Wireless power transmission in endoscopy capsules.

The operating life of endoscopy capsules is limited by the batteries needed for use. The capacity of corresponding batteries, however, is too short to cover the total period of gastrointestinal transit. To overcome this limitation, a novel kind of wireless power transmission was used. It utilizes a permanent magnetic cylinder located outside the patient's body and is turned by an electric motor, thereby generating a rotating magnetic field. This field in turn causes the motor, by a permanent magnetic sphere, located in a liquid bearing inside the endoscopy capsule, to rotate synchronously. The sphere induces an alternating voltage in coils inside the capsule and thus provides the necessary power. This arrangement was able to transmit power of up to 170 mW. This value is clearly higher than the minimum power of 100 mW needed to operate the electronics of the endoscopy capsules that are actually in use. The volume of both the sphere and the induction coil is smaller than the batteries that are actually integrated in the capsules. By this means, the operating time may be prolonged, in principle up to arbitrary values.

Static magnetic fields affect capillary flow of red blood cells in striated skin muscle.

Blood flowing in microvessels is one possible site of action of static magnetic fields (SMFs). We evaluated SMF effects on capillary flow of red blood cells (RBCs) in unanesthetized hamsters, using a skinfold chamber technique for intravital fluorescence microscopy. By this approach, capillary RBC velocities (v(RBC)), capillary diameters (D), arteriolar diameters (D(art)), and functional vessel densities (FVD) were measured in striated skin muscle at different magnetic flux densities. Exposure above a threshold level of about 500 mT resulted in a significant (P < 0.001) reduction of v(RBC) in capillaries as compared to the baseline value. At the maximum field strength of 587 mT, v(RBC) was reduced by more than 40%. Flow reduction was reversible when the field strength was decreased below the threshold level. In contrast, mean values determined at different exposure levels for the parameters D, D(art), and FVD did not vary by more than 5%. Blood flow through capillary networks is affected by strong SMFs directed perpendicular to the vessels. Since the influence of SMFs on blood flow in microvessels directed parallel to the field as well as on collateral blood supply could not be studied, our findings should be carefully interpreted with respect to the setting of safety guidelines.

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.

Heating potential of iron oxides for therapeutic purposes in interventional radiology.

RATIONALE AND OBJECTIVES: In addition to their diagnostic applications, iron oxides could be used therapeutically to eliminate tumors with heat if their heating powers are adequate. The authors therefore examined the specific absorption rate (SAR) of different iron oxide (magnetite) samples suspended in water and in liquid or solidified gel. MATERIALS AND METHODS: The authors compared two ferromagnetic fine powders (total particle size, >350 nm and 100 nm), five superparamagnetic ferrofluidic samples (total particle size, 10-280 nm), and a commercially available contrast medium (ferumoxides injectable solution, Endorem). The SARs of the magnetic material-suspended in distilled water or in liquid or solid agar-were estimated from time-dependent calorimetric measurements during exposure to an alternating current magnetic field (amplitude, 6.5 kA/m; frequency, 400 kHz). RESULTS: SARs varied considerably between the different iron oxide samples. The highest value was found for a ferrofluidic sample (>93 W/g), while Endorem had little heating power (<0.1 W/g). The SAR was clearly dependent on the aggregation state of the matrix only for the large-particle-size ferromagnetic sample, yielding the highest values for particle suspensions in water (74 W/g) and lowest for solid agar (8 W/g). The heating power of the smaller-particle-size ferromagnetic sample did not exceed 8 W/g. CONCLUSION: Heating powers differed according to the interaction of multiple physical parameters. Iron oxides should be selected carefully for therapeutic applications in magnetic heating.