688 research outputs found
Total-body contrast-enhanced MRA on a short, wide-bore 1.5-T system: intra-individual comparison of Gd-BOPTA and Gd-DOTA
Total-body contrast-enhanced MRA (CE-MRA) provides information of the entire vascular system according to a one-stop-shop approach. Short, wide-bore scanners have not yet been used for total-body CE-MRA, probably due to their restricted field of view in the z-direction. The purpose of this feasibility study is to introduce an image protocol for total-body MRA on a short, wide-bore system. The protocol includes five to six table-moving steps and two injection runs. Two pharmacologically different contrast materials (CM) were applied in ten healthy volunteers in view of possible CM-dependent influences on the protocol outcome (Gd-Bopta, Gd-Dota). Differences consisted of significantly higher CNR with Gd-Bopta with a mean of 73.8 ± 38.7 versus 69.1 ± 34.3 (p = 0.008), significantly better arterial visualization values with Gd-Dota with a mean of 1.26 ± 0.44 versus 1.53 ± 0.73 (p = 0.003) and a tendency to less venous overlay with Gd-Dota, mean 1.19 ± 0.44 and 1.34 ± 0.72, respectively (p = 0.065) (two-tailed Wilcoxon matched-pairs test). Overall 94% of the steps were valued as qualitatively excellent or good. The good results with both CM suggest a transfer to further patient evaluatio
Categorification of a frieze pattern determinant
Broline, Crowe and Isaacs have computed the determinant of a matrix
associated to a Conway-Coxeter frieze pattern. We generalise their result to
the corresponding frieze pattern of cluster variables arising from the
Fomin-Zelevinsky cluster algebra of type A. We give a representation-theoretic
interpretation of this result in terms of certain configurations of
indecomposable objects in the root category of type A.Comment: 14 pages; 8 figures. Sections 1-3 rewritten, postponing the cluster
interpretation until Section 3. Minor correction
Cycle-finite module categories
We describe the structure of module categories of finite dimensional algebras
over an algebraically closed field for which the cycles of nonzero
nonisomorphisms between indecomposable finite dimensional modules are finite
(do not belong to the infinite Jacobson radical of the module category).
Moreover, geometric and homological properties of these module categories are
exhibited
Vestibular disease in dogs: association between neurological examination, MRI lesion localisation and outcome.
OBJECTIVES
To determine whether the neurological examination correctly distinguishes between central and peripheral vestibular lesions in dogs.
MATERIALS AND METHODS
Retrospective study on dogs with vestibular disease presenting to two referral clinics in Germany.
RESULTS
Ninety-three dogs were included; neurological examination suggested central vestibular disease in 62 and a peripheral lesion in 31. MRI diagnosis was central vestibular disease in 68 dogs and peripheral in 25. Of the 62 dogs with a lesion localisation diagnosed as central vestibular by neurological exam, 61 were correctly identified (98.4%). Twenty-four of the 31 dogs diagnosed with a peripheral lesion by neurological exam had a consistent lesion on MRI (77.4%).
CLINICAL SIGNIFICANCE
The neurological examination is efficient at identifying lesions in the central vestibular system but less so for peripheral lesions. Therefore it is prudent to recommend imaging in dogs that show signs of peripheral vestibular syndrome but do not rapidly respond to treatment
Torsion pairs and rigid objects in tubes
We classify the torsion pairs in a tube category and show that they are in
bijection with maximal rigid objects in the extension of the tube category
containing the Pruefer and adic modules. We show that the annulus geometric
model for the tube category can be extended to the larger category and
interpret torsion pairs, maximal rigid objects and the bijection between them
geometrically. We also give a similar geometric description in the case of the
linear orientation of a Dynkin quiver of type A.Comment: 25 pages, 13 figures. Paper shortened. Minor errors correcte
A static test-bed for the evaluation and optimization of multihop wireless network protocols, Journal of Telecommunications and Information Technology, 2008, nr 2
We investigate the performance of multicast transmissions in a simple stationary wireless multihop ad hoc network test-bed. We compare several methods for MANET multicast using implementations for the protocols MOLSR, SMOLSR and SMF with an approach that uses explicit multicast and link-layer retries for reliable multicast. Results from the test-bed are compared with simulation results. We find that implementing a combination of explicit multicast with a retry mechanism gives the most promising results in test-bed and simulation compared with other approaches
Unenhanced helical computed tomography vs intravenous urography in patients with acute flank pain: accuracy and economic impact in a randomized prospective trial
Abstract.: Unenhanced helical computed tomography (UHCT) has evolved into a well-accepted alternative to intravenous urography (IVU) in patients with acute flank pain and suspected ureterolithiasis. The purpose of our randomized prospective study was to analyse the diagnostic accuracy of UHCT vs IVU in the normal clinical setting with special interest on economic impact, applied radiation dose and time savings in patient management. A total of 122 consecutive patients with acute flank pain suggestive of urolithiasis were randomized for UHCT (n=59) or IVU (n=63). Patient management (time, contrast media), costs and radiation dose were analysed. The films were independently interpreted by four radiologists, unaware of previous findings, clinical history and clinical outcome. Alternative diagnoses if present were assessed. Direct costs of UHCT and IVU are nearly identical (310/309 Euro). Indirect costs are much lower for UHCT because it saves examination time and when performed immediately initial abdominal plain film (KUB) and sonography are not necessary. Time delay between access to the emergency room and start of the imaging procedure was 32h 7min for UHCT and 36h 55min for IVU. The UHCT took an average in-room time of 23min vs 1h 21min for IVU. Mild to moderate adverse reactions for contrast material were seen in 3 (5%) patients. The UHCT was safe, as no contrast material was needed. The mean applied radiation dose was 3.3mSv for IVU and 6.5mSv for UHCT. Alternative diagnoses were identified in 4 (7%) UHCT patients and 3 (5%) IVU patients. Sensitivity and specificity of UHCT and IVU was 94.1 and 94.2%, and 85.2 and 90.4%, respectively. In patients with suspected renal colic KUB and US may be the least expensive and most easily accessable modalities; however, if needed and available, UHCT can be considered a better alternative than IVU because it has a higher diagnostic accuracy and a better economic impact since it is more effective, faster, less expensive and less risky than IVU. In addition, it also has the capability of detecting various additional renal and extrarenal pathologie
Degenerate flag varieties: moment graphs and Schr\"oder numbers
We study geometric and combinatorial properties of the degenerate flag
varieties of type A. These varieties are acted upon by the automorphism group
of a certain representation of a type A quiver, containing a maximal torus T.
Using the group action, we describe the moment graphs, encoding the zero- and
one-dimensional T-orbits. We also study the smooth and singular loci of the
degenerate flag varieties. We show that the Euler characteristic of the smooth
locus is equal to the large Schr\"oder number and the Poincar\'e polynomial is
given by a natural statistics counting the number of diagonal steps in a
Schr\"oder path. As an application we obtain a new combinatorial description of
the large and small Schr\"oder numbers and their q-analogues.Comment: 25 page
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