GI MRI Flashcards
What are the common MRI exams in the abdomen?
- Liver
- MRCP
- small bowel
- Pancreas
- Rectum
-Fistula
What does ANTT stand for?
Aseptic Non-touch technique
How long do we have to observe after contrast injection?
30 mins
What are the common drugs used in GI MRI?
Buscopan - antispasmodic
Primovist - contrast (liver specific)
Gadovist - contrast
Mannitol - sugar based molecule - it distends the bowel to view lumen/ walls
What are the T1 sequences used for GI imaging?
Fast field echoes (FLASH, FSE or SPGR)
3D spoiled GE with fat sat (VIBE / eTHRIVE)
How do fluids appear and what’s the weighting of T1/2 balanced gradients?
T1 weighing but with T2 bright fluids
Why do we do a DWI?
- DWI shows active disease
- Tumours in the rectum
- Inflammation in small bowel
May reduce the need for contrast
Why do T2 images with longer TEs
To differentiate between cysts and Haemangioma
What happens to cysts and haemangiomas with long TEs?
Haemangiomas - lose signal after longer TE
Cysts remain high signal
How long to liver scans take?
45 min
NBM 4 hours prior
Why do we use MRI for liver scanning?
Characterisation of liver lesions/ staging of tumours
Cirrhosis or fatty liver
Which contrast do we use for liver scanning?
Primovist or gadovist
What a re the special considerations with primovist?
What level risk is it?
All pt must have eGFR
Medium risk
transient dysponea in 30% of patients
Can lengthen QT interval - contraindicated with arrhythmias
How do we characterise liver lesions on MRI?
5 stages
- Pre-contrast
- arterial - full contrast after st bolus for liver (25-30 sec)
- Portal venous phase (80 - 1.20 sec)
- 3 min post con = equilibrium phase
- 15 min post con = delayed phase
How much primovist is excreted in the billary tree?
50%
How much contrast will Met’s take up?
None
How do they differentiate between lesions in MRI with contrast?
Different lesions will take up and eliminate at different times
How do haemangiomas take up contrast?
They take contrast up rapidly, starting at the outside then filling in centripetally
How does focal nodual hyperplasia appear on MRI?
Holds onto contrast - scar on liver with central dark patch
How does cirrhosis appear on MRI
Fibrosed and irregular contour
How do we assess fatty liver on MRI?
What the TE of the 2 phases?
We use dual echo fast field T1
During TI relaxation fats and water relax at different speeds due to the different density in hydrogen protons
H Out of phase = TE = 2.3ms
H Inphase = TE- 4.6ms
How big should a spleen be?
No more than 14 cm but average 11 -12cm
What is MRCP and what’s it used for?
How long does it take?
MR cholangiopancreatography
Is used to look for obstruction of bile and pancreatic ducts causes _ stones/ tumours etc.
Non - con and no drug _ -takes 15 min
NBM - hours
Which weighting is a MRCP?
T2. Long TE only signal from fluids
What is involved in MRI pancreas?
30 min - NBM 4 hours
Dynamic contrast scan
Used to look for Ca in head of pancreas
IPMN - Introduction papillarymuscneus neoplasm
What is the name of small bowel MRI?
MR enterography
What is involved with Small bowel MR(SMBO)?
Can be contrast or non con
20 min with 1 hour prep and 4 hour NBM
+/- Gadovist, Buscopan, mannitol
What is SMBO MR used to for?
To distinguish between IBS and IBD
To monitor Crohn’s disease, and to look for strictures
What is the prep for SMBO MR?
Mannitol
- Long chain, sugar molecule
- 200 mils monitor in 1200 mils of water over 45 minutes
- Laxative effect and descends the bowel
Buscopan
- Anti spasmodic
- IM or IV
- Acting
- Minimises, peristatic motion and reduces flow voids on T2 TSE
What are the 3 stages of enhancement for small bowel?
- Homogeneous
- Mucosal
- Layered
1-3 increasing severity
What is the definition of a fistula?
Abnormal tract
Leads from One mucus surface to another
Or
From Mucus surface to the skin
What is the definition of a sinus?
An abnormal tract from the skin or mucus surface to a deep, seated area of suppuration (pus)
What are the symptoms of anal fistulas?
- Pain/throbbing
*redness and swelling - offensive discharge
- Passing blood/ pus when defecting
- occasionally causes bowel incontinence
What is involved in an MR Fistula and what are they used for?
Non con and no drug
20 min - no NBM
Demonstrated disease progression
Predicts prognosis
What does Dixon MR fat suppressed show?
Fistula detail more clear
What does MR Dixon in phase echo show?
Anatomy clearly
What are the treatments for anal fistulas?
Fistulotomy - cutting open the fistula - heals into a flat scar
Setons procedure - Silicone strong placed in fistula to allow drainage
What is involved with MR rectum?
Non con - around 45 min no NBM needed
Used to stage rectal carcinoma and decide treatment protocols
Drugs - IM/IV Buscopan
