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G Layer

Publications and source records attributed to G Layer.

At least 55 records · Page 3Linked to original sources
PubMed1994

[The value of MR tomography after transsphenoidal hypophyseal resection. A retrospective comparison between endocrinology, operation and MRT].

Postoperative magnetic resonance images of 40 patients after transsphenoidal surgery for pituitary adenoma were evaluated retrospectively. The signal intensities of packing material and residual tumour were analysed. T1-weighted spin-echo sequences were obtained in coronal and sagittal views with and without intravenous injection of contrast media. Residual tumour demonstrated homogeneous or inhomogeneous signal intensity on the native scan with homogeneous or inhomogeneous enhancement. Packing material demonstrated a homogeneous signal intensity on the images obtained without injection of contrast media with a peripheral enhancement or alternate layers of low and intermediate signal intensity with alternate enhancement after injection of contrast media. In 5 of 54 examinations different results were found in MRI, endocrinology and surgery (two false negative and one false positive MRI in correlation with endocrinology; two residual tumours on MRI where surgery was supposed to be complete). Application of intravenous contrast media facilitates the interpretation of postoperative examination of the pituitary gland as well as comparison with preoperative examinations and the knowledge of the intraoperative procedure.

Adenoma↗
PubMed1994

[MR tomography and bone marrow scintigraphy in the screening of skeletal metastases in patients with breast carcinoma].

46 patients with recently diagnosed carcinoma of the breast were included in a prospective comparative study of MRI and bone marrow scintigraphy. The aim of the study was to compare these procedures within a histologically unified patient collective. It was shown that MRI was superior to bone marrow scintigraphy in respect of sensitivity (92% vs 58%) and specificity (97% vs. 85%), although only about three quarters of the marrow spaces are examined by MRI screening. Bone marrow scintigraphy suffered particularly from a relatively high number of false positive findings (haemangiomas, degenerative changes). MRI remains the method of choice for investigating the bone marrow.

Bone Marrow↗
PubMed1994

[Evaluation of rapid gradient-echo and turbo-spin-echo sequences in MRT of focal liver lesions using 0.5 tesla].

The value of rapid T1- and T2-weighted fast field (T1-FFE, T2-FFE) gradient-echo sequences and T2 weighted turbo-spin echo (TSE) sequences in the diagnosis of focal liver lesions using 0.5 Tesla was compared with conventional spin-echo sequences (SE). Amongst 88 liver lesions T1-SE sequences showed 98%, T2-TSE sequences showed 92%, T2-SE sequence showed 84%, T1-FFE sequence showed 78% and T2-FFE sequence showed 69%. Direct comparison has shown that TSE sequences are able to demonstrate significantly more lesions (p < 0.05) than T2-SE sequences. Quantitative assessment has shown that the tumor/liver contrast/noise ratio in the T1-SE sequence was 118% higher than in the T1-FFE sequence (p < 0.001). Comparison of T2 weighted sequences has shown that the tumour/liver contrast/noise ratio was 45% higher in the TSE sequence than in the T2-SE and 239% higher than in the T2-FFE sequence (p < 0.001). The results indicate that the TSE sequence should be used instead of the conventional T2-SE sequence because of the reduced time (about 40%), due to improved image quality and increased demonstration rate of liver lesions. Neither T1-FFE nor T2-FFE are suitable, when using moderate field strength, to replace T1-SE or TSE sequences.

Adenocarcinoma↗
PubMed1994

Mitochondrial encephalomyopathy: correlation of P-31 exercise MR spectroscopy with clinical findings.

PURPOSE: To evaluate the sensitivity of standardized exercise phosphorus-31 magnetic resonance (MR) spectroscopy in screening for subclinical muscle involvement in mitochondrial encephalomyopathy and to estimate if changes seen at biopsy have functional consequences. MATERIALS AND METHODS: Exercise MR spectroscopy was performed in 52 examinations of 18 healthy volunteers and 14 patients with defects of mitochondrial respiratory chain enzymes. Calculation and kinetic analysis of the phosphocreatine (PCr) index and pH time courses were standardized with a microcomputer program. RESULTS: PCr index scores and conventional test scores matched in 10 of 14 cases. No obvious correlation existed between pH parameters and clinical score. Muscle affection, according to pH parameter score, was rated moderate (n = 3), severe (n = 1), or maximum (n = 2) in six of 14 cases in which clinical test scores showed only mild affection. CONCLUSION: Exercise MR spectroscopic PCr index parameters provide diagnostic information on skeletal muscle involvement in patients with mitochondrial encephalopathy. The sensitivity of the PCr index parameter seems equal or superior to that of conventional diagnostic tests. The role of pH parameters, however, has yet to be defined.

Adult↗
PubMed1994

Cerebral MR in ophthalmoplegia plus.

PURPOSE: To evaluate MR patterns in ophthalmoplegia plus and correlate them with clinical symptoms. METHODS: MR was performed on a 1.5-T whole-body scanner with T2-weighted gradient-echo and spin-echo images. The retrospective analysis included 19 patients with clinically established diagnoses of ophthalmoplegia plus. RESULTS: Two types of cerebral MR abnormalities were found in ophthalmoplegia plus: brain atrophy and hyperintensities restricted to the white matter and basal ganglia, which appeared as either focal or diffuse areas of high signal intensity and were of strictly supratentorial location. No specific distribution was found. These findings differ markedly from infarction-like lesions found in mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes. CONCLUSIONS: MR is sensitive for the detection of central nervous system involvement in ophthalmoplegia plus, but findings are nonspecific. However, cerebral MR in ophthalmoplegia plus is different from other mitochondrial encephalomyopathies and underlines the clinical differentiation of mitochondrial encephalomyopathies.

Adolescent↗
PubMed1994

Disseminated bone marrow metastases from primary breast cancer: detection and follow-up by radioimmune bone marrow scintigraphy.

Bone scintigraphy of a 40-yr-old patient suffering from primary breast cancer suggested the possibility of diffuse metastases. Bone marrow scintigraphy using 99mTc-labeled monoclonal antibodies (BW 250/183) demonstrated diffuse destruction of bone marrow due to metastatic disease and consecutive bone marrow extension. Bone marrow scintigraphy was highly sensitive in detecting progression of disease in this asymptomatic patient.

Adult↗
PubMed1993

Ultrasound image properties influenced by abdominal wall thickness and composition.

The influence of different examination conditions on the ultrasound B-scan was investigated using a tissue-mimicking phantom and a computerized ultrasound system. Several fat-muscle combinations simulated differences in abdominal wall thickness and composition. The analysis of the ultrasound images was performed by use of statistical parameters applied in ultrasound tissue characterization, thereby the influence of the abdominal wall thickness and composition on the ultrasound image brightness, microtexture, and macrotexture (image sharpness) was studied. An increasing fat path caused a decrease in ultrasound image brightness and microtexture. The macrotexture was largely unaffected. Muscle tissue alone had a weak influence on the microtexture parameters. Our results show that an increase in the fat layer of the abdominal wall causes a darker, unsharp image and may lead to false diagnoses, especially in adiposity. Furthermore, fat-muscle combinations caused a decrease in image brightness and contrast. The decrease in these image properties was dependent on the thickness of the combination as well as on the frequency of the transducer. The effects were stronger for high-frequency transducers.

Abdominal Muscles↗
PubMed1993

[Differentiating between tumor and implant material in the postoperative sella using MRT].

MRT criteria have been developed to distinguish between tumour and implant material following examination of 50 patients who had transsphenoidal hypophysectomies for tumours. Judgements were based on the postoperative hormonal status and the operation notes. Following contrast injection of Gd-DTPA and using T1 weighted spin-echo sequences, implant material appeared as sandwich-like, linear or circular structures. Residual recurrent tumour produced homogenous or non-homogenous aspects without marginal enhancement in 84% of cases. Postoperative displacement of the infundibulum to the opposite side was observed in 73% of patients with tumour remnants. Sensitivity of MRT was 70%, specificity 95%. There was a positive predictive value of 94% and a negative predictive value of 72% with an accuracy of 81%. This provides assistance in differentiating between tumour remnants and implant material. MRT is recommended as a method of examination for hypophyseal tumours to evaluate the success of surgery and where there is clinical doubt concerning residual or recurrent tumour.

Adenoma↗
PubMed1993

[Metabolic studies of the calf musculature with 31P-MR spectroscopy in arterial obstructive disease before and after lumbar sympatholysis].

In 9 patients with arterial occlusive disease of grade IV according to Fontaine, energy metabolism was measured in the calf muscle during rest, before and after lumbar sympatholysis, by means of 31phosphorus MR spectroscopy. The concentration of inorganic phosphate (Pi) and phosphocreatine (PCr) relative to high energy phosphates, as well as the pH value in muscle cells were assessed, and the quotient Pi/PCr was calculated for estimation of energy reserves. Before sympatholysis, normal concentrations of the energy suppliers ATP and PCr were unexpectedly found in combination with reduced cellular energy reserves. After lumbar sympatholysis, in most cases no significant changes of muscle energy metabolism were detected. Independent of the muscle energy supply, a slight increase in energy supply without returning to normal values was found in only three patients. In most patients the clinical symptoms had improved at least to some extent.

Adult↗
PubMed1993

Recurrent rectal cancer: diagnosis with dynamic MR imaging.

PURPOSE: To evaluate whether dynamic magnetic resonance (MR) imaging can increase the diagnostic accuracy in suspected local recurrence of rectal carcinoma. MATERIALS AND METHODS: Eighteen patients (seven men, 11 women, aged 26-78 years) with 19 suspect lesions were examined. T1-weighted (pre- and postcontrast) and T2-weighted spin-echo images were read by three observers. Computed tissue-specific enhancement parameters were obtained and displayed on gray-scale images (pharmacokinetic mapping). RESULTS: Reading of the spin-echo images yielded a sensitivity of 91%-100% (confidence interval, 67%, 100%), a specificity of 29%-43% (12%, 67%), and an accuracy of 71%-75% (48%, 91%). Analysis of the MR data showed greater (P = .0038) and faster (P = .0018) enhancement of malignant lesions (n = 12) compared with benign lesions (n = 7). CONCLUSION: Pharmacokinetic mapping of dynamic MR imaging data allows in vivo insight into tissue physiopathology, helping differentiate benign from malignant pelvic lesions in rectal cancer.

Adult↗
PubMed1993

[Magnetic resonance tomography in epilepsy].

The most important causes of focal epilepsy are hippocampal sclerosis, circumscribed tumors, vascular malformations, trauma and perinatal damage. At the moment MRI is the best radiological imaging modality for localizing and characterizing a focus. In many cases, however, even MRI is negative. Especially in hippocampal sclerosis the diagnostic role of MRI is still not well established. Diagnostic criteria are side differences with hippocampal atrophy and circumscribed signal increase on T2-weighted images of the affected temporal lobe. Circumscribed lesions caused by tumors or vascular malformations are demonstrated very reliably by paracoronal T2-weighted sequences. Routine administration of the paramagnetic contrast material Gd-DTPA is not necessary.

Adolescent↗
PubMed1993

["Spectroscopic imaging." A new MR technique in the diagnosis of epilepsy?].

The technique of magnetic resonance spectroscopy fuses spectroscopic methods with the two-dimensional illustration of the metabolite concentrations by parallel acquisition of multiple single voxels from small tissue compartments. Therefore it is not necessary to define a voxel of interest before data acquisition. The interpretation of metabolite images is much easier than the analysis of single spectra, and metabolite concentrations on the right and left sides can be compared. The method has already proved reliable for brain tumors. The application of the procedure to patients suffering from epilepsy is described here in for the first time. Even in the temporal region, where most epileptogenic foci have their origin, one can obtain metabolite images of diagnostic quality without susceptibility artifacts. The epileptogenic focus is lateralized correctly, in accordance with electrophysiological and surgical evaluation, even in those cases where standard magnetic resonance imaging is normal. According to our preliminary findings the epileptogenic focus is characterized by a signal loss of N-acetyl-aspartate and creatine.

Adult↗
PubMed1993

[Intracranial ECoG electrodes. Location determination using three-dimensional reconstruction of MR data of the brain as a component of the presurgical diagnosis of epilepsy].

Subdural strip electrodes or intracerebral electrodes are required in order to precisely localize epileptic foci, which is mandatory for epilepsy surgery. The subdural electrodes are inserted via a borehole and thus precise positioning cannot be directly monitored. Therefore, the location of the electrodes in relation to the gyri and sulci has to be determined by imaging techniques. In this study, a three-dimensional magnetic resonance imaging (3D MRI) technique was used for visualization of intracranial EEG electrodes. A 3D gradient echo sequence with thin slices of 1 mm is required for the assessment of the gyral anatomy of the brain surface. Using a short repetition time of 30 ms good image quality within an acceptable acquisition time of about 15 min was possible. Post-processing with 3D surface reconstruction was performed using a Sun workstation. Three-dimensional reconstruction allows a more precise delineation of the localization of the EEG electrodes and the simultaneous display of the adjacent brain structures. Misplacement of intracranial electrodes is readily detected. 3D MRI with 3D surface reconstruction proved superior to 2D imaging and CT for the assessment of EEG electrode localization.

Electrodes↗
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↗
PubMed1992

[Manganese-DPDP in the MR tomography of malignant liver tumors. The initial results with a new hepatobiliary contrast agent].

The new hepatobiliary contrast agent Mangan-DPDP, unlike extracellular Gd-DTPA, leads to a constant increase in signal intensity of normal liver tissue in MR imaging of the liver which lasts at least for 30 minutes. In 19 patients with malignant liver tumors there was no difference in the contrast between tumor and liver when using a dose of 5 or 10 mumol/kg. Contrast enhanced T1-w SE- and T1-w GE sequences show a significant increase in tumor/liver contrast compared with T1-weighted unenhanced sequences. This increase was also significant when compared with T2-w SE sequences. In 16% additional focal lesions were detected on the enhanced scan.

Adult↗
PubMed1992

[MR venography in deep venous thromboses of the leg and pelvis. A comparison of 2D single layer images and 3D MIP reconstructions with phlebography].

A total of 22 MR venograms were performed in 7 volunteers and 15 patients suspected of deep vein thrombosis of the lower limb and pelvis. MR findings were compared to conventional venography in all patients. MR venography is a reliable method for the exclusion of thrombosis proximal to the popliteal vein. In the calf veins, diagnosis of thrombosis is not yet reliable. For MR venography 2D-time-of-flight-inflow-technique and secondary 3D-MIP reconstructions were used and compared to each other. With both methods there were no false negative results in comparison to conventional venography. 2D single slice MR venography showed two false positive results in iliac and one in popliteal vein. MIP 3D reconstructions led to seven false positive results (three iliac, two femoral, two popliteal). The exclusive interpretation of MIP-3D reconstruction is not reliable for decision-making in deep venous thrombosis.

Adult↗