相关论文
2011 - Nano letters
Silica-coated gold nanorods as photoacoustic signal nanoamplifiers.

Photoacoustic signal generation by metal nanoparticles relies on the efficient conversion of light to heat, its transfer to the environment, and the production of pressure transients. In this study we demonstrate that a dielectric shell has a strong influence on the amplitude of the generated photoacoustic signal and that silica-coated gold nanorods of the same optical density are capable of producing about 3-fold higher photoacoustic signals than nanorods without silica coating. Spectrophotometry measurements and finite difference time domain (FDTD) analysis of gold nanorods before and after silica coating showed only an insignificant change of the extinction and absorption cross sections, hence indicating that the enhancement is not attributable to changes in absorption cross section resulting from the silica coating. Several factors including the silica thickness, the gold/silica interface, and the surrounding solvent were varied to investigate their effect on the photoacoustic signal produced from silica-coated gold nanorods. The results suggest that the enhancement is caused by the reduction of the gold interfacial thermal resistance with the solvent due to the silica coating. The strong contrast enhancement in photoacoustic imaging, demonstrated using phantoms with silica-coated nanorods, shows that these hybrid particles acting as "photoacoustic nanoamplifiers" are high efficiency contrast agents for photoacoustic imaging or photoacoustic image-guided therapy.

2015 - NeuroImage
A computational atlas of the hippocampal formation using ex vivo, ultra-high resolution MRI: Application to adaptive segmentation of in vivo MRI

Automated analysis of MRI data of the subregions of the hippocampus requires computational atlases built at a higher resolution than those that are typically used in current neuroimaging studies. Here we describe the construction of a statistical atlas of the hippocampal formation at the subregion level using ultra-high resolution, ex vivo MRI. Fifteen autopsy samples were scanned at 0.13 mm isotropic resolution (on average) using customized hardware. The images were manually segmented into 13 different hippocampal substructures using a protocol specifically designed for this study; precise delineations were made possible by the extraordinary resolution of the scans. In addition to the subregions, manual annotations for neighboring structures (e.g., amygdala, cortex) were obtained from a separate dataset of in vivo, T1-weighted MRI scans of the whole brain (1mm resolution). The manual labels from the in vivo and ex vivo data were combined into a single computational atlas of the hippocampal formation with a novel atlas building algorithm based on Bayesian inference. The resulting atlas can be used to automatically segment the hippocampal subregions in structural MRI images, using an algorithm that can analyze multimodal data and adapt to variations in MRI contrast due to differences in acquisition hardware or pulse sequences. The applicability of the atlas, which we are releasing as part of FreeSurfer (version 6.0), is demonstrated with experiments on three different publicly available datasets with different types of MRI contrast. The results show that the atlas and companion segmentation method: 1) can segment T1 and T2 images, as well as their combination, 2) replicate findings on mild cognitive impairment based on high-resolution T2 data, and 3) can discriminate between Alzheimer's disease subjects and elderly controls with 88% accuracy in standard resolution (1mm) T1 data, significantly outperforming the atlas in FreeSurfer version 5.3 (86% accuracy) and classification based on whole hippocampal volume (82% accuracy).

2010 - Brain : a journal of neurology
Imaging memory in temporal lobe epilepsy: predicting the effects of temporal lobe resection

Functional magnetic resonance imaging can demonstrate the functional anatomy of cognitive processes. In patients with refractory temporal lobe epilepsy, evaluation of preoperative verbal and visual memory function is important as anterior temporal lobe resections may result in material specific memory impairment, typically verbal memory decline following left and visual memory decline after right anterior temporal lobe resection. This study aimed to investigate reorganization of memory functions in temporal lobe epilepsy and to determine whether preoperative memory functional magnetic resonance imaging may predict memory changes following anterior temporal lobe resection. We studied 72 patients with unilateral medial temporal lobe epilepsy (41 left) and 20 healthy controls. A functional magnetic resonance imaging memory encoding paradigm for pictures, words and faces was used testing verbal and visual memory in a single scanning session on a 3T magnetic resonance imaging scanner. Fifty-four patients subsequently underwent left (29) or right (25) anterior temporal lobe resection. Verbal and design learning were assessed before and 4 months after surgery. Event-related functional magnetic resonance imaging analysis revealed that in left temporal lobe epilepsy, greater left hippocampal activation for word encoding correlated with better verbal memory. In right temporal lobe epilepsy, greater right hippocampal activation for face encoding correlated with better visual memory. In left temporal lobe epilepsy, greater left than right anterior hippocampal activation on word encoding correlated with greater verbal memory decline after left anterior temporal lobe resection, while greater left than right posterior hippocampal activation correlated with better postoperative verbal memory outcome. In right temporal lobe epilepsy, greater right than left anterior hippocampal functional magnetic resonance imaging activation on face encoding predicted greater visual memory decline after right anterior temporal lobe resection, while greater right than left posterior hippocampal activation correlated with better visual memory outcome. Stepwise linear regression identified asymmetry of activation for encoding words and faces in the ipsilateral anterior medial temporal lobe as strongest predictors for postoperative verbal and visual memory decline. Activation asymmetry, language lateralization and performance on preoperative neuropsychological tests predicted clinically significant verbal memory decline in all patients who underwent left anterior temporal lobe resection, but were less able to predict visual memory decline after right anterior temporal lobe resection. Preoperative memory functional magnetic resonance imaging was the strongest predictor of verbal and visual memory decline following anterior temporal lobe resection. Preoperatively, verbal and visual memory function utilized the damaged, ipsilateral hippocampus and also the contralateral hippocampus. Memory function in the ipsilateral posterior hippocampus may contribute to better preservation of memory after surgery.

1997 - Journal of Magnetic Resonance Imaging
Water diffusion and exchange as they influence contrast enhancement

The contrast‐enhanced magnetic resonance imaging (MRI) signal is rarely a direct measure of contrast concentration; rather it depends on the effect that the contrast agent has on the tissue water magnetization. To correctly interpret such studies, an understanding of the effects of water movement on the magnetic resonance (MR) signal is critical. In this review, we discuss how water diffusion within biological compartments and water exchange between these compartments affect MR signal enhancement and therefore our ability to extract physiologic information. The two primary ways by which contrast agents affect water magnetization are discussed: (1) direct relaxivity and (2) indirect susceptibility effects. For relaxivity agents, for which T1 effects usually dominate, the theory of relaxation enhancement is presented, along with a review of the relevant physiologic time constants for water movement affecting this relaxation enhancement. Experimental issues that impact accurate measurement of the relaxation enhancement are discussed. Finally, the impact of these effects on extracting physiologic information is presented. Susceptibility effects depend on the size and shape of the contrast agent, the size and shape of the compartment in which it resides, as well as the characteristics of the water movement through the resulting magnetic field inhomogeneity. Therefore, modeling of this effect is complex and is the subject of active study. However, since susceptibility effects can be much stronger than relaxivity effects in certain situations, they may be useful even without full quantitation.

2002 - Journal of Magnetic Resonance Imaging
Neurostimulation systems for deep brain stimulation: In vitro evaluation of magnetic resonance imaging–related heating at 1.5 tesla

To assess magnetic resonance imaging (MRI)‐related heating for a neurostimulation system (Activa® Tremor Control System, Medtronic, Minneapolis, MN) used for chronic deep brain stimulation (DBS).

2011 - Investigative Radiology
Multicenter Surveillance of Women at High Genetic Breast Cancer Risk Using Mammography, Ultrasonography, and Contrast-Enhanced Magnetic Resonance Imaging (the High Breast Cancer Risk Italian 1 Study): Final Results

Objectives:To prospectively compare clinical breast examination, mammography, ultrasonography, and contrast-enhanced magnetic resonance imaging (MRI) in a multicenter surveillance of high-risk women. Materials and Methods:We enrolled asymptomatic women aged ≥25: BRCA mutation carriers; first-degree relatives of BRCA mutation carriers, and women with strong family history of breast/ovarian cancer, including those with previous personal breast cancer. Results:A total of 18 centers enrolled 501 women and performed 1592 rounds (3.2 rounds/woman). Forty-nine screen-detected and 3 interval cancers were diagnosed: 44 invasive, 8 ductal carcinoma in situ; only 4 pT2 stage; 32 G3 grade. Of 39 patients explored for nodal status, 28 (72%) were negative. Incidence per year-woman resulted 3.3% overall, 2.1% <50, and 5.4% ≥50 years (P < 0.001), 4.3% in women with previous personal breast cancer and 2.5% in those without (P = 0.045). MRI was more sensitive (91%) than clinical breast examination (18%), mammography (50%), ultrasonography (52%), or mammography plus ultrasonography (63%) (P < 0.001). Specificity ranged 96% to 99%, positive predictive value 53% to 71%, positive likelihood ratio 24 to 52 (P not significant). MRI showed significantly better negative predictive value (99.6) and negative likelihood ratio (0.09) than those of the other modalities. At receiver operating characteristic analysis, the area under the curve of MRI (0.97) was significantly higher than that of mammography (0.83) or ultrasonography (0.82) and not significantly increased when MRI was combined with mammography and/or ultrasonography. Of 52 cancers, 16 (31%) were diagnosed only by MRI, 8 of 21 (38%) in women <50, and 8 of 31 (26%) in women ≥50 years of age. Conclusion:MRI largely outperformed mammography, ultrasonography, and their combination for screening high-risk women below and over 50.

2003 - The Journal of Neuroscience
Error Monitoring Using External Feedback: Specific Roles of the Habenular Complex, the Reward System, and the Cingulate Motor Area Revealed by Functional Magnetic Resonance Imaging

The dopaminergic system has been shown to be involved in the processing of rewarding stimuli, specifically of errors in reward prediction, in animal studies as well as in recent neuroimaging studies in humans. Furthermore, a specific role of dopamine in the human homolog of the rostral cingulate motor area (rCMA) was proposed in a recent model of error detection. Negative feedback as well as self-detected errors elicit a negative event-related brain potential probably generated in the rCMA. We performed two experiments using functional magnetic resonance imaging to investigate the brain activity related to negative and positive feedback in a dynamically adaptive motion prediction task. Whereas positive feedback raised hemodynamic activity in the ventral striatum (nucleus accumbens), negative feedback activated the rCMA, the inferior anterior insula, and the epithalamus (habenular complex). These data demonstrate the role of the habenular complex in the control of the human reward system, a function previously hypothesized on the basis of animal research. The rCMA reacted only to errors with negative feedback but not to errors without feedback, which ruled out an influence of response conflict or uncertainty on its role in error detection by external signals.

1992 - Archives of general psychiatry
Brain morphology and schizophrenia. A magnetic resonance imaging study of limbic, prefrontal cortex, and caudate structures.

We used magnetic resonance imaging to examine the morphologic characteristics of the amygdala/hippocampus, prefrontal cortex, and caudate nucleus in 29 healthy volunteers matched for age, gender, and head of household socioeconomic status and 44 patients with chronic schizophrenia. Total volumes of these structures were determined from 3-mm contiguous coronal sections. Schizophrenic patients, compared with healthy controls, had significantly smaller right and left amygdala/hippocampal complex volumes, smaller right and left prefrontal volumes, and larger left caudate volumes. A secondary analysis revealed reductions in the right and left amygdala and the left hippocampus. In addition, prefrontal white matter, but not gray matter, was reduced in the schizophrenic patients. Moreover, the right white matter volume in schizophrenic patients was significantly related to right amygdala/hippocampal volume (r = .39), data that provide preliminary support for a hypothesis of abnormal limbic-cortical connection in schizophrenia. We studied the implications of these data for the pathophysiology of schizophrenia.

2003 - The Journal of Neuroscience
Differential Response Patterns in the Striatum and Orbitofrontal Cortex to Financial Reward in Humans: A Parametric Functional Magnetic Resonance Imaging Study

Responses to monetary reward in humans have been assessed in a number of recent functional imaging studies, and it is clear that the neuronal substrates of financial reinforcement overlap extensively with regions responding to primary reinforcers, such as food. Money has the practical advantage of being an objectively quantifiable reinforcer. In this study, we exploit this advantage using a parametric functional magnetic resonance imaging design to look at the patterns of responding to systematically varying reward values. Twelve healthy volunteers were scanned during performance of a rewarded target detection task, in which the reward value varied between task blocks. We observed three distinct patterns of responding in different regions. Amygdala, striatum, and dopaminergic midbrain responded to the presence of rewards, regardless of value. In contrast, premotor cortex showed a linear increase in response with increasing reward value. Finally, medial and lateral foci of orbitofrontal cortex responded nonlinearly, such that response was enhanced for the lowest and highest reward values relative to the midrange. These results suggest functional distinction in response patterns within a distributed reward system.

2003 - British Journal of Surgery
Preoperative assessment of prognostic factors in rectal cancer using high‐resolution magnetic resonance imaging

The aim was to determine the accuracy of preoperative magnetic resonance imaging (MRI) in the evaluation of pathological prognostic factors that influence local recurrence and survival in rectal cancer.

1990 - The New England journal of medicine
Quantitation of muscle glycogen synthesis in normal subjects and subjects with non-insulin-dependent diabetes by 13C nuclear magnetic resonance spectroscopy.

To examine the extent to which the defect in insulin action in subjects with non-insulin-dependent diabetes mellitus (NIDDM) can be accounted for by impairment of muscle glycogen synthesis, we performed combined hyperglycemic-hyperinsulinemic clamp studies with [13C]glucose in five subjects with NIDDM and in six age- and weight-matched healthy subjects. The rate of incorporation of intravenously infused [1-13C]glucose into muscle glycogen was measured directly in the gastrocnemius muscle by means of a nuclear magnetic resonance (NMR) spectrometer with a 15.5-minute time resolution and a 13C surface coil. The steady-state plasma concentrations of insulin (approximately 400 pmol per liter) and glucose (approximately 10 mmol per liter) were similar in both study groups. The mean (+/- SE) rate of glycogen synthesis, as determined by 13C NMR, was 78 +/- 28 and 183 +/- 39 mumol-glucosyl units per kilogram of muscle tissue (wet weight) per minute in the diabetic and normal subjects, respectively (P less than 0.05). The mean glucose uptake was markedly reduced in the diabetic (30 +/- 4 mumol per kilogram per minute) as compared with the normal subjects (51 +/- 3 mumol per kilogram per minute; P less than 0.005). The mean rate of nonoxidative glucose metabolism was 22 +/- 4 mumol per kilogram per minute in the diabetic subjects and 42 +/- 4 mumol per kilogram per minute in the normal subjects (P less than 0.005). When these rates are extrapolated to apply to the whole body, the synthesis of muscle glycogen would account for most of the total-body glucose uptake and all of the nonoxidative glucose metabolism in both normal and diabetic subjects. We conclude that muscle glycogen synthesis is the principal pathway of glucose disposal in both normal and diabetic subjects and that defects in muscle glycogen synthesis have a dominant role in the insulin resistance that occurs in persons with NIDDM.

2008 - Radiology
Comparison of dynamic susceptibility-weighted contrast-enhanced MR methods: recommendations for measuring relative cerebral blood volume in brain tumors.

PURPOSE To investigate whether estimates of relative cerebral blood volume (rCBV) in brain tumors, obtained by using dynamic susceptibility-weighted contrast material-enhanced magnetic resonance (MR) imaging vary with choice of data acquisition and postprocessing methods. MATERIALS AND METHODS Four acquisition methods were used to collect data in 22 high-grade glioma patients, with informed written consent under HIPAA-compliant guidelines approved by the institutional review board. During bolus administration of a standard single dose of gadolinium-based contrast agent (0.1 mmol per kilogram of body weight), one of three acquisition methods was used: gradient-echo (GRE) echo-planar imaging (echo time [TE], 30 msec; flip angle, 90 degrees ; n = 10), small-flip-angle GRE echo-planar imaging (TE, 54 msec; flip angle, 35 degrees ; n = 7), or dual-echo GRE spiral-out imaging (TE, 3.3 and 30 msec; flip angle, 72 degrees ; n = 5). Next, GRE echo-planar imaging (TE, 30 msec; flip angle, 90 degrees ; n = 22) was used to collect data during administration of a second dose of contrast agent (0.2 mmol/kg). Subsequently, six methods of analysis were used to calculate rCBV. Mean rCBV values from whole tumor, tumor hot spots, and contralateral brain were normalized to mean rCBV in normal-appearing white matter. RESULTS Friedman two-way analysis of variance and Kruskal-Wallis one-way analysis of variance results indicated that qualitative rCBV values were dependent on acquisition and postprocessing methods for both tumor and contralateral brain. By using the nonparametric Mann-Whitney test, a consistently positive (greater than zero) tumor-contralateral brain rCBV ratio resulted when either the preload-postprocessing correction approach or dual-echo acquisition approach (P < .008 for both methods) was used. CONCLUSION The dependence of tumor rCBV on the choice of acquisition and postprocessing methods is caused by their varying sensitivities to T1 and T2 and/or T2* leakage effects. The preload-correction approach and dual-echo acquisition approach are the most robust choices for the evaluation of brain tumors when the possibility of contrast agent extravasation exists.

2011 - Journal of clinical oncology : official journal of the American Society of Clinical Oncology
Prospective study of breast cancer incidence in women with a BRCA1 or BRCA2 mutation under surveillance with and without magnetic resonance imaging.

PURPOSE The sensitivity of magnetic resonance imaging (MRI) for breast cancer screening exceeds that of mammography. If MRI screening reduces mortality in women with a BRCA1 or BRCA2 mutation, it is expected that the incidence of advanced-stage breast cancers should be reduced in women undergoing MRI screening compared with those undergoing conventional screening. PATIENTS AND METHODS We followed 1,275 women with a BRCA1 or BRCA2 mutation for a mean of 3.2 years. In total, 445 women were enrolled in an MRI screening trial in Toronto, Ontario, Canada, and 830 were in the comparison group. The cumulative incidences of ductal carcinoma in situ (DCIS), early-stage, and late-stage breast cancers were estimated at 6 years in the cohorts. RESULTS There were 41 cases of breast cancer in the MRI-screened cohort (9.2%) and 76 cases in the comparison group (9.2%). The cumulative incidence of DCIS or stage I breast cancer at 6 years was 13.8% (95% CI, 9.1% to 18.5%) in the MRI-screened cohort and 7.2% (95% CI, 4.5% to 9.9%) in the comparison group (P = .01). The cumulative incidence of stages II to IV breast cancers was 1.9% (95% CI, 0.2% to 3.7%) in the MRI-screened cohort and 6.6% (95% CI, 3.8% to 9.3%) in the comparison group (P = .02). The adjusted hazard ratio for the development of stages II to IV breast cancer associated with MRI screening was 0.30 (95% CI, 0.12 to 0.72; P = .008). CONCLUSION Annual surveillance with MRI is associated with a significant reduction in the incidence of advanced-stage breast cancer in BRCA1 and BRCA2 carriers.

1992 - Circulation
Diagnosis of Thoracic Aortic Dissection: Magnetic Resonance Imaging Versus Transesophageal Echocardiography

BackgroundAortic dissection requires prompt and reliable diagnosis to reduce the high mortality. The purpose of this study was to assess the reliability of both ECG-triggered magnetic resonance imaging (MRI) and transesophageal two-dimensional echocardiography combined with color-coded Doppler flow imaging (TEE) for the diagnosis of thoracic aortic dissection and associated epiphenomena. Methods and ResultsFifty-three consecutive patients with clinically suspected aortic dissection were subjected to a dual noninvasive imaging protocol in random order; imaging results were compared and validated against the independent morphological “gold standard” of intraoperative findings (n=27), necropsy (n=7), and/or contrast angiography (n=53). No serious side effects were encountered with either imaging method. In contrast to a precursory screening transthoracic echogram, the sensitivities of both MRI and TEE were 100% for detecting a dissection of the thoracic aorta irrespective of its location. The specificity of TEE, however, was lower than the specificity of MRI for a dissection (TEE, 68.2% versus MRI, 100%; p<0.005), which resulted mainly from false-positive TEE findings confined to the ascending segment of the aorta (TEE, 78.8% versus MRI, 100%; p<0.01). In addition, MRI proved to be more sensitive than TEE in detecting the formation of thrombus in the false lumen of both the aortic arch (p<0.01) and the descending segment of the aorta (p<0.05). There were no discrepancies between the two imaging techniques in detecting the site of entry to a dissection, aortic regurgitation, or pericardial effusion. ConclusionsBoth MRI and TEE are atraumatic, safe, and highly sensitive methods to identify and classify acute and subacute dissections of the entire thoracic aorta. TEE, however, is associated with lower specificity for lesions in the ascending aorta. These results may still favor TEE as a semi-invasive diagnostic procedure after a precursory screening transthoracic echogram in suspected aortic dissection, but they establish Mil as an excellent method to avoid false-positive findings. Anatomic mapping by MRI may emerge as the most comprehensive approach and morphological standard to guide surgical interventions.

2007 - Current medical imaging reviews
Dynamic Contrast Enhanced Magnetic Resonance Imaging in Oncology: Theory, Data Acquisition, Analysis, and Examples.

Dynamic contrast enhanced MRI (DCE-MRI) enables the quantitative assessment of tumor status and has found application in both pre-clinical tumor models as well as clinical oncology. DCE-MRI requires the serial acquisition of images before and after the injection of a paramagnetic contrast agent so that the variation of MR signal intensity with time can be recorded for each image voxel. As the agent enters into a tissue, it changes the MR signal intensity from the tissue to a degree that depends on the local concentration. After the agent is transported out of the tissue, the MR signal intensity returns to its' baseline value. By analyzing the associated signal intensity time course using an appropriate mathematical model, physiological parameters related to blood flow, vessel permeability, and tissue volume fractions can be extracted for each voxel or region of interest.In this review we first discuss the basic physics of this methodology, and then present technical aspects of how DCE-MRI data are acquired and analyzed. We also discuss appropriate models of contrast agent kinetics and how these can be used to elucidate tissue characteristics of importance in cancer biology. We conclude by briefly summarizing some future goals and demands of DCE-MRI.

2003 - Circulation: Journal of the American Heart Association
Quantitative Magnetic Resonance Imaging Analysis of Neovasculature Volume in Carotid Atherosclerotic Plaque

Background—Neovasculature within atherosclerotic plaques is believed to be associated with infiltration of inflammatory cells and plaque destabilization. The aim of the present investigation was to determine whether the amount of neovasculature present in advanced carotid plaques can be noninvasively measured by dynamic, contrast-enhanced MRI. Methods and Results—A total of 20 consecutive patients scheduled for carotid endarterectomy were recruited to participate in an MRI study. Images were obtained at 15-second intervals, and a gadolinium contrast agent was injected coincident with the second of 10 images in the sequence. The resulting image intensity within the plaque was tracked over time, and a kinetic model was used to estimate the fractional blood volume. For validation, matched sections from subsequent endarterectomy were stained with ULEX and CD-31 antibody to highlight microvessels. Finally, all microvessels within the matched sections were identified, and their total area was computed as a fraction of the plaque area. Results were obtained from 16 participants, which showed fractional blood volumes ranging from 2% to 41%. These levels were significantly higher than the histological measurements of fractional vascular area. Nevertheless, the 2 measurements were highly correlated, with a correlation coefficient of 0.80 (P <0.001). Conclusions—Dynamic contrast-enhanced MRI provides an indication of the extent of neovasculature within carotid atherosclerotic plaque. MRI therefore provides a means for prospectively studying the link between neovasculature and plaque vulnerability.

2013 - Science
Nuclear Magnetic Resonance Spectroscopy on a (5-Nanometer)3 Sample Volume

Nanoscale NMR with Diamond Defects Although nuclear magnetic resonance (NMR) methods can be used for spatial imaging, the low sensitivity of detectors limits the minimum sample size. Two reports now describe the use of near-surface nitrogen-vacancy (NV) defects in diamond for detecting nanotesla magnetic fields from very small volumes of material (see the Perspective by Hemmer). The spin of the defect can be detected by changes in its fluorescence, which allows proton NMR of organic samples only a few nanometers thick on the diamond surface. Mamin et al. (p. 557) used a combination of electron spin echoes and pulsed NMR manipulation of the proton spins to detect the very weak fields. Staudacher et al. (p. 561) measured statistical polarization of a population of about 104 spins near the NV center with a dynamical decoupling method. The optical response of the spin of a near-surface atomic defect in diamond can be used to sense proton magnetic fields. [Also see Perspective by Hemmer] Application of nuclear magnetic resonance (NMR) spectroscopy to nanoscale samples has remained an elusive goal, achieved only with great experimental effort at subkelvin temperatures. We demonstrated detection of NMR signals from a (5-nanometer)3 voxel of various fluid and solid organic samples under ambient conditions. We used an atomic-size magnetic field sensor, a single nitrogen-vacancy defect center, embedded ~7 nanometers under the surface of a bulk diamond to record NMR spectra of various samples placed on the diamond surface. Its detection volume consisted of only 104 nuclear spins with a net magnetization of only 102 statistically polarized spins.

2004 - JAMA
Magnetic resonance imaging of the breast prior to biopsy.

CONTEXT Breast magnetic resonance imaging (MRI) has been shown to have high sensitivity for cancer detection and is increasingly used following mammography to evaluate suspicious breast lesions. OBJECTIVE To determine the accuracy of breast MRI in conjunction with mammography for the detection of breast cancer in patients with suspicious mammographic or clinical findings. DESIGN, SETTING, AND PATIENTS Prospective multicenter investigation of the International Breast MR Consortium conducted at 14 university hospitals in North America and Europe from June 2, 1998, through October 31, 2001, of 821 patients referred for breast biopsy for American College of Radiology category 4 or 5 mammographic assessment or suspicious clinical or ultrasound finding. INTERVENTIONS MRI examinations performed prior to breast biopsy; MRI results were interpreted at each site, which were blinded to pathological results. MAIN OUTCOME MEASURES Area under the receiver operating characteristic curve (AUC), sensitivity, and specificity of breast MRI. RESULTS Among the 821 patients, there were 404 malignant index lesions, of which 63 were ductal carcinoma in situ (DCIS) and 341 were invasive carcinoma. Of the 417 nonmalignant index lesions, 366 were benign, 47 showed atypical histology, and 4 were lobular carcinoma in situ. The AUC pooled over all institutions was 0.88 (95% confidence interval [CI], 0.86-0.91). MRI correctly detected cancer in 356 of 404 cancer cases (DCIS or invasive cancer), resulting in a sensitivity of 88.1% (95% CI, 84.6%-91.1%), and correctly identified as negative for cancer 281 of 417 cases without cancer, resulting in a specificity of 67.7% (95% CI, 62.7%-71.9%). MRI performance was not significantly affected by mammographic breast density, tumor histology, or menopausal status. The positive predictive values for 356 of 492 patients was 72.4% (95% CI, 68.2%-76.3%) and of mammography for 367 of 695 patients was 52.8% (95% CI, 49.0%-56.6%) (P<.005). Dynamic MRI did not improve the AUC compared with 3-dimensional MRI alone, but the specificity of a washout pattern for 123 of 136 patients without cancer was 90.4% (95% CI, 84%-95%). CONCLUSIONS Breast MRI has high sensitivity but only moderate specificity independent of breast density, tumor type, and menopausal status. Although the positive predictive value of MRI is greater than mammography, MRI does not obviate the need for subsequent tissue sampling in this setting.

1986 - Stroke
Incidental subcortical lesions identified on magnetic resonance imaging in the elderly. II. Postmortem pathological correlations.

The pathological correlates of subcortical lesions noted on magnetic resonance imaging (MRI) in the elderly are not known. Postmortem in vitro proton MRI was performed on the brains of seven consecutive elderly patients dying of nonneurologic causes. Scans were done in the fresh and fixed states with the specimen immersed in saline and formaldehyde respectively. A 1.5 Tesla superconductive system was used with a multiple spin-echo protocol generating T2 weighted images. Subcortical MRI lesions were localized in three dimensions and identified at brain cutting. In addition, pathological correlations were obtained from an eighth patient who underwent MRI eleven days before death. Histological examinations were performed in a blinded fashion, including control areas from the same brains. Subcortical MRI lesions were found to be associated with arteriosclerosis, dilated perivascular spaces, and vascular ectasia (p less than 0.05). These histological changes were characteristic of "état criblé" which, like subcortical MRI lesions, is associated with age and hypertension. Shrinkage (or atrophy) of the brain parenchyma around ectatic blood vessels would result in an extensive network of tunnels filled with extracellular water. The proton MRI signal from such areas of the brain would be increased. Gliosis and small areas of infarction occasionally coexisted with "état criblé," but these were not present in all areas with MRI lesions and could not be distinguished by MRI signal alone. In conclusion, clinical and pathological correlations lend support to the uniform hypothesis that MRI provides a nonspecific index of brain parenchymal alterations caused by aging and chronic cerebrovascular disease.

2004
Magnetic nanoparticle design for medical diagnosis and therapy

Magnetic nanoparticles have attracted attention because of their current and potential usefulness as contrast agents for magnetic resonance imaging (MRI) or colloidal mediators for cancer magnetic hyperthermia. This review examines these in vivo applications through an understanding of the involved problems and the current and future possibilities for resolving them. A special emphasis is made on magnetic nanoparticle requirements from a physical viewpoint (e.g. relaxivity for MRI and specific absorption rate for hyperthermia), the factors affecting their biodistribution (e.g. size, surface hydrophobic/hydrophilic balance, etc.) and the solutions envisaged for enhancing their half-life in the blood compartment and targeting tumour cells.

Comparison of Magnetic Properties of MRI Contrast Media Solutions at Different Magnetic Field Strengths

J. Mintorovitch
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M. Requardt
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M. Rohrer
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Hans Bauer
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H. Weinmann

Abstract:Rationale and Objectives:To characterize and compare commercially available contrast media (CM) for magnetic resonance imaging (MRI) in terms of their relaxivity at magnetic field strengths ranging from 0.47 T to 4.7 T at physiological temperatures in water and in plasma. Relaxivities also were quantified in whole blood at1.5 T. Methods:Relaxivities of MRI-CM were determined by nuclear magnetic resonance (NMR) spectroscopy at 0.47 T and MRI phantom measurements at 1.5 T, 3 T, and 4.7 T, respectively. Both longitudinal (T1) and transverse relaxation times (T2) were measured by appropriate spin-echo sequences. Nuclear magnetic resonance dispersion (NMRD) profiles were also determined for all agents in water and in plasma. Results:Significant dependencies of relaxivities on the field strength and solvents were quantified. Protein binding leads to both increased field strength and solvent dependencies and hence to significantly altered T1 relaxivity values at higher magnetic field strengths. Conclusions:Awareness of the field strength and solvent associated with relaxivity data is crucial for the comparison and evaluation of relaxivity values. Data observed at 0.47 T can thus be misleading and should be replaced by relaxivities measured at 1.5 T and at 3 T in plasma at physiological temperature.

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