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Biomedical subjects

M V Knopp

Publications and source records attributed to M V Knopp.

At least 127 records · Page 7Linked to original sources
PubMed1996

Effect of radiation on blood volume in low-grade astrocytomas and normal brain tissue: quantification with dynamic susceptibility contrast MR imaging.

OBJECTIVE: The purpose of this study was to determine whether it is possible to measure radiation-induced changes in blood volume in low-grade astrocytomas and in normal brain tissue. SUBJECTS AND METHODS: The passage of a bolus of gadopentetate dimeglumine was monitored on a series of 55 T2*-weighted simultaneous dual fast low-angle shot MR images with a standard 1.5-T MR imaging system. Absolute blood volumes were calculated as the area under the tissue concentration-time curve in regions of interest and normalized to the arterial input function. We performed 41 examinations on 19 patients with grade II astrocytomas. For comparison, 13 patients were studied after whole-brain irradiation. RESULTS: A reduction in blood volume (mean +/- SD in milliliters per 100 g) within the tumors from 12.2 +/- 8.7 to 6.5 +/- 5.3 after fractionated conformation radiotherapy was detected, although there was no consistent pattern in different patients. An insignificant reduction was noted in normal gray (9.2 +/- 2.8 to 7.4 +/- 3.2) and white (4.4 +/- 1.9 to 4.1 +/- 2.3) matter outside the target volume. Conversely, we observed a significantly lower blood volume in gray (6.3 +/- 1.2) and white (3.1 +/- 1.0) matter after whole-brain radiotherapy. CONCLUSION: Our results show that a reduction of blood volume in astrocytomas and normal brain tissue after radiotherapy can be quantified by use of dynamic susceptibility contrast MR imaging. Thus, functional monitoring of tumor response and of normal tissue effects becomes possible.

Adolescent↗
PubMed1996

Pelvic lesions in patients with treated cervical carcinoma: efficacy of pharmacokinetic analysis of dynamic MR images in distinguishing recurrent tumors from benign conditions.

OBJECTIVES: Dynamic MR image series were analyzed with a pharmacokinetic two-compartment model. To preserve the spatial resolution of the dynamic MR images, the pharmacokinetic parameters were computed pixel by pixel, color coded, and superimposed on conventional MR images (pharmacokinetic mapping). The efficacies of pharmacokinetic mapping and conventional MR imaging in distinguishing between recurrent tumors and benign conditions in patients who have pelvic lesions after treatment of cervical carcinoma were compared. MATERIALS AND METHODS: Twenty-one women with 24 suspected pelvic lesions and a history of treated cervical carcinoma (stages IB-IIIA) were included in this study. Patients had been treated before MR imaging with surgery or irradiation alone (eight patients) or a combination of the two (13 patients). Patients were referred because of our findings from CT examinations and/or clinical examinations. Of 24 suspected lesions, 17 were histologically verified as tumor recurrences and seven were classified as benign masses (histologically diagnosed as fibrosis and granulation tissue). T1- and T2-weighted spin-echo images were interpreted by three observers. During and after constant-rate infusion of gadopentetate dimeglumine, the kinetics of lesion response were determined with a strongly T1-weighted saturation recovery turbo-fast low-angle shot sequence. The signal-time curves for the suspected lesions were analyzed within the framework of a pharmacokinetic two-compartment model and displayed as color-coded images. The calculated pharmacokinetic parameters (amplitude [A] and tissue distribution time [t21]) were evaluated retrospectively to obtain optimal threshold values for differentiating malignant lesions from benign lesions. RESULTS: Analysis of the pharmacokinetic mapping data showed significantly shorter (p < .005) and stronger (p < .001) contrast medium enhancement of malignant lesions (t21, 24 sec; A, 1.5 arbitrary units) than of benign lesions (t21, 65 sec; A, 0.7), resulting in a sensitivity of 100%, a specificity of 88%, and an accuracy of 96%. Interpretation of the lesions on conventional T2-weighted MR images resulted in a sensitivity of 90%, a specificity of 38%, and an accuracy of 74%. CONCLUSION: Analysis of color-coded pharmacokinetic maps is more effective than conventional MR imaging in distinguishing between malignant and benign conditions in patients who have pelvic lesions after treatment of cervical carcinoma.

Carcinoma, Squamous Cell↗
PubMed1996

[Quantitative magnetic resonance tomography and the severity of deficits in dementia of the Alzheimer type].

The aim of the present study was to investigate the severity of dementia of the Alzheimer type (DAT) with respect to morphological changes revealed by quantitative magnetic resonance imaging (MRI). Seventeen patients with DAT (NINCDS-ADRDA guidelines) and 10 healthy elderly controls were included. The severity of dementia was evaluated on the Mini Mental State Examination (MMSE), the Global Deterioration Scale (GDS) and the Brief Cognitive Rating Scale (BCRS). Three-dimensional MRI sequences were acquired using a 1.5-T Siemens Magnetom. Whole-brain volume and the volume of the amygdala-hippocampus complex (AHC) were assessed using the newly developed software NMRWin. This software provides a semi-automated measure of the whole brain volume, while measurement of substructures requires manual guidance. In addition, the ventricle-brain ratio (VBR) was assessed. All morphometric parameters differed significantly between the two groups. AHC volumes discriminated best between them with only a small overlap. These findings were confirmed when only the data of the mildly demented patients were included in the analysis. The degree of AHC atrophy exceeded that of generalized cerebral atrophy. The severity of dementia as indicated by the MMSE, GDS and BCRS scores was correlated significantly with the volumes of the AHC bilaterally, but not with whole-brain volume or with VBR. These results underline the importance of the mesial temporal substructures in the etiology and progression of DAT and indicate that the volume of the AHC can be monitored by MRI and may be used to follow up the disease process.

Aged↗
PubMed1996

[Blood volume changes after the radiotherapy of the central nervous system].

BACKGROUND: The pathogenesis of late delayed radiation damage in normal brain tissue is most likely due to damage to the vascular endothelium. The mitotic activity of gliomas was shown to correlate with the tumor induced angiogenesis. Dynamic susceptibility contrast MR imaging (DSC MRI) allows the measurement of the cerebral hemodynamics based on the indicator dilution theory. We describe theory and technique of the method and present our experience with blood volume measurements after irradiation of the CNS. METHODS: We established a double slice technique on a standard 1.5 T MR system without hardware modifications, which allows an absolute quantification of the blood volume in regions of interest (ROI) within the brain. Fifty-five T2* weighted double slice images were acquired before, during and after bolus injection of Gd-DTPA (0.1 mmol/kg in 5 sec.) using a SD FLASH sequence (simultaneous dual fast low angle shot, TR/TE1/TE2 31/16/25, flip angle 10 degrees). Concentration-time curves were calculated from the measured signal-time curves. Blood volume values in tissue were normalised and calculated in absolute values (ml/100 g) based on the knowledge of the arterial input function (AIF), which was measured in the brain supplying arteries. The whole procedure requires only 2 to 3 minutes, the time for post processing is about 15 to 20 minutes. RESULTS: Blood volume parameter images of representative cases demonstrate the blood volume changes after radiotherapy. A reduction in blood volume could be observed in normal brain tissue and low-grade gliomas, while recurrent tumors were accompanied by a local increase in blood volume. CONCLUSIONS: Radiation induced blood volume changes in the CNS can be measured using dynamic susceptibility contrast MR imaging. The measurements in normal brain tissue allow a functional in-vivo analysis of late delayed radiation reactions of the CNS. The definite value of intratumoral blood volume measurements for determination of the therapeutic success and for differentiation of recurrences versus radionecroses remains to be clarified in further studies.

Adult↗
PubMed1995

Pharmacokinetic mapping of the breast: a new method for dynamic MR mammography.

A dynamic contrast-enhanced MRI technique for whole breast examinations is presented. The fast kinetics of tissue response during and after constant-rate intravenous infusion of gadolinium diethylenetriaminopentaacetic acid was resolved using a strongly T1-weighted saturation recovery TurboFLASH sequence that makes it possible to acquire signal-time courses sequentially from 15 adjacent slices with a temporal sampling rate of 21 s. On the basis of the mathematically established and experimentally verified linear relationship between the measured saturation recovery TurboFLASH signal variation and the gadolinium diethylenetriaminopentaacetic acid concentration in the tissue, the signal-time courses were analyzed within the framework of pharmacokinetic modeling. In our study, the tissue response was parameterized adequately using an open linear two-compartment model. With this approach, the tissue specific information contained in the signal-time course can be described using only two parameters: an amplitude A, reflecting the degree of MR signal enhancement, and an exchange parameter k21, characterizing vascular permeability and perfusion of the tissue. A clearly arranged representation of the large amount of data (480 saturation recovery TurboFLASH breast images/examination) was accomplished by means of color coding of the computed parameters, resulting in one color-coded pharmacokinetic parameter map/cross-section.

Breast↗
PubMed1995

1H MR spectroscopy in patients with metastatic brain tumors: a multicenter study.

In a cooperative study involving six clinical MR centers, localized 1H MR spectroscopy was used to characterize untreated metastatic brain tumors (40 cases, 45 lesions). Cubic volumes (3.4 or 8 cm3) filled for more than 50% by metastatic brain tissue were examined by single-voxel double spin echo MRS, by using chemical shift selective imaging (CHESS) pulses for water suppression and TE = 135 ms. Choline (Cho), creatine (Cr) and N-acetyl aspartate (NAA) levels in brain metastases of mammary carcinoma (n = 13), lung cancer (n = 11) and melanoma (n = 10) were similar. Metastasis NAA/Cho signal intensity ratio varied between 0.00 and 1.17, compared with 2.68 +/- 0.56 (SD) in lobus occipitalis and 1.94 +/- 0.63 in corpus nuclei caudati region (P < 0.0001, both). 1H MR spectroscopy, although not suited to recognize the primary tumor of metastases, could serve as a clinical test for excluding (metastatic) tumor as cause of solitary focal brain disorders that are hard to diagnose with current imaging methods.

Adult↗
PubMed1995

Sensorimotor cortex and supplementary motor area changes in schizophrenia. A study with functional magnetic resonance imaging.

BACKGROUND: Neurological soft signs (NSS) such as a disturbed finger-to-thumb opposition are frequently found in schizophrenia. To identify the underlying cerebral changes we investigated sensorimotor cortex and supplementary motor area (SMA) activation during finger-to-thumb opposition using functional magnetic resonance imaging (fMRI). METHOD: Ten DSM-III-R schizophrenics and seven healthy controls were included. All subjects were right-handed. fMRI was carried out in a resting condition followed by an activation state (finger-to-thumb opposition) and the activities in the sensorimotor cortices and SMA recorded. RESULTS: All subjects showed a significant activation of the SMA and both ipsilateral and contralateral sensorimotor cortices. In the controls, ipsilateral finger-to-thumb opposition was associated with a greater left than right hemispheric sensorimotor cortex coactivation. When compared with the healthy controls, the schizophrenic patients showed a decreased activation of both sensorimotor cortices and SMA, as well as a reversed lateralisation effect. CONCLUSION: Sensorimotor cortex and SMA dysfunction are associated with motor disturbances in schizophrenia.

Adult↗
PubMed1995

Elimination of gadolinium-DTPA by peritoneal dialysis.

Magnetic resonance urography (MRU) after i.v. injection of gadolinium-DTPA (0.1 mmol/kg bodyweight) was performed in a patient with transplant dysfunction after renal allograft transplantation. Renal replacement therapy was accomplished by means of peritoneal dialysis. Gadolinium-DTPA concentrations in urine and dialysate were measured repeatedly during a 48-h period with inductively coupled plasma atomic emission spectrometry. The total 24-h creatinine clearance was 10.8 ml/min on day 1 and 13.7 ml/min on day 2. The corresponding total gadolinium clearance was 12.8 ml/min and 15.8 ml/min respectively. Gadolinium-DTPA was removed from the body through peritoneal dialysis at a mean clearance rate of 5.13 ml/min. Plasma half-life of gadolinium-DTPA was prolonged to 9 h. No side-effects due to gadolinium-DTPA were noted. MRU provided a better visualization of the morphology of the urinary tract than scintigraphic studies. By measuring the changes of signal intensity, the gadolinium excretion could be calculated.

Adult↗
PubMed1995

[Functional magnetic resonance tomography of movement disorders in patients with schizophrenia].

UNLABELLED: Neurological soft signs (NSS), which are minor motor and sensory deficits, e.g., during finger-to-thumb opposition, are frequently found in schizophrenia. The purpose of this study was to investigate differences in the cerebral activation pattern in ten schizophrenic patients and ten healthy volunteers using functional MRI. METHODS: fMRI was performed using a modified FLASH sequence (TR/TE/alpha = 100/60/40 degrees) and a conventional 1.5 T MR scanner. Color-coded statistical parametric maps based on Student's t-test were calculated. Activation strength was quantified using a 5 x 6 grid over-lay. RESULTS: The volunteers showed a higher activation strength during left hand movement compared to right hand movement. This lateralization effect was reversed in patients who showed overall reduced activation strength. CONCLUSIONS: Disturbed interhemispheric balance in schizophrenic patients during motor task performance can be demonstrated using fMRI. These findings support the hypothesis that changes in the sensorimotor cortex may be involved in the development of NSS.

Adult↗
PubMed1995

[Diagnosis of recurrence of cervix carcinoma using dynamic MRI: correlation of pharmacokinetic analysis and histopathology].

PURPOSE: The aim of the study was to evaluate the value of dynamic magnetic resonance imaging (MRI) to classify suspect lesions into benign and malignant in patients previously treated for cancer of the cervix. MATERIALS AND METHODS: Eleven patients with 14 suspect lesions after treatment of cervical carcinoma were examined by dynamic contrast-enhanced MRI. The imaging findings were compared to the giant cross-section specimen as the reference standard. Computed tissue-specific enhancement parameters were obtained (pharmacokinetic mapping) and displayed as color-coded images. The regions of interest were retrospectively defined according to the pharmacokinetic images over the most suspect areas. Therein, the threshold values were determined that achieved the greatest overall accuracy and a low rate of false-positive results. RESULTS: Analysis of the lesions on T2-weighted images revealed sensitivity of 88%, specificity of 40%, and accuracy of 71%. Analysis of the dynamic MR data showed significantly shorter (p < 0.01) and stronger (p < 0.001) contrast media enhancement of malignant (n = 9) than benign lesions (n = 5). CONCLUSION: Pharmacokinetic mapping appears to yield important information for dividing suspect lesions into malignant and benign following treatment of cervical cancer.

Adult↗
PubMed1995

[Fast MRI contrast medium dynamics for characterization of tumors. Experiences with functional MR-mammography].

METHODS: MRI studies with high temporal resolution can be achieved with an optimized saturation recovery TurboFLASH sequence, which allows a more detailed characterization of contrast enhancement in tissue as is available with the current FLASH 3D techniques. A two compartment model allows characterization of signal time curves with three parameters, Amp (amplitude), k21 (distribution rate constant) and kel (elimination rate constant). RESULTS: In a prospective study on 314 patients with indetermined breast lesions signal-time-curves revealed differences in the k21 parameter between benign (0.56 +/- 0.46) and malignant lesions (1.25 +/- 0.80) (p < 0.0001) as well as between different histological classifications. CONCLUSION: The introduced MR-technique enables a better evaluation of the vascular permeability for the MR contrast media in lesions. Distinct differences were detected, which are influenced by elevated expression of angiogenesis factors such as the vascular endothelial growth factor.

Breast↗
PubMed1994

Functional magnetic resonance imaging at 1.5 T: activation pattern in schizophrenic patients receiving neuroleptic medication.

Activation of the cerebral cortex during motor task performance can be visualised with functional MRI. A modified FLASH sequence (TR/TE/alpha 100/60/40 degrees, first order flow rephased, fat suppression, reduced bandwidth 28 Hz/pixel, 120 repetitions, three cycles of rest and finger movement for each hand) on a standard 1.5 T clinical imager was used to investigate 10 schizophrenic patients receiving clozapine and 10 healthy volunteers. All subjects were right-handed. Color-coded statistical parametric maps (SPM) based on the Student's t-test were calculated. A grid overlay was used for global and regional quantification. Activation strength was defined as the mean t-value of the respective region. All patients and volunteers showed a significant activation in the contralateral and ipsilateral sensorimotor cortex during motor task performance. The schizophrenic patients showed a significantly reduced global activation strength compared with healthy volunteers (p < .005). Selective evaluation of left-hand compared to right-hand movement demonstrated an increase in global activation strength in volunteers in contrast to a decrease in patients. Furthermore a reduced coactivation in the dominant left hemisphere was found in patients compared to volunteers during movement of the ipsilateral (left) hand. We conclude that alterations of the right and left hemispheric balance can be detected in schizophrenic patients using functional MRI at 1.5 T. These changes may indicate a disturbed interhemispheric interaction in schizophrenia. The reduction in cortical activation may result from several causes, however, taken together with previous studies and the underlying physiological effects, the most likely explanation is a combined effect of the disease and the neuroleptic medication.

Adolescent↗
PubMed1994

Functional 2D and 3D magnetic resonance imaging of motor cortex stimulation at high spatial resolution using standard 1.5 T imager.

This paper reports the effects of motor cortex stimulation of normal volunteers using conventional MR imaging techniques on standard 1.5 T clinical scanner. Improvement in signal-to-noise (S/N) ratio has been achieved by using a commercially available eye/ear surface coil with a loop of 8.5 cm in diameter. Magnet shimming with all first order coils was performed to the volunteer's head resulting in a magnetic field homogeneity of about 0.1-0.2 ppm. The imaging technique used was an optimized conventional 2D and 3D, first order flow rephased, gradient-echo sequence (FLASH) with fat-suppression and reduced bandwidth (16-28 Hz/pixel) and TR = 80-120 ms, TE = 60 ms, flip angle = 40 degrees, matrix = 128 x 128, FOV = 150-250 mm, slice-thickness = 2-5 mm, NEX = 1, and a total single scan time for one image of about 12-16 s. In the 3D FLASH measurements, a slab of 32 mm thickness with 16 partitions was evaluated. The motor cortex stimulation was achieved by touching each finger to thumb in a sequential, self-paced, and repetitive manner. During stimulation, an increase in signal of order 10-20% was detected in the motor and sensory cortex due to reduced partial volume effects and optimized S/N for the measurements at small voxel size. 3D FLASH imaging at high spatial resolution shows good anatomical correlation of signal increase with gray matter of the motor and sensory cortex. The reported data demonstrate the technical feasibility of functional 2D and 3D MR imaging at high spatial resolution using optimized conventional sequences and equipment.

Humans↗
PubMed1994

The pulmonary artery acceleration time determined with the MR-RACE-technique: comparison to pulmonary artery mean pressure in 12 patients.

The goal of our study was to evaluate a rapid noninvasive MR technique for quantification of the pulmonary artery acceleration time (PAT) and other parameters of pulmonary hemodynamics and to correlate with pulmonary artery mean pressure (mPAP). The PAT known as "time-to-peak" out of Doppler echocardiographic measurements normally shows significant inverse correlation with mPAP. With the MR-RACE-Technique (RACE: Real time ACquisition and Evaluation of motion) blood velocity measurements can be obtained with a total acquisition time of a few seconds. The application of this technique to the pulmonary artery has not been reported before. Out of the RACE velocity wave form PAT can be obtained with a temporal resolution of about 15 ms. To explore the relationship between PAT and mPAP, right heart catheterization and MR-RACE measurements were performed in 12 patients with different pulmonary vascular abnormalities. Results of MR-RACE were compared with those of mPAP measured by right heart catheter and showed significant inverse correlation (r = -0.82, p = .0011, n = 12). The ability of MR-RACE to enable measurements of blood flow with profiles may be important for characterizing pulmonary and cardiovascular abnormalities.

Aged↗
PubMed1994

3D MPRAGE evaluation of lesions in the posterior cranial fossa.

Standard spin-echo images of the posterior cranial fossa are usually impaired by pulsation artifacts. We evaluated a heavily T1 weighted MPRAGE sequence (TR/TE/alpha/TI = 10/4/10-15 degrees/200-350) for detection of intracerebral lesions in the posterior fossa in 11 patients. Overall quality of the MPRAGE images was superior due to the lack of pulsation artifacts, high S/N and excellent gray-white matter contrast. Lesion detection was better in one patient, equal in six and inferior in four patients compared to SE technique. A cerebellar metastasis (8 mm) in one patient was completely blurred from pulsation artifacts on the SE images. Whereas multiple small lesions (< or = 4 mm) with discrete contrast enhancement were missed on the MPRAGE images in three patients. We conclude, that the MPRAGE sequence yields high quality images with isotropic spatial resolution in a reasonable time. But MPRAGE with these parameters can not replace standard SE images in screening the posterior fossa, because of a decreased sensitivity in the detection of small contrast-enhancing lesions.

Adolescent↗
PubMed1994

PET imaging of lung tumours and mediastinal lymphoma.

Positron emission tomography (PET) of the lung is evaluated regarding its clinical practicability for staging of bronchogenic carcinomas and lymphomas. Stringent quality control, optimized acquisition and reconstruction techniques are of crucial importance. An analysis of 50 PET studies for tumour (T) and lymphnode (N) staging in comparison to CT shows that PET has the highest diagnostic accuracy to classify lesions and is the most promising technique for non-invasive staging. PET cannot be the first imaging modality, but if unnecessary or invasive procedures can be avoided, the additional expense of a PET study seems justified.

Humans↗