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Biomedical subjects

R Felix

Publications and source records attributed to R Felix.

At least 505 records · Page 28Linked to original sources
PubMed1993

[The value of magnetic resonance tomography and computed tomography in the tumor staging of laryngeal and hypopharyngeal carcinomas].

43 patients with malignant tumours of the larynx or hypopharynx were examined by MRT and CT to compare their accuracy for T-staging. There was histological confirmation in all cases. Histological studies showed an accuracy in T-staging of 90% for MRT and 82% for CT. Differentiation between stages T2/T3 and T3/T4 is possible in most cases by either method. A source of error is the difficulty of differentiating oedema or inflammatory changes from tumour. This led to occasional overinterpretation of the T4 stage. Demonstration of cartilage involvement was easier with MRT (88%) than with CT (84%). The use of Gd-DTPA with T1 weighted and proton weighted sequences allows earlier diagnosis of cartilage invasion. Early cartilage involvement may be missed by CT when it is seen on MRT. In addition, the ability to produce coronal and sagittal images by MRT makes this superior to CT in judging tumour extension.

Carcinoma↗
PubMed1993

[Venous MR angiography for the primary diagnosis and follow-up of sinus venous thrombosis. The correlation with the clinical picture and DSA].

30 patients clinically suspected of suffering from venous sinus thrombosis were examined by MRT with venous MR angiography (FLASH 2-D). In 8 patients selective arterial angiography was also performed and 5 patients were followed up by MR angiography after an interval of three months. The MRT images and individual MR angiography images were analysed and 3-D reconstruction performed. In 11 patients MR angiography correctly demonstrated venous sinus thrombosis; the most frequently affected were the superior sagittal sinus, the ascending cerebral veins and the transverse sinus. Compared with DSA, magnetic resonance angiography achieved a high degree of accuracy in our patients. It was significantly better in evaluating the basal sinus system whereas thrombosis of individual ascending veins was better shown by DSA. In summary, primary use of MRT and MR angiography is recommended for the diagnosis of venous sinus thrombosis.

Adult↗
PubMed1993

3-D computation of E fields by the volume-surface integral equation (VSIE) method in comparison with the finite-integration theory (FIT) method.

An algorithm has been developed for calculation of 3-dimensional E fields by the volume-surface integral equation (VSIE) method. Integration over surface elements is performed by elementary analytical formulas, assuming a linear interpolation of surface charges. Grid points at electrical interfaces are split off, well considering the E field behavior at these contours, specifically at sharp bends and multimedia junctions. Averaging procedures are utilized in order to avoid undefined or infinite values at critical points. The VSIE is solved by iteration using GMRES ("general minimum residuum") solver on a SUN workstation SPARC-IPX or Cray XMP, whereby convergence speed decreases considerably as the heterogeneity of the problem increases. Computation time (e.g., 20 min on a supercomputer for approximately 30,000 cells) needs to be reduced by further code development. Results for 3-D test cases (plane wave illuminating a layered cylinder) generally agree well with the finite-integration-theory (FIT) method if high E field gradients occur perpendicular to electrical boundaries. The VSIE method predicts slightly higher E fields only in critical regions. On the other hand, the FIT method at present is more efficient with respect to computation time for large domains with high cell numbers (> 100,000 cells).

Algorithms↗
PubMed1993

Contrast-enhanced transcranial Doppler US with a new transpulmonary echo contrast agent based on saccharide microparticles.

The purpose of this first patient study (phase II) was to evaluate the clinical usefulness of a new echo contrast agent at transcranial Doppler ultrasonography (US). Twenty patients were selected from a group of 242 patients undergoing conventional transcranial Doppler US who had low (n = 18) or absent (n = 2) Doppler signals from the middle cerebral artery (MCA). The extent and duration of Doppler signal increase was measured in 30 MCAs and in 14 basilar arteries following the intravenous injection of a transpulmonary galactose microparticle suspension (SH U 508 A) at three concentrations (200, 300, and 400 mg/mL). Doppler waveform analysis became possible in 93% (28 of 30) of the MCAs following injection. The maximal increase in average Doppler signal intensity (11 dB at 200 mg/mL, 15 dB at 300 mg/mL, and 17 dB at 400 mg/mL) and the increase in average duration of the signal enhancement (163 seconds at 200 mg/mL, 219 seconds at 300 mg/mL, and 240 seconds at 400 mg/mL) depended on contrast agent concentration. Doppler waveform analysis became possible in 79% (11 of 14) of the basilar arteries. The intravenous injection of this new echo contrast agent markedly increases Doppler signal intensity in patients with nondiagnostic results at conventional Doppler US.

Basilar Artery↗
PubMed1993

Skull base tumors: gadodiamide injection--enhanced MR imaging--drop-out effect in the early enhancement pattern of paragangliomas versus different tumors.

A phase III trial was conducted in 40 patients with known or suspected skull base tumors to evaluate the safety and efficacy of high-dose gadodiamide injection for use as a paramagnetic contrast medium in conventional and dynamic magnetic resonance (MR) imaging. Contrast material enhancement was assessed dynamically with use of a gradient-recalled sequence. The time-intensity curve of selected regions of interest showed a reproducible dropout effect in the form of a dip in the curve during the early enhancement of the sigmoid sinus and jugular bulb; the same phenomenon was observed in all glomus tumors of the skull base, regardless of size or location. In contrast, schwannomas, meningiomas, and a variety of other lesions showed a continuous increase in the time-intensity curve. The drop-out sign, which is probably a result of a paramagnetic phenomenon during the early phase of enhancement, seems to be specific for glomus tumors. High-dose gadodiamide injection may show a specific dynamic pattern for glomus tumors, allowing differentiation from other tumors of the middle and posterior skull base.

Drug Combinations↗
PubMed1993

Comparison of lactotrope subtypes of neonatal and adult male rats: plaque assays and patch-clamp studies.

We examined the differences in lactotrope number and function between pituitary cultures from neonatal (10-day-old) and adult male rats. Basal hormone release was measured with the reverse hemolytic plaque assay. Whole cell Ba2+ currents through Ca2+ channels were recorded from identified prolactin (PRL) secretors with the patch-clamp technique. Lactotropes were classified in two groups according to the relative amount of PRL released: small-plaque (SP) secretors accounted for 6% of all cells in both neonatal and adult pituitary cultures, whereas large-plaque (LP) secretors comprised 13% of the adult pituitary cells but were scarce in cultures from neonates. Simultaneous plaque assays for PRL and growth hormone (GH) showed that in adults as well as in neonates the number of SP and LP secretors was similar to the number of lactosomatotropes (PRL cells that also release GH) and classical lactotropes (PRL-only cells), respectively. Ba2+ current density at positive membrane potentials was markedly higher in adult LP secretors than in neonatal or adult SP lactotropes. We conclude that the appearance of LP secretors constitutes a major postnatal change within the rat lactotrope population. These cells present a large activity of high-threshold Ca2+ channels in the plasma membrane, release PRL at high basal rates, and may correspond to classical lactotropes. The results further suggest that neonatal lactotrope-like cells persist during development and give place to adult SP secretors.

Aging↗
PubMed1993

Acute fracture of the femoral neck: assessment of femoral head perfusion with gadopentetate dimeglumine-enhanced MR imaging.

OBJECTIVE: Evaluation of the perfusion and viability of the femoral head after fracture of the femoral neck is important because the outcome of conservative treatment or joint-preserving surgery is adversely affected by the development of capital osteonecrosis. We evaluated the use of MR imaging, before and after IV administration of gadopentetate dimeglumine, for assessing perfusion of the femoral head in 13 patients with acute fracture of the femoral neck. SUBJECTS AND METHODS: Multiecho (1600/30-240 [TR/TE]) MR images were obtained before contrast administration and gradient-echo (315/14, 90 degrees flip angle) MR images were obtained both before and after contrast administration. MR findings were correlated with findings on superselective digital subtraction angiograms of the vessels supplying the femoral head and with clinical-radiographic follow-up for at least 12 months. RESULTS: Digital subtraction angiography showed impaired blood supply to the femoral head in five patients. On contrast-enhanced MR images of these patients, the femoral head did not enhance and was lower in signal intensity than were the enhancing femoral shaft and neck distal to the fracture and the enhancing femoral head on the unaffected side. In the patients with persistent perfusion, contrast-enhanced MR images showed a uniform increase in signal intensity in the femoral shaft and neck as well as the femoral head; the femoral head on the fractured side showed contrast enhancement similar to that on the healthy side. CONCLUSION: These preliminary results indicate that contrast-enhanced MR imaging may be useful for noninvasive evaluation of femoral head perfusion after fracture of the femoral neck. MR findings also may aid the clinician in deciding between joint-preserving therapy and hip arthroplasty.

Acute Disease↗
PubMed1993

[Indications and methods of peri-radicular therapy and facet block].

A CT-guided pain therapy can be an additional tool in cases with vertebrally caused problems and lesions. The axial CT scan in the altered vertebral segment allows a controlled puncture of the radicular or articular regions and a helpful pain therapy with different injections. The procedure is performed in outpatients.

Analgesia, Epidural↗
PubMed1993

[Magnetic resonance tomography of new rupture of the anterior talofibular ligament].

Twenty acutely traumatised patients with a rupture of the anterior talofibular ligament were studied by MRI. The results of 3D-studies were correlated with conventional stress x-ray studies. The ruptured ligament was directly visualised in all cases as a thickened structure of high signal intensity. In case of complete ruptured ligaments free flowing ligamentous structures were seen in the signal intense exudation in the ankle joint. MRI can help to decide between surgery or conservative therapy.

Adolescent↗
PubMed1993

[Magnetic resonance tomographic characterization of intracranial tumors by evaluating the blood-brain barrier and regional cerebral circulation].

The aim of this prospective study was to characterize intracranial tumors on the basis of the degree of blood-brain-barrier (BBB) disruption and tumor blood flow (TBF). We studied 28 patients with brain tumors by MRI. BBB disruption was demonstrated by a pathological increase of signal intensity in T1-weighted spin-echo images (1.5 T, TR = 600 ms, TE = 10 ms, alpha = 90 degrees) after intravenous gadolinium-DTPA injection. TBF flow was assessed by an MRI-method based on the signal intensity decrease in T2-weighted gradient-echo images (TR = 25 ms, TE = 20 ms, alpha = 10 degrees) immediately after gadolinium-DTPA bolus injection. Typical constellations include intake BBB and low TBF in low-grade intraaxial tumors (astrocytoma I/II), disrupted BBB and heterogeneous TBF in high-grade intraaxial tumors (glioblastomas and metastases), and disrupted BBB and high TBF in extraaxial tumors (meningeomas). This study demonstrates the quasi-simultaneous assessment of the blood-brain-barrier and tumor blood flow. The results support the concept that additional uncorrelated information is obtained from the assessment of regional cerebral blood flow that may be helpful for the differential diagnosis of brain tumors.

Astrocytoma↗
PubMed1993

Femoral head perfusion in patients with femoral neck fracture and femoral head necrosis.

Femoral head perfusion in adults was studied by superselective i.a. DSA in 35 normal subjects, in 9 patients with medial femoral neck fracture preoperatively, and in 36 patients with femoral head necrosis before bone grafting, and as therapeutic control after grafting. All patients with femoral neck fracture showed an interruption of the proximal nutrient branches. In 93% of the cases with femoral head necrosis, these branches were rarefied or the medial circumflex femoral artery was interrupted. Postoperative DSA after pedicled pelvic bone graft revealed a regularly perfused graft in 82%. Superselective i.a. DSA is a valuable procedure for the therapeutic decision in selected patients with femoral neck fracture as well as before pedicled pelvic bone grafting and as therapeutic control after grafting.

Adult↗