Ultrasonography in gastroenterology.

Ultrasonography (US) is a safe and available real-time, high-resolution imaging method, which during the last decades has been increasingly integrated as a clinical tool in gastroenterology. New US applications have emerged with enforced data software and new technical solutions, including strain evaluation, three-dimensional imaging and use of ultrasound contrast agents. Specific gastroenterologic applications have been developed by combining US with other diagnostic or therapeutic methods, such as endoscopy, manometry, puncture needles, diathermy and stents. US provides detailed structural information about visceral organs without hazard to the patients and can play an important clinical role by reducing the need for invasive procedures. This paper presents different aspects of US in gastroenterology, with a special emphasis on the contribution from Nordic scientists in developing clinical applications.

Bowel perfusion measured with dynamic contrast-enhanced ultrasound predicts treatment outcome in patients with Crohn's disease.

BACKGROUND: To improve management of patients with Crohn's disease (CD), objective measurements of the degree of local inflammation in the gastrointestinal wall are needed. Increased microvessel density and perfusion are typical features of acute inflammation and can be estimated with contrast-enhanced ultrasound (CEUS). The aim of the study was to investigate whether CEUS can provide prognostic information about patients treated medically for an acute exacerbation of CD. METHODS: Fourteen patients with CD who received medical treatment for acute exacerbation with systemic steroids or tumor necrosis factor-α inhibitors were prospectively recruited. The patients were examined with clinical scoring, blood tests, and CEUS at time 0, 1, 3, and 12 months after initiation of the treatment. Outcome was treatment efficacy or treatment failure defined as change in medical treatment after 1 month or later. The perfusion analysis was performed with a commercially available software program that analyzes the contrast intensity in a selected area, fits the data to a standardized time-intensity curve, and derives several relative perfusion parameters. RESULTS: Six of the 14 patients had treatment failure during the study period. There was a significant difference between the groups for peak contrast enhancement (P = 0.013), rate of wash-in (P = 0.020) and wash-out (P = 0.008), and the area under the time-intensity curve in the wash-in phase (0.013) at the examination 1 month after the start of treatment. CONCLUSIONS: Perfusion analysis of the intestinal wall with CEUS 1 month after starting treatment in patients with CD can provide prognostic information regarding treatment efficacy.

Characterization of solid focal pancreatic lesions using endoscopic ultrasonography with real-time elastography.

OBJECTIVES. The aim of this study was to evaluate the diagnostic potential of strain assessment in solid focal pancreatic lesions using real-time elastography in combination with endoscopic ultrasonography (EUS). MATERIAL AND METHODS. Forty-eight solid focal pancreatic lesions in 39 patients were included prospectively over a 3-year period and studied by EUS with real-time elastography (EUS-RTE). Lesions previously described as cystic by CT were not included. Distribution patterns of tissue strain were assessed using strain ratio (SR) measurements, continuous visual analog scale (VAS), and a visual categorical score (VCS), based on color coding of relative strain. Final diagnosis was based on histopathology, fine-needle aspiration cytology, and/or follow-up for ≥6 months. RESULTS. The 48 lesions included 11 adenocarcinomas, 7 malignant neuroendocrine tumors (NETs), 11 benign or indeterminate NETs, 8 focal pancreatic lesions, 2 microcystic adenomas, and 9 other benign lesions. Malignant lesions had significantly higher median SR (7.05 vs. 1.56) and VAS scores (93.0 vs. 63.5) than benign lesions. A receiver operation characteristic curve analysis showed sensitivity of 67% and specificity of 71%, when using SR = 4.4 as a cut-off for malignancy. The highest SR values were found in two benign microcystic adenomas. CONCLUSIONS. EUS-RTE with SR measurements and VAS evaluation demonstrated a significant strain difference between benign and malignant lesions. However, the variation within the entities was substantial and some benign lesions presented with low strain. Benign lesions were generally characterized by a strain similar to reference tissue, whereas malignant lesions were harder. The recorded strain pattern in individual lesions must be interpreted with caution.

Quantitative contrast-enhanced ultrasound comparison between inflammatory and fibrotic lesions in patients with Crohn's disease.

The aim of this study was to determine whether there are differences in absolute blood flow between patients with Crohn's disease with inflammation or fibrosis using contrast-enhanced ultrasound. Eighteen patients with fibrotic disease and 19 patients with inflammation were examined. Video sequences of contrast data were analyzed using a pharmacokinetic model to extract the arterial input and tissue residue functions with a custom software, enabling calculation of the absolute values for mean transit time, blood volume and flow. Feasibility of the examination was 89%. The fibrosis group had lower blood volume (0.9 vs. 3.4 mL per 100 mL tissue; p = 0.001) and flow (22.6 vs. 45.3 mL/min per 100 mL tissue; p = 0.003) compared with the inflammation group. There was no significant difference in mean transit time (3.9 vs. 5.5 s). In conclusion, absolute perfusion measurement in the gastrointestinal wall using contrast-enhanced ultrasound is feasible. There seems to be reduced blood volume and blood flow in patients with fibrotic disease.

High-frequency ultrasonographic imaging of the gastrointestinal wall.

The gastrointestinal (GI) tract, with its layered structure, can be imaged by ultrasound using a transabdominal approach or intraluminal high-frequency probes. New ultrasound technology can be used to characterize tissue hardness, study motility in real-time, direct diagnostic and therapeutic intervention, evaluate GI wall perfusion and tissue viability, and perform 3D imaging. Ultrasound is a safe imaging modality, and development of smaller devices has improved its application as a flexible clinical tool, which also can be used bedside. Recently, microbubbles have been injected into the blood stream loaded with contrast agents, or other diagnostic and therapeutic agents. Such bubbles can be destroyed by ultrasound waves, thus releasing their content at a given area of interest. In this article, we present a review of the GI wall anatomy and discuss currently available ultrasound technology for diagnosis and treatment of GI wall disorders.

Mechanosensation and mucosal blood perfusion in the esophagus of healthy volunteers studied with a multimodal device incorporating laser Doppler flowmetry and endosonography.

Both mechanical and ischemic mechanisms can cause gastrointestinal pain. We investigated whether discomfort and pain caused by bag distension in the esophagus of healthy subjects correlated best with mechanical forces (stress), deformation (strain), or mucosal perfusion. Twenty-nine subjects underwent ramp bag distension using a novel catheter design incorporating high-frequency intraluminal ultrasound, laser Doppler flowmetry, and manometry. Perfusion, pressure, and geometric data were analyzed at visual analog scale (VAS) levels 1-7 in 19 subjects. The circumferential stress increased exponentially as a function of volume, whereas strain showed a linear increase. The perfusion showed a modest decline, on average 15% from baseline to VAS = 7. A significant association was found between the sensory response and stress and strain (P < 0.05). No significant association was found between the sensory response and perfusion. In conclusion, the discomfort and pain response to bag distension in the esophagus is likely to be caused by mechanical rather than ischemic mechanisms.

Sonography of the small intestine.

In the last two decades, there has been substantial development in the diagnostic possibilities for examining the small intestine. Compared with computerized tomography, magnetic resonance imaging, capsule endoscopy and double-balloon endoscopy, ultrasonography has the advantage of being cheap, portable, flexible and user- and patient-friendly, while at the same time providing the clinician with image data of high temporal and spatial resolution. The method has limitations with penetration in obesity and with intestinal air impairing image quality. The flexibility ultrasonography offers the examiner also implies that a systematic approach during scanning is needed. This paper reviews the basic scanning techniques and new modalities such as contrast-enhanced ultrasound, elastography, strain rate imaging, hydrosonography, allergosonography, endoscopic sonography and nutritional imaging, and the literature on disease-specific findings in the small intestine. Some of these methods have shown clinical benefit, while others are under research and development to establish their role in the diagnostic repertoire. However, along with improved overall image quality of new ultrasound scanners, these methods have enabled more anatomical and physiological changes in the small intestine to be observed. Accordingly, ultrasound of the small intestine is an attractive clinical tool to study patients with a range of diseases.

Freehand real-time elastography: impact of scanning parameters on image quality and in vitro intra- and interobserver validations.

Real-time elastography is a method for visualization of the elastic properties of soft tissue and may potentially enable differentiation between malignant and benign pathologic lesions. Our aim was to validate the method on a tissue-mimicking (TM) phantom and to evaluate the influence of different scanning parameters and investigator variability. A TM-phantom containing eight spherical inclusions with known storage modulus was examined using two different transducers on an ultrasound (US) scanner equipped with software for real-time elasticity imaging. The ultrasound transducers were moved vertically in a repetitive manner to induce strain. Two investigators performed series of standardized elastography scans applying a 0-4 categorical quality scale to evaluate the influence of seven parameters: dynamic range of elasticity, region-of-interest, frequency of transducer movement, rejection of elastogram noise, frame rate, persistence and smoothing. Subsequently, repeated examinations of four selected inclusions were performed using a visual analog scale (VAS) where investigators marked a 100 mm horizontal line representing the span in image quality based on experience from the first examination. The hardest and softest inclusions were imaged more clearly than the inclusions with elasticity more similar to the background material. Intraobserver agreement on elastogram quality was good (kappa: 0.67 - 0.75) and interobserver agreement average (kappa: 0.55 - 0.56) when using the categorical scale. The subsequent VAS evaluation gave intraclass-correlation coefficients for the two observers of 0.98 and 0.93, respectively, and an interclass-correlation coefficient of 0.93. Real-time elastography adequately visualized isoechoic inclusions with different elastic properties in a TM-phantom with acceptable intra- and interobserver agreement. Dynamic range of elasticity was the parameter with most impact on the elastographic visualization of inclusions.

Crohn's disease: Comparison of in vitro ultrasonographic images and histology.

OBJECTIVE: To examine some typical histological findings in Crohn's disease using high-frequency ultrasound and to define the echo properties of these findings. MATERIAL AND METHODS: Bowel resection specimens from 14 patients operated on for Crohn's disease were examined with a 10 MHz linear array ultrasound transducer in a saline reservoir. Needles were placed in the specimen corresponding to the ultrasound plane. After formalin fixation, histological sections were taken according to these markings. Fifty-eight ultrasonographic images with 123 regions of interest were compared with corresponding histology. RESULTS: A thickened muscularis mucosae (>0.3 mm) was found in 48 of 69 regions of interest on histology. Submucosa with slight to moderate fibrosis was imaged as an echo-rich layer with sporadic, echo-poor elements (36/56), while severe fibrosis was seen as an echo-rich layer with diffuse, echo-poor elements (40/55). Muscularis propria with slight to moderate fibrosis was seen as an echo-poor layer with sporadic, echo-rich elements (49/66) while severe fibrosis was seen as an echo-poor layer with diffuse, echo-rich elements (17/22). Crohn's rosary was seen as echo-poor extensions of the 4th echo layer (31/50). CONCLUSIONS: Typical histological findings in Crohn's disease such as a thickened muscularis mucosae and Crohn's rosary can be imaged with high-frequency ultrasound in vitro. Fibrosis in the submucosa and muscularis propria is associated with decreasing and increasing echogenicity, respectively.

Advanced imaging and visualization in gastrointestinal disorders.

Advanced medical imaging and visualization has a strong impact on research and clinical decision making in gastroenterology. The aim of this paper is to show how imaging and visualization can disclose structural and functional abnormalities of the gastrointestinal (GI) tract. Imaging methods such as ultrasonography, magnetic resonance imaging (MRI), endoscopy, endosonography, and elastography will be outlined and visualization with Virtual Reality and haptic methods. Ultrasonography is a versatile method that can be used to evaluate antral contractility, gastric emptying, transpyloric flow, gastric configuration, intragastric distribution of meals, gastric accommodation and strain measurement of the gastric wall. Advanced methods for endoscopic ultrasound, three-dimensional (3D) ultrasound, and tissue Doppler (Strain Rate Imaging) provide detailed information of the GI tract. Food hypersensitivity reactions including gastrointestinal reactions due to food allergy can be visualized by ultrasonography and MRI. Development of multi-parametric and multi-modal imaging may increase diagnostic benefits and facilitate fusion of diagnostic and therapeutic imaging in the future.

Morphology and motor function of the gastrointestinal tract examined with endosonography.

Endosonography is a useful tool for studying the morphology and motor function of the gastrointestinal tract. Intraluminal ultrasonography is the common denomination of ultrasound examinations using intracorporal transducers which are inserted into the GI tract. Thus, the visceral wall and adjacent structures can be imaged in detail. This review describes the usefulness of endosonography in gastroenterology, in particular with respect to studies of the biomechanical and motor function of the gastrointestinal tract. New techniques such as 3-D EUS, elastography and strain rate imaging are discussed.

In vitro strain measurement in the porcine antrum using ultrasound doppler strain rate imaging.

Strain rate imaging (SRI) enables study of deformation in soft tissues. The aim of this study was to evaluate the accuracy of SRI in measuring strain in the porcine antral wall in vitro. An experimental set-up enabled controlled distension of a porcine stomach in a saline reservoir. Radial strain obtained by SRI was compared with radial strain calculated from B-mode ultrasonography. Circumferential strain obtained by SRI was compared with circumferential strain calculated from sonomicrometry. The agreement between radial strain values measured by SRI and B-mode, along and across several ultrasound (US) beams, using US frequency 6.7 MHz and strain length (SL) = 1.9 mm was = -1.0 +/- 12.1% and 0.5 +/- 13.4%, respectively (mean difference +/- 2SD%) and it was better than with SL 1.2 mm. Compared with sonomicrometry, SRI-determined circumferential strain using 6.7 MHz and SL = 1.9 mm was less accurate, whether averaging along or across several US beams (-9.2 +/- 46.7% and 13.8 +/- 51.2%, respectively). In conclusion, SRI gave accurate measurement of radial strain of the antral wall, but seemed to be less accurate for measurement of circumferential strain for this in vitro set-up.

3-D endobronchial ultrasonography--a post mortem study.

Endobronchial ultrasonography (EBUS) using balloon-embedded probes may cause airway obstruction and requires a rapid scanning procedure. Three-dimensional (3-D) postprocessing of sequential 2-D images may allow detailed studies on a rapidly acquired image volume. We applied a 3-D reconstruction program on EBUS recordings acquired with a radial-scanning probe during a controlled pullback procedure in water-filled airways in five corpses. The aim was to acquire EBUS images under optimized conditions and to test a 3-D software program for postprocessing. Under post mortem conditions, 3-D images were obtained, allowing any-plane imaging and measurements, application of different rendering and visualization algorithms and merging of overlapping volumes.

Ultrasonography and three-dimensional methods of the upper gastrointestinal tract.

Improved technology and new clinical methods have expanded the possibilities of using ultrasound in the daily routine of gastroenterology. Gastrointestinal ultrasonography can, in principle, be applied in two different ways in patient management. It can be used as one imaging modality among others, for which the clinicians refer the patient to a radiologist, but it can also be used as a clinical tool, similar to the stethoscope, expanding on the clinical findings and paving the way for efficient work-up of patients. Furthermore, ultrasonography has scientific applications; for example, strain rate imaging and three-dimensional ultrasound are advanced methods that allow highly specified and detailed examination of the tissue or organ of interest.

In vitro evaluation of ultrasound Doppler strain rate imaging: modification for measurement in a slowly moving tissue phantom.

Doppler strain rate imaging (SRI) was evaluated in vitro using a silicone strip phantom mimicking slowly moving tissue. A test apparatus was developed that enabled controlled strain experiments with variable strain and strain rate to be performed. SRI strain was measured at eight different calculated strains (range 5.7 to 63.4 %) at three different pump speeds with tissue velocity 0.1, 0.5 and 1.0 mm/s. The effect of varying tissue velocity and strain sample size on the measured SRI strain was elaborated. SRI strains agreed well with calculated values for strain when SRI strain was measured as the average over the whole strip cross-section and the strain sample size was 1.9 mm (mean difference = 2.78%, limits of agreement +/- 9.97% for tissue velocity 1.0 mm/s, n = 8). The variance was substantial if single central samples were used, especially for strain sample size of 0.8 mm (mean difference = -7.47%, limits of agreement +/- 20.90 for tissue velocity 0.5 mm/s, n = 24). Increasing the strain sample size to 1.9 mm removed some of the underestimation (giving mean difference of -4.46%, n = 24). We found low intra- and interobserver variation. This study indicates that, for the SRI method to give accurate estimates of strain, strain sample size should be in the region of 2 mm. Averaging over several ultrasound (US) beams increased the accuracy further.

[Mobile ultrasonography in a medical department]. / Mobilultralyd i en medisinsk avdeling.

BACKGROUND: We examined the usefulness and image quality of a mobile miniaturised ultrasound scanner in a medical ward. MATERIAL AND METHODS: The instrument (SonoSite 180), weighing 2.4 kg, is a hand-carried system powered by batteries. In 25 days we recruited consecutively 36 patients aged 23-92. Four different operators evaluated the use of the scanner. We examined one group of patients with relatively simple diagnostic challenges (e.g. gallbladder stone) and one group of patients demanding more advanced visualisation (e.g. peptic ulcer, colitis). RESULTS: The scanner was easy to carry around and scanning was initiated in 10 seconds. We found satisfactory image quality on 81% of the examinations, despite the fact that in 28% of cases, bowel air and abdominal fat impaired acoustic penetration. Average scanning time was 7 +/- 3 minutes. In 83% of cases, mobile scanning adequately solved the clinical problem. Diagnostic work-up or treatment was changed because of scanning in 39% of the patients. In 64% of cases, standard-procedure referral to the department of radiology was avoided. In 81% of the examinations the operator was very satisfied with the scanner, also in cases that required advanced visualisation. INTERPRETATION: This mobile scanner was simple to use and gave quick results in a medical ward. The operators were very satisfied: mobile scanning changed diagnostic work-up or treatment in 4 out of 10 cases. Mobile ultrasound scanning enables early diagnosis and seems to promote an efficient flow of patients in a hospital unit.

Strain during gastric contractions can be measured using Doppler ultrasonography.

This study was undertaken to explore if strain of the muscle layers within the gastric wall could be measured by transabdominal strain rate imaging (SRI), a novel Doppler ultrasound (US) method. A total of 9 healthy fasting subjects (8 women, 1 man; ages 22 to 55 years) were studied and both grey-scale and Doppler US data were acquired with a 5- to 8-MHz linear transducer in cineloops of 97 to 256 frames. Rapid stepwise inflation (5 to 60 mL) of an intragastric bag was carried out and bag pressure and SRI were measured simultaneously. SRI enabled detailed studies of layers within the gastric wall in all subjects. Great variations in strain distribution of the muscle layers were found. Radial strain was much higher in the circular than in the longitudinal muscle layer. Strains derived from SRI correlated well with strains obtained with B-mode measurements (r = 0.98, p < 0.05). During balloon distension, we found an inverse correlation between pressure and radial strain (r = -0.87, p < 0.05). Intraobserver correlation of strain estimation was r = 0.98 (p < 0.05) and intraobserver agreement was 0.2% +/- 18.6% (mean difference +/- 2SD, % strain). Interobserver correlation was r = 0.84 (p < 0.05) and interobserver agreement was 6.9% +/- 56.8%. SRI enables detailed mapping of radial strain distribution of the gastric wall and correlates well with B-mode measurements and pressure increments.

Food allergy and intolerance: response to intestinal provocation monitored by endosonography.

OBJECTIVE: Objective assessment of adverse reactions to food is a long-felt want. We report our preliminary experience with a new endosonographic allergen provocation test. METHODS: Twenty patients were examined, seven patients having food allergy and 13 having food intolerance. The duodenal mucosa was challenged with allergen extracts via a nasoduodenal tube. The responses were recorded using a miniprobe for endosonography through the tube. Thereafter, intestinal lavage was performed by giving 2 l PEG solution containing micro Ci (51)CrEDTA. The gut lavage fluid and urine for 5 h were collected. RESULTS: Increased mucosal thickness in response to provocation was recorded in 11 patients, but not more often or pronounced in the allergic than in the intolerance group. Interestingly, increased mucosal thickness associated with a new echogenic layer was seen in two patients and a sustained duodenal contraction, lasting 15-20 min associated with pain, in another two. Intestinal permeability and inflammatory mediators were not significantly different in the two groups. CONCLUSION: In patients with self-reported adverse reactions to food abnormal responses to duodenal provocation may be recognised by endosonography. However, neither endosonography nor intestinal permeability or faecal calprotectin responses were able to distinguish between food allergy and intolerance. Sustained duodenal contractions in response to food might be a cause of abdominal pain.