Study of stomach motility using the relaxation of magnetic tracers

Abstract

Magnetic tracers can be observed in the interior of the human body to give information about their quantity, position and state of order. With the aim of detecting and studying the degree of disorder of these tracers after they have been previously magnetized inside the stomach, a system composed of magnetization coils and magnetic detectors was developed. Helmholtz coils of diameter 84 cm were used to magnetize the sample and the remanent magnetization (RM) was detected with two first-order gradiometric fluxgate arrays each with a 15 cm base line, sensitivity of 0.5 nT and common mode rejection (CMR) of at least 10. The system allows simultaneous measurement in the anterior and posterior projections of the stomach. Measurements of the time evolution of the RM were performed in vitro and in normal subjects after the ingestion of a test meal labelled with magnetic particles. The data were fitted with an exponential curve and the relaxation time tau was obtained. Initial studies were performed to ascertain the action of a drug that is known to affect the gastric motility, showing that the decay of the remanent magnetization was indeed due to stomach contractions.

Intragastric movement assessment by measuring magnetic field decay of magnetised tracer particles in a solid meal

“…The mean B: decay observed in this study was remarkably slower than when BAFFA and co-workers used yoghurt as test meal and reported a zero field after less than 200 s (BAFFA et al, 1993) and decay halftimes around 100 s (CARNEIRO et al, 1999). Yoghurt was also used in a previous study (FORSMAN, 1994), where the results indicated a mono-exponential decay with halftimes of 300-800 s. The same study hinted at a faster decay when the yoghurt was eaten after a solid meal.…”

“…Thus, the rate of decay correlates with the intragastric movements, and with the grinding and mixing of food. Previous studies utilising this method (BAFFA et al, 1993;FORSMAN, 1994;CARNEIRO et al, 1999) have all included a semifluid test meal (yoghurt). This study included a solid test meal (pancakes), which has previously been used in a similar method, where the amplitude of the remanent field was used to measure gastric emptying (FORSMAN, 1998).…”

Pharyngeal Clearance and Pharyngeal Transit Time Determined by a Biomagnetic Method in Normal Humans

“…Conventional radiology gives both anatomical and functional information [6,7] but uses large amounts of radiation; this limits the number of studies per patient. Scintigraphy [8±10] allows precise quanti®cation but gives poor anatomical information.The biomagnetic method is noninvasive, causes no discomfort to the patient, does not use radiation, and has already been used to study motility functions associated with gastric emptying [11], orocecal transit time [12], gastric contractions [13], esophageal transit time [14], segmental transit time [15,16], and mixing of food in the stomach [17]. The electrical activity of the gastrointestinal tract has also been studied by measuring the magnetic ®elds produced by the depolarization currents of the stomach [18,19] and the gut [20].…”

Spatiotemporal evaluation of human colon motility using three-axis fluxgates and magnetic markers

“…Some representative work was carried out by BASILE et al (1992) using an MM to measure oro-anal transit times; FORSMAN (1998) used a magnetic powder to measure gastric emptying; CARNEIRO et al (1999) intragastric motion. As fax as colonic motility is concerned, FERREIRA et al (2005) showed the usefulness of magnetic tracers, magnetised in situ, for assessment of contractile activity.…”

“…Their main advantage is high stability with temperature, and their main disadvantages axe both their size and cost (RIPKA et al, 2001). They have been intensively used in GI system studies, mainly in combination with magnetic tracers (FORSMAN, 1998;2000;CARNEIRO et al, 1999). In this work, the combination of a portable magnetic probe and an MM was implemented to study the spatiotemporal mechanical activity of the human colon, in healthy subjects, where measurements of the contractile activity were taken.…”