GI MRI Flashcards
(38 cards)
what is ghosting artefact
Ghosting is a type of structured noise appearing as repeated versions of the main object (or parts thereof) in the image
caused by patient or object motion during image acquisition
what are 2 methods used to prevent ghosting artefact
- breath holding
- respiratory triggering (using navigators)
how is breath holding done, what sequence is used why etc
- fast sequences (so data can be acquired within one breath hold e.g GRE)
- breath hold for 15-25s
- images taken on expiration
- coaching prior to scan
why are images taken on expiration not inspiration
patients will always expire to the same extent but they won’t necessarily breath in the same depth each time
how does respiratory triggering using navigators work
- liver dome navigators using additional pulses (positioned over diaphragm) to detect change in signal between lung/air and liver
- on expiration, diaphragm rises and imaging aqcuired
what anti-spasmodic agent is used for GI
buscopan (stops peristalsis)
why should buscopan not be used on patients with cardiac disease
can increase heart rate
side effects of buscopan
blurred vision (short term)
urine retention in men
rare: can trigger acute-angle closure glaucoma (manifests as acurte red eye)
primary cancer with liver mets is palliative, what does this mean
relieving symptoms without dealing with the cause of the condition.
what contrast agent is used for the liver /GBCA gadolinium based contrast agent
PRIMOVIST (liver specific GBCA)
GADOVIST (extracellular GBCA)
difference in diffusion and enhancement between primovist and gadovist?
primovist
- diffuses into extracellular matrix then taken up by HEPATOCYTES (in liver)
- hepatocyte enhancement 20min post injection
gadovist
- diffuses into ECM
- good for imaging hepatocelluclar carcinoma as often Hillary obstruction impedes excretion of primovist
difference between excretion of primovist and gadovist
primovist: 50% excreted in pee and 50% in bile via common Hillary duct
gadovist: excreted fully in urine
what are some things to consider before giving GBCA
egfr
allergies
renal function etc
what 4 sequences are done for liver MRI and why
T1W GRE (identify fatty lesion)
CE T1W (demonstrates vascularity and presence of hepatocytes)
T2W (identify fluid in cysts etc)
DWI (to confirm diagnosis) (no breath holding needed)
e.g with primovist, you should see hepatocyte enhancement 20 mins post contrast but if you can see regions of the liver where it is dark, it can show there is restricted diffusion in liver so mass
what does MRCP stand for/what is it
magnetic resonance cholangiopancreatography
(imaging of gall bladder, bile ducts and pancreas)
why would you do MRCP
- abnormal liver function test (LFT)
- dilated common bile duct but no stones found on US
- pancreatic cysts
what quadrant is pain found when dealing with liver/billary issues
right upper quadrant
what procedure is done to remove obstructing stone in bile ducts
ERCP
- endoscopic retrograde cholangiopancreatography
for an MRCP how many hours prior should the patient stop eating and why
4 hours nothing by mouth (NBM)
fluid in stomach and bowel will affect the T2 sequence used for MRCP
what are 3 sequences needed for MRCP and why
T2 HASTE AXIAL AND CORONAL (EPI)
(breath hold)(shows path of CBD)
T2 SPACE 3D (SE)
(visualisation of CBD)
T2 HASTE CORONAL OBLIQUE (identify filling defects e.g gall stones)
what does a gallstone look like on a T2W image
dark / hypo intense, surrounded by hyper intense bile fluid
what are the 4 main sequences used for pancreas mri and why
T2 HASTE AXIAL (identify pancreas)
T2 SPACE CORONAL (show pancreatic duct)
DIFFUSION AXIAL (characterise lesion)
T1 VIBE AXIAL (spoiled gre) (pre contrast)
what contrast agent is used in pancreatic mri
gadovist (extracellular GBCA)
