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Biomedical subjects

R Felix

Publications and source records attributed to R Felix.

At least 307 records · Page 17Linked to original sources
PubMed1997

[A phase-I/II study on the local hyperthermia of cervical N2/N3 lymph node metastases].

BACKGROUND: Patients with advanced lymph node metastases from head and neck tumors at stage N2/N3 (i.e. UICC IV) present a difficult therapeutic problem. Despite combined radio-chemotherapy and hyperfractionated and/or accelerated fractionation regimens, local control of these tumors remains unsatisfactory. For this reason, the value of local radio wave/microwave hyperthermia was examined for this patient group in a phase I/II study.

Adult↗
PubMed1997

[Characteristics of normal cross-sectional anatomy of the skin in high resolution magnetic resonance tomography].

PURPOSE: To characterize human skin qualitatively and quantitatively using high-resolution magnetic resonance tomography (MRT) and to compare skin thickness measurements from MRT and histological specimens. MATERIAL AND METHODS: The skin of 84 persons was examined by use of a 2.5 cm coil in a whole-body tomography (gradient field strength 1.5 T) at a linear resolution of 100 microns. To evaluate the ability to identify various skin structures, following an initial visual description, the signal-noise and contrast-noise ratios were analyzed and the MRT-image compared to the corresponding histological specimen. RESULTS: Using the high-resolution coil, epidermis, dermis and subcutis were discernible. Problem areas included the cheek, distal leg and foot. Reproducible measuring of skin thickness with MRT is possible, but it does not correlate well with conventional histologic measurements.

Adolescent↗
PubMed1997

[Multi-media presentation of radiologic image data with the Internet].

AIM: Recent developments of the Internet (World Wide Web) allow the integration of audio, video, digital film sequences, and three-dimensional data. The applicability of these innovations for medical documentation is demonstrated. METHODS: Our existing software for medical image processing and 3D reconstruction was extended to provide images, film sequences, and complex 3D models in an Internet-compatible data format. RESULTS: The multimedia results of the image processing were integrated into Internet documents. Specialized programs are no longer necessary for visualization. The Internet software allows for user-friendly handling and interactive presentation of the 2D and 3D data. CONCLUSIONS: The Internet offers public-domain software for display of images, audio/video, and 3D data. Thus, the tools of the Internet represent an ideal basis for local hospital information systems, computer-aided medical education, and teleconferencing.

Computer Communication Networks↗
PubMed1997

[Dosage values for characterization of patient exposure in computerized tomography and their significance for risk assessment].

In order to evaluate patients' exposure to radiation in computed tomography, dose quantities such as the computed tomography dose index (CTDI), multiple scan average dose (MSAD) and dose free in air on the axis of rotation are used. The CTDI and the MSAD, derivable from the CTDI, are a good measure for the absorbed doses in the examined volume, but they do not take the biological sensitivity of the organs into account and do not describe the radiogenic risk that is actually relevant for patients and doctors. The dose on the axis of rotation is not an accurate measure of the effective dose and the radiogenic risk. The declaration of a limit for the dose on the axis of rotation should take the different regions into account, in order to guarantee acceptable image quality on one hand and to avoid an unnecessarily high risk on the other side. As physical dose quantities, the CTDI, MSAD and dose on the axis of rotation are useful to characterize and differentiate between programs and systems concerning radiation exposure.

Humans↗
PubMed1997

The Doppler guide wire: clinical applications in neuroendovascular treatment.

The application of Doppler-tipped guide wires to measure blood flow velocity in coronary and peripheral arteries has been described previously as a valuable means of functional assessment in interventional cardiological procedures. In animal studies intravascular Doppler has been used in the cerebrovascular system, and this appears to be an important field of application for this new technique. We used intravascular haemodynamic monitoring by the Doppler guide wire during neuroendovascular procedures in patients with different cerebrovascular diseases and evaluated the clinical feasibility of the method. We found it a safe technique which complements morphological angiographic information with valuable functional data. Further studies may be expected to demonstrate the relation of flow parameters to clinical outcome.

Adult↗
PubMed1997

Registered image subtraction for CT-, MR- and coronary angiography.

Conventional post-processing of digital subtraction angiography (DSA) by 3D spiral CT, 3D MRI and 2D DSA is often hampered by extended artefacts due to patient movements during examination. In this paper an image registration procedure prior to the digital subtraction is introduced allowing an enhanced visualization of the contrast agent. The object displacement is detected by analysis of image deformations in small local regions. The motion pattern is used to compute a new synthetic mask of maximum congruence with the contrast medium image. This new mask image is then used in the subsequent subtraction. The algorithm works fully automatically and does not need any interactive placement of landmarks. Results obtained from subtraction of uncorrected and corrected sequences were compared with each other. The registration procedure provided good results in the suppression of subtraction artefacts and in the enhancement of vascular structures. Results are presented from subtraction of 2D and 3D data from CTA, MR mammography and coronary angiography.

Artifacts↗
PubMed1997

MR anatomy and small lesions of the eye: improved delineation with a special surface coil.

To develop an improved investigation protocol for MRI studies of intraocular lesions, imaging with a small surface coil (diameter 6 cm) was compared with a standard surface coil (diameter 11 cm). Both coils were assessed initially on an eye phantom and then by studying 22 patients with uveal melanoma and similar lesions of the eye. The influence of bandwidth and field or view (FOV) were systematically studied and evaluated quantitatively. A smaller bandwidth improved image quality independent of surface coil size. The subsequent secondary increase in chemical shift artefact was acceptable. Smaller FOVs (60-80 mm) necessitated the use of a smaller surface coil. A smaller bandwidth also proved to be advantageous with the use of the smaller surface coil. In conclusion, a smaller-diameter surface coil improves MR imaging of ocular lesions. Pulse sequences with a small bandwidth maintain an acceptable signal-to-noise ratio when the FOV is reduced.

Artifacts↗
PubMed1997

Intestinal disease in acquired immunodeficiency: evaluation by CT.

Intestinal symptoms affect most AIDS patients at some point in their disease. The purpose of this study was to evaluate the use of CT in this setting. A total of 339 abdominal CT exams were reviewed for signs of intestinal disease. Abdominal CT scans of 45 patients with intestinal symptoms were compared with colonoscopy and histologic data. The CT results were correlated with CD4( +) T-lymphocyte counts and patient survival. More than 14 % of all abdominal CT exams displayed signs of enteric disease. Of the 45 patients studied with both CT and colonoscopy, 35 (78 %) had signs of intestinal disease by CT. Of these 35 patients, colonoscopic signs of an intestinal lesion were found in 29 and histologic proof of disease was established in 30 cases. Colonoscopy and histology detected 8 lesions missed by CT. There were 14 cases of unspecific colitis, 15 cases of cytomegalovirus (CMV) colitis, and 4 cases of enteric tuberculosis as per biopsy. Five patients presented with Kaposi's sarcoma and 1 with a non-Hodgkin's lymphoma. Neither colonoscopic nor CT signs of intestinal disease did reliably distinguish between histologic subgroups. Specifically, CMV colitis could not be distinguished from unspecific colitis. CD4( +) T-lymphocyte counts for histologic subgroups were not significantly different, either. No colonoscopic or histologic feature predicted survival, whereas low CD4 counts and ascites on CT indicated a poor prognosis. Whereas CT detects signs of intestinal disease in most AIDS patients, these signs remain largely unspecific. Colonoscopy and biopsies provide no consistently valid standard with which to compare CT because of controversial sensitivity and specificity of these methods. The CT technique detects small bowel as well as extraintestinal disease. Therefore, CT is an important diagnostic modality in abdominal disease of immunocompromised patients.

AIDS-Related Opportunistic Infections↗
PubMed1997

Nicotinic antagonist administration into the ventral hippocampus and spatial working memory in rats.

Nicotinic acetylcholine receptors are important for maintaining optimal memory performance. In order to more fully characterize the involvement of nicotinic systems in memory, the contributions of nicotinic acetylcholine receptor subtypes were investigated. This study targeted the alpha 7 and alpha 4 beta 2 nicotinic receptors in the ventral hippocampus, an area known to be important for spatial working memory. Antagonists of alpha 7 and alpha 4 beta 2 receptors were locally infused into the ventral hippocampus of rats and the effects on memory were examined with the radial-arm maze. The subtype-specific competitive antagonists infused into separate groups of rats were methyllycaconitine citrate (an alpha 7 antagonist) and dihydro-beta-erythroidine hydrobromide (an alpha 4 beta 2 antagonist). Their effects on radial-arm maze performance were contrasted with the non-specific competitive antagonist, D-tubocurarine chloride. Significant deficits in radial-arm maze choice accuracy performance were found at 78.7 micrograms/side for methyllycaconitine and at 106.9 micrograms/side for dihydro-beta-erythroidine. Increased response latency was also seen at these doses. Tubocurarine induced seizures at doses previously reported to have no effect. Wet dog shakes were seen in most rats at 0.1 microgram/side with tubocurarine, 26.3 micrograms/side with methyllycaconitine and 106.9 micrograms/side with dihydro-beta-erythroidine. This study suggests that both alpha 7 and alpha 4 beta 2 nicotinic acetylcholine receptor subtypes are involved in working memory formation and that the hippocampus is a critical site for nicotinic cholinergic involvement in memory function, though the high doses of antagonists needed to produce the memory impairment may have had less than completely specific effects.

Aconitine↗
PubMed1997

Clinical significance of magnetic resonance cholangiopancreatography (MRCP) compared to endoscopic retrograde cholangiopancreatography (ERCP).

BACKGROUND AND STUDY AIMS: The clinical importance of magnetic resonance cholangiopancreatography (MRCP) as a noninvasive diagnostic modality for investigation of the biliary tree and pancreatic duct system is under debate. Using endoscopic retrograde cholangiopancreatography (ERCP) as the gold standard, this study determined in a prospective, blinded fashion the sensitivity and further statistic values of MRCP findings for evaluation of the biliary and pancreatic tract. PATIENTS AND METHODS: Seventy-eight patients referred for ERCP were studied prospectively with MRCP and ERCP during a 12-month period. All images were interpreted on a blinded basis by two radiologists. Any dilations, strictures, and intraductal abnormalities were recorded and correlated with the clinical diagnoses. RESULTS: MRCP images of diagnostic quality were obtained in 76 of the 78 patients (97%). Magnetic resonance cholangiography (MRC) showed sensitivities (and positive predictive values) of 71% (62%) for recognition of normal bile ducts, 83% (91%) for recognition of dilation, 85% (100%) for recognition of strictures, 77% (91%) for correct stricture location, and 80% (100%) for diagnosing bile duct calculi. In addition, the sensitivity of MRC in classifying benign and malignant strictures was 50% and 80%, respectively. The statistical values (sensitivity and positive predictive value) for magnetic resonance pancreatography findings were determined for the recognition of normal pancreatic ducts (33% and 50%), recognition of dilation (62% and 100%), recognition of strictures (76% and 87%) and correct location (66% and 100%), diagnosis of benign strictures (87% and 87%) and malignant strictures (60% and 75%), and for diagnosing pancreatic duct stones (60% and 100%). CONCLUSIONS: MRCP is capable of providing diagnostic information equivalent to ERCP in many patients, and should be applied whenever established techniques provide no results, or inadequate results.

Adolescent↗
PubMed1997

Magnetic resonance imaging--guided abdominal interventional radiology: laser-induced thermotherapy of liver metastases.

The aim of this study was to evaluate the clinical benefit of magnetic resonance imaging--guided laser-induced thermotherapy (LITT) for the minimally invasive treatment of liver metastases, with regard to survival rates and local tumor control. Magnetic resonance--guided LITT under local anesthesia was carried out in 134 consecutive patients aged 28-84 (mean age 69), with a total of 383 liver metastases. The major groups were liver metastases from colorectal cancer (88 patients) and liver metastases from breast cancer (20 patients), as well as metastases of miscellaneous primary tumors (26 patients). A total of 1048 laser applications were carried out. Cumulative survival times were calculated using the Kaplan-Meier method. All of the patients tolerated the procedure under local anesthesia well, and no severe complications or side effects were observed. During the follow-up period, 29 of the 134 patients treated died. The mean survival time was 35 months in the colorectal cancer group, 30 months in the breast cancer group, and 34 months in the group with miscellaneous primary tumors. The statistical assessment of the equality of survival distribution showed no significant differences between the three groups (Breslow test P = 0.35, Tarone-Ware test P = 0.49). These results suggest that in patients with liver metastases, local tumor destruction using minimally invasive percutaneous LITT under local anesthesia results in improved clinical outcomes, independently of the type of primary tumor.

Abdomen↗
PubMed1997

[CT volumetry of the liver before transplantation].

PURPOSE: Purpose of the study was to assess the predictive accuracy of preoperative CT volumetry for water displacement volume after liver transplantation. METHODS: In a retrospective study the liver volume of 52 patients who underwent an orthotopic liver transplantation, was calculated preoperatively based on incremental and spiral computed tomography (CT). The calculated values were compared with the liver volume measured by water displacement and weight of the extirpated liver. RESULTS: Marked differences of 19-21.5% were seen between calculated CT volume and water displacement volume for the entire group, and of 12.4-16.9% for livers with a plausible physical liver density (0.9 and 1.1 g/cm3). In this group, 68-86% of the livers were in the acceptable tolerance range for a predictive accuracy (+10% to -20%). Other error sources, such as the breathing shift of the abdominal organs and interobserver variability (1.5-2.7%), were of minor importance for volume calculation. CONCLUSION: In conclusion, both incremental CT and spiral CT are reliable methods for the preoperative estimation of the liver volume, whereas best accordance with the corrected water displacement volume was obtained using the individual segmentation thresholds.

Adolescent↗
PubMed1997

[Iron oxide contrast media improve the magnetic resonance imaging of the portal vein system--an animal experimental study].

PURPOSE: The aim was to demonstrate that intravenous superparamagnetic iron oxide contrast agents improve the delineation of the portal venous system. MATERIAL AND METHODS: The portal venous system of 8 minipigs was demonstrated by a FLASH 2-D MRA-sequence. Scans were acquired before and after intravenous administration of 10 and 20 mumol/kg of a superparamagnetic iron oxide contrast agent (SHU 555 A). Signal intensities were measured in the portal vein and hepatic parenchyma and contrast-to-noise ratios were calculated. RESULTS: Following a cumulative dose of 10 mumol iron oxide, hepatic parenchymal signal intensity decreased to 67 +/- 6%, following 20 mumol to 29 +/- 4%, and following 40 mumol to 13 +/- 2% of control (p < 0.0001). These effects improved the contrast-to-noise ratio of the portal vein (469 +/- 114%, 858 +/- 243%, and 957 +/- 272% of control in the left portal vein main branch, p = 0.02). CONCLUSION: A decrease in hepatic parenchymal signal due to a magnetic susceptibility effect accounts for an improvement of portal venous conspicuity following intravenous administration of iron oxide contrast medium.

Animals↗
PubMed1997

[Magnetic resonance tomography and endosonography in the preoperative staging of advanced rectal carcinomas after hyperthermoradiochemotherapy].

PURPOSE: Comparison of diagnostic accuracy of staging of endorectal sonography (ES) and body coil MRI after preoperative hyperthermoradiochemotherapy in patients with advanced rectal cancer. METHODS: Prospective analysis of MRI and ES in 30 patients after hyperthermoradiochemotherapy and correlation with histopathological patterns. RESULTS: T-staging by MRI was correct in 47% and by ES in 53% of the cases. Despite similar accuracy of staging in T0- and T1-tumours, we found different accuracies concerning T2-tumour staging about 63% versus 73% (MRI/ES), concerning perirectal infiltration 70% for both techniques, concerning invasion of adjacent organs 90% versus 87%, and concerning lymph node metastases without respect to the N-stage 63% versus 63%. CONCLUSION: Both imaging modalities provide useful information for operation planning despite limited accuracy after hyperthermoradiochemotherapy. The body coil MRI does not seem to be severely inferior to ES in post-therapeutic staging, despite better contour line imaging by ES. With respect to the determination of invasion of other organs, MRI seems to be more useful.

Adult↗
PubMed1997

[How certain is teleradiological telediagnosis for the tomographic procedure?].

PURPOSE: To define the value of teleradiographic studies, a comparison was carried out between digitised copies of CT examinations of the skull with the original images. Differences in image quality obtained from a digital scanner and a camera were quantified. MATERIAL AND METHOD: 56 CT examinations of the skull, 28 of which had discrete abnormalities, were chosen for ROC analysis. The original films were digitised with a Vidar VXR-12 scanner and Panasonic WV-160 and WV-BP 500 cameras. The images were evaluated by five radiologists after image transfer with Video Conference software to a personal computer. RESULTS: For the analysis of the films the area under the ROC curve was 0.91 +/- 0.04, for the digital scanner it was 0.85 +/- 0.04, for camera WV-BP 500 0.89 +/- 0.06 and for camera WE-160 0.87 +/- 0.09. Comparison with the film findings showed. a minimal p-value of 0.17 which indicated that there was no significant reduction in diagnostic value following digitization. CONCLUSION: The probable reason for the slight deterioration using the digital scanner was the reduction to 75 dpi compared with 134 dpi on the CT films. The cameras produce image noise comparable to CT with low window settings and reduced local resolution. We expect similar results for CT with soft tissue windows or for MRT of the skull. Conventional radiographs containing high local resolution, wide grey scale and low image noise would presumably make higher demands on methods of digitization.

Computers↗
PubMed1997

[Fractal surface analysis of intrapulmonary space-occupying lesions from high-resolution CT studies].

PURPOSE: The visual assessment of shape and surface structures of pulmonary nodules (PN) (smooth edges vs. spiculae) serves as a qualitative, subjective criterion in differential diagnosis. These properties must be quantified by computer-assisted evaluation, an adequate mathematical model, and new quantitative shape parameters. METHODS: 12 patients were investigated by high resolution CT. Based on 3D reconstructions with increasing thresholds, the PN surface S, volume V, fractal dimension (FD = In(S)/ In(square root of V)), and fractal index (F1 = square root of S/ square root of V) were calculated. RESULTS: The relations between the reconstruction threshold and the calculated tumour surface, respective volume, are of a fractal nature: S = c1 x thres1/d, V = c2 x thres1/D (c1, c2, d, D: real constants). Whereas the absolute values of surface and volume strongly depend on the chosen threshold (mean volume differences of 249%), the derived parameter of the fractal dimension for a specific PN is nearly constant for all thresholds under review (r = 0.998, SD = 0.05). CONCLUSIONS: FD and FI are new diagnostic features for the assessment of PN surface structure and morphology. Thus, the assessment of pulmonary nodules can be supported by new quantitative parameters representing surface irregularity due to invasive tumour growth into adjacent tissue.

Aged↗