1. 
   

   What are the advantages and limitations of abdominal ultrasound?

   
   
2. 
   

   What are the indications for gastrointestinal (GI) fluoroscopy?

   
   
3. 
   

   What are the advantages of computed tomography (CT) when compared with magnetic resonance imaging (MRI) for imaging abdominal structures?

   
   
4. 
   

   What are the indications for nuclear medicine imaging studies?

Radiologists expect to provide guidance in the use of advanced medical imaging tests in the care of acutely ill patients requiring hospitalization. This chapter is intended to present the thought processes that radiologists commonly use rather than dictate a particular test for a particular patient or situation.

Before ordering advanced imaging, it is always important to consider whether the information may be provided by prior studies. The KUB (Kidneys Ureter and Bladder) is often ordered as a screening examination but also serves as the initial default imaging examination when selection of a more specific test cannot be made, as when a patient has diffuse abdominal pain without any localizing signs. No preparation is required. The radiation exposure is slightly higher than a chest radiograph. Although originally IV and PO contrast material was administered in conjunction with plain film radiography, this is no longer common practice. However, in the acutely ill patient who has received one or more contrast agents for a prior study, the KUB can provide additional information without readministration of contrast material, especially for patients with abdominal pain occurring during or shortly after imaging of a different region of the body. A rudimentary intravenous pyelogram (IVP) can be obtained following contrast-enhanced head or chest CT or even cardiac catheterization. The period of time over which the visualization persists will be inversely proportional to the patient’s estimated glomerular filtration rate (eGFR) over several hours. The oral contrast material administered for an abdominal CT scan will be concentrated within the colon and often remain visible for several days.

Ultrasound can be the best possible examination for the acutely ill hospitalized patient. It is relatively inexpensive, uses no ionizing radiation, and tailored examinations can be performed at the patient’s bedside if necessary. Ultrasound is enhanced by passage through water and stopped by air and bone. It is therefore able to detect a pleural effusion and guide thoracentesis of small to moderate pleural effusions. The information provided depends very much on the operator even with complete video recording. Ultrasound is a very useful tool for the interventional radiologist and may be chosen by the radiologist for a variety of biopsies including liver and prostate.

Abdominal US

In the abdomen, renal and gallbladder ultrasounds are standard examinations. A screening abdominal ultrasound will also include images of the liver, spleen, and pancreas. The confirmation of a simple cyst can exclude more significant pathology in many organs, including ovaries, kidneys, and liver. In order to visualize the pancreas, the ultrasonographer will either compress the air out of the stomach or have the patient drink water to allow the stomach to act as an acoustical window, enhancing the through transmission of the sound waves to the pancreas behind the stomach. The tail of the pancreas may be inadequately examined due to air in the adjacent small bowel.

Pelvic US

Pelvic ultrasound imaging may be performed transabdominally through a full urinary bladder to provide an acoustical window or transvaginally for imaging ovaries. Ultrasound routinely evaluates pregnancies for diagnosis, prognosis, and on occasion, treatment of fetal disease.

Vascular US

Vascular ultrasound can identify DVT that prevents veins from collapsing when compressed. This is most helpful in the lower extremities and cannot be performed in regions, such as the pelvis, in which the veins cannot be directly compressed.

Limited GI fluoroscopy involves contrast administration followed by obtaining a KUB. A full fluoroscopic examination includes a physical examination by the radiologist to localize the patient’s pain with palpation of the opacified structures of the gastrointestinal tract. During fluoroscopy, X-rays strike a fluorescent screen on which an image can be simultaneously formed and viewed. In early fluoroscopy units, the image was inferior, especially with larger patients, and the examination had to be performed in the dark (always literally, sometimes figuratively!) after the radiologist had first adapted his eyes to the dark by wearing red goggles. With modern equipment, which incorporates an image intensification system, the images can be viewed on a television monitor in comfortably subdued light.

The nature of the fluoroscopic examination provides physiologic as well as anatomic and pathologic information. The patient’s position or physiologic state may be changed to provoke the chief complaint. The study begins with a supine view of the abdomen and continues with the radiologist at the bedside during the administration of contrast. With fluoroscopy, the radiologist can view the image directly on a television screen in real time without exposing an image and waiting for it to be processed. This “real-time” evaluation is especially useful for studying a dynamic, constantly changing system such as inducing gastroesophageal reflux. Attached to the image intensification tower is a device for making and transferring digital images to a picture archiving and storage system (PACS). During the examination, the radiologist will “spot image” areas of interest that he or she discovers fluoroscopically, and areas not optimally demonstrated on the overhead images, such as the convolutions of the sigmoid colon and the duodenal bulb. The spot images are not meant to replace or necessarily duplicate the overhead images the technologist takes. Many areas need to be “unfolded” and will be seen well only on adequately positioned spot images. The advantage of this system is that a permanent record can be made when the patient is perfectly positioned; otherwise one runs the risk of missing the abnormality on the overheads, which are exposed according to a set routine. Movie cameras (cine) and magnetic tape or computer-based recorders can be adapted to the basic system; the advance allows a dynamic recording of the constantly-in-motion GI tract for later review, and permanent storage if desired. This advance is particularly useful for interpreting and storing a videofluoroscopic study of the swallowing mechanism.

Patient Preparation

Patient preparation varies from no preparation, to nothing orally and full bowel preparation, depending on the examination. Patient preparation should also include planning for the excretion of contrast material that will be concentrated in the colon and potentially cause severe constipation. Fluid and physical movement, such as walking, are most helpful. Should follow-up working images of the abdomen or chest be obtained, one should pay attention to whether retained barium is present.

It is useful to watch several of these studies being performed in order to realize the best studies require active participation by the patient, moving through a series of positions that may include prone and every angle between prone and supine. GI fluoroscopy exams that require fasting are generally scheduled in the morning. In the afternoon, the same fluoroscopy suite may be used to study swallowing function in patients who are at risk for aspiration. Non-GI fluoroscopic examinations including retrograde cystography and joint arthroscopy, and chest fluoroscopy will also generally be scheduled after the completion of the GI fluoroscopy schedule.

Advance Communication with Radiologist to Tailor Study to the Patient

Examinations can be tailored to the specific needs and issues of the patient. Discussion in advance with the radiologist allows for more input than generally conveyed when ordering the examination. The examination types are used as starting points. A video swallow examination of the oropharynx is performed with a variety of liquid and solid contrast materials to determine risk for aspiration and identify protective positions in which a patient may swallow particular types of food safely. A barium swallow examination will briefly study the oropharynx and then focus on the esophagus itself in the erect position followed by the supine position. The stomach may be incompletely studied although the term “barium swallow” is also sometimes used as a synonym for the upper GI examination that includes the barium swallow with detailed examination of the stomach and duodenum. Delayed images to follow oral contrast material through the small bowel add the element of a small bowel follow-through to the upper GI examination.

The small bowel can be difficult to completely image and specialized small bowel enema, or enteroclysis, can be performed to identify rare small bowel lesions. For this examination, a feeding tube is placed through the nose to allow the contrast material to be delivered directly into the duodenum. The preparation may involve laxatives as well as a liquid diet for 24 hours or more prior to the enteroclysis. Medications that slow transit through the GI tract may need to be discontinued prior to the examination. Barium enema examinations may be performed with single or double contrast material. A limited study may be adequate to localize colonic obstruction such as seen with apple core colon cancer lesions in the sigmoid colon. Retained fecal material can interfere with the detection of polyps. Barium enema may be performed following incomplete colonoscopy to supplement the examination without repeating the preparation. The appendix and terminal ileum may be filled by the retrograde flow of contrast material.

Abdominal CT scanning may be performed as a screening examination or with a very specific protocol focusing on a single region or physiologic process. Thus it is very important to convey the reason for the examination to the radiologist in order for the examination to provide the needed diagnostic information. The information provided to the radiologist will determine the suitability of the examination performed to answer clinical questions at the time of examination and later on during the course of patient hospitalization. In many institutions, the pelvis will be included in a complete abdomen CT, while in some institutions a specific order may be required to include the pelvis. Pelvic CT can generally be ordered without an abdominal CT although this is most commonly done for pelvic fractures and on occasion for gynecological disease.

Abdominal Pain