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.

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.

Does soluble triggering receptor expressed on myeloid cells-1 play any role in the pathogenesis of septic shock?

In order to define the significance of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) upon progression from sepsis or severe sepsis to septic shock a prospective study was designed with 90 enrolled patients with septic syndrome due to ventilator-associated pneumonia. Blood was sampled on seven consecutive days upon initiation of symptoms and concentrations of tumour necrosis factor-alpha (TNFalpha), interleukin-6 (IL-6), IL-8 and sTREM-1 were estimated in serum by an enzymeimmunoassay. No differences in concentrations of TNFalpha, IL-6 and IL-8 were found between patients with sepsis, severe sepsis and septic shock on the first day of presentation of symptoms. Patients presenting with septic shock had concentrations of sTREM-1 significantly higher than both patients with sepsis and severe sepsis on the first day; no difference was found between patients with sepsis and severe sepsis. A positive correlation was detected between sTREM-1 and the white blood cell count. Serum levels of sTREM-1 were significantly lower in patients where VAP resolved compared to those where VAP did not resolve; similar findings were noted between patients who eventually survived and those who died. IL-6 followed the kinetics of sTREM-1 in correlation to patients's prognosis; levels of TNFalpha and IL-8 were unrelated to prognosis. It is concluded that sTREM-1 is particularly increased upon evolution from sepsis or severe sepsis to septic shock. Its sustained increase is an indication of poor outcome. The underlined pathophysiological role of sTREM-1 for the transition from sepsis or severe sepsis to septic shock might constitute a novel target for immunomodulatory therapy.

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.

Inflammatory myofibroblastic tumor with CNS involvement

BACKGROUND

Inflammatory myofibroblastic tumors (IMT) represent a spectrum of neoplasms that occur in the mesentery and retroperitoneum and less frequently in the mediastinum of children and young adults. Transformation into inflammatory fibrosarcoma and metastases are rare.

CASE REPORT

We report the case of a 16-year-old patient with an inflammatory myofibroblastic tumor of the mesentery with mediastinal metastases. Partial remission was obtained by chemotherapy with ifosfamide, dactinomycine, and vincristine. Two months later, relapse with infiltration of the meninges developed, and the patient died.

CONCLUSION

This case demonstrates unusual features of an IMT: presentation with metastases, excellent response to chemotherapy, dissemination to the CNS.

McLeod syndrome: a novel mutation, predominant psychiatric manifestations, and distinct striatal imaging findings

The McLeod syndrome is an X-linked disorder caused by mutations of the XK gene encoding the XK protein. The syndrome is characterized by absent Kx erythrocyte antigen, weak expression of Kell blood group system antigens, and acanthocytosis. In some allelic variants, elevated creatine kinase, myopathy, neurogenic muscle atrophy, and progressive chorea are found. We describe a family with a novel point mutation in the XK gene consisting of a C to T base transition at nucleotide position 977, introducing a stop codon. Among seven affected males, five manifested with psychiatric disorders such as depression, bipolar disorder, or personality disorder, but only two presented with chorea Positron emission tomography and magnetic resonance volumetry revealed reduced striatal 2-fluoro-2-deoxy-glucose (FDG) uptake and diminished volumes of the caudate nucleus and putamen that correlated with disease duration. In contrast, none of 12 female mutation carriers showed psychiatric or movement disorders. However, a semidominant effect of the mutation was suggested by erythrocyte and blood group mosaicism and reduced striatal FDG uptake without structural abnormalities. Therefore, patients with psychiatric signs or symptoms segregating in an X-linked trait should be examined for acanthocytosis and Kell/Kx blood group serology.

Spatial relationship between vestibular schwannoma and facial nerve on three-dimensional T2-weighted fast spin-echo MR images

BACKGROUND AND PURPOSE

During surgical removal of a vestibular schwannoma, correct identification of the facial nerve is necessary for its preservation and continuing function. We prospectively analyzed the spatial relationship between vestibular schwannomas and the facial nerve using 3D T2-weighted and postcontrast T1-weighted spin-echo (SE) MR imaging.

METHODS

Twenty-two patients with a unilateral vestibular schwannoma were examined with MR imaging. The position and spatial relationship of the facial nerve to adjacent tumor within the internal auditory canal (IAC) and cerebellopontine angle cistern (CPA) were assessed on multiplanar reformatted 3D T2-weighted fast spin-echo (FSE) images and on postcontrast transverse and coronal T1-weighted SE images. The entrance of the nerve into the bony canal at the meatal foramen and the nerve root exit zone along the brain stem were used as landmarks to follow the nerve course proximally and distally on all images.

RESULTS

The spatial relationship between vestibular schwannoma and facial nerve could not be detected on postcontrast T1-weighted SE images. In 86% of the patients, the position of the nerve in relation to the tumor was discernible on multiplanar reformatted 3D T2-weighted FSE images. In tumors with a maximal diameter up to 10 mm, the entire nerve course was visible; in tumors with a diameter of 11 to 24 mm, only segments of the facial nerve were visible; and in tumors larger than 25 mm, the facial nerve could not be seen, owing to focal nerve thinning and obliteration of landmarks within the IAC and CPA.

CONCLUSION

Identification of the facial nerve and its position relative to an adjacent vestibular schwannoma is possible on multiplanar reformatted 3D T2-weighted FSE images but not on postcontrast T1-weighted SE images. Detection of this spatial relationship depends on the tumor's size and location.

Comparison of cerebral blood volume measured by near infrared spectroscopy and contrast enhanced magnetic resonance imaging

Cerebral blood volume (CBV) can be quantified by both near infrared spectroscopy (NIRS) and magnetic resonance imaging (MRI). The aim is to compare CBV results obtained by NIRS and MRI in adult patients. 10 adult patients, 6 females and 4 males, age median 24 (range 21 to 76) years, were included in this study. All needed a MRI investigation with contrast medium for clinical reasons. The NIRS instrument, the Cerebral RedOx Monitor 2020 from Critikon, quantifies cerebral haemoglobin concentration using a sensor with two receiving channels at different distances. Geometrical detector arrangements of this type enable a ratio measurement to be achieved, which reduces the contribution of the skull and skin, thus allowing quantification. Cerebral haemoglobin concentration can be converted in CBV, as the haemoglobin concentration in the blood is known. CBV can be quantified by MRI using an indicator dilution method. The method requires an injection of a paramagnetic contrast agent. The input function can be measured at the throat and thus perfusion images can be quantified. CBV was measured by NIRS just before the patient entered the magnet and after he had left it. The sensor for the NIRS measurement was applied to the patients front three times for 1 minute to each side, avoiding the sinuses. CBV was determined by contrast enhanced MRI between the NIRS measurements. The mean CBV (NIRS) was 8.6 (SD 1.3) ml/100 g and CBV (MRI) was 7.1 (SD 2.5). The correlation between CBV (NIRS) and CBV (MRI) was Pearson's correlation coefficient -0.297 (p = 0.204) respectively Spearman's rho (nonparametric) -0.266 (p = 0.257). The CBV values obtained by NIRS and MRI, even though they are in the same range, do not correlate.

Transient oedema of the cervical spinal cord

Transient but very intense oedema of the cervical spinal cord was observed in two patients with obstruction of the cerebrospinal fluid (CSF) pathways. Both presented with hydrocephalus, one due to an infratentorial obstructing mass and the other due to postmeningitic adhesive obstruction of the outlet foramina of the fourth ventricle. In animal experiments with obstruction of CSF pathways (due to outlet foramina obstruction or to downward tentorial herniation) flattening and stretching of the ependymal cells along the central canal is observed, followed by disruption and splitting of the ependymal lining and then by extracellular oedema of the subependymal tissue. Without treatment, frank cavity formation develops in a fourth stage. In our two patients, however, most probably because of appropriate decompressive therapy, the oedema disappeared completely without a residual spinal cord lesion.

Higher-order spectral analysis in laser-Doppler flowmetry signal processing

This paper presents an application of higher order statistics and spectra to the problem of laser-Doppler Flowmetry (LDF) for microcirculation monitoring. The proposed signal processing technique computes the bispectra of LDF signals after appropriate pre-processing and extracts features which can be used for classification of the signals to a normal or patient category. Bispectra are defined in terms of the third-order moments or cumulants of signals and are shown to contain valuable information for the above classification of LDF signals. Experimental studies, including (a) a set of 17 normal subjects and 69 patients with Raynaud's phenomenon and (b) 50 LDF-signals separated to four groups from patients that have different pathologic characteristics, are described and results are presented which illustrate the performance of the proposed approach when applied to the LDF signals.

Ramsay Hunt syndrome associated with brain stem enhancement

Postcontrast T1-weighted MR images in a patient with Ramsay Hunt syndrome showed an enhancing lesion in the region of the nucleus of the pontine facial nerve and abnormal enhancement of the intrameatal, labyrinthine, and tympanic facial nerve segments and of the geniculate ganglion, as well as enhancement of the vestibulocochlear nerve and parts of the membranous labyrinth. This enhancement most probably resulted from a primary neuritis of the intrameatal nerve trunks of the seventh and eighth cranial nerves.

3D T2-weighted fast spin-echo MRI sialography of the parotid gland

The diagnostic value of 3D T2-weighted MRI sialography and 2D T2-weighted fast spin-echo (FSE) images for delineation of the normal duct system and characterisation of parotid gland duct pathology was compared in a prospective study. We studied eight healthy volunteers and 18 patients with pathology of the parotid gland (tumours in 3, sialolithiasis in 6, Sjögren's disease in 4, recurrent or chronic parotitis in 4, post-traumatic stricture of the main parotid duct in 1). A heavily T2-weighted 3D FSE sequence was compared with a conventional 2D T2-weighted FSE sequence. The normal main parotid duct was always visible on 3D sialography and seen in 68% of the 2D T2-weighted FSE studies. The diagnostic reliability of both sequences for diagnosis of luminal concretions in sialolithiasis and dilatation of the duct in duct stricture or chronic parotitis was equal, although slight intraglandular dilatation was appreciated only on 3D sialography. Extraductal pathology resulting in obstruction or displacement of ducts was better characterised on 2D T2-weighted images. However, 3D MRI sialography offered the advantage of postprocessing with overview images and multiple maximum-intensity projection images in any plane.

A new correlation-based fuzzy logic clustering algorithm for fMRI

Fuzzy logic clustering algorithms are a new class of processing strategies for functional MRI (fMRI). In this study, the ability of such methods to detect brain activation on application of a stimulus task is demonstrated. An optimization of the selected algorithm with regard to different parameters is proposed. These parameters include (a) those defining the pre-processing procedure of the data set; (b) the definition of the distance between two time courses, considered as p-dimensional vectors, where p is the number of sequential images in the fMRI data set; and (c) the number of clusters to be considered. Based on the assumption that such a clustering algorithm should cluster the pixel time courses according to their similarity and not their proximity (in terms of distance), cross-correlation-based distances are defined. A clear mathematical description of the algorithm is proposed, and its convergence is proven when similarity measures are used instead of conventional Euclidean distance. The differences between the membership function given by the algorithm and the probability are clearly exposed. The algorithm was tested on artificial data sets, as well as on data sets from six volunteers undergoing stimulation of the primary visual cortex. The fMRI maps provided by the fuzzy logic algorithm are compared to those achieved by the well established cross-correlation technique.

T2-weighted three-dimensional fast spin-echo MR in inflammatory peripheral facial nerve palsy

PURPOSE

Our objective was to identify histologically and intraoperatively verified focal nerve thickening of the distal intrameatal segment on three-dimensional fast spin-echo (FSE) T2-weighted MR images as a new diagnostic criterion in patients with inflammatory peripheral facial nerve palsy.

METHODS

Twenty-two patients with clinically diagnosed unilateral (n = 20) or bilateral (n = 2) inflammatory peripheral facial nerve palsy were examined on a 1.5-T MR imager using noncontrast and contrast-enhanced T1-weighted SE sequences and 3-D T2-weighted FSE sequences with secondary reformations. Abnormal contrast enhancement and possible focal nerve thickening of the distal intrameatal segment, labyrinthine nerve segment, and geniculate ganglion region were analyzed prospectively.

RESULTS

In all patients, the T1-weighted postcontrast SE images showed characteristic smooth, linear, abnormally intense contrast enhancement of the distal intrameatal segment, indicating peripheral inflammatory nerve palsy. In 23 nerves (96%) a focal bulbous nerve thickening of the distal intrameatal segment was observed on 3-D T2-weighted FSE images. In 100% of patients with peripheral inflammatory facial nerve palsy, postcontrast T1-weighted SE images showed a smooth, linear, and abnormally intense contrast enhancement of the distal intrameatal segment; reformatted very thin 3-D T2-weighted FSE images showed a focal bulbous nerve thickening of the distal intrameatal segment in 96% of patients. These findings corresponded to intraoperative and histologic findings.

CONCLUSION

Three-dimensional T2-weighted FSE sequences are fast and cheap compared with T1-weighted postcontrast images, but secondary reformations are time-consuming and require exact anatomic knowledge for careful analysis of the different nerve segments.