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Biomedical subjects

W A Kaiser

Publications and source records attributed to W A Kaiser.

At least 127 records · Page 7Linked to original sources
PubMed1994

Dynamic magnetic resonance imaging of the contralateral testis in patients with malignant tumor of the testis.

OBJECTIVES: Dynamic magnetic resonance imaging (MRI) was tested using a dynamic technique to evaluate the possibility of differentiating between normal contralateral testes and testes with a carcinoma in situ. METHODS: Since March 1990, 20 volunteers and 21 patients with a malignant tumor of the testis were examined in a field strength of 1.5 Tesla (Philips Gyroscan S15) with a multislice T1-weighted fast field echo sequence before and every 63 seconds after the injection of 0.1 mmol/kg gadolinium-diethylenetriamine pentaacetic acid. RESULTS: Significant differences (p < 0.001) in signal changes of contralateral testes were detected in dynamic MRI. This increased signal enhancement is detected even 45 months after orchiectomy in the contralateral testes. The signal increase is reduced in follow-up controls. These observations are explained by an increased perfusion which seems to be induced after a postoperative irritation, an unspecific inflammation, or postoperative bleeding. CONCLUSIONS: To avoid false-positive diagnoses of tumors or carcinomata in situ in contralateral testes, these increased enhancements caused by postoperative reactions have to be kept in mind.

Adult↗
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

False-positive results in dynamic MR mammography. Causes, frequency, and methods to avoid.

Numerous studies have shown that MR mammography (MRM) yields the highest sensitivity in the diagnosis of early and small breast cancers. The multifocality of breast cancers can be recognized only with MRM. This article evaluates the false-positive results of dynamic MRM. The causes of false diagnoses are also examined and ways to avoid them are suggested.

Breast↗
PubMed1994

[Differentiation of testicular diseases using dynamic MRT].

Sonography and colour-coded Doppler sonography are the methods of first choice in diagnosing tumors of the testes. The present study aimed at resolving whether dynamic MRT can improve diagnostic relevance in diseases of the testes compared with conventional spin echo images. The testes of 20 healthy volunteers and of 16 patients of the Department of Urology of the University of Bonn were examined by means of MR tomography. Within 12 hours after MR tomography the patients were surgically explored, biopsied and if necessary orchiectomised. Results obtained with the volunteers were uniform and well reproducible, independent of external influences. On comparing the maximal enhancement curves of the examined various testicular tumors with the standard values established by examining the healthy volunteers, the curves obtained with the malignant testicular tumors were always clearly above the chosen confidence range of 3 standard deviations so that malignancy diagnosis was easy. However, the degree of maximal enhancement did not enable us to arrive at a conclusion in respect of the tumor type or the degree of malignancy. The greatest enhancement occurred with the tumor of Sertoli's cell which could thus be clearly differentiated against the other malignant testicular tumors. Due to masking of the gadolinium effect by haemosiderin deposits, haemorrhagica in the tumor tissue should be excluded by means of T2-weighted spin echo sequences before following up a suspicion of malignant testicular tumor. Benign intratesticular changes could be safely separated from malignant findings by means of the maximal enhancement curve lying in the normal range or below the curve of the volunteers. As with other organs, dynamic MR tomography yields definitely more and better information than conventional MR tomography also in the diagnosis of testicular tumours. However, these "pros" do not offset the "cons" of high costs of such examinations, so that both conventional sonography and angiodynography remain the routine methods of choice. Indication for MR examination on suspicion of testicular tumour is therefore confined to cases where sonographic findings are clinically equivocal or technically unsatisfactory.

Adult↗
PubMed1993

[Modern diagnostics of the breast].

A diagnosis of breast cancer as early as possible is most important for a good prognosis. Among previous imaging modalities (mammography, sonography, DSA, thermography, CT) only mammography was able to prove a significant reduction of mortality, but unfortunately only for women above 50 years of age. Magnetic resonance mammography (MRM) is under technical and clinical evaluation for more than 8 years. Special surface coils and a variety of measurement sequences have been tested. By using "dynamic MRM", i.e., the repetitive imaging of the same slices before and at short time intervals after the injection of contrast medium, a high sensitivity (97.3%) and specificity (96.9%) was found in detecting breast cancers of different histology. In this study especially clinically or mammographically difficult cases were included in order to test the efficacy of dynamic MRM. Breast cancer can be proven or excluded with a very high degree of confidence. Conventional mammography had been yielding a vast number of false positive findings. With MRM, therefore, the number of biopsies can be substantially reduced. The remarkable uniformity of the maximum rate of signal enhancement in carcinomas may be explained by the changed vascularisation of malignant tumours based on early tumour angiogenesis. This change in vascularisation can be detected by combining the use of contrast medium with a high contrast sensitive measurement technique. This method seems to be much more reliable than mammographic or sonographic procedures. MRM needs further technical improvements. Since breast cancer is still the most frequent cause of cancer in women in the Western hemisphere, MRM should be used in all cases where is a discrepancy among radiographic, sonographic or clinical findings. However, MRM examinations should be performed only by experienced examiners, since a variety of pitfalls must be avoided.

Adenofibroma↗
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

[Initial results of in vivo 31P-NMR spectroscopy of the spleen in patients with splenomegaly].

In-vivo 31P-NMR spectroscopy of the spleen was carried out in 15 patients with splenomegaly from various causes (Hodgkin's disease, non-Hodgkin lymphoma, polycythaemia vera, chronic lymphatic leukaemia, chronic myeloid leukaemia). Volume selection was with the ISIS technique, voxel size was between 3 x 5 x 5 and 8 x 6 x 7 cm3. There was a markedly elevated (PM+Pi)/beta-NTP quotient (mean 3.41 with a standard deviation of 0.37) (p < 0.001) and raised PDE/beta/NTP quotient as compared with 8 normals, who showed an (PME+Pi)/beta-NTP quotient of 2.32 and a PDE/beta/NTP quotient of 1.11. These raised quotients were interpreted as indicating increased membrane phospholipid metabolism due to increased cell turnover. The data suggest there may be some clinical value in performing 31P-NMR spectroscopy for defining splenic involvement in myeloproliferative diseases but further confirmatory studies will be necessary.

Adult↗
PubMed1993

[MR mammography].

For a favorable prognosis breast cancer must be diagnosed as early as possible. Among the available imaging modalities (mammography, sonography, DSA, thermography, CT) only mammography has been able to demonstrate a significant reduction in mortality, but unfortunately only for women above 50 years of age. Magnetic resonance mammography (MRM) has been under technical and clinical evaluation for more than 10 years. Special surface coils and a variety of measurement sequences have been tested. By using "dynamic MRM," i.e., repetitive imaging of the same slices before and at short time intervals after the injection of a contrast medium, high sensitivity (98.9%) and specificity (97.2%) was found in detecting breast cancers of different histologies. In this study, especially clinically or mammographically difficult cases were included in order to test the efficacy of dynamic MRM. Breast cancer can be proven or excluded with a very high degree of confidence. A vast number of false-positive findings that plague conventional mammography will no longer require biopsy. The remarkable uniformity of the maximum rate of signal enhancement in carcinomas may be explained by the altered vascularization of malignant tumors based on early tumor angiogenesis. This change in vascularization can be detected by combining the use of contrast medium with a highly sensitive measurement technique.(ABSTRACT TRUNCATED AT 250 WORDS)

Breast Neoplasms↗
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

[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↗
PubMed1992

[MR mammography in patients at risk].

Dynamic MR mammography (MRM) has high sensitivity for the demonstration of carcinomas. 63 carcinomas were examined by this technique and all showed a signal increase of more than 90% 60 seconds after the injection of 0.1 mmol/kg Gd-DTPA and an almost constant signal intensity (carcinoma plateau) for a further 7 minutes. These characteristic changes applied only to active tumour areas and not to necrotic or fibrotic tumour regions. A possible explanation is the altered vascular architecture due to the growth of malignant tumours. In the presence of a suspect mammogram a carcinoma can be excluded with a high degree of certainty in the absence of contrast enhancement. Signal enhancement in 54 histologically proven cases of non-proliferative mastopathy and in 52 cases of proliferative mastopathy could be reliably distinguished from carcinomas (p less than 0.001). In rare cases of proliferative mastopathy the signal changes were suspicious of a carcinoma. Normal signal increase does not exclude proliferative mastopathy with certainty. Patients with increased contrast uptake should be regarded as "high-risk" and examined at regular intervals.

Breast↗
PubMed1992

[In-vivo 31P-NMR-spectroscopy in patients with dilated cardiomyopathy].

In vivo 31P-NMR spectra of heart muscle were obtained in 7 patients with dilating cardiomyopathies and in 10 normal subjects, using an ISIS technique with a 1.5 Tesla body scanner (Philips Gyroscan S15) and the results of the two groups were compared. These results were easily reproduced. In patients with cardiomyopathy there was a significant (p < 0.05) reduction of the PCr/ATP ratio as an expression of abnormal energy metabolism. Two patients with mild clinical symptoms and only slightly reduced functional measurements showed no significant changes in the 31P-NMR spectrum. The patients with the largest reduction of the PCr/ATP index also showed the most marked changes in functional measurements. The PCr/ATP ratio (as also suggested by animal experiments) appears to be a suitable non-invasive indicator for the diagnosis and staging of myocardial changes in dilating cardiomyopathies.

Adenosine Triphosphate↗
PubMed1992

MRI and MRS of the skeletal muscle.

Magnetic resonance imaging and spectroscopy were performed in several types of muscular disorders. In acute stages, 31P spectra showed remarkable changes compared with normals, and T2-weighted MR images were most sensitive in delineating the pathology. Fatty degeneration of muscle in chronic diseases yielded high contrast in T1-weighted MRI and could be quantified by 1H-MRS including the chemically selective determination of proton T1 values. In order to evaluate true abundance rations of phosphorus metabolites, 31P relaxation times T1 of muscle were measured by localized inversion recovery.

Acute Disease↗
PubMed1990

[A new multislice measurement sequence for the complete dynamic MR examination of the larger organs: application to the breast].

Our experience indicates that the most accurate information concerning abnormalities in the breast is obtained by a dynamic technique, in which the signal intensity before and after contrast medium injection is compared. Up to the present, only a small number of sections (1 to 5) could be obtained by dynamic MR, so that only 30-50% of the breast, depending on its size, could be examined. The availability of gradient systems, with rapid switching and high gradient amplitude and duty cycle, makes it possible to obtain a larger number of sections. A new multi-section gradient echo sequence is described, which enables one to examine the entire breast using a dynamic technique (136 images of both breasts in 14.4 minutes). Subsequent automatic post-processing, using a graphic programme, results in quantitative evaluation of the contrast images. This new sequence can be applied to dynamic MR investigations of all large organs.

Breast↗
PubMed1989

[Magnetic resonance tomography of the breast. The results of 253 examinations].

Requirements for diagnostic magnetic resonance imaging (MRI) of breast disease were defined on the basis of 253 examinations over 4 1/2 years. The results were compared with those of mammography in 207, with histological findings in 145 cases. Examinations after injection of 0.1 mmol/kg Gd-DTPA (gadolinium diethylene-triamino-penta-acetate) and measurement of the same sections at short intervals proved to be the most informative MRI technique for the differentiation of benign and malignant changes. Carcinomas had a rapid initial rise in signal of more than 90% over the pre-injection level within one minute of contrast-medium administration. In 163 of 207 cases MRI provided information additional to mammography (confirmation or exclusion of a carcinoma; exact localization of a malignant process; differentiation between carcinoma and scar tissue; diagnosis of a tumour close to the thoracic cavity; changes near a prosthesis). Analysing only the examinations done with contrast-medium (144), there was a 99% sensitivity. There have been no false-negatives so far. Despite the high cost and time required, MRI of the breast is indicated when mammography, ultrasound and clinical features provide unclear and (or) discrepant findings.

Breast↗
PubMed1989

[A prototype double coil for MR breast measurement].

The first application of a double coil for routine MR mammography is described: by this method it is possible to examine both breasts simultaneously. This is important in order to halve the time of the examination and to allow comparison of the two breasts during dynamic contrast studies. The reduction in signal-to-noise ratio, compared with a single coil and flow artifacts of the heart do not interfere with diagnosis. The axillary region is better shown than with a single coil. Examination of 22 patients with subsequent histological control has shown that the information about signal increase after the injection of Gd-DTPA obtained from single coil can be applied equally to the double coil.

Axilla↗