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1.
Magn Reson Med ; 86(1): 320-334, 2021 07.
Artigo em Inglês | MEDLINE | ID: mdl-33645815

RESUMO

PURPOSE: To develop an improved reconstruction method, k-space subtraction with phase and intensity correction (KSPIC), for highly accelerated, subtractive, non-contrast-enhanced MRA. METHODS: The KSPIC method is based on k-space subtraction of complex raw data. It applies a phase-correction procedure to restore the polarity of negative signals caused by subtraction and an intensity-correction procedure to improve background suppression and thereby sparsity. Ten retrospectively undersampled data sets and 10 groups of prospectively undersampled data sets were acquired in 12 healthy volunteers. The performance of KSPIC was compared with another improved reconstruction based on combined magnitude subtraction, as well as with conventional k-space subtraction reconstruction and magnitude subtraction reconstruction, both using quantitative metrics and using subjective quality scoring. RESULTS: In the quantitative evaluation, KSPIC had the best performance in terms of peak SNR, structural similarity index measure, contrast-to-noise ratio of artery-to-background and sharpness, especially at high acceleration factors. The KSPIC method also had the highest subjective scores for all acceleration factors in terms of vessel delineation, image noise and artifact, and background contamination. The acquisition can be accelerated by a factor of 20 without significant decreases of subjective scores. The optimal size of the phase-correction region was found to be 12-20 pixels in this study. CONCLUSION: Compared with combined magnitude subtraction and conventional reconstructions, KSPIC has the best performance in all of the quantitative and qualitative measurements, permitting good image quality to be maintained up to higher accelerations. The KSPIC method has the potential to further reduce the acquisition time of subtractive MRA for clinical examinations.


Assuntos
Angiografia por Ressonância Magnética , Técnica de Subtração , Artefatos , Artéria Femoral/diagnóstico por imagem , Humanos , Processamento de Imagem Assistida por Computador , Estudos Retrospectivos
2.
Magn Reson Med ; 85(2): 694-708, 2021 02.
Artigo em Inglês | MEDLINE | ID: mdl-32754954

RESUMO

PURPOSE: To correct the intensity difference of static background signal between bright blood images and dark blood images in subtractive non-contrast-enhanced MR angiography using robust regression, thereby improving static background signal suppression on subtracted angiograms. METHODS: Robust regression (RR), using iteratively reweighted least squares, is used to calculate the regression coefficient of background tissues from a scatter plot showing the voxel intensity of bright blood images versus dark blood images. The weighting function is based on either the Euclidean distance from the estimated regression line or the deviation angle. Results from RR using the deviation angle (RRDA), conventional RR using the Euclidean distance, and ordinary leastsquares regression were compared with reference values determined manually by two observers. Performance was evaluated over studies using different sequences, including 36 thoracic flow-sensitive dephasing data sets, 13 iliac flow-sensitive dephasing data sets, and 26 femoral fresh blood imaging data sets. RESULTS: RR deviation angle achieved robust and accurate performance in all types of images, with small bias, small mean absolute error, and high-correlation coefficients with reference values. Background tissues, such as muscle, veins, and bladder, were suppressed while the vascular signal was preserved. Euclidean distance gave good performance for thoracic and iliac flow-sensitive dephasing, but could not suppress background tissues in femoral fresh blood imaging. Ordinary least squares regression was sensitive to outliers and overestimated regression coefficients in thoracic flow-sensitive dephasing. CONCLUSION: Weighted subtraction using RR was able to acquire the regression coefficients of background signal and improve background suppression of subtractive non-contrast-enhanced MR angiography techniques. RR deviation angle has the most robust and accurate overall performance among three regression methods.


Assuntos
Meios de Contraste , Angiografia por Ressonância Magnética , Artéria Femoral , Sensibilidade e Especificidade , Técnica de Subtração
3.
Proc Natl Acad Sci U S A ; 117(4): 2092-2098, 2020 01 28.
Artigo em Inglês | MEDLINE | ID: mdl-31964840

RESUMO

Our purpose is to investigate the feasibility of imaging tumor metabolism in breast cancer patients using 13C magnetic resonance spectroscopic imaging (MRSI) of hyperpolarized 13C label exchange between injected [1-13C]pyruvate and the endogenous tumor lactate pool. Treatment-naïve breast cancer patients were recruited: four triple-negative grade 3 cancers; two invasive ductal carcinomas that were estrogen and progesterone receptor-positive (ER/PR+) and HER2/neu-negative (HER2-), one grade 2 and one grade 3; and one grade 2 ER/PR+ HER2- invasive lobular carcinoma (ILC). Dynamic 13C MRSI was performed following injection of hyperpolarized [1-13C]pyruvate. Expression of lactate dehydrogenase A (LDHA), which catalyzes 13C label exchange between pyruvate and lactate, hypoxia-inducible factor-1 (HIF1α), and the monocarboxylate transporters MCT1 and MCT4 were quantified using immunohistochemistry and RNA sequencing. We have demonstrated the feasibility and safety of hyperpolarized 13C MRI in early breast cancer. Both intertumoral and intratumoral heterogeneity of the hyperpolarized pyruvate and lactate signals were observed. The lactate-to-pyruvate signal ratio (LAC/PYR) ranged from 0.021 to 0.473 across the tumor subtypes (mean ± SD: 0.145 ± 0.164), and a lactate signal was observed in all of the grade 3 tumors. The LAC/PYR was significantly correlated with tumor volume (R = 0.903, P = 0.005) and MCT 1 (R = 0.85, P = 0.032) and HIF1α expression (R = 0.83, P = 0.043). Imaging of hyperpolarized [1-13C]pyruvate metabolism in breast cancer is feasible and demonstrated significant intertumoral and intratumoral metabolic heterogeneity, where lactate labeling correlated with MCT1 expression and hypoxia.


Assuntos
Neoplasias da Mama/diagnóstico por imagem , Imageamento por Ressonância Magnética/métodos , Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Neoplasias da Mama/patologia , Isótopos de Carbono/química , Isótopos de Carbono/metabolismo , Feminino , Humanos , Subunidade alfa do Fator 1 Induzível por Hipóxia/genética , Subunidade alfa do Fator 1 Induzível por Hipóxia/metabolismo , L-Lactato Desidrogenase/genética , L-Lactato Desidrogenase/metabolismo , Imageamento por Ressonância Magnética/instrumentação , Transportadores de Ácidos Monocarboxílicos/genética , Transportadores de Ácidos Monocarboxílicos/metabolismo , Proteínas Musculares/genética , Proteínas Musculares/metabolismo , Ácido Pirúvico/química , Ácido Pirúvico/metabolismo , Simportadores/genética , Simportadores/metabolismo
4.
Neuroimage ; 189: 171-179, 2019 04 01.
Artigo em Inglês | MEDLINE | ID: mdl-30639333

RESUMO

Hyperpolarized 13C Magnetic Resonance Imaging (13C-MRI) provides a highly sensitive tool to probe tissue metabolism in vivo and has recently been translated into clinical studies. We report the cerebral metabolism of intravenously injected hyperpolarized [1-13C]pyruvate in the brain of healthy human volunteers for the first time. Dynamic acquisition of 13C images demonstrated 13C-labeling of both lactate and bicarbonate, catalyzed by cytosolic lactate dehydrogenase and mitochondrial pyruvate dehydrogenase respectively. This demonstrates that both enzymes can be probed in vivo in the presence of an intact blood-brain barrier: the measured apparent exchange rate constant (kPL) for exchange of the hyperpolarized 13C label between [1-13C]pyruvate and the endogenous lactate pool was 0.012 ±â€¯0.006 s-1 and the apparent rate constant (kPB) for the irreversible flux of [1-13C]pyruvate to [13C]bicarbonate was 0.002 ±â€¯0.002 s-1. Imaging also revealed that [1-13C]pyruvate, [1-13C]lactate and [13C]bicarbonate were significantly higher in gray matter compared to white matter. Imaging normal brain metabolism with hyperpolarized [1-13C]pyruvate and subsequent quantification, have important implications for interpreting pathological cerebral metabolism in future studies.


Assuntos
Encéfalo/diagnóstico por imagem , Encéfalo/metabolismo , Isótopos de Carbono , Imageamento por Ressonância Magnética/métodos , Neuroimagem/métodos , Ácido Pirúvico , Adulto , Feminino , Humanos , Masculino
5.
Magn Reson Med ; 81(3): 1769-1783, 2019 03.
Artigo em Inglês | MEDLINE | ID: mdl-30444041

RESUMO

PURPOSE: To evaluate the performance of acceleration-dependent vascular anatomy for non-contrast-enhanced MR venography (ADVANCE-MRV) in femoral veins and to investigate whether venous signal uniformity can be improved by applying multiple acquisitions with different flow suppressions or multiple flow suppressions in 1 acquisition. METHODS: The ADVANCE-MRV method uses flow-sensitized modules to acquire a dark-artery image set and a dark-artery vein set, which are subsequently subtracted. Ten healthy volunteers were imaged using the ADVANCE-MRV sequence with improved venous suppression uniformity in the dark-artery vein images achieved by applying multiple flow suppressions in the same acquisition or by combining multiple images acquired with different flow suppressions. The performance of the improved technique was also evaluated in 13 patients with lower-limb deep venous thrombosis. RESULTS: Multiple-preparation and multiple-acquisition approaches all improved venous signal uniformity and reduced the signal void artifacts observed in the original ADVANCE-MRV images. The multiple-acquisition approaches achieved excellent blood signal uniformity and intensity, albeit at the cost of an increase in the total acquisition time. The double-preparation approach demonstrated good performance in all measurements, providing a good compromise between signal uniformity and acquisition time. The blood signal spatial variation and its variation using different gradient amplitudes were reduced by 20% and 29%. All patient images showed uniform and bright venous signal in nonoccluded sections of vein. CONCLUSION: The enhanced ADVANCE-MRV methods substantially improved signal uniformity in healthy volunteers and patients with known deep venous thrombosis. The double-preparation approach gave good-quality femoral vein images, providing improved venous signal uniformity without increasing acquisition time in comparison to the original sequence.


Assuntos
Extremidade Inferior/diagnóstico por imagem , Angiografia por Ressonância Magnética/métodos , Adolescente , Adulto , Idoso , Algoritmos , Artérias/diagnóstico por imagem , Simulação por Computador , Feminino , Veia Femoral/diagnóstico por imagem , Voluntários Saudáveis , Humanos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Masculino , Pessoa de Meia-Idade , Movimento (Física) , Flebografia , Veia Poplítea/diagnóstico por imagem , Reprodutibilidade dos Testes , Veias/diagnóstico por imagem , Trombose Venosa/diagnóstico por imagem , Adulto Jovem
6.
Acta Radiol ; 59(4): 418-424, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-28707958

RESUMO

Background Dedicated blood-pool contrast agents combined with optimal angiographic protocols could improve the diagnostic accuracy of thoracic magnetic resonance angiography (MRA). Purpose To assess the clinical utility of Gadofesveset-enhanced imaging and compare an optimized steady-state (SS) sequence against conventional first-pass dynamic multi-phase (DMP) imaging. Material and Methods Twenty-nine patients (17 men, 12 women; mean age = 42.7, age range = 18-72 years) referred for MR thoracic venography were recruited. Imaging was performed on a 1.5T MRI system. A blood-pool contrast agent (Gadofesveset) was administered intravenously. Thirty temporal phases were acquired using DMP. This was immediately followed by a high-resolution SS sequence. Three radiologists in consensus reviewed seven thoracic vascular segments after randomizing the acquisition order. Image quality, stenoses, thromboses, and artifacts were graded using a categorical scoring system. The image quality for both approaches was compared using Wilcoxon's signed-rank test. McNemar's test was used to compare the proportions of stenosis grades, thrombus and artifacts. Results SS had significantly better image quality than DMP (3.14 ± 0.73 and 2.92 ± 0.60, respectively; P < 0.001). SS identified fewer stenoses (>50%) than DMP; the differences in stenosis categorizations was statistically significant ( P = 0.013). There was no significant difference in the proportions of vessels with thromboses ( P = 0.617). DMP produced more artifacts than SS (101 versus 85); however, the difference was not statistically significant ( P = 0.073). Conclusion Gadofesveset-enhanced thoracic angiography is clinically feasible. SS imaging produces better image quality and fewer artifacts than conventional DMP imaging.


Assuntos
Meios de Contraste , Gadolínio , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Angiografia por Ressonância Magnética/métodos , Compostos Organometálicos , Adolescente , Adulto , Idoso , Artefatos , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Tórax/irrigação sanguínea , Tórax/diagnóstico por imagem , Adulto Jovem
7.
Br J Radiol ; 90(1075): 20160875, 2017 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-28511589

RESUMO

OBJECTIVE: To aid the extraction of the portal venous input function (PVIF) from axial dynamic contrast-enhanced CT images of the liver, eliminating the need for full manual outlining of the vessel across time points. METHODS: A cohort of 20 patients undergoing perfusion CT imaging of the liver was examined. Dynamic images of the liver were reformatted into contiguous thin slices. A region of interest was defined within a transverse section of the portal vein on a single contrast-enhanced image. This region of interest was then computationally projected across all thin slices for all time points to yield a semi-automated PVIF curve. This was compared against the "gold-standard" PVIF curve obtained by conventional manual outlining. RESULTS: Bland-Altman plots of curve characteristics indicated no substantial difference between automated and manual PVIF curves [concordance correlation coefficient in the range (0.66, 0.98)]. No substantial differences were shown by Bland-Altman plots of derived pharmacokinetic parameters when a suitable kinetic model was applied in each case [concordance correlation coefficient in range (0.92, 0.95)]. CONCLUSION: This semi-automated method of extracting the PVIF performed equivalently to a "gold-standard" manual method for assessing liver function. Advances in knowledge: This technique provides a quick, simple and effective solution to the problems incurred by respiration motion and partial volume factors in the determination of the PVIF in liver dynamic contrast-enhanced CT.


Assuntos
Hepatopatias/diagnóstico por imagem , Fígado/irrigação sanguínea , Fígado/diagnóstico por imagem , Veia Porta/diagnóstico por imagem , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Tomografia Computadorizada por Raios X/métodos , Algoritmos , Meios de Contraste/farmacocinética , Humanos , Iohexol/farmacocinética , Iopamidol/farmacocinética , Movimento (Física) , Sensibilidade e Especificidade
8.
J Med Imaging Radiat Oncol ; 61(5): 636-642, 2017 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-28432731

RESUMO

INTRODUCTION: Hepatic morphology changes are well described in Primary Sclerosing Cholangitis and characterised by a combination of atrophy and hypertrophy changes. This study investigates the relationship between progression of these changes over time and clinical outcome in patients with PSC. METHODS: Fifty-three patients with PSC (mean age 44, 28 males and 25 females) who underwent serial MRI liver studies at least one year apart were identified. The first and the last MRI studies were selected for the retrospective analysis. Three radiologists reviewed and compared both studies for changes in hepatic morphology, specifically atrophy and/or hypertrophy. The imaging findings were correlated with adverse clinical outcomes defined as death or liver transplantation and with serum bilirubin. RESULTS: There was a mean interval of 60 months between MRI examinations and a mean clinical follow-up period thereafter of 22 months. Thirty-three (62.3%) patients had stable hepatic morphology, whilst 20 (37.7%) patients showed hepatic morphology changes (atrophy: 13 patients, 24%; hypertrophy: 16 patients, 30%). Eleven patients (21%) died or underwent liver transplantation. There was a significant correlation between interval hepatic atrophy and adverse clinical outcomes (P = 0.001). Significant correlations were found between increasing serum bilirubin level and interval hepatic atrophy, hepatic hypertrophy and combined changes (P = 0.025, P = 0.022, P = 0.027, respectively). CONCLUSION: Hepatic morphology changes over time in patients with PSC are heterogeneous with some patients developing atrophy and/or hypertrophy whilst other patients remain stable. In this retrospective study, progressive hepatic atrophy showed significant association with adverse clinical outcome defined by either death or liver transplantation.


Assuntos
Colangite Esclerosante/diagnóstico por imagem , Colangite Esclerosante/patologia , Imageamento por Ressonância Magnética/métodos , Adulto , Bilirrubina/sangue , Colangite Esclerosante/mortalidade , Colangite Esclerosante/cirurgia , Progressão da Doença , Feminino , Humanos , Transplante de Fígado , Masculino , Estudos Retrospectivos
9.
Br J Radiol ; 90(1070): 20160813, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-27936892

RESUMO

This short commentary provides the MRI community in the UK with practical advice on the impact of the Control of Electromagnetic Fields at Work Regulations 2016 in clinical and research settings. The regulations are the UK implementation of the European Union Physical Agents (Electromagnetic Fields) Directive, which has been the subject of much discussion and concern over the past 13 years. However, thanks to concessions achieved through negotiation, and sensible and proportionate transposition into UK law by the Health and Safety Executive, the negative consequences that were foreseen have been averted. MRI activities are exempt from the occupational exposure limits contained in the regulations, subject to meeting certain conditions. The commentary gives advice on compliance with these conditions and on how to satisfy the other requirements of the regulations, all of which are either already required under existing legislation or represent good MR safety practice.


Assuntos
Campos Eletromagnéticos , Imageamento por Ressonância Magnética/métodos , Doenças Profissionais/prevenção & controle , Exposição Ocupacional/prevenção & controle , Guias de Prática Clínica como Assunto , Segurança de Equipamentos , Humanos , Reino Unido
11.
J Magn Reson Imaging ; 45(6): 1846-1853, 2017 06.
Artigo em Inglês | MEDLINE | ID: mdl-27902859

RESUMO

PURPOSE: To evaluate the diagnostic performance of velocity- and acceleration-sensitized noncontrast-enhanced magnetic resonance angiography (NCE-MRA) of the infrageniculate arteries using contrast-enhanced MRA (CE-MRA) as a reference standard. MATERIALS AND METHODS: Twenty-four patients with symptoms of peripheral arterial disease were recruited. Each patient's infrageniculate arterial tree was examined using a velocity-dependent flow-sensitized dephasing (VEL-FSD) technique, an acceleration-dependent (ACC-FSD) technique, and our conventional CE-MRA technique performed at 1.5T. The images were independently reviewed by two experienced vascular radiologists, who evaluated each vessel segment to assess visibility, diagnostic confidence, venous contamination, and detection of pathology. RESULTS: In all, 432 segments were evaluated by each of the three techniques by each reader in total. Overall diagnostic confidence was rated as moderate or high in 98.5% of segments with CE-MRA, 92.1% with VEL-FSD, and 79.9% with ACC-FSD. No venous contamination was seen in 96% of segments with CE-MRA, 72.2% with VEL-FSD, and 85.8% with ACC-FSD. Per-segment, per-limb, and per-patient sensitivities for detecting significant stenotic disease were 63.4%, 73%, and 92%, respectively, for ACC-FSD, and 65.3%, 87.2%, and 96% for VEL-FSD, and as such no significant statistical change was detected using McNemar's chi-squared test with P-values of 1.00, 0.13, and 0.77 obtained, respectively. CONCLUSION: Flow-dependent NCE-MRA techniques may have a role to play in evaluation of patients with peripheral vascular disease. Increased sensitivity of a velocity-based technique compared to an acceleration-based technique comes at the expense of greater venous contamination. LEVEL OF EVIDENCE: 2J. Technical Efficacy: Stage 2 J. MAGN. RESON. IMAGING 2017;45:1846-1853.


Assuntos
Aumento da Imagem/métodos , Perna (Membro)/irrigação sanguínea , Perna (Membro)/diagnóstico por imagem , Angiografia por Ressonância Magnética/métodos , Doença Arterial Periférica/diagnóstico por imagem , Processamento de Sinais Assistido por Computador , Idoso , Idoso de 80 Anos ou mais , Feminino , Humanos , Interpretação de Imagem Assistida por Computador/métodos , Perna (Membro)/patologia , Masculino , Pessoa de Meia-Idade , Doença Arterial Periférica/patologia , Reprodutibilidade dos Testes , Sensibilidade e Especificidade
12.
Magn Reson Imaging ; 37: 46-50, 2017 04.
Artigo em Inglês | MEDLINE | ID: mdl-27746391

RESUMO

PURPOSE: Hepatic magnetic resonance elastography (MRE) is currently a breath-hold imaging technique. Patients with chronic liver disease can have comorbidities that limit their ability to breath-hold (BH) for the required acquisition time. Our aim was to evaluate whether stiffness measurements obtained from a navigator-triggered MRE acquisition are comparable to standard expiratory breath-hold, inspiratory breath-hold or free-breathing in healthy participants. MATERIALS AND METHODS: Twelve healthy participants were imaged using the four methods on a clinical 1.5T MR system equipped with a product MRE system. Mean liver stiffness, and measurable area of stiffness (with a confidence threshold >95%) were compared between sequences using the concordance correlation coefficient. Repeatability of each sequence between two acquisitions was also assessed. RESULTS: The standard BH expiratory technique had high concordance with the navigated technique (r=0.716), and low concordance with the BH inspiration (r=0.165) and free-breathing (r=0.105) techniques. The navigator-triggered technique showed no statistical difference in measurable area of liver or in repeatability compared with the standard expiratory acquisition (p=0.997 and p=0.407 respectively). The free-breathing technique produced less measurable liver area and was less repeatable than the alternative techniques. The increase in acquisition time for navigator techniques was 3min 6s compared to standard expiratory breath-hold. CONCLUSION: Navigator-based hepatic MRE measurements are comparable to the reference standard expiratory breath-hold acquisition in healthy participants.


Assuntos
Suspensão da Respiração , Técnicas de Imagem por Elasticidade , Fígado/diagnóstico por imagem , Respiração , Adulto , Estudos de Coortes , Feminino , Voluntários Saudáveis , Humanos , Processamento de Imagem Assistida por Computador , Hepatopatias , Imageamento por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Padrões de Referência , Reprodutibilidade dos Testes , Adulto Jovem
13.
NMR Biomed ; 29(4): 387-99, 2016 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-27414749

RESUMO

Dissolution dynamic nuclear polarization (DNP) enables the metabolism of hyperpolarized (13)C-labelled molecules, such as the conversion of [1-(13)C]pyruvate to [1-(13)C]lactate, to be dynamically and non-invasively imaged in tissue. Imaging of this exchange reaction in animal models has been shown to detect early treatment response and correlate with tumour grade. The first human DNP study has recently been completed, and, for widespread clinical translation, simple and reliable methods are necessary to accurately probe the reaction in patients. However, there is currently no consensus on the most appropriate method to quantify this exchange reaction. In this study, an in vitro system was used to compare several kinetic models, as well as simple model-free methods. Experiments were performed using a clinical hyperpolarizer, a human 3 T MR system, and spectroscopic imaging sequences. The quantitative methods were compared in vivo by using subcutaneous breast tumours in rats to examine the effect of pyruvate inflow. The two-way kinetic model was the most accurate method for characterizing the exchange reaction in vitro, and the incorporation of a Heaviside step inflow profile was best able to describe the in vivo data. The lactate time-to-peak and the lactate-to-pyruvate area under the curve ratio were simple model-free approaches that accurately represented the full reaction, with the time-to-peak method performing indistinguishably from the best kinetic model. Finally, extracting data from a single pixel was a robust and reliable surrogate of the whole region of interest. This work has identified appropriate quantitative methods for future work in the analysis of human hyperpolarized (13)C data.


Assuntos
Espectroscopia de Ressonância Magnética/métodos , Ácido Pirúvico/metabolismo , Animais , Isótopos de Carbono , Feminino , Neoplasias Mamárias Animais/patologia , Modelos Biológicos , Ratos Endogâmicos F344 , Tela Subcutânea/patologia
15.
Ann Hepatol ; 15(3): 363-76, 2016.
Artigo em Inglês | MEDLINE | ID: mdl-27049490

RESUMO

BACKGROUND AND AIMS: We conducted an individual participant data (IPD) pooled analysis on the diagnostic accuracy of magnetic resonance elastography (MRE) to detect fibrosis stage in liver transplant recipients. MATERIAL AND METHODS: Through a systematic literature search, we identified studies on diagnostic performance of MRE for staging liver fibrosis, using liver biopsy as gold standard. We contacted study authors for published and unpublished IPD on age, sex, body mass index, liver stiffness, fibrosis stage, degree of inflammation and interval between MRE and biopsy; from these we limited analysis to patients who had undergone liver transplantation. Through pooled analysis using nonparametric two-stage receiver-operating curve (ROC) regression models, we calculated the cluster-adjusted AUROC, sensitivity and specificity of MRE for any (≥ stage 1), significant (≥ stage 2) and advanced fibrosis (≥ stage 3) and cirrhosis (stage 4). RESULTS: We included 6 cohorts (4 published and 2 unpublished series) reporting on 141 liver transplant recipients (mean age, 57 years; 75.2% male; mean BMI, 27.1 kg/m2). Fibrosis stage distribution stage 0, 1, 2, 3, or 4, was 37.6%, 23.4%, 24.8%, 12% and 2.2%, respectively. Mean AUROC values (and 95% confidence intervals) for diagnosis of any (≥ stage 1), significant (≥ stage 2), or advanced fibrosis (≥ stage 3) and cirrhosis were 0.73 (0.66-0.81), 0.69 (0.62-0.74), 0.83 (0.61-0.88) and 0.96 (0.93-0.98), respectively. Similar diagnostic performance was observed in stratified analysis based on sex, obesity and inflammation grade. CONCLUSIONS: In conclusion, MRE has high diagnostic accuracy for detection of advanced fibrosis and cirrhosis in liver transplant recipients, independent of BMI and degree of inflammation.


Assuntos
Técnicas de Imagem por Elasticidade/métodos , Fibrose/diagnóstico por imagem , Transplante de Fígado/efeitos adversos , Imageamento por Ressonância Magnética , Área Sob a Curva , Biópsia , Feminino , Fibrose/etiologia , Humanos , Masculino , Pessoa de Meia-Idade , Valor Preditivo dos Testes , Curva ROC , Reprodutibilidade dos Testes , Fatores de Risco , Índice de Gravidade de Doença , Resultado do Tratamento
16.
World J Radiol ; 8(1): 59-72, 2016 Jan 28.
Artigo em Inglês | MEDLINE | ID: mdl-26834944

RESUMO

Magnetic resonance elastography (MRE) is an innovative imaging technique for the non-invasive quantification of the biomechanical properties of soft tissues via the direct visualization of propagating shear waves in vivo using a modified phase-contrast magnetic resonance imaging (MRI) sequence. Fundamentally, MRE employs the same physical property that physicians utilize when performing manual palpation - that healthy and diseased tissues can be differentiated on the basis of widely differing mechanical stiffness. By performing "virtual palpation", MRE is able to provide information that is beyond the capabilities of conventional morphologic imaging modalities. In an era of increasing adoption of multi-parametric imaging approaches for solving complex problems, MRE can be seamlessly incorporated into a standard MRI examination to provide a rapid, reliable and comprehensive imaging evaluation at a single patient appointment. Originally described by the Mayo Clinic in 1995, the technique represents the most accurate non-invasive method for the detection and staging of liver fibrosis and is currently performed in more than 100 centers worldwide. In this general review, the mechanical properties of soft tissues, principles of MRE, clinical applications of MRE in the liver and beyond, and limitations and future directions of this discipline -are discussed. Selected diagrams and images are provided for illustration.

17.
J Magn Reson Imaging ; 44(3): 739-44, 2016 09.
Artigo em Inglês | MEDLINE | ID: mdl-26892734

RESUMO

PURPOSE: To evaluate the utility of oxygen challenge and report on temporal changes in blood oxygenation level-dependent (BOLD) contrast in normal liver, hepatocellular carcinoma (HCC) and background fibrosis. MATERIALS AND METHODS: Eleven volunteers (nine male and two female, mean age 33.5, range 27-41 years) and 10 patients (nine male and one female, mean age 68.9, range 56-87 years) with hepatocellular carcinoma on a background of diffuse liver disease were recruited. Imaging was performed on a 3T system using a multiphase, multiecho, fast gradient echo sequence. Oxygen was administered via a Hudson mask after 2 minutes of free-breathing. Paired t-tests were performed to determine if the mean pre- and post-O2 differences were statistically significant. RESULTS: In patients with liver fibrosis (n = 8) the change in T2* following O2 administration was elevated (0.88 ± 0.582 msec, range 0.03-1.69 msec) and the difference was significant (P = 0.004). The magnitude of the BOLD response in patients with HCC (n = 10) was larger, however the response was more variable (1.07 ± 1.458 msec, range -0.93-3.26 msec), and the difference was borderline significant (P = 0.046). The BOLD response in the volunteer cohort was not significant (P = 0.121, 0.59 ± 1.162 msec, range -0.81-2.44 msec). CONCLUSION: This work demonstrates that the BOLD response following oxygen challenge within cirrhotic liver is consistent with a breakdown in vascular autoregulatory mechanisms. Similarly, the elevated BOLD response within HCC is consistent with the abnormal capillary vasculature within tumors and the arterialization of the blood supply. Our results suggest that oxygen challenge may prove a viable BOLD contrast mechanism in the liver. J. Magn. Reson. Imaging 2016;44:739-744.


Assuntos
Carcinoma Hepatocelular/metabolismo , Cirrose Hepática/metabolismo , Imageamento por Ressonância Magnética/métodos , Oxigênio/metabolismo , Circulação Renal , Hipóxia Tumoral , Adulto , Idoso , Idoso de 80 Anos ou mais , Velocidade do Fluxo Sanguíneo , Carcinoma Hepatocelular/complicações , Carcinoma Hepatocelular/diagnóstico por imagem , Feminino , Humanos , Cirrose Hepática/diagnóstico por imagem , Masculino , Taxa de Depuração Metabólica , Pessoa de Meia-Idade , Consumo de Oxigênio , Fatores de Tempo , Adulto Jovem
18.
Eur Radiol ; 26(5): 1431-40, 2016 May.
Artigo em Inglês | MEDLINE | ID: mdl-26314479

RESUMO

OBJECTIVES: We conducted an individual participant data (IPD) pooled analysis on diagnostic accuracy of MRE to detect fibrosis stage in patients with non-alcoholic fatty liver disease (NAFLD). METHODS: Through a systematic literature search, we identified studies of MRE (at 60-62.5 Hz) for staging fibrosis in patients with NAFLD, using liver biopsy as gold standard, and contacted study authors for IPD. Through pooled analysis, we calculated the cluster-adjusted AUROC, sensitivity and specificity of MRE for any (≥stage 1), significant (≥stage 2) and advanced (≥stage 3) fibrosis and cirrhosis (stage 4). RESULTS: We included nine studies with 232 patients with NAFLD (mean age, 51 ± 13 years; 37.5% males; mean BMI, 33.5 ± 6.7 kg/m(2); interval between MRE and biopsy <1 year, 98.3%). Fibrosis stage distribution (stage 0/1/2/3/4) was 33.6, 32.3, 10.8, 12.9 and 10.4%, respectively. Mean AUROC (and 95% CIs) for diagnosis of any, significant or advanced fibrosis and cirrhosis was 0.86 (0.82-0.90), 0.87 (0.82-0.93), 0.90 (0.84-0.94) and 0.91 (0.76-0.95), respectively. Similar diagnostic performance was observed in stratified analysis based on sex, obesity and degree of inflammation. CONCLUSIONS: MRE has high diagnostic accuracy for detection of fibrosis in NAFLD, independent of BMI and degree of inflammation. KEY POINTS: • MRE has high diagnostic accuracy for detection of fibrosis in NAFLD. • BMI does not significantly affect accuracy of MRE in NAFLD. • Inflammation had no significant influence on MRE performance in NAFLD for fibrosis.


Assuntos
Técnicas de Imagem por Elasticidade/métodos , Cirrose Hepática/diagnóstico por imagem , Fígado/patologia , Hepatopatia Gordurosa não Alcoólica/diagnóstico por imagem , Biópsia , Técnicas de Imagem por Elasticidade/normas , Feminino , Hepatite/diagnóstico por imagem , Hepatite/patologia , Humanos , Cirrose Hepática/patologia , Masculino , Pessoa de Meia-Idade , Obesidade/patologia , Sensibilidade e Especificidade
19.
Eur Radiol ; 25(10): 2851-8, 2015 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-25903705

RESUMO

OBJECTIVE: Hepatorenal syndrome (HRS) is the most lethal cause of renal impairment in cirrhosis. Magnetic resonance elastography (MRE) is a diagnostic test that characterises tissues based on their biomechanical properties. The aim of this study was to assess the feasibility of MRE for detecting HRS in cirrhotic patients. METHODS: A prospective diagnostic investigation was performed. Renal MRE was performed on 21 hospitalised patients with cirrhosis and ascites. Six patients had HRS, one patient had non-HRS renal impairment, and 14 patients had normal renal function. The MRE-measured renal stiffness was compared against the clinical diagnosis as determined by clinical review alongside laboratory and radiologic results. RESULTS: The MRE-measured renal stiffness was significantly lower in patients with HRS (median stiffness of 3.30 kPa at 90 Hz and 2.62 kPa at 60 Hz) compared with patients with normal renal function (median stiffness of 5.08 kPa at 90 Hz and 3.41 kPa at 60 Hz) (P ≤ 0.014). For the detection of HRS, MRE had an area under the receiver operating characteristic curve of 0.94 at 90 Hz and 0.89 at 60 Hz. MRE had excellent inter-rater agreement, as assessed by Bland-Altman and intraclass correlation coefficient (> 0.9). CONCLUSION: MRE shows potential in the detection of HRS. KEY POINTS: • Magnetic resonance elastography (MRE) shows promise in the detection of hepatorenal syndrome. • MRE has the potential to track renal disease in a clinical population. • MRE is a reliable diagnostic test with excellent inter-rater agreement.


Assuntos
Ascite/complicações , Técnicas de Imagem por Elasticidade/métodos , Síndrome Hepatorrenal/diagnóstico por imagem , Cirrose Hepática/complicações , Adulto , Ascite/patologia , Feminino , Humanos , Cirrose Hepática/patologia , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Curva ROC , Insuficiência Renal/diagnóstico por imagem , Insuficiência Renal/patologia
20.
Can J Gastroenterol Hepatol ; 29(5): 253-7, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25874649

RESUMO

Renal impairment is common in liver disease and may occur as a consequence of the pathophysiological changes that underpin cirrhosis or secondary to a pre-existing unrelated insult. Nevertheless, the onset of renal impairment often portends a worsening prognosis. Hepatorenal syndrome remains one of the most recognized and reported causes of renal impairment in cirrhosis. However, other causes of renal impairment occur and can be classified into prerenal, intrinsic or postrenal, which are the subjects of the present review.


Assuntos
Síndrome Hepatorrenal , Cirrose Hepática/complicações , Insuficiência Renal/etiologia , Humanos , Cirrose Hepática/fisiopatologia , Prognóstico , Insuficiência Renal/patologia
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