Biomedical subjects

M V Knopp

Publications and source records attributed to M V Knopp.

At least 55 records · Page 3Linked to original sources

PubMed1999

Estimating kinetic parameters from dynamic contrast-enhanced T(1)-weighted MRI of a diffusable tracer: standardized quantities and symbols.

We describe a standard set of quantity names and symbols related to the estimation of kinetic parameters from dynamic contrast-enhanced T(1)-weighted magnetic resonance imaging data, using diffusable agents such as gadopentetate dimeglumine (Gd-DTPA). These include a) the volume transfer constant K(trans) (min(-1)); b) the volume of extravascular extracellular space (EES) per unit volume of tissue v(e) (0 < v(e) < 1); and c) the flux rate constant between EES and plasma k(ep) (min(-1)). The rate constant is the ratio of the transfer constant to the EES (k(ep) = K(trans)/v(e)). Under flow-limited conditions K(trans) equals the blood plasma flow per unit volume of tissue; under permeability-limited conditions K(trans) equals the permeability surface area product per unit volume of tissue. We relate these quantities to previously published work from our groups; our future publications will refer to these standardized terms, and we propose that these be adopted as international standards.

Contrast Media↗

PubMed1999

Multicompartment analysis of gadolinium chelate kinetics: blood-tissue exchange in mammary tumors as monitored by dynamic MR imaging.

The blood-tissue exchange kinetics of gadopentetate were studied in 49 malignant and benign mammary tumors. Signal enhancement was monitored simultaneously in the aorta and in tumor for 10.5 minutes after the beginning of a 1 minute i.v. infusion of the contrast medium (CM). Kinetic analysis was based on a model with two compartments for systemic pharmacokinetics and up to three kinetically distinct compartments for tumor. Kinetic heterogeneity, ie, two or more compartments with different exchange rate constants in a given tumor, was found in 85% of carcinomas, 38% of fibroadenomas, and 14% of mastopathic tumors. The within-tumor average of CM exchange rates was 1.22 (0.62-1.65) min(-1) in carcinomas, 0.38 (0.26-0.60) min(-1) in fibroadenomas, and 0.16 (0. 12-0.20) min(-1) in mastopathies (median and interquartile distances). The area under the signal enhancement-time curve of the aorta varied 4.5-fold between individuals. It is concluded that individual CM kinetics in arterial blood should be taken into account when CM exchange rates between blood and tumor are to be determined and that a kinetic model for potentially malignant tumors should allow for kinetic heterogeneity.

Adenocarcinoma↗

PubMed1999

Pathophysiologic basis of contrast enhancement in breast tumors.

While the diagnostic benefits of gadolinium (Gd)-chelate contrast agents are firmly established in magnetic resonance imaging (MRI) of tumors, the pathophysiologic basis of the enhancement observed and its histopathologic correlate remained vague. Tumor angiogenesis is fundamental for growth and metastasis and also of interest in new therapeutic concepts. By correlative analysis of a) histology; b) vascular density (CD31); and c) vascular permeability (vascular permeability factor/vascular endothelial growth factor [VPF/VEGF]), we found a) significantly (P < 0.001) faster exchange rates in malignant compared with benign breast lesions; b) distinct differences in enhancement characteristics between the histologic types (invasive ductal carcinoma, invasive lobular carcinoma, and ductal carcinoma in situ); and c) dependence of enhancement kinetics on the VPF/VEGF expression. The pathophysiologic basis for the differences in contrast enhancement patterns of tumors detectable by MRI is mainly due to vascular permeability, which leads to more characteristic differences than vascular density. MRI is able to subclassify malignant breast tumors due to their different angiogenetic properties.

Adult↗

PubMed1999

MR microcirculation assessment in cervical cancer: correlations with histomorphological tumor markers and clinical outcome.

This article reviews the experience available to date on microcirculation assessment in cancer of the cervix including correlation studies of magnetic resonance (MR) microcirculatory parameters with histo-morphometric predictors and direct correlation with patient outcome. The data suggest that MR microcirculation parameters do not always correlate with histo-morphometric parameters, while there is evidence that MR parameters predict patients' treatment outcome. These observations raise the issue that perhaps the histo-morphometric parameters, accepted gold standards for tumor angiogenesis and prognostic factors, reflect anatomical information at a "static" single time point and may not always provide sufficient information on the "dynamic" microcirculation function of the tumor. MR microcirculation assessment reflects both anatomical and functional information and may provide this additional information on the "dynamic" angiogenic and metabolic status of a tumor. Therefore, assessment of tumor microcirculation may augment the individual risk profile in cervical cancer patients and has the potential to impact on therapy selection and treatment outcome.

Contrast Media↗

PubMed1999

Evaluation of angiogenesis and perfusion of bone marrow lesions: role of semiquantitative and quantitative dynamic MRI.

Magnetic resonance imaging (MRI) is a noninvasive technique that complements computed tomography (CT), conventional X-ray, and bone marrow biopsies by sampling a large volume of musculoskeletal bone and providing information that aids the diagnosis, staging, and follow-up of various lesions. Although less sensitive to the mineral components of bones, the MRI appearance of physiologic bone marrow is mainly a reflection of the relative amounts of red marrow, yellow marrow, and trabecular bone. Therefore, use of T1-and T2-weighted MR sequences with or without fat suppression currently remains the most common approach to musculoskeletal bone lesion imaging. An additional imaging strategy to characterize various bone lesions is the application of contrast-enhanced dynamic MRI. This article examines semiquantitative and quantitative dynamic imaging, evaluation, and postprocessing techniques in various benign and malignant musculoskeletal lesions. Practical guidelines for performing a dynamic contrast-enhanced MR examination are proposed.

Bone Marrow Neoplasms↗

PubMed1999

Contrast agents for MRA: future directions.

The purpose of this review is to outline recent developments in contrast agents for magnetic resonance angiography (MRA) and to give some idea of what the future might hold. Up to now, non-binding gadolinium (Gd) chelates have been the agents used for MRA. Modified paramagnetic Gd-based agents with varying degrees of protein interaction have been developed, and these, together with new superparamagnetic compounds, are currently under clinical evaluation. It is likely that two different types of contrast agent will soon be available: extracellular agents for first-pass MRA and intravascular agents mainly for steady-state MRA. Several agents also exhibit certain tissue specific properties in addition to conventional extracellular properties. This will lead to more comprehensive imaging approaches.

Contrast Media↗

PubMed1999

High-resolution pulmonary arterio- and venography using multiple-bolus multiphase 3D-Gd-mRA.

The purpose of this study was to demonstrate selective visualization of pulmonary arteries and veins with high spatial resolution for improved detection of vascular pathologies. Time-resolved pulmonary three-dimensional gadolinium-enhanced magnetic resonance angiograms (3D-Gd-MRA) were acquired with an ultrashort 3D fast low-angle shot (FLASH) sequence (TR/TE 2.3/0.9 msec) using asymmetric k-space sampling in readout, phase-encoding, and partition directions. In a single breath-hold four consecutive acquisitions were performed with a scan time of 6.28 seconds for each phase. A spatial resolution of 1.9 x 1.4 x 2 mm(3) could be achieved for a 12 cm thick 3D volume. To exploit the intrinsic enhancement kinetics of the pulmonary vascular system, the infusion of two gadolinium chelate boli was synchronized with the acquisition of the first and third data sets. This infusion strategy created two predominantly pulmonary arterial and venous data sets with the arterial and venous signal being maximally anti-correlated in time. A further separation of arterial and venous signal could be achieved by means of a correlation analysis. Eight patients with suspected thrombi in the pulmonary veins were studied. The calculated correlation angiographies provided high-quality pulmonary arterio- and venograms. Background signal was completely eliminated, allowing maximum intensity projection analysis of the full data set. In 7/8 patients no venous contamination of the arterial phase and vice versa was found. Patency of the pulmonary arteries and veins could be reliably assessed to the level of the segmental vessels. The combination of ultrafast multiphase 3D-Gd-MRA and dual-bolus injection with a correlation analysis of vascular signal provides high-resolution pulmonary arterio- and venograms. This imaging strategy initiates a new competitor to X-ray angiography.

Adult↗

PubMed1999

Comprehensive MR evaluation of renovascular disease in five breath holds.

To detect a renal artery stenosis and assess its hemodynamic and functional significance in five breath holds. In a single MR exam, T1 weighted FLASH and T2 weighted fast spin echo techniques are used to assess renal morphology, multiphase 3D gadolinium (Gd) MRA to evaluate the renal arteries, and a segmented EPI cine phase-contrast technique to measure renal artery blood flow. A standardized image analysis is performed to assess kidney size, corticomedullar differentiation (CMD), parenchymal enhancement, the degree of renal artery stenosis, abnormalities in blood flow pattern, and any associated abdominal vascular disease. Multiphase 3D-Gd-MRA accurately assesses atherosclerotic renal artery disease particularly in the presence of an associated aortic aneurysm. Delayed parenchymal enhancement, loss of CMD, and decrease in kidney size can be detected. In combination with decreased systolic velocity components, the diagnosis of a hemodynamically and functionally significant stenosis can be made. High-resolution single-phase 3D-Gd-MRA is preferable for evaluation of fibromuscular dysplasia or hypoplastic vessels. The combination of different breath hold techniques in a single, standardized MR exam allows to detect the hemodynamic and functional significance of a renal artery stenosis.

Aged↗

PubMed1999

Off-label use and reimbursement of contrast media in MR.

Use of an approved contrast agent for a clinical purpose not contained in the package insert is not in violation of current U.S. Acts providing that it is in the course of routine medical practice, not part of an investigation into safety or effectiveness and not commercialized through advertising. The Food and Drug Administration does not have the authority to regulate the use of approved contrast media in any manner that radiologists believe, in their professional judgment, would best serve the patient. Moreover, the use of an approved contrast agent for a clinical purpose not explicitly contained in the labeling does not expose the radiologist to malpractice liability. Regarding reimbursement, there is no guarantee that any payer will reimburse a provider for use of a contrast agent outside of package insert indications. The best way to influence reimbursement is to provide the payer with detailed information prior to claim submission.

Contrast Media↗

PubMed1999

Motor dysfunction and sensorimotor cortex activation changes in schizophrenia: A study with functional magnetic resonance imaging.

Recent studies demonstrate a diminished activation of the sensorimotor cortex and supplementary motor area (SMA) in schizophrenia which may be involved in the pathogenesis of neurological soft signs (NSS). Yet, the question whether a retarded motor performance may account for these changes remained to be clarified. Twelve DSM-III-R schizophrenics and 12 healthy controls were included. All subjects were right-handed. Nine patients received clozapine, two conventional neuroleptics, and one was drug-free. Functional magnetic resonance imaging (fMRI) was obtained in a resting condition and during pronation/supination at three speed levels (low, medium, and high) with motor performance recorded simultaneously using a pronation/supination device. While measures of motor retardation (i.e., repetition rate and amplitude of the movements) did not differ between patients and controls, the variability of performance was significantly (P < 0.05) increased in the patients' group. In addition, patients with schizophrenia showed a significantly (P < 0.05) decreased activation of the sensorimotor cortices. Similar, although nonsignificant (P = 0.09) activation changes were observed in the SMA. Activation differences were more pronounced at a slow speed and in the drug-free patient. These results confirm a diminished sensorimotor cortex and SMA activation and indicate that variability of performance rather than retarded performance per se may correspond to these changes.

Adult↗

PubMed1999

Cervical carcinoma: standard and pharmacokinetic analysis of time-intensity curves for assessment of tumor angiogenesis and patient survival.

Since detailed knowledge regarding the pathophysiological properties which in turn are responsible for differences in contrast enhancement--remain fairly undetermined, it was the aim of this study (i) to examine the association of standard and pharmacokinetic analysis of time-intensity curves in dynamic MRI with histomorphological markers of tumor angiogenesis (microvessel density [MVD]; vascular endothelial growth factor [VEGF]); and (ii) to determine the ultimate value of a histomorphological and a dynamic MRI approach by correlation of those data with disease outcome in patients with primary cancer of the uterine cervix. Pharmacokinetic parameters (amplitude A, exchange rate constant k21) and standard parameters (maximum signal intensity (SI)-increase [SI-I] over baseline and steepest SI-upslope per second [SI-U/s]) were calculated from contrast-enhanced dynamic MR imaging series in 37 patients with biopsy-proven primary cervical cancer. On the surgical whole mount specimens, histomorphological markers of tumor angiogenesis (MVD, VEGF) were compared with similar sized and positioned regions-of-interest (ROIs) on the MRI-derived parameters. For MRI and histomorphological data, Kaplan-Meier survival curves were calculated and compared using log-rank statistics. A significant association was found between MVD and amplitude A (P < 0.01) and SI-I (P < 0.05). No significant relationships were observed between the VEGF expression and all dynamic MRI parameters. Kaplan-Meier curves based on k21 and SI-U/s showed that tumors with high k21 and SI-U/s values had a significantly (P < 0.05, 0.001, respectively) worse disease outcome than tumors with low k2, and SI-U/s values. None of the histomorphological gold standard markers for assessing tumor angiogenesis (MVD, VEGF) had any significant power to predict patient survival. It is concluded that (1) the pathophysiological basis for differences in dynamic MRI is MVD but not VEGF-expression; (2) a functional, dynamic MRI approach (both standard and a pharmacokinetic analysis) may be better suited to assess angiogenic activity in terms of patient survival than current histomorphological-based markers of tumor angiogenesis; and [3] compared with standard analysis, a simple pharmacokinetic analysis of time-intensity curves is not superior to assess MVD or patient survival.

Adult↗

PubMed1999

[Fluid-attenuated-inversion-recovery (FLAIR) imaging in the diagnosis of cerebral gliomas and metastases].

This study demonstrates the value of a fast fluid-attenuated inversion-recovery (FLAIR) technique in the assessment of cerebral gliomas and metastases. Thirty-five patients with cerebral gliomas and 12 patients with a total of 39 cerebral metastases were examined by T2/proton density-weighted fast spin echo, fast FLAIR with and without contrast medium and contrast-enhanced T1-weighted spin echo using identical slice parameters. The images were evaluated using quantitative and qualitative criteria. Quantitative criteria were tumor-to-background and tumor-to-cerebrospinal fluid contrast and contrast-to-noise. The qualitative evaluation was performed as a multireader analysis concerning lesion detection, lesion delineation and image artifacts. In the qualitative evaluation, all readers found fast FLAIR to be superior to fast spin echo in the exact delineation of cerebral tumors (P < 0.001) and the delineation of enhancing and non-enhancing tumor parts. Fast FLAIR was superior in the delineation of cortically located and small lesions but was limited in lesions adjacent to the ventricles. Fast FLAIR provided significantly better tumor-to-CSF contrast and tumor-to-CSF contrast-to-noise (P < 0.001). The tumor-to-background contrast and tumor-to-background contrast-to-noise of the fast FLAIR images were lower than that of T2-weighted spin-echo images but were significantly increased after the application of contrast medium. FLAIR images had a more image artifacts, but these influenced the image interpretation in only two patients. Signal hyperintensities at the ventricular border were present in 92% of the patients. These are common findings in fast FLAIR and should be included in image interpretation.

Brain Neoplasms↗

PubMed1999

[MRI of the kidneys. New diagnostic strategies].

AIM: New diagnostic strategies for evaluation of the kidney by fast MR imaging techniques. MATERIAL AND METHODS: A comprehensive morphologic and functional evaluation of the kidney is proposed using fast MR imaging of renal morphology, multiphase 3D gadolinium MR angiography, MR urography and MR flow measurements. A single MR examination is designed to grade renovascular disease and assess the hemodynamic and functional significance, detect and characterize renal lesions and evaluate the urinary tract. RESULTS: The combined analysis of morphologic and functional data allows reliable assessment of renal artery stenosis, benign and malignant renal masses and diseases of the renal collecting system and ureters, as well as congenital abnormalities in good agreement to the results of conventional imaging modalities. The improved tissue contrast and additional functional information compensates for the disadvantage of a lower spatial resolution. CONCLUSION: Combined morphologic and functional MR examination represents a reliable, non-invasive and cost-effective alternative imaging modality for comprehensive diagnostic evaluation of renal disease.

Acute Kidney Injury↗

PubMed1999

[The simultaneous determination of the arterial input function for dynamic susceptibility-weighted magnetic resonance tomography of the A. carotis interna and the A. cerebri media].

PURPOSE: The determination of the arterial input function (AIF) is necessary for absolute quantification of the regional cerebral blood volume and blood flow using dynamic susceptibility contrast MRI. The suitability of different vessels (ICA--internal carotid artery, MCA--middle cerebral artery) for AIF determination was compared in this study. METHODS: A standard 1.5 T MR system and a simultaneous dual FLASH sequence (TR/TE1/TE2/alpha = 32/15/25/10 degrees) were used to follow a bolus of contrast agent. Slice I was chosen to cut the ICA perpendicularly. Slice II included the MCA. Seventeen data sets from ten subjects were evaluated. RESULTS: The number of AIF-relevant pixels, the area under the AIF and the maximum concentration were all lower when the AIF was determined from the MCA compared to the ICA. Additionally, the mean transit time (MTT) and the time to maximum concentration (TTM) were longer in the MCA, complicating the computerized identification of AIF-relevant pixels. Data from one subject, who was examined five times, demonstrated that the intraindividual variance of the measured parameters was markedly lower than the interpersonal variance. CONCLUSIONS: It appears to be advantageous to measure the AIF in the ICA rather than the MCA.

Adult↗

PubMed1999

Abdominal aortic aneurysm. Detection of multilevel vascular pathology by time-resolved multiphase 3D gadolinium MR angiography: initial report.

OBJECTIVE: To evaluate multiphasic 3D gadolinium-enhanced magnetic resonance angiography (3D-Gd-MRA) for detection of vascular pathology at multiple levels of the aorta and iliac arteries. METHODS: In 18 patients with abdominal aortic aneurysm (n = 13), dissection (n = 3), or both (n = 2), multiphase 3D-Gd-MRA was performed acquiring five consecutive (6.8 seconds) 3D data sets in a single breath-hold. In each of the five time-resolved phases, vessel visibility of the abdominal aortic branches and iliac arteries was assessed. The extent of vessel involvement by the aneurysm or dissection seen on multiphase 3D-Gd-MRA was compared with standard imaging and surgical findings. Digital subtraction angiography was available for comparison in 4 cases, CT angiography in 10 cases. RESULTS: Due to the delayed filling of the aortic aneurysm, the proximal aortic branches and the aneurysm neck demonstrated an inversely related enhancement compared with the distal abdominal and iliac vessels (P < 0.001). Review of all five phases of multiphase 3D-Gd-MRA allowed optimal visualization of each vessel segment without any artifacts due to parenchymal or venous overlay. In dissections, review of three phases was required (P < 0.001) for diagnostic evaluation of the true and false lumens. Substantially more vessel involvement was detected on multiphase 3D-Gd-MRA; this was surgically confirmed in 10 of 11 cases and affected therapy management in 11 of 18 cases. CONCLUSIONS: Multiphase 3D-Gd-MRA is a convenient, robust, and safe technique for presurgical anatomic mapping of complex aortic aneurysms and dissections.

Aortic Dissection↗

PubMed1999

Non-invasive assessment of renal artery stenosis: current concepts and future directions in magnetic resonance angiography.

Magnetic resonance angiography is undergoing rapid development as a non-invasive technique to reliably assess renal artery stenosis. Invasive X-ray angiography is currently the gold standard imaging technique and gives excellent spatial resolution. However, its disadvantages include a necessary exposure to radiation and the need for iodinated contrast media. While magnetic resonance angiography does not have these disadvantages, its spatial resolution is inherently lower. On the other hand, magnetic resonance angiography enables true three-dimensional imaging. The use of rapid imaging techniques allows multiple image acquisition within one breath-hold thereby permitting the visualization of distinct vascular phases. The limitation in spatial resolution can be overcome readily by combining morphologic imaging with functional information on the hemodynamic relevance. This can be achieved by means of magnetic resonance phase contrast flow measurements. The use of such a combined approach enables the grading of vascular stenosis based on the combination of morphology and functional information. Magnetic resonance angiography is already able to demonstrate a clinical utility equivalent to that of invasive procedures, indicating that it is likely to become a premier method for the diagnosis and follow up of renovascular disease.

Angiography, Digital Subtraction↗

PubMed1999

Hepatic lesions: morphologic and functional characterization with multiphase breath-hold 3D gadolinium-enhanced MR angiography--initial results.

PURPOSE: To investigate multiphase (arterial, portal venous, and late venous phases) breath-hold three-dimensional (3D) gadolinium-enhanced magnetic resonance (MR) angiography for the detection and functional characterization of hepatic lesions. MATERIALS AND METHODS: Breath-hold fast spoiled gradient-echo 3D gadolinium-enhanced MR angiography was performed in 18 patients with 35 hepatic lesions. Measurements of signal intensity were obtained for 27 seconds in each phase, with 23-second delays between the three phases. Lesion-liver visibilities at each phase on the MR angiographic, precontrast T1-weighted, T2-weighted, and postcontrast T1-weighted images were compared. The MR angiographic functional lesion characterization was based on the combined assessment of spatial variations and the evolution of contrast material enhancement in all three phases. RESULTS: All 35 lesions were correctly characterized on the MR angiographic images, which is significantly (P < .01) better than the precontrast T1-weighted (n = 14 [40%]), T2-weighted (n = 23 [66%]), and postcontrast T1-weighted (n = 25 [71%]) imaging results. Analysis of the spatial variations and the evolution of contrast material enhancement significantly (P < .01) improved lesion characterization in 66% (23 of 35) of all lesions. CONCLUSION: Multiphase breath-hold 3D gadolinium-enhanced MR angiography is feasible and robust and significantly improves the morphologic detection of benign or malignant lesions during the early arterial phase. It further improves the functional characterization of hepatic lesions, combining an arterial, portal-venous, and late MR angiographic phase of contrast enhancement.

Adult↗

PubMed1999

Cerebral gliomas and metastases: assessment with contrast-enhanced fast fluid-attenuated inversion-recovery MR imaging.

The effect of contrast material on fast fluid-attenuated inversion-recovery (FLAIR) magnetic resonance images was evaluated for 16 patients with enhancing gliomas and 12 patients with cerebral metastases. Because of a marked T1 effect, fast FLAIR imaging provided a marked contrast enhancement, resulting in the highest tumor-to-background contrast ratio compared with standard imaging techniques.

Adult↗