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We evaluated the impacts of COVID-19 on multi-organ and metabolic function in patients following severe hospitalised infection compared to controls. Patients (n = 21) without previous diabetes, cardiovascular or cerebrovascular disease were recruited 5-7 months post-discharge alongside controls (n = 10) with similar age, sex and body mass. Perceived fatigue was estimated (Fatigue Severity Scale) and the following were conducted: oral glucose tolerance (OGTT) alongside whole-body fuel oxidation, validated magnetic resonance imaging and spectroscopy during resting and supine controlled exercise, dual-energy X-ray absorptiometry, short physical performance battery (SPPB), intra-muscular electromyography, quadriceps strength and fatigability, and daily step-count. There was a greater insulin response (incremental area under the curve, median (inter-quartile range)) during the OGTT in patients [18,289 (12,497-27,448) mIU/min/L] versus controls [8655 (7948-11,040) mIU/min/L], P < 0.001. Blood glucose response and fasting and post-prandial fuel oxidation rates were not different. This greater insulin resistance was not explained by differences in systemic inflammation or whole-body/regional adiposity, but step-count (P = 0.07) and SPPB scores (P = 0.004) were lower in patients. Liver volume was 28% greater in patients than controls, and fat fraction adjusted liver T1, a measure of inflammation, was raised in patients. Patients displayed greater perceived fatigue scores, though leg muscle volume, strength, force-loss, motor unit properties and post-exercise muscle phosphocreatine resynthesis were comparable. Further, cardiac and cerebral architecture and function (at rest and on exercise) were not different. In this cross-sectional study, individuals without known previous morbidity who survived severe COVID-19 exhibited greater insulin resistance, pointing to a need for physical function intervention in recovery.
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COVID-19 , Resistência à Insulina , Humanos , COVID-19/fisiopatologia , Feminino , Masculino , Pessoa de Meia-Idade , Resistência à Insulina/fisiologia , SARS-CoV-2 , Glicemia/metabolismo , Fadiga/fisiopatologia , Teste de Tolerância a Glucose , Adulto , Força Muscular/fisiologia , Idoso , Músculo Esquelético/fisiopatologia , Músculo Esquelético/metabolismoRESUMO
BACKGROUND: In respiratory medicine, there is a need for sensitive measures of regional lung function that can be performed using standard imaging technology, without the need for inhaled or intravenous contrast agents. PURPOSE: To describe VOxel-wise Lung VEntilation (VOLVE), a new method for quantifying regional lung ventilation (V) and perfusion (Q) using free-breathing proton MRI, and to evaluate VOLVE in healthy never-smokers, healthy people with smoking history, and people with chronic obstructive pulmonary disease (COPD). STUDY TYPE: Prospective pilot. POPULATION: Twelve healthy never-smoker participants (age 30.3 ± 12.5 years, five male), four healthy participants with smoking history (>10 pack-years) (age 42.5 ± 18.3 years, one male), and 12 participants with COPD (age 62.8 ± 11.1 years, seven male). FIELD STRENGTH/SEQUENCE: Single-slice free-breathing two-dimensional fast field echo sequence at 3 T. ASSESSMENT: A novel postprocessing was developed to evaluate the MR signal changes in the lung parenchyma using a linear regression-based approach, which makes use of all the data in the time series for maximum sensitivity. V/Q-weighted maps were produced by computing the cross-correlation, lag and gradient between the respiratory/cardiac phase time course and lung parenchyma signal time courses. A comparison of histogram median and skewness values and spirometry was performed. STATISTICAL TESTS: Kruskal-Wallis tests with Dunn's multiple comparison tests to compare VOLVE metrics between groups; Spearman correlation to assess the correlation between MRI and spirometry-derived parameters; and Bland-Altman analysis and coefficient of variation to evaluate repeatability were used. A P-value <0.05 was considered significant. RESULTS: Significant differences between the groups were found for ventilation between healthy never-smoker and COPD groups (median XCCV, LagV, and GradV) and perfusion (median XCCQ, LagQ, and GradQ). Minimal bias and no significant differences between intravisit scans were found (P range = 0.12-0.97). DATA CONCLUSION: This preliminary study showed that VOLVE has potential to provide metrics of function quantification. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY: Stage 1.
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There has been growing interest in using quantitative magnetic resonance imaging (MRI) to describe and understand the pathophysiology of acute kidney injury (AKI). The ability to assess kidney blood flow, perfusion, oxygenation, and changes in tissue microstructure at repeated timepoints is hugely appealing, as this offers new possibilities to describe nature and severity of AKI, track the time-course to recovery or progression to chronic kidney disease (CKD), and may ultimately provide a method to noninvasively assess response to new therapies. This could have significant clinical implications considering that AKI is common (affecting more than 13 million people globally every year), harmful (associated with short and long-term morbidity and mortality), and currently lacks specific treatments. However, this is also a challenging area to study. After the kidney has been affected by an initial insult that leads to AKI, complex coexisting processes ensue, which may recover or can progress to CKD. There are various preclinical models of AKI (from which most of our current understanding derives), and these differ from each other but more importantly from clinical AKI. These aspects are fundamental to interpreting the results of the different AKI studies in which renal MRI has been used, which encompass different settings of AKI and a variety of MRI measures acquired at different timepoints. This review aims to provide a comprehensive description and interpretation of current studies (both preclinical and clinical) in which MRI has been used to assess AKI, and discuss future directions in the field. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY: Stage 3.
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Non-alcoholic fatty liver disease (NAFLD) is the liver manifestation of the metabolic syndrome with global prevalence reaching epidemic levels. Despite the high disease burden in the population only a small proportion of those with NAFLD will develop progressive liver disease, for which there is currently no approved pharmacotherapy. Identifying those who are at risk of progressive NAFLD currently requires a liver biopsy which is problematic. Firstly, liver biopsy is invasive and therefore not appropriate for use in a condition like NAFLD that affects a large proportion of the population. Secondly, biopsy is limited by sampling and observer dependent variability which can lead to misclassification of disease severity. Non-invasive biomarkers are therefore needed to replace liver biopsy in the assessment of NAFLD. Our study addresses this unmet need. The LITMUS Imaging Study is a prospectively recruited multi-centre cohort study evaluating magnetic resonance imaging and elastography, and ultrasound elastography against liver histology as the reference standard. Imaging biomarkers and biopsy are acquired within a 100-day window. The study employs standardised processes for imaging data collection and analysis as well as a real time central monitoring and quality control process for all the data submitted for analysis. It is anticipated that the high-quality data generated from this study will underpin changes in clinical practice for the benefit of people with NAFLD. Study Registration: clinicaltrials.gov: NCT05479721.
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Hepatopatia Gordurosa não Alcoólica , Humanos , Hepatopatia Gordurosa não Alcoólica/diagnóstico por imagem , Hepatopatia Gordurosa não Alcoólica/patologia , Estudos de Coortes , Fígado/diagnóstico por imagem , Fígado/patologia , Cirrose Hepática/diagnóstico por imagem , Cirrose Hepática/patologia , Imageamento por Ressonância Magnética/métodos , BiomarcadoresRESUMO
Recent advances in multiparametric magnetic resonance imaging (MRI) allow multiple quantitative measures to assess kidney morphology, tissue microstructure, oxygenation, kidney blood flow, and perfusion to be collected in a single scan session. Animal and clinical studies have investigated the relationship between the different MRI measures and biological processes, although their interpretation can be complex due to variations in study design and generally small participant numbers. However, emerging themes include the apparent diffusion coefficient derived from diffusion-weighted imaging, T1 and T2 mapping parameters, and cortical perfusion being consistently associated with kidney damage and predicting kidney function decline. Blood oxygen level-dependent (BOLD) MRI has shown inconsistent associations with kidney damage markers but has been predictive of kidney function decline in several studies. Therefore, multiparametric MRI of the kidneys has the potential to address the limitations of existing diagnostic methods to provide a noninvasive, noncontrast, and radiation-free method to assess whole kidney structure and function. Barriers to be overcome to facilitate widespread clinical application include improved understanding of biological factors that impact MRI measures, development of a larger evidence base for clinical utility, standardization of MRI protocols, automation of data analysis, determining optimal combination of MRI measures, and health economic evaluation.
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Nefropatias , Oxigênio , Animais , Humanos , Rim/patologia , Imageamento por Ressonância Magnética/métodos , Nefropatias/patologia , Circulação RenalRESUMO
BACKGROUND: Acute kidney injury (AKI) is associated with a marked increase in mortality as well as subsequent chronic kidney disease (CKD) and end-stage kidney disease. We performed multiparametric magnetic resonance imaging (MRI) with the aim of identifying potential non-invasive MRI markers of renal pathophysiology in AKI and during recovery. METHODS: Nine participants underwent inpatient MRI scans at time of AKI; seven had follow-up scans at 3 months and 1 year following AKI. Multiparametric renal MRI assessed total kidney volume (TKV), renal perfusion using arterial spin labelling, T1 mapping and blood oxygen level-dependent (BOLD) R2* mapping. RESULTS: Serum creatinine concentration had recovered to baseline levels at 1-year post-AKI in all participants. At the time of AKI, participants had increased TKV, increased cortex/medulla T1 and reduced cortical perfusion compared with the expected ranges in healthy volunteers and people with CKD. TKV and T1 values decreased over time after AKI and returned to expected values in most but not all patients by 1 year. Cortical perfusion improved to a lesser extent and remained below the expected range in the majority of patients by 1-year post-AKI. BOLD R2* data showed a non-significant trend to increase over time post-AKI. CONCLUSIONS: We observed a substantial increase in TKV and T1 during AKI and a marked decrease in cortical perfusion. Despite biochemical recovery at 1-year post-AKI, MRI measures indicated persisting abnormalities in some patients. We propose that such patients may be more likely to have further AKI episodes or progress to CKD and further longitudinal studies are required to investigate this. .
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BACKGROUND: Multi-parametric magnetic resonance imaging (MRI) provides the potential for a more comprehensive non-invasive assessment of organ structure and function than individual MRI measures, but has not previously been comprehensively evaluated in chronic kidney disease (CKD). METHODS: We performed multi-parametric renal MRI in persons with CKD (n = 22, 61 ± 24 years) who had a renal biopsy and measured glomerular filtration rate (mGFR), and matched healthy volunteers (HV) (n = 22, 61 ± 25 years). Longitudinal relaxation time (T1), diffusion-weighted imaging, renal blood flow (phase contrast MRI), cortical perfusion (arterial spin labelling) and blood-oxygen-level-dependent relaxation rate (R2*) were evaluated. RESULTS: MRI evidenced excellent reproducibility in CKD (coefficient of variation <10%). Significant differences between CKD and HVs included cortical and corticomedullary difference (CMD) in T1, cortical and medullary apparent diffusion coefficient (ADC), renal artery blood flow and cortical perfusion. MRI measures correlated with kidney function in a combined CKD and HV analysis: estimated GFR correlated with cortical T1 (r = -0.68), T1 CMD (r = -0.62), cortical (r = 0.54) and medullary ADC (r = 0.49), renal artery flow (r = 0.78) and cortical perfusion (r = 0.81); log urine protein to creatinine ratio (UPCR) correlated with cortical T1 (r = 0.61), T1 CMD (r = 0.61), cortical (r = -0.45) and medullary ADC (r = -0.49), renal artery flow (r = -0.72) and cortical perfusion (r = -0.58). MRI measures (cortical T1 and ADC, T1 and ADC CMD, cortical perfusion) differed between low/high interstitial fibrosis groups at 30-40% fibrosis threshold. CONCLUSION: Comprehensive multi-parametric MRI is reproducible and correlates well with available measures of renal function and pathology. Larger longitudinal studies are warranted to evaluate its potential to stratify prognosis and response to therapy in CKD.
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Testes de Função Renal/métodos , Rim/fisiopatologia , Imageamento por Ressonância Magnética/métodos , Circulação Renal , Insuficiência Renal Crônica/patologia , Feminino , Taxa de Filtração Glomerular , Humanos , Masculino , Pessoa de Meia-Idade , Insuficiência Renal Crônica/metabolismo , Reprodutibilidade dos TestesRESUMO
Noninvasive methods of magnetic resonance imaging (MRI) can quantify parameters of kidney function. The main purpose of this study was to determine baseline values of such parameters in healthy volunteers. In 28 healthy volunteers (15 women and 13 men), arterial spin labeling to estimate regional renal perfusion, blood oxygen level-dependent transverse relaxation rate (R2*) to estimate oxygenation, and apparent diffusion coefficient (ADC), true diffusion (D), and longitudinal relaxation time (T1) to estimate tissue properties were determined bilaterally in the cortex and outer and inner medulla. Additionally, phase-contrast MRI was applied in the renal arteries to quantify total renal blood flow. The results demonstrated profound gradients of perfusion, ADC, and D with highest values in the kidney cortex and a decrease towards the inner medulla. R2* and T1 were lowest in kidney cortex and increased towards the inner medulla. Total renal blood flow correlated with body surface area, body mass index, and renal volume. Similar patterns in all investigated parameters were observed in women and men. In conclusion, noninvasive MRI provides useful tools to evaluate intrarenal differences in blood flow, perfusion, diffusion, oxygenation, and structural properties of the kidney tissue. As such, this experimental approach has the potential to advance our present understanding regarding normal physiology and the pathological processes associated with acute and chronic kidney disease.
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Rim/diagnóstico por imagem , Rim/fisiologia , Adulto , Índice de Massa Corporal , Superfície Corporal , Água Corporal/metabolismo , Feminino , Voluntários Saudáveis , Humanos , Rim/anatomia & histologia , Córtex Renal/metabolismo , Medula Renal/metabolismo , Imageamento por Ressonância Magnética , Masculino , Oxigênio/sangue , Circulação Renal , Adulto JovemRESUMO
OBJECTIVES: To assess the feasibility of using an optimised ultra-high-field high-spatial-resolution low-distortion arterial spin labelling (ASL) MRI acquisition to measure focal haemodynamic pathology in cortical lesions (CLs) in multiple sclerosis (MS). METHODS: Twelve MS patients (eight female, mean age 50 years; range 35-64 years) gave informed consent and were scanned on a 7 Tesla Philips Achieva scanner. Perfusion data were collected at multiple post-labelling delay times using a single-slice flow-sensitive alternating inversion recovery ASL protocol with a balanced steady-state free precession readout scheme. CLs were identified using a high-resolution Phase-Sensitive Inversion Recovery (PSIR) scan. Significant differences in perfusion within CLs compared to immediately surrounding normal appearing grey matter (NAGMlocal) and total cortical normal appearing grey matter (NAGMcortical) were assessed using paired t-tests. RESULTS: Forty CLs were identified in PSIR scans that overlapped with the ASL acquisition coverage. After excluding lesions due to small size or intravascular contamination, 27 lesions were eligible for analysis. Mean perfusion was 40 ± 25 ml/100 g/min in CLs, 53 ± 12 ml/100 g/min in NAGMlocal, and 53 ± 8 ml/100 g/min in NAGMcortical. CL perfusion was significantly reduced by 23 ± 9% (mean ± SE, p = 0.013) and 26 ± 9% (p = 0.006) relative to NAGMlocal and NAGMcortical perfusion, respectively. CONCLUSION: This is the first ASL MRI study quantifying CL perfusion in MS at 7 Tesla, demonstrating that an optimised ASL acquisition is sensitive to focal haemodynamic pathology previously observed using dynamic susceptibility contrast MRI. ASL requires no exogenous contrast agent, making it a more appropriate tool to monitor longitudinal perfusion changes in MS, providing a new window to study lesion development. KEY POINTS: ⢠Perfusion can be quantified within cortical lesions in multiple sclerosis using an optimised high spatial resolution arterial spin Labelling MRI acquisition at ultra-high-field. ⢠The majority of cortical lesions assessed using arterial spin labelling are hypo-perfused compared to normal appearing grey matter, in agreement with dynamic susceptibility contrast MRI literature. ⢠Arterial spin labelling MRI, which does not involve the injection of a contrast agent, is a safe and appropriate technique for repeat scanning of an individual patient.
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Artérias Cerebrais/diagnóstico por imagem , Circulação Cerebrovascular/fisiologia , Substância Cinzenta/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Esclerose Múltipla/diagnóstico , Fluxo Sanguíneo Regional/fisiologia , Adulto , Artérias Cerebrais/fisiopatologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Esclerose Múltipla/fisiopatologia , Marcadores de SpinRESUMO
BACKGROUND: Renal flow abnormalities are believed to play a central role in the pathogenesis of nephropathy and in primary and secondary hypertension, but are difficult to measure in humans. Handgrip exercise is known to reduce renal arterial flow (RAF) by means of increased renal sympathetic nerve activity. METHODS: To monitor medullary and cortical oxygenation under handgrip exercise-reduced perfusion, we used contrast- and radiation-free magnetic resonance imaging (MRI) to measure regional changes in renal perfusion and blood oxygenation in ten healthy normotensive individuals during handgrip exercise. We used phase-contrast MRI to measure RAF, arterial spin labeling to measure perfusion, and both changes in transverse relaxation time (T2*) and dynamic blood oxygenation level-dependent imaging to measure blood oxygenation. RESULTS: Handgrip exercise induced a significant decrease in RAF. In the renal medulla, this was accompanied by an increase of oxygenation (reflected by an increase in T2*) despite a significant drop in medullary perfusion; the renal cortex showed a significant decrease in both perfusion and oxygenation. We also found a significant correlation (R2=0.8) between resting systolic BP and the decrease in RAF during handgrip exercise. CONCLUSIONS: Renal MRI measurements in response to handgrip exercise were consistent with a sympathetically mediated decrease in RAF. In the renal medulla, oxygenation increased despite a reduction in perfusion, which we interpreted as the result of decreased GFR and a subsequently reduced reabsorptive workload. Our results further indicate that the renal flow response's sensitivity to sympathetic activation is correlated with resting BP, even within a normotensive range.
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Força da Mão , Córtex Renal/irrigação sanguínea , Córtex Renal/metabolismo , Medula Renal/irrigação sanguínea , Medula Renal/metabolismo , Adulto , Velocidade do Fluxo Sanguíneo/fisiologia , Exercício Físico/fisiologia , Feminino , Voluntários Saudáveis , Humanos , Córtex Renal/inervação , Medula Renal/inervação , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Oxigênio/sangue , Artéria Renal/fisiologia , Circulação Renal/fisiologia , Sistema Nervoso Simpático/fisiologia , Adulto JovemRESUMO
BACKGROUND & AIMS: Advancing liver disease results in deleterious changes in a number of critical organs. The ability to measure structure, blood flow and tissue perfusion within multiple organs in a single scan has implications for determining the balance of benefit vs. harm for therapies. Our aim was to establish the feasibility of magnetic resonance imaging (MRI) to assess changes in Compensated Cirrhosis (CC), and relate this to disease severity and future liver-related outcomes (LROs). METHODS: A total of 60 patients with CC, 40 healthy volunteers and 7 patients with decompensated cirrhosis were recruited. In a single scan session, MRI measures comprised phase-contrast MRI vessel blood flow, arterial spin labelling tissue perfusion, T1 longitudinal relaxation time, heart rate, cardiac index, and volume assessment of the liver, spleen and kidneys. We explored the association between MRI parameters and disease severity, analysing differences in baseline MRI parameters in the 11 (18%) patients with CC who experienced future LROs. RESULTS: In the liver, compositional changes were reflected by increased T1 in progressive disease (pâ¯<0.001) and an increase in liver volume in CC (pâ¯=â¯0.006), with associated progressive reduction in liver (pâ¯<0.001) and splenic (pâ¯<0.001) perfusion. A significant reduction in renal cortex T1 and increase in cardiac index and superior mesenteric arterial blood flow was seen with increasing disease severity. Baseline liver T1 (pâ¯=â¯0.01), liver perfusion (pâ¯<0.01), and renal cortex T1 (pâ¯<0.01) were significantly different in patients with CC who subsequently developed negative LROs. CONCLUSIONS: MRI enables the contemporaneous assessment of organs in liver cirrhosis in a single scan without the requirement for a contrast agent. MRI parameters of liver T1, renal T1, hepatic and splenic perfusion, and superior mesenteric arterial blood flow were related to the risk of LROs. LAY SUMMARY: This study assesses the changes to structure, blood flow and perfusion that occur in the key organs (liver, spleen and kidney) associated with severe liver disease (Compensated Cirrhosis), using magnetic resonance imaging. The magnetic resonance imaging measures which changed with disease severity and were related to negative liver-related clinical outcomes are described.
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Cirrose Hepática/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Idoso , Feminino , Humanos , Rim/diagnóstico por imagem , Fígado/diagnóstico por imagem , Masculino , Pessoa de Meia-Idade , Fluxo Sanguíneo Regional , Índice de Gravidade de Doença , Baço/diagnóstico por imagemRESUMO
PURPOSE: In vivo 31 P magnetic resonance spectroscopy (MRS) magnetization transfer (MT) provides a direct measure of neuronal activity at the metabolic level. This work aims to use functional 31 P MRS-MT to investigate the change in cerebral adenosine triphosphate (ATP) metabolic rates in healthy adults upon repeated visual stimuli. METHODS: A magnetization saturation transfer sequence with narrowband selective saturation of γ-ATP was developed for 31 P MT experiments at 3 T. RESULTS: Using progressive saturation of γ-ATP, the intrinsic T1 relaxation times of phosphocreatine (PCr) and inorganic phosphate (Pi) at 3 T were measured to be 5.1 ± 0.8 s and 3.0 ± 1.4 s, respectively. Using steady-state saturation of γ-ATP, a significant 24% ± 14% and 11% ± 7% increase in the forward creatine kinase (CK) pseudo-first-order reaction rate constant, k1 , was observed upon visual stimulation in the first and second cycles, respectively, of a paradigm consisting of 10-minute rest followed by 10-minute stimulation, with the measured baseline k1 being 0.35 ± 0.04 s-1 . No significant changes in forward ATP synthase reaction rate, PCr/γ-ATP, Pi/γ-ATP, and nicotinamide adenine dinucleotide/γ-ATP ratios, or intracellular pH were detected upon stimulation. CONCLUSION: This work demonstrates the potential of studying cerebral bioenergetics using functional 31 P MRS-MT to determine the change in the forward CK reaction rate at 3 T. Magn Reson Med 79:22-30, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
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Trifosfato de Adenosina/química , Mapeamento Encefálico/métodos , Espectroscopia de Ressonância Magnética , Neurônios/patologia , Isótopos de Fósforo/química , Encéfalo/diagnóstico por imagem , Creatina Quinase/metabolismo , Humanos , Concentração de Íons de Hidrogênio , Cinética , Magnetismo , Modelos Estatísticos , Método de Monte CarloRESUMO
BACKGROUND & AIMS: Hepatic venous pressure gradient (HVPG) measurement is currently the only validated technique to accurately evaluate changes in portal pressure. In this study, we evaluate the use of non-contrast quantitative magnetic resonance imaging (MRI) as a surrogate measure of portal pressure. METHODS: Thirty patients undergoing HVPG measurement were prospectively recruited. MR parameters of longitudinal relaxation time (T1), perfusion of the liver and spleen (by arterial spin labelling), and blood flow in the portal, splanchnic and collateral circulation (by phase contrast MRI) were assessed. We estimated the liver stiffness measurement (LSM) and enhanced liver fibrosis (ELF) score. The correlation of all non-invasive parameters with HVPG was evaluated. RESULTS: The mean (range) HVPG of the patients was 9.8 (1-22) mmHg, and 14 patients (48%) had clinically significant portal hypertension (CSPH, HVPG ⩾10mmHg). Liver T1 relaxation time, splenic artery and superior mesenteric artery velocity correlated significantly with HVPG. Using multiple linear regression, liver T1 and splenic artery velocity remained as the two parameters in the multivariate model significantly associated with HVPG (R=0.90, p<0.001). This correlation was maintained in patients with CSPH (R=0.85, p<0.001). A validation cohort (n=10) showed this linear model provided a good prediction of HVPG. LSM and ELF score correlated significantly with HVPG in the whole population but the correlation was absent in CSPH. CONCLUSIONS: MR parameters related to both hepatic architecture and splanchnic haemodynamics correlate significantly with HVPG. This proposed model, confirmed in a validation cohort, could replace the invasive HVPG measurement. LAY SUMMARY: In patients with cirrhosis, the development and progression of portal hypertension is related to worse outcomes. However, the standard technique of assessing portal pressure is invasive and not widely used in clinical practice. Here, we have studied the use of non-invasive MRI in evaluating portal pressure. The MRI measures of liver architecture and blood flow in the splenic artery correlated well with portal pressure. Therefore, this non-invasive method can potentially be used to assess portal pressure in clinical trials and monitoring treatment in practice.
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Hipertensão Portal , Humanos , Cirrose Hepática , Imageamento por Ressonância Magnética , Pressão na Veia PortaRESUMO
PURPOSE: To dynamically quantify pancreatic perfusion and flow within the arteries supplying the pancreas in response to secretin stimulation. MATERIALS AND METHODS: Twelve healthy male subjects were scanned at 1.5T with arterial spin labeling to measure tissue perfusion and phase contrast magnetic resonance imaging (MRI) to measure vessel flow. Superior mesenteric (SMA), gastroduodenal (GDA), common hepatic (HA), and splenic (SA) arterial flow and pancreatic perfusion were serially measured for 50 minutes following 1 IU/kg intravenous secretin. The significance of differences between timepoints was tested using a repeated measures one-way analysis of variance (ANOVA). RESULTS: Baseline blood flow (mean ± SEM or median [IQR]) for SMA, HA, SA, and GDA was 7.6 ± 1.3, 4.0 ± 0.5, 8.2 ± 0.8, and 0.9 (0.8-1.4) ml/s, respectively. Baseline pancreatic perfusion was 200 ± 25 ml/100g/min. Blood flow increased in the SMA (234%, P < 0.0001) and GDA (155%, P = 0.015) immediately after secretin injection. Reduced HA blood flow was observed after 10 minutes (P = 0.066) with no change in SA flow (P = 0.533). Increased pancreatic perfusion was maintained for 40 minutes after injection with a maximal increase at 5 minutes (16.8%, P = 0.025). CONCLUSION: Intravenous secretin resulted in significant temporal changes in pancreatic perfusion and arterial blood flow.
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Imageamento por Ressonância Magnética , Pâncreas/irrigação sanguínea , Secretina/administração & dosagem , Adulto , Análise de Variância , Meios de Contraste , Fármacos Gastrointestinais/administração & dosagem , Humanos , Aumento da Imagem , Masculino , Pâncreas/efeitos dos fármacos , Pâncreas/fisiologia , Fluxo Sanguíneo Regional/fisiologia , Marcadores de Spin , Tempo , Adulto JovemRESUMO
The binocular disparity between the views of the world registered by the left and right eyes provides a powerful signal about the depth structure of the environment. Despite increasing knowledge of the cortical areas that process disparity from animal models, comparatively little is known about the local architecture of stereoscopic processing in the human brain. Here, we take advantage of the high spatial specificity and image contrast offered by 7 tesla fMRI to test for systematic organization of disparity representations in the human brain. Participants viewed random dot stereogram stimuli depicting different depth positions while we recorded fMRI responses from dorsomedial visual cortex. We repeated measurements across three separate imaging sessions. Using a series of computational modeling approaches, we report three main advances in understanding disparity organization in the human brain. First, we show that disparity preferences are clustered and that this organization persists across imaging sessions, particularly in area V3A. Second, we observe differences between the local distribution of voxel responses in early and dorsomedial visual areas, suggesting different cortical organization. Third, using modeling of voxel responses, we show that higher dorsal areas (V3A, V3B/KO) have properties that are characteristic of human depth judgments: a simple model that uses tuning parameters estimated from fMRI data captures known variations in human psychophysical performance. Together, these findings indicate that human dorsal visual cortex contains selective cortical structures for disparity that may support the neural computations that underlie depth perception.
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Imageamento por Ressonância Magnética , Disparidade Visual/fisiologia , Córtex Visual/irrigação sanguínea , Córtex Visual/fisiologia , Adulto , Mapeamento Encefálico , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Oxigênio/sangue , Estimulação Luminosa , ProbabilidadeRESUMO
OBJECTIVES: To identify priority medicines policy issues for New Zealand. SETTING: Stakeholders from a broad range of healthcare and policy institutions including primary, secondary and tertiary care. PARTICIPANTS: Exploratory, semistructured interviews were conducted with 20 stakeholders throughout New Zealand. PRIMARY AND SECONDARY OUTCOME MEASURES: The interviews were digitally recorded, transcribed and coded into INVIVO 10, then compared and grouped for similarity of theme. Perceptions, experiences and opinions regarding New Zealand's medicines policy issues were recorded. RESULTS: A large proportion of stakeholders appeared to be unaware of New Zealand's (NZ) medicines policy. In general, the policy was considered to offer consistency to guide decision-making. In the context of Pharmaceutical Management Agency's (PHARMAC's) fixed budget for procuring and subsidising medicines, there was reasonable satisfaction with the range of medicines available-rare disorder medicines being the clear exception. Concerns raised were by whom and how decisions are made and whether desired health outcomes are being measured. Other concerns included inconsistencies in evidence and across health technologies. Despite attempts to improve the situation, lower socioeconomic groups (including rural residents) Maori and Pacific ethnicities and people with rare disorders face challenges with regards to accessing medicines. Other barriers include, convenience to and affordability of prescribers and the increase of prescription fees from NZ$3 to NZ$5. Concerns related to the PHARMAC of New Zealand included: a constraining budget; non-transparency of in-house analysis; lack of consistency in recommendations between the Pharmacology and Therapeutics Advisory Committee. Constraints and inefficiencies also exist in the submission process to access high-cost medicines. CONCLUSIONS: The results suggest reasonable satisfaction with the availability of subsidised medicines. However, some of the major challenges include access to medicines in vulnerable groups, increasing costs and demand for new medicines, access to prescribers, budgetary constraints, cultural and health literacy, patient affordability and evidence requirement for gaining subsidy for medicines.
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Controle de Medicamentos e Entorpecentes , Medicamentos sob Prescrição/provisão & distribuição , Custos de Medicamentos , Humanos , Nova Zelândia , Medicamentos sob Prescrição/economiaRESUMO
PURPOSE OF REVIEW: Recent data have highlighted the importance of quantitative measures of organ perfusion and functional reserve. Magnetic resonance imaging allows the assessment of markers of perfusion without the use of contrast media. Techniques such as arterial spin labelling (ASL) and blood oxygen level-dependent (BOLD) imaging have been available for some time, but advances in the technology and concerns over the safety of contrast media in renal disease have spurred renewed interest and development. RECENT FINDINGS: ASL measures perfusion, whereas BOLD imaging provides a marker of blood oxygenation, arising from the compound effect of a number of measures including perfusion, blood volume and oxygen consumption; thus, the techniques are complementary rather than analogous. They were initially confined to brain imaging as inherently low signal, susceptibility effects and motion limited their use in thoracic and abdominal organs. Advances in technology have led to robust sequences that can quantify clinically relevant changes and correlate well with reference standards. Novel approaches are likely to accelerate translation into clinical practice. SUMMARY: The noninvasive and repeatable nature of ASL and BOLD imaging makes it likely that they will be increasingly used in clinical research. Using a developmental framework, we suggest that the application of these techniques to thoracic and abdominal organs requires validation before they are suitable for generalized clinical use. The demand for these techniques is likely to be driven by the incentive to avoid the use of contrast media.