Magnetic resonance imaging (MRI) and diseases of the liver and biliary tract. Part 1. Basic principles, MRI in the assessment of diffuse and focal hepatic disease

Magnetic resonance imaging (MRI) relies on the physical properties of unpaired protons in tissues to generate images. Unpaired protons behave like tiny bar magnets and will align themselves in a magnetic field. Radiofrequency pulses will excite these aligned protons to higher energy states. As they return to their original state, they will release this energy as radio waves. The frequency of the radio waves depends on the local magnetic field and by varying this over a subject, it is possible to build the images we are familiar with. In general, MRI has not been sufficiently sensitive or specific in the assessment of diffuse liver disease for clinical use. However, because of the specific characteristics of fat and iron, it may be useful in the assessment of hepatic steatosis and iron overload. Magnetic resonance imaging is useful in the assessment of focal liver disease, particularly in conjunction with contrast agents. Haemangiomas have a characteristic bright appearance on T-2 weighted images because of the slow flowing blood in dilated sinusoids. Focal nodular hyperplasia (FNH) has a homogenous appearance, and enhances early in the arterial phase after gadolinium injection, while the central scar typically enhances late. Hepatic adenomas have a more heterogenous appearance and also enhance in the arterial phase, but less briskly than FNH. Hepatocellular carcinoma is similar to an adenoma, but typically occurs in a cirrhotic liver and has earlier washout of contrast. The appearance of metastases depends on the underlying primary malignancy. Overall, MRI appears more sensitive and specific than computed tomography with contrast for the detection and evaluation of malignant lesions. (C) 2000 Blackwell Science Asia Pty Ltd.

Magnetic resonance imaging and diseases of the liver and biliary tract. Part 2. Magnetic resonance cholangiography and angiography and conclusions

Magnetic resonance cholangiography (MRC) relies on the strong T-2 signal from stationary liquids, in this case bile, to generate images. No contrast agents are required, and the failure rate and risk of serious complications is lower than with endoscopic retrograde cholangiopancreatography (ERCP). Data from MRC can be summated to produce an image much like the cholangiogram obtained by using ERCP. In addition, MRC and conventional MRI can provide information about the biliary and other anatomy above and below a biliary obstruction. This provides information for therapeutic intervention that is probably most useful for hilar and intrahepatic biliary obstruction. Magnetic resonance cholangiography appears to be similar to ERCP with respect to sensitivity and specificity in detecting lesions causing biliary obstruction, and in the diagnosis of choledocholithiasis. It is also suited to the assessment of biliary anatomy (including the assessment of surgical bile-duct injuries) and intrahepatic biliary pathology. However, ERCP can be therapeutic as well as diagnostic, and MRC should be limited to situations where intervention is unlikely, where intrahepatic or hilar pathology is suspected, to delineate the biliary anatomy prior to other interventions, or after failed or inadequate ERCP. Magnetic resonance angiography (MRA) relies on the properties of flowing liquids to generate images. It is particularly suited to assessment of the hepatic vasculature and appears as good as conventional angiography. It has been shown to be useful in delineating vascular anatomy prior to liver transplantation or insertion of a transjugular intrahepatic portasystemic shunt. Magnetic resonance angiography may also be useful in predicting subsequent variceal haemorrhage in patients with oesophageal varices. (C) 2000 Blackwell Science Asia Pty Ltd.

Processing of urinary pheromones in Antechinus stuartii (Marsupialia: Dasyuridae): Functional magnetic resonance imaging of the brain

Little is known of the neural mechanisms of marsupial olfaction. However, functional magnetic resonance imaging (fMRI) has made it possible to visualize dynamic brain function in mammals without invasion. In this study, central processing of urinary pheromones was investigated in the brown antechinus, Antechinus stuartii, using fMRI. Images were obtained from 18 subjects (11 males, 7 females) in response to conspecific urinary olfactory stimuli. Significant indiscriminate activation occurred in the accessory olfactory bulb, entorhinal, frontal, and parietal cortices in response to both male and female urine. The paraventricular nucleus of hypothalamus, ventrolateral thalamic nucleus, and medial preoptic area were only activated in response to male urine. Results of this MRI study indicate that projections of accessory olfactory system are activated by chemo-sensory cues. Furthermore, it appears that, based on these experiments, urinary pheromones may act on the hypothalamo-pituitary-adrenocortical axis via the paraventricular nucleus of the hypothalamus and may play an important role in the unique life history pattern of A. stuartii. Finally, this study has demonstrated that fMRI may be a powerful tool for investigations of olfactory processes in mammals.

CLINICAL TUMOR DIMENSIONS MAY BE USEFUL TO PREVENT GEOGRAPHIC MISS IN CONVENTIONAL RADIOTHERAPY OF UTERINE CERVIX CANCER-A MAGNETIC RESONANCE IMAGING-BASED STUDY

Purpose: To evaluate the risk of geographic miss associated with the classic four-field ""box"" irradiation technique and to define the variables that predict this risk. Materials and Methods: The study population consisted of 80 patients with uterine cervix cancer seen between 2001 and 2006. Median age was 55 years (23-82 years), and 72 (90%) presented with squamous cell carcinoma. Most patients (68.7%) presented with locally advanced disease (IIb or more). Magnetic resonance imaging findings from before treatment were compared with findings from simulation of the conventional four-field ""box"" technique done with rectal contrast. Study variables included tumor volume; involvement of vagina, parametrium, bladder, or rectum; posterior displacement of the anterior rectal wall; and tumor anteroposterior diameter (APD). Margins were considered adequate when the target volume (primary tumor extension, whole uterine body, and parametrium) was included within the field limits and were at least 1 cm in width. Results: Field limits were inadequate in 45 (56%) patients: 29 (36%) patients at the anterior and 28 (35%) at the posterior border of the lateral fields. Of these, 12 patients had both anterior and posterior miss, and this risk was observed in all stages of the disease (p = 0.076). Posterior displacement of the anterior rectal wall beyond S2-S3 was significantly correlated with the risk of geographic miss (p = 0.043). Larger tumors (APD 6 cm or above and volume above 50 cm(3)) were also significantly correlated with this risk (p = 0.004 and p = 0.046, respectively). Conclusions: Posterior displacement of the anterior rectal wall, tumor APD, and volume can be used as guidance in evaluating the risk of geographic miss. (C) 2009 Elsevier Inc.

Magnetic Resonance Angiography in Extracranial Giant Cell Arteritis

Background: Noninvasive diagnosis of giant cell arteritis (GCA) remains challenging, particularly with regard to evaluation of extracranial arterial disease. Objectives: The objective of the study was to retrospectively review extracranial involvement in patients with GCA and/or polymyalgia rheumatica (PMR), evaluated with magnetic resonance imaging (MRI), especially 3-dimensional contrast-enhanced magnetic resonance angiography images of the aortic arch and its branches. Methods: Clinical information, biopsy status, and MRI examinations of 28 patients with GCA/PMR were reviewed. Patient images were mixed randomly with 20 normal control images and were independently reviewed by 2 radiologists. Interobserver agreement for detection of arterial stenosis was determined by the k coefficient. Results: Both readers described vascular alterations in keeping with extracranial GCA in 19 of 28 patients (67%) with good interobserver agreement (k = 0.73) and with even higher agreement on diagnosing nonocclusive versus occlusive disease (k = 1.00). The most common lesions were bilateral axillary stenosis or obstructions, observed by both readers in 8 patients (28%). Among the 19 patients with magnetic resonance angiography lesions in the subclavian/axillary arteries, 12 (75%) had biopsy-proven GCA, but only 5 (41%) of these patients had clinical features of large artery disease. Conclusions: In our series review, MRI could provide accurate information on involvement of the aortic arch and its branches in extracranial GCA, depicting different degrees of stenosis. Our analysis also illustrates that occult large artery vasculitis should be considered in patients without biopsy-proven GCA, patients with classic GCA but without clinical signs of large artery disease, and in patients initially diagnosed as having PMR.

Magnetic resonance imaging quantification of regional cerebral blood flow and cerebrovascular reactivity to carbon dioxide in normotensive and hypertensive rats

Hypertension afflicts 25% of the general population and over 50% of the elderly. In the present work, arterial spin labeling MRI was used to non-invasively quantify regional cerebral blood flow (CBE), cerebrovascular resistance and CO(2) reactivity in spontaneously hypertensive rats (SHR) and in normotensive Wistar Kyoto rats (WKY), at two different ages (3 months and 10 months) and under the effects of two anesthetics, alpha-chloralose and 2% isoflurane (1.5 MAC). Repeated CBE measurements were highly consistent, differing by less than 10% and 18% within and across animals, respectively. Under alpha-chloralose, whole brain CBE at normocapnia did not differ between groups (young WKY: 61 3 ml/100 g/min; adult WKY: 62 +/- 4 ml/100 g/min; young SHR: 70 +/- 9 ml/100 g/min: adult SHR: 69 8 ml/100 g/min), indicating normal cerebral autoregulation in SHR. At hypercapnia, CBE values increased significantly, and a linear relationship between CBE and PaCO(2) levels was observed. In contrast, 2% isoflurane impaired cerebral autoregulation. Whole brain CBE in SHR was significantly higher than in WKY rats at normocapnia (young SHR: 139 +/- 25 ml/100 g/min; adult SHR: 104 +/- 23 ml/100 g/min; young WKY: 55 +/- 9 ml/100 g/min; adult WKY: 71 +/- 19 ml/100 g/min). CBE values increased significantly with increasing CO(2): however, there was a clear saturation of CBF at PaCO(2) levels greater than 70 mm Hg in both young and adult rats, regardless of absolute CBE values, suggesting that isoflurane interferes with the vasoclilatory mechanisms of CO(2). This behavior was observed for both cortical and subcortical structures. Under either anesthetic, CO(2) reactivity values in adult SHR were decreased, confirming that hypertension, when combined with age, increases cerebrovascular resistance and reduces cerebrovascular compliance. Published by Elsevier Inc.

Prostate Cancer: The Role of Multiparametric Magnetic Resonance Imaging

Multiparametric Magnetic Resonance Imaging has been increasingly used for detection, localization and staging of prostate cancer over the last years. It combines high-resolution T2 Weighted-Imaging and at least two functional techniques, which include Dynamic Contrast–Enhanced Magnetic Resonance Imaging, Diffusion-Weighted Imaging, and Magnetic Resonance Imaging Spectroscopy. Although the combined use of a pelvic phased-array and an Endorectal Coil is considered the state-of-the-art for Magnetic Resonance Imaging evaluation of prostate cancer, Endorectal Coil is only absolute mandatory for Magnetic Resonance Imaging Spectroscopy at 1.5 T. Sensitivity and specificity levels in cancer detection and localization have been improving with functional technique implementation, compared to T2 Weighted-Imaging alone. It has been particularly useful to evaluate patients with abnormal PSA and negative biopsy. Moreover, the information added by the functional techniques may correlate to cancer aggressiveness and therefore be useful to select patients for focal radiotherapy, prostate sparing surgery, focal ablative therapy and active surveillance. However, more studies are needed to compare the functional techniques and understand the advantages and disadvantages of each one. This article reviews the basic principles of prostatic mp-Magnetic Resonance Imaging, emphasizing its role on detection, staging and active surveillance of prostate cancer.

Vascular lesions of the lumbar epidural space: magnetic resonance imaging features of epidural cavernous hemangioma and epidural hematoma

The authors report the magnetic resonance imaging diagnostic features in two cases with respectively lumbar epidural hematoma and cavernous hemangioma of the lumbar epidural space. Enhanced MRI T1-weighted scans show a hyperintense signal rim surrounding the vascular lesion. Non-enhanced T2-weighted scans showed hyperintense signal.

Magnetic resonance imaging determinants of intraindividual variability in the elderly: combined analysis of grey and white matter.

Elderly individuals display a rapid age-related increase in intraindividual variability (IIV) of their performances. This phenomenon could reflect subtle changes in frontal lobe integrity. However, structural studies in this field are still missing. To address this issue, we computed an IIV index for a simple reaction time (RT) task and performed magnetic resonance imaging (MRI) including voxel based morphometry (VBM) and the tract based spatial statistics (TBSS) analysis of diffusion tensor imaging (DTI) in 61 adults aged from 22 to 88 years. The age-related IIV increase was associated with decreased fractional anisotropy (FA) as well as increased radial (RD) and mean (MD) diffusion in the main white matter (WM) fiber tracts. In contrast, axial diffusion (AD) and grey matter (GM) densities did not show any significant correlation with IIV. In multivariate models, only FA has an age-independent effect on IIV. These results revealed that WM but not GM changes partly mediated the age-related increase of IIV. They also revealed that the association between WM and IIV could not be only attributed to the damage of frontal lobe circuits but concerned the majority of interhemispheric and intrahemispheric corticocortical connections.

Delineating Dementia with Lewy Bodies: Can Magnetic Resonance Imaging Help?

As future treatments increasingly target the protein chemistry underlying the different dementias, itbecomes crucially important to distinguish between the dementias during life. Neither specific proteinnor genetic markers are as yet available in clinical practice. However, neuroimaging is an obviouscandidate technique that may yield enhanced diagnostic accuracy when applied to thedementias. The physiopathology and anatomopathology is complex in dementia with Lewy bodies(DLB). Besides the relative sparing of medial temporal lobe structures in DLB in comparison toAlzheimer's disease, no clear signature pattern of cerebral atrophy associated with DLB has beenestablished so far. Among others, one reason may be the difficulty in visualizing the small brainnuclei that are differentially involved among the dementias. While we think that structural magneticresonance imaging neuroimaging should be part of the diagnostic workup of most dementia syndromesdue to its usefulness in the differential diagnosis, its contribution to a positive diagnosis ofDLB is as yet limited. The development of different neuroimaging techniques may help distinguishreliably DLB from other neurodegenerative disorders. However, in order to become accepted as partof standard care, these techniques must still prove their effectiveness under routine conditions suchas those encountered by the general practitioner.

Coronary magnetic resonance imaging.

Coronary magnetic resonance imaging is a powerful non-invasive technique for the combined assessment of coronary artery anatomy and function. In the present review article, challenges in coronary artery imaging are discussed and results obtained in both healthy volunteers and patients with cardiovascular disease are presented. This includes a short overview of coronary artery vessel lumen and wall imaging, contrast agents, permeability of the coronary vessel wall, high-field imaging and imaging of endothelial function.

Mapping complex tissue architecture with diffusion spectrum magnetic resonance imaging.

Methods are presented to map complex fiber architectures in tissues by imaging the 3D spectra of tissue water diffusion with MR. First, theoretical considerations show why and under what conditions diffusion contrast is positive. Using this result, spin displacement spectra that are conventionally phase-encoded can be accurately reconstructed by a Fourier transform of the measured signal's modulus. Second, studies of in vitro and in vivo samples demonstrate correspondence between the orientational maxima of the diffusion spectrum and those of the fiber orientation density at each location. In specimens with complex muscular tissue, such as the tongue, diffusion spectrum images show characteristic local heterogeneities of fiber architectures, including angular dispersion and intersection. Cerebral diffusion spectra acquired in normal human subjects resolve known white matter tracts and tract intersections. Finally, the relation between the presented model-free imaging technique and other available diffusion MRI schemes is discussed.

Diffusion spectrum magnetic resonance imaging (DSI) tractography of crossing fibers.

MRI tractography is the mapping of neural fiber pathways based on diffusion MRI of tissue diffusion anisotropy. Tractography based on diffusion tensor imaging (DTI) cannot directly image multiple fiber orientations within a single voxel. To address this limitation, diffusion spectrum MRI (DSI) and related methods were developed to image complex distributions of intravoxel fiber orientation. Here we demonstrate that tractography based on DSI has the capacity to image crossing fibers in neural tissue. DSI was performed in formalin-fixed brains of adult macaque and in the brains of healthy human subjects. Fiber tract solutions were constructed by a streamline procedure, following directions of maximum diffusion at every point, and analyzed in an interactive visualization environment (TrackVis). We report that DSI tractography accurately shows the known anatomic fiber crossings in optic chiasm, centrum semiovale, and brainstem; fiber intersections in gray matter, including cerebellar folia and the caudate nucleus; and radial fiber architecture in cerebral cortex. In contrast, none of these examples of fiber crossing and complex structure was identified by DTI analysis of the same data sets. These findings indicate that DSI tractography is able to image crossing fibers in neural tissue, an essential step toward non-invasive imaging of connectional neuroanatomy.

18F-fluorodeoxyglucose positron emission tomography/computed tomography and magnetic resonance imaging in patients with liver metastases from uveal melanoma: results from a pilot study.

PURPOSE: F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) and MRI are used for detecting liver metastases from uveal melanoma. The introduction of new treatment options in clinical trials might benefit from early response assessment. Here, we determine the value of FDG-PET/CT with respect to MRI at diagnosis and its potential for monitoring therapy. MATERIAL AND METHODS: Ten patients with biopsy-proven liver metastases of uveal melanoma enrolled in a randomized phase III trial (NCT00110123) underwent both FDG-PET coupled with unenhanced CT and gadolinium-diethylene triamine pentaacetic acid-enhanced liver MRI within 4 weeks. FDG-PET and MRI were evaluated blindly and then compared using the ratio of lesion to normal liver parenchyma PET-derived standardized uptake value (SUV). The influence of lesion size and response to chemotherapy were studied. RESULTS: Overall, 108 liver lesions were seen: 34 (31%) on both modalities (1-18 lesions/patient), four (4%) by PET/CT only, and 70 (65%) by MRI only. SUV correlated with MRI lesion size (r=0.81, P<0.0001). PET/CT detected 26 of 33 (79%) MRI lesions of more than or equal to 1.2 cm, whereas it detected only eight of 71 (11%) lesions of less than 1.2 cm (P<0.0001). MRI lesions without PET correspondence were small (0.6±0.2 vs. 2.1±1.1 cm, P<0.0001). During follow-up (six patients, 30 lesions), the ratio lesion-to-normal-liver SUV diminished in size-stable lesions (1.90±0.64-1.46±0.50, P<0.0001), whereas it increased in enlarging lesions (1.56±0.40-1.99±0.56, P=0.032). CONCLUSION: MRI outweighs PET/CT for detecting small liver metastases. However, PET/CT detected at least one liver metastasis per patient and changes in FDG uptake not related to size change, suggesting a role in assessing early therapy response.

Characterization of myocardial deformation in patients with different etiologies of left ventricular hypertrophy by using strain distribution from Magnetic Resonance Imaging

Introducción y objetivos. Se ha señalado que, en la miocardiopatía hipertrófica (MCH), la desorganización de las fibras regionales da lugar a segmentos en los que la deformación es nula o está gravemente reducida, y que estos segmentos tienen una distribución no uniforme en el ventrículo izquierdo (VI). Esto contrasta con lo observado en otros tipos de hipertrofia como en el corazón de atleta o la hipertrofia ventricular izquierda hipertensiva (HVI-HT), en los que puede haber una deformación cardiaca anormal, pero nunca tan reducida como para que se observe ausencia de deformación. Así pues, proponemos el empleo de la distribución de los valores de strain para estudiar la deformación en la MCH. Métodos. Con el empleo de resonancia magnética marcada (tagged), reconstruimos la deformación sistólica del VI de 12 sujetos de control, 10 atletas, 12 pacientes con MCH y 10 pacientes con HVI-HT. La deformación se cuantificó con un algoritmo de registro no rígido y determinando los valores de strain sistólico máximo radial y circunferencial en 16 segmentos del VI. Resultados. Los pacientes con MCH presentaron unos valores medios de strain significativamente inferiores a los de los demás grupos. Sin embargo, aunque la deformación observada en los individuos sanos y en los pacientes con HVI-HT se concentraba alrededor del valor medio, en la MCH coexistían segmentos con contracción normal y segmentos con una deformación nula o significativamente reducida, con lo que se producía una mayor heterogeneidad de los valores de strain. Se observaron también algunos segmentos sin deformación incluso en ausencia de fibrosis o hipertrofia. Conclusiones. La distribución de strain caracteriza los patrones específicos de deformación miocárdica en pacientes con diferentes etiologías de la HVI. Los pacientes con MCH presentaron un valor medio de strain significativamente inferior, así como una mayor heterogeneidad de strain (en comparación con los controles, los atletas y los pacientes con HVI-HT), y tenían regiones sin deformación.