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H J Zabel

Publications and source records attributed to H J Zabel.

14 recordsLinked to original sources
PubMed1992

Radiotherapy treatment planning of basal meningiomas: improved tumor localization by correlation of CT and MR imaging data.

A localization technique, based on three-dimensional CT and MR imaging data for precision radiotherapy of basal meningiomas, is presented. Indications for radiotherapy included unresected tumors, gross disease remaining despite surgery, and recurrences. The patient's head was fixed in a stereotactic localization system which is usable at the CT, MR and the linear accelerator installations. The geometrical distortion of MR imaging data was evaluated in three dimensions by phantom measurements. The geometrical distortion was "corrected" (reducing displacements to the size of a pixel) by calculations based on modelling the distortion as a fourth order two-dimensional polynomial. The target volume was defined in three-dimensional MR imaging data after application of 0.1 mmol/kg b.w. Gd-DTPA solution and transferred precisely from MR onto CT data to provide a map of the radiation attenuation coefficient for dose calculation. The superior soft tissue contrast of MR showed an excellent tumor delineation especially when the bony base of the skull obscured the target in CT images. Target volume, calculated dose distribution, and critical structures could be transferred between CT and MR imaging data and displayed as three-dimensional shaded structures for better assessment for matching of target volume and dose distribution. With the described planning system a more precise target definition of basal meningiomas was possible by integration of the superior tumor delineation in MR compared with CT.

Computer Graphics↗
PubMed1992

Correction of spatial distortion in magnetic resonance angiography for radiosurgical treatment planning of cerebral arteriovenous malformations.

A treatment planning system based on magnetic resonance (MR) angiographic imaging data for the radiosurgery of inoperable cerebral arteriovenous malformations is reported. MR angiography was performed using a three-dimensional (3D) velocity-compensated fast imaging with steady-state precession (FISP) sequence. Depending on the individual MR system, inhomogeneities and nonlinearities induced by eddy currents during the pulse sequence can distort the images and produce spurious displacements of the stereotactic coordinates in both the x-y plane and the z axis. If necessary, these errors in position can be assessed by means of two phantoms placed within the stereotactic guidance system--a "2D-phantom" displaying "pincushion" distortion in the image, and a "3D-phantom" displaying displacement, warp, and tilt of the image plane itself. The pincushion distortion can be "corrected" (reducing displacements from 2-3 mm to 1 mm) by calculations based on modeling the distortion as a fourth order 2D polynomial. Displacement, warp, and tilt of the image plane may be corrected by adjustment of the gradient shimming currents. After correction, the accuracy of the geometric information is limited only by the pixel resolution of the image (= 1 mm). Precise definition of the target volume could be performed by the therapist either directly in the MR images or in calculated projection MR angiograms obtained by a maximum intensity projection algorithm. MR angiography provides a sensitive, noninvasive 3D method for defining target volume and critical structures, and for calculating precise dose distributions for radiosurgery of cerebral arteriovenous malformations.

Humans↗
PubMed1991

Treatment of the Dunning prostate rat tumor R3327-AT1 with pulsed high energy ultrasound shock waves (PHEUS): growth delay and histomorphologic changes.

We are interested in the interaction of pulsed high energy shock waves (PHEUS) on soft tissues treated in situ to evaluate its potential for therapeutic use. The experimental apparatus built by us was adapted from a lithotripter designed for clinical use. For the present studies we used the R3327-AT1 Dunning prostate tumor growing s.c. in the thigh of Copenhagen rats. The treatments consisted of four groups of eight animals each who received 500 or 2000 pulses at 1 or 5 Hz. Sham-treated tumor bearing animals served as controls (n = 11). During each PHEUS treatment, petechial bleeding of the skin at the point of entry and exit of sound appeared. Sonication at a repetition rate of five Hz seemed to induce more macroscopic damage in terms of hematomas and skin effects. The cytotoxic effects of PHEUS to tumor tissue were sufficient to induce a significant delay (p less than 0.05) in tumor growth but no clear-cut dose relationship was established. Histological studies revealed widespread early rupture of the fine vasculature with extravasation of erythrocytes. By 72 hr., in PHEUS treated tumors, a large necrosis was seen within the central zone which was never observed in sham-treated tumors. Our results clearly indicate that PHEUS has a cytotoxic potential. The observation of a rapid onset of hemostasis, stark hemorrhage and necrosis in the treatment field would suggest that vascular damage is an important contributing factor.

Animals↗
PubMed1989

[Non-invasive follow-up control of tumor therapy following chemotherapy using 31P-MR spectroscopy in whole body tomography].

The 31P Magnetic Resonance Spectroscopy allows to monitor noninvasively and in vivo the energy and phospholipid metabolism of tissue. At present the high technical demand prevents the application of this new modality in the clinical routine. By means of some cases the advantages and limitations of the 31P-MRS are demonstrated. Recent results show that 31P-MRS monitors effects on the metabolism of tumor cells as early as two days after onset of chemotherapy. Further clinical studies and technical developments are necessary to render 31P-MRS a clinic routine examination.

Computer Graphics↗
PubMed1988

[In vivo 31 phosphorus spectroscopy of tumors: pre-, intra- and post-therapy].

Using 31P-MR spectroscopy spectra with good signal-to-noise ratio were obtained in five different types of tumours (Ewing's sarcoma, osteosarcoma, malignant melanoma, metastases from a squamous cell carcinoma, parotid adenoma). Surface coils were used. Short- and long-term follow-up after chemotherapy was possible in some cases. In the short-term follow-up, changes in the phosphocreatine and inorganic phosphate resonances could be observed within minutes after the start of the infusion. In the longer follow-ups, changes in phosphodiester and phosphomonoester resonances were observed within two days. There were no significant changes in tissue pH during treatment, but increased pH values were observed in all tumours.

Adenoma↗
PubMed1988

Monitoring human tumor response to therapy by means of P-31 MR spectroscopy.

Tumors in 23 patients were studied by means of in vivo phosphorus-31 magnetic resonance (MR) spectroscopy. In five patients, the response to chemotherapy and radiation therapy was monitored in a long-term follow-up study. In one patient, the P-31 MR spectra were recorded during the infusion of chemotherapeutic drugs. In comparison with healthy muscle tissue of patients, the tumors showed elevated inorganic phosphate, phosphomonoester, and phosphodiester peaks and reduced creatine phosphate peaks, whereas the nucleoside 5'-triphosphate levels remained nearly unchanged. Tumor treatment resulted in changes in the ratio of the signal intensity value of creatine phosphate to that of inorganic phosphate and in the sum of these values. In an osteosarcoma, an initial response followed by renewed tumor growth was clearly indicated by changes in these parameters. In the short-term follow-up examination, slight spectral changes were observed during the infusion of chemotherapeutic drugs. Changes in the concentrations of phosphorus metabolites during therapy can therefore be monitored in human tumors by means of P-31 MR spectroscopy.

Antineoplastic Agents↗
PubMed1987

High-quality MR imaging with flexible transmission line resonators.

A novel type of surface coil suitable for human magnetic resonance (MR) imaging is described. The radio frequency receiving unit consists of a coaxial transmission line resonator (TLR). Its high filling factor and loaded Q-value of about 140 result in a high signal-to-noise ratio and thus a high-quality image. The coaxial Faraday shield eliminates di-electric losses and capacitive detuning of conductive samples. The stabilizing effect of the TLR makes it unnecessary to tune the coil between imaging of patients. The TLR can be immediately adapted to the individual body contours of a patient. Regions of the body traditionally difficult to image (e.g., throat) are easily examined due to the flexibility of the coaxial cables. These advantages coupled with ease of handling and shorter preparation time have made the TLR a proved tool that has been successfully used in many areas of diagnostic MR imaging.

Equipment Design↗
PubMed1985

[Picture documentation in ultrasonic diagnosis].

In addition to a written report, ultrasound findings also require picture documentation. Cuts in physician fees warrant optimal cost-effectiveness in ultrasound documentation. Of the presently available equipment for permanent image recording off the monitor and direct electronic recording the following are to be discussed and compared: Polaroid recording, X-ray film, 35 mm roll film, dry silver paper, video-tape, floppy-disc, optical disc recorder and electronic still camera. The costs per picture, including investment and operating costs in relation to annual number of examinations, are calculated for the various systems.

Copying Processes↗
PubMed1983

Stereotactic computer tomography with a modified Riechert-Mundinger device as the basis for integrated stereotactic neuroradiological investigations.

For stereotactic biopsy, intracavitary and interstitial irradiation of intracranial tumours, stereotactic CT investigations are of utmost importance. Target-points within a tumour as well as the tumour-outlines have to be transferred precisely from transverse and longitudinal CT sections to stereotactic X-ray images. For this purpose, the stereotactic apparatus of Riechert and Mundinger has been equipped with a fixation system of carbon fibre and a measuring phantoma of plexiglass with embedded steel wires allowing stereotactic CT scanning without artefacts. The stereotactic coordinates (x, y, z) of any target point can be taken directly from transverse CT images with high accuracy. The tumour outlines can be transferred to the stereotactic coordinate system from longitudinal CT reconstructions using special computer programmes. Precise transfer is possible if the CT investigation is performed stereotactically.

Brain Neoplasms↗
PubMed1983

Liver tissue characterization using computerized echography.

A digital echographic data acquisition and evaluation system was used in a clinical study including more than 100 patients with various local or diffuse liver tissue alterations. For diagnosis two decision methods are applied: first linear discriminant analysis and second a Bayesian method. Each A-scan is represented by a set of various numerical parameters from which only the most signal-distinctive ones are used for evaluation. The diagnostic results which will be presented and discussed have proved the method to be very sensitive and specific.

Diagnostic Errors↗
PubMed1977

[Computed tomography of the whole body as a means of radiation planning (author's transl)].

Computed tomography of the whole body offers the first possibility to obtain individual tomographs with high resolution and in correct scale from all regions of the body. Using the "Sicograph", large-sized copies are obtained, which are therefore particularly useful for radiation planning. The size and location of tumors relative to critical organs can be determined exactly. The efficacy of radiation therapy in every individual case may be estimated on the basis of the controlled course (radiobiological information), [2,4,6,11,16,17,18,24,30], and the necessary modifications of the therapeutic schedule can be adopted early, allowing the complete utilization of the advantages of the shrinking field technique [8,19,26]. Since ultrasonic tomographs in many cases furnish additional information, we regard the combination of computed and ultrasonic tomography as the best way to obtain an accuracy of radiation planning previously unknown.

Humans↗
PubMedDate not supplied

Impact of hyperthermic regional perfusion therapy on cell metabolism of malignant melanoma monitored by 31P MR spectroscopy.

For the first time, the influence of hyperthermic regional perfusion therapy on tumor cell metabolism has been monitored by means of 31P MR spectroscopy. Shortly after treatment, a complete depletion of high energy phosphates, a significant increase of inorganic phosphate, phosphomono- and phosphodiester resonances and a decrease of pH have been observed. Healthy muscle tissue showed only minor effects caused by this aggressive therapy. The time course of the transient variation of phosphate metabolite concentrations is explained in the framework of a simple pathophysiological model. The results demonstrate that the imediate effect of chemotherapy on tumor tissue can be detected by 31P MRS before any clinical signs of tumor response are visible.

Antineoplastic Agents↗
PubMedDate not supplied

Combined use of stereotaxic CT and angiography for brain biopsies and stereotaxic irradiation.

A Riechert Mundinger stereotaxic device was modified to enable artifact-free computed tomographic (CT) scanning with the stereotaxic frame attached to the patient's head. A localization system was developed allowing determination of the XYZ coordinates of the target point directly from the CT cut. Angiography was performed intraoperatively with the stereotaxic frame attached. Coronal and sagittal CT reconstructions were enlarged to the radiographic magnification to allow direct comparison with angiography. CT offered optimum localization of the target, whereas angiography determined the safest approach. Computer programs were developed to enable three-dimensional radiotherapy planning. 125I seeds were implanted for treatment of low-grade gliomas and solid craniopharyngiomas. Yttrium-90 was applied in cystic craniopharyngiomas. Intracavitary rhenium-186 application was abandoned because of frequent cyst recurrence and leakage from the cyst.

Biopsy, Needle↗