CT Abdomen: benefits, risk, preparation, and how it’s done

Introduction

Computed tomography uses a combination of X-rays and computer technology to produce axial images (slices) of the body. A CT scan shows detailed images of any part of the body, including the bones, muscles, fat, organs, and blood vessels. CT is a sensitive and noninvasive method for diagnosing problems in the abdomen and pelvis area e.g. bladder, uterus, prostate, liver, spleen, and bowels. A CT scan of the abdomen and pelvis is also the first line for detecting solid organ injury after trauma. CT scans are more detailed than standard X-rays.

Some Indications

Acute abdominal pain
Trauma
Renal stones
appendicitis
pancreatitis
diverticulitis
abdominal aortic aneurysm or dissection
bowel obstruction
cancer staging

Benefits

Viewing a CT scan, an experienced radiologist can diagnose many causes of abdominal pain or injury from trauma with very high accuracy, enabling faster treatment and often eliminating the need for additional, more invasive diagnostic procedures.
When pain is caused by infection and inflammation, the speed, ease and accuracy of a CT examination can reduce the risk of serious complications, such as those caused by a burst appendix or an infected fluid collection and the subsequent spread of infection.
CT scanning is painless, noninvasive and accurate.
A major advantage of CT is its ability to image bone, soft tissue and blood vessels all at the same time.
Unlike conventional x-rays, CT scanning provides very detailed images of many types of tissue as well as the lungs, bones, and blood vessels.
CT examinations are fast and simple; in emergency cases, they can reveal internal injuries and bleeding quickly enough to help save lives.
CT is less sensitive to patient movement than MRI.
CT can be performed if the patient has an implanted medical device of any kind, unlike MRI.
A diagnosis determined by CT scanning may eliminate the need for exploratory surgery and surgical biopsy.
No radiation remains in a patient’s body after a CT examination.
X-rays used in CT scans should have no immediate side effects.

Contrast administration

Not all scans use a contrast medium; in those that do, it is given through an IV injection or orally. The IV contrast medium improves the image quality by highlighting certain structures, such as arteries, and making them more visible on the scan. Oral (sometimes rectal) contrast may be used depending on the indications for the scan. A dilute (2% w/v) suspension of barium sulphate is most commonly used. The concentrated barium sulphate preparations used for fluoroscopy, e.g. barium enema, are too dense and cause severe artefacts on CT. Iodinated contrast agents may be used if barium is contraindicated (for example, suspicion of perforated bowel injury). Other agents may be required to optimise the imaging of specific organs, such as rectally administered gas (air or carbon dioxide) or fluid (water) for a colon study, or oral water for a stomach study.

Risks of CT scan

Exposure to Radiation:

There is always a slight chance of cancer from excessive exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk. Radiation exposure during pregnancy may lead to birth defects. Therefore, the patient’s history should be taken carefully and a pregnancy test should be done before CT scan. Also, It is the responsibility of the referring physician to investigate the patient’s past record of radiation exposure, such as previous CT scans and other types of X-rays, so repetition of scans can be avoided. Risks associated with radiation exposure may be related to the cumulative number of X-ray examinations and/or treatments over a long period of time. The benefits vs risks of CT scan should be considered so unnecessary scan can be avoided. The risk of radiation exposure from CT is very small compared to the benefits especially when the CT scan is considered by the referring physician as an important tool for diagnosis according to the patient’s history and symptoms.

Allergy to Contrast Media:

There is a risk for allergic reaction to the contrast media. The risk of serious allergic reaction to contrast materials that contain iodine is extremely rare, and radiology departments are well-equipped to deal with them. Patients who are allergic to or sensitive to medications should notify their doctor. Patients should be asked if they have ever had a reaction to contrast media. Also, patients should be asked if they have a history of seafood allergy, heart disease, asthma, diabetes, or thyroid problems. Any of those conditions may increase the risk of an unusual adverse effect. If a patient says yes to one of these conditions, a radiologist should be informed before the CT scan. Every hospital has its own policy regarding contrast media allergy, but usually, doctors may prescribe medications (usually a steroid) to reduce the risk of an allergic reaction. If the patient takes metformin/Glucophage, or a related medication, they may be asked to stop taking the medication for at least 48 hours after the contrast is administered, as it may cause a condition called metabolic acidosis, or an unsafe change in your blood pH.

Kidney Damage from Contrast Media

Patients with kidney failure or other kidney problems should notify their doctor. Lab investigation regarding kidney function (creatinine level) should be taken before the CT scan. In some cases, the contrast media can cause kidney failure, especially if the patient is dehydrated or already has underlying kidney disease.

Preparation

A radiology nurse or technologist will ask the patient a few questions regarding their medical history and allergies.
Explain the procedure to the patient.
Patients who are diabetic and taking Glucophage will need clearance from their referring physician before the exam.
If the CT scan requested without contrast, the patient can eat, drink and take their prescribed medications prior to the exam, but in the case of IV contrast requested, NPO for at least four hours before scanning. Insert a patent IV cannula. Creatinine should be documented and consent must also be signed by the patient.
Appropriate precautions must be taken prior to the scan to ensure that the patient has adequate renal function and no history of allergy before prescribing intravenous iodinated contrast.
In the case of oral contrast requested, the patient will be asked to wait 90 minutes after drinking for the contrast to reach abdomen/pelvis area.
The patient may be asked to change into a patient gown. If so, a gown will be provided for them. A locker will be provided to secure personal belongings. Inform the patient to remove all piercings and leave all jewellery and valuables in the locker.

How it is done

Position the patient on the exam table, most often, the patient will be asked to lie flat on their back with both arms over the head. If the IV contrast is requested, it may be given through an injection in IV during scanning according to the protocol assigned by the radiologist e.g. arterial phase, portoveneous phase, and delayed phase. At least one of these protocols is requested and sometimes all of them are requested by the radiologist depending on the patient’s disease history. In other words, scan protocols are adapted for the specific diagnostic problem. The IV contrast may cause the patient to experience a warm sensation all over their body and a metal taste in the mouth. This is normal.

The table will slide into the scanner. The scanner is open at the back and the front, allowing the patient to see out. The technologist should be always see and hear the patient during scanning. The patient will be asked to hold very still and at times to hold the breath because movement causes blurred images. This procedure usually takes approximately 15-30 minutes. CT scans use X-ray and computer analysis to create detailed pictures of the human body.

After the Scan

There are no restrictions placed on the patient after this procedure. They may eat and drive as normal. If the patient takes metformin/Glucophage, or a related medication, they may be asked to stop taking the medication for at least 48 hours after the contrast is administered.
If the patient received an injection of contrast media, they should drink plenty of liquid to help flush it out of their system.

Results

Images can be reformatted (coronal-sagittal) for viewing on picture archiving and communication system (PACS) workstations. Additional manipulation can be done on PACS or dedicated workstations, providing for multi planar and 3-dimensional views of organs, vessels, and bones. With the use of appropriate luminal and intravenous contrast agents, information can be obtained on lesion characteristics based on tissue attenuation changes, detailed 3-dimensional arterial anatomy, and/or luminal surface contour (eg, in virtual colonoscopy).

The study will be read by a Radiologist (imaging physician) who specialises in the interpretation of CT scans. The results will be sent to the referring physician who will discuss these results with the patient and explain what they mean in relation to their health.