All bariatric patients presenting for gastric bypass surgery routinely undergo a preoperative abdominal ultrasound examination to evaluate for gallstones. If a patient undergoing gastric bypass surgery has gallstones, they may be offered a cholecystectomy during their gastric bypass surgery, as a gastric bypass may prevent future endoscopic management of biliary stone disease.

Although an ultrasound exam can easily evaluate for gallstones, in obese patients the image quality can be compromised by the distribution of fat. Patients with predominantly subcutaneous fat have poor image quality due to the attenuation of the ultrasound beam as it penetrates through the thickness of the fat (Fig. 20.2).

On postoperative day two, patients typically undergo a barium swallow study. The study is conducted by having the patient first swallow water-soluble contrast while standing in a left lateral oblique position. Using real-time fluoroscopy, contrast is visualized extending down the esophagus, through the gastric pouch and into jejunal bowel loops. The radiologist assesses for any extravasation of contrast into the peritoneum or into the excluded gastric segment. The radiologist also observes the degree of small bowel dilation and transit time through the small bowel assessing for a small bowel obstruction.

Although a barium swallow can be performed using real-time fluoroscopy in a majority of obese patients, the limitation in some morbidly obese patients is the ability for the patient to fit in the space between the table and the image intensifier (Fig. 20.3). If the patient girth exceeds this space, then the fluoroscopic study is severely limited as it cannot be performed in real time. The solution in such a situation is to have the patient swallow contrast and obtain intermittent chest and abdominal radiographs (Fig. 20.4). The limitation of this technique is the inability to view the flow of contrast in real time and thereby potentially missing a small extravasation.

When patients present postoperatively with abdominal pain and fever, the critical clinical concerns are whether there is an anastomotic leak causing an abscess and peritonitis or whether there is a bowel obstruction. Of all the imaging modalities to evaluate these questions, the best imaging modality again is an a­bdominal CT. If a bariatric patient can fit on the CT scanner, CT is the best tool to evaluate these conditions. If patients exceed either the CT table weight limit or gantry diameters, serious clinical decisions arise as the patients’ remaining options are to admit and observe or a ­surgical exploration. X-rays and fluoroscopy looking for free air or obstruction can guide this decision.

After choosing the correct imaging modality based on the patient’s clinical need, the next question to address is whether the patient can fit on the imaging equipment.

For all cross-sectional imaging including CT, MRI, and fluoroscopy, there are industry standard table weight limits and gantry diameters (Table 20.1). Standard table weight limit/gantry diameter for CT is 450 lb/70 cm. For MRI the limits are 350 lb/60 cm. For fluoroscopy the limits are 350 lb/45 cm. Although CT tables are built to physically accommodate up to 1,500 lb, the table weight limits exist to support the motor mechanism that moves the patient into the scanner to an accuracy rate of 0.25 mm [5, 6]. Exceeding the table weight limits risks damage to this table motor mechanism.

For patients who do not exceed the table weight limit, another limitation to consider is their abdominal diameter. For all imaging equipment, except for ultrasound or nuclear medicine, there is an aperture limit that patients must be able to fit into. Industry standard gantry diameter for CT is 70 cm, for the MR bore it is 60 cm, and for fluoroscopy it is 45 cm (Fig. 20.5a). These measurements and limits vary by specific model and should be reviewed.

For physicians caring for obese patients and ordering these imaging studies, both the weight and abdominal diameter must be relayed to the radiologists or technologists prior to ordering the study. Transporting patients down for an imaging study only to discover the patient cannot fit causes undue anxiety to the patient, can potentially cause injuries to technologists attempting to move patients, can potentially damage imaging equipment, and at the very least, disrupts the CT schedule for other patients as the weight and body diameter information is being searched for by the technologists. Therefore, all obese patients must be weighed on admission. Also, ideally the ­widest abdominal diameters must be measured. A unique approach to measure patient diameter is to fashion a hula hoop in the size of the CT gantry [9]. The hula hoop can be taken to the patient’s ­bedside and placed around the widest portion of the patient to ensure that they will fit within the aperture of the scanner.

This brings to question the solutions if patients exceed the table and gantry limits. One solution is to consider alternative imaging modalities that can attempt to answer the clinical question. For example, when patients exceed the 350 Ib weight limit of the typical fluoroscopic table, we consider either standing chest/abdomen radiographs or place the patient on a 450 Ib CT table, or utilize an abdominal ultrasound, which has no weight or gantry limits. Another solution is to refer patients to outpatient facilities or other hospitals that have larger scanners. In recent years, manufacturers have developed larger CT and MRI scanners that can accommodate larger patients. There are CT scanners that can accommodate patients up to 650 lb and gantry diameters up to 82 cm (Fig. 20.5b).