The impact of athrosclerosis on cognition and disability in multiple sclerosis patients: the ATHUS score.

AIM: Atherosclerosis of the large arteries of the neck could be related to the cognitive and motor deficit. We investigated if the atherosclerosis of common carotid and femoral arteries in patients with multiple sclerosis (MS) is directly linked with a disability and has an inverse relationship with cognitive performance. METHODS: We enrolled, in this prospective study, a random sample of 105 patients with MS and 22 healthy controls. All participants received a comprehensive neuropsychological assessment. The physical disability was quantified with the Expanded Disability Status Scale (EDSS). We utilized ultrasound of the carotid and femoral arteries to evaluate the degree of stenosis and intima-media thickness (IMT). We created a novice ultrasound index of atherosclerosis (ATHUS score) based on the arterial stenosis and the IMT of the carotid and femoral arteries. We then compared the results of the psychometric assessment and EDSS with the ATHUS score. RESULTS: The analysis demonstrated that higher cognitive function is correlated with lower values of ATHUS score (p =0.01). Also, there was a direct correlation between the ATHUS score and EDSS (p =0.001). CONCLUSION: Our results suggest that the degree of atherosclerosis, as calculated by the ATHUS score, is directly related to low cognitive score and higher sensory and motor disability. HIPPOKRATIA 2019, 23(2): 81-86.

Gas spectroscopy through multimode self-mixing in a double-metal terahertz quantum cascade laser.

A multimode self-mixing terahertz-frequency gas absorption spectroscopy is demonstrated based on a quantum cascade laser. A double-metal device configuration is used to expand the laser's frequency tuning range, and a precision-micromachined external waveguide module is used to enhance the optical feedback. Methanol spectra are measured using two laser modes at 3.362 and 3.428 THz, simultaneously, with more than eight absorption peaks resolved over a 17 GHz bandwidth, which provide the noise-equivalent absorption sensitivity of 1.20×10-3 cm-1 Hz-1/2 and 2.08×10-3 cm-1 Hz-1/2, respectively. In contrast to all previous self-mixing spectroscopy, our multimode technique expands the sensing bandwidth and duty cycle significantly.

Silver-based surface plasmon waveguide for terahertz quantum cascade lasers.

Terahertz-frequency quantum cascade lasers (THz QCLs) based on ridge waveguides incorporating silver waveguide layers have been investigated theoretically and experimentally, and compared with traditional gold-based devices. The threshold gain associated with silver-, gold- and copper-based devices, and the effects of titanium adhesion layers and top contact layers, in both surface-plasmon and double-metal waveguide geometries, have been analysed. Our simulations show that silver-based waveguides yield lower losses for THz QCLs across all practical operating temperatures and frequencies. Experimentally, QCLs with silver-based surface-plasmon waveguides were found to exhibit higher operating temperatures and higher output powers compared to those with identical but gold-based waveguides. Specifically, for a three-well resonant phonon active region with a scaled oscillator strength of 0.43 and doping density of 6.83 × 1015 cm-3, an increase of 5 K in the maximum operating temperature and 40% increase in the output power were demonstrated. These effects were found to be dependent on the active region design, and greater improvements were observed for QCLs with a larger radiative diagonality. Our results indicate that silver-based waveguide structures could potentially enable THz QCLs to operate at high temperatures.

Extraction-controlled terahertz frequency quantum cascade lasers with a diagonal LO-phonon extraction and injection stage.

We report an extraction-controlled terahertz (THz)-frequency quantum cascade laser design in which a diagonal LO-phonon scattering process is used to achieve efficient current injection into the upper laser level of each period and simultaneously extract electrons from the adjacent period. The effects of the diagonality of the radiative transition are investigated, and a design with a scaled oscillator strength of 0.45 is shown experimentally to provide the highest temperature performance. A 3.3 THz device processed into a double-metal waveguide configuration operated up to 123 K in pulsed mode, with a threshold current density of 1.3 kA/cm2 at 10 K. The QCL structures are modeled using an extended density matrix approach, and the large threshold current is attributed to parasitic current paths associated with the upper laser levels. The simplicity of this design makes it an ideal platform to investigate the scattering injection process.

Active phase-nulling of the self-mixing phase in a terahertz frequency quantum cascade laser.

We demonstrate an active phase-nulling scheme for terahertz (THz) frequency quantum cascade lasers (QCLs) under optical feedback, by active electronic feedback control of the emission frequency. Using this scheme, the frequency tuning rate of a THz QCL is characterized, with significantly reduced experimental complexity compared to alternative approaches. Furthermore, we demonstrate real-time displacement sensing of targets, overcoming the resolution limits imposed by quantization in previously implemented fringe-counting methods. Our approach is readily applicable to high-frequency vibrometry and surface profiling of targets, as well as frequency-stabilization schemes for THz QCLs.

Three-dimensional terahertz imaging using swept-frequency feedback interferometry with a quantum cascade laser.

We demonstrate coherent three-dimensional terahertz imaging by frequency modulation of a quantum cascade laser in a compact and experimentally simple self-mixing scheme. Through this approach, we can realize significantly faster acquisition rates compared to previous schemes employing longitudinal mechanical scanning of a sample. We achieve a depth resolution of better than 0.1 µm with a power noise spectral density below -50 dB/Hz, for a sampling time of 10 ms/pixel.

Terahertz inverse synthetic aperture radar imaging using self-mixing interferometry with a quantum cascade laser.

We propose a terahertz (THz)-frequency synthetic aperture radar imaging technique based on self-mixing (SM) interferometry, using a quantum cascade laser. A signal processing method is employed which extracts and exploits the radar-related information contained in the SM signals, enabling the creation of THz images with improved spatial resolution. We demonstrate this by imaging a standard resolution test target, achieving resolution beyond the diffraction limit.

A Case of Transient Ischemic Attack in a patient with Ulcerative Colitis.

Arterial stroke is a rare complication of Ulcerative Colitis (UC) and so far there are no guidelines for the treatment of stroke in these patients. The pathogenesis of thrombosis in UC remains uncertain. This case is one of the few published reports on the relationship between stroke associated with UC and the factor V Leiden mutation.

The pharyngo-tympano-stapedial variant of the middle meningeal artery. A case report.

Atypical origin of the middle meningeal artery from the cervical internal carotid artery is a rare angiographic finding. We describe a case of the pharyngo-tympano-stapedial variant of the middle meningeal artery in a young patient. In this vascular variation the proximal segment of the middle meningeal artery, corresponding to an annexed inferior tympanic artery, originates from the cervical carotid artery. Then over the promontory it unites with the superior tympanic artery and continues with its intracranial course via the petrous branch.

Endovascular occlusion of a lacerated primitive trigeminal artery during surgical resection of clival chordoma. a case report.

We describe a case of a persistent primitive trigeminal artery (PPTA) coexistent with a clival chordoma. During surgery of the tumor, the partially incorporated PPTA was inadvertently traumatized and ruptured. The operation was discontinued and the PPTA was endovascularly occluded permitting further safe resection of the tumor.

Preliminary experience with visualization of intracortical fibers by focused high-resolution diffusion tensor imaging.

BACKGROUND AND PURPOSE: The inherent low anisotropy of gray matter and the lack of adequate imaging sensitivity and resolution has, so far, impeded depiction of axonal fibers to their intracortical origin or termination. We tested the hypothesis that an experimental approach with high-resolution diffusion tensor imaging (DTI) provides anisotropic data for fiber tractography with sufficient sensitivity to visualize in vivo the fine distribution of white matter bundles at the intracortical level. MATERIALS AND METHODS: We conducted phantom measurements of signal-to-noise ratio (SNR) and obtained diffusion tensor maps of the occipital lobe in 6 healthy volunteers using a dedicated miniature phased array detector at 3T. We reconstructed virtual fibers using a standard tracking algorithm. RESULTS: The coil array provided a SNR of 8.0 times higher at the head surface compared with a standard quadrature whole head coil. Diffusion tensor maps could be obtained with an in-plane resolution of 0.58 x 0.58 mm(2). The axonal trajectories reconstructed from the diffusion data penetrate into the cortical ribbon perpendicular to the pial surface. This is the expected pattern for the terminations of thalamocortical afferent fibers to the middle layers of the occipital cortex and is consistent with the known microstructural organization of the mammalian cerebral cortex. CONCLUSION: High-resolution DTI reveals intracortical anisotropy with a distinct parallel geometrical order, perpendicular to the pial surface, consistent with structures that may be identified as the terminal afferents in cortical gray matter.

Combining fMRI and DTI: a framework for exploring the limits of fMRI-guided DTI fiber tracking and for verifying DTI-based fiber tractography results.

A powerful, non-invasive technique for estimating and visualizing white matter tracts in the human brain in vivo is white matter fiber tractography that uses magnetic resonance diffusion tensor imaging. The success of this method depends strongly on the capability of the applied tracking algorithm and the quality of the underlying data set. However, DTI-based fiber tractography still lacks standardized validation. In the present work, a combined fMRI/DTI study was performed, both to develop a setup for verifying fiber tracking results using fMRI-derived functional connections and to explore the limitations of fMRI based DTI fiber tracking. Therefore, a minor fiber bundle that features several fiber crossings and intersections was examined: The striatum and its connections to the primary motor cortex were examined by using two approaches to derive the somatotopic organization of the striatum. First, an fMRI-based somatotopic map of the striatum was reconstructed, based on fMRI activations that were provoked by unilateral motor tasks. Second, fMRI-guided DTI fiber tracking was performed to generate DTI-based somatotopic maps, using a standard line propagation and an advanced fast marching algorithm. The results show that the fiber connections reconstructed by the advanced fast marching algorithm are in good agreement with known anatomy, and that the DTI-revealed somatotopy is similar to the fMRI somatotopy. Furthermore, the study illustrates that the combination of fMRI with DTI can supply additional information in order to choose reasonable seed regions for generating functionally relevant networks and to validate reconstructed fibers.

Influence of SENSE on image properties in high-resolution single-shot echo-planar DTI.

Limited spatial resolution is a key obstacle to the study of brain white matter structure with diffusion tensor imaging (DTI). In its frequent implementation with single-excitation spin-echo echo-planar sequences, DTI's ability to resolve small structures is strongly restricted by T2 and T2* decay, B0 inhomogeneity, and limited signal-to-noise ratio (SNR). In this work the influence of sensitivity encoding (SENSE) on diffusion-weighted (DW) image properties is investigated. Computer simulations showed that the PSF becomes narrower with increasing SENSE reduction factors, R, enhancing the intrinsic resolution. After a brief theoretical discussion, we describe the estimation of SNR on a pixel-by-pixel basis as a function of R. The mean image SNR behavior is manifold: SENSE is capable of increasing SNR efficiency by reducing the echo time (TE). Each SNR(R) curve reveals a maximum that depends on the amount of partial Fourier encoding used. The overall best SNR efficiency for an eight-element head coil array and a b-factor of 1000 s/mm2 is achieved at R = 2.1 and partial Fourier encoding of 60%. In vivo tensor maps of volunteers and a patient, with an in-plane resolution of 0.78 x 0.78 mm2, are also presented to demonstrate the practical implementation of the parallel approach.

Resolving fiber crossing using advanced fast marching tractography based on diffusion tensor imaging.

Magnetic resonance diffusion tensor tractography is a powerful tool for the non-invasive depiction of the white matter architecture in the human brain. However, due to limitations in the underlying tensor model, the technique is often unable to reconstruct correct trajectories in heterogeneous fiber arrangements, such as axonal crossings. A novel tractography method based on fast marching (FM) is proposed which is capable of resolving fiber crossings and also permits trajectories to branch. It detects heterogeneous fiber arrangements by incorporating information from the entire diffusion tensor. The FM speed function is adapted to the local tensor characteristics, allowing in particular to maintain the front evolution direction in crossing situations. In addition, the FM's discretization error is reduced by increasing the number of considered possible front evolution directions. The performance of the technique is demonstrated in artificial data and in the healthy human brain. Comparisons with standard FM tractography and conventional line propagation algorithms show that, in the presence of interfering structures, the proposed method is more accurate in reconstructing trajectories. The in vivo results illustrate that the elucidated major white matter pathways are consistent with known anatomy and that multiple crossings and tract branching are handled correctly.

Trapped microcatheter from vessel spasm: safe removal after double microcatheter technique and local papaverine infusion.

SUMMARY: In a child undergoing combined transarterial and direct percutaneous puncture embolization of an extensive and complex facial arteriovenous malformation, severe arterial spasm fixed a flow-directed microcatheter in an ethmoidal branch of the left ophthalmic artery. Multiple traction attempts failed to remove the microcatheter. After catheterization of the distal, post central retinal artery part of the same ophthalmic artery, with a second flow-directed microcatheter and following intraarterial papaverine injection through this second microcatheter, the fixed microcatheter could be removed without complication. This case demonstrates a technique that can be attempted before deciding to leave the microcatheter in the patient or to remove it surgically.

Endovascular treatment of cerebral arteriovenous malformations with emphasis on the curative role of embolisation.

SUMMARY: Valavanis A, Pangalu A, Tanaka M. Endovascular treatment of cerebral arteriovenous malformations with emphasis on the curative role of embolisation. Schweiz Arch Neurol Psychiatr 2004;155:341-7. Cerebral arteriovenous malformations are complex and only partially understood vascular lesions of the central nervous system with a natural history characterised by significant morbidity and mortality mainly due to an increased hemorrhagic risk, Microneurosurgical removal, radiosurgical obliteration and neuroendovascular embolisation are the principal therapeutic modalities applied individually or in various combinations according to varying selection criteria for the treatment of cerebral arteriovenous malformations. In this context embolisation plays a central role cither as a complementary or as the sole treatment technique. This report summarises the evolutive 18 years of continuous experience of the senior author with the neuroradiological evaluation and endovascular treatment of 644 patients with a cerebral arteriovenous malformation. Special emphasis is given to the underlying concepts and specific endovascular techniques developed for the complete, i.e. curative embolisation of cerebral arteriovenous malformations. Precise angiographic analysis of the vascular composition and intrinsic angioarchitecture of the nidus of the arteriovenous malformation by super-selective microcatheterisation is required to identify the types of feeding arteries and patterns of their supply, the number and vascular connections of nidal compartments, the types of arteriovenous shunts, the morphology of the vascular spaces composing the nidus and the number and exit patterns of draining veins. Complete angiographic investigation for recognition of secondarily induced phenomena of the cerebral vasculature, such as arterial and venous high-flow angiopathy and so-called perinidal angiogenesis is essential for a comprehensive evaluation and assessment of the associated haemorrhagic risk. Based on a precise topographic classification, detailed angioarchitectural analysis, application of superselective multimicrocatheterisation techniques along with a controlled intranidal injection of non-absorbable liquid embolic materials, nearly 40% of cerebral arteriovenous malformations can be completely and stably obliterated and therefore curatively treated by single session or multistaged embolisation with a morbidity of 1.3% and a mortality of 13%. which arc lower than the known natural history of this disease.

Normalisation of ocular pulse amplitude after embolisation of dural cavernous sinus arteriovenous fistula.

BACKGROUND: The difference in the ocular pulse amplitude between an individual's eyes may reflect abnormalities of the cerebrovascular circulation and has been shown to be helpful in assessing patients with cavernous sinus arteriovenous fistulas. HISTORY AND SIGNS: A 71-year-old woman presented with episcleral injection, proptosis, bruit and retro-orbital pain on the left side. Ocular pulse amplitude as measured by dynamic contour tonometry was 4.38 +/- 1.23 mm Hg in the right and 9.57 +/- 2.71 mm Hg in the left eye. Angiography revealed the haemodynamics of a dural left cavernous sinus arteriovenous fistula. THERAPY AND OUTCOME: Successful occlusion of the fistula was performed by transvenous embolisation. After embolisation, ocular pulse amplitude was 2.84 +/- 0.60 mm Hg in the right and 1.88 +/- 0.29 mm Hg in the left eye. CONCLUSION: In this case of a dural arteriovenous fistula the ocular pulse amplitude as measured by dynamic contour tonometry parallels closely both clinical findings and neuroimaging.

SENSE-DTI at 3 T.

While holding vast potential, diffusion tensor imaging (DTI) with single-excitation protocols still faces serious challenges. Limited spatial resolution, susceptibility to magnetic field inhomogeneity, and low signal-to-noise ratio (SNR) may be considered the most prominent limitations. It is demonstrated that all of these shortcomings can be effectively mitigated by the transition to parallel imaging technology and high magnetic field strength. Using the sensitivity encoding (SENSE) technique at 3 T, brain DTI was performed in nine healthy volunteers. Despite enhanced field inhomogeneity, parallel acquisition permitted both controlling geometric distortions and enhancing spatial resolution up to 0.8 mm in-plane. Heightened SNR requirements were met in part by high base sensitivity at 3 T. A further significant increase in SNR efficiency was accomplished by SENSE acquisition, exploiting enhanced encoding speed for echo time reduction. Based on the resulting image data, high-resolution tensor mapping is demonstrated.