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H J Ostertag

Publications and source records attributed to H J Ostertag.

5 recordsLinked to original sources
PubMed1995

[Calculating local doses in the area of a positron emission tomograph].

UNLABELLED: The assessment of local doses in the vicinity of a planned positron emission tomograph is an important aspect of site planning. METHODS: Using a fictitious site plan for a positron emission tomograph and assuming realistic protocols for patient studies, a complete dose calculation was carried out. The calculation was based on 960 patient studies per year and included 380 cardiological, 290 neurological, and 290 oncological studies. RESULTS: The calculation resulted in local doses between 0.7 and 16.0 mSv/y at different positions in the environment of the PET system. Based on these results, the radiation exposure of the personnel working in the PET area was assessed, and additional shielding or protection measures were proposed. CONCLUSIONS: The method presented can easily be applied to any PET site plan and any study protocol. It enables the user to do a detailed and sophisticated assessment of local doses and easily to include modifications of the study protocols or of the site geometry.

Body Burden↗
PubMed1994

Functional MR mapping of activated cortical areas.

Magnetic resonance imaging (MRI) has recently been demonstrated to be sensitive to changes in neuronal activity of cortical areas. We report our initial experiences with functional MR brain mapping at high spatial resolution using a conventional whole-body MR system. A total of 10 visual and motor cortex activation studies were carried out on 8 healthy volunteers. In each examination, a time course series of 15 strongly T2*-weighted FLASH images was measured from three adjacent slices. The image analysis revealed a subtle but highly significant signal increase in cortical layers of gray matter in primary and associative visual as well as sensorimotoric cortex regions during periods of excessive brain activity provoked by photic stimuli or motoric tasks, respectively. To correlate brain structure and brain function, the computed MR brain activation maps were directly superimposed on T1-weighted anatomic spin-echo images. With this advance into the area of functional neuroimaging, MRI is moving into an established domain of positron emission tomography (PET). We, therefore, discuss the advantages and limitations of the MR method in comparison to PET as far as this can be done at present.

Adult↗
PubMed1991

Non-uniformity measurements in PET.

To gain practical experience with the procedures suggested by the EEC task group on performance evaluation of positron tomographs, the non-uniformity of the Scanditronix PC 2048-7WB positron tomograph was measured. The test was performed using both a cylindrical head phantom and the EEC body phantom. According to the recommendation of the task group, 2 million counts were collected in each emission scan as a standard. As to be expected, non-uniformity decreased when more counts were collected or a wider reconstruction filter was used. Non-uniformity increased when going from the head phantom to the body phantom leaving all parameters unchanged. It was concluded that this effect was caused by increased noise due to the larger attenuation lengths but not to attenuation correction. The preliminary results of this study show that counting statistics dominates non-uniformity in the count range of about 2 million counts per image. Measured non-uniformity values are in the range of +/- 30%.

Equipment Design↗