Jelena Curcic

Prospective self-gating for simultaneous compensation of cardiac and respiratory motion.

Segmented cardiac acquisitions generally require the use of an electrocardiogram (ECG) in combination with a breathhold or a respiratory navigator placed on the diaphragm. These techniques necessitate patient cooperation and increase the complexity of cardiac imaging. The ECG signal may be distorted inside the magnet by interferences from radiofrequency and gradient action. Breathhold acquisition limits the total scan time, while navigators on the diaphragm might not fully reflect respiratory‐induced motion of the heart. To overcome some of these problems, several self‐gating (SG) or “wireless” techniques have recently been presented. All of these approaches, however, are based on either cardiac triggering or respiratory gating, or the data are processed retrospectively, reducing the efficiency of data acquisition. In this work a prospective SG approach for free‐breathing imaging is presented that requires neither ECG gating nor respiratory navigation. The motion data used for cardiac triggering and respiratory gating are extracted from the repeatedly acquired k‐space center. Based on computer simulations and in vivo data of the heart, it is shown that cardiac as well as respiratory motion can be accurately extracted in real time. Using the method proposed, the scan efficiency could be significantly increased while preserving image quality relative to retrospective SG approaches. Magn Reson Med 60:683–690, 2008.

Measuring the interaction of meal and gastric secretion: a combined quantitative magnetic resonance imaging and pharmacokinetic modeling approach

Background  The stimulation and intragastric accumulation of gastric secretion has been recognized as an important factor in gastroesophageal reflux disease. However, the interaction of gastric secretion and meal emptying has not been fully understood. Current methods to assess gastric secretion are either invasive or unable to provide information on its volume, distribution and dynamics. The aim of this study was to quantify the interaction between meal emptying and meal induced gastric secretion by using quantitative magnetic resonance imaging (MRI) and pharmacokinetic analysis.

Gastroesophageal Junction: Structure and Function as Assessed by Using MR Imaging

PURPOSE To develop and validate magnetic resonance (MR) imaging protocols for quantitative assessment of the structural and functional properties of the gastroesophageal junction (GEJ) and to compare MR imaging detection of reflux events against concurrent manometry as a reference method. MATERIALS AND METHODS The local ethics committee approved this study, and written informed consent was obtained. Twelve healthy volunteers were examined. Three-dimensional models of the GEJ and proximal portion of the stomach were reconstructed from high-spatial-resolution anatomic MR images to assess the insertion angle of the esophagus into the stomach and proximal stomach distention before and after ingestion of a large test meal. A linear mixed-effects model was used to detect differences in the insertion angle and proximal stomach distention with respect to the respiratory cycle and gastric filling. Additionally, dynamic MR imaging at high temporal resolution was used to detect reflux events. RESULTS The esophageal insertion angle, given in units of plane angle (radians), was more acute in expiration than in inspiration (0.57 vs 0.73 radian, P = .004) but was not affected by feeding. Progressive distention of the proximal stomach was observed from baseline compared with the postprandial period (0.95 vs 0.65 radian(-1), P < .05). Eighteen reflux events detected by using MR imaging were also detected by using manometry. CONCLUSION 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.

Abnormal Structure and Function of the Esophagogastric Junction and Proximal Stomach in Gastroesophageal Reflux Disease

OBJECTIVES:This study applies concurrent magnetic resonance imaging (MRI) and high-resolution manometry (HRM) to test the hypothesis that structural factors involved in reflux protection, in particular, the acute insertion angle of the esophagus into the stomach, are impaired in gastroesophageal reflux disease (GERD) patients.METHODS:A total of 24 healthy volunteers and 24 patients with mild-moderate GERD ingested a test meal. Three-dimensional models of the esophagogastric junction (EGJ) were reconstructed from MRI images. Measurements of the esophagogastric insertion angle, gastric orientation, and volume change were obtained. Esophageal function was assessed by HRM. Number of reflux events and EGJ opening during reflux events were assessed by HRM and cine-MRI. Statistical analysis applied mixed-effects modeling.RESULTS:The esophagogastric insertion angle was wider in GERD patients than in healthy subjects (+7°±3°; P=0.03). EGJ opening during reflux events was greater in GERD patients than in healthy subjects (19.3 mm vs. 16.8 mm; P=0.04). The position of insertion and gastric orientation within the abdomen were also altered (both P<0.05). Median number of reflux events was 3 (95% CI: 2.5–4.6) in GERD and 2 (95% CI: 1.8–3.3) in healthy subjects (P=0.09). Lower esophageal sphincter (LES) pressure was lower (−11±2 mm Hg; P<0.0001) and intra-abdominal LES length was shorter (−1.0±0.3 cm, P<0.0006) in GERD patients.CONCLUSIONS: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.

Imaging gastric structuring of lipid emulsions and its effect on gastrointestinal function: a randomized trial in healthy subjects

BACKGROUND Efficient fat digestion requires fat processing within the stomach and fat sensing in the intestine. Both processes also control gastric emptying and gastrointestinal secretions. OBJECTIVE We aimed to visualize the influence of the intragastric stability of fat emulsions on their dynamics of gastric processing and structuring and to assess the effect this has on gastrointestinal motor and secretory functions. DESIGN Eighteen healthy subjects with normal body mass index (BMI) were studied on 4 separate occasions in a double-blind, randomized, crossover design. Magnetic resonance imaging (MRI) data of the gastrointestinal tract and blood triglycerides were recorded before and for 240 min after the consumption of the following 4 different fat emulsions: lipid emulsion 1 (LE1; acid stable, 0.33 μm), lipid emulsion 2 (LE2; acid stable, 52 μm), lipid emulsion 3 (LE3; acid unstable, solid fat, 0.32 μm), and lipid emulsion 4 (LE4; acid unstable, liquid fat, 0.38 μm). RESULTS Intragastric emulsion instability was associated with a change in gastric emptying. Acid-unstable emulsions exhibited biphasic and faster emptying profiles than did the 2 acid-stable emulsions (P ≤ 0.0001). When combined with solid fat (LE3), different dynamics of postprandial gallbladder volume were induced (P ≤ 0.001). For acid-stable emulsions, a reduction of droplet size by 2 orders of magnitude [LE1 (0.33 μm) compared with LE2 (52 μm)] delayed gastric emptying by 38 min. Although acid-stable (LE1 and LE2) and redispersible (LE4) emulsions caused a constant increase in blood triglycerides, no increase was detectable for LE3 (P < 0.0001). For LE3, MRI confirmed the generation of large fat particles during gastric processing, which emptied into and progressed through the small intestine. CONCLUSIONS MRI allows the detailed characterization of the in vivo fate of lipid emulsions. The acute effects of lipid emulsions on gastric emptying, gallbladder volume, and triglyceride absorption are dependent on microstructural changes undergone during consumption. Gastric peristalsis and secretion were effective at redispersing pools of liquid fat in the stomach. This trial was registered at clinicaltrials.gov as NCT01253005.

The gastro‐esophageal reflux barrier: biophysical analysis on 3D models of anatomy from magnetic resonance imaging

Background  The function and structure of the gastro‐esophageal junction (GEJ) determine its efficacy as a reflux barrier. This study presents a novel methodology for the quantitative assessment of GEJ and proximal gastric morphology from magnetic resonance (MR) imaging. Based on this data we propose a new conceptualization of the hypothesis that a flap valve mechanism contributes to reflux protection.

Effects of baclofen on the functional anatomy of the oesophago-gastric junction and proximal stomach in healthy volunteers and patients with GERD assessed by magnetic resonance imaging and high-resolution manometry: a randomised controlled double-blind study.

The mechanism of reflux protection may involve a ‘flap valve’ at the oesophago‐gastric junction (OGJ).

Free-Breathing Quantitative Dynamic Contrast-Enhanced Magnetic Resonance Imaging in a Rat Liver Tumor Model Using Dynamic Radial T1 Mapping

Objectives:The high sensitivity to motion artifacts is a major limiting factor for applying the dynamic 3D T1-weighted gradient-echo (3D T1w GRE) technique for dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) experiments in small rodents. Dynamic quantification of the relaxation rate R1 (1/T1) presents an alternative approach to reduce these motion artifacts. In this work, an optimized 2D single-shot Look-Locker based T1 mapping technique, named GOLD, applying radial sampling in the golden-angle view order and contrast-enhancing k-space filter was evaluated for its use in free-breathing quantitative DCE-MRI of rat liver on a clinical 1.5 T MRI system. Materials and Methods:In vitro measurements and initial in vivo experiments in healthy rats were performed to evaluate the accuracy and resilience of the GOLD technique to motion artifacts. Unifocal hepatocellular carcinoma (HCC) was established in 20 male Buffalo rats. Twelve days after tumor cell implantation, animals were screened for intrahepatic tumor nodules by high-resolution T2-weighted MRI. Quantitative DCE-MRI experiments applying bolus injected gadopentetate dimeglumine were performed in 11 HCC-bearing rats using the GOLD technique. For comparison, a standard 3D T1w GRE sequence was applied in 6 additional rats. Results:Phantom experiments showed good agreement for T1 values measured by the GOLD method and an inversion recovery spectroscopy measurement. The in vivo experiments in healthy rats confirmed the robustness of the GOLD method in T1 value determination and its resilience to motion artifacts. Gadopentetate dimeglumine concentration (CGd) time curves determined from free-breathing GOLD-based DCE-MRI experiments of HCC-bearing rats allowed reliable and robust pharmacokinetic modeling (Ktrans, ve, lag time Td, and slow washout rate rwo) of tumor, liver, and spinal muscle. In comparison to the dynamic 3D T1w GRE, the GOLD method showed less variation and jitter in the CGd time curves and significantly increased accuracy (in terms of the goodness of fit) in the pharmacokinetic modeling. Significant differences were detected for Ktrans and ve with the 3D T1w GRE method apparently underestimating those parameters. Conclusions:The GOLD technique allowed dynamic sampling of 2D axial T1 maps of the rat abdomen with 6-second temporal resolution enabling simultaneous and robust pharmacokinetic modeling of HCC, normal liver, and spinal muscle.

Validation of a golden angle radial sequence (GOLD) for abdominal T1 mapping during free breathing: Demonstrating clinical feasibility for quantifying gastric secretion and emptying

To validate a magnetic resonance imaging sequence suitable for quantitative assessment of acid suppression by a proton pump inhibitor (PPI) on gastric secretion and emptying in clinical practice.

The visualisation and quantification of human gastrointestinal fat distribution with MRI: a randomised study in healthy subjects.

We aimed to study the fate of fat during digestion. For this purpose, we validated and investigated the non-invasive quantification of gastric and duodenal fat emptying and emulsion processing (creaming and phase separation) using the MRI method iterative decomposition with echo asymmetry and least squares estimation (IDEAL). In total, twelve healthy subjects were studied on two separate visits in a single-blind, randomised, cross-over design study. IDEAL was utilised to repeatedly acquire quantitative fat fraction maps of the gastrointestinal tract after infusion of one of two fat emulsions: E1 (acid stable, droplet size 0·33 mm) and E4 (acid unstable, 0·38 mm). In vitro and in vivo validation was carried out using diluted emulsion and gastric content samples, respectively, and resulted in Lins concordance correlation coefficients of 1·00 (95% CI 0·98, 1·00) and 0·91 (95% CI 0·87, 0·94), respectively. Fat fraction maps and intragastric emulsion profiles enabled the identification of features of intraluminal phase separation and creaming that were not visible in conventional MRI. Gastric fat emptying was faster for E4 compared with E1 with a difference of 2·5 (95% CI 1·9, 3·1) ml/h. Duodenal content volumes were larger for E1 than for E4 with a difference of 4·9 (95% CI 3·9, 8·5) ml. This study demonstrated that with IDEAL it was possible (1) to visualise the intragastric and duodenal fat distribution and (2) to quantify the differences in emptying, phase separation and creaming of an acid-stable and an acid-unstable emulsion. This method has potential to bridge the gap between current in vitro digestive models and in vivo behaviour and to be applied in the development of effective functional foods.