Search PubMed⌕ Search

Biomedical subjects

M Reiser

Publications and source records attributed to M Reiser.

At least 415 records · Page 23Linked to original sources
PubMed1996

Effects of partial volume and phase shift between fat and water in gradient-echo magnetic resonance-mammography.

The signal modulations caused by partial volume effect and phase shift between fat and water signal in gradient-echo magnetic resonance mammography (GRE MR-mammography) have been calculated. Based on this, the theoretical sensitivity and specificity of GRE MR-mammography has been investigated considering different evaluation methods for the gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA)-based signal enhancement. The results show that both in- and out-of-phase sequences suffer from partial volume effects in voxels that contain both fat and water. This can decrease sensitivity to Gd-DTPA uptake in small, fat-embedded lesions or in pathology that contains fat interspersed histologically. Additionally, out-of-phase sequences can suffer from phase cancellation effects that can further decrease their sensitivity to Gd-DTPA uptake. In the worst case signal can actually decrease during Gd-DTPA influx. Determination of enhancement relative to the baseline value can decrease the specificity of GRE MR-mammography in the out-of-phase condition and decrease the sensitivity in the in-phase condition. These effects are less pronounced when enhancement is calculated relative to fat. These effects need to be understood since Gd-DTPA uptake is the prime indicator of malignancy in MR-mammography.

Breast↗
PubMed1996

[Computerized tomography of malignancies of the oral cavity, the oropharynx and hypopharynx and invasiveness].

Carcinomas of the oral cavity, oropharynx and hypopharynx represents 5% of all malignant neoplasms. The vast majority, over 90%, are squamous cell carcinomas; less common are lymphomas and tumors of the minor salivary glands. In general, the clinical findings already suggest the presence of a tumor. Therefore, the role of imaging is precise tumor localisation and staging of the malignancy. CT is still the gold standard, although MRI is gaining more importance. We present the CT appearance of most frequent malignancies of the oral cavity, oro- and hypopharynx, discussing briefly the pertinent anatomy.

Carcinoma, Squamous Cell↗
PubMed1996

[Value of fat signal suppression MRI pulse sequences for diagnosis of malignant tumors in the area of the head-neck].

PURPOSE: Evaluation of frequency-selective fat saturation (FS) and short-tau inversion recovery (STIR) fat suppression (FU) in MRI of patients with malignant head and neck tumors. METHODS: Forty-five patients with biopsy-proven carcinomas of the extracranial head and neck were examined with MRI at 1.0 T. A T2-weighted TSE sequence with and without STIR-FU and a T1-weighted SE sequence with and without FS were compared in axial slices. RESULTS: STIR-FU was successful in all and FS in 85-88% of the head examinations (nasopharynx, sinuses, oropharynx, and oral cavity) and 33-46% of the neck examinations (hypopharynx and larynx). When visualization and delineation of tumors were ranked on a four-point scale (0-3), respective mean values for images with/without FU or FS were 2.6/1.9 for T2-TSE in all examinations, 2.2/1.7 (nasopharynx and sinuses) and 1.3/1.4-1.6 (oropharynx, oral cavity, hypopharynx, and larynx) for T1-SE without contrast media administration (CM) and 2.3/2.1 (nasopharynx and sinuses) and 2.4-2.5/1.9-2.0 (oropharynx, oral cavity, hypopharynx, and larynx) with CM. CONCLUSIONS: STIR-T2-TSE was a technically reliable pathfinder for localization and extension of both tumors and lymph nodes. FS-T1-SE was technically unreliable in examinations of the hypopharynx and larynx. With CM, FS-T1-SE was most useful for MRI of carcinomas of the oral cavity and oropharynx. In the nasopharynx and sinuses, T1-SE with CM and FS-T1-SE with or without CM were equal for tumor visualization and delineation.

Adipose Tissue↗
PubMed1996

[Initial results with MRI-controlled laser-induced interstitial thermotherapy of head and neck tumors].

Laser-induced interstitial thermo-therapy (LITT) was introduced as a minimally invasive form of therapy for tumors in different anatomic regions. However, in the orofacial region, it has not been used so far for inoperable T4 carcinomas. Since vascular and neural structures are often close to the tumor or are even involved, online monitoring of LITT is necessary. The aim of our study was to establish a method of monitoring LITT with MRI (magnetic resonance imaging) in the orofacial region. Five patients with T4 carcinomas of the orofacial region underwent LITT under anesthesia. A 1.5 T whole-body imager with a circular polarized head coil was used. Before and after the intervention, the region of interest was studied using T1- and T2-weighted sequences in axial and coronal planes, with and without contrast enhancement (intravenous Gd-DTPA). Temperature distribution was monitored with a T1-weighted 2D-FLASH (fast low angle shot) sequence. The positioning of the optical fibers was monitored with MRI. Nd:YAG laser equipment was used for laser application. The necrosis was best seen on contrast-enhanced MRI. Immediately after LITT, the outcome could be determined by MRI. We proposed that MRI-guided LITT be used for neoplasms in the orofacial region at advanced stages.

Aged↗
PubMed1996

[Functional MRI of the pharynx in obstructive sleep apnea using rapid 2D FLASH sequences].

Functional imaging of the pharynx used to be the domain of cineradiography, CT and ultrafast CT. The development of modern MRI techniques led to new access to functional disorders of the pharynx. The aim of this study was to implement a new MRI technique to examine oropharyngeal obstructive mechanisms in patients with obstructive sleep apnea (OSA). Sixteen patients suffering from OSA and 6 healthy volunteers were examined on a 1.5 T whole-body imager ("Vision", Siemens, Erlangen Medical Engineering, Germany) using a circular polarized head coil. Imaging was performed with 2D flash sequences in midsagittal and axial planes. Patients and volunteers were asked to breathe normally through the nose and to simulate snoring and the Mueller maneuver during magnetic resonance imaging (MRI). Prior to MRI, all patients underwent an ear, nose and throat (ENT) examination, functional fiberoptic nasopharyngoscopy and polysomnography. A temporal resolution of 6 images/s and an in-plane resolution of 2.67 x 1.8 mm were achieved. The mobility of the tongue, soft palate and pharyngeal surface could be clearly delineated. The MRI findings correlated well with the clinical examinations. We propose ultrafast MRI as a reliable and non-invasive method of evaluating pharyngeal obstruction and their levels.

Adult↗
PubMed1996

[A method of computer-assisted, 3-dimensional subtraction angiography using spiral roentgen computerized tomography].

The objective of this study was to develop a method for 3D subtraction CT angiography and to optimize the visualization after semi-automatic segmentation. Ten patients with aneurysms of the abdominal aorta were examined using spiral CT. To reconstruct the vessels, as well as adjacent organs such as the liver and kidneys, one image data volume was acquired before and after injection of the contrast agent. The CT scans were obtained with a Siemens Somatom Plus 4. To improve the results of automatic segmentation, as well as visualization by maximum intensity projection (i.e. removal of bony structures), subtraction of both image volumes is necessary. However, small translation shifts disturb the subtraction process and produce artificial contours. To calculate the disparities along the three coordinate axes of two corresponding image volumes, a cepstrum filter is applied to a pair of image volumes. After detection of the disparities, which manifest as bright spots, the real shift of the two subsignals can be calculated. Translation of the corresponding image volume pairs to their correct positions improves the subtraction process. In all cases the size of the aneurysm and the abdominal organs could be better segmented and visualized. Application of the cepstrum filter and subtraction of the image volumes before and after contrast medium injection completely removes the bony structures in the image data and results in superior visualization results.

Angiography, Digital Subtraction↗
PubMed1996

[MRI of the pancreas: value, technique and applications].

MR imaging of the pancreas is compromised by several problems: motion artifacts from breathing, cardiac and vascular pulsation, and bowel peristalsis. These limitations can be overcome by modern scanner- and software technology. In the meantime, MRI of the pancreas can compete with well established methods as ultrasound and computed tomography (CT). In addition, new sequences provide imaging modalities comparable to angiography and ERCP. In the future, the value and the efficacy of MRI in comparison to CT, and its clinical impact has to be evaluated in clinical studies. In this article, we review the technical development of MRI of the pancreas, and discuss its clinical use.

Artifacts↗
PubMed1996

[MRI of the pancreas: radiologic-pathologic correlation].

The typical MRI features of the most common pancreatic diseases, such as pancreatitis and adenocarcinoma of the pancreas, have been established. However, even in these common pancreatic disorders, MRI correlation with the underlying pathology is limited for clinical reasons. We emphasize MR-pathological correlation of inflammatory and neoplastic pancreatic changes, including pancreatitis, adenocarcinoma, acinar cell carcinoma, rare cystic and solid pancreatic neoplasms, and islet cell tumors. By highlighting the correlation of key pathological features with MR findings, a better understanding of the MR appearance of pancreatic pathology can be provided. In addition, MRI may prove a powerful tool in detection and characterization of pancreatic tumors.

Adenocarcinoma↗
PubMed1996

[Techniques and applications of MR pancreatography in comparison with endoscopic retrograde pancreatography].

Using heavily T2 weighted sequences, magnetic resonance tomography allows the delineation of the pancreatic duct system with high contrast. The development of fast and ultrafast imaging sequences results in a variety of different technical approaches already published. Aim of this article is the review of the different approaches and results published. In addition, we compare MRP in 34 patients with results of ERP using a snap-shot sequence approach. In this study, MRP has a sensitivity of 83.3% a specifity of 90.9% and accuracy of 83.3% regarding detection of duct changes like stenosis, occlusion and duct dilatation. Our results indicate, that MR-pancreaticography can be a valuable adjunct to MR-imaging of the pancreas.

Adult↗
PubMed1996

[Differentiation of solitary pulmonary coin lesions by high-resolution computerized tomography].

PURPOSE: The aim of this prospective study was not to describe individual morphological findings in benign and malignant solitary intrapulmonary nodules; it was instead to examine in a critical manner the indications for differentiation found in the literature in order to facilitate safe differential diagnosis of benign and malignant nodules. PATIENTS AND METHODS: A total of 64 solitary pulmonary nodules were examined with high-resolution computed tomography and correlated with histological findings. Only lesions that had been removed by surgery were used. No lesion was excluded on the grounds of size. RESULTS: Useful characteristics for the differentiation of benign from malignant pulmonary nodules were: diameter and density of the lesion, air inclusion, unsharp and dystelectatic margin, the presence of spicules, length of spicules, spicules extending to the visceral pleura, pleural tail sign and cirumscribed pleural thickening. CONCLUSION: For the differentiation of benign and malignant solitary pulmonary nodules meticulous assessment of the margin of the nodule is necessary. Using the criteria mentioned, a sensitivity of 85% and a specifity of 78% can be achieved for the identification of malignant pulmonary nodules. Since it was not possible to differentiate between benign and malignant nodules with certainty using imaging methods, the chance of patient survival could only be promoted by early surgery.

Adult↗
PubMed1996

[MRI monitoring before, during and after interstitial laser-induced hyperthermia of benign prostatic hyperplasia. Initial clinical experiences].

PURPOSE: To assess the clinical value of MRI in patients with benign prostatic hyperplasia (BPH) before, during, and after interstitial laser-induced thermotherapy (LITT) of the prostate. METHODS: Ten patients with symptomatic BPH had MRI examinations of the prostate 48 h before and after LITT. Online monitoring with MRI at 1.5 T of interstitial Nd:YAG laser energy deposition in the prostate was performed in two patients, repeating a T1-weighted FLASH sequence (TR 100 ms, TE 5 ms, flip angle 90 degrees) every 20 s. Follow-up MRI examinations 2-3 weeks, 6-8 weeks, and 6-12 months after LITT were carried out in eight patients, using T2-weighted FSE images and contrast-enhanced T1-weighted SE images. RESULTS: The prostate was well delineated in all patients on T2-weighted FSE images, with a rather homogeneous peripheral gland and an inhomogeneous central gland. Volume measurements yielded reproducibilities of 3.2%-4.7%. Signal intensity in the FLASH sequence decreased during LITT, both in the prostate in vivo and in specimens of bovine prostate and seminal vesicles in vitro, with signal developments running in parallel. Areas of energy deposition and signal alteration were not sharply delineated. The latter margin of the laser-induced lesions could not be predicted from the FLASH images, while the tip of the laser fibre was easily recognized. Contrast-enhanced T1-weighted MR images immediately after LITT clearly demarcated low signal intensity laser lesions from high signal intensity surrounding prostate tissue. Follow-up examinations showed a decrease of 20% of prostate volume over a period of 6-12 months after LITT. Correlation between prostate volume development and lesion volume alteration was 0.85-0.90 (P = 0.002-0.007) at all follow-up times. CONCLUSIONS: MRI allows rather precise recognition of intraprostatic alterations after LITT, including volume changes over a period of up to 1 year after therapy that can be predicted immediately after LITT. While laser energy deposition in the prostate can be monitored by MRI with T1-weighted FLASH sequences as a function of temperature alteration, it is not possible to determine the lesion margins immediately from the FLASH images. Online temperature development map generation will be necessary to influence on-going LITT procedures with MRI.

Aged↗
PubMed1996

Assessment of normal patellar cartilage volume and thickness using MRI: an analysis of currently available pulse sequences.

OBJECTIVE: The objective of this study was to analyse the potential of magnetic resonance imaging for valid determination of patellar cartilage thickness, comparing currently available pulse sequences. DESIGN: In six patients and one cadaver the cartilage was repetitively imaged employing three spin-echo and six three-dimensional gradient-echo sequences. In the cadaveric specimen the total volume and the regional distribution of cartilage thickness were assessed and compared with the values obtained from anatomical sections by image analysis. RESULTS AND CONCLUSIONS: The FLASH and fat-suppressed FLASH sequences allowed the most accurate determination of the cartilage volume and thickness. Fat-suppression considerably increased the contrast of the cartilage to the synovial fluid, fat and bone marrow, yielding higher reproducibility of the volumetric measurements. The remaining difference from the anatomical volume and thickness may be because the calcified cartilage is not delineated by magnetic resonance imaging.

Adult↗
PubMed1996

Degenerative disk vascularization on MRI: correlation with clinical and histopathologic findings.

OBJECTIVE: This prospective study was designed to determine the MRI features, clinical significance, and correlation to histopathologic findings of secondary vascularized degenerative intervertebral disks. MATERIALS AND METHODS: Fifty-three patients with localized painful spine syndrome were investigated prospectively by contrast-enhanced MRI. Pain was not predominantly radiating and there was no clinical evidence of spinal infection. In all patients sagittal SE T1-weighted, fast SE T2-weighted or turbo-STIR, and T1-weighted frequency-selective fat-suppressed images were obtained. RESULTS: We identified 37 vascularized disks in 26 patients. In 18 patients the changes had occurred spontaneously, in 6, the affected disk had been operated on previously, and 2 patients had spondylolisthesis. In 15 patients, vascularization was accompanied by medullary edema adjacent to the vertebral endplates. In one of the vascularized disks, herniation was also found. In seven patients, ventral diskectomy was performed. Histopathologic findings confirmed disk vascularization in six of seven cases. CONCLUSIONS: Degenerative, band-like disk vascularization is a feature which is associated with local pain. It was demonstrated by contrast-enhanced MRI. Degenerative disk vascularization is an important differential diagnosis to bacterial spondylodiskitis. It can be a cause of pain in patients with postdiskectomy syndrome.

Diagnosis, Differential↗
PubMed1996

Physiological and pharmacological profile of trans-azetidine-2,4-dicarboxylic acid: metabotropic glutamate receptor agonism and effects on long-term potentiation.

In this study, we biochemically analysed the effects of the novel metabotropic glutamate receptor agonist trans-azetidine-2,4-dicarboxylic acid and examined its role in hippocampal long-term potentiation. In cell lines expressing metabotropic receptor 1 or 5 subtypes, the compound stimulated phosphoinositide hydrolysis with EC50 values of 189.4 +/- 6.4 and 32.2 +/- 8.3 microM, respectively. In hippocampal slices, trans-azetidine-2,4-dicarboxylic acid also increased phosphoinositide hydrolysis, yet failed to show any effect on forskolin-stimulated formation of cyclic AMP, even if 1 mM azetidine was applied. Since trans-azetidine-2,4-dicarboxylic acid (20 mM in 5 microliters) injected cerebroventricularly prolongs long-term potentiation induced by weak tetanization, a possible interaction with N-methyl-D-aspartate receptors was investigated using patch-clamp techniques. Neither facilitation of N-methyl-D-aspartate (500 microM) currents nor induction of non-specific currents was observed in the presence of 50 and 500 microM azetidine. Strong tetanus-induced long-term potentiation in the dentate gyrus of freely moving rats was not influenced by azetidine. In combination with the antagonist (R,S)-alpha-methyl-4-carboxyphenylglycine (200 mM in 5 microliters), however, the potentiation was attenuated and returned to baseline within 90 min. Blockade of N-methyl-D-aspartate receptors using 2-amino-5-phosphonopentanoate (20 mM in 5 microliters) prevented the potentiation in controls, but not in the azetidine group, where normal potentiation was observed for both the population spike amplitude and the excitatory postsynaptic potential. These data suggest that (i) trans-azetidine-2,4- dicarboxylic acid is an agonist at glutamate metabotropic receptors; (ii) a facilitation of induction and maintenance of long-term potentiation via N-methyl-D-aspartate receptors seems unlikely; and (iii) pharmacological activation of metabotropic receptors prior to tetanization appears to bypass the N-methyl-D-aspartate receptor dependence of the potentiation. In conclusion, a role for metabotropic glutamate receptors in both short-term and long-term potentiation is indicated by these data.

Animals↗
PubMed1996

[Digital luminescence radiography in comparison with the conventional film-screen technique in diagnosis of fractures].

PURPOSE: The accuracy of digital luminescence radiography was compared with that of conventional film/screen techniques, using animal preparations and clinical examinations. MATERIAL AND METHOD: Fine fissures were made in 8 animal bones and these were examined radiologically. The digital examinations were carried out with and without edge enhancement. 208 patients were examined in a similar way. Film quality and assessment of the fractures were evaluated quantitatively. RESULTS: In no instance did either of the digital methods provide inferior quality when compared with conventional films. ROC analysis for evaluation of fractures in patients, using an experienced radiologist, showed no significant difference between the various methods (ROC areas: conventional 0.947, digital 0.958, digital with edge enhancement 0.943). With a less experienced observer there were significant advantages for both digital methods (ROC areas: 0.851, 0.886, 0.908). CONCLUSION: Our investigation has proved that fractures which are difficult to see can be reliably demonstrated by digital luminescence radiography.

Animals↗
PubMed1996

[Infiltration patterns of plasmacytomas in magnetic resonance tomography].

PURPOSE: To define the different infiltration patterns in the spine in multiple myeloma, in correlation with histological and clinical findings. Quantitative signal evaluation with contrast media (Gd-DTPA). To compare the results in MRI with X-ray films. MATERIAL AND METHODS: 61 patients with proven multiple myeloma and 50 controls were examined (1.0 Tesla, T1-w SE, opposed phase GE images). RESULTS: Five infiltration patterns with different clinical stages were detected: normal bone marrow (11%) in cases of low interstitial marrow infiltration (biopsy), pure diffuse infiltration (25%), focal involvement (33%), combined diffuse/focal infiltration (23%) and a "salt-and pepper" pattern (8%). In diffuse plasmacytoma the 40% signal intensity increase was modification of diffuse infiltration. MRI proved to be more sensitive than radiography. CONCLUSION: MRI is able to show the type and the extension of bone marrow infiltration in multiple myeloma. Diffuse involvement can be objective with gadopentetate dimeglumine.

Adult↗