Radiography and ultrasonography are the most important imaging modalities to evaluate the small intestine of veterinary patients because they are noninvasive and inexpensive and often can be performed without sedation or anesthesia.1–4 Abnormalities of the small intestine, including perforation (especially without pneumoperitoneum), obstruction, and abnormal motility, may be difficult to identify with conventional radiography and ultrasonography. Therefore, radiographic and ultrasonographic contrast studies may be helpful to identify these small intestinal abnormalities.2–5
In veterinary medicine, barium sulfate is the most commonly used positive-contrast medium for radiographic study of the gastrointestinal tract, partly because it is cost-effective.2,3,6 However, the study can take approximately 3 to 5 hours2,3 to complete and be nondiagnostic when barium flocculation occurs.5,6 Additionally, barium in the lungs and abdominal cavity, because of esophageal and intestinal perforation or devitalization, causes severe inflammation.2,7–9 Barium administration is contraindicated for people and dogs with a high risk of pulmonary aspiration because of vomiting or high suspicion of gastrointestinal tract perforation and when other procedures (eg, esophagogastroduodenoscopy, abdominal ultrasonography, or abdominal surgery) are to immediately follow contrast radiography. Rather, an iodinated contrast medium may be a better choice of contrast agent in these situations; also, iodinated contrast radiographic studies can take only 1 to 2 hours to complete.2,3,6–9
Iodinated contrast medium can be ionic or nonionic. Ionic iodinated contrast medium is contraindicated in puppies, kittens, and dehydrated patients because of its hyperosmolarity.8,10,11 After its oral administration, fluid movement from the blood vessels into the lumen of the gastrointestinal tract may cause hypovolemic shock; after pulmonary aspiration of ionic iodinated contrast medium, fluid may move into the alveoli, causing pulmonary edema.8,10,11 Alternatively, nonionic iodinated contrast medium is considered safer because it has lower osmolarity and, therefore, is not expected to cause hypovolemic shock.8,10–12 Yet, nonionic iodinated contrast medium has a high cost, low viscosity, and reduced contrast effect over time.2,3,13 Because this medium has low viscosity, the gastrointestinal tract mucosa can be difficult to evaluate, and because of absorption and dilution of the medium as time elapses after its administration, its contrast effect decreases.
Carboxymethylcellulose is a nontoxic, nonimmune, biodegradable, and bioabsorbable substance that is used in cosmetics and medicines and as a food additive. As a radiographic contrast medium, it is useful because of its low risk of causing adverse events, especially when it is aspirated into the lungs and leaks into the abdominal cavity.14–23 Also, CMC is not absorbed by the small intestine and is viscous, unlike nonionic iodinated contrast medium; therefore, visualization of the small intestinal mucosa and lumen is improved because CMC coats the mucosa and its contrast effect is not diluted. In people and dogs, CMC has been administered with barium to prevent barium flocculation and shorten radiographic study time.1,13,20,21
Small intestinal motility and wall structure (eg, thickness and layering) can be assessed with ultrasonography. However, accurate small intestinal ultrasonography requires an experienced sonographer and sufficient time because the structure of the small intestine is complex and small intestinal walls are frequently obscured by intraluminal gas.2–4,7 Ideally, ultrasonography should precede barium contrast radiography because barium absorbs ultrasonic waves, thereby reducing ultrasonographic image quality.3,24
Ultrasonography after oral administration of polyethylene glycol solution to people with celiac or Crohn disease reveals that this solution adequately distended the small intestinal lumen and improved visualization of the small intestinal walls.4,23 Ultrasonography after administration of polyethylene glycol to people with Crohn disease is also as useful as abdominal contrast (barium) radiography to detect small intestinal lesions.23 Therefore, oral administration of a contrast medium, other than barium, to dogs may also be helpful for detecting small intestinal lesions ultrasonographically.
The goal of the study reported here was to evaluate MCMs that combined the respective advantages and offset the respective disadvantages of a nonionic iodinated contrast medium and CMC such that the MCM can be used to optimally evaluate the small intestine of dogs radiographically and ultrasonographically, especially when contrast radiography precedes ultrasonography. We hypothesized that the MCM with the largest volume of iohexol per kilogram of a dog's body weight would provide the best small intestinal radiographic images. Also, we believed each MCM would facilitate ultrasonographic assessment of the small intestine.
The study was supported in part by the Research Institute for Veterinary Science at Seoul National University.
The authors declare that there were no conflicts of interest.
Modified contrast medium
EVA-HF525 machine, GEMSS, Gyeonggi-do, Republic of Korea.
ProSound Alpha 7, Hitachi-Aloka, Tokyo, Japan.
Carboxymethylcellulose sodium salt, Sigma Chemical Co, St Louis, Mo and Kukjeon Pharm, Seoul, Republic of Korea.
Magnetic stirrer, MS 300, BANTE, Shanghai, China.
Omnipaque 300, GE Healthcare, Cork, Ireland.
Vet PACS, Infinitt Healthcare Co Ltd, Seoul, Republic of Korea.
SPSS Statistics for Windows, version 23.0, IBM Corp, Armonk, NY.
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Scoring system for assessing the degree of radiographic small intestinal contrast enhancement.
|Excellent (4)||Small intestinal segment with greater contrast enhancement vs bone; no superimposition with other structures.|
|Very good (3)||Small intestinal segment with equal contrast enhancement vs bone; no superimposition with other structures.|
|Good (2)||Small intestinal segment with less contrast enhancement vs bone; no superimposition with other structures.|
|Fair (1)||Small intestinal segment with less contrast enhancement vs bone and unclear margin; no superimposition with other structures.|
|Poor (0)||Small intestinal segment with little contrast enhancement; no superimposition with other structures.|
Scoring system for assessing the radiographic clarity of a contrast-enhanced small intestinal segment when superimposed by ≥ 1 contrast-enhanced small intestinal segment.
|Excellent (4)||Superimposition of ≥ 2 contrast-enhanced small intestinal segments that were distinguishable by ≥ 80%; no superimposed bone.|
|Very good (3)||Superimposition of ≥ 2 contrast-enhanced small intestinal segments that were distinguishable by ≥ 60% and < 80%; no superimposed bone.|
|Good (2)||Superimposition of ≥ 2 contrast-enhanced small intestinal segments that were distinguishable by ≥ 40% and < 60%; no superimposed bone.|
|Fair (1)||Superimposition of ≥ 2 contrast-enhanced small intestinal segments that were distinguishable by ≥ 20% and < 40%; no superimposed bone.|
|Poor (0)||Superimposition of ≥ 2 contrast-enhanced small intestinal segments that were distinguishable by < 20%; no superimposed bone.|
Scoring system for assessing the radiographic clarity of a contrast-enhanced small intestinal segment when superimposed with bone.
|Excellent (4)||Contrast-enhanced small intestinal segment distinguishable by ≥ 80% from superimposed bone.|
|Very good (3)||Contrast-enhanced small intestinal segment distinguishable by ≥ 60% and < 80% from superimposed bone.|
|Good (2)||Contrast-enhanced small intestinal segment distinguishable by ≥ 40% and < 60% from superimposed bone.|
|Fair (1)||Contrast-enhanced small intestinal segment distinguishable by ≥ 20% and < 40% from superimposed bone.|
|Poor (0)||Contrast-enhanced small intestinal segment distinguishable by < 20% from superimposed bone.|
Scoring system for assessing the radiographic appearance of the ileocolic junction and cecum.
|Excellent (4)||Marked contrast enhancement of the ileocolic junction and cecum.|
|Very good (3)||Moderate contrast enhancement of the ileocolic junction and cecum.|
|Good (2)||Moderate contrast enhancement of either (not both) the ileocolic junction or cecum.|
|Fair (1)||Mild contrast enhancement of either (not both) the ileocolic junction or cecum.|
|Poor (0)||No contrast enhancement of the ileocolic junction and cecum.|