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At least 667 records · Page 37Linked to original sources
PubMed1993

Adipose tissue distribution as assessed by magnetic resonance imaging and total body fat by magnetic resonance imaging, underwater weighing, and body-water dilution in healthy women.

A method for estimating total body fat (TBF) and the amount and distribution of adipose tissue in humans by using magnetic resonance imaging (MRI) is described. Thirty transaxial images of subjects were taken by a nuclear magnetic imager (0.02 T). Adipose tissue volume was calculated from adipose tissue area in each image and from the distances between images. The CV when estimating total volume of body adipose tissue was 1.5%. TBF of healthy Swedish women was estimated by the MRI method (n = 25), by underwater weighing (UWW) (n = 20), and by body-water dilution (BWD) (n = 23). When assessed by MRI and BWD, women contained 1.4 +/- 2.9% less and 4.7 +/- 4.0% more TBF, respectively, than when assessed by UWW. On average, 74.2% of total adipose tissue volume was situated subcutaneously. Subcutaneous fat:fat-free body weight and nonsubcutaneous fat:fat-free body weight were both significantly correlated with percent TBF but the women stored excess fat subcutaneously rather than nonsubcutaneously.

Adipose Tissue↗
PubMed2004

Relationship of structural magnetic resonance imaging, magnetic resonance perfusion, and other disease factors to neuropsychological outcome in sickle cell disease.

OBJECTIVE: To investigate the relationship between neuropsychological functioning and radiographic findings in children with sickle cell disease (SCD) with no history of clinical neurological events. METHODS: Thirty-one patients with SCD randomly selected from a regional treatment center underwent neuropsychological and disease severity assessments. Of these, 22 also had structural magnetic resonance imaging and magnetic resonance perfusion studies performed. RESULTS: Forty-five percent of the imaged subgroup showed imaging abnormalities that were found to be correlated with disease severity but not neuropsychological level of performance indices. A significant relationship, however, was found between imaging abnormalities and increased variability in neuropsychological performance. CONCLUSIONS: These results corroborate the high rate of rheologic and vascular pathology in SCD and underscore the importance of representing neuropsychological functioning in multiple ways.

Adolescent↗
PubMed1998

Co-registration of cortical magnetic stimulation and functional magnetic resonance imaging.

Functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS) are noninvasive techniques recently used to investigate cortical motor physiology. However, these modalities measure different phenomena, and in studies of human motor control they have given inconsistent results. We have developed a reproducible technique which co-registers TMS and fMRI, using a frameless method. In four normal subjects, the TMS map and fMRI activation were present on the primary motor cortex contralateral to the target hand, with some extension into primary sensory cortex. fMRI activation alone was also present in the medial motor cortex bilaterally and in the sensorimotor cortex ipsilateral to the target hand. This technique allows a more comprehensive evaluation of the physiologic events involved in motor control.

Adult↗
PubMed1985

Combined use of magnetic resonance imaging (MRI) and spectroscopy (MRS) by whole body magnets in studying skeletal muscle morphology and metabolism.

As a pilot study, 31-P-spectra of the quadriceps femoris muscle (1.5T) and proton images of the right thigh (.5T) were performed in two cyclists (T) and two untrained (UT) subjects. During ischemia, while MRI did not show any change, phosphocreatine (PCr) concentration decreased and inorganic phosphate (Pi) increased. Recovery occurred within 3 minutes. Ergometric bicycle tests were performed outside the magnet. Submaximal workload (UT 150W/T 260W, 3.5 minutes) caused transient minimal changes in phosphorus metabolites. Supramaximal, partially anaerobic exercise (UT 320W/T 350W, 3.5 minutes) induced similar changes in heart rate, oxygen uptake rate, and plasma lactate in both groups. Decrease of the PCr/Pi ratio, however, was more pronounced in UT subjects and clearly lasted longer. If methodical problems can be resolved, combined MRS and MRI in whole body magnets may become a standard noninvasive modality, adding unique information on morphology (organ volume) and local metabolism to classic mechanical and global physiologic data.

Adult↗
PubMed1996

Fourier phase mapping of the human heart. The use of spatial modulation of magnetization cine magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Fourier phase mapping of cine cardiac magnetic resonance (MR) imaging offers noninvasive analysis of temporal cardiac activation patterns. The aim of our investigation was to extend this analysis to intramyocardial dynamics. METHODS: A fast-imaging with steady-state precision (FISP) two-dimensional gradient echo spatial modulation of magnetization (SPAMM) sequence and a segmented two-dimensional FISP-SPAMM sequence were applied to acquire cine MR images of the complete cardiac cycle on a 1.5-tesla imager. Signal intensity data were submitted to pixel-wise Fourier phase analysis. Color-encoded amplitude and phase maps were displayed for visual analysis. RESULTS: Using the unsegmented SPAMM two-dimensional FISP sequence, a more consistent tag-to-myocardium contrast and a higher number of cardiac phases was achieved than by using the segmented version of this sequence. The typical tag displacement reflected complex intramyocardial dynamics, including rotation. Phase mapping displayed a pattern of contraction consistent with electrophysiologic concepts of cardiac activation. In contrast, the segmented sequence did not reflect any differences in the onset of cardiac contraction, although tag displacement was apparent with this sequence as well. CONCLUSIONS. Fourier phase mapping of cardiac MR imaging tagging studies allows for noninvasive analysis of intramyocardial activation patterns. A temporal resolution of 50 mseconds per image at a heart rate of 75 beats per minute allows for an assessment of spatial differences in the onset of myocardial activation.

Adult↗
PubMed1997

Secretory and nonsecretory pituitary adenomas are distinguishable by 1/T1 magnetic relaxation rates at very low magnetic fields in vitro.

RATIONALE AND OBJECTIVES: The authors investigated whether hormonally active and inactive pituitary adenomas can be discriminated in vitro by magnetic resonance (MR) imaging-related data. METHODS: 1/T1 nuclear magnetic relaxation dispersion profiles were measured for 39 fresh surgical specimens of secreting and nonsecreting adenomas, classified using clinical criteria or preoperative serum hormone levels. Nonsecreting adenomas were subdivided into hormone-producing and nonhormone-producing by immunostains. At five fields (0.00024 to 1.2 tesla [T]), mean 1/T1 was analyzed for statistically significant differences among these three tumor categories. RESULTS: Mean 1/T1 was significantly higher (P < 0.02) for hormone-secreting than for nonsecreting adenomas at fields below 0.24 T; no significant difference existed at typical MR imaging fields (0.5 to 1.5 T). Mean 1/T1 for hormone-producing and nonhormone-producing, nonsecreting adenomas were not significantly different at any field. CONCLUSIONS: Because 1/T1 at low fields is related to 1/T2 at imaging fields, it may be possible to detect hormone secretion of pituitary adenomas noninvasively by MR imaging.

Adenoma↗
PubMed1998

Renal anatomic changes on magnetic resonance imaging and gadolinium-enhanced magnetic resonance angiography after renal revascularization. Original investigation.

RATIONALE AND OBJECTIVES: The anatomic and hemodynamic renal changes after renal arterial revascularization (RAR) were investigated. METHODS: Thirty-seven kidneys and 40 renal arteries were evaluated in 20 patients by using magnetic resonance imaging/magnetic resonance angiography (MRI/MRA) to assess pre- and post-RAR renal length and mass, parenchymal thickness, renal enhancement, renal artery caliber, poststenotic dilation, and signal dephasing on 3D phase contrast (PC). The kidneys and renal arteries were segregated into three groups. Group 1 included 16 patients who benefited from RAR (defined as clinical improvement based on decreased serum creatinine or fewer number of antihypertensive medications) in whom 26 renal arteries in 25 kidneys were studied. Intervention included renal artery endarterectomy (n = 20); aortorenal bypass (n = 3); renal artery reimplantation (n = 3); and percutaneous transluminal angioplasty (PTA; n = 1). A total of 27 interventions was performed, as PTA failed for one patient who subsequently underwent aortorenal bypass before reimaging. Group 2 included four patients who did not clinically benefit. A total of eight revascularized arteries were studied in seven kidneys. In group 3, six renal arteries in five kidneys from groups 1 and 2 without RAS/RAR were analyzed as an internal control. RESULTS: Technical success (defined as increased vessel caliber after intervention) was achieved in 33 of the 34 revascularized arteries. A statistically significant increase in renal length occurred regardless of clinical outcome (pre-RAR, 9.5 cm; post-RAR, 10.5 cm; P < 0.0001). Parenchymal thickness and renal mass, however, improved only in patients who benefited clinically from RAR. Parenchymal enhancement was unchanged in any of the groups studied. No significant morphologic changes were detected in the control group. CONCLUSIONS: Magnetic resonance imaging and Gd-MRA detect anatomic and hemodynamic changes that occur with renal revascularization.

Adult↗
PubMed2003

Magnetic resonance imaging and magnetic resonance cholangiopancreaticography for diagnosis and pre-interventional evaluation of a fluid thoracic mass.

Differential diagnoses of various types of thoracic cystic masses are a prerequisite for appropriate management strategies. Mediastinal pancreatic pseudocysts are rare but life-threatening complications of pancreatitis. They may appear as a thoracic mass on X-rays and need to be differentiated from other lesions. This report demonstrates that magnetic resonance cholangiopancreaticography, which is not included in current algorithms, is a valuable diagnostic tool in such cases. We summarize the advantages and disadvantages of magnetic resonance cholangiopancreaticography and show how pre-interventional identification of pancreatic origin and exclusion of necrotic debris guided the therapeutic management of the patient. However, after 3 weeks of successful percutaneous drainage, infectious complications necessitated surgical intervention.

Cholangiography↗
PubMed2006

Coronary magnetic resonance angiography using magnetization-prepared contrast-enhanced breath-hold volume-targeted imaging (MPCE-VCATS).

OBJECTIVES: Coronary artery x-ray angiography (XRA) is currently the gold standard for the assessment of coronary artery disease. A substantial minority of patients referred for coronary angiography have no significant coronary artery disease. The purpose of this study is to evaluate magnetization-prepared contrast-enhanced breath-hold volume-targeted imaging (MPCE-VCATS), a new 3-dimensional breath-hold coronary magnetic resonance angiography (MRA) technique, in detecting hemodynamically significant coronary artery stenoses in a patient population, with XRA correlation. MATERIALS AND METHODS: A total of 19 subjects who were referred for conventional coronary angiography were enrolled in the study. ECG-triggered MPCE-VCATS coronary artery scans were acquired for the left main coronary artery (LCA), left anterior descending (LAD), and right coronary artery (RCA). Coronary MRA and XRA results were compared. RESULTS: The overall sensitivity, accuracy, and negative predictive value for diagnosing any hemodynamically significant coronary artery disease (> or =50% diameter reduction) was 91%, 80%, and 90%, respectively. The sensitivity of the technique in the LCA, LAD, and RCA was 100%, 100% and 78%, respectively. The negative predictive value of the technique was 100%, 100%, and 71%, respectively. DISCUSSION: MPCE-VCATS is a promising technique for coronary artery imaging. It has a relatively high sensitivity as well as a high NPV. The results of the study may indicate a future role for the technique in obviating the need for some patients to undergo XRA.

Aged↗
PubMed2002

Classification of disease subgroup and correlation with disease severity using magnetic resonance imaging whole-brain histograms: application to magnetization transfer ratios and multiple sclerosis.

This paper presents a new approach to characterize subtle diffuse changes in multiple sclerosis (MS) using histograms derived from magnetization transfer ratio (MTR) images. Two major parts dominate our histogram analysis; 1) Classification of MTR histograms into control and MS subgroups; 2) Correlation with current disability, as measured by the EDSS scale (a measure of disease severity). Two data reduction schemes are used to reduce the complexity of the analysis: linear discriminant analysis (LDA) and principal component analysis (PCA). LDA is better for the classification of MTR histograms as it takes into account the between-class variation. By using LDA, the space of MTR histograms is transformed to the optimal discriminant space for a nearest mean classifier. In contrast, PCA is useful for correlation with current disability as it takes into account the variation within each subgroup in its process. A multiple regression analysis is used to evaluate the multiple correlation of those principal components with the degree of disability in MS. This is the first application of such classification and correlation techniques to magnetic resonance imaging histogram data. Our MTR histogram analysis approach give improved classification success and improved correlation compared with methods that use traditional histogram features such as peak height and peak location.

Adult↗
PubMedDate not supplied

Artifacts due to residual magnetization in three-dimensional magnetic resonance imaging.

An artifact is identified in magnetic resonance images produced by the three-dimensional FLASH technique, which features a short repetition time TR. The artifact is caused by differential spoiling of transverse magnetization by the phase-encoding gradients. The image intensity in different slices becomes altered, especially for short TR and large flip angle, which are conditions for achieving strong T1-weighted contrast. The effectiveness of spoiler gradient and rephasing gradients in suppressing the artifact is evaluated experimentally in images of a uniform phantom. Spoiler gradients that are incremented in amplitude cause even more slices to deviate in intensity, and are therefore less effective than in two-dimensional techniques. Rephasing gradients make the slices uniformly intense, but also enhance the intensity of tissues that have longer T2. The further addition of constant spoiler gradients has reduced this intensity increase by one-half and allowed for an intensity difference between white matter and gray matter comparable to without a rephasing gradient.

Diagnostic Errors↗
PubMedDate not supplied

Nonlinear magnetic stereotaxis: three-dimensional, in vivo remote magnetic manipulation of a small object in canine brain.

In a series of in vivo experiments on five adult canines, a small cylindrical permanent magnet (approximately 5-mm diameter x 5 mm long) was magnetically moved under fluoroscopic guidance from an occipital-lobe burr hole to a predetermined destination within the brain and then removed. On three of the animals, dorsal and temporal skull markers were used to establish a coordinate system against which the motions of the seed were referenced. These procedures were sufficiently accurate to permit the guided motion of the seed along nonlinear paths within the brain, including traversal of the midline through the corpus callosum. For removal, the seed could be steered either to a frontal lobe location for extraction through an auxiliary burr hole, or back to the same burr hole through which it had been inserted. This article discusses the way in which stereotactic motions were obtained, the performance limits of the instrumentation and the precision of motion achieved.

Animals↗
PubMedDate not supplied

Magnetic resonance imaging of hematomas in a 0.02 T magnetic field.

One intramuscular calf hematoma, 2 ankle hematomas and 4 cephalhematomas were imaged at various ages in a low magnetic field (0.02 T). At least one spin echo (SE) multislice image and a series of inversion recovery images (IR) were made varying the inversion time for estimation of the relaxation time T1. T1 tended to shorten and T2 to stay unchanged. With an unsuitable pulse sequence the hematomas were not visible. They were best seen with short TIs. The images of one of the ankle hematomas and the calf hematoma were compared with sonographic findings. The appearances of the hematomas varied during aging with both imaging modalities. The hematomas were easier to detect with magnetic resonance imaging than with ultrasound, also when aging.

Adult↗
PubMed2002

Interhemispheric reorganization of motor hand function to the primary motor cortex predicted with functional magnetic resonance imaging and transcranial magnetic stimulation.

The objective of this study was presurgical assessment of reorganization of motor hand function in an 11-year-old girl with intractable epilepsy and a right-sided hemiplegia resulting from an extensive perinatal left hemispheric stroke. Prior to a left functional hemispherectomy, functional magnetic resonance imaging (MRI) showed that both nonparetic and paretic motor hand function predominantly activated the right primary motor cortex, whereas no activation was found in the left hemisphere. Transcranial magnetic stimulation of the right central area yielded responses in both the nonparetic and the paretic hand, whereas no responses were obtained after stimulation of the affected hemisphere. Both techniques indicated that motor function was mediated by corticospinal fibers originating from the undamaged (primary) motor cortex and predicted no further loss of motor hand function after surgery. Indeed, subsequent functional hemispherectomy induced no new sensorimotor deficits. Functional MRI was repeated 22 months after surgery and matched preoperative sensorimotor functional MRI findings, confirming reorganization of the primary motor cortex. No additional reorganization was introduced by surgery.

Brain Infarction↗
PubMed2004

Magnetization transfer magnetic resonance imaging in the assessment of neurological diseases.

In several white matter diseases of the central nervous system (CNS), and in particular in multiple sclerosis, conventional magnetic resonance imaging (MRI) has proved to be sensitive for detecting lesions and their changes over time. However, conventional MRI is not able to characterize and quantify the tissue damage within and outside such lesions. Magnetization transfer MRI (MT-MRI) is a quantitative MRI technique with the potential to overcome this limitation and, as a consequence, to provide additional information about the nature and the extent of tissue damage. Metrics derived from MT-MRI can quantify the structural changes occurring within and outside lesions visible on conventional MRI scans. The present review summarizes the major contributions given by MT-MRI to provide an accurate in vivo picture of the heterogeneity of CNS pathology and, ultimately, to improve our ability to monitor the evolution of various neurological conditions.

Central Nervous System Diseases↗
PubMed2003

Highly efficient endosomal labeling of progenitor and stem cells with large magnetic particles allows magnetic resonance imaging of single cells.

Tracking transplanted stem cells using magnetic resonance imaging (MRI) could offer biologic insight into homing and engraftment. Ultrasmall dextran-coated iron oxide particles have previously been developed for uptake into cells to allow MRI tracking. We describe a new application of much larger, micron-scale, iron oxide magnetic particles with enhanced MR susceptibility, which enables detection of single cells at resolutions that can be achieved in vivo. In addition, these larger particles possess a fluorophore for histologic confirmation of cell distribution. We demonstrate highly efficient, nontoxic, endosomal uptake of these particles into hematopoietic CD34+ cells and mesenchymal stem cells documented by confocal and electron microscopy. Labeled cells retain biologic activity with preservation of colony-forming ability and differentiation capacity. MRI studies could detect labeled CD34+ cells and mesenchymal stem cells (MSCs) at single cell resolution. This appears to be a promising tool for serial noninvasive monitoring of in vivo cell homing and localization using MRI.

Animals↗
PubMed1993

The etiology of posterior circulation infarcts: a prospective study using magnetic resonance imaging and magnetic resonance angiography.

In a prospective study of 70 patients with infarcts in the posterior circulation admitted consecutively to a population-based primary-care center, we assessed infarct location and etiology using magnetic resonance imaging, three-dimensional time-of-flight magnetic resonance angiography, and noninvasive cardiac tests. The brainstem (mainly the paramedian pons) was the most commonly infarcted site (41/70, 59%), followed by the cerebellum (33/70, 47%). Combined supra- and infratentorial multiple vertebrobasilar infarcts occurred in 11 patients (16%). Overall, 27 patients (39%) had > or = 50% stenosis or occlusion of the basilar artery. There were other large-artery lesions in 19 patients (27%), including vertebral (V2-V4) stenosis or occlusion (in seven) and dolichoectatic vertebral/basilar arteries (in 12). Fifteen of the 70 patients had a potential cardiac source of embolism, which coexisted with large-artery disease in more than one-third of the cases. Cerebellar infarct without concomitant brainstem or occipital infarct was associated with cardioembolism (67%), while isolated paramedian pontine or midbrain infarct was associated with basilar artery stenosis (71%), suggesting in situ occlusion of the mouth of the perforators off the stenosed basilar artery. After exclusion of other potential causes of stroke, presumed small-artery disease associated with chronic hypertension remained the likely etiology in only 11 patients (16%), but these infarcts were not associated with any of the classical lacunar syndromes. Our findings emphasize the high frequency of severe intracranial large-artery disease in posterior circulation infarcts.

Aged↗
PubMed1999

Regional left ventricular myocardial contraction abnormalities and asynchrony in patients with hypertrophic cardiomyopathy evaluated by magnetic resonance spatial modulation of magnetization myocardial tagging.

Global left ventricular (LV) pump function is generally preserved in patients with hypertrophic cardiomyopathy (HCM). However, it is unknown whether regional myocardial contractility is impaired, especially in nonhypertrophied regions. The purpose of this study was to evaluate regional LV myocardial contraction in patients with HCM using magnetic resonance (MR) spatial modulation of magnetization (SPAMM) myocardial tagging. The study group comprised 20 patients with asymmetric septal hypertrophy (HCM group) and 16 age-matched normal patients (control group), and data were collected using transthoracic M-mode and 2-dimensional echocardiography, and MR SPAMM myocardial tagging. The systolic strain ratio, maximum systolic strain velocity, and time from end-diastole to maximum systolic strain (deltaT) in the anterior, ventricular septal, inferior and lateral regions for 2 LV short-axis sections at the levels of the chordae tendineae and papillary muscles were measured at 50-ms intervals by MR myocardial tagging. The end-diastolic anterior and ventricular septal wall thicknesses and LV mass index were significantly different between the HCM and control groups. The systolic strain ratio for all 4 walls, particularly the anterior and ventricular septal regions, was significantly lower in the HCM group. In the HCM group, the maximum systolic strain velocity was significantly lower and deltaT was significantly shorter for all 4 walls, particularly the anterior and ventricular septal regions. The standard deviation for the deltaT, calculated from the deltaT for the 8 regions of the 2 LV short-axis sections, was significantly greater in the HCM group. In conclusion, regional LV myocardial contraction is impaired in both hypertrophied and nonhypertrophied regions, and systolic LV wall asynchrony occurs in patients with HCM.

Adult↗