Fast T 1 mapping techniques are a valuable means of quantitatively assessing the distribution and dynamics of intravenously or orally applied paramagnetic contrast agents (CAs) by noninvasive imaging. In this study a fast T 1 mapping technique based on the variable flip angle (VFA) approach was optimized for accurate T 1 quantification in abdominal contrast-enhanced (CE) MRI. Optimization methods were developed to maximize the signal-to-noise ratio (SNR) and ensure effective RF and gradient spoiling, as well as a steady state, for a defined T 1 range of 100 -800 ms and a limited acquisition time. We corrected B 1 field inhomogeneities by performing an additional measurement using an optimized fast B 1 mapping technique. Highprecision in vitro and abdominal in vivo T 1 maps were successfully generated at a voxel size of 2.8 ؋ 2.8 ؋ 15 mm 3 and a temporal resolution of 2.

Conventional measurement of gastric secretion is invasive and cannot assess the intra-gastric distribution of gastric contents or the effects of secretion on gastric function. This study assessed the effect of gastric secretion on gastric volume responses and emptying (GE) using a validated fast T(1) mapping magnetic resonance imaging (MRI) technique. Twelve healthy participants were studied in the fasted state and after 200 kcal Gadolinium-DOTA labelled glucose meal during intravenous infusion of pentagastrin or placebo in double-blind, randomized order. Total gastric volume (TGV) and gastric content volume (GCV) was assessed by MRI volume scans and secretion by fast T(1) mapping. Data was described by the kappa-coefficient (volume change after meal ingestion), by GE half time (T(50)) and maximal GE rate (GER(max)) derived all from a GE model. Pentagastrin increased GCV and TGV compared to placebo [kappa(GCV):1.6 +/- 0.1 vs 0.6 +/- 0.1; kappa(TGV): 1.6 +/- 0.1 vs 0.7 +/- 0.1; P < 0.001]. T(1) maps revealed a secretion layer above the meal, the volume of which was associated with kappa (R(2) = 83%, P < 0.001). TGV and GCV change were similar in both conditions (kappa; P = ns). T(50) was higher for pentagastrin than for placebo (84 +/- 7 vs 56 +/- 4min, P < 0.001); however, GER(max) was similar (5.9 +/- 0.6 vs 4.9 +/- 0.4 mL min(-1), P = ns). This study shows volume and distribution of gastric secretion can be quantified in-vivo by non-invasive MRI T(1) mapping. Increased GCV drove TGV accommodation without evidence of a direct effect of pentagastrin or excess acid on gastric function. Secretion increases GCV thus prolongs GE as assessed by T(50); however, GE rate is unchanged.

The stomach maintains the rate of gastric emptying despite radical changes in body position and intragastric distribution of gastric contents. In SP, hydrostatic pressure (modulated by gastric tone) dictates the gastric emptying. In UDP, gastric emptying also appears to be mediated by continuous adaptation of gastric tone. These findings provide support for the hypothesis that the mechanism of gastric emptying resembles a "pressure pump" rather than a "peristaltic pump". Institute of Diagnostic Radiology, University Hospital Zurich, Switzerland Abstract Objective. Gastric contents empty from the stomach despite frequent changes in body position. The mechanism that maintains gastric emptying independent of position is poorly understood. The aim of this study was to determine the effects of body position on gastric emptying and motor function. Material and methods. Twelve volunteers were investigated in seated position (SP) and upside-down position (UDP) after ingestion of 300 ml water. Magnetic resonance imaging provided a non-invasive assessment of gastric emptying and volumes, intragastric distribution and peristaltic function. Results. A marked difference in distal/proximal intragastric distribution between UDP and SP was present (7% versus 40%; pB/ 0.01). Gastric-emptying time was similar but emptying pattern was linear in UDP and exponential in SP. Peristalsis was slower in UDP than SP (2.75 versus 2.96 min (1 ; pB/ 0.01), but no correlation was found between peristaltic frequency and the rate of gastric emptying in either position. Postprandial volume response (gastric relaxation) was greater in UDP than SP (280 versus 250 ml; p B/ 0.05). A correlation was found between gastric relaxation and gastricemptying time in SP (r 2 0/0.46) but not in UDP. Conclusions. The stomach maintains the rate of gastric emptying despite radical changes in body position and intragastric distribution of gastric contents. In SP, hydrostatic pressure (modulated by gastric tone) dictates the gastric emptying. In UDP, gastric emptying also appears to be mediated by continuous adaptation of gastric tone. These findings provide support for the hypothesis that the mechanism of gastric emptying resembles a ''pressure pump'' rather than a ''peristaltic pump''.

Diagnostic reference levels (DRLs) were established for 21 indication-based CT examinations for adults in Switzerland. One hundred and seventy-nine of 225 computed tomography (CT) scanners operated in hospitals and private radiology institutes were audited on-site and patient doses were collected. For each CT scanner, a correction factor was calculated expressing the deviation of the measured weighted computed tomography dose index (CTDI) to the nominal weighted CTDI as displayed on the workstation. Patient doses were corrected by this factor providing a realistic basis for establishing national DRLs. Results showed large variations in doses between different radiology departments in Switzerland, especially for examinations of the petrous bone, pelvis, lower limbs and heart. This indicates that the concept of DRLs has not yet been correctly applied for CT examinations in clinical routine. A close collaboration of all stakeholders is mandatory to assure an effective radiation protection of patients. On-site audits will be intensified to further establish the concept of DRLs in Switzerland.

Purpose:To determine the effect of the right decubitus lying body position (RP) on relevant parameters of human gastric motor function in healthy volunteers. Materials and Methods:Postprandial gastric function after ingestion of a solid/liquid meal (150 g/150 mL) was assessed over 90 minutes in volunteers in the RP and seated position (SP). Ten healthy volunteers were imaged using two MRI systems that differed in architecture and field strength. Stomach and intragastric air volume, intragastric meal distribution, gastric emptying, and gastric peristalsis were compared between the RP and SP.Results: Body position did not affect gastric relaxation (RP, 372 mL vs. SP, 384 mL) and initial gastric volumes (stomach: RP, 458 mL vs. SP, 462 mL; meal: RP, 377 mL vs. SP, 399 mL; intragastric air: RP, 110 mL vs. SP, 98 mL). Postprandial stomach volume and gastric activity (RP and SP, 3.1 minute -1 ) were also similar. Meal emptying showed different characteristics, resulting in a significant but small difference in meal volume of -43 mL at t ϭ 90 minutes (P Ͻ 0.05). Conclusion:Gastric MRI in RP is feasible for clinical research assessing gastric motor function. The subtle difference in meal emptying may be induced by posture-dependent vagal activity. This study confirms that MRI is a highly sensitive imaging technique for assessing gastrointestinal function in humans. MAGNETIC RESONANCE IMAGING (MRI) has been established as a valuable technique in human gastrointestinal (GI) research for analyzing gastric function (1-4). In comparison with radionuclide and ultrasound imaging methods, MRI offers improved spatial and temporal image resolution, and thus is ideal for noninvasive and reliable assessment of GI physiology (5). It will therefore play an important role in GI research and clinical diagnosis in the future (6,7).The most common body position during and following meal ingestion is sitting; however, the horizontally aligned whole-body architecture of modern high-field MRI systems restricts measurements of organ function to the lying body position. Several studies using ␥-scintigraphy (8 -12), intraluminal manometry (9), and MRI (13) have shown that posture influences gastric function, and thus may present a limitation for gastric MRI. In those studies, however, gastric emptying was analyzed only at discrete time points, and peristaltic motility was determined as antropyloroduodenal pressure events. Differences in the gastric emptying rate and the number of antropyloric contraction waves were detected between the lying and seated positions. Because of the very different measurement principles involved (i.e., radioactive decay vs. hydrostatic pressure vs. MR), scintigraphy and manometry data are not directly comparable with data derived using MRI. To evaluate gastric MRI for its use in clinical research and diagnosis of GI pathophysiology, one must simultaneously investigate gastric emptying, stomach volume, intragastric meal distribution, and gastric peristalsis in the lying position and detect differences compared to th...

Purpose: To evaluate the noninvasive quantification of gastric secretion volume after administration of a labeled viscous glucose solution by fast T 1 mapping. Materials and Methods:T 1 values of a series of labeled and diluted glucose solutions were measured in vitro to characterize the interrelationship between T 1 and contrast agent concentration (C Gd ) as well as the dependency of relaxivity and reference T 1 (T 10 ) on the macromolecular concentration. Abdominal T 1 mapping in five healthy volunteers of different body mass index was performed after filling an intragastric balloon with a labeled and diluted glucose solution. In additional ex vivo experiments, T 1 values of gastric (GJ) and duodenal juice (DJ) and 0.1 N HCl solution were determined. Results:A linear relationship between relaxivity and macromolecular concentration and between T 10 and macromolecular concentration was found. The in vitro T 1 -C Gd calibration curve was successfully validated in all volunteers. T 1 values of GJ, DJ, and HCl (2939 msec vs. 2858 msec vs. 2760 msec) were close to the T 1 of water (Ϸ3000 msec). Conclusion:The presented method allows one to noninvasively quantify the spatial distribution of gastric secretory products in the human stomach and provides a valuable tool for evaluating the efficacy of drugs to stimulate/inhibit gastric secretion.

GERD patients have a wider esophagogastric insertion angle and have altered gastric morphology; structural changes that could compromise reflux protection by the "flap valve" mechanism. In addition, the EGJ opens wider during reflux in GERD patients than in healthy volunteers: an effect that facilitates volume reflux of gastric contents.

MR imaging methods were developed and validated for the assessment of GEJ structure and function (a) to describe the effects of respiration and feeding on the reflux barrier and (b) to detect reflux events in real time. Anatomic and dynamic MR imaging may be useful techniques in the assessment of GEJ physiology and reflux.