Eckhard Hempel

Impairment in basal limbic function in schizophrenia during affect recognition

Patients with schizophrenia routinely fail to perform affect recognition tasks as accurately as healthy controls. The investigation of performance-related changes in cerebral activation in healthy subjects may facilitate the understanding of adaptation processes to different levels of difficulty and help to interpret the activation changes found in schizophrenic patients. Nine first hospitalized partly remitted schizophrenic patients and 10 healthy controls participated in an fMRI study with a facial affect discrimination and labeling task. Seven of the 10 healthy subjects were reexamined with changed stimulus conditions adapted according to the mean accuracy scores detected in schizophrenic patients. Controls showed a significantly increased activation of the right gyrus frontalis medialis with rising task difficulty during both tasks. The schizophrenic patients demonstrated a significantly decreased activation of the anterior cingulate during facial affect discrimination and of the amygdala-hippocampal complex bilaterally during facial affect labeling. In addition, an increased activation of the gyrus frontalis medialis bilaterally became apparent in the schizophrenic patients. It is suggested that the latter may reflect a compensatory effort for deficits in more basal limbic functions.

Toward clinical X-ray phase-contrast CT: demonstration of enhanced soft-tissue contrast in human specimen.

Objectives:X-ray computed tomography (CT) using phase contrast can provide images with greatly enhanced soft-tissue contrast in comparison to conventional attenuation-based CT. We report on the first scan of a human specimen recorded with a phase-contrast CT system based on an x-ray grating interferometer and a conventional x-ray tube source. Feasibility and potential applications of preclinical and clinical phase-contrast CT are discussed. Materials and Methods:A hand of an infant was scanned ex vivo at 40 kVp tube voltage. The simultaneously recorded attenuation and phase-contrast CT images were quantitatively compared with each other, by introducing a specific Hounsfield unit for phase-contrast imaging. Results:We observe significantly enhanced soft-tissue contrast in the phase images, when compared with the attenuation data. Particularly, tendons and ligaments appear with strongly increased contrast-to-noise ratio. Conclusions:Our results demonstrate the huge potential of phase-contrast CT for clinical investigations of human specimens and, potentially, of humans. Because the applied technique works efficiently with conventional x-ray tubes and detectors, it is suitable for the realization of preclinical and clinical phase-contrast CT systems.

Inverse geometry for grating-based x-ray phase-contrast imaging

Phase-contrast imaging using conventional polychromatic x-ray sources and grating interferometers has been developed and demonstrated for x-ray energies up to 60 keV. Here, we conduct an analysis of possible grating configurations for this technique and present further geometrical arrangements not considered so far. An inverse interferometer geometry is investigated that offers significant advantages for grating fabrication and for the application of the method in computed tomography (CT) scanners. We derive and measure the interferometer’s angular sensitivity for both the inverse and the conventional configuration as a function of the sample position. Thereby, we show that both arrangements are equally sensitive and that the highest sensitivity is obtained, when the investigated object is close to the interferometer’s phase grating. We also discuss the question whether the sample should be placed in front of or behind the phase grating. For CT applications, we propose an inverse geometry with the sample ...

Phase-contrast imaging and tomography at 60 keV using a conventional x-ray tube source

Phase-contrast imaging at laboratory-based x-ray sources using grating interferometers has been developed over the last few years for x-ray energies of up to 28 keV. Here, we show first phase-contrast projection and tomographic images recorded at significantly higher x-ray energies, produced by an x-ray tube source operated at 100 kV acceleration voltage. We find our measured tomographic phase images in good agreement with tabulated data. The extension of phase-contrast imaging to this significantly higher x-ray energy opens up many applications of the technique in medicine and industrial nondestructive testing.

Improvement of auditory hallucinations and reduction of primary auditory area's activation following TMS

BACKGROUND In the present case study, improvement of auditory hallucinations following transcranial magnetic stimulation (TMS) therapy was investigated with respect to activation changes of the auditory cortices. METHODS Using functional magnetic resonance imaging (fMRI), activation of the auditory cortices was assessed prior to and after a 4-week TMS series of the left superior temporal gyrus in a schizophrenic patient with medication-resistant auditory hallucinations. RESULTS Hallucinations decreased slightly after the third and profoundly after the fourth week of TMS. Activation in the primary auditory area decreased, whereas activation in the operculum and insula remained stable. CONCLUSIONS Combination of TMS and repetitive fMRI is promising to elucidate the physiological changes induced by TMS.

Simulation of X-ray Phase-contrast Computed Tomography of a Medical Phantom Comprising Particle and Wave Contributions

We present a simulation framework for X-ray phase-contrast computed tomography imaging (PCTI) inheriting the wave- as well as the particle-behavior of photons. The developed tool includes the modeling of a partially coherent X-ray source, the propagation of the X-ray photons through samples, and the interfering properties of photons. Hence, the simulation is capable of physically modeling a grating-based interferometric imaging system reported in e.g. Pfeiffer et al.5 The information gained comprises the three potentially measurable images, which are the absorption image, the phase image, and the darkfield image. Results on such a setup concerning spatial and temporal coherence will be shown. Samples consisting of elements and structures similar to biological tissue were implemented to demonstrate the applicability on medical imaging. For the purpose of CT-imaging a head-like phantom was simulated and the results show the advantage of PCTI for thick biological objects. The simulation was developed with a modular concept so that the influences of each imaging component can be considered seperately. Thus the grating based interferometry for X-ray phase-contrast imaging can be optimized towards dedicated medical applications using this simulation-tool.

Phase-Contrast Imaging and Tomography at 60 keV using a Conventional X-ray Tube

Phase-contrast imaging using grating interferometers has been developed over the last few years for x-ray energies of up to 28 keV. We have now developed a grating interferometer for phase-contrast imaging that operates at 60 keV x-ray energy. Here, we show first phase-contrast projection and CT images recorded with this interferometer using an x-ray tube source operated at 100 kV acceleration voltage. By comparison of the CT data with theoretical values, we find that our measured phase images represent the refractive index decrement at 60 keV in good agreement with the theoretically expected values. The extension of phase-contrast imaging to this significantly higher x-ray energy opens up many new applications of the technique in industry, medicine, and research.