Biomedical subjects

P Reimer

Publications and source records attributed to P Reimer.

At least 37 records · Page 2Linked to original sources

PubMed2001

Ex vivo evaluation of novel miniaturized laser-induced interstitial thermotherapy applicators for effective small-volume tissue ablation.

RATIONALE AND OBJECTIVES: For effective small-volume tissue ablation in clinical and experimental settings, smaller laser-induced interstitial thermotherapy (LITT) applicator designs are required. The aim of this study was to compare the ablation properties of recently developed ultrasmall and small to standard LITT applicators. METHODS: Laser-induced interstitial thermotherapy was performed on liver samples using ultrasmall, small, and standard LITT applicators. Thermotherapy was monitored by magnetic resonance imaging, and lesion sizes were measured for each image. True lesion sizes were then determined macroscopically and by histology. RESULTS: For continuous laser application over 5 minutes, maximum power settings were 5 W for the ultrasmall and small applicators and 10 W for the standard applicator. Given identical LITT settings, lesion volume measured by magnetic resonance imaging was significantly larger and histological tissue damage was more severe with the ultrasmall and small applicators than with the standard applicator. CONCLUSIONS: Small and ultrasmall LITT applicators can be used for effective tissue ablation of small target volumes in experimental and clinical applications.

Animals↗

PubMed2001

Renal tolerance of a neutral gadolinium chelate (gadobutrol) in patients with chronic renal failure: results of a randomized study.

PURPOSE: To assess the renal tolerance of 1.0 mol/L gadobutrol as an electrically neutral contrast agent at magnetic resonance (MR) imaging in patients with impaired renal function. MATERIALS AND METHODS: Twenty-one patients with impaired renal function were enrolled in this prospective randomized study and classified into two subgroups according to their creatinine clearance: group 1 (n = 12), less than 80 mL/min (<1.33 mL/sec) and greater than 30 mL/min (>0.50 mL/sec); group 2 (n = 9), less than 30 mL/min (<0.50 mL/sec) and not requiring dialysis. Gadobutrol (1.0 mol/L) was injected intravenously at randomly assigned doses of either 0.1 or 0.3 mmol per kilogram of body weight. Changes in vital signs, clinical chemistry, and urinalysis results, including creatinine clearance, were monitored before, at 6 hours, and then every 24 hours until 72 hours (group 1) or 120 hours (group 2) after intravenous injection of gadobutrol. Hematologic results were checked every other day. RESULTS: No serious adverse event occurred, and no clinically relevant changes in vital signs, hematologic results, clinical chemistry, or urinalysis results were detected in the observation period. Markers for glomerular filtration (creatinine, cystatin C, beta2-microglobulin, creatinine clearance) and tubular function (N-acetyl-beta-D-glucosaminidase, alpha1-microglobulin) were unaffected by gadobutrol in both groups. CONCLUSION: Gadobutrol did not affect renal function and, therefore, proved to be a safe MR contrast agent in patients with impaired renal function. Even in patients with marginal excretory function (creatinine clearance, <30 mL/min [<0.50 mL/sec]), prehydration or treatment with diuretics or hemodialysis are not required after the administration of gadobutrol.

Adult↗

PubMed2001

Three-dimensional contrast-enhanced MR angiography of endovascular covered stents in patients with peripheral arterial occlusive disease.

OBJECTIVE: Three-dimensional contrast-enhanced MR angiography was performed to study MR characteristics of Hemobahn devices. MATERIALS AND METHODS: Changes in endoluminal signal intensities and the precision of the endoluminal diameter measurement were investigated in phantom studies for different concentrations of gadopentetate dimeglumine. Before and after the Hemobahn devices had been implanted, 10 patients with peripheral arterial occlusive disease were examined on MR imaging and three-dimensional contrast-enhanced MR angiography. RESULTS: Phantom experiments using three-dimensional MR angiography showed stent-related signal void as a dark ring in the axial image orientation, providing a precise delineation of the stent--vessel border (mean endoluminal diameter, 8.2 mm; SD, 0.6 mm). Changes in endoluminal signal intensity were evaluated quantitatively. Stent-related artifacts did not compromise diagnostic imaging quality. All Hemobahn devices were found to be patent without migration of an implanted graft. In one patient, an extensive perigraft reaction (edema and contrast-enhanced perivascular tissue) was postinterventionally detected on MR imaging and corresponded to clinically evident postimplantation symptoms. CONCLUSION: Three-dimensional contrast-enhanced MR angiography is a suitable tool to follow up the implantation of Hemobahn devices and to detect intra- and extraluminal abnormalities.

Aged↗

PubMed2000

Detection of articular cartilage lesions: experimental evaluation of low- and high-field-strength MR imaging at 0.18 and 1.0 T.

The objective of this study was to compare the diagnostic performance of a dedicated orthopedic magnetic resonance (MR) imaging system (0.18 T) and a conventional MR imaging system (1.0 T) in the detection of articular cartilage lesions. Fifty knee joint specimens of pigs with artificially created articular cartilage lesions of different diameters, grades (2-3), and localizations, as well as 50 joints with intact articular cartilage, were imaged at 0. 18 and 1.0 T. Diagnostic performance was determined by means of receiver operating characteristics (ROC) analysis with three independent observers. For none of the pulse sequences used at 0.18 T or 1.0 T areas under ROC curves (A(z)) showed significant differences between the three observers. A(z) values from averaged data were as follows: a) 0.18 T: T1-weighted spin echo (SE): 0.70, proton-density-weighted SE: 0.59, T2-weighted SE: 0.61, two-dimensional (2D) gradient-echo (GRE): 0.73, 3D GRE: 0.75; and b) 1.0 T: T1-weighted SE: 0.73, fat-suppressed T2-weighted turbo-SE: 0. 79, 2D fast low-angle shot (FLASH): 0.79, fat-suppressed 3D FLASH: 0. 96, and water-excited 3D double-echo steady state (DESS): 0.96. With the use of 3D pulse sequences, the high-field system demonstrated a significantly better diagnostic performance than the low-field system in the detection of grades 2 and 3 articular cartilage lesions (P < 0.001).

Animals↗

PubMed2000

Cerebral MR perfusion imaging: first clinical application of a 1 M gadolinium chelate (Gadovist 1.0) in a double-blinded randomized dose-finding study.

The purpose of this study was to evaluate efficacy and safety of the 1 M gadolinium chelate Gadovist 1.0 for assessment of cerebral hemodynamics with dynamic susceptibility contrast-enhanced magnetic resonance (MR) imaging. Eighty-nine patients with carotid artery stenosis or cerebral infarcts were included in this multicenter, double-blinded study using five dose groups from 0.1 to 0.5 mmol/kg. Imaging was performed with 1-T scanners using a T2*-weighted fast low-angle shot (FLASH) sequence. Dose-dependent changes in quantitative and qualitative parameters describing signal-time curves and relative regional cerebral blood volume maps were investigated. For safety evaluation, vital signs, clinical and laboratory tests, and adverse events were assessed. The quantitative measurements revealed an optimal dose of 0.4 mmol/kg. The qualitative evaluation revealed that the required qualitative assessment for clinical purposes was already reached at a dose of 0. 3 mmol/kg. No significant changes in vital signs and laboratory tests were found. No serious adverse events were observed. The combined results revealed the dose of 0.3 mmol/kg as the diagnostically adequate dose given the gradient-echo sequence and field strength used. Gadovist 1.0 has been shown to be a safe and well-tolerated contrast agent. J. Magn. Reson. Imaging 2000;12:371-380.

Adolescent↗

PubMed2000

Persistent polyclonal B-cell lymphocytosis--an important differential diagnosis of B-cell chronic lymphocytic leukemia.

Over the last 17 years, 83 cases of polyclonal B-cell lymphocytosis (PPBL) have been published. This rare hematological disorder of unknown etiology is characterized by morphologically atypical lymphocytes, polyclonal immunoglobulin M production in association with smoking, female gender, and HLA-DR7 phenotype. We studied another male patient with PPBL. In contrast to normal B-cells, PPBL cells showed no response to interleukin-4 with regard to CD23 and human leukocyte antigen-DR expression. F2mu antibodies failed to co-stimulate interleukin-4-mediated CD23 expression. Crosslinking membrane immunoglobulin M receptors by F2mu resulted in elevated human leukocyte antigen-DR expression but did not induce in vitro proliferation of PPBL cells. This indicates a different activation and differentiation status than normal B-cells.

Adult↗

PubMed2000

Dynamic MR imaging of liver metastases with Gd-EOB-DTPA.

PURPOSE: To assess liver and lesion enhancements by dynamic MR imaging after bolus injection of the hepatobiliary contrast agent gadolinium ethoxybenzyl-diethylenetriamine-pentaacetic acid (Gd-EOB-DTPA) in patients with liver metastases and to compare the effect of different doses. MATERIAL AND METHODS: A randomized double-blinded trial with doses of 12.5, 25 and 50 micromol/kg Gd-EOB-DTPA was performed in 35 patients with liver metastases. Liver enhancement, tumor enhancement and liver lesion contrast-to-noise (C/N) ratios were calculated from breath-hold gradient echo images (100/5/80 degrees) recorded precontrast and at different times up to 10 min postcontrast. RESULTS: Normal liver showed a characteristic enhancement pattern, with a rapid enhancement in the first 45 s postcontrast and a slight but significant further increase up to 600 s. The initial enhancement in the lesions was also pronounced, but the enhancement was slightly decreased after 240 s postcontrast. At dose levels of 12.5 and 25 micromol/kg Gd-EOB-DTPA, C/N ratios significantly increased compared to baseline from 90 to 600 s. Postcontrast C/N-values obtained using 50 micromol/kg Gd-EOB-DTPA were not significantly increased, except for the examinations 480 s postcontrast. CONCLUSION: In liver metastases, C/N ratios obtained with doses of 12.5 and 25 micromol/kg Gd-EOB-DTPA were slightly superior to 50 micromol/kg Gd-EOB-DTPA. This finding is probably due to a more pronounced extracellular effect of the contrast medium at higher doses.

Adult↗

PubMed2000

Pharmacokinetics of 1M gadobutrol in patients with chronic renal failure.

RATIONALE AND OBJECTIVES: To investigate the pharmacokinetics of 1M gadobutrol as a new neutral MR contrast agent in patients with impaired renal function. METHODS: Twenty-one patients with impaired renal function and any indication for a contrast-enhanced MRI were enrolled into this prospective study and classified in two subgroups according to their creatinine clearance (group 1, 30-80 mL/ min; group 2, 30 mL/min or less, not requiring dialysis). Eleven patients were assigned to the lower dose of 0.1 mmol Gd/kg and 10 patients to the higher dose of 0.3 mmol Gd/kg. To calculate pharmacokinetic parameters, urine and venous blood samples were drawn at baseline and up to 72 hours for group 1 and 120 hours for group 2 after administration of gadobutrol. RESULTS: The predominant extracellular distribution of gadobutrol at steady state did not change according to the degree of renal impairment. The mean elimination half-life of gadobutrol increased to 7.4 +/- 2.6 hours (0.1 mmol/kg) and 5.4 +/- 1.5 hour (0.3 mmol/kg) in group 1 and to 17.9 +/- 6.2 hours (0.1 mmol/kg) and 20.4 +/- 16.9 hours (0.3 mmol/kg) in group 2, compared with 1.5 hours in healthy volunteers. The relation between serum (tbeta) and urine (t(elim)) elimination half-lives, as well as total serum and renal clearance, indicated renal elimination as the main pathway of elimination. The recovery of gadobutrol in the urine of group 1 was complete within 72 hours for both dosage levels. Patients with severe renal impairment showed a mean recovery of 80.1% (0.1 mmol/kg) and 85.3% (0.3 mmol/kg) within the observation period of 120 hours. CONCLUSIONS: The half-life of gadobutrol is prolonged in patients with impaired renal function, but elimination by means of the kidneys is the predominant route.

Case-Control Studies↗

PubMed2000

Hypertension associated with multiple renal arteries may be renin-dependent.

OBJECTIVE: Subjects with multiple renal arteries have been shown to suffer more frequently from hypertension and to have higher blood pressures than subjects whose kidneys are supplied by single renal arteries. This study was carried out to determine whether subjects with multiple renal arteries also have higher renin activity. METHODS: We studied 62 consecutive patients who had undergone angiography for various reasons. They were divided into two groups. Group A comprised 29 patients whose kidneys were supplied by single arteries (male :female ratio 1.63, mean age 51.8 +/- 1.9 years) while Group B comprised 33 patients with multiple renal arteries (male:female ratio 2, mean age 47.3 +/- 2.3 years). RESULTS: Before stimulation with frusemide, the plasma renin in Group A was 0.79 +/- 0.13 ng angiotensin l/ml per h, while in Group B the corresponding figure was 1.73 +/- 0.38 ng angiotensin l/ml per h. This difference was statistically significant (P= 0.0127). Thirty minutes later the plasma renin level in Group A was 2.43 +/- 0.37 ng angiotensin l/ml per h versus a level of 3.86 +/- 0.53 ng angiotensin l/ml per h in Group B (P= 0.0169). Again, 30 minutes later the level was 2.59 +/- 0.4 ng angiotensin l/ ml per h in Group A, versus 3.79 +/- 0.59 ng angiotensin l/ ml per h in Group B (P= 0.0495). CONCLUSIONS: We conclude that patients with multiple renal arteries constitute a group who have high plasma renin activity and may therefore be prone to develop arterial hypertension.

Adult↗

PubMed2000

Hepatic lesion detection and characterization: value of nonenhanced MR imaging, superparamagnetic iron oxide-enhanced MR imaging, and spiral CT-ROC analysis.

PURPOSE: To determine the accuracy for detection and characterization of focal hepatic lesions of nonenhanced, superparamagnetic iron oxide (SPIO)-enhanced, or a combination of nonenhanced and SPIO-enhanced MR imaging and contrast-enhanced spiral computed tomography (CT). MATERIALS AND METHODS: Spiral CT and T2-weighted SPIO-enhanced (ferucarbotran-enhanced) MR imaging were performed in 35 patients within 2 weeks before surgery for malignant hepatic lesions. Only malignant lesions with histopathologic proof were considered. A total of 875 images with and 800 images without focal lesions were presented to five readers, who were asked to assess the presence and characterization of lesions by using a five-point confidence scale. Receiver operating characteristic analysis was performed. RESULTS: Nonenhanced and SPIO-enhanced images together and SPIO-enhanced images alone yielded the best performance for lesion detection. No differences were found among all imaging techniques with regard to lesion characterization (benign vs malignant). The combined approach resulted in larger area under the ROC curve (A(z) = 0.9062) and accuracy (85.3%) (P < 0.02), as compared with SPIO-enhanced MR imaging (A(z) = 0.8667; accuracy, 73.1%). CONCLUSION: SPIO-enhanced T2-weighted MR imaging was more accurate than nonenhanced T1-weighted and T2-weighted MR imaging and contrast-enhanced spiral CT for the detection of focal hepatic lesions. The combined analysis of nonenhanced and SPIO-enhanced images was more accurate in the characterization of focal hepatic lesions than was review of SPIO-enhanced images alone.

Contrast Media↗

PubMed2000

Optimized activation of the primary sensorimotor cortex for clinical functional MR imaging.

BACKGROUND AND PURPOSE: One application of functional MR imaging is to identify the primary sensorimotor cortex (M1 and S1) around the central sulcus before brain surgery. However, it has been shown that undesirable coactivation of nonprimary motor areas, such as the supplementary motor area and the premotor area, can interfere with the identification of the primary motor cortex, especially in patients with distorted anatomic landmarks. We therefore sought to design a simple functional MR imaging paradigm for selective activation of the primary sensorimotor cortex. METHODS: Different paradigms using finger tapping for motor activation were examined and compared with respect to the distribution of activated voxels in primary and nonprimary cortical areas. Studies were conducted in 14 healthy volunteers using a blood oxygen level-dependent multislice echo-planar imaging sequence. RESULTS: The most selective activation of the primary sensorimotor cortex was obtained with a paradigm combining right-sided finger tapping as the activation condition with left-sided finger tapping as the control condition. Analysis of the signal time course of primary and nonprimary areas revealed that the highly selective primary motor activation was due to it being restricted to contralateral finger movements, as opposed to the nonprimary motor areas, which were activated by ipsilateral, contralateral, and bilateral finger movements alike. CONCLUSION: When performing functional MR imaging to determine the location of the primary sensorimotor cortex, one should compare unilateral voluntary movements as the activation condition with contralateral movements as the control condition to accentuate activation of the primary motor area and to suppress undesirable coactivation of nonprimary motor areas.

Adult↗

PubMed1999

A multicenter, randomized, double-blind study to evaluate the safety, tolerability, and efficacy of OptiMARK (gadoversetamide injection) compared with Magnevist (gadopentetate dimeglumine) in patients with liver pathology: results of a Phase III clinical trial.

The purpose of this study was to evaluate the safety and efficacy of OptiMARK (gadoversetamide injection) compared with Magnevist (gadopentetate dimeglumine) in hepatic MRI of patients with suspected liver pathology. A Phase III, multicenter, randomized, double-blind, parallel group study was performed in adults with suspected liver pathology. All patients underwent contrast-enhanced computed tomography within 3 weeks prior to magnetic resonance scanning. Ninety-nine patients received OptiMARK, and 94 patients received Magnevist at a dose of 0.1 mmol/kg. Precontrast T1- and T2-weighted spin-echo imaging and T1-weighted gradient-echo imaging were performed, followed by T1-weighted gradient-echo imaging at 15-20 seconds, 1 minute, and 5 minutes after intravenous contrast injection. Three primary efficacy endpoints (confidence in lesion diagnosis, level of conspicuity, and lesion border delineation) were evaluated on the precontrast image set and compared with the pre plus postcontrast image set. Vital signs, physical examination, electrocardiograms (ECGs), and laboratory parameters (chemistry, hematology, and urinalysis) were measured at various time points. Adverse events were recorded. The study design and statistical analyses were chosen to demonstrate presumed equivalence of OptiMARK and Magnevist. There were no statistically significant differences in efficacy between OptiMARK and Magnevist as assessed by either blinded readers or the on-site principal investigators. No serious or unexpected adverse events were noted. Of the 193 patients receiving contrast media, 82 experienced a total of 154 adverse events. Thirty-three (21.4%) of these 154 adverse events were felt by the on-site investigators to be probably related to either study agent: 15 events in 9 patients in the OptiMARK group, and 18 events in 13 patients in the Magnevist group. Headache was the most common adverse event, occurring in 10.1% of the OptiMARK patients and 12.8% of the Magnevist patients. No clinically relevant trends were observed in any laboratory parameter or ECG findings in either treatment group. The results demonstrate the safety, efficacy, and equivalence of OptiMARK and Magnevist at a dose of 0.1 mmol/kg in hepatic magnetic resonance imaging of patients with suspected liver pathology.

Contrast Media↗

PubMed1999

Contrast-enhanced 3D-MRA of the upper abdomen with a bolus-injectable SPIO (SH U 555 A).

The purpose of this study was to study temporal changes in signal intensity of liver, spleen, abdominal vessels, and focal liver lesions following iv bolus injection of a superparamagnetic iron oxide (SPIO) using a breath-held three-dimensional magnetic resonance angiography (3D-MRA) sequence. Dynamic SH U 555 A-enhanced 3D-MRA studies were performed in 20 patients with focal liver lesions. Sequential coronal 3D-MRA-FISP scans were acquired (TR 5.0 msec, TE 2.0 msec, flip angle 25 degrees, 140 x 256 matrix, and 80 mm slab) within 15 seconds. Scanning was started immediately after bolus injection of 10 micromol Fe/kg bodyweight and was repeated at multiple time points (baseline and 30, 60, 90, 120, 180, 240, 300, 360, and 420 seconds). Signal intensity values of liver, focal liver lesions, spleen, the portal venous system, the abdominal aorta, and the inferior vena cava were obtained to calculate relative enhancement (ENH = [SI post - SI pre]/SI pre x 100). Visibility of vessels was assessed by consensus of two readers. Signal enhancement within abdominal vessels peaked during the first pass; however, significant signal enhancement was still present 420 seconds following injection. The liver and the spleen also demonstrated a biphasic enhancement pattern with prolonged parenchymal enhancement. Dynamic MRA with bolus injectable SH U 555 A is clinically feasible, and significant vessel enhancement can be achieved even at the dose of 10 micromol Fe/kg bodyweight. However, further refinements are required to improve contrast effects.

Abdomen↗

PubMed1999

RES-specific imaging of the liver and spleen with iron oxide particles designed for blood pool MR-angiography.

The purpose of this study was to determine the dependency of liver- and spleen-enhancement on particle size and dose of bolus-injectable iron oxides designed for blood-pool MR-angiography (MRA). The superparamagnetic iron oxide SHU 555 A [particle size 65 nm (group 1)] and three derivatives designed for blood-pool MRA (groups 2-4) with smaller hydrodynamic diameters (46/33/21 nm) were i.v. injected in New Zealand White rabbits at doses of 10, 20, or 40 micromol Fe/kg bw. MRI was performed before, 2, and 24 hours after contrast application using T1-weighted SE and T2-weighted TSE sequences. In addition splenic tissue was harvested post mortem and scanned ex vivo. All iron oxides significantly decreased the SI of liver and spleen in T1- and T2-weighted images at 2 and 24 hours after application of contrast media (P < 0.01). The signal intensity was inversely related to the dose applied. Decreasing particle size resulted in a lower signal enhancement in liver and spleen. However, ultra-small superparamagnetic iron oxides suited for blood-pool MRA (USPIOs, group 4) still revealed a significant signal enhancement in the liver and spleen even 24 hours after contrast application (< - 60%, 40 micromol Fe/kg bw). They might thus be used for comprehensive abdominal studies including contrast enhanced MR-angiography and RES-specific imaging.

Analysis of Variance↗

PubMed1999

Does a higher concentration of gadolinium chelates improve first-pass cardiac signal changes?

The purpose of this study was to evaluate first-pass cardiac signal changes with a higher concentrated gadolinium-chelate (gadobutrol) and its influence on bolus geometry. Phantom studies and in vivo first-pass cardiac studies were performed in rabbits (n = 8 experiments) under general anesthesia at 1.0 T using an ultrafast T1-weighted Turbo-fast low-angle shot (FLASH) sequence (TR/TE 4.7/1. 6 msec, alpha = 90 degrees ) with a time resolution of 870 msec. Gadobutrol was injected as an intravenous bolus at two concentrations (0.5 and 1.0 mol Gd/L) and five doses (0.3, 0.15, 0.1, 0.055, and 0.03 mmol Gd/kg bw). The blood-pool gadolinium compound gadopentetate dimeglumine-polylysine (0.15, 0.075, 0.05, and 0.015 mmol Gd/kg bw, 0.5 mol Gd/L) and the standard extracellular gadopentetate dimeglumine (0.1 and 0.05 mmol Gd/kg bw, 0.5 mol Gd/L) served as reference agents. Cardiac signal changes were calculated from serial signal intensity measurements. Maximum signal intensity changes and best peak profiles during first pass of the right and left ventricle were observed with a dose of 0.03 mmol Gd/kg bw gadobutrol using T1-weighted Turbo-FLASH. At the low application volumes used, the higher concentration of 1.0 mol Gd/L gadobutrol did not increase the degree of signal intensity changes or sharpen the bolus profile. First-pass cardiac signal changes using T1-weighted Turbo-FLASH with the new extracellular contrast agent gadobutrol are best observed at a dose of 0.03 mmol Gd/kg bw. There is no advantage to the concentrated formulation (1 mol Gd/L gadobutrol) when using small injection volumes. J. Magn. Reson. Imaging 1999;10:806-812.

Animals↗

PubMed1999

Phase-contrast MR angiography of peripheral arteries: technique and clinical application.

This articles describes Phase-Contrast-MRA (PC-MRA) techniques and their current clinical applications for peripheral arteries based on more than 250 clinical MRA studies performed at two institutions. PC-MRA depends on phase shifts caused by blood flow and thus this technique permits the use of coronal or sagittal slice orientations with large FOV's along the direction of the vessel of interest. Clinical applications focus on patients with peripheral arterial occlusive disease (PAOD) describing the role and limitations of PC-MRA for the work-up of stenoses, occlusions, aneurysms, and postsurgical follow-up. Recommendations for clinical routine are provided. A combined MR angiographic approach with various MRA techniques depending on the vessel segment to be imaged, PC-flow velocity measurements, and high-resolution scans of the vessel wall may turn out to be diagnostically effective and provide a comprehensive test for PAOD within the near future.

Aneurysm↗

PubMed1999

Clinical applications of functional MRI at 1.0 T: motor and language studies in healthy subjects and patients.

In this article we describe clinical applications of functional MRI (fMRI) at 1.0 T. All experiments were performed on a commercially available 1.0-T system (Magnetom Impact Expert, Siemens AG, Erlangen, Germany) using a blood oxygen level-dependent (BOLD)-sensitive multi-slice EPI technique (TE 66 ms, 4 mm slice thickness, 210 mm field of view, 64 x 64 acquisition matrix). Different paradigms for localization of the motor cortex and for language lateralization were tested in healthy subjects and patients. Methodological considerations concerning the development of the paradigms are also described. In all healthy subjects, motor activation elicited BOLD signal changes in the sensorimotor cortex, permitting identification of primary motor and sensory cortical areas. Furthermore, focal activation of different cortical areas by a language task was possible in 6 of 10 subjects. Nineteen motor studies were performed in 18 patients with supratentorial lesions, in most cases prior to neurosurgical procedures. In 14 studies, fMRI results demonstrated the localization of the motor hand areas relative to the lesion. The results proved valuable for preoperative planning and contributed to therapeutical decisions. We conclude that functional MRI for clinically relevant applications, such as localization of motor and language function, is feasible even at a field strength of 1.0 T without dedicated equipment.

Adult↗

PubMed1999

Contrast mechanisms in MR imaging.

This paper is a brief introduction to tissue-specific parameters and the utilization of various MR imaging sequences to display these parameters in order to differentiate normal from pathologic tissue and function. The three dominant tissue-specific parameters discussed are proton density, longitudinal relaxation time T1, and transverse relaxation time T2. For the utilization of gradient-echo sequences, transverse relaxation time T2(*) is introduced, more dependent on the environment or tissue interfaces than on the tissue itself. Another tissue-specific parameter is the concentration of macromolecules and their hydration layers as targeted with magnetization transfer imaging. Still another tissue-specific parameter is the chemical environment. Functional parameters that influence the contrast are diffusion, perfusion, flow, or motion. The sequence-related utilization of these tissue-specific parameters start with magnetization preparation as in spectral suppression of fat signal, relaxation-dependent elimination of fat or cerebrospinal fluid (CSF) signal, simple inversion pulse, magnetization transfer saturation, or diffusion weighting. Possible contrast mechanisms for the tissue-specific parameters are discussed for each of the commonly used sequences, whether of spin-echo type or of gradient-echo type, with or without magnetization preparation, conventional single-echo acquisition, or contemporary multiecho acquisition.

Contrast Media↗