Imaging the abdomen Flashcards
List the imaging modalities for the abdomen
X-ray (plain film) / Fluoroscopy
Ultrasound (US)
Computed Tomography (CT)
Magnetic Resonance Imaging (MRI)
Which imaging modalities are cross sectional?
CT, MRI and ultrasound
What is the difference between spatial and contrast resolution?
Spatial- Number of megapixels
Contrast- differentiation of different soft tissue- Density, water or fat content
Which imaging modality is planar?
X-RAY
How do you differentiate between T1 and T2 weighted images?
T1 : fluid is black
T2 : fluid is white
What is contrast?
Agent used to increase contrast resolution (ie. highlight specific areas/organs)
Is given intravenously (IV), or enteral (oral/PR) before a scan
Is either more or less dense than surrounding tissues (for XR/CT), or paramagnetic (for MRI)
What is paramagnetic?
Affects the magnetic field
Give the pros and cons of X-ray
Pros: Cheap, Quick, Easy for patient, High spatial resolution (good for bone), Low radiation dose
Cons: Poor contrast resolution (poor for soft tissue) Planar imaging (superimposes structures)
Give the pros and cons of CT
Pros: Quick, widely available
Cross sectional images
High Contrast resolution (good for soft tissue)
Cons: Radiation dose, IV Contrast risks
Give the pros and cons of ultrasound
Pros: Cheap, Quick, No radiation, Cross sectional images, US guided interventions
Cons: Saved images are only a snapshot of examination (report operator dependant)
Give the pros and cons of MRI
Pros: Contrast resolution, Specific applications (e.g. Spine, MSK), No radiation
Cons: Limited availability, Patient experience (duration, claustrophobia), Expense, Magnet / Contrast risks
What are the risk of IV contrast?
Allergy
Kidney- renal dysfunction made worse - nephrotoxicity
What the difference between hollow and solid visceral imaging?
Hollow- tends to have gas
Solid- more tissue
What is the difference between intraperitoneal and retro-peritoneal?
Intraperitoneal- Inside the peritoneal and is coated all the way round
Retroperitoneal- behind the peritoneum on one said covered
What is the difference between the systemic and portal circulation?
Systemic- Blood around the body
Portal- blood from the gut to the liver
Give examples of solid abdominal viscera
Liver, spleen and pancreas
What are the liver segments divided by?
Divided by portal vein (horizontally) & hepatic (vertically) veins (portal triad)
What is a good first line test of the liver?
Ultrasound
What is it called where there is colour on the ultrasound?
Doppler
Colour gives a clue about velocity
What colour does fluid appear on an ultrasound?
Black
How does the liver appear on ultrasound?
Grainy with black vessels and bile ducts
Why should patients needing a gallbladder ultrasound be nil by mouth before?
Gall bladder contracts after you eat
Gain a better image
On CT what is white?
Bone
On CT what is black?
Air
On CT when would the vessels appear white?
When contrast has been injected
How long should you wait to get an arterial phase scan?
30 seconds
How long should you wait to get a portal venous scan?
60-90 seconds
Why may dilated bile ducts be seen?
Blockage present
What is a good first line test to image the bowel?
X-ray in AP view
What is a double contrast enema?
Barium and then air
Why is double contrast enema good?
polyps and tumours
What is difficult about double contrast enema?
Difficult in elderly patients
What is done now instead of barium enemas?
CT colonography
What is MRI of the small bowel used for?
Inflammatory bowel diseases
