Ultrasound Strain Rate Imaging in Functional Dyspepsia : in-vitro and clinical evaluation

Functional dyspepsia (FD) is a chronic condition that is characterized by abdominal pain or discomfort, nausea, vomiting, early satiation and abdominal fullness. The Rome III classification of functional gastrointestinal disorders defines two distinct entities of functional dyspepsia (FD), namely “epigastric pain syndrome” (EPS) and “postprandial distress syndrome” (PDS). Strain rate imaging (SRI) is a new ultrasound modality that is used to give a quantitative measure of deformation. The method was developed to study the cardiac muscle during health and disease. In this doctoral thesis we used SRI to study antral contractions in healthy volunteers and in patients with FD. The original cardiac SRI method was first adjusted to be able to detect signals from slowly contracting tissues. The accuracy of the adjusted method was tested in a rubber phantom mimicking the antral muscular wall in thickness, homogeneity and contraction velocity (paper I). We found that SRI strains agreed well with calculated values for strain when SRI strain was measured as the average over several US beams and the strain sample size was 1.9 mm. The variance was substantial if single samples were used, especially for a small strain sample size (0.8 mm). The results showed low inter and intraobserver variation. With the new parameters acquired from that study, the method was then applied in an ex-vivo porcine antral wall (paper II). The agreement between radial strain values measured by SRI and B-mode, along and across several ultrasound beams, using US frequency 6.7 MHz and strain length (SL) = 1.9 mm was good and it was better than with SL 1.2 mm. The method was then applied on the stomachs of healthy individuals (paper III). 1 Erythromycin, a prokinetic agent, was also used to induce contractions. SRI enabled detailed strain estimation of individual antral contractions and the typical motility pattern during fasting that includes a migrating motor complex activity was recognised. Erythromycin influenced antral contractility and increased the number of lumen occlusive contractions. The method was then applied in a cohort of patients with FD and healthy volunteers. FD patients were allocated one of FD subgroups: EPS or PDS. Antral strain in EPS patients was significantly higher than both in controls and PDS patients during fasting and postprandially. PDS patients had lower strain than controls during fasting, but not postprandially. The area of the proximal stomach during fasting was significantly larger in FD than in controls. The accommodation response ratio was significantly higher in controls than in FD. Gastric emptying fraction at 20 and 40 min postprandially was significantly larger in controls than in FD. The symptom score in the fasting state and the area under the curve in the postprandial state were significantly higher in FD patients than in HC for all the symptoms. We conclude that SRI can be a valuable method to noninvasively quantify antral contractions and that anterior radial strain measured by SRI can discriminate between HC and subgroups of FD