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Biomedical subjects

R Felix

Publications and source records attributed to R Felix.

At least 235 records · Page 13Linked to original sources
PubMed1999

Uveal melanoma: correlation of histopathologic and radiologic findings by using thin-section MR imaging with a surface coil.

PURPOSE: To evaluate whether the different signal intensities at magnetic resonance (MR) imaging of melanoma are associated with a higher content of melanin. MATERIALS AND METHODS: In a prospective study, MR imaging and ophthalmoscopic examination findings in 42 patients (19 women, 23 men; age range, 30-87 years) with uveal melanoma were compared with histopathologic examination findings obtained after enucleation. MR imaging was performed with 2-mm sections by using a 5-cm surface coil. T1- and T2-weighted images were obtained before and after contrast material administration. RESULTS: In 33 (79%) of the patients, there was homogeneous tumor pigmentation, whereas in nine (21%) patients, there was inhomogeneous bipartite tumor pigmentation. Compared with the histopathologic data, the results of qualitative evaluation were accurate in 29 (58%) of 50 and in 26 (53%) of 49 tumorous areas on T1- and T2-weighted images, respectively. Quantitative evaluation yielded better results, especially at T1-weighted imaging; an 86% correlation was found. Because of methodological reasons, only the superficial pigmentation of inhomogeneous tumors could be evaluated with ophthalmoscopy. CONCLUSION: Thin-section MR imaging of the eye enables an accurate prediction of melanomatous pigmentation with quantitative evaluation of plain T1-weighted images and is superior to ophthalmoscopy in cases of inhomogeneous pigmentation.

Adult↗
PubMed1999

Relationships between physical dose quantities and patient dose in CT.

Patient dose in CT is usually expressed in terms of organ dose and effective dose. The latter is used as a measure of the stochastic risk. Determination of these doses by measurements or calculations can be time-consuming. We investigated the efficacy of physical dose quantities to describe the organ dose and effective dose. For various CT examinations of the head, neck and trunk, organ doses and effective doses were determined using conversion factors. Dose free-in-air on the axis of rotation (Dair) and weighted computed tomography dose index (CTDIw) were compared with the absorbed doses of organs which are located totally within the body region examined. Dose-length product (DLP) was compared with the effective dose. The ratio of the organ dose to CTDIw was 1.37 (0.87-1.79) mSv mGy-1. DLP showed a significant correlation with the effective dose (p < 0.005). The average ratio of effective dose to DLP was 0.28 x 10(-2) mSv (mGy cm)-1 for CT of the head, 0.62 x 10(-2) mSv (mGy cm)-1 for CT of the neck and 1.90 x 10(-2) mSv (mGy cm)-1 for CT of the trunk. CTDIw and DLP can be used for estimating the organ dose and effective dose associated with CT examinations of the head, neck and trunk.

Female↗
PubMed1999

1H and 31P NMR characterisation of a double breast coil for spectroscopic measurements and imaging.

For the first time a double turn breast coil has been described which can be used for 1H imaging, 1H spectroscopy and 31P spectroscopy. The paper describes basic technical features of the coil, coil design, B1 field/excitation field distribution for 1H and 31P, sensitivity, and feasibility for 31P spectroscopic in vivo studies. The main advantage of the double frequency tuneable coil is that 1H imaging for tumor localization and 31P spectroscopy for response control can be done without an additional repositioning of the patient.

Breast Neoplasms↗
PubMed1999

Motion artifacts in cardiac CT. The Novacor left ventricular assist device and its implications for clinical imaging.

PURPOSE: Cardiovascular applications of CT are primarily limited by temporal resolution of the scanner. Recent development in scanner technology has greatly increased temporal resolution. We here describe a standardized method of assessing temporal properties of various CT techniques. MATERIAL AND METHODS: The Novacor left ventricular assist device was mounted in a water-filled circulation phantom and scanned at different pump rates with a spiral CT unit and an electron beam unit. We also evaluated the use of ECG-triggered subsecond scanning on a spiral CT unit. RESULTS: Using the fastest conventional scanning protocol, severe motion artifacts occurred. These artifacts could not be reproduced from image to image, even if the pump rate was adjusted to scan rate (l/s). Electron beam tomography (EBT) reproducibly yielded few artifacts at 100 ms and practically no artifacts at 50 ms scanning time. Even without ECG-triggering, pump motion could be reproduced as a cine-cycle. With the ECG-triggered partial scanning CT technique, limited motion artifacts could be reproduced during diastole at a heart rate of 70-80 beats/min. CONCLUSION: The Novacor ventricular assist device may serve as a benchmark test in the evaluation of new scanning techniques for cardiovascular CT. While EBT presently remains the only CT technique to freeze cardiac motion throughout its cycle, ECG-triggered subsecond scans may, under certain conditions, capture cardiac anatomy in diastole.

Artifacts↗
PubMed1999

Signal-enhanced color Doppler sonography of deep venous thrombosis in the lower limbs and pelvis.

Detection of Doppler signal tends to be more difficult in peripheral veins owing to low flow velocity. This can be caused by nonoccluding thrombosis, post-thrombotic wall changes, or a deep anatomic location of pelvic veins. The last-mentioned frequently is accompanied by interference by bowel gas. In addition, inappropriate insonation angles adversely affect the outcome of color-coded Doppler interrogation. The purpose of the present study was to evaluate the effectiveness of signal-enhanced color Doppler sonography on peripheral veins in 31 patients clinically suspected of having deep vein thrombosis. As a result of diagnostic uncertainty, additional enhanced studies were performed on 43 venous segments. The enhancement led to a decrease in false-positive results (from four patients to one patient) and false-negative results (from four patients to two patients) compared to unenhanced studies. Evaluation of the deeply located pelvic veins profited the most through signal enhanced Doppler sonography.

Adult↗
PubMed1999

Staging and monitoring of malignant lymphoma of the bone: comparison of 67Ga scintigraphy and MRI.

UNLABELLED: The aim of this study was two-fold: to compare 67Ga scintigraphy with MRI (a) for the staging of malignant lymphoma of the bone and (b) with regard to accuracy in detecting residual disease after first-line chemotherapy for restaging. METHODS: Twenty-one patients with 36 malignant osseous lesions were examined, including 7 patients with primary or multifocal osseous lymphoma and 14 patients with malignant lymphoma and simultaneous or secondary involvement of the bone. After first-line therapy, MRI and 67Ga scintigraphy were performed on 13 patients. The remission status based on all clinical and radiological findings during the follow-up was used as the gold standard. RESULTS: The osseous lesions were located on the axial skeleton in 64% of patients and on the appendicular skeleton in 36%. 67Ga scintigraphy detected 77% of the osseous lesions examined by MRI. For restaging after first-line therapy, MRI had a sensitivity of 90% and a specificity of 80% when dynamic MRI information was included. There were several false-positive results as a result of the pathologic increase in signal intensity ratios of reactive hematopoietic regions after chemotherapy. For 67Ga scintigraphy, a sensitivity of 70% and a specificity of 93% were calculated. CONCLUSION: These data show that monitoring malignant lymphoma of the bone still presents diagnostic problems. Given the high sensitivity of MRI and the high specificity of 67Ga scintigraphy but the limited specificity of MRI and sensitivity of 67Ga scintigraphy, both methods are valuable but should be used as complementary diagnostic tools.

Adolescent↗
PubMed1999

[Results of "cross-over implantation of Palmaz-stents" with cross-over sheaths].

PURPOSE: Presentation of technique of cross-over stent implantation of Palmaz stents using a cross-over sheath. MATERIAL AND METHODS: Between 1996 and March 1997 72 patients presenting symptoms of peripheral artery disease received 136 Palmaz stents, which were implanted in a cross-over technique with the aid of a cross-over sheath. RESULTS: As indications for stent implantation occurred: occlusion (n = 14), recoil (n = 11), distinctive calcification (n = 32), recurring stenosis/occlusion (n = 32), perforation (n = 3), dissection (n = 31), and aneurysms (n = 2). The cross-over technique with the aid of a cross-over sheath was successful in all 136 cases. Within the first 24 hours 3 acute reocclusions occurred (all femoral). For stents placed in the iliac artery the primary patency rate was 93.3% at 12 months and for stents placed in the femoral artery 72.0%. Furthermore, this techniques allows for simultaneous stenting of pelvic, femoral or lower leg arteries (n = 17). By using this technique, stenting of the distal external iliacal artery, common femoral artery (CFA) and proximal superficial femoral artery becomes either possible for the first time or easier. CONCLUSION: If Palmaz stents with a length of 2-7.8 cm should be implanted in the cross-over technique, the use of a cross-over sheath is recommended.

Aged↗
PubMed1999

Anomalous origin of the right vertebral artery: review of the literature and case report of right vertebral artery origin distal to the left subclavian artery.

We present the case of a 57-year-old patient who was admitted to the hospital for preoperative cerebral angiography because of an intraspinal mass at the level of C1 and C2. Angiographic examination revealed an abnormal origin of the right vertebral artery, which normally originates from the right subclavian artery. Thus, the right vertebral artery was the last branch of the supraaortic vessels. We also review herein the incidence of the various anomalous origins of the right vertebral artery in the literature and discuss their potential embryologic development and clinical significance.

Cerebral Angiography↗
PubMed1999

[MRI in the diagnosis and differential diagnosis of radiocarpal diseases and injuries].

Advances in MRI technology have greatly improved visualization of the radio-carpal region. With todays high-resolution imaging, even very small anatomic structures like the triangular fibrocartilage may be seen. Established indications include the osteonecroses (scaphoid and lunate); however, MR images always should be evaluated in conjunction with plain radiographs. By delineating bone marrow edema, MRI is well suited for the detection of microfractures. Visualization of small soft tissue tumors, soft tissue extension of bone tumors and for staging of tumors in general may also be regarded as indications generally agreed upon. Promising indications include pathology of ligaments and similar structures.

Arthritis, Rheumatoid↗
PubMed1999

Voltage-dependent Ca2+ channel alpha2delta auxiliary subunit: structure, function and regulation.

Voltage-dependent Ca2+ channels are heteromultimeric proteins consisting minimally of a alpha1 main subunit and auxiliary alpha2delta, and beta subunits. The alpha1 subunit forms the ion-conducting pore and contains receptor sites for ligands that modify channel activity. The auxiliary subunits appear to be necessary for the expression of the native kinetic properties of the channel. In particular, the alpha2delta complex, with the transmembrane domain-containing delta subunit arising as a result of proteolysis from the C-terminal end of a alpha2delta precursor, has shown to modify the biophysical and pharmacological properties of the alpha1 subunit in different model systems. Structure-function studies have provided insight into the molecular mechanisms through which alpha2delta exerts its actions and revealed that both allosteric modulation and cellular localization of the Ca2+ channel complex are important mechanisms for alpha2delta regulation of ionic current. Recent studies have shown that the alpha2delta subunit can also support pharmacological interactions with therapeutic agents for the treatment of neurological disorders.

Acetates↗
PubMed1999

WWW-based access to radiological patient data: two years of experience.

UNLABELLED: This paper describes the theoretical concept behind, the technical implementation of, and the experiences created with a self-developed system to access radiological patient data by WWW-technology. MATERIALS AND METHODS: The WWW-system interfaces the RIS via HL7 and the PACS via DICOM. Core components are a secure Web-Server and an underlying database system (DB). The DB contains all relevant information from the RIS and thumbnails of corresponding images archived in the PACS. After authorization, the user receives this information in the form of dynamically generated Web pages. By mouse-clicking a thumbnail, the original DICOM-image is sent. It is displayed with a helper application (DICOM-Viewer), allowing all kinds of image manipulation and post-processing. RESULTS: Determined advantages of the system were: platform independence, security features, a fixed link of image and report, universal availability, and simple usage. The only critical issue was performance. Cost savings could be seen in: a reduction of DICOM workstations, employment of all available hardware, and reduced training and teaching efforts. CONCLUSIONS: The author believes that a WWW-based concept is the only feasible approach which is in the same way technically possible, clinically acceptable, and financially affordable in order to grant a variety of users access to radiological data--although improvements in performance have to made by, e.g., closer implementation of those systems to the RIS and PACS architecture, and by employing high-grade image compression.

Equipment Design↗
PubMed1998

Imaging in epidural lipomatosis.

This paper reviews the literature concerning symptomatic epidural lipomatosis. The different diagnostic procedures (conventional myelography, computed tomography, and magnetic resonance imaging) and therapeutic approaches (including medical treatment, surgery, and dietary influence) are discussed.

Journal Article↗
PubMed1998

Rationale for using invasive thermometry for regional hyperthermia of pelvic tumors.

PURPOSE: Invasive thermometry for regional hyperthermia is time-consuming, uncomfortable, and risky for the patient. We tried to estimate the benefit/cost ratio of invasive thermometry in regional hyperthermia using the radiofrequency system BSD-2000. METHODS AND MATERIALS: We evaluated 182 patients with locally advanced pelvic tumors that underwent regional hyperthermia. In every patient a tumor-related temperature measurement point was obtained either by invasive or minimally invasive catheter measurement tracks. In the earlier period for every patient an intratumoral measurement point was decided as obligatory and intratumoral catheters were implanted intraoperatively, CT guided, or under fluoroscopy. In the later period, invasive thermometry often was avoided, if a measurement point in or near the tumor was reached by an endoluminally inserted catheter (rectal, vaginal, cervical, urethral, or vesical). For every patient side effects and complications referred to thermometry were evaluated and compared with the potential benefit of the invasively achieved temperature data. The suitability of endolumimally registered temperatures is analyzed to estimate local feasibility (specific absorption rate achieved) and local effectiveness (thermal parameters correlated with response). RESULTS: In 74 of 182 patients invasive thermometry was performed, at most CT-guided for soft tissue sarcomas and rectal recurrences. In 14 of 74 (19%) side effects such as local inflammation, pain, or abscess formation occurred that enforced removal of the catheter. However, local problems were strongly correlated with the dwell time of the catheter and nearly never occurred for dwell times less than 5 days. Fortunately, no fatal complications (e.g., bleeding or perforation) occurred during or after implantation which could be attributed to the invasive thermometry procedure. Endoluminal tumor-related temperature rises per time unit (to estimate power density) were correlated with intratumoral rises at the same patients (where both measurements were available). For a subgroup of patients pooled in two Phase II studies with rectal (n = 37) and cervical (n = 18) carcinomas thermal parameters derived from endoluminal measurements were correlated with response or local control, resp. CONCLUSIONS: If a tumor-related endoluminal temperature measurement point is available, additional invasive thermometry gives no further information to improve the power deposition pattern. For primary rectal and cervical cancer, and probably as well for prostate, bladder and anal cancer, endoluminal measurements are suitable to estimate local feasibility and effectiveness. Therefore, invasive thermometry is dispensable in the majority of patients. In some selected cases, temperature measurement in the tumor center is required to estimate the maximum temperature. In those cases, dwell time of catheters should be minimized--and it should be considered to perform invasive thermometry at the beginning (one or two heat treatments).

Catheterization↗
PubMed1998

Evidence for a 95 kDa short form of the alpha1A subunit associated with the omega-conotoxin MVIIC receptor of the P/Q-type Ca2+ channels.

Neuronal voltage-dependent Ca2+ channels have been isolated previously and shown to contain a primary alpha1 pore-forming subunit as well as auxiliary alpha2delta and beta subunits, in addition to an uncharacterized 95 kDa protein. In the present study, using multiple approaches, we have extensively characterized the molecular structure of the 95 kDa protein. Separation of the P/Q- and N-type neuronal Ca2+ channels showed that the 95 kDa protein is associated exclusively with the omega-Conotoxin MVIIC receptor of the P/Q-type channels. Analysis of purified synaptic plasma membranes and the isolated P/Q-type channels, using alpha1A-specific antibodies, suggested a structural relationship between the alpha1A subunit and the 95 kDa protein. This finding was supported by protein-protein interaction data, which revealed that the beta subunit can associate with the 95 kDa protein in addition to the alpha1A subunit. Changes in electrophoretic mobility after enzymatic treatment with Endo F indicated that the 95 kDa protein is glycosylated. Furthermore, microsequencing of the 95 kDa protein yielded 13 peptide sequences, all of which are present in the first half of the alpha1A subunit up to amino acid 829 of the cytoplasmic linker between repeats II and III. Taken together, our results strongly suggest that the 95 kDa glycoprotein associated with the P/Q-type Ca2+ channels is a short form of the alpha1A subunit.

Amino Acid Sequence↗
PubMed1998

Radiochemotherapy and hyperthermia in the treatment of rectal cancer.

We evaluated the use of regional hyperthermia with radio-chemotherapy in a phase I/II study on locally advanced rectal carcinomas. Thirty-four patients with primary advanced (stage T3/T4) rectal carcinomas (24 patients) or recurring rectal carcinomas (6 patients) were treated using preoperative radiochemo-thermotherapy. Initial tumour staging was carried out clinically (degree of fixation) and using endorectal ultrasonography and CT. Radiotherapy was carried out with the patient prone (on a belly board) at 5 x 1.8 Gy per week up to 45 Gy at the reference point. 5-Fluorouracil (300-500 mg/m2) was administered with low-dose leucovorin (50 mg) on days 1-5 and 22-26. Patients were treated with regional hyperthermia each week prior to radiotherapy, using the Sigma-60 ring of the BSD-2000 system. Temperature/position curves and temperature/time curves were recorded via endocavitary catheters (tumour contact, bladder, vagina). Following endosonographic and clinical restaging, the operation was carried out 4-6 weeks after the end of preoperative therapy. In cases where tumours were unresectable, a boost of up to 60 Gy was given. Twenty-three of the 34 patients (68%) proved to be curatively resectable. Of these patients, 70% were downstaged endosonographically during preoperative therapy. The actuarial survival rates among these patients were 85% (primary rectal cancer) and 60% (recurrences) at 30 months. All in all, the preoperative multimodal therapy was well tolerated, and premature termination was necessary in only two cases. The quality of temperature distribution (T90, cum min T90 > 40.5 degrees C) depends on the power level and relative power density. The response (particularly downstaging) correlates significantly with the quality parameters of the temperature distributions. This regimen proved practical and effective, with encouraging downstaging rates and local control rates.

Adult↗
PubMed1998

In a resource-poor country, mutation identification has the potential to reduce the cost of family management for hereditary nonpolyposis colorectal cancer.

PURPOSE: Colonoscopic surveillance of family members at risk of hereditary nonpolyposis colorectal cancer is difficult in a resource-poor country because of its expense. For family members who live in remote areas, poor communication and limited access to sophisticated medical care make surveillance even more difficult. The identification of the mutation causing the disease will simplify surveillance. Our aim was to assess the impact of mutation analysis on the management of a South African family with more than 150 members at risk for hereditary nonpolyposis colorectal cancer. METHODS: We studied a family that met the Amsterdam criteria for hereditary nonpolyposis colorectal cancer. Colorectal cancer affected 27 members in three generations (evidence from histology in 12, barium enema in 1, and family statements in 14 family members). Leukocyte DNA from family members was tested for linkage to candidate loci for colorectal cancer, and DNA from formalin-fixed cancers from six family members was studied for microsatellite instability. DNA from all available family members was then screened for mutations in the hMLH1 gene. The number of individuals at 50 percent risk was calculated by family pedigree and compared with the number who have the mutation. RESULTS: A disease-causing mutation in exon 13 of hMLH1 segregated with the disorder in members of this kindred. Test results of 100 chromosomes from population-matched controls were negative. Sixty family members between the ages of 16 and 50 years are at 50 percent risk for colon cancer by pedigree analysis, but of these, only 26 (43 percent) have the mutation. CONCLUSION: A mutation in the DNA repair gene hMLH1 was found in family members with hereditary nonpolyposis colorectal cancer and in some unaffected relatives previously at 50 percent risk, but not in unrelated subjects. The blood test for the mutation will simplify management, counseling, and surveillance and help to establish prophylactic colectomy.

Chromosome Segregation↗
PubMed1998

[Phase II study on preoperative radio-chemo-thermotherapy in locally advanced rectal carcinoma].

BACKGROUND: Recent studies show that preoperative radio-chemotherapy can increase resectability and local control of locally advanced rectal carcinomas. Additional regional hyperthermia might increase remission rates and tumor response. We therefore tested regional hyperthermia together with radio-chemotherapy in a phase-II study on locally advanced rectal carcinomas. PATIENTS AND METHODS: Thirty-seven patients with primary advanced stage uT3/T4 rectal carcinomas were treated with preoperative radio-chemo-thermo-therapy. The initial tumor depth was determined using endosonography, CT, and MRI. Radiotherapy was carried out in prone position (on a belly board) using standard techniques, with 5 x 1.8 Gy per week up to 45 Gy at the reference point. 5-Fluorouracil (300 to 500 mg/m2) was administered with low doses of leucovorin (50 mg) on days 1 to 5 and 22 to 28. The patients were treated with regional hyperthermia each week prior to radiotherapy and simultaneously with chemotherapy, using the Sigma 60 ring from the BSD-2000 system. Temperature/position curves and temperature/time curves were recorded in endocavitary (endorectal) catheters in tumor contact and as well in bladder and vagina. Following endosonographic restaging, the operation was carried out 4 to 6 weeks after the end of preoperative therapy and adjuvant chemotherapy continued in four cycles. In cases where tumors were non-resectable, a boost up to 64 Gy was aimed. RESULTS: Thirty-one of the 37 patients (84%) with primary carcinoma proved locally R0-resectable. In addition we had 1 R1-resection (3%) and 5 non-resectable tumors (13%). Among the resected tumors, 53% experienced a reduction of depth infiltration from the initial endosonographic stage during preoperative therapy. The actuarial survival rate after 4 years is 65% (free of progression 57%). The actuarial 4-year survival rate was particularly favorable for the group of responders. Overall, the preoperative multimodal therapy was well tolerated, and premature termination was only necessary in 1 case (3%). Grade III/IV toxicities in the intestine and skin were reduced as far as possible by field blockings and cooling of the perineal region. They occurred only in 5/37 patients (13%) at the intestine and in 6/37 patients (16%) at the skin. The thermal data were subjected to a statistical analysis. The quality of temperature distribution (T90, cum min T90 > or = 40.5 degrees C) depends on the power level and relative power density. The response (reduction of tumor size or depth infiltration) correlated significantly with quality parameters of the temperature distributions. This dependency is found as a trend for progression-free survival, too. CONCLUSIONS: Preoperative radio-chemo-thermo-therapy proved to be practical and effective, with encouraging remission rates and excellent local control rates. For this reason, a phase-III study to test regional hyperthermia has been initiated. At the same time, certain technical improvements are still under development for regional hyperthermia.

Adult↗