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At least 793 records · Page 44Linked to original sources
PubMed2004

Dynamic magnetic resonance tomography and proton magnetic resonance spectroscopy of prostate cancers in rats treated by radiotherapy.

RATIONALE AND OBJECTIVES: To establish an experimental setting for monitoring perfusion and metabolism in orthotopic prostate cancer at 1.5 T using dynamic contrast-enhanced magnetic resonance imaging (DCE MRI) and 1H-MR spectroscopy (MRS). METHODS: Dunning rat prostate cancer cells were injected into the prostate by open surgery. Twelve tumor-bearing rats (5 of these irradiated) and 6 healthy controls were followed up using gadolinium-diethylenetriaminepentaacetic acid -enhanced dynamic MRI and 1H-MRS. Amplitude and the exchange rate constant kep were calculated (2-compartment model). From 1H-MR spectra, ratios of choline (Cho) and creatine (tCr) were calculated. All tumors were examined histologically. RESULTS: On DCE MRI parameter maps, tumors showed increased vascularization. kep and microvessel density were correlated (r = 0.97). Tumors showed elevated Cho/tCr and an unexpected lipid fraction (2.0-2.2 parts per million). Irradiation slowed tumor growth significantly. Changes of perfusion and metabolism could be detected in all tumors during follow up. CONCLUSION: DCE MRI and 1H-MRS has potential to characterize orthotopic Dunning prostate cancer in rats, which is a promising model similar to human prostate carcinomas.

Animals↗
PubMed2004

Renal embolization: feasibility of magnetic resonance-guidance using active catheter tracking and intraarterial magnetic resonance angiography.

RATIONALE AND OBJECTIVES: Magnetic resonance (MR)-guidance of endovascular interventions offers various advantages, including the absence of ionizing radiation, excellent soft tissue contrast, and multiplanar and functional imaging capabilities. The objective of this study was to assess the feasibility of MR-guided renal embolization using active catheter tracking with automatic slice positioning and intraarterial contrast-enhanced MR angiography (MRA). MATERIALS AND METHODS: MR-guided embolization of 16 kidneys was attempted in 15 pigs using real-time tracking of active 5-Fr. catheters. Embolization was monitored by selective intraarterial projection MRA. Intraarterial three-dimensional (3D) MRA was used for the assessment of embolization results. Additional pathologic correlation was available in 2 animals. The image quality of intraarterial 3D contrast-enhanced-MRA was rated by an independent radiologist who was not involved in the animal experiments. RESULTS: Active catheter tracking with automatic slice positioning allowed reliable catheter guidance and catheterization of the renal artery in all animals. Embolization was successful in all kidneys (11 left, 5 right), as verified by intraarterial 3D contrast-enhanced MRA (ce-MRA) and/or pathology. The image quality of intraarterial 3D ce-MRA was rated excellent in 10 animals, moderate in 4 animals, and poor in 1 animal. CONCLUSION: Renal embolization using active catheter tracking and intraarterial ce-MRA is feasible. Selective intraarterial ce-MRA allows the assessment of blood supply and organ perfusion before, during, and after therapeutic interventions, thereby complementing MR-guided endovascular interventions.

Animals↗
PubMed2005

Magnetic resonance-guided percutaneous angioplasty of femoral and popliteal artery stenoses using real-time imaging and intra-arterial contrast-enhanced magnetic resonance angiography.

OBJECTIVE: The aim of this study was to demonstrate the possibility of performing magnetic resonance (MR)-guided interventional therapy for femoral and popliteal artery stenoses with commercially available materials supported by MR real-time imaging and intra-arterial MR angiography. MATERIALS AND METHODS: A total of 15 patients suffering from symptomatic arterial occlusive disease of the lower limbs with 19 stenoses were included. Interventional intra-arterial digital subtraction angiography was performed before and after angioplasty on each patient as standard of reference. MR images were acquired on a 1.5-T MR scanner. A fast-low-angle shot (FLASH) 3D sequence was applied for a contrast enhanced MR-angiography (ceMRA). A total of 5 mL of diluted gadodiamide was injected via the arterial access. Maximum intensity projections (MIPs) were used as roadmaps and localizers for the interactive positioning of a continuously running 2D-FLASH sequence with a temporal solution of 2 images/second. The lesion was crossed by a balloon-catheter, which was mounted on a guidewire. The visibility was provided by the radiopaque markers on the balloon and was improved by injection of 1 mL of gadolinium into the balloon. Postinterventional control was performed by intra-arterial MR angiography and catheter angiography. RESULTS: Stenoses were localized by intra-arterial MR angiography. The guidewire/balloon combination was visible, and the balloon was placed correctly to cover the entire stenoses. Balloon dilation reduced the degree of stenosis by approximately 57% on average. No complications were observed. CONCLUSION: MR-guided balloon dilation of femoral and popliteal artery stenoses supported by real-time MR imaging and intra-arterial MR angiography is feasible with commercially available materials.

Aged↗
PubMed2004

Magnetic resonance-guided placement of aortic stents grafts: feasibility with real-time magnetic resonance fluoroscopy.

PURPOSE: The artifact behavior of different aortic stent-grafts was evaluated with real-time magnetic resonance (MR) imaging, and the feasibility of real-time MR-guided stent-graft placement in the abdominal aorta was tested. MATERIALS AND METHODS: Seven different stent-grafts and their deployment systems were analyzed in an in vitro setting regarding their artifacts on different real-time MR images with cartesian, spiral, and radial k-space filling. The device and the real-time sequence with the fewest artifacts were used for an in vivo study in a swine model. In four animals, a straight aortic stent-graft was placed in the infrarenal abdominal aorta under real-time MR guidance. Results were controlled with MR angiography, multislice spiral computed tomography, and digital subtraction angiography. RESULTS: The in vitro study proved only one of the seven stent grafts (including deployment systems) to be suitable for real-time MR-guided intervention. MR-guided placement of the stent-grafts was possible in all animals. In one animal, the stent-graft dislocated during withdrawal of the deployment system as a result of a mismatch between stent-graft diameter and size of the infrarenal aorta. CONCLUSION: Real-time MR-guided placement of stent-grafts in the abdominal aorta with use of commercially available standard instruments is feasible. However, for clinical use, dedicated devices and deployment systems producing less artifacts are required.

Angiography, Digital Subtraction↗
PubMed1999

Hemodynamic and metabolic aspects of photosensitive epilepsy revealed by functional magnetic resonance imaging and magnetic resonance spectroscopy.

PURPOSE: To study in humans the hemodynamic and metabolic consequences of both photic stimulation-triggered and spontaneous generalized epileptiform discharges. METHODS: Simultaneous EEG, functional magnetic resonance imaging (fMRI) and MR spectroscopy were performed in a 1.5-T scanner in 16 patients with generalized epilepsy, including nine with photosensitive epilepsy, and 12 normal subjects. RESULTS: With a flash stimulation duration of 2 s, prominent visual cortex activation was seen in all normals and patients. There were no fMRI-registered hemodynamic abnormalities found in relation to the brief photoparoxysmal spike-wave activity evoked in the photosensitive patients. However, irrespective of the presence of a spike-wave response to the photic stimulation, the photosensitive patients showed four unique findings compared with normals: (a) slightly, but significantly, increased lactate levels in the occipital cortex in the resting state, (b) an increased area of visual cortical activation with photic stimulation, (c) simultaneous with the occipital cortex stimulus-induced increased fMRI signal there were noncontiguous areas of signal attenuation most prominent in perirolandic regions, and (d) a marked decrement (undershoot) of fMRI signal intensity immediately after the photic stimulation in the occipital cortex and in the region of the posterior cingulate gyrus. CONCLUSIONS: These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients.

Adolescent↗
PubMed1999

Photosensitive epilepsy studied by functional magnetic resonance imaging and magnetic resonance spectroscopy.

PURPOSE: To study metabolic and hemodynamic correlates of photic stimulation-triggered discharges. METHODS: Simultaneous EEG, functional MRI (tMRI) and magnetic resonance spectroscopy (MRS) were performed in nine patients with photosensitive epilepsy and in 12 normal subjects. RESULTS: Prominent visual cortex activation was seen in all normal subjects and patients, and no tMRI-registered hemodynamic abnormalities were correlated with the brief photoparoxysmal spike-wave activity evoked in the photosensitive patients. However, irrespective of the presence of a spike-wave response to the photic stimulation, the photosensitive patients showed four findings not seen in the normal subjects: (a) slightly, but significantly, elevated lactate levels in the occipital cortex in the resting state; (b) an increased area of visual cortical activation with photic stimulation; (c) simultaneous with the occipital cortex stimulus-induced increased fMRI signal, there were noncontiguous areas of signal attenuation most prominent in perirolandic regions; and (d) a marked decrement (undershoot) of fMRI signal intensity immediately after the photic stimulation in the occipital cortex and in the region of the posterior cingulate gyrus. CONCLUSIONS: These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients.

Adolescent↗
PubMed2001

Neuronal damage in the interval form of CO poisoning determined by serial diffusion weighted magnetic resonance imaging plus 1H-magnetic resonance spectroscopy.

In a patient with the interval form of carbon monoxide (CO) poisoning diffusion weighted MRI and proton magnetic resonance spectroscopy (1H-MRS) were serially performed immediately after the appearance of delayed sequelae (the 23rd day after exposure). During the period in which few clear findings were evident on MRI T2 weighted images, a high signal area in the cerebral white matter and relative decrease in the apparent diffusion coefficient (ADCav) were already apparent on diffusion weighted images, with these findings thought to sensitively reflect the tissue injury associated with the onset of sequelae. The decrease in relative ADCav persisted until the 38th day after exposure. Subsequently, ADCav gradually increased, and in the cerebral white matter showed higher values in the 118th day after exposure than immediately after the onset of sequelae. During this period, on 1H-MRS choline containing compounds showed persistently high values throughout the course, with N-acetylaspartate depletion and the appearance of a lactate peak later in the course. These findings, with regional specificity in the cerebral white matter, reflect the developmental process of the white matter lesions in the interval form of CO poisoning in which demyelination progresses leading to neuronal necrosis. Serial diffusion weighted imaging plus 1H-MRS measurements are useful in determining the tissue damage and long term outcome of delayed sequelae associated with the interval form of CO poisoning.

Brain↗
PubMed2000

Impact on stroke subtype diagnosis of early diffusion-weighted magnetic resonance imaging and magnetic resonance angiography.

BACKGROUND AND PURPOSE: The purpose of the present study was to assess the diagnostic usefulness of early diffusion-weighted MRI (DWI) and MR angiography (MRA) in patients with ischemic stroke. Past approaches to stroke diagnosis required a series of diagnostic tests over several days of hospitalization. New magnetic resonance methodologies that include DWI and MRA may allow more rapid characterization of stroke pathophysiology. However, no previous study has assessed the impact on formal stroke subtype diagnosis of early imaging with DWI/MRA. METHODS: We analyzed 46 consecutive patients with acute ischemic stroke who underwent DWI/MRA within 24 hours of admission. Initial diagnoses were rendered with use of the 2 most widely used formal stroke subtype classification schemes, the TOAST and the Oxfordshire methods, which were applied to patients after CT/conventional MRI but before DWI/MRA. Modified TOAST and Oxfordshire diagnoses were then rendered based on the results of day 1 DWI, MRA, and DWI plus MRA. Final TOAST/Oxfordshire diagnoses at discharge were taken as the gold standard. RESULTS: Compared with final diagnoses, pre-MRI TOAST diagnoses matched final diagnoses in 48%, improving to 83% after DWI alone, 56% after MRA alone, and 94% after DWI plus MRA. For the TOAST diagnostic subtypes of large-vessel atherothromboembolism and small-vessel disease, pre-MRI diagnoses matched final diagnoses in 56% and 35% of patients, respectively, improving to 89% and 100% after DWI/MRA. Pre-MRI Oxfordshire diagnoses matched final diagnoses in 67% of patients, improving to 100% after DWI. CONCLUSIONS: The use of DWI/MRA within 24 hours of hospitalization substantially improves the accuracy of the diagnosis of early ischemic stroke subtype. When initial management and clinical trial eligibility decisions are influenced by stroke subtype, day 1 multimodal MRI is advantageous as a guide to therapy.

Female↗
PubMed2002

Pulmonary embolism: comparison of angiography with spiral computed tomography, magnetic resonance angiography, and real-time magnetic resonance imaging.

In the last decade, spiral computed tomography (CT) and magnetic resonance (MR) angiography (MRA) have become a viable alternative to conventional angiography in the diagnosis of acute pulmonary embolism. However, patients with dyspnea are often unable to hold their breath for a longer time and thus image degradation is frequently observed. Consequently, an imaging sequence that allows free breathing is desirable. The aim of this animal study was to compare contrast-enhanced spiral CT, MRA and a real-time MR sequence, the latter without breath-hold, with pulmonary angiography as reference gold standard. Nine pigs with artificially induced pulmonary embolism underwent this multimodality comparison. All images were independently evaluated for the presence of pulmonary emboli by two reviewers. Forty-three filling defects were detected by conventional angiography on lobar and segmental levels. Sensitivity of CT images was 72.1 and 69.8% for Readers 1 and 2, respectively, and sensitivity of MRA images was 79.1 and 81.4%. With real-time MR imaging, however, the detection rate was 97.7% for both readers. We conclude that, under experimental conditions, real-time MR imaging without the use of radiation or iodinated contrast material is comparable with angiography in the detection of pulmonary emboli.

Angiography, Digital Subtraction↗
PubMed1999

Magnetic resonance imaging and magnetic resonance spectroscopy assessment of brain function in experimental animals and man.

This paper introduces the basic principles and techniques of functional magnetic resonance imaging (fMRI) and spectroscopy (MRS). Examples are given of single event human fMRI studies on control subjects, and a graded activation protocol applied to Parkinsonian patients. Possibilities are discussed for using fMRI techniques to study the neural substrate of various pharmacological agents, including drugs of abuse. The application of these pharmacological MRI (phMRI) studies to animal models and the associated technical issues are also addressed. The use of MRS in studying brain status and function is reviewed, with particular emphasis on 13C isotopic labelling studies.

Animals↗
PubMed2006

Magnetic resonance imaging and magnetic resonance spectroscopy study of deficits in hippocampal structure in fire victims with recent-onset posttraumatic stress disorder.

OBJECTIVE: To explore hippocampal structural abnormalities in fire victims with recent-onset posttraumatic stress disorder (PTSD). METHOD: We compared 12 patients with recent-onset PTSD diagnosed according to DSM-IV criteria 6 to 8 months after a major fire with 12 individuals without PTSD who were victims of the same fire accident. Voxel-based morphometry (VBM) and magnetic resonance spectroscopy (MRS) were combined to examine hippocampal structural abnormalities in patients with recent-onset PTSD. RESULTS: Results of VBM showed that the grey matter density of the left hippocampus was lower in the group with PTSD than it was in the group without PTSD. Results of MRS showed that the ratio of N-acetyl asparate and creatine in the left hippocampus was significantly lower in patients with PTSD than in control subjects. CONCLUSION: Patients with recent-onset PTSD had hippocampal structural abnormalities.

Adult↗
PubMed2005

Carbon monoxide brain toxicity: clinical, magnetic resonance imaging, magnetic resonance spectroscopy, and neuropsychological effects in 9 people.

Carbon monoxide (CO) exposure is a common cause of toxic brain damage, whereby effects range from transient neurological dysfunction to coma and death. A spectrum of severity of magnetic resonance imaging (MRI) findings after CO brain toxicity, including globus pallidus and white matter lesions, is well documented. Reports of MR spectroscopy (MRS) findings re main sparse. This article reports 9 people exposed to CO because of an apartment house's faulty gas heater. Four, with transient loss of consciousness after chronic moderate level CO exposure, suffered intellectual impairment without MRI abnormalities. The MRS of 1 individual demonstrated decreased n-acetyl aspartase in the basal ganglia, bilaterally. Of 5 exposed to high levels for about 12 hours, 1 died prior to clinical and/or MRI evaluation. One who suffered coma recovered but was lost to evaluation. Three, who were unconscious for hours to days, exhibited T2 MRI white matter signal abnormalities. MRS showed decreased basal ganglia n-acetyl aspartase in 2. One of these suffers a Parkinsonian syndrome. All 3 are intellectually impaired. This study demonstrates that although MRI and MRS are useful markers of CO-induced brain damage, they are not always sensitive to resultant intellectual dysfunction.

Acute Disease↗
PubMed1995

Plasticity of central motor and sensory pathways in a case of unilateral extensive cortical dysplasia: investigation of magnetic resonance imaging, transcranial magnetic stimulation, and short-latency somatosensory evoked potentials.

We studied a 13-year-old girl with unilateral extensive cortical dysplasia who had mild hemiparesis with mirror movement and no sensory deficit. Transcranial focal magnetic stimulation (TMS) to the unaffected hemisphere elicited bilateral motor evoked potentials (MEPs) of the abductor pollicis brevis muscle (APB) with similar latency and amplitude. The scalp positions where the MEP amplitudes were highest were at the same site in the unaffected hemisphere for both APBs. TMS to the affected heimsphere showed no MEP for either APB. These data indicated that the APB response of the paretic side originated from the same motor cortex as for the contralateral APB, probably due to axonal sprouting. In the study of short-latency somatosensory evoked potentials, the cortical representation point of the paretic hand sensation was in the ipsilateral unaffected hemisphere; this point was located anterior to the cortical representation point of the contralateral hand sensation. We conclude that reorganization of primary motor and sensory cortex occurs when there is unilateral extensive brain damage in early gestation.

Adolescent↗
PubMed1997

Magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) of intracranial lipomas.

We show a detailed magnetic resonance (MR) examination of two rare pericallosa lipomas with a fat suppression imaging sequence and proton MR spectroscopy. For comparison, subcutaneous fat and lipids in glioblastomas were examined with H MR spectroscopy in vivo and ex vivo. Fat suppression makes the identification of lipomas simple. It is suggested that H MR spectroscopy shows no differences in the aliphatic chain length of lipoma and subcutaneous fat, whereas lipids in glioblastomas have a much shorter chain length. Chain length of fatty acids in lipoma measured with in vivo MR spectroscopy are in concordance with data from the literature.

Adipose Tissue↗
PubMed1989

Magnetic resonance imaging and 31P magnetic resonance spectroscopy for evaluating focal cerebral ischemia.

Recent advances in magnetic resonance (MR) imaging and MR spectroscopy (MRS) allow the noninvasive in vivo study of a variety of anatomical, physiological, and biochemical alterations that may occur in different cerebral pathologies. The authors have investigated the use of MR imaging and MRS to monitor the evolution of experimental focal cerebral ischemia in rats. Permanent focal cerebral ischemia was induced in 36 rats, and 12 normal rats were used as a control group. Changes in high-energy phosphate metabolites were followed in vivo using MRS during the 1st hour and at 3 and 6 hours after ischemic insult. Changes in vivo MR images were evaluated at 1, 3, 6, 12, and 24 hours after ischemic insult. Significant decreases (p less than 0.05) in phosphocreatine/inorganic phosphate ratios and intracellular pH values occurred immediately after the induction of ischemia. The presence of an infarcted area seen on MR images was a constant finding at 3 hours after ischemic insult, and was well defined and localized at 12 and 24 hours. The location of areas of infarction seen on MR images correlated well with areas identified histopathologically. The T1 and T2 MR relaxation times were significantly increased 3 hours after ischemic insult and remained prolonged for at least 24 hours. The results show that MR imaging is a sensitive method to measure cerebral infarction, and that MRS is a sensitive measure of changes that occur in the early phases of ischemia, perhaps when cellular changes may still be reversible. At 3 and 6 hours after the ischemic insult, however, 31P-MRS spectra may appear to be "normal" despite the presence of well-documented areas of infarction.

Animals↗
PubMed1998

High-resolution T2-reversed magnetic resonance imaging on a high magnetic field system. Technical note.

Because of the high signal-to-noise (S/N) ratio, T2-weighted images obtained using high-field magnetic resonance (MR) imaging systems can be expected to provide high anatomical and contrast resolution. Furthermore, the improved structural and contrast resolution of these high S/N T2-weighted images can be processed for optimum perceptual resolution through the application of gray-scale reversal and expansion of the gray-scale window, known as T2-reversed (T2R) imaging. In this study, the authors investigated high-resolution T2R MR imaging performed on a high-field (3-tesla) system for its clinical utility in detecting various physiological and pathological conditions.

Adolescent↗
PubMed2004

Evaluation of the response of metastatic brain tumors to stereotactic radiosurgery by proton magnetic resonance spectroscopy, 201TlCl single-photon emission computerized tomography, and gadolinium-enhanced magnetic resonance imaging.

OBJECT: The goal of this study was to investigate the usefulness of proton (1H) magnetic resonance (MR) spectroscopy to evaluate the response of metastatic brain tumors to stereotactic radiosurgery (SRS) in comparison with Gd-enhanced MR imaging and single-photon emission computerized tomography with administration of thallium-201 chloride (201TlCl-SPECT). METHODS: Forty patients with a total of 47 metastatic brain tumors were evaluated. The primary lesion was identified in all cases. Stereotactic radiosurgery was effective in 37 lesions. All patients were examined using Gd-enhanced MR imaging before and after SRS. Thalium-201 chloride was administered to 27 patients with 34 tumors and SPECT images were obtained. Proton MR spectroscopy was performed in 36 patients who harbored 43 tumors. On Gd-enhanced MR images, a decrease in the volume of the Gd-enhanced lesion and a change in the enhanced effect in the lesion after treatment were recognized as showing the effectiveness of SRS between 1 and 3 months or more (mean 8.54 +/- 3.58 weeks). In 201TlCl-SPECT studies, the ratio of lesion to normal brain decreased from 2 weeks to 2 months (mean 5.03 +/- 2.77 weeks) after radiosurgery. On 1H-MR spectroscopy images a high choline (Cho) peak and a lipid-dominant (Lip) peak were observed in 25 lesions and a high Cho peak and a lactate-dominant (Lac) peak were observed in 12 lesions before SRS. A decrease in the Cho peak, a disappearance of the Lac peak, and an increase in the Lip peak were observed between 1 week and 1 month (mean 2.76 +/- 1.62 weeks) after treatment. CONCLUSIONS: Based on histopathological findings obtained at autopsy or at surgery, we assume that a high Cho peak may be observed in viable tumor tissue and a Lip peak in areas of necrosis. The results indicate that 1H-MR spectroscopy is potentially a more sensitive tool in evaluating the response to SRS than 201TlCl-SPECT or Gd-enhanced MR imaging and that it can be used earlier for this purpose than those other imaging methods.

Adult↗
PubMed2000

Differentiation between hemosiderin- and ferritin-bound brain iron using nuclear magnetic resonance and magnetic resonance imaging.

MRI is an optimal clinical (research) tool to provide information on brain morphology and pathology and to detect metal ions that possess intrinsic magnetic properties. Non-heme iron is abundantly present in the brain in three different forms: "low molecular weight" complexes, iron bound to "medium molecular weight complexes" metalloproteins such as transferrin, and "high molecular weight" complexes as ferritin and hemosiderin. The total amount and form of iron may differ in health and disease, and MRI can possibly quantify and monitor such changes. Ferritin-bound iron is the main storage form of iron and is present predominantly in the extrapyramidal nuclei where its amounts normally increase as a function of age. Ferritin is water soluble and shortens both, T1 and T2 relaxation, with as result a signal change on the MR images. Hemosiderin, a degradation product of ferritin, is water-insoluble with a stronger T2 shortening effect than ferritin. The larger cluster size of hemosiderin and its water-insolubility also explain a lack of significant T1-shortening effect on T1-weighted images. Using both in vitro specimens and intact brain tissue in vivo we demonstrate here that MRI may be able to distinguish between ferritin- and hemosiderin-bound iron.

Aged↗