Abdominal Imaging

Question 1

Types of imaging modalities

Answer 1

Plain abdominal x-ray
Computed tomography (CT)
Contrast
Ultrasound
Endoscopy
Laparoscopy

Question 2

Common uses of plain abdominal x-ray (AXR)

Answer 2

Looking for foreign bodies and dilated loops of bowel (sign of intestinal obstruction)

Question 3

Ionising radiation plain abdominal x-ray

Answer 3

It exposes the patient to the equivalent of approximately 4 months of background radiation

Question 4

Plain abdominal x-ray

Answer 4

Limited use as the anatomy is more complex than thoracic anatomy and most abdominal tissues are of similar density so differentiation of different structures is very difficult

Question 5

Uses of computed tomography CT

Answer 5

Widely used in abdominal imaging for many pathologies
Very often used with a contrast agent

Question 6

Ionising radiation and CT

Answer 6

Frequently used
much greater dose of ionising radiation
Exposes the patient to the equivalent of approximately 4.5 years of background radiation

Question 7

Computed tomography CT

Answer 7

Created by directing a very large dose of x-rays at the patient from various angles and reproducing the image digitally producing 3D images
Viewers need to scroll through the series of images to see each part of the abdomen

Question 8

How to identify small intestine on x-ray

Answer 8

Lines going across the tube - plicae circularis

Question 9

Width of normal small intestine on x-ray

Answer 9

Up to 3cm

Question 10

Width of normal large intestine on x-ray

Answer 10

Up to 6cm

Question 11

How to identify large intestine on x-ray

Answer 11

Haustral folds across tube

Question 12

Largest part of large intestine

Answer 12

Caecum

Question 13

Width of normal caecum on x-ray

Answer 13

Up to 9cm

Question 14

Uses of contrast

Answer 14

Barium swallow
Barium enema
CT abdomen with contrast
CT aortogram
Trauma CT

Question 15

Examples of contrast agents

Answer 15

Iodine
Barium (for x-rays and CT)
Gadolinium (for MRI)

Question 16

What contrast is used for x-rays or CT

Answer 16

Barium

Question 17

Which contrast is used for MRI

Answer 17

Gadolinium

Question 18

Contrast agents

Answer 18

Radio-opaque liquids that are used to increase differentiation between different tissues
Can be swallowed or inserted into the GI tract via the rectum before x-rays or CT scans to visualise the GI tract
It is not absorbed so is later excreted via the anus

Question 19

Axial CT image

Answer 19

Standing at feet and looking up patient

Question 20

Administration of contrast

Answer 20

• Contrast agents can be swallowed or inserted into the GI tract via the rectum before X-rays or CT scans to visualise the GI tract. The contrast is not absorbed so is later excreted via the anus.
• Contrast agents can also be injected into the veins or arteries during X-rays, CTs or MRIs to visualise the blood vessels. This is particularly useful as it can help radiologists to identify inflammation, cancer, blockage of a blood vessel and bleeding, amongst other things. The contrast is then filtered out of the blood by the kidneys and excreted in the urine.

Question 21

When is contrast injected into vein or arteries

Answer 21

Identification of inflammation, cancer, blockage of a blood vessel and bleeding

Question 22

Uses of ultrasound

Answer 22

liver, gallbladder, biliary tree, aorta, kidneys, bladder volume, vascular access, free fluid in the abdomen, pregnancy/foetal scans, uterus, ovaries, testicles.

Question 23

Why are ultrasound not as useful as CT

Answer 23

Produce a 2D image which is less detailed

Question 24

Ultrasound

Answer 24

uses sound waves of a higher frequency than we can hear which are directed from a probe towards the target structure, reflected off it and received back at the probe. The time taken and amplitude of the rebound wave are detected and used to calculate the densities and depths of the structures. Images are viewed ‘real-time’ on a screen and the probe can be placed wherever necessary to view the desired organ.

Question 25

Are ultrasounds harmful

Answer 25

non-ionising so theoretically cause no harm to the patient.

Question 26

Performing an ultrasound

Answer 26

relatively difficult to perform and interpret so specialist training is required, but non-radiologist clinicians can also be trained to use ultrasound such as in the emergency department and critical care.

Question 27

Endoscopy

Answer 27

• Very frequently used to directly visualise the lumen of hollow organs using a camera.
• Non-ionising because it’s just a camera, but patients may require sedation for the procedure, and there are risks of perforation of stomach or intestine.

Question 28

Uses of endoscopy

Answer 28

visualise the lumen and walls of the oesophagus, stomach, small and large intestine (e.g. looking for a source of bleeding or cancer, or removing foreign bodies)

Question 29

Capsule endoscopy

Answer 29

sometimes used where a camera the size of a pill is swallowed. It photographs the GI tract as it passes through and is retrieved after it is excreted.

Question 30

Laparoscopy

Answer 30

• ‘Keyhole surgery’ - involves making small finger-sized holes in the anterior abdominal wall and inserting cameras to visualise the peritoneal cavity. Can be used just to have a look, but often progresses to actual surgery if something needs removing or cauterising

Question 31

Advantages of abdominal x-ray (AXR)

Answer 31

• Relatively quick and easy to acquire
• Lower radiation dose than CT
• Can be interpreted by non-radiologists

Question 32

Disadvantages of abdominal x-ray (AXR)

Answer 32

• Poor differentiation between structures so only useful for a few clinical presentations
• Ionising radiation

Question 33

Advantages of CT

Answer 33

• Relatively quick and easy to acquire
• Very good differentiation of structures (particularly when used with contrast)

Question 34

Disadvantages of CT

Answer 34

• High ionising radiation dose
• Patients need to lie still for the scan
• Requires a radiologist to formally interpret images

Question 35

Advantages of contrast

Answer 35

• Used during other imaging methods to greatly increase differentiation of tissues and assess for other pathology that may not be visible otherwise (see above)

Question 36

Disadvantages of contrast

Answer 36

• IV contrast is potentially associated with ‘Contrast-Induced Nephropathy’ (damage to the kidneys as they try to filter the contrast out of the blood)
• Some patients can have an allergic reaction to contrast agents

Question 37

Advantages of ultrasound

Answer 37

• Logistically very easy to acquire images as US machines can be brought to the patient’s bed side.
• Non-ionising
• Can be repeated to assess for change
• Multiple uses (see above)
• Non-radiologists can be trained to perform certain more simplistic scans and interpret images

Question 38

Disadvantages of ultrasound

Answer 38

• Formal ultrasound scans by trained ultrasonographers are often not available ‘out of hours’ in most hospitals.
• Images are 2-dimensional and only of small areas of the body, so utility of images is limited to answering very specific clinical questions

Question 39

Advantages of endoscopy

Answer 39

• Non-ionising
• Direct visualisation images
• Ability to take biopsies or perform certain procedures during endoscopy

Question 40

Disadvantages of endoscopy

Answer 40

• Uncomfortable procedure, so patients may require sedation (which has its own risks)
• Risk of perforation of hollow organs

Question 41

Advantages of laparoscopy

Answer 41

• Non-ionising
• Direct visualisation images
• Ability to perform surgical procedures during laparoscopy

Question 42

Disadvantages of laparoscopy

Answer 42

• Patients require general anaesthesia (which has its own significant risks)
• Risk of surgical complications (e.g. bleeding, infection, damage to organs, herniation, wound breakdown etc.)

Question 43

Basic abdominal anatomy CT

Answer 43

CT scans produce a series of images, not a single image like a plain X-ray, so you may need to scroll through the images and view different planes to see different organs.

Question 44

Basic abdominal anatomy

Answer 44

• Small bowel is often located in the centre of the abdomen and has numerous plicae circulares which span the full width of the lumen. Large bowel is often located around the outside and has haustra which are further apart and don’t span the full width of the lumen.
• ‘3, 6, 9 rule’ - the maximum ‘normal’ diameter of the small intestine is roughly 3cm, large intestine is 6cm and caecum is 9cm. Any larger than this suggests dilated bowel and possibly obstruction.