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J Hennig

Publications and source records attributed to J Hennig.

195 records · Page 11Linked to original sources
PubMedDate not supplied

Single-shot diffusion-weighted RARE sequence: application for temperature monitoring during hyperthermia session.

A diffusion-sensitive single-shot RARE (rapid acquisition with relaxation enhancement) sequence was implemented on a 2T whole-body MRI system. The sequence was optimized for diffusion-based MR thermometry, both on a conventional whole-body gradient system and on a high-performance gradient insert. The use of spin-echo versus stimulated-echo diffusion weighting is discussed as a function of gradient performance. Diffusion-based temperature mapping was used to observe the effect of the geometry of the antenna used for radiofrequency (RF) hyperthermia on the temperature distribution. Temperature changes of +/-.5 degrees C in gel and +/-2 degrees C in a muscle sample in vitro could be detected within 16 seconds (gel) or 1 minute (muscle) at a spatial resolution of 2 x 2 x 8 mm. Temperature changes in vivo were also observed on human muscle cooled with ice with comparable sensitivity for the measured apparent diffusion coefficient (ADC) values.

Animals↗
PubMedDate not supplied

Direct absolute quantification of metabolites in the human brain with in vivo localized proton spectroscopy.

The absolute concentrations of the three major brain metabolites observable by in vivo proton spectroscopy--N-acetylaspartate(NAA), creatine and phosphocreatine (Cr and PCr) and choline (Cho)--have been measured at four standardized localizations in 34 healthy volunteers by in vivo localized proton spectroscopy using an external reference sample. The results show that the concentration of Cr and PCr as observed by in vivo MRS (5-6 mmol/L) is lower than that measured by other methods. The results are concordant with the hypothesis, that the Cr and PCr resonance as observed by proton spectroscopy is due mainly to PCr, whereas Cr remains invisible by being attached to a larger molecule. It is also demonstrated, that Cr and PCr is higher in the cerebellum than in the cerebrum, whereas NAA remains constant within the margin of error (8-9 mmol/L).

Aspartic Acid↗
PubMedDate not supplied

Decoupling of the short-term hemodynamic response and the blood oxygen concentration.

Neuronal activation leads to an increase in the local cortical perfusion. The exact regulatory mechanisms leading to these changes are still unknown. To elucidate the role of oxygen in the initial hemodynamic regulation, a disactivation paradigm was performed with fMRI. A stimulus was applied following a previous extended activation in order to evoke physiological variations of the local oxygen concentration. The results demonstrate that the initial hemodynamic response time is independent of the local blood oxygen concentration.

Adult↗
PubMedDate not supplied

Detection of BOLD changes by means of a frequency-sensitive trueFISP technique: preliminary results.

A new method is introduced to detect magnetic field modulation arising from brain activation-induced BOLD effects. This approach uses a two-dimensional high-bandwidth, high-resolution conventional gradient-echo steady-state imaging sequence known as TrueFISP. The ability to visualize changes in oxygen saturation comes from the fact that the method is sensitive to the local field. As is well known, as the oxygen saturation changes so does the local field associated with the venous blood. We demonstrate that it is possible to visualize not only venous blood with this approach on a macroscopic level for major veins, but also to measure conventional oscillatory like signal changes during activated and resting states. Unfortunately, the method has two major drawbacks. First, a long TR is needed to maximize signal changes and, second, the field must be very well shimmed or numerous experiments need to be run to find the activation, as the signal response is sensitive to the starting frequency in the resting state. Nevertheless, these images can be compared directly with anatomical images collected with the same method without the need for distortion correction.

Brain↗
PubMedDate not supplied

Lowering of body temperature affects human platelet functions and norepinephrine release.

The effect of lowering body temperature on plasma epinephrine, norepinephrine, and platelet density distribution and volume was studied in a placebo-controlled double-blind study. Lowering of body core temperature was induced by either exposure to a cold environment at a temperature of 5 degrees C (CT) or by a single dose of the 5-HT1A agonist ipsapirone (IPS). A third group exposed to an ambient temperature of 28 degrees C was given placebo (PLAC). All of the three groups were investigated in a climate chamber. In the CT group the density distribution of blood platelet subpopulations was shifted to an increase in less dense platelets that were more sensitive towards aggregation-inducing agents. The mean platelet volume in this subpopulation was decreased. Epinephrine was not affected, whereas the increase of norepinephrine was correlated with an increase of platelets that were more sensitive to aggregation-inducing agents in the CT group but not in the PLAC and IPS groups.

Adult↗
PubMedDate not supplied

Fast and exact flow measurements with the fast Fourier flow technique.

The fast Fourier flow technique offers a convenient way for extremely exact flow measurements. In combination with ECG gating, arterial flow can be studied. The total acquisition time for a single measurement is about 10 s, an ECG-gated cine sequence can be acquired in about 4 min. Fast Fourier flow can, therefore, be easily combined with a conventional imaging examination.

Blood Circulation↗
PubMedDate not supplied

Clinical applications and methodological developments of the RARE technique.

The RARE technique is an extremely useful tool for clinical diagnosis, since it delivers images comparable to those produced by X-ray myelography and X-ray urography. Contrary to these methods, RARE does not use the application of contrast agents. A low-flip-angle variant called FLARE (fast low angle refocused echo imaging) makes this technique accessible for high-field systems.

Humans↗
PubMedDate not supplied

MR imaging of flow using the steady state selective saturation method.

The steady state selective saturation method is a fast and efficient technique to study flow with magnetic resonance imaging. The pulse sequence used generates no signal from stationary matter and simultaneously optimizes signal flowing into a predetermined volume. The method can be used to generate three-dimensional angiography in less than 5 min. Other modifications allow the quantitative measurement of flow velocities and distinction of veins and arteries according to the direction of flow.

Arteries↗
PubMedDate not supplied

Cardiac phase contrast gradient echo MRI: characterization of abnormal left ventricular wall motion in patients with ischemic heart disease.

PURPOSE: In our patient study, we examined the clinical usefulness of phase contrast velocity mapping for the detection and characterization of localized abnormalities of left ventricular motion. MATERIALS AND METHODS: Velocity encoding is based on the fact that motion in the presence of a magnetic field gradient causes a change of the phase of the MRI signal that is proportional to the velocity of tissue motion. Left ventricular motion was characterized by parameters describing rotation and contraction/dilatation, respectively. We examined 34 patients with localized abnormalities of left ventricular motion due to ischemic heart disease. RESULTS: Three patients could not be sufficiently evaluated due to technical problems including varying positions of the heart during successive breathhold periods. In 27 of the remaining 31 patients, MRI could demonstrate abnormal radial velocities that corresponded fully or partly with perfusion deficits in single photon emission computed tomography or positron emission tomography. The abnormalities were most pronounced in early diastole. Rotational velocities did not show any regional changes. CONCLUSION: Our study showed that our technique is suitable for the detection and characterization of localized abnormalities of left ventricular motion in patients with ischemic heart disease.

Adult↗
PubMedDate not supplied

The influence of gliomas and nonglial space-occupying lesions on blood-oxygen-level-dependent contrast enhancement.

BACKGROUND AND PURPOSE: Functional MR (fMR) imaging with blood-oxygen-level-dependent (BOLD) contrast enhancement is increasingly used as a noninvasive tool for presurgical mapping in patients with intracranial tumors. Most physiologic studies of task-related BOLD contrast enhancement have involved healthy volunteers. Therefore, it is not known whether BOLD contrast is evoked in the same way in or adjacent to tumor tissue. The purpose of this study was to study the influence of different intracranial tumors on BOLD contrast enhancement. METHODS: fMR mapping of the sensorimotor cortex was successfully performed in 15 of 21 patients with intracranial space-occupying lesions by using a bimanual motor task. Tumors were located either within the sensorimotor area itself or in adjacent brain areas, inducing changes of signal intensity on T2-weighted images along the pre- or postcentral gyrus. Space-occupying lesions were divided into a group comprising gliomas (seven cases) and a group comprising nonglial space-occupying lesions (three metastases, two cavernomas, one abscess, one arteriovenous malformation, one meningioma). A hemispheric activation index was calculated using the volume of activation on the affected and on the contralateral hemisphere. Hemispheric activation indices of gliomas and nonglial lesions were compared statistically. RESULTS: The activated volume in the hemispheres ipsilateral to the nonglial lesions was 14% larger than in the contralateral hemisphere, whereas in the hemispheres ipsilateral to gliomas, the activated volume decreased by 36% in comparison with the contralateral hemisphere. The difference between nonglial lesions and gliomas was significant (P < .05). CONCLUSION: The generation of BOLD contrast enhancement is reduced near gliomas but is not affected by nonglial tumors.

Brain Diseases↗
PubMedDate not supplied

Toxicological evaluation of a new benzonaphtyridone derivative (IF C-45).

DL50 for 10-gamma-dimethylaminopropyl-7-chlorobenzo(b)-(1-8)-naphtyridone-5 hydrochloride (IF C-45) determined on several species of animals at different ways of administration, had values similar to those of imipramine and amitryptyline. IF C-45 a-cumulates in 34-4% of A-DL50. The evaluation of chronic toxicity was performed on rats, giving IF C-45 daily for 3 months the doses of 30, 25 and 12-5 mg/kg. The results of hematological, biochemical and histological estimations did not show in these animals any marked toxic effects.

Alanine Transaminase↗
PubMedDate not supplied

Rapid nontomographic approach to MR myelography without contrast agents.

A modification of the rapid acquisition with relaxation enhancement imaging method allows the acquisition of a highly T2-weighted image in 2.5 s. By omitting the slice selection gradient, this technique yields a superimposed image of the CSF in the spinal canal. This image (magnetic resonance myelogram) contains much of the same information as an X-ray myelogram.

Contrast Media↗
PubMedDate not supplied

Extended preoperative polyvinyl alcohol microembolization of intracranial meningiomas: assessment of two embolization techniques.

PURPOSE: To evaluate the efficacy of preoperative meningioma devascularization with small polyvinyl alcohol (PVA) particles. METHODS: In 34 patients with intracranial meningiomas, CT, MR, 1H MR spectroscopy, MR volumetric measurements, intraoperative ultrasound, and histopathologic findings were used to compare the efficacy of two embolization techniques: 1) administration of 150- to 300-microns PVA particles in the usual suspension, and 2) administration of 50- to 150-microns PVA particles in a highly diluted suspension. RESULTS: Angiography after embolization demonstrated the total elimination of tumor blush in all patients. Contrast-enhanced MR after the administration of 150- to 300-microns PVA particles revealed a reduction of tumor enhancement in only two out of 14 patients. Only after the use of small particles could significant tumor necrosis be depicted on MR and confirmed histopathologically after surgery. In 12 of 20 patients, 30% to 95% of the whole tumor was necrotic with 17% to 20% reduction of tumor volume in four cases, leading to recovery from the initial neurologic deficits. In three of 20 patients without sufficient steroid medication before the treatment, tumor swelling occurred. Postembolization MR disclosed a tumor volume increase of 10% to 20% in these patients. 1H MR spectroscopy of the tumors showed an increase of lactate and aliphatic lipid compounds after embolization, indicating tumor infarction. Surgical removal of effectively embolized meningiomas without significant blood loss was possible. The appearance of the tumor at operation, ultrasound examination, and the histopathologic examination of different parts of the tumor confirmed the preoperative MR findings suggesting necrosis. CONCLUSION: Extended microembolization with 50- to 150-microns PVA particles improves the surgical treatment of meningiomas, as compared with larger particle embolization. It may also be the only treatment required in older or high-risk patients. The protective effect of steroid medication before the endovascular treatment of meningiomas is suggested by our study.

Adult↗
PubMedDate not supplied

Grading and therapy monitoring of astrocytomas with 1H-spectroscopy: preliminary study.

We examined 11 patients (9 male and 2 female, age 41 +/- 13) presenting astrocytomas of different malignancy grade (WHO) with single voxel (PRESS) and double voxel (STABLE) spectroscopy techniques. The content of choline in the tumors was determined as a function of their grade of malignity and a significant correlation was found. The measurements were repeated after interstitial radiosurgery. Observed spectra changes induced by this stereotactic treatment with 125I-seed demonstrated the possibility of therapy monitoring.

Adult↗