PubMed Health⌕ Search

Biomedical subjects

D Rüfenacht

Publications and source records attributed to D Rüfenacht.

At least 19 recordsLinked to original sources
PubMed2006

Comment on 'the use of the Henyey-Greenstein phase function in Monte Carlo simulations in biomedical optics'.

In this letter the authors highlight the presence of an error appearing in the discussion of the note 'The use of the Henyey-Greenstein phase function in Monte Carlo simulations in biomedical optics' previously published by them (Binzoni et al 2006 Phys. Med. Biol. 51 N313). In the light of this error, the discussion and conclusions in the original paper are revised in this letter and the role of the use of the phase functions in MC simulations, interpreted in probabilistic terms, is better clarified. The exact definition for the probability density function for the deflection angle, in the case of the Henyey-Greenstein model, is also given.

Algorithms↗
PubMed2006

The use of the Henyey-Greenstein phase function in Monte Carlo simulations in biomedical optics.

Monte Carlo (MC) simulations are often at the heart of the testing procedure in biomedical optics. One of the critical points in MC simulations is to define the new photon direction after each scattering event. One of the most popular solutions is to use the Henyey-Greenstein phase function or some linear combinations of it. In this note, we demonstrate that randomly generating the angle defining the new direction of a photon after a collision, by means of the Henyey-Greenstein phase function, is not equivalent to generating the cosine of this angle, as is classically done. In practice, it is demonstrated that for a nearly isotropic medium (asymmetry parameter g approximately 0) this discrepancy is not large, however for an anisotropic medium as is typically found in vivo (e.g. g = 0.98) the two methods give completely different results.

Algorithms↗
PubMed2006

Combined IV-intra-arterial thrombolysis: a color-coded duplex pilot study.

The authors compared the transcranial color-coded duplex pattern of the middle cerebral arteries (MCAs) before and after IV and combined IV-intra-arterial (IV-IA) thrombolysis in consecutive first-ever stroke patients. Patients receiving combined IV-IA thrombolysis showed greater improvement in flow signal and higher incidence of complete MCA recanalization vs those receiving IV thrombolysis, especially when the MCA was occluded or had only minimal flow.

Aged↗
PubMed2006

Absorption and scattering coefficient dependence of laser-Doppler flowmetry models for large tissue volumes.

Based on quasi-elastic scattering theory (and random walk on a lattice approach), a model of laser-Doppler flowmetry (LDF) has been derived which can be applied to measurements in large tissue volumes (e.g. when the interoptode distance is >30 mm). The model holds for a semi-infinite medium and takes into account the transport-corrected scattering coefficient and the absorption coefficient of the tissue, and the scattering coefficient of the red blood cells. The model holds for anisotropic scattering and for multiple scattering of the photons by the moving scatterers of finite size. In particular, it has also been possible to take into account the simultaneous presence of both Brownian and pure translational movements. An analytical and simplified version of the model has also been derived and its validity investigated, for the case of measurements in human skeletal muscle tissue. It is shown that at large optode spacing it is possible to use the simplified model, taking into account only a 'mean' light pathlength, to predict the blood flow related parameters. It is also demonstrated that the 'classical' blood volume parameter, derived from LDF instruments, may not represent the actual blood volume variations when the investigated tissue volume is large. The simplified model does not need knowledge of the tissue optical parameters and thus should allow the development of very simple and cost-effective LDF hardware.

Absorption↗
PubMed2004

Mapping human skeletal muscle perforator vessels using a quantum well infrared photodetector (QWIP) might explain the variability of NIRS and LDF measurements.

Near-infrared spectroscopy (NIRS) and laser Doppler flowmetry (LDF) have become the techniques of choice allowing the non-invasive study of local human skeletal muscle metabolism and blood perfusion on a small tissue volume (a few cm3). However, it has been shown that both NIRS and LDF measurements may show a large spatial variability depending on the position of the optodes over the investigated muscle. This variability may be due to local morphologic and/or metabolic characteristics of the muscle and makes the data interpretation and comparison difficult. In the present work, we use a third method to investigate this problem which permits fast, non-invasive mapping of the intramuscular vessel distribution in the human vastus latelralis muscle. This method uses an advanced, passive, infrared imaging sensor called a QWIP (quantum well infrared photodetector). We demonstrate, using a recovery-enhanced infrared imaging technique, that there is a significant presence of perforator vessels in the region of interest of approximately 30 x 18 cm (the number of vessels being: 14, 9, 8, 33, 17 and 18 for each subject, respectively). The presence of these vessels makes the skeletal muscle highly inhomogeneous, and may explain the observed NIRS and LDF spatial variability. We conclude that accurate comparison of the metabolic activity of two different muscle regions is not possible without reliable maps of vascular 'singularities' such as the perforator vessels, and that the QWIP-based imaging system is one method to obtain this information.

Adult↗
PubMed2004

Diffusion-weighted MRI in cortical ischaemia.

We carried out MRI on 16 male and three female comatose patients, aged 2 days to 79 years, with suspected cortical ischaemia referred from our intensive care units. Using a head coil, and following standard imaging, including coronal fluid-attenuated inversion-recovery images, we performed diffusion-weighted imaging (DWI) using a whole-brain multislice single-shot echo-planar sequence with b 0 and 1000 s/mm2: 5-mm slices covering the whole brain, TR 7000 TE 106 ms, 128 x 128 pixels, field of view 250 mm, one excitation. Maps of apparent diffusion coefficients (ADC) were generated automatically. DWI showed cortical, basal ganglia and watershed-area high signal in all cases, associated with a decrease in ADC to 60- 80% of normal. DWI showed lesions not seen (40%) or underestimated (40%) on conventional T2-weighted imaging. Within 24 h of the onset of symptoms, DWI showed changes not readily detectable on T2-weighted images. The cortical high signal on DWI and the ADC changes, suggesting severe ischaemia rather than oedema, was found in areas known to be affected by cortical laminar necrosis. Extension to the brain stem and white matter was associated with a higher likelihood of death.

Adolescent↗
PubMed2001

Progressive melorheostosis in the peripheral and axial skeleton with associated vascular malformations: imaging findings over three decades.

A 28-year old woman presented with Léri's disease (melorheostosis) and the rare combination of complex vascular malformations and lymphatic anomalies. Multifocal melorheostosis was segmental and unilateral, located in the left axial and peripheral skeleton, fifth thoracic vertebral body, fifth rib. left upper limb and lumbosacral spine (third lumbar body to first sacral segment). Sacral involvement was associated with spinal canal stenosis. Additionally the patient had multiple nevi and had suffered from left hemiplegia since birth. Lymphangiectasia of the mesentery and thorax led to chylothorax resistant to therapy for which the patient underwent a pleuropericardiectomy. Death ensued due to respiratory failure.

Adult↗
PubMed2000

A real-time flat-panel X-ray pixel imaging system for low-dose medical diagnostics and craniofacial applications.

The aim of this study was to evaluate on-line performance of a real-time digital imaging system based on amorphous silicon technology and to compare it with conventional film-screen equipment. The digital detecting imager consists of (1) a converter, which transforms the energy of the incident X rays into light; (2) a real-time digital detecting system, capable of producing as many as 10 pictures per second using a large-area pixel matrix (20 x 20 cm2) based on solid-state amorphous silicon sensor technology with a pitch of 400 microns; and (3) appropriate computer tools for control, real-time image treatment, data representation, and off-line analysis. Different phantoms were used for qualitative comparison with the conventional film-screen technique, with images obtained with both systems at the normal dose (used as a reference), as well as with dose reduction by a factor of 10 to 100. Basic image quality parameters evaluated showed that the response of the detector is linear in a wide range of entrance air kerma; the dynamic range is higher compared with the conventional film-screen combination; the spatial resolution is 1.25 lp per millimeter, as expected from the pixel size; and good image quality is ensured at doses substantially lower than for the film-screen technique. The flat-panel X-ray imager based on amorphous silicon technology implemented in standard radiographic equipment permits acquisition of real-time images in radiology (as many as 10 images per second) of diagnostic quality with a marked reduction of dose (as much as 100 times) and better contrast compared with the standard film technique. Preliminary results obtained with a 100-micron pitch imager based on the same technology show better quality but a less substantial dose reduction. Applications in craniofacial surgery look promising.

Analog-Digital Conversion↗
PubMed1996

Trisacryl gelatin microspheres for therapeutic embolization, I: development and in vitro evaluation.

PURPOSE: To develop a precisely calibrated, perfectly spherical, stainable, soft, and implantable but nonresorbable particulate embolization material. METHODS: Calibrated particles with a trisacryl gelatin polymer core and hydrophilic surface characteristics were obtained by reversed emulsion synthesis followed by application of a wet-sieving technique. Particles were suspended in saline, bottled, and sterilized. Quality control included analysis of particle diameters before and after sieving and of suspension sterility and apyrogenicity. Particles were subsequently tested to ascertain their compatibility with commercially available microcatheters. RESULTS: The resulting embolization material consisted of spherical, stainable microspheres of medical grade with diameters ranging from 130 microns to 1200 microns. Sieving the suspension produced particle groups of homogeneous size (accuracy, +/- 20-100 microns). At injection, the particles showed no tendency to build aggregates or to obstruct the microcatheters. CONCLUSION: Precisely calibrated and easy-to-use microspheres were obtained that satisfied the biomedical requirements for implantation as an embolization material.

Animals↗
PubMed1996

Trisacryl gelatin microspheres for therapeutic embolization, II: preliminary clinical evaluation in tumors and arteriovenous malformations.

PURPOSE: To evaluate an embolic agent that is precisely calibrated, perfectly spherical in shape, and soft but nonresorbable for use in the embolization of vascular disease of the head, neck, and spine in humans. METHODS: We used supple, hydrophilic, and calibrated trisacryl gelatin microspheres 200, 400, 600, 800 and 1000 microns in diameter for superselective embolization in 105 patients (27 tumors, 14 facial arteriovenous malformations [AVMs], 37 spinal cord AVMs, 21 cerebral AVMs, and 6 miscellaneous diseases). We used particles in 200 to 600 microns in diameter for tumors and for facial AVMs, particles 400 to 600 microns in diameter for spinal cord AVMs, and particles over 1000 micros in diameter for cerebral AVMs. RESULTS: Delivery of the embolic material was easy: microspheres did not aggregate and catheters did not become obstructed by particles. It was possible to control the embolization through precise accounting of the amount of microspheres and matching of the particle size to the size of the pathologic vascular network. CONCLUSION: The microspheres are easy to use and allow precise control of the embolization procedure. Their physical characteristics make them a safe embolic agent.

Adolescent↗
PubMed1995

Acute embolic carotid occlusion after cardiac catheterization: effect of local intra-arterial urokinase thrombolysis.

A 64-year-old woman developed a severe embolic cerebral attack with total left hemiplegia approximately 30 hours after cardiac catheterization for mitral stenosis. She underwent intra-arterial thrombolysis of the right internal carotid artery four and one-half hours after the onset of neurologic deficit with subsequent recanalization of the occluded vessel and near complete neurologic recovery.

Acute Disease↗
PubMed1993

[Positron emission tomography (PET) in the preoperative evaluation of cervical lymph node metastasis of ORL cancer].

The distribution of specific radiolabeled biological compounds in tumor tissues can be imaged by positron emission tomography (PET). The substance used is fluorodeoxyglucose, labeled with the positron emitter fluorine-18. This substance is partly trapped in tumor cells with increased glucose metabolism. This noninvasive imaging technique allows to assess quantitatively and in three dimensions the extent of metastatic disease in ENT cancer. The case presented illustrates the important value we foresee for this new imaging modality in the presurgical staging of cervical metastatic disease of ENT tumors. Sensitivity and specificity of the PET-FDG imaging technique for the loco-regional staging of ENT cancer are, according to preliminary results of an ongoing, prospective clinical study, very high.

Aged↗
PubMed1993

Occlusive hyperemia: a theory for the hemodynamic complications following resection of intracerebral arteriovenous malformations.

An alternative theory is proposed to explain the brain edema and hemorrhage that may occur after resection of high-flow intracerebral arteriovenous malformations (AVM's). This theory, termed "occlusive hyperemia," is based on a retrospective analysis of operative dictations along with postoperative imaging studies (191 angiograms and 273 computerized tomography scans) in 295 cases of intracerebral AVM's operated on at the Mayo Clinic between 1970 and 1990. In this series, 34 cases (12%) of postoperative deterioration were documented, of which 15 were due to incomplete resection of the AVM. Of the remaining 19 cases, six had brain edema alone and 13 had hemorrhage with edema, despite complete excision of the AVM. In these 19 cases, the AVM's were greater than 6 cm in diameter in 10 patients, between 3 and 6 cm in six, and less than 3 cm in three. Obstruction of the venous drainage system was observed in 14 (74%) of the 19 cases. Ten of these 14 were due to obstruction of the primary venous drainage of the brain parenchyma immediately surrounding the lesions, while four were due to obstruction of other venous structures. In no case was a rapid circulation identified on postoperative angiograms. The flow pattern was slow or stagnant in former AVM feeders and their parenchymal branches. It is proposed that postoperative intracranial hemorrhage and/or brain edema in AVM patients may be due to: 1) obstruction of the venous outflow system of brain adjacent to the AVM, with subsequent passive hyperemia and engorgement; and 2) stagnant arterial flow in former AVM feeders and their parenchymal branches, with subsequent worsening of the existing hypoperfusion, ischemia, and hemorrhage or edema into these areas. Supportive hemodynamic evidence for this theory was derived from the literature.

Adult↗
PubMed1992

Endovascular treatment of vertebral arteriovenous fistula.

The clinical and angiographic features of 46 vertebral arteriovenous fistulas (AVFs) seen during a 12-year period (45 patients) were reviewed. Fourteen patients were asymptomatic, with vertebral AVF discovered at routine clinical examination. Specific symptoms at presentation in the other patients were tinnitus (n = 21), vertigo (n = 6), neurologic deficit (n = 3), and pain (n = 2). Of the 46 AVFs, 19 (41%) were caused by trauma and 27 (59%) were spontaneous. The fistula was found at C-1 to C-2 in 21 (46%) cases, at C-2 to C-5 in five (11%), and below C-5 in 20 (44%). Thirty-four patients (35 vertebral AVFs) were treated with the endovascular technique. Embolization was performed with latex balloons filled with contrast medium in most cases. Endovascular therapy resulted in complete occlusion in 32 cases (91%) and partial occlusion in three (9%). The vertebral artery could not be preserved in three patients. Endovascular balloon treatment of vertebral AVFs is effective in occluding the shunt, avoids general anesthesia and surgical intervention, and results in minimal morbidity. Endovascular therapy is the treatment of choice for vertebral AVF.

Adolescent↗
PubMed1991

Endovascular occlusion of vertebral arteries in the treatment of unclippable vertebrobasilar aneurysms.

Twenty-one patients with aneurysms of the vertebrobasilar circulation underwent unilateral or bilateral endovascular occlusion of the vertebral artery. Six patients presented with subarachnoid hemorrhage (SAH), 10 with mass effect, four with mass effect and SAH, and one with ischemic symptoms. Thirteen patients had good outcomes with complete clinical and angiographic cure. Six patients had partial thrombosis of their aneurysms. There was one death and one treatment failure. One patient suffered transient stroke. It is concluded that endovascular occlusion of the vertebral artery following test occlusion is a safe and effective treatment for proximal aneurysms of the vertebrobasilar circulation.

Adolescent↗
PubMed1991

Endovascular occlusion of intracranial vessels for curative treatment of unclippable aneurysms: report of 16 cases.

Among 121 intracerebral aneurysms presenting at one institution between 1984 and 1989, 16 were treated by endovascular means. All 16 lesions were intradural and intracranial, and had failed either surgical or endovascular attempts at selective exclusion with parent vessel preservation. The lesions included four giant middle cerebral artery (MCA) aneurysms, one giant anterior communicating artery aneurysm, six giant posterior cerebral artery aneurysms, one posterior inferior cerebellar artery aneurysm, one giant mid-basilar artery aneurysm, two giant fusiform basilar artery aneurysms, and one dissecting vertebral artery aneurysm. One of the 16 patients failed an MCA test occlusion and was approached surgically after attempted endovascular selective occlusion. Treatment involved pretreatment evaluation of cerebral blood flow followed by a preliminary parent vessel test occlusion under neuroleptic analgesia with vigilant neurological monitoring. If the test occlusion was tolerated, it was immediately followed by permanent occlusion of the parent vessel with either detachable or nondetachable balloon or coils. The follow-up period ranged from 1 to 8 years. Excellent outcomes were obtained in 12 cases with complete angiographic obliteration of the aneurysm and no new neurological deficits and/or improvement of the preembolization symptoms. Four patients died: two related to the procedure, one secondary to rupture of another untreated aneurysm, and the fourth from a postoperative MCA thrombosis after having failed endovascular test occlusion. The angiographic, clinical, and cerebral blood flow criteria for occlusion tolerance are discussed.

Aged↗
PubMed1988

Pre-operative embolization of naso-pharyngeal angiofibromas. Report of 58 cases.

58 patients with a juvenile nasopharyngeal angiofibroma have been treated by a combined neuroradiological-surgical method. In the cases with smaller tumor extension, fed only by the external carotid arteries or with only slight participation of the internal carotid arteries, the external carotid arteries alone have been embolized using particles. In the cases with marked participation of the internal carotid arteries these vessels were also embolized. In the first group there have been no complications and no recurrences. In the latter (31 cases) there have been three temporary minor complications and 11 recurrences.

Adolescent↗