOI (VOIHigh ). Differences in 18 F-fluoride uptake between bone abnormalities, BML, and osteophyte grades and adjacent cartilage grades on MRI were identified using Mann-Whitney U-tests. RESULTS: SUVmax in all subchondral bone lesions (BML, osteophytes, sclerosis) was significantly higher than that of normal-appearing bone on MRI (P < 0.001 for all). Of the 172 high-uptake regions on 18 F-fluoride PET, 63 (37%) corresponded to normal-appearing subchondral bone on MRI. Furthermore, many small grade 1 osteophytes (40 of 82 [49%]), often described as the earliest signs of osteoarthritis (OA), did not show high uptake. Lastly, PET SUVmax in subchondral bone adjacent to grade 0 cartilage was significantly lower compared to that of grades 1-2 (P < 0.05) and grades 3-4 cartilage (P < 0.001). CONCLUSION: PET/MRI can simultaneously assess multiple early metabolic and morphologic markers of knee OA across multiple tissues in the joint. Our findings suggest that PET/MR may detect metabolic abnormalities in subchondral bone, which appear normal on MRI. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;45:1736-1745.


Assuntos
Doenças Ósseas Metabólicas/diagnóstico , Doenças Ósseas Metabólicas/metabolismo , Fluordesoxiglucose F18/farmacocinética , Imagem por Ressonância Magnética/métodos , Osteoartrite do Joelho/diagnóstico por imagem , Osteoartrite do Joelho/metabolismo , Tomografia por Emissão de Pósitrons/métodos , Adulto , Biomarcadores/metabolismo , Doenças Ósseas Metabólicas/complicações , Meios de Contraste/farmacocinética , Feminino , Humanos , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Masculino , Imagem Multimodal/métodos , Osteoartrite do Joelho/complicações , Compostos Radiofarmacêuticos/farmacocinética , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Distribuição Tecidual
14.
J Cereb Blood Flow Metab ; 36(5): 842-61, 2016 05.
Artigo em Inglês | MEDLINE | ID: mdl-26945019

RESUMO

Noninvasive imaging of cerebral blood flow provides critical information to understand normal brain physiology as well as to identify and manage patients with neurological disorders. To date, the reference standard for cerebral blood flow measurements is considered to be positron emission tomography using injection of the [(15)O]-water radiotracer. Although [(15)O]-water has been used to study brain perfusion under normal and pathological conditions, it is not widely used in clinical settings due to the need for an on-site cyclotron, the invasive nature of arterial blood sampling, and experimental complexity. As an alternative, arterial spin labeling is a promising magnetic resonance imaging technique that magnetically labels arterial blood as it flows into the brain to map cerebral blood flow. As arterial spin labeling becomes more widely adopted in research and clinical settings, efforts have sought to standardize the method and validate its cerebral blood flow values against positron emission tomography-based cerebral blood flow measurements. The purpose of this work is to critically review studies that performed both [(15)O]-water positron emission tomography and arterial spin labeling to measure brain perfusion, with the aim of better understanding the accuracy and reproducibility of arterial spin labeling relative to the positron emission tomography reference standard.


Assuntos
Artérias/diagnóstico por imagem , Circulação Cerebrovascular , Angiografia por Ressonância Magnética/métodos , Tomografia por Emissão de Pósitrons/métodos , Marcadores de Spin , Encéfalo/irrigação sanguínea , Humanos , Radioisótopos de Oxigênio , Tomografia por Emissão de Pósitrons/normas , Água
15.
Quant Imaging Med Surg ; 6(6): 756-771, 2016 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28090451

RESUMO

Early detection of musculoskeletal disease leads to improved therapies and patient outcomes, and would benefit greatly from imaging at the cellular and molecular level. As it becomes clear that assessment of multiple tissues and functional processes are often necessary to study the complex pathogenesis of musculoskeletal disorders, the role of multi-modality molecular imaging becomes increasingly important. New positron emission tomography-magnetic resonance imaging (PET-MRI) systems offer to combine high-resolution MRI with simultaneous molecular information from PET to study the multifaceted processes involved in numerous musculoskeletal disorders. In this article, we aim to outline the potential clinical utility of hybrid PET-MRI to these non-oncologic musculoskeletal diseases. We summarize current applications of PET molecular imaging in osteoarthritis (OA), rheumatoid arthritis (RA), metabolic bone diseases and neuropathic peripheral pain. Advanced MRI approaches that reveal biochemical and functional information offer complementary assessment in soft tissues. Additionally, we discuss technical considerations for hybrid PET-MR imaging including MR attenuation correction, workflow, radiation dose, and quantification.

16.
Neuroimage ; 125: 920-931, 2016 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-26549301

RESUMO

New MRI methods for noninvasive imaging of baseline oxygen extraction fraction (OEF) in the brain show great promise. Quantitative O2 imaging (QUO2) applies a biophysical model to measure OEF in tissue from BOLD, cerebral blood flow (CBF), and end-tidal O2 (ETO2) signals acquired during two or more gas manipulations. Alternatively, quantitative susceptibility mapping (QSM) maps baseline OEF along cerebral vessels based on the deoxyhemoblogin (dHb) susceptibility shift between veins and water. However, these approaches have not been carefully compared to each other or to known physiological signals. The aims of this study were to compare OEF values by QUO2 and QSM; and to see if baseline OEF relates to BOLD and CBF changes during a visual task. Simultaneous BOLD and arterial spin labeling (ASL) scans were acquired at 7T in 11 healthy subjects continuously during hypercapnia (5% CO2, 21% O2), hyperoxia (100% O2), and carbogen (5% CO2, 95% O2) for QUO2 analysis. Separate BOLD-ASL scans were acquired during a checkerboard stimulus to identify functional changes in the visual cortex. Gradient echo phase images were also collected at rest for QSM reconstruction of OEF along cerebral veins draining the visual cortex. Mean baseline OEF was (43.5±14)% for QUO2 with two gases, (42.3±17)% for QUO2 with three gases, and (29.4±3)% for QSM across volunteers. Three-gas QUO2 values of OEF correlated with QSM values of OEF (P=0.03). However, Bland-Altman analysis revealed that QUO2 tended to measure higher baseline OEF with respect to QSM, which likely results from underestimation of the hyperoxic BOLD signal and low signal-to-noise ratio of the ASL acquisitions. Across subjects, the percent CBF change during the visual task correlated with OEF measured by 3-gas QUO2 (P<0.04); and by QSM (P=0.035), providing evidence that the new methods measure true variations in brain physiology across subjects.


Assuntos
Mapeamento Encefálico/métodos , Encéfalo/irrigação sanguínea , Circulação Cerebrovascular/fisiologia , Neuroimagem/métodos , Oxigênio/análise , Adulto , Calibragem , Feminino , Humanos , Masculino
17.
Magn Reson Med ; 73(6): 2152-62, 2015 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-24986223

RESUMO

PURPOSE: To introduce the wave-CAIPI (controlled aliasing in parallel imaging) acquisition and reconstruction technique for highly accelerated 3D imaging with negligible g-factor and artifact penalties. METHODS: The wave-CAIPI 3D acquisition involves playing sinusoidal gy and gz gradients during the readout of each kx encoding line while modifying the 3D phase encoding strategy to incur interslice shifts as in 2D-CAIPI acquisitions. The resulting acquisition spreads the aliasing evenly in all spatial directions, thereby taking full advantage of 3D coil sensitivity distribution. By expressing the voxel spreading effect as a convolution in image space, an efficient reconstruction scheme that does not require data gridding is proposed. Rapid acquisition and high-quality image reconstruction with wave-CAIPI is demonstrated for high-resolution magnitude and phase imaging and quantitative susceptibility mapping. RESULTS: Wave-CAIPI enables full-brain gradient echo acquisition at 1 mm isotropic voxel size and R = 3 × 3 acceleration with maximum g-factors of 1.08 at 3T and 1.05 at 7T. Relative to the other advanced Cartesian encoding strategies (2D-CAIPI and bunched phase encoding) wave-CAIPI yields up to two-fold reduction in maximum g-factor for nine-fold acceleration at both field strengths. CONCLUSION: Wave-CAIPI allows highly accelerated 3D acquisitions with low artifact and negligible g-factor penalties, and may facilitate clinical application of high-resolution volumetric imaging.


Assuntos
Mapeamento Encefálico/métodos , Aumento da Imagem/métodos , Processamento de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Imagem por Ressonância Magnética/métodos , Algoritmos , Humanos
18.
Neuroimage ; 104: 146-55, 2015 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-25300201

RESUMO

There is an unmet medical need for noninvasive imaging of regional brain oxygenation to manage stroke, tumor, and neurodegenerative diseases. Oxygenation imaging from magnetic susceptibility in MRI is a promising new technique to measure local venous oxygen extraction fraction (OEF) along the cerebral venous vasculature. However, this approach has not been tested in vivo at different levels of oxygenation. The primary goal of this study was to test whether susceptibility imaging of oxygenation can detect OEF changes induced by hypercapnia, via CO2 inhalation, within selected a priori brain regions. Ten healthy subjects were scanned at 3T with a 32-channel head coil. The end-tidal CO2 (ETCO2) was monitored continuously and inspired gases were adjusted to achieve steady-state conditions of eucapnia (41±3mmHg) and hypercapnia (50±4mmHg). Gradient echo phase images and pseudo-continuous arterial spin labeling (pcASL) images were acquired to measure regional OEF and CBF respectively during eucapnia and hypercapnia. By assuming constant cerebral oxygen consumption throughout both gas states, regional CBF values were computed to predict the local change in OEF in each brain region. Hypercapnia induced a relative decrease in OEF of -42.3% in the straight sinus, -39.9% in the internal cerebral veins, and approximately -50% in pial vessels draining each of the occipital, parietal, and frontal cortical areas. Across volunteers, regional changes in OEF correlated with changes in ETCO2. The reductions in regional OEF (via phase images) were significantly correlated (P<0.05) with predicted reductions in OEF derived from CBF data (via pcASL images). These findings suggest that susceptibility imaging is a promising technique for OEF measurements, and may serve as a clinical biomarker for brain conditions with aberrant regional oxygenation.


Assuntos
Veias Cerebrais/metabolismo , Hipercapnia/sangue , Consumo de Oxigênio/fisiologia , Adulto , Mapeamento Encefálico , Dióxido de Carbono/metabolismo , Dióxido de Carbono/farmacologia , Artérias Cerebrais/anatomia & histologia , Artérias Cerebrais/metabolismo , Veias Cerebrais/anatomia & histologia , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Imagem por Ressonância Magnética/métodos , Masculino , Córtex Pré-Frontal/metabolismo , Marcadores de Spin , Adulto Jovem
19.
J Cereb Blood Flow Metab ; 35(1): 131-9, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25352043

RESUMO

Quantitative oxygen extraction fraction (OEF) in cortical veins was studied in patients with multiple sclerosis (MS) and healthy subjects via magnetic resonance imaging (MRI) phase images at 7 Tesla (7 T). Flow-compensated, three-dimensional gradient-echo scans were acquired for absolute OEF quantification in 23 patients with MS and 14 age-matched controls. In patients, we collected T2*-weighted images for characterization of white matter, deep gray matter, and cortical lesions, and also assessed cognitive function. Variability of OEF across readers and scan sessions was evaluated in a subset of volunteers. OEF was averaged from 2 to 3 pial veins in the sensorimotor, parietal, and prefrontal cortical regions for each subject (total of ~10 vessels). We observed good reproducibility of mean OEF, with intraobserver coefficient of variation (COV)=2.1%, interobserver COV=5.2%, and scan-rescan COV=5.9%. Patients exhibited a 3.4% reduction in cortical OEF relative to controls (P=0.0025), which was not different across brain regions. Although oxygenation did not relate with measures of structural tissue damage, mean OEF correlated with a global measure of information processing speed. These findings suggest that cortical OEF from 7-T MRI phase is a reproducible metabolic biomarker that may be sensitive to different pathologic processes than structural MRI in patients with MS.


Assuntos
Encéfalo/metabolismo , Metabolismo Energético , Imagem por Ressonância Magnética , Esclerose Múltipla/metabolismo , Esclerose Múltipla/patologia , Oxigênio/metabolismo , Adulto , Encéfalo/irrigação sanguínea , Encéfalo/patologia , Estudos de Casos e Controles , Veias Cerebrais/metabolismo , Cognição/fisiologia , Feminino , Humanos , Masculino , Esclerose Múltipla/psicologia , Testes Neuropsicológicos , Oxigênio/sangue , Estudos Prospectivos , Reprodutibilidade dos Testes
20.
J Magn Reson Imaging ; 42(2): 290-6, 2015 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-25407671

RESUMO

BACKGROUND: To assess the test-retest reproducibility of cortical mapping of T2 * relaxation rates at 7 Tesla (T) MRI. T2 * maps have been used for studying cortical myelo-architecture patterns in vivo and for characterizing conditions associated with changes in iron and/or myelin concentration. METHODS: T2 * maps were calculated from 7T multi-echo T2 *-weighted images acquired during separate scanning sessions on 8 healthy subjects. The reproducibility of surface-based cortical T2 * mapping was assessed at different depths of the cortex; from pial surface (0% depth) towards gray/white matter boundary (100% depth), across cortical regions and hemispheres, using coefficients of variation (COVs = SD/mean) between each couple (scan-rescan) of average T2 * measurements. RESULTS: Average cortical T2 * was significantly different among 25%, 50%, and 75% depths (analysis of variance, P < 0.001). Coefficient of variations were very low within cortical regions, and whole cortex (average COV = 0.83-1.79%), indicating a high degree of reproducibility in T2 * measures. CONCLUSION: Surface-based mapping of T2 * relaxation rates as a function of cortical depth is reproducible and could prove useful for studying the laminar architecture of the cerebral cortex in vivo, and for investigating physiological and pathological states associated with changes in iron and/or myelin concentration.


Assuntos
Algoritmos , Mapeamento Encefálico/métodos , Córtex Cerebral/anatomia & histologia , Interpretação de Imagem Assistida por Computador/métodos , Imagem por Ressonância Magnética/métodos , Adulto , Feminino , Humanos , Aumento da Imagem/métodos , Masculino , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
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