Quantitative Analyse der Diffusions-Tensor-Bildqualität (DTI) unter Verwendung von paralleler Bildgebung in der Hochfeld-MRT bei 1,5 und 3 Tesla

Das Ziel unserer Studie war die Entwicklung eines methodischen Ansatzes zur quantitativen Evaluierung und Analyse der Bildqualität diagnostischer Diffusions-Tensor-Bildgebung (DTI) unter Verwendung paralleler Bildgebung (PAT) bei 1.5 T und 3.0 T MR-Tomographen. Im Rahmen einer prospektiven Studie wurden 26 gesunde Probanden (14 w, 12 m, mittleres Alter 33 J) an einem 1.5 T MRT-Gerät und einem 3.0 T MRT-Scanner des gleichen Herstellers untersucht. Es wurden standardisierte diffusionsgewichtete Aufnahmen mittels einer Spin-Echo EPI-Sequenz angefertigt, unter Verwendung zweier verschiedener Voxel-Größen (1.8×1.8×3.6 = 11.7 mm³ und 2×2×2 = 8 mm³) sowie dreier verschiedener Averages mit 8, 4 und 2 Mittelungen bei vergleichbaren Sequenparametern bei beiden Magnetfeldstärken. Eine parallele Bildgebung mittels eines GRAPPA-Rekonstruktionsalgorithmus mit Beschleunigungsfaktoren von 2 und 3 wurde eingesetzt. Nach Wiederholung der Bildakquisitionen wurde das Signal-zu-Rausch-Verhältnis (SNR) anhand von Differenz-Bildern ermittelt. Die Region-of-Interest-basierte (ROI) quantitative Analyse wurde mittels am Scanner implementierter Software durch Positionierung der ROIs in drei verschiedenen Hirnarealen bestimmt. Für jede ROI wurden Mittelwert, Standardabweichung und Pixelanzahl bestimmt. Um die inhomogene Verteilung des Rauschens bei Einsatz paralleler Bildgebung zu berücksichtigen, wurden SNR-Verhältnisse anhand der Standardabweichung in den Differenz-Aufnahmen berechnet. Nach Normalisierung der Ergebnisse auf das SNR-Verhältnis der anisotropen 11.7-mm³ Messungen mit 8 Mittelungen bei 1.5 T, konnte ein SNR-Verhältnis von 178,2% für die gleiche Sequenz bei 3.0 T gemessen werden. Die SNR-Verhältnisse der Messungen mit 2 Mittelungen unterschieden sich deutlich mit 50,8% für Messungen bei 1,5 T bzw. 94,1% bei 3.0 T. Für Messungen bei isotroper Auflösung und 4 Mittelungen betrugen die entsprechenden Werte 49,9% bei 1,5 T und 95,2% bei 3.0 T. Die DTI-Bildgebung bei 3.0 T erzielt bessere Bildqualität bezüglich des Signal-zu-Rausch-Verhätnisses im Vergleich zu 1.5 T. Das gleiche SNR wie bei 1.5 T kann bei 3.0 T erreicht werden, hier jedoch mit erhöhter isotroper Auflösung und reduzierter Messzeit (4 Mittelungen anstelle von 8 Mittelungen). Damit sind die notwendigen Voraussetzungen gegeben, um höher aufgelöste Darstellungen von morphologisch veränderten Hirnveränderungen anzufertigen und gleichzeitig die Untersuchungszeit zu verkürzen. Desweiteren ist zu erwarten, dass auch die Darstellung von Hirnbahnen der weißen Substanz (Fibertracking) durch diese Erkenntnisse weiter verbessert werden kann. Um eine genauere Quantifizierung und eine exaktere Erfassung von Veränderungen mittels DTI zu erzielen, sollte diese Untersuchung, soweit verfügbar, bei 3 Tesla durchgeführt werden

Feasibility of low-dose digital pulsed video-fluoroscopic swallow exams (VFSE): effects on radiation dose and image quality

Background: Fluoroscopy is a frequently used examination in clinical routine without appropriate research evaluation latest hardware and software equipment. Purpose: To evaluate the feasibility of low-dose pulsed video-fluoroscopic swallowing exams (pVFSE) to reduce dose exposure in patients with swallowing disorders compared to high-resolution radiograph examinations (hrVFSE) serving as standard of reference. Material and Methods: A phantom study (Alderson-Rando Phantom, 60 thermoluminescent dosimeters [TLD]) was performed for dose measurements. Acquisition parameters were as follows: (i) pVFSE: 76.7 kV, 57 mA, 0.9 Cu mm, pulse rate/s 30;(ii) hrVFSE: 68.0 kV, 362 mA, 0.2 Cu mm, pictures 30/s. The dose area product (DAP) indicated by the detector system and the radiation dose derived from the TLD measurements were analyzed. In a patient study, image quality was assessed qualitatively (5-point Likert scale, 5 = hrVFSE;two independent readers) and quantitatively (SNR) in 35 patients who subsequently underwent contrast-enhanced pVFSE and hrVFSE. Results: Phantom measurements showed a dose reduction per picture of factor 25 for pVFSE versus hrVFSE images (0.0025 mGy versus 0.062 mGy). The DAP (mu Gym 2) was 28.0 versus 810.5 (pVFSE versus hrVFSE) for an average examination time of 30 s. Direct and scattered organ doses were significantly lower for pVFSE as compared to hrVFSE (P< 0.05). Image quality was rated 3.9 +/- 0.5 for pVFSE versus the hrVFSE standard;depiction of the contrast agent 4.8 +/- 0.3;noise 3.6 +/- 0.5 (P< 0.05);SNR calculations revealed a relative decreased of 43.9% for pVFSE as compared to hrVFSE. Conclusion: Pulsed VFSE is feasible, providing diagnostic image quality at a significant dose reduction as compared to hrVFSE

The T-pod is as stable as supraacetabular fixation using 1 or 2 Schanz screws in partially unstable pelvic fractures: a biomechanical study

Introduction: Unstable fractures of the pelvis remain the predominant cause of severe hemorrhage, shock and early death in severely injured patients. The use of pelvic binders has become increasingly popular, particularly in the preclinical setting. There is currently insufficient evidence available about the stability of the pelvic binder versus supraacetabular fixation using 1 or 2 Schanz screws. We aimed to analyze the stability of the pelvic binder and supraacetabular fixateurs using either 1 or 2 Schanz screws in a cadaver model of an induced pelvic B-type fracture. Materials and methods: The study was undertaken in 7 human fresh-frozen cadaveric pelvises with induced AO-type B fractures. Three stabilization techniques were compared: T-POD (pelvic bandage), supraacetabular external fixator with 1 pin on each side and external fixator with 2 pins on each side. Stability and stiffness were analyzed in a biomechanical testing machine using a 5-step protocol with static and dynamic loading, dislocation data were retrieved by ultrasound sensors at the fracture sites. Results: No significant differences in fracture fragment displacement were detected when using either the T-POD, a 1-pin external fixator or a 2-pin external fixator (P > 0.05). The average difference in displacement between the three methods was < 1 mm. Conclusions: Pelvic binders are suitable for reduction of pelvic B-type fractures. They provide stability comparable to that of supraacetabular fixators, independently of whether 1 or 2 Schanz screws per side are used. Pelvic binders provide sufficient biomechanical stability for transferring patients without the need to first replace them with surgically applied external fixators. However, soft tissue irritation has to be taken into consideration and prolonged wear should be avoided. Level of evidence: Level III

Comparison of ABR and ASSR using narrow-band-chirp-stimuli in children with cochlear malformation and/or cochlear nerve hypoplasia suffering from severe/profound hearing loss

Objectives In pediatric audiology, objective techniques for hearing threshold estimation in infants and children with profound or severe hearing loss play a key role. Auditory brainstem responses (ABR) and auditory steady-state responses (ASSR) are available for frequency-dependent hearing threshold estimations and both techniques show strong correlations but sometimes with considerable differences. The aim of the study was to compare hearing threshold estimations in children with and without cochlear and cochlear nerve malformations. Methods Two groups with profound or severe hearing loss were retrospectively compared. In 20 ears (15 children) with malformation of the inner ear and/or cochlear nerve hypoplasia and a control group of 20 ears (11 children) without malformation, ABR were measured with the Interacoustics Eclipse EP25 ABR system® (Denmark) with narrow-band CE-chirps® at 500, 1000, 2000 and 4000 Hz and compared to ASSR at the same center frequencies under similar conditions. Results ABR and ASSR correlated significantly in both groups (r = 0.413 in malformation group, r = 0.82 in control group). The malformation group showed a significantly lower percentage of “equal” hearing threshold estimations than the control group. In detail, patients with isolated cochlear malformation did not differ significantly from the control group, whereas patients with cochlear nerve hypoplasia showed significantly greater differences. Conclusion ABR and ASSR should be used jointly in the diagnostic approach in children with suspected profound or severe hearing loss. A great difference in hearing threshold estimation between these techniques could hint at the involvement of cochlear nerve or cochlear nerve hypoplasia itself

Brain atrophy in primary progressive aphasia involves the cholinergic basal forebrain and Ayala's nucleus

Primary progressive aphasia (PPA) is characterized by left hemispheric frontotemporal cortical atrophy. Evidence from anatomical studies suggests that the nucleus subputaminalis (NSP), a subnucleus of the cholinergic basal forebrain, may be involved in the pathological process of PPA. Therefore, we studied the pattern of cortical and basal forebrain atrophy in 10 patients with a clinical diagnosis of PPA and 18 healthy age-matched controls using high-resolution magnetic resonance imaging (MRI). We determined the cholinergic basal forebrain nuclei according to Mesulam's nomenclature and the NSP in MRI reference space based on histological sections and the MRI scan of a post-mortem brain in cranio. Using voxel-based analysis, we found left hemispheric cortical atrophy in PPA patients compared with controls, including prefrontal, lateral temporal and medial temporal lobe areas. We detected cholinergic basal forebrain atrophy in left predominant localizations of Ch4p, Ch4am, Ch4al, Ch3 and NSP. For the first time, we have described the pattern of basal forebrain atrophy in PPA and confirmed the involvement of NSP that had been predicted based on theoretical considerations. Our findings may enhance understanding of the role of cholinergic degeneration for the regional specificity of the cortical destruction leading to the syndrome of PPA