Biomedical subjects

M V Knopp

Publications and source records attributed to M V Knopp.

At least 91 records · Page 5Linked to original sources

PubMed1997

Angiogenesis of uterine cervical carcinoma: characterization by pharmacokinetic magnetic resonance parameters and histological microvessel density with correlation to lymphatic involvement.

Dynamic studies of Gd-based contrast agents in magnetic resonance imaging (MRI) are increasingly being used for tumor characterization as well as therapy response monitoring. Because detailed knowledge regarding the pathophysiological properties, which in turn are responsible for differences in contrast enhancement, remains fairly undetermined, it was the aim of this project to: (a) examine the relationship between contrast-enhanced dynamic MRI-derived characteristics and histological microvessel density counts, a recognized surrogate of tumor angiogenesis, from primary or recurrent cancers of the uterine cervix; and (b) correlate these parameters with lymphatic involvement to characterize tumor aggressiveness in terms of lymphatic spread. Pharmacokinetic parameters (amplitude, A; exchange rate constant, k21) were calculated from a contrast-enhanced dynamic MRI series in 55 patients (ages 25-72 years; mean, 50 years) with biopsy-proven primary (n = 42) or recurrent (n = 13) uterine cervical cancer. Both pharmacokinetic parameters were correlated to histologically determined microvessel density counts (factor VIII-related antigen) and other pathological tumor characteristics obtained from the operative specimens after radical surgery. In addition, the magnetic resonance and histological data were correlated to the presence or absence of lymphatic system involvement. Pharmacokinetic MRI-derived parameters (A and k21) increased with increasing histological microvessel density counts with r = 0.41 and 0.50, respectively. Lymphatic involvement was more comprehensibly assessed by the pharmacokinetic parameter k21 compared with histological microvessel density, resulting in a higher sensitivity, overall accuracy, and comparable specificity. Contrast-enhanced MRI parameters might prove to be applicable for estimation of tumor angiogenesis in uterine cervical cancer; thus, MRI may become an additional tool to characterize malignant progression in terms of lymphatic involvement in uterine cervical cancer.

Adenocarcinoma↗

PubMed1997

[Contrast-enhanced MR "magnetization transfer technique". Improved tumor contrast, delineation and visibility of intracranial malignant gliomas and metastases in radiosurgical treatment planning].

AIMS: To improve tumor conspicuity and delineation on contrast-enhanced T1-weighted MR images with and without magnetization transfer (MT) contrast as a strategy to improve the macroscopic boost volume definition in the planning process of radiosurgery in patients with high grade gliomas or metastatic brain lesions. PATIENTS AND METHODS: Thirty-two patients (mean age 47 years) with histologically proven or suspected high grade glioma (n = 12) or metastatic brain lesions (n = 20) were prospectively examined by MR imaging. After the administration of gadolinium dimeglumine (0.1 mmol/kg body weight) the lesions were imaged with a T1-weighted MT-fast low angle shot (FLASH) pulse sequence and with a conventional T1-weighted SE sequence without MT saturation. RESULTS: The mean CNR of enhancing lesions on T1-weighted MT-FLASH was 15 +/- 5 compared to 11 +/- 4 on SE images, representing a significant (p < .01) improvement. The mean tumor diameter of malignant gliomas was significantly (p < .01) larger measured on T1-weighted MT-FLASH images compared to those obtained from T1-weighted SE images and were comparable for metastatic lesions. Lesion conspicuity and delineation were improved in 50% of patients with high grade gliomas and in 35% of patients with brain metastases. Lesion conspicuity was markedly improved in the posterior fossa. Additional contrast enhancing lesions were detected in 10% of patients with metastases on MT-FLASH images. CONCLUSIONS: It is concluded that contrast-enhanced MT-FLASH images may improve lesion detection and delineation in the planning process of radiosurgery in patients with intracranial high grade gliomas or metastases or even alter the treatment approach.

Adult↗

PubMed1997

Functional neuroimaging in the assessment of CNS neoplasms.

Assessment of CNS neoplasms has focused traditionally on morphological analysis. Recent developments in MR sequence design now enable functional assessments. T1-weighted, as well as T2(*)-weighted, dynamic, gadolinium-enhanced, imaging can be used for assessment of vascularisation, permeability, and microcirculation of CNS neoplasms. Characterisation of cerebrovascular blood flow is possible using dynamic MR angiography, while neurofunctional imaging enables visualisation of local alterations in neuronal activity in stimulated cortical areas. Diffusion-weighted imaging can be used for improved delineation of neoplasms, while chemical shift imaging allows metabolic mapping of lesions and surrounding tissues. Implementation of these techniques can improve characterisation, information for therapy, planning and prognosis in clinical imaging of CNS neoplasms.

Brain↗

PubMed1997

[Invasive cervix carcinoma (pT2b-pT4a). Value of conventional and pharmacokinetic magnetic resonance tomography (MRI) in comparison with extensive cross sections and histopathologic findings].

PURPOSE: To compare staging of advanced primary cervical carcinoma (pT2b-pT4a) by conventional and pharmacokinetic magnetic resonance imaging (MRI) with the giant cross section specimen and histopathological findings. MATERIALS AND METHODS: Seventeen patients with biopsy-proven cancer of the cervix and clinically suspected invasive cancer (FIGO IIB-IVA) were prospectively examined by conventional (T2 and contrast-enhanced T1-weighted spin echo images) and pharmacokinetic MRI. All MRI findings were compared with the giant cross section specimen and histopathology as the standard of reference. For pharmacokinetic MRI, a saturation recovery TurboFLASH sequence was used with a high temporal resolution of 13 s per ten sections. Signal time changes were analyzed using a pharmacokinetic model and the computed parameter values were visualized by color-coded overlay. RESULTS: Analysis of parametrial invasion on T2-weighted images resulted in an accuracy of 85% and 73% on contrast-enhanced T1-weighted images and on pharmacokinetic MR images respectively. Accuracy of analysis of bladder and/or rectal wall invasion was significantly (P < 0.05) higher on pharmacokinetic MR images (88%) than on T2-weighted images (67%). Contrast-enhanced T1-weighted spin-echo images improved staging accuracy compared with T2-weighted images (76% vs 67%). CONCLUSION: At present, conventional T2-weighted SE images are superior to contrast-enhanced T1-weighted SE and pharmacokinetic MR images in depicting infiltration of the parametrium. However, suspected infiltration of the bladder and/or rectum (pT4a) is diagnosed more accurately on pharmacokinetic images than on conventional MR images.

Adolescent↗

PubMed1997

[Functional MR urography in patients with kidney transplantation].

PURPOSE: To assess the value of functional magnetic resonance urology for the noninvasive postoperative evaluation of renal transplants. METHODS: A saturation inversion projection sequence allows the selective imaging of strongly T1 weighted signal from the MR contrast agent. A control slab leads to images comparable to conventional urography which can be acquired as a sequence with four images per minute. RESULTS: 15 patients with urologic questionable findings after renal transplantation were studied. FMRU revealed in 6 patients normal findings, in 6 moderate dilatation of the renal pelvis without any urodynamic relevant obstruction. 3 pathologic findings, ureteral leak, ureteropelvic-junction obstruction and ureteral stenosis were diagnosed and consequently surgically treated. The imaging quality in all studies was diagnostic and urologically relevant. CONCLUSION: FMRU can be used as a noninvasive technique for the assessment of renal transplant in cases with suspicion of complication in the excretory system.

Adult↗

PubMed1997

[Morphologic MR imaging with T1-weighted sequences for radiotherapy goal volume definition of intracranial tumors. Comparison with FLASH-Turbo-FLASH and SE sequences].

INTRODUCTION: The goal of this study was to compare contrast-enhanced T1-weighted Flash and Turbo-Flash sequences with conventional spin-echo sequences as a basis for planning high-precision radiotherapy. METHODS: A total of 25 consecutive patients with different intracranial tumors and a disrupted blood-brain barrier were studied. T1-weighted Flash, Turbo-Flash and conventional spin-echo images were evaluated after controlled 30-s infusion of 0.1 mmol/kg body weight of Gd-DTPA. The evaluation of the three sequences included the measurement of the spinal- and contrast-to-noise ratios, the visual inspection of the tumors and artifacts, and the measurement of tumor size. RESULTS: The signal- and contrast-to-noise ratios were significantly (P < 0.05-0.01) lower for Flash and Turbo-Flash than for conventional spin-echo sequences. However, visual inspection of the contrast-enhancing tumors revealed in 23 and 24 of 25 lesions on Flash and Turbo-Flash images, respectively, good or very good tumor visibility when compared with conventional spin-echo images with a reduction of imaging time by a factor of 7-8. Flash and Turbo-Flash sequences were more prone to susceptibility artifacts, conventional spin-echo sequences more to pulsation artifacts in the posterior fossa. Tumor sizes were comparable in all three techniques. CONCLUSION: At present, conventional spin-echo images are superior to fast Flash and ultrafast Turbo-Flash sequences as a basis for accurate target volume definition in high-precision radiotherapy. However, fast Flash and Turbo-Flash images may be a practicable alternative to conventional spin-echo images for tumors in the posterior fossa or in patients unable to tolerate a stereotactic fixation device. Despite some limitations, Turbo-Flash sequences enable fast dynamic MR imaging combined with an acceptable morphology, which may be sufficient to target volume planning in high-precision radiotherapy.

Adult↗

PubMed1997

[Methodological approaches to quantitative evaluation of microcirculation in tissues with dynamic magnetic resonance tomography].

The development of rapid magnetic resonance imaging (MRI) sequences makes it possible to detect the fast kinetics of tissue response after intravenous administration of paramagnetic contrast media (CM), reflecting the status of tissue microcirculation. In this paper, the basic physical and tracer kinetic principles of dynamic relativity and susceptibility contrast MRI techniques are reviewed. The quantitative analysis of the acquired dynamic image data is broken up into an MR specific part, in which the observed signal variations are related to the CM concentration in the tissue, and an MR independent part, in which the computed concentration-time-courses are analyzed by tracer kinetic modeling. The purpose of the applied models is to describe the underlying physiological processes in mathematical terms and thus to enable the estimation of tissue specific parameters from measured dynamic image series. Whereas the capillary permeability can be estimated from dynamic relativity contrast enhanced MRI studies, the regional blood volume as well as the regional blood flow can be determined from dynamic susceptibility contrast enhanced image series. However, since there are no intravascular but only diffusible CM available at present, the application of the susceptibility technique is currently restricted to brain tissues with intact blood brain barrier. The practical realization of both dynamic MRI techniques is demonstrated by case studies.

Blood Flow Velocity↗

PubMed1997

[Classification of hemodynamic changes in renal artery stenosis using cine magnetic resonance phase contrast flow measurements].

PURPOSE: To evaluate the use of high-temporal resolution cine MR phase-contrast flow measurements for assessment of flow dynamics in renal artery stenosis (RAS). MATERIAL AND METHODS: In a dog model, cine MR flow measurements were validated by comparing the MR flow data to an invasive transit-time ultrasound reference technique for different degrees of RAS. Cardiac-gated MR flow curves were recorded in 56 renal arteries of 28 patients with a temporal resolution of at least 32 ms. In all cases RAS was confirmed by digital subtraction angiography (DSA). Abnormalities of flow dynamics were assessed in the calculated flow curves using the MR parameters mean flow, maximum velocity, and time to systolic maximum. RESULTS: By means of the MR blood flow parameters high-grade stenoses (> 50%, n = 23) were detected with sensitivity of 100% and specificity of 94% with reference to DSA. The overall differentiation between stenoses (n = 37) and non-stenosed vessels (n = 19) revealed a sensitivity of 87% and a specificity of 100%. CONCLUSION: Analysis of cardiac-gated MR flow curves provides a non-invasive method to assess the hemodynamic significance of RAS and thus allows a functional evaluation in relation to the morphologic characteristics of the stenosis.

Adolescent↗

PubMed1997

[Magnetic resonance urography. First clinical results].

We report our preliminary results using a new magnetic resonance imaging technique for visualization of the urinary tract. Using the paramagnetic contrast medium gadolinium diethylene triamine penta-acetic acid (DTPA), we were able to obtain images of the urinary tract comparable to those obtained by conventional excretory urography. The major advantage of our technique is that besides good morphologic visualization, the excretion of gadolinium-DTPA can be studied simultaneously. We demonstrate our preliminary results in selected cases.

Adult↗

PubMed1997

Creatine deficiency syndrome caused by guanidinoacetate methyltransferase deficiency: diagnostic tools for a new inborn error of metabolism.

Hepatic guanidinoacetate methyltransferase deficiency induces a deficiency of creatine/phosphocreatine in muscle and brain and an accumulation of guanidinoacetic acid (GAA), the precursor of creatine. We describe a patient with this defect, a 4-year-old girl with a dystonic-dyskinetic syndrome in addition to developmental delay and therapy-resistant epilepsy. Several methods were used in the diagnosis of the disease: (1) the creatinine excretion in 24-hour urine was significantly lowered, whereas the creatinine concentration in plasma and in randomly collected urine was not strikingly different from control values; (2) the Sakaguchi staining reaction of guanidino compounds in random urine samples indicated an enhanced GAA excretion; (3) GAA excretion measured quantitatively by guanidino compound analysis using an amino acid analyzer was markedly elevated in random urine samples; (4) in vivo 1H magnetic resonance spectroscopy (MRS) revealed a strong depletion of creatine and an accumulation of GAA in brain; (5) in vivo phosphorus 31 MRS showed a strong decrease of the phosphocreatine resonance and a resonance identified as guanidinoacetate phosphate; and (6) in vitro 1H MRS showed an absence of creatine and creatinine resonances in cerebrospinal fluid and the occurrence of GAA in urine. For early detection of this disease, we recommend the Sakaguchi staining reaction of urine from patients with dystonic-dyskinetic syndrome, seizures, and psychomotor retardation. Positive results should result in further investigations including quantitative guanidino compound analysis and both in vivo and in vitro MRS. Although epilepsy was not affected by orally administered creatine (400 to 500 mg/kg per day), this treatment resulted in clinical improvement and an increase of creatine in cerebrospinal fluid and brain tissue.

Amino Acid Metabolism, Inborn Errors↗

PubMed1997

Quantitative magnetic resonance imaging in geriatric depression and primary degenerative dementia.

Quantitative magnetic resonance imaging (MRI) was used to investigate volumes of different brain structures in 19 patients with late-onset major depression (DSM-III-R), 27 patients with Alzheimer's disease (NINCDS-ADRDA criteria) and 13 age matched controls. 3-D MRI sequences were acquired using a Siemens 1.5 T scanner. Whole brain volume, CSF volume, volume of the frontal and temporal lobes and the volume of the amygdala-hippocampus complex were assessed using the software NMR Win. Compared to the controls, depressed patients showed a significantly lower whole brain volume and a significantly higher CSF volume, whereas volumes of the frontal and temporal lobes as well as the amygdala-hippocampus complex volumes were not significantly decreased. In addition, depressed patients exhibited a higher ventricle-brain ratio suggesting a higher degree of central atrophy compared to healthy individuals. In contrast, Alzheimer patients showed significantly lower volumes than depressed patients and controls with respect to all volumetric parameters. Although the findings indicate the presence of brain atrophy in patients with late-onset depression, the pattern of volumetric changes in these patients differs markedly from that observed in patients with primary degenerative dementia.

Aged↗

PubMed1997

Contrast-enhanced magnetization transfer imaging: improvement of brain tumor conspicuity and delineation for radiosurgical target volume definition.

PURPOSE: To assess the contrast-noise-ratio (CNR), and thus tumor conspicuity and delineation, on contrast-enhanced T1-weighted magnetization transfer (MT) images compared to conventional T1-weighted spin echo (SE) images as a strategy to improve definition of the macroscopic boost volume in radiosurgery treatment planning in patients with high grade gliomas or metastatic brain lesions. MATERIALS AND METHODS: Fifty patients (mean age, 51 years) with histologically proven or suspected high grade glioma or cerebral metastases were prospectively examined by MR imaging. Following gadolinium dimeglumine administration (0.1 mmol/kg body weight) the brain was imaged with both a T1-weighted MT-fast low angle shot (FLASH) pulse sequence and with a conventional T1-weighted SE sequence without MT saturation. Lesion conspicuity, size and CNR were compared for both techniques. RESULTS: The mean tumor diameter of malignant gliomas was significantly (P < 0.01) larger when measured on T1-weighted MT-FLASH images compared to T1-weighted SE images and was comparable for metastatic lesions. The mean CNR of enhancing lesions on T1-weighted MT-FLASH was 14 +/- 5 compared to 10 +/- 4 on SE images, representing a significant (P < 0.05) improvement. Lesion conspicuity and delineation was improved in 10 of 20 patients (50%) with high grade gliomas and in 15 of 30 patients (50%) with metastases. Additional contrast enhancing lesions were detected in 8 of 30 patients (27%) with metastases on MT-FLASH images. Lesion conspicuity was markedly improved in the posterior fossa. DISCUSSION: Contrast-enhanced T1-weighted MT-FLASH images improve lesion detection and delineation in the planning process of radiosurgery in patients with intracranial high grade gliomas or metastases and may even alter the treatment approach.

Adult↗

PubMed1997

Intracranial meningeomas: time- and dose-dependent effects of irradiation on tumor microcirculation monitored by dynamic MR imaging.

The purpose of this study was the characterization of the time- and dose-dependent effects of irradiation on tumor microcirculation by means of dynamic MR imaging and correlation of the estimated data with tumor response in patients with meningeomas. Dynamic MR imaging studies were performed in 20 patients with intracranial meningeomas prior to (n = 20) and at 6 (n = 17), 18 (n = 17), and 50 wk (n = 14) after the end of radiotherapy. In seven of these patients, dynamic measurements were also performed during fractionated radiotherapy after approximate 20 Gy and 54 Gy. During and after short-time infusion of gadopentetate dimeglumine, the kinetics of lesion response was resolved using a strongly T1-weighted saturation recovery TurboFLASH (SRTF) sequence. The signal-time courses of the suspected lesions were analyzed using a pharmacokinetic two-compartment model. The calculated parameters amplitude A (reflecting gadopentetate dimeglumine accumulation in the extracellular space) and exchange rate constant k21 (depending on vascular permeability and blood flow) were displayed as color-coded images and analyzed as a function of time of therapy and radiation dose. All meningeomas showed a high exchange rate constant k21 (median, 5.7 min-1; range, 1.9-23.0 min-1) and a high amplitude A (median, 1.5 arbitrary units; range, 1.1-2.7) prior to X-ray treatment. During radiotherapy we found a dose related significant (p < .01) increase of k21 accompanied by an increase of the amplitude A as compared to the pretreatment values. Analysis of tumor volume 6, 18, and 50 wk after X-ray treatment revealed two different groups. In the responder group (n = 13) the median of the tumor volume decreased from 10.0 to 7.5 cm3. For this group, we found a significant drop (p < .01) of the median of the amplitude A and a decrease of the exchange rate constant k21. In the nonresponder group (n = 4) the median of the tumor volume increased after radiation from 3.5 to 4.5 cm3. The pharmacokinetic analysis revealed a decrease of the amplitude A-and an increase of the exchange rate constant k21. The response of meningeomas to radiotherapy is influenced by the effect of X-rays on tumor microcirculation. This effect on tumor microcirculation can be derived by analysis of pharmacokinetic maps obtained from dynamic MR images. Furthermore, these pharmacokinetic maps can possibly be used to differentiate groups of patients who respond or do not respond to radiotherapy and, thus, could benefit from another treatment modality.

Contrast Media↗

PubMed1997

Serial MR imaging of intracranial metastases after radiosurgery.

PURPOSE: To evaluate the spatiotemporal evolution of radiosurgical induced changes both in metastases and in normal brain tissue adjacent to the lesions by serial magnetic resonance (MR) imaging. METHODS AND MATERIALS: Thirty-five intracranial metastases of different primaries were treated in 25 patients by single high-dose radiosurgery. MR images acquired before radiosurgery were available in all patients. Sixty-three follow-up MR studies were performed in these patients including T2- and contrast-enhanced T1-weighted MR images. The average follow-up time was 9 +/- 5 months (mean +/- standard deviation [SD]). Based on contrast-enhanced T1-weighted MR images, tumor response was radiologically classified in the following four groups: stable disease was assumed if the average tumor diameter after treatment did not show a tumor shrinkage of more than 50% and an increase of more than 25%, partial remission as a shrinkage of tumor size of more than 50%, a disappearance of contrast-enhancing tumor as a complete remission, and an increase of tumor diameter of more than 25% as tumor progress. Moreover, we analysed signal changes on T2-weighted images in brain parenchyma adjacent to the enhancing metastases. RESULTS: The overall mean survival time was 10.5 +/- 7 months, with a 1-year actuarial survival rate of 40%. Stable disease, partial or complete remission of the metastatic tumor was observed in 22 patients (88%). Central or homogeneous loss of contrast enhancement appeared to be a good prognostic sign for stable disease or partial remission. This association was statistically significant (p < 0.05). Three patients (12%) suffered from tumor progression. In eight patients (32%) with stable disease or partial remission, signal changes on T2-weighted images were observed in tissue adjacent to the contrast enhancing lesions. A progression of the high signal on T2-weighted images was seen in seven of the eight patients between 3 and 6 months after therapy, followed by a signal regression 6-18 months after irradiation. CONCLUSION: MR imaging is a sensitive imaging tool to evaluate tumor response as well as the presence or absence of adjacent parenchymal changes following radiosurgery. Loss of homogeneous or central contrast enhancement on Gd-enhanced MR images appeared to be a good prognostic sign for tumor response. Tumor shrinkage seems not to be dependent on time. In addition, most cases of radiation induced changes in normal brain parenchyma observed on T2-weighted images seem to be self limited.

Brain↗

PubMed1997

Quantitative magnetic resonance imaging and neuropsychological functions in dementia of the Alzheimer type.

BACKGROUND: The aim of the present study was to investigate neuropsychological functions in dementia of the Alzheimer type (DAT) with respect to morphological changes that were revealed by quantitative magnetic resonance imaging (MRI). METHODS: Twenty patients with DAT (NINCDS-ADRDA criteria) and 10 healthy age and sex matched controls were included. The neuropsychological function was evaluated on a test battery covering the severity of dementia, verbal and visual memory, concentration and attention, language skills and general intelligence as well as activities of daily living. 3D MRI sequences were acquired using a 1.5 T Siemens MAGNETOM. Whole brain volume, total intracranial volume (TIV), volume of the frontal and temporal lobes and volumes of the amygdalahippocampus complex (AHC) were assessed using the newly developed software NMR Win. RESULTS: Apart from TIV all morphometric parameters differed significantly between the diagnostic groups. AHC volumes discriminated best between the groups, with only a small overlap. AHC atrophy exceeded generalized atrophy. These findings were confirmed when the data were reanalysed after dividing the DAT patients into a mildly and moderately affected group. The severity of dementia was significantly correlated with the volumes of the AHC and the volumes of the temporal lobes bilaterally, but not with the whole brain volume and the volumes of the frontal lobes. CONCLUSIONS: These results underline the important role of the temporal substructures for aetiology and progression of DAT. They indicate that the volume of the AHC can be monitored by MRI and may be used to follow up the disease process.

Aged↗

PubMed1997

Renal artery stenosis: grading of hemodynamic changes with cine phase-contrast MR blood flow measurements.

PURPOSE: To analyze the blood flow dynamics in renal artery stenosis with high-temporal-resolution cine phase-contrast magnetic resonance (MR) flow measurements. MATERIALS AND METHODS: Cine phase-contrast MR flow measurements were invasively validated with real-time intraoperative transit-time ultrasound (US). In 23 patients, 48 renal artery stenoses were confirmed at digital subtraction angiography. Cardiac-gated cine phase-contrast MR flow measurements were obtained in 32-msec intervals, and flow curves were calculated for the whole cardiac cycle. Hemodynamic parameters evaluated included the decrease in mean flow and the delay and reduction in the systolic velocity maximum due to decrease in or absence of the early systolic peak. RESULTS: Overall differentiation between renal artery stenosis (n = 31) and nonstenosed vessels (n = 17) with cine phase-contrast MR revealed a sensitivity of 90% and specificity of 94% compared with findings at digital subtraction angiography. High-grade stenoses (>50%, n = 19) were detected with cine phase-contrast MR with sensitivity of 100% and specificity of 93%. CONCLUSION: Quantitative and qualitative analysis of cardiac-gated cine phase-contrast MR flow velocity curves provided a highly accurate method to detect hemodynamic abnormalities in patients with suspected renal artery stenosis.

Adolescent↗

PubMed1997

Noninvasive analysis of renal artery blood flow dynamics with MR cine phase-contrast flow measurements.

It was the aim of this study to quantify the measurement of pulsatile flow in the renal artery with the noninvasive magnetic resonance cine phase-contrast (MRCPC) method and combine it with the simultaneous assessment of pulsatile flow with a transit-time ultrasound (TTUS) flowmeter. In seven foxhounds with a chronically implanted precalibrated TTUS flow probe, MRCPC flow measurements were made in the renal artery with a temporal resolution of 32 ms. Mean and pulsatile flow signal were compared by the simultaneous ipsi- or contralateral measurement of the renal blood flow signal by both methods (TTUS and MRCPC). In addition, comparative MRCPC and TTUS flow measurements were made with artificial renal artery stenosis and after the administration of angiotensin II. The mean flow data assessed by the noninvasive MRCPC flow measurements showed an excellent correlation with corresponding TTUS recording (r = 0.99). The MRCPC flow signal displayed a waveform of the renal artery flow profile that was very similar to the TTUS flow pulse. The hemodynamic changes induced by angiotensin II or due to renal artery stenosis were also reliably detected by MRCPC. MRCPC provides a reliable noninvasive method for the quantification of mean blood flow and the assessment of the pulsatile flow signal in the renal artery and proves to be sensitive to hemodynamic changes of pathophysiological importance. Alternatively, the method may be used for studies in physiology that demand a noninvasive approach.

Angiotensin II↗

PubMed1997

Hyperpolarized gases--a new type of MR contrast agents?

The nuclear spin polarization of noble gases can be strongly enhanced by laser optical pumping followed by electron-nuclear polarization transfer. Direct optical pumping of metastable 3He atoms has been shown to produce enormous polarization in the order of 0.4-0.6. This is about 10(5) times greater than the polarization of water protons at thermal equilibrium used at conventional MR imaging. We demonstrate that hyperpolarized 3He gas can be applied to nuclear MR imaging of human organs with air-filled spaces. In vivo 3He MR experiments were performed in a whole-body MR scanner with a superconducting magnet ramped down to 0.8 T and at 1.5 T using a double resonant Helmholtz coil operating at 63.6 and 48.6 MHz for 1H and 3He, respectively. Anatomical details of the lungs of a volunteer were visualized with the FLASH technique demonstrating the potential of the method for fast imaging of airways in the human body and for pulmonary ventilation studies.

Contrast Media↗