Understanding the Process of an Abdominal CT Scan

An abdominal CT (computed tomography) scan is a non-invasive imaging test that helps doctors to visualize the organs and tissues within the abdomen. This comprehensive guide provides a detailed overview of what happens during this procedure, from preparation to the actual scanning process.

Preparation Steps

Before undergoing an abdominal CT scan, patients need to follow specific preparation steps to ensure the best possible images are obtained. This is particularly important for the contrast solution, which plays a critical role in the imaging process.

1. Fasting and Contrast Solution Patients are required to fast for approximately two hours prior to the scan. This precaution is taken to reduce the risk of nausea and vomiting, which could lead to choking or aspiration if vomit is inhaled. Since the introduction of newer, less reactive contrast solutions, these risks have reduced, but the precaution still exists.

2. Contrast Drink One hour before the scan, patients will consume a 1-liter solution of contrast. This solution is a mixture of water and iodine, which is visible on the CT scan. This helps to visualize the inside lining of the gut and any abnormalities in the gastrointestinal tract. The taste can be improved by adding cordial, making the experience more comfortable for patients.

3. Cannula Insertion During the scan, a cannula (a small plastic tube) is inserted into a vein, usually in the elbow crease. This is used to inject the iodine-based contrast solution, ensuring clear visualization of vascular tissues such as the liver, kidneys, and blood vessels. The contrast is kept warm to maintain its runniness, facilitating a smooth injection process. Generally, the larger veins in the elbow are used rather than smaller veins in the hands to prevent blockages. The injection volume for an average adult is typically 75 mL, administered over about 75 seconds, to reach the desired phase of circulation before the scan.

Scan Procedure

Patients are positioned on a scan table, and the table is raised to center the patient within the imaging machine. The arms are raised over the head to minimize radiation exposure for the abdomen. The head remains outside the machine to maintain a clear view of the abdominal region.

1. Positioning The patient’s ID is verified, and the risk of allergic reactions or kidney problems from the iodine contrast are assessed. If all checks out, the process continues. Patients typically remove metal jewelry or clothing with metal, usually by pulling jeans down to the knees and covering with a sheet.

2. Patient Monitoring The scanned organs are instructed to breathe in and hold their breath, a technique that helps to reduce motion artifacts in the images. This is particularly important during an abdominal scan, where multiple breath holds are performed to ensure accurate images. Two planning scans (scouts/topos) are conducted to determine the correct imaging region, followed by a main scan. The injection of contrast is performed remotely by a pressure injector, allowing the radiographer to monitor the process from an adjacent room. Care is taken to watch for any signs of complications such as high pressure, vessel leakage, or allergic reactions. Medical staff must be present at all times during the contrast injection to handle any emergencies that may occur.

3. Scanning Once the patient is in position and the injection is complete, the machine instructs the patient to breathe in and hold their breath. The scan begins 75 seconds after the injection, taking approximately 5 minutes in total. The scan may be particularly uncomfortable for patients with shoulder issues, as they need to keep their arms raised over their heads.

Following the scan, if the patient is an outpatient, the cannula is removed. Patients can resume their normal activities after the scan, provided there are no other tests scheduled on the same day.

Post-Scanning Considerations

The iodine-based contrast is excreted through the kidneys, and patients should stay well-hydrated to aid this process. Abdominal CT scan protocols can vary based on the specific clinical needs, patient's kidney function, age, and other factors.

Key Points to Consider Abdominal CT scans can vary depending on the clinical indication, patient history, and the facility's specific protocols. For certain conditions, such as kidney stones, contrast scans may not be necessary, as they can obscure the diagnostic images. During the COVID-19 pandemic, some sites stopped providing oral contrast, as the benefits were deemed outweighed by the risks of patient crowding.

In conclusion, an abdominal CT scan is a crucial diagnostic tool that requires careful preparation, patient positioning, and attention to detail during the scanning process. Following these steps ensures the most accurate and reliable imaging results for optimal clinical decision-making.