Off-label use of Angio-Seal vascular closure device for brachial artery puncture closure-deployment modification and initial results after transbrachial PTA.
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Adult↗
Biomedical subjects
D Bilecen
Publications and source records attributed to D Bilecen.
Efficient haemodialysis despite complete central venous thrombosis.
Two cases with a fully functional haemodialysis access, in spite of complete thrombotic occlusion of the ipsilateral subclavian and/or brachiocephalic vein are reported. The coincidentally detected complete venous occlusions may indicate that occult venous stenosis or thrombosis is more frequent than generally assumed. In order to avoid deterioration of the haemodynamic situation interventions may be withheld unless clinical problems related to a diminished outflow occur.
Aged↗
Low-dose intra-arterial contrast-enhanced MR aortography in patients based on a theoretically derived injection protocol.
Multiple intra-arterial contrast agent injections are necessary during MR-guided endovascular interventions. In respect to the approved limits of maximum daily gadolinium dose, a low-dose injection protocol is mandatory. The objective of this study was to derive and apply a low-dose injection protocol for intra-arterial 3D contrast-enhanced MR aortography in patients. Injection rate (Qinj), concentration of injected gadolinium [Gd]inj and aortal blood flow rate (Qblood) were included for the theoretical evaluation of signal intensity (SI) of the arterial lumen. SI simulations were carried out at Qinj=2 versus 4 ml/s in the [Gd]inj range between 0-500 mM. Qinj and [Gd]inj with SI above the 75% threshold of the maximal SI were regarded as optimal injection parameters. [Gd]inj=50 mM and Qinj=4 ml/s were considered as optimal and were administered in five patients for 3D MR aortography. All images revealed clear delineation of the abdominal aorta and its major branches. Mean+/-SD of contrast-to-noise ratios of the abdominal aorta, common iliac and renal artery were 70.2+/-15.2, 58.6+/-12.3 and 67.4+/-12.3. Approximately seven intra-aortal injections would be permissible in patients during MR-guided interventions without exceeding the maximal dose of gadolinium.
Aged↗
[MR-diagnostig of arthrosclerosis].
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Arterial Occlusive Diseases↗
Cuff-compression of the proximal calf to reduce venous contamination in contrast-enhanced stepping-table magnetic Resonance angiography.
PURPOSE: To minimize venous overlay at the calf station in contrast-enhanced three-dimensional (3D) stepping-table magnetic resonance angiography (MRA) using a continuous cuff-compression technique during MR data acquisition. MATERIAL AND METHODS: Within 14 months, 32 patients suffering from symptomatic peripheral arterial occlusive disease (PAOD) with a bilateral ankle-brachial index (ABI) of 0.8 or below were consecutively enrolled in this study. Unilateral cuff-compression of the proximal calf was applied in the study group (n = 14). The control group (n = 18) underwent no compression. All patients underwent three-step 3D contrast-enhanced magnetic resonance angiography (3D CE-MRA) according to the institute's protocol. Venous contamination scores (vcs) at the calf station were blindly ranked by a 1 to 3 rating score (3 = major venous contamination). The vcs values of the control group were regarded as standard. Statistical significance between both groups was evaluated with a paired t test. RESULTS: Symmetric venous contamination was observed within the control group with a mean vcs of 2.2+/-0.6 on the left side and 2.2+/-0.7 on the right side with deltavcsleft-right of 0.1+/-0.2 (P>0.1). In the study group, asymmetric venous contamination was determined with vcsmean = 2.3+/-0.6 for the uncompressed side and vcsmean =1.4+/-0.5 for the compressed side and a deltavcsuncomp-comp of 0.9+/-0.5 (P<0.00005). The control group and the uncompressed side of the study group showed no significant difference in venous contamination (P > 0.1). CONCLUSION: Subdiastolic cuff-compression of the proximal calf is an easily applicable and inexpensive technique by which to reduce venous contamination of the calf station in stepping-table MR angiography and to improve evaluation of the infrapopliteal arteries.
Aged↗
Preliminary experience with dynamic MR projection angiography in the evaluation of cervicocranial steno-occlusive disease.
The application of a contrast-enhanced, two-dimensional MR technique, which provides dynamic projection angiograms at a subsecond temporal frame rate for depiction of the cervical and intracranial arteries, was evaluated in three healthy volunteers and seven patients with various cervicocranial steno-occlusive diseases. Intra-arterial digital subtraction angiography (DSA) served as standard of reference for findings in the patients. Magnetic resonance projection angiography (MRPA) was performed on a standard 1.5-T clinical MR imaging system at intravenous injection of a single dose of contrast agent (0.1 mmol/kg GdDTPA-BMA). Sixty consecutive images of the cerebral circulation were acquired at a temporal frame rate of 900 ms per image in the coronal plane. The collateral flow and the perfusion of the compromised vessel territory were readily assessed by MPRA in patients with occlusion of the internal cerebral artery (ICA) or middle cerebral artery (MCA). The leptomeningeal collateralisation of these patients was displayed in a dynamic fashion. Furthermore, quantitative perfusion measurement provided a difference between both MCA territories in the time to peak (deltaDTTP) of the contrast bolus of 1.12 +/- 0.28 s in five patients with severe stenosis or occlusion of the ICA (healthy volunteers 0.19 +/- 0.05 s). However, important pathological findings, such as the evaluation of carotid artery stenoses and the intracranial collateral flow pattern in patients with severe carotid stenoses, were not sufficiently assessable as compared with DSA. We conclude that the possibility of obtaining simultaneously information about morphology and perfusion dynamics of the cervicocranial vessels is unique in MPRA as compared with other MR techniques. However, in the applied form, the technique is not a reliable tool for the complete evaluation of the cervicocranial vessels in patients with steno-occlusive disease.
Adult↗
Auditory system: functional magnetic resonance imaging.
Functional MR imaging (fMRI) is being used increasingly to explore the human central auditory system. The considerable background noise produced by echo-planar imaging (EPI) and other fMRI sequences, however, interferes in an unpredictable way with the experimental stimuli. Several approaches exist to overcome this problem. Each has its advantages and disadvantages. These different approaches allow researchers to tailor the experimental designs to specific research questions. Recent studies have yielded significant information about human auditory function. Compared with other sensory systems such as the visual system, the auditory database still is relatively small. It is expected that novel methodologic approaches will stimulate scientific exploration of auditory processing and eventually lead to clinically meaningful applications of auditory fMRI.
Auditory Cortex↗
Effect of ethanol on BOLD response to acoustic stimulation: implications for neuropharmacological fMRI.
The effects of ethanol on acoustically stimulated blood oxygenation level-dependent (BOLD) signal response in healthy humans was examined with echo planar functional magnetic resonance imaging (fMRI). An acquisition mode minimizing neuronal activation by scanner noise in combination with acoustic excitation by a pulsed 1000-Hz sine tone was used. Paradigms were repeated three times before and after the ingestion of 0.7 g of ethanol/kg(body weight). Linear correlation analyses (r>/=0.40) revealed bilateral BOLD responses in the auditory cortex. Significant voxels covered a cortical volume of approximately 3 ml that was reduced by approximately 40% after ethanol. The BOLD signal change initially reaching approximately 3% was reduced by 12-27%, depending on the definition of the region of interest for signal quantitation. Because ethanol produces vasodilation, the hemodynamic contribution to the BOLD signal change was estimated by modeling the relationship between regional cerebral blood flow (rCBF) and BOLD signal changes. Assuming a baseline flow increase by 10% after ethanol intake, the resulting 'Flow-BOLD-Dependence' (FBD) curve suggested that the ethanol-related BOLD signal reduction was approximately 7-12% greater than the reduction contributed purely by vasodilation. However, simultaneous determination of rCBF and regional cerebral blood volume would be required for an exact quantitation of the neuronally induced BOLD response. Although the FBD model needs empirical validation, its cautious implementation appears to be helpful if fMRI is used in combination with vasoactive drugs.
Acoustic Stimulation↗
Cortical reorganization after acute unilateral hearing loss traced by fMRI.
Unilateral acoustic stimulation produces a functional MRI (fMRI)-blood-oxygenation-level-dependent (BOLD) response mainly in the contralateral auditory cortex. In unilateral deaf patients, the BOLD response is bilateral. We studied a subject with sudden hearing loss after cochlear nerve resection before and repeatedly after surgery. During normal bilateral hearing, contralateral cortical BOLD responses were found. Progressing compensatory reorganization with bilateral representation of unilateral stimulation was detected over a period of approximately 1 year.
Acute Disease↗
Dynamic susceptibility contrast MR imaging of plaque development in multiple sclerosis: application of an extended blood-brain barrier leakage correction.
Since the pathogenesis of multiple sclerosis (MS) lesions is not yet fully understood, we investigated the potential of dynamic susceptibility contrast (DSC) magnetic resonance (MR) perfusion imaging for a better characterization of lesion pathology. Twenty-five MS patients were examined on a 1.5 T scanner. A single dose of gadolinium (Gd)-DOTA contrast agent was injected, and echoplanar images were acquired every 0.5 seconds for 1 minute. From the signal intensity-versus-time curves, the relative cerebral blood volume (rCBV) was evaluated for regions in plaques and in gray and white matter. The rCBV calculated for acute, Gd-enhancing plaques was corrected for the effects of blood-brain barrier leakage, using a new correction algorithm. Acute plaques had significantly higher blood volumes than normal-appearing white matter (P < = 0.01). Chronic plaques that appeared hypointense on T(1)-weighted images had lower rCBV than T(1)-isointense plaques (P < = 0.03). Our results indicate that the acute phase in MS is accompanied by vasodilation. In later stages of gliosis, the perfusion decreases with increasing axonal injury. Although the DSC technique is less sensitive than conventional MR imaging, the information provided is essentially different from that obtained with any other MR method.
Adult↗
[Detection of central auditory compensation in unilateral deafness with functional magnetic resonance tomography].
BACKGROUND: Functional magnetic resonance imaging (fMRI) is a noninvasive method to detect focal brain activity at high spatial resolution. Acoustic stimulation induces an increase of regional cerebral blood flow in the primary auditory cortex. This entails an increased concentration of diamagnetic oxyhemoglobin in the capillaries and the venous system. The resulting decrease of the local magnetic susceptibility was detected as a signal increase in T2*-weighted images. The central auditory pathways predominantly cross to the contralateral hemisphere in normally hearing subjects. The aim of the present study was to investigate the primary auditory cortex after acoustic stimulation in unilateral deaf patients using fMRI. METHODS: Magnetic resonance images were acquired on a 1.5 T Siemens Vision scanner. For fMRI, a single shot gradient recalled, echo planar imaging (EPI) sequence with decreasing excitation order was used, allowing the aquisition of 9 slices within 1.8 s. The 9 slices covered a slab of 3.6 cm in cranio-caudal extension in the region of the temporal lobes. For statistical processing of the raw image data the SPM96 software package was used. A p-value of p < 0.01 was applied to differentiate between activated and non-activated. The resulting functional activation maps were superimposed onto the EPI scan. The number of activated pixels was used to quantitate the cortical response upon acoustic stimulation. Stimulation consisted of a 1000-Hz sine tone (100 dB SPL at the distal end of the head phone, pulsed at 6 Hz) to which the patients were asked to listen passively. A piezoelectric loudspeaker was mounted on the subject table and connected to a plastic tube system leading to a combination of bilateral ear- and headphones. Auditory paradigms require disentangling experimental excitation from the scanner noise that approximates 90 dB. Headphones suppress noise by approximately 30 dB. To decrease the acoustic background-to-stimulation ratio and to keep background noise constant during stimulation and resting, we employed short scanning (1.8 s) and long resting periods (10.2 s; TR = 12 s). This acquisition mode allows sufficient recovery during off-periods and sufficient excitation during on-periods. 14 unilateral deaf patients were examined. The mean duration of deafness was 22.5 years. RESULTS: Acoustic stimulation of the deaf ear revealed only weak cortical activation which could be explained by sound transmission via bone conduction to the other ear. A significant increase of BOLD (blood oxygen level dependent)-activation in the primary auditory cortex could be demonstrated in all patients after stimulation of the hearing ear. However, remarkable individual differences were noticed concerning the absolute number of activated pixels. The lateralization ratio was calculated by the number of activated pixels on the hearing side divided by the number of activated pixels on the deaf side. A mean lateralization ratio of 0.9 (Stdv +/- 0.6) was found. The mean lateralization ratio for patients with a right deaf ear (n = 8) and those with a left deaf ear (n = 5) was 1.1 (Stdv +/- 0.7) and 0.6 (Stdv +/- 0.3) respectively. However, the difference was not significant (Wilcoxon test: p = 0.08). CONCLUSIONS: Central-auditory compensation by bilateral cortical activation was demonstrated in unilateral deaf patients. Moreover, a tendency towards a dominance of the left primary auditory cortex was found, although the difference between both hemispheres was not significant. The lateralization ratio in unilateral deaf patients is similar to findings after binaural stimulation in normally hearing subjects.
Acoustic Stimulation↗
Cerebral dural arteriovenous fistulas: detection by dynamic MR projection angiography.
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Adult↗
Titration of the BOLD effect: separation and quantitation of blood volume and oxygenation changes in the human cerebral cortex during neuronal activation and ferumoxide infusion.
Most functional magnetic resonance imaging (fMRI) techniques are sensitive to susceptibility variations and rely on the change in blood oxygenation level in response to neuronal activation (BOLD). The BOLD effect is accompanied by a change in cerebral blood flow (rCBF) and cerebral blood volume (rCBV). Intravascular contrast agents, such as magnetite nanoparticles, can be used to measure changes in rCBV. A new measuring protocol has been developed that enables the separate quantification of changes in blood volume and oxygenation levels. A combination of alternating acoustic stimulation blocks and infusion of a superparamagnetic contrast agent offers the possibility to disentangle the competing influences of oxygenation and blood volume changes. Serial blood sampling during infusion was used to assess the actual contrast agent concentration during infusion in order to calculate absolute blood volume changes during neuronal resting and activation states. Magn Reson Med 42:829-836, 1999.
Acoustic Stimulation↗
Motor, somatosensory and auditory cortex localization by fMRI and MEG.
Functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG) were performed in six subjects during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using identical stimulation paradigms. Both functional imaging modalities localized brain activity in adjacent areas of anatomically correct cortex. The mean distances measured between fMRI activity and the corresponding MEG dipoles were 10.1 mm (motor), 10.7 mm (somatosensory), 13.5 mm (auditory right hemisphere) and 14.3 mm (auditory left hemisphere). The distances found may reflect the correlation between electrophysiological and hemodynamic responses due to the different underlying substrates of neurophysiology measured by fMRI and MEG: BOLD contrast vs neuronal biomagnetic activity.
Adult↗
The MR tomograph as a sound generator: fMRI tool for the investigation of the auditory cortex.
An automatic fMRI protocol for the investigation of the human auditory cortex has been developed. For the activation of the auditory system, the scanner noise itself is the source of sound. Rapid switching of B0 gradients allows the generation of tones of defined frequencies and amplitude on a conventional scanner without hardware change. No additional device for sound generation or sound delivery is needed. The proposed technique allows functional MRI of the auditory cortex in a clinical routine session.
Acoustic Stimulation↗
Tonotopic organization of the human auditory cortex as detected by BOLD-FMRI.
Functional magnetic resonance imaging is a noninvasive and nonradioactive method for the detection of focal brain activity. In the present study the auditory cortex was investigated in nine normal subjects who were binaurally stimulated using pulsed sine tones of 500 Hz and 4000 Hz. The BOLD (blood oxygenation level dependent) signal change coincided with the stimulation paradigm and was detected in the plane of the superior temporal gyrus. The comparison of the spatial distribution of activated areas revealed a different behavior for the two frequencies. The present findings underline the existence of a frequency specific organization in the medio-lateral, fronto-occipital and cranio-caudal extension in both hemispheres of the auditory cortex in human. The activated areas for the high tone were found more frontally and medially orientated than the low tone stimulated areas. Furthermore, a slight cranio-caudal shift was observed for the higher frequency, more pronounced in the right than in the left temporal lobe. Finally, for most of the subjects investigated the BOLD activation area of the 500 Hz sine tone was larger than that of the 4000 Hz stimulation. Both frequencies showed a lateralization of signal response to the left temporal lobe.
Acoustic Stimulation↗
[Visualization of central auditory processes with functional magnetic resonance tomography].
BACKGROUND: Central auditory processes can be visualized using functional MRI in a non-invasive manner and at high spatial resolution. Acoustic stimulation leads to an increase of blood flow of activated areas in the plane of the superior temporal gyrus. Radiologically, this may be visualized based on the long T2-relaxation time of oxyhemoglobin. PATIENTS: Ten normal-hearing subjects with ages between 28 and 38 years took part in the investigations. They received binaural, monaural right, and monaural left stimulation with pulsed sine tones of 1000 Hz at a pulse rate of 6 Hz and a sound pressure level of 100 dB SPL. Tonotopic organization of the auditory cortex was visualized using stimulation by pulsed sine tones of 500 Hz and 4000 Hz. RESULTS: Following monaural acoustic stimulation, increased activity of the contralateral auditory cortex could be demonstrated in 9 subjects. In one subject, bilateral activity was noted. Concerning the tonotopic organization of the auditory cortex, we could show that the higher frequencies were localized more medially and anteriorly; the lower frequencies were localized more laterally and posteriorly in the superior temporal gyrus. However, considerable overlap was noted. CONCLUSIONS: The overlap of the different frequencies could explain the controversial discussion of the tonotopic organization of the auditory cortex. The results of the monaural acoustic stimulation show clearly the predominant signal increase of contralateral areas in the primary auditory cortex. These results confirm the opinion of the current textbooks that the fiber of the auditory pathways mostly cross. Further investigations using functional MRI are necessary for better understanding of physiological and pathophysiological central-auditory processes.
Acoustic Stimulation↗
Auditory cortical responses in hearing subjects and unilateral deaf patients as detected by functional magnetic resonance imaging.
Functional magnetic resonance imaging is a non-invasive method for the detection of focal brain activity at high spatial resolution. Acoustic stimulation leads to a blood oxygenation level dependent signal change in the plane of the superior temporal gyrus. The dependence of this response in the auditory cortex on binaural, monaural left and monaural right acoustic stimulation for 10 healthy subjects and five monaural deaf patients is described. Acoustic stimulation consists of 1000 Hz pulsed sine tones at a pulse rate of 6 Hz and a sound pressure level of 95 dB. For monaural stimulation, normal-hearing subjects revealed a strong lateralization of cortical response towards the contralateral hemisphere. The lateralization ratios between left and right hemispheric response areas were 3.4-5.2 for monaural stimulation and nearly balanced for binaural stimulation. Additionally, the sum of cortical activation volumes induced by monaural left and right stimulation was approximately 30% smaller than for binaural stimulation, indicating either inhibitory mechanisms or neuronal facilitation within the auditory pathways. For monaural deaf subjects the lateralization ratio between left to right response was just 1.3 towards the contralateral hemisphere of the healthy ear, which is comparable to binaural responses of normal-hearing subjects. This observation seems to indicate a plasticity or a reorganization of auditory pathways of monaural deaf patients.
Adult↗