Christoph Werner

A novel magnetic method for examination of bowel motility

In contrast to the well-developed methods for morphological diagnosis of the gastrointestinal tract, there is no comparatively satisfying technique for functional disorders. One important example is irritable bowel syndrome (IBS), a disorder that affects a high percentage of all individuals. It can only be diagnosed by excluding organic diseases and by considering symptom criteria. In this case, the examination of the motility of the bowel may be a promising way to differentiate between the two major mechanisms of IBS: increased sensitivity of the intestine and altered gastrointestinal motility. To this aim, a recently developed method for monitoring magnetic markers in the gastrointestinal tract was utilized that works without the use of ionizing radiation. We give a short description of this method, showing a spatial resolution of 3-4 mm and a temporal resolution of 330 ms, and report on examples of the first in vivo experiments. Typical monitoring results are shown for the esophagus, the stomach, and the duodenum. The motility behavior is described for the lower parts of the gut as well. The advantages and drawbacks of this type of magnetic marker monitoring are discussed with special consideration of the noninvasive examination of the motility in different sections of the gut.

ROC analysis for assessment of lesion detection performance in 3D PET: influence of reconstruction algorithms.

Image quality in positron emission tomography (PET) can be assessed with physical parameters, as spatial resolution and signal-to-noise ratio, or using psychophysical approaches, which include the observer performance and the considered task (ROC analysis). For PET in oncology, such a task is the detection of hot lesions. The aim of the present study was to assess the lesion detection performance due to adequate modeling of the scanner and the measurement process in the image reconstruction process. We compared the standard OSEM software of the manufacturer with a sophisticated fully 3D iterative reconstruction technique (USC MAP). A rectangular phantom with 6 oblique line sources in a homogeneous background (2.6 kBq/ml 18F) was imaged dynamically with an ECAT EXACT HR+ scanner in 3D mode. Reconstructed activity contrasts varied between 15 and 0, as the line sources were filled with 11C (3.2 MBq/ml). Measured attenuation and standard randoms, dead time, and scatter corrections of the manufacturer were employed. For the ROC analysis, a software tool presented a cut-out of the phantom (15 x 15 pixels) to two observers. These cut-outs were rated (5 classes) and the area Az under the ROC curve was determined as a measure of detection performance. The improvement for Az with USC MAP compared to the OSEM reconstructions ranged between 0.02 and 0.23 for signal-to-noise ratios of the background between 2.8 and 3.1 and lesion contrast between 2.1 and 4.2. This study demonstrates that adequate modeling of the measurement process in the reconstruction algorithm improves the detection of small hot lesions markedly.

Magnetic Marker Monitoring Using a Permanent Magnetic Sphere Oriented by a Rotating Magnetic Field

Magnetic marker monitoring (MMM) is a diagnostic technique known since about 1990 and mainly applied for motility assessment in the digestive tract. A particularly favorable MMM method uses a rotating marker, which can be aligned along an externally applied magnetic field HP. This novel method of rotating magnetic marker monitoring (RMMM) provides the starting point for the construction of small portable monitoring equipment. Friction effects and background fields, however, may cause deviations of the magnetically determined marker position from the actual location. In order to determine the magnitude of possible deviations, we measured the effect of friction acting on the marker in its bearing case by means of a realistic measuring principle and found a torque of static friction ranging from 10−7 N·m (air as bearing liquid) to about 10−6 N·m (special silicone oil). The torque linearly increases with increasing rotational frequency of the marker sphere. Furthermore, we estimated the influence of a background field HB by applying the method of look-up table and found that the operating distance D for monitoring mainly depends on the ratio HP/HB. Our preliminary set-up is working with pulsed HP fields and provides D ≈ 20 cm. However, D can be enlarged with increasing amplitude of HP. Taking into account practical demands of RMMM applications as well as technical restrictions, we propose means to enlarge the operating distance. It should be pointed out that the rotating marker can be used for remote controlled drug release as well.