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Biomedical subjects

R Felix

Publications and source records attributed to R Felix.

At least 181 records · Page 10Linked to original sources
PubMed2000

Channelopathies: ion channel defects linked to heritable clinical disorders.

Electrical signals are critical for the function of neurones, muscle cells, and cardiac myocytes. Proteins that regulate electrical signalling in these cells, including voltage gated ion channels, are logical sites where abnormality might lead to disease. Genetic and biophysical approaches are being used to show that several disorders result from mutations in voltage gated ion channels. Understanding gained from early studies on the pathogenesis of a group of muscle diseases that are similar in their episodic nature (periodic paralysis) showed that these disorders result from mutations in a gene encoding a voltage gated Na(+) channel. Their characterisation as channelopathies has served as a paradigm for other episodic disorders. For example, migraine headache and some forms of epilepsy have been shown to result from mutations in voltage gated Ca(2+) channel genes, while long QT syndrome is known to result from mutations in either K(+) or Na(+) channel genes. This article reviews progress made in the complementary fields of molecular genetics and cellular electrophysiology which has led to a better understanding of voltage gated ion channelopathies in humans and mice.

Animals↗
PubMed2000

Transarterial chemoembolization for hepatocellular carcinoma: volumetric and morphologic CT criteria for assessment of prognosis and therapeutic success-results from a liver transplantation center.

PURPOSE: To evaluate the prognostic value of volumetric computed tomography (CT) for therapy control in patients treated with repeated transarterial chemoembolization (TACE) for hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Eighty-five patients with histologically proved HCC underwent 182 TACE procedures with 50 mg/m(2) doxorubicin hydrochloride, 50 mg/m(2) cisplatin, 10 mL/m(2) iodized oil, and amilomer microspheres. The volumes of liver and tumor were measured with a region-of-interest CT technique. Iodized oil retention was estimated with CT performed 24-48 hours after treatment. RESULTS: Tumor volume expressed as a percentage of liver volume was less than 5% in 26, less than 15% in 33, and 15% or greater in 26 patients. The overall 1-year survival rate was 57.6% (mean, 534 days; median, 428 days). There was a statistically significant prolongation of survival when the tumor volume was less than 200 mL (P <.02) and less than 5% of the liver volume (P <.01). Complete (>/=75%) and good (50%-74%) iodized oil retention raised the median survival significantly (P <.001 and P <.07, respectively). Significantly reduced survival correlated with diffuse tumor growth pattern (P <.05) and presence of more than nine lesions (P <.03). CONCLUSION: TACE resulted in significant prolongation of survival in patients with tumor volumes of less than 200 mL, tumor-to-liver volume ratios of less than 5%, and iodized oil retention greater than or equal to 75%.

Adult↗
PubMed2000

Arterial switch procedure for D-transposition of the great arteries: quantitative midterm evaluation of hemodynamic changes with cine MR imaging and phase-shift velocity mapping-initial experience.

PURPOSE: To evaluate cine magnetic resonance (MR) imaging and phase-shift velocity mapping for assessment of the hemodynamic relevance of stenotic segments or specific hemodynamic changes in the great vessels after an arterial switch procedure for correction of D-transposition of the great arteries. MATERIALS AND METHODS: Twenty consecutive patients (age range, 2-17 years) with an acoustic window that was insufficient for Doppler transthoracic echocardiography were included in the study. Flow and diameter measurements of the pulmonary arterial trunk and its primary branches were performed with phase-shift velocity mapping and cine MR imaging. RESULTS: There were good correlations between pressure gradients in the pulmonary arteries estimated with MR imaging and those measured with Doppler echocardiography (r = 0.83, n = 15) and cardiac catheterization (r = 0.90, n = 13). Cine MR imaging revealed that the diameters of the right and left pulmonary arteries decreased with the expansion of the aorta during systole, which increased the peak velocity. This temporary stenosis was more severe in the right than in the left pulmonary artery and was accompanied by a significantly (P <.05) lower volume flow in the right artery. CONCLUSION: The anatomic situation after arterial switch repair tended to produce temporary stenoses in the primary pulmonary arterial branches, with significant changes in hemodynamics. These changes may affect the long-term outcome and go undetected with other imaging modalities.

Adolescent↗
PubMed2000

Detection of focal liver lesions at biphasic spiral CT: randomized double-blind study of the effect of iodine concentration in contrast materials.

PURPOSE: To evaluate the effect of iodine concentration on the detection of focal liver lesions at biphasic spiral computed tomography (CT). MATERIALS AND METHODS: One hundred two patients (64 men, 38 women) with neoplastic (n = 85) and nonneoplastic focal lesions (n = 17) were prospectively assigned to biphasic injection group A or B and received 180 mL of iopromide containing 370 or 300 mg of iodine per milliliter, respectively, during spiral CT. Comparison included assessment of quantitative and qualitative parameters. RESULTS: Hepatic time-attenuation curves and mean hepatic enhancement in the portal venous phase and aortic time-attenuation curves in both arterial and portal venous phases were statistically superior in group A compared with group B. There was no significant difference in the mean enhancement in all lesions in either group. In contrast, among patients with hepatocellular carcinoma, mean contrast enhancement in lesions in the arterial phase was significantly superior in group A compared with group B. Blinded readers classified hepatic attenuation and lesion visibility as very good and as improved significantly more often in group A than in group B. CONCLUSION: A decrease in iodine concentration significantly affects aortic and hepatic contrast enhancement and may impair the detectability of focal liver lesions during biphasic spiral CT.

Adult↗
PubMed2000

Perfusion abnormalities of kidney parenchyma: microvascular imaging with contrast-enhanced color and power Doppler ultrasonography--preliminary results.

The purpose of this study was to evaluate the feasibility of microvascular imaging using contrast-enhanced color and power Doppler sonography. Ten patients with a focal lesion of the kidney were examined. Three patients were investigated with the polymeric butylcyanacrylate-based contrast agent SHU 563A, and the remaining patients were investigated with the galactose-based agent Levovist. It was possible to observe the microvascularization with Levovist during the blood pool phase of the agent over a period of 1 to 3 s at 1 min and 2 min after injection. With SHU 563A, microvascular imaging was possible 0.50 s after injection and lasted for 10.35 min. No intratumoral signals were seen in cysts (n = 6) and the investigated abscess. Weak intratumoral polychromatic effects were observed in both renal cell carcinomas in this series. Metastasis could be differentiated from healthy parenchyma due to lack of the polychromatic effect. SHU 563A is appropriate for performing microvascular imaging. The Levovist-induced polychromatic effects are smaller, of shorter duration, and observable only during the blood pool phase; thus, the expected diagnostic benefit is limited.

Blood Vessels↗
PubMed2000

High-resolution MR imaging of the carpal tunnel and the wrist. Application of a 5-cm surface coil.

PURPOSE: To make a comparative analysis of transversal tomograms obtained by high-resolution MR imaging with frozen cross-sections of an anatomical forearm specimen. Twenty-two healthy volunteers were also examined using the same coil system to test for a range of possible clinical applications and for the depiction of morphological and morphometrical values of normal anatomy in vivo. MATERIAL AND METHODS: MR images of the carpal tunnel of 22 healthy volunteers were obtained with a 1.5-T whole-body system with a 5-cm surface coil. Measurements were recorded with a field-of-view between 50x50 mm2 and 60x60 mm2 in a 256x256 pixel matrix for the T1 sequence. A slice thickness of 2 mm was used. The images were acquired using a T1-weighted SE sequence (TR/TE 500/38 ms) and a T2-weighted SE sequence (TR/TE 2000/70 ms). Additionally, a formalin-fixed anatomical forearm specimen was imaged for anatomic correlation. The imaged transversal cross-section levels in the specimen were subsequently freeze-sectioned. The anatomical structures of the MR findings were identified and compared with the macroscopical sections of the specimen. RESULTS: Based on the good depiction of details at this coil system with a pixel size in T1 of 0.195x0.195 mm, high-resolution MR imaging enabled identification of the interior structures of the carpal tunnel, as well as delineation of connective tissue. The clinical value of high-resolution MR includes the diagnosis of carpal tunnel syndrome and inflammatory disorders of the wrist. CONCLUSION: Our results support the feasibility of high-resolution MR imaging of the carpal tunnel and the wrist using small surface coils.

Carpal Bones↗
PubMed2000

Contrast-enhanced high resolution magnetic resonance imaging of pigmented malignant melanoma using Mn-TPPS4 and Gd-DTPA: experimental results.

The aim of this study was to evaluate the potential of the paramagnetic metalloporphyrin Mn-TPPS4 (using Gd-DTPA as the reference) for magnetic resonance imaging (MRI) of pigmented malignant melanoma in an animal model. High resolution MRI (2.0 T, 2.0 cm surface coil, T1-weighted FLASH two-dimensional sequence) was performed on 15 mice (C57bl6) with intracutaneous implanted melanoma (B16F1) before and after intravenous administration of Gd-DTPA (Magnevist, Schering AG, Berlin, Germany) and Mn-TPPS4 (Porphyrin Products, Logan, Utah, USA). The images were evaluated quantitatively by calculating the percentage enhancement, the slope of the signal intensity-to-time curves, the percentage increase in the signal intensity, and the signal-to-noise and contrast-to-noise ratios. The qualitative evaluation was accomplished by visual assessment of the enhancement, the demarcation of the tumours from the surrounding tissue, and the homogeneity of the tumours. Contrast medium-enhanced images showed an increase in signal intensity for all the tumours, with no significant difference between the contrast media. Specific accumulation of the contrast media in the melanoma could not be proved. Demarcation of tumours from the surrounding tissue is better after administration of contrast media; regressive changed areas were better depicted.

Animals↗
PubMed2000

Pre-operative staging of cervical cancer: comparison of magnetic resonance imaging (MRI) and computed tomography (CT) with histologic results.

Thirty-two patients with histologically confirmed cervical carcinoma were preoperatively investigated using MRI; in addition, a CAT-scan was performed on 15 of these patients. The diagnostic results using both modalities were compared with the histological findings (after hysterectomy according to Wertheim-Meigs, including lymph node dissection in the pelvic and, in part, in para-aortal regions). Determination of tumour volume was possible with high accuracy using MRI. Accuracy in assessing the parametria was 86%, vagina 90%, bladder and rectum 97%. The shortcoming of MRI is still the detection of infiltrated lymph nodes. The accuracy of 69% achieved for lymph nodes is equal to results with computed tomography. The general accuracy for our patients in staging was 81% for MRI versus 47% for CT. MRI-based diagnosis enables us to determine a correct tumour staging preoperatively, and is therefore very helpful in planning an adequate therapy. If MRI were used more widely it would contribute to simplification and shortening of the preoperative diagnostic procedure in patients with cervical carcinoma.

Adult↗
PubMed2000

CSF flow studies of intracranial cysts and cyst-like lesions achieved using reversed fast imaging with steady-state precession MR sequences.

BACKGROUND AND PURPOSE: Differentiating between intracranial cysts or cyst-like structures and communicating or noncommunicating cysts is often not possible with cranial CT or nonfunctional MR imaging. We evaluated a retrospective ECG-gated fast imaging with steady-state precession (PSIF) MR sequence with optional cine mode to differentiate cystic masses from enlarged CSF spaces and to determine the accuracy of detecting communication between cysts and neighboring CSF spaces. METHODS: Fourteen patients with intracranial cystic masses underwent CSF flow studies with an ungated and a retrospective ECG-gated cine-mode PSIF sequence in addition to spin-echo imaging. Findings were evaluated retrospectively by using a five-point rating scale and without knowledge of clinical or other imaging findings. Results were compared with intraoperative findings or with results of intrathecal contrast studies. RESULTS: Eighteen arachnoid cysts and one enlarged cisterna magna were diagnosed. Improved differentiation between cysts and enlarged CSF spaces was obtained with cine-mode PSIF imaging in six lesions (six patients). Increased diagnostic certainty as to communication between cysts and CSF spaces was obtained in 18 cysts (13 patients). Diagnoses were verified by membranectomy in five lesions, by CT cisternography in five lesions, and indirectly by shunting in one cystic lesion. In one case, MR diagnosis was not confirmed by CT cisternography. CONCLUSION: Cine-mode MR imaging with a retrospective ECG-gated flow-sensitive PSIF sequence contributed to the certainty of communication between arachnoid cysts and neighboring CSF spaces with an accuracy of 90%, using surgical findings or intrathecal contrast studies as reference. Differentiation between intracranial cysts and enlargement of CSF spaces and other cystic masses was improved in 25% of cases.

Adolescent↗
PubMed2000

[Use of patient-related contrast media protocols in cardiovascular computerized tomography].

PURPOSE: To determine the temporal variability of the time to maximum aortic density after peripheral venous contrast injection in cardiovascular CT studies and to calculate potential contrast agent savings of selecting scan delay from test bolus kinetics. METHODS: A peripheral contrast bolus was administered intravenously in 138 consecutive patients to determine the time to maximum density in a left ventricular or aortic region of interest by electron beam CT. 20 EKG-triggered scans were acquired within 70 heartbeats. The deviation of the time to maximum density from a standard, fixed scan delay was determined. RESULTS: Mean time to maximum density was 22 s, and the average deviation from that mean was 5 s. At an injection rate of 4 cc/s, this deviation implies that determining the individual scan delay from a test bolus injection may potentially save 20 cc contrast per patient. This amount of contrast agent, in turn, is required for the test bolus. CONCLUSION: Deriving the individual scan delay from test bolus kinetics may improve image contrast in cardiovascular CT studies without additional contrast expense.

Adult↗
PubMed2000

[Dynamic magnetic resonance tomography (MRI): a follow-up study after femur core decompression and instillation of recombinant human bone morphogenetic protein-2 (rhBMP-2) in avascular femur head necrosis].

OBJECT: The aim of the study was to test the use of dynamic magnetic resonance imaging study with Gd-DTPA-application and the dynamic changes of signal intensity at patients with avascular femoral head necrosis after having installed rhBMP-2 and/or decompressed the core. MATERIAL AND METHODS: Six patients with avascular necrosis of the femoral head ARCO-stage I- or II-lesions were treated surgically by femoral head core decompression. Three of these patients were additionally treated with rhBMP-2-instillation. The progression or regression could be confirmed by T1- and T2-weighted spinecho-sequences (zero, four, ten, sixteen weeks and 24 months follow up). RESULTS: Corresponding ARCO-classification with partly more sensitive measurement of vitality signs in comparison to the optical x-ray classification. The objective, quantitative measurement of signal intensity post contrast medium reduces the influence of experience and level of education. The dynamic sequences results are reproducible. CONCLUSION: The dynamic magnetic resonance imaging study after Gd-DTPA-application and the dynamic changes of signal intensity after Gd-DTPA enhancement in the necrotic areas of the femoral head were the important subject of our study and it seems, that these sequencies and the ascertainment of signal intensity changes will be an efficient method for judgement of vitality, vascularisation and perfusion after therapeutical intervention. Combination of femoral head core decompression and rhBMP-2-instillation for the purpose of osseous regeneration seems to stabilize the affection.

Adult↗
PubMed2000

Molecular genetics improves the management of hereditary non-polyposis colorectal cancer.

BACKGROUND: The syndrome of hereditary non-polyposis colorectal cancer (HNPCC) can be diagnosed fairly accurately using clinical criteria and a family history. Identifying HNPCC helps to prevent large-bowel cancer, or allows cancer to be treated at an early stage. Once the syndrome has been diagnosed a family member's risk can be judged approximately from a family tree, or it can now be predicted accurately if the causative mutation is known. OBJECTIVE: This study involved attempts to improve the management of a family with HNPCC over a period of 10 years. Clinical diagnostic criteria, colonoscopic surveillance, surgical treatment, genetic counselling, molecular genetic research, and finally predictive genetic testing were applied as they evolved during this time. SUBJECTS AND METHODS: A rural general practitioner first noted inherited large-bowel cancer in the family and began screening subjects as they presented, using rigid sigmoidoscopy at the local hospital. At the time that the disorder was recognised as being HNPCC (1987), screening by means of colonoscopy at our university hospital was aimed primarily at first-degree relatives of affected individuals. After realising how many were at risk, screening was brought closer to the family. A team of clinicians and researchers visited the local hospital to identify and counsel those at risk and to perform screening colonoscopy. Family members were recruited for research to find the gene and its mutation that causes the disease, to develop an accurate predictive test and to reduce the number of subjects undergoing surveillance colonoscopies. RESULTS: There are approximately 500 individuals in this family. In the 10 years of this study the number of subjects who have been counselled for increased genetic risk or who have requested colonoscopic surveillance for HNPCC in this kindred has increased from 20 to 140. After the causative mutation was found in the hMLH1 gene on chromosome 3, a test for it has reduced the number of subjects who need screening colonoscopy by over 70%. A protocol has been devised to inform family members, to acquire material for research in order to provide genetic counselling for (pre-test and post-test) risk, and to test for the mutation. Eventually, identifying those with the mutation should focus surveillance accurately. CONCLUSIONS: The benefits of restricting screening to subjects with the mutation that causes colorectal cancer and of performing operations to prevent cancer are hard to measure accurately. However, it is likely that at least half the family members will be able to avoid colonoscopic screening, some deaths from cancer should be prevented, and the cost of preventing and treating cancer in the family should fall substantially.

Adult↗
PubMed2000

[Indirect MR arthrography in the diagnosis of rotator cuff lesions].

PURPOSE: To determine the value of indirect MR arthrography in lesions of the rotator cuff, prospectively versus arthroscopy. METHODS: 63 patients with suspected shoulder pathology were examined: oblique-coronary and axial T1w sequences, axial FLASH-2D sequences, furthermore oblique-coronary T2- and PD-weighted sequences were taken. After intravenous administration of 0.1 mmol Gd-DTPA/kilogram body weight and active motion of the shoulder T1w sequences were repeated. Signal intensities (SI) inside the tendon were quantitatively measured by the ROI technique (region-of-interest) and the percentual contrast-enhancement CE was calculated. In 32 patients the results were confirmed by surgical follow-up. RESULTS: The mean SI measured in the supraspinous tendon were higher in lesions (degeneration, impingement, partial and total rupture), before as well as after contrast medium, compared to intact findings (p < 0.05). Similarly the percentual CE (p < 0.05) was higher. We detected 9 total ruptures and three impingements (for both sensitivity before/after Gd-DTPA 100%), furthermore 6 partial ruptures. Of the latter three were false positive and one false negative, leading to a sensitivity of 75% and a specificity of 50%. CONCLUSION: The visualization of rotator cuff lesions can be optimized with indirect MR arthrography. The detection of partial ruptures remains faulty, because the exact demarcation of degenerative change and partial rupture is still difficult.

Adolescent↗
PubMed2000

[New ways of imaging diagnosis of the heart with electron beam tomography].

Electron beam computed tomography is a noninvasive imaging tool for diagnosing heart disease. The method offers new insights into coronary heart disease, because the quantification of coronary artery calcification provides a fast, low-risk and cost efficient estimation of coronary risk with greater prognostic power than traditional risk estimates. With intravenous administration of an x-ray contrast agent, EBCT can detect coronary artery stenoses more accurately than other noninvasive methods. The quantification of myocardial blood flow by EBCT represents a realistic alternative to other methods of assessing myocardial perfusion. High temporal resolution allows for detailed analysis of cardiac dynamics. Other applications include the work-up of cardiac masses, pericardial disease, and investigations of the great vessels. As a dedicated cardiac imaging tool, EBCT provides new insights into cardiac physiology and disease, and offers a quantitative approach to many diagnostic problems. Limited availability, radiation exposure, and the need for a iodinated contrast agent still make EBCT an accessory modality at this time.

Calcinosis↗
PubMed2000

A windows based viewing application for image postprocessing in DICOM format.

OBJECTIVE: To design, implement and evaluate a PC-based medical viewing application including image postprocessing for DICOM images for use within an existing hospital infrastructure. MATERIAL AND METHODS: A user-friendly DICOM compliant viewing application including image postprocessing (spatial frequency and contrast enhancement) and HL7 communication ability was designed and implemented on PC basis to run under Windows OS. To assess its quality compared to high-end workstations, an ROC analysis was performed. RESULTS: The use of image postprocessing on a PC significantly improved the perception of low-contrast details in computed radiographs. Review at a radiological workstation was superior to review at a PC with image postprocessing.

Computer Communication Networks↗
PubMed1999

Voltage-dependent Ca(2+) channel subunit expression and immunolocalization in mouse spermatogenic cells and sperm.

Though voltage-dependent Ca(2+) channels contribute to the orchestration of sperm differentiation and function, many questions remain concerning their molecular architecture. This study shows that alpha(1A) and alpha(1C) Ca(2+) channel pore-forming subunits are expressed in spermatogenic cells. In addition, it provides what is to our knowledge the first evidence for the presence of the Ca(2+) channel beta auxiliary subunits in spermatogenic cells and sperm. Using RT-PCR we demonstrated the expression of all four known genes encoding the beta subunits in spermatogenic cells. Specific antibodies detected three of these proteins in spermatogenic cells and sperm. In spermatogenic cells both alpha(1) and beta subunits are diffusely distributed throughout the cytoplasm while in sperm they appear to be regionally localized.

Animals↗
PubMed1999

Scanning E-field sensor device for online measurements in annular phased-array systems.

PURPOSE: A measurement device for noninvasive and simultaneous control of antennas during regional radiofrequency (rf) hyperthermia and, subsequently, the estimation of the power distribution in the interior of patients are essential preconditions for further technological progress. Aiming at this, the feasibility of an electro-optical electric field sensor was investigated during clinical rf hyperthermia. MATERIAL AND METHODS: The electro-optical electric field (E-field) sensor is based on lithiumniobate crystals and the Mach-Zehnder interferometer structure, and was tested in an earlier phantom study. For this study, a mechanical scanning device was developed allowing the registration of the E-field during clinical application. Data were recorded along a curve in the water bolus of the SIGMA 60 applicator of the annular phased-array system BSD-2000 (BSD Medical Corp., Salt Lake City, UT) close to the base points of the flat biconical dipole antennas. The results were compared with modeling calculations using the finite-difference time-domain (FDTD) method. For the latter, different antenna models were assumed. For systematic registration of the E-field curves in amplitude and phase, we employed an elliptical lamp phantom with fat-equivalent ring (filled with saline solution) and an elliptical polyacrylamide phantom with acrylic glass wall. Further measurements were carried out during the treatment of 5 patients with 20 hyperthermia treatments. RESULTS: Data of both phantom and patient measurements can be satisfactorily described by the FDTD method, if the antenna model is refined by taking into account the conical form of the dipoles and the special dielectric environment of the feeding point. Phase deviations can be entered ex posteriori for correction in the calculation algorithm. A comparison of amplifier power measurement (forward and backward power) and bolus E-field scans near the antenna base points demonstrates that E-field measurements between antennas and patient are a necessity for the appropriate characterization of antenna radiation properties. These measurements are sensitive to variations of the lossy medium in position and shape, and can be correctly predicted with current models. However, the differences between different patients are moderate and unspecific in both calculations and measurements, with fluctuations at maximum of 30 degrees in phases and 40% in amplitudes. CONCLUSIONS: The measurement method presented here turned out to be a practical tool for online registration of E-fields in phases and amplitudes along arbitrary curves in a water bolus or phantom. It can be utilized to evaluate antenna design and modeling calculations and leads, thus, to a better understanding of complicated multiantenna systems. In clinical routine, it can be employed as input for patient-specific hyperthermia planning and, finally, for the realization of online control with subsequent optimization of the power distribution in the patient.

Algorithms↗