Finite element analysis in asymptomatic, symptomatic, and ruptured abdominal aortic aneurysms: in search of new rupture risk predictors.

OBJECTIVES: To compare biomechanical rupture risk parameters of asymptomatic, symptomatic and ruptured abdominal aortic aneurysms (AAA) using finite element analysis (FEA). STUDY DESIGN: Retrospective biomechanical single center analysis of asymptomatic, symptomatic, and ruptured AAAs. Comparison of biomechanical parameters from FEA. MATERIALS AND METHODS: From 2011 to 2013 computed tomography angiography (CTA) data from 30 asymptomatic, 15 symptomatic, and 15 ruptured AAAs were collected consecutively. FEA was performed according to the successive steps of AAA vessel reconstruction, segmentation and finite element computation. Biomechanical parameters Peak Wall Rupture Risk Index (PWRI), Peak Wall Stress (PWS), and Rupture Risk Equivalent Diameter (RRED) were compared among the three subgroups. RESULTS: PWRI differentiated between asymptomatic and symptomatic AAAs (p < .0004) better than PWS (p < .1453). PWRI-dependent RRED was higher in the symptomatic subgroup compared with the asymptomatic subgroup (p < .0004). Maximum AAA external diameters were comparable between the two groups (p < .1355). Ruptured AAAs showed the highest values for external diameter, total intraluminal thrombus volume, PWS, RRED, and PWRI compared with asymptomatic and symptomatic AAAs. In contrast with symptomatic and ruptured AAAs, none of the asymptomatic patients had a PWRI value >1.0. This threshold value might identify patients at imminent risk of rupture. CONCLUSIONS: From different FEA derived parameters, PWRI distinguishes most precisely between asymptomatic and symptomatic AAAs. If elevated, this value may represent a negative prognostic factor for asymptomatic AAAs.

First-principles calculations of the Urbach tail in the optical absorption spectra of silica glass.

We present density-functional theory calculations of the optical absorption spectra of silica glass for temperatures up to 2400 K. The calculated spectra exhibit exponential tails near the fundamental absorption edge that follow the Urbach rule in good agreement with experiments. We discuss the accuracy of our results by comparing to hybrid exchange correlation functionals. We show that the Urbach rule holds in a frequency interval where optical absorption is Poisson distributed with very large statistical fluctuations. In this regime, a direct relation between the optical absorption coefficient and electronic density of states is derived, which provides a link between photoemission and absorption spectra and is used to determine the lower bound to the Urbach frequency regime.

Magnetic resonance-guided laparoscopic interstitial laser therapy of the liver.

BACKGROUND: There is a necessity for an imaging method during laparoscopy to get a three-dimensional access to the target. In this study we evaluated laparoscopic interstitial laser therapy of the liver under magnetic resonance imaging guidance. METHODS: Five domestic pigs underwent laparoscopy in an open-configuration magnetic resonance system. Under simultaneous real-time magnetic resonance imaging interstitial laser therapy was applied to the liver. Magnetic resonance images, macroscopic aspects of the lesions, and light microscopic findings were compared. RESULTS: The interventions could be safely performed. There was no image artifact caused by instruments or by the carbon dioxide. Dynamic gadolinium-enhanced imaging proved to significantly predict the macroscopic volume of the laser lesions. CONCLUSIONS: Magnetic resonance-guided laparoscopic interstitial laser therapy of the liver combines the advantages of minimal invasive surgery and magnetic resonance imaging. Further development should focus on laparoscopic instruments and temperature sensitive sequences.

[Active instrumental guidance in interventional MR tomography: introduction to a new concept]. / Aktive Instrumentenführung in der interventionellen MR-Tomographie: Einführungen in ein neues Konzept.

PURPOSE: An active MR-based guidance system for visualisation of invasive instruments is described. METHODS: The principle of MR tracking is based on the integration of a miniaturised coil into the tip of the instrument itself. A phantom experiment was designed to demonstrate the localising accuracy of this technique. In addition, biocompatibility and warming effects were evaluated. Preliminary intravascular applications that were performed in animal experiments under MR guidance included embolisation, vascular occlusion as well as transjugular intrahepatic punctures. Percutaneous biopsies, cholecystostomies and laparoscopic applications were also evaluated with MR tracking. RESULTS: Phantom experiments confirmed an excellent localisation accuracy of MR tracking compared top conventional radiography. At a field strength of 0.5 T, the temperature increase remained below 2 degrees C. Results of phantom experiments revealed a potential of significant heating dependent on the sequence parameters employed. MR tracking allowed a robust, simultaneously biplanar visualisation of the instrument tips in real time. Based on MR "road map" images, various intravascular and percutaneous interventions were successfully performed in vivo under MR guidance. CONCLUSIONS: MR tracking is a flexible concept permitting monitoring in the guidance of instruments in an MR environment. Various preliminary in vitro and in vivo experiments demonstrate safety, localisation accuracy and feasibility of this biplanar localisation technique in real time.

[Interactive stereotaxic interventions in superconducting, open 0.5-Tesla MRI tomography]. / Interaktive, stereotaktische Interventionen im supraleitenden, offenen 0.5-Tesla-MR-Tomographen.

PURPOSE: Evaluation of an interactive, stereotactic biopsy device integrated in an open superconductive 0.5 tesla MR-scanner with a vertical gap. MATERIAL AND METHODS: In addition to "in-vitro" experiments performed on a plexiglas phantom with holes of varying diameters (5-20 mm) biopsies on eleven patients (7 women, 4 men; average age 55 years) were performed in the interventional MR-system. Lesions in the abdomen (n = 6), muscle (n = 1), thyroid (n = 3) and breast (n = 1) were targeted with 18-20 G aspiration biopsy needles of 5-15 cm length. The intervention was interactively guided by a fast T1-weighted 2-D gradient echo sequence. RESULTS: All of the 15 and 20 mm holes of the phantom, but only 83% of the 10 and 5 mm holes were hit. No complications occurred during the MR-guided patient procedures. All lesions (mean size 3.5 cm, distance from the skin 2 cm to 10 cm) were biopsied successfully. The fast image acquisition in combination with the stereotactic technique enables interactive control of the needle. CONCLUSIONS: Stereotactic, interactively controlled biopsies in the interventional MR are technical feasible. However, the range of meaningful indications for MR-guided biopsies is limited.

Comparison of mRAST and CAP with skin end point titration for Alternaria tenuis and dermatophagoides pteronyssinus.

There has been a recent explosion of new in vitro tests for the diagnosis of allergies. At present there is no general agreement on which type of in vitro test is best. Recently our hospital switched in vitro testing from the modified radioallergosorbent system (mRAST) to the Pharmacia CAP system (CAP). While changing in vitro testing techniques, 47 patients were tested with both the mRAST and CAP tests. Comparisons were made between the mRAST and CAP results of Alternaria tenuis and Dermatophagoides pteronyssinus allergens. These results were then compared with the results of patients who also underwent intradermal skin testing based on end point titration techniques.

A multidimensional approach in testing nootropic drug effects (Cerebrolysin).

In an attempt to improve indicators of validity for the therapeutic efficacy of nootropics, the effects of Cerebrolysin(R) were compared across three different dimensions of variables in a randomized placebo-controlled double-blind study. A group of 27 geriatric patients suffering from an organic brain syndrome with moderate cognitive impairment of a vascular or/and degenerative nature received a series of ten Cerebrolysin + multivitamin infusions. They were compared to a second group with 14 clinically comparable patients, who received multivitamin infusions alone. Pre-posttreatment differences from (1) clinical scales (SCAG, Plutchik Geriatric Rating Scale and a self-evaluation scale); (2) psychometric test performance (trail-making and maze subtests from the Nürnberg Age Inventory); and (3) event-related brain activity (contingent negative variation (CNV) amplitude) were in favor of the Cerebrolysin-treated group. A high degree of association as well as high classification rates (95% joint correct classification) underlined their clinical significance. It was concluded that the multidimensional measurement approach could increase the clinical validity of nootropic drug effects.

[Therapy of organic brain syndrome with nicergoline given once a day]. / Therapie des hirnorganischen Psychosyndroms mit Nicergolin in täglicher Einmalgabe.

In a double-blind, active-controlled study 30 patients with mild to moderate multiinfarct dementia diagnosed according to DSM III definition were treated by either 20 mg nicergoline or 4.5 mg co-dergocrine mesilate once daily during eight weeks. Therapeutic effects on symptoms of the organic brain syndrome were quantitatively measured by standardized psychological and psychometric methods evaluating cognitive and thymopsychic functions. Main criteria, which were tested by inferential analysis, were SCAG total score (Sandoz Clinical Assessment Geriatric Scale), SCAG overall impression and the AD Test (alphabetischer Durchstreichtest). Other results were assessed by descriptive statistics. Both treatments resulted in a statistically significant improvement in most of the tested functions. The effects of 4.5 mg co-dergocrine mesilate s.i.d. were in accordance with published results. Although differing slightly with respect to individual results 20 mg of nicergoline once daily showed the same efficacy on the whole.

[Rare aortic diseases: infections, tumors, congenital anomalies]. / Seltene Aortenerkrankungen: Infektionen, Tumoren, angeborene Fehlbildungen.

Congenital malformations, tumors and aortic infections are rare and mostly asymptomatic. Unspecific clinical symptoms may cause delayed verification of the underlying disease. Contrast enhanced computer tomography- and magnetic resonance angiography are important sectional imaging methods for diagnostic completion. Consistent guidelines concerning diagnosis and therapy of rare aortic diseases are non-existent. Aortic tumors must be resected by open surgery, aortic infections in general require medical treatment and anomalies, if indicated, are treated more and more by endovascular or hybrid procedures. Therefore, it is recommended to treat these entities in an interdisciplinary approach in specialized aortic centers.

Interatomic potentials for the Be-C-H system.

Analytical bond-order potentials for beryllium, beryllium carbide and beryllium hydride are presented. The reactive nature of the formalism makes the potentials suitable for simulations of non-equilibrium processes such as plasma-wall interactions in fusion reactors. The Be and Be-C potentials were fitted to ab initio calculations as well as to experimental data of several different atomic configurations and Be-H molecule and defect data were used in determining the Be-H parameter set. Among other tests, sputtering, melting and quenching simulations were performed in order to check the transferability of the potentials. The antifluorite Be(2)C structure is well described by the Be-C potential and the hydrocarbon interactions are modelled by the established Brenner potentials.

Thalamic degeneration.

A man of 61 died after an illness of 20 years duration. The clinical picture displayed progressive dementia, loss of memory, apathy, inertia, emotional lability, temporal and local disorientation, visual hallucination and apraxia. Neuropathological findings predominated in the thalamus and displayed extensive nerve cell loss and gliosis in the anterior, medial, and posterior formations, whereas the lateral formations were somewhat better preserved. The lateral amygdala were severely affected. The cortex showed widespread moderate damage in the third or fourth layer which are interpreted as transneuronal degeneration. In addition moderate atrophy of the vestibular nuclei, the inferior olives and the cerebellum was noted. This case seems to be one of the very rare examples of isolated thalamic degeneration according to Martin (1975).

[The usefulness of event-related negativity in demonstrating the therapeutic effects of nootropic drugs using cerebrolysin as an example]. / Die Brauchbarkeit der ereigniskorrelierten Negativität zum Nachweis therapeutischer Wirkungen von Nootropika am Beispiel von Cerebrolysin.

This study investigated the usefulness of the Contingent Negative Variation (CNV) in the assessment of therapeutic efficacy of a nootropic substance, Cerebrolysin. A total of 41 geriatric patients with the diagnosis of moderate organic brain syndrome of different etiology were included in this randomized placebo-controlled double-blind study. After ten Cerebrolysin- plus multi-vitamins-Infusions, the treatment group of 27 patients showed a significant CNV-amplitude increase as compared to pre-treatment values. In the placebo group of 14 patients CNV-amplitudes even decreased after ten Infusions with multi-vitamins alone. These findings were interpreted in line with the vigilance model of nootropic drug effects as a vigilance-increasing effect of Cerebrolysin, i.e. as an increased neuronal performance readiness. The results confirmed the usefulness of the CNV method by providing an EEG-index of nootropic drug effects.

[Minimally invasive surgery with MRI imaging]. / Minimal invasive Chirurgie unter MR-Bildgebung.

The main shortcoming of conventional laparoscopic procedures is the lack of a truely three-dimensional view. The development of a open-configured MR-imaging system (0.5 Tesla, General Electric, USA) with free access to the patient, allows the performance of minimal invasive procedures under MR-guidance. Advantages inherent to minimal invasive surgery can now be combined with the ideal tissue discrimination and the temperature sensitivity of MR-imaging. This new method can be used for diagnostic as well as for therapeutic interventions, especially interstitial therapy of inoperable metastases of parenchymal organs.

[Magnetic resonance controlled minimal invasive surgery: initial results and perspectives]. / Magnet-Resonanz-geführte minimal-invasive Chirurgie: Erste Resultate und Perspektiven.

The development of an open-configured MR-imaging system opens new perspectives in minimal invasive surgery. The combination of laparoscopy and real-time MR imaging allows the guidance of diagnostic interventions as well as interstitial therapies of parenchymal organs. In the near future, tumor diagnosis, therapy and follow-up can be done using the same technique.

MR-guided cholecystostomy: assessment of biplanar, real-time needle tracking in three pigs.

PURPOSE: To demonstrate the feasibility of magnetic resonance (MR)-guided cholecystostomy using active, real-time, biplanar MR tracking in animal experiments. METHODS: Experiments were performed on three fully anesthetized pigs in an interventional MR system (GE open). The gallbladder was displayed in two orthogonal planes using a heavily T2-weighted fast spin-echo sequence. These "cholangio roadmaps" were displayed on LCD monitors positioned in front of the interventionalist. A special coaxial MR-tracking needle, equipped with a small receive-only coil at its tip, was inserted percutaneously into the gallbladder under continuous, biplanar MR guidance. The MR-tracking sequence allowed sampling of the coil (needle tip) position every 120 msec. The position of the coil was projected onto the two orthogonal "cholangio roadmap" images. RESULTS: Successful insertion of the needle was confirmed by aspiration of bile from the gallbladder. The process of aspiration and subsequent instillation of Gd-DTPA into the gallbladder was documented with fast gradient-recalled echo imaging. CONCLUSION: Biplanar, active, real-time MR tracking in combination with "cholangio roadmaps" allows for cholecystostomies in an interventional MRI environment.

Biopsy needle susceptibility artifacts.

Understanding the appearance of thin metallic structures in magnetic resonance imaging is important for evaluating the potential role of MRI in guiding and monitoring percutaneous interventions. As most MR compatible instruments are made from materials with a susceptibility different from water, their visibility is enhanced beyond what is expected on the grounds of displaced water alone. Unfortunately, this artifactually enhanced visibility is not constant, but instead depends on a variety of factors. This article presents computer simulations of the image distortion resulting from magnetic susceptibility differences between a needle and the surrounding tissue. The simulations show not only an artifact size that is dependent on needle composition, orientation, and pulse sequence, but also a corresponding shift of the artifact center away from the actual center of the needle. These effects place limits on the accuracy of MRI-guided needle tip placement.

Imaging temperature changes in an interventional 0.5 T magnet: in-vitro results.

BACKGROUND AND OBJECTIVE: To evaluate the ability of monitoring laser induced temperature changes in an open, interventional 0.5 T magnet, adopting fast T1-weighted sequences. MATERIALS AND METHODS: A fast gradient echo- (FGRE) and a fast spoiled gradient echo-sequence (FSPGR), both enabling an image update every 2.5 s, were investigated for their ability to visualize laser tissue effects at 5 Watt. Laser induced temperature was fluorooptically measured and correlated with signal intensity (SI) changes depicted by magnetic resonance imaging (MRI). MRI-lesions were compared with macroscopic findings. RESULTS: SI changes on FGRE images appeared as early as 15 s following the onset of laser application and were significantly more pronounced than those seen on FSPGR images (p < .0001). A correlation of r = 0.94 (FGRE) and r = 0.92 (FSPGR) between temperature and SI loss was established. Owing to a steeper slope, the FGRE sequence was considered more sensitive to temperature changes. The areas of macroscopic tissue change correlated with those of SI loss, but lesion size was generally underestimated by MRI. CONCLUSION: Laser monitoring is possible with rapid image updates in a midfield (0.5 T) interventional MRI environment using fast gradient echo sequence designs.

Intravascular MR imaging of atherosclerotic plaque: ex vivo analysis of human femoral arteries with histologic correlation.

PURPOSE: To assess the potential role of intravascular magnetic resonance (MR) imaging with receiver coils mounted to an inflatable balloon in characterizing atherosclerotic plaque. MATERIALS AND METHODS: Twelve human harvested segmental femoral arteries with atherosclerotic changes were studied with a 5-F imaging balloon catheter equipped with a single-loop wire receiver coil. Imaging was performed with an open-configuration 0.5-T (n = 6) or a 1.5-T (n = 6) MR system, with T1- and T2-weighted sequences. Histologic analysis was the reference standard, and MR images were analyzed with regard to vessel wall thickness, plaque area, and components. RESULTS: Images acquired at 1.5 T were characterized by better in-plane resolution (117 x 104 microm). Resolution at 0.5 T (234 x 178 microm) was sufficient to discriminate the wall layers. On T2-weighted images, adventitia, media, and thickened intima could be discriminated. T1-weighted images did not permit differentiation between wall layers. There was good correlation between MR and histologic measurements of wall thickness (r = .97) and plaque area (r = .98). Plaque characterization was possible on T2-weighted images. Calcified plaque was identified as areas of low signal intensity (134 +/- 98) and could be differentiated from fibrous structures containing collagen (1,968 +/- 680) or fatty components (762 +/- 394). CONCLUSION: Intravascular MR imaging on the basis of the balloon catheter design enables differentiation of wall layers and plaque components.

Active biplanar MR tracking for biopsies in humans.

OBJECTIVE: The purpose of this study was to assess the potential of active biplanar MR needle tracking in a 0.5-T open-configuration MR system. A needle design characterized by an integrated internal signal source was used. To evaluate the performance of this new technique in vivo as well as in vitro, procedures were performed on patients. CONCLUSION: The results of this study prove that the biplanar tracking concept can be applied in a clinical environment. The applicability of biplanar tracking is further enhanced by integrating an internal signal source.