M104 T1 L14 Flashcards
What are the imaging modalities for the abdomen?
X-ray (plain film) / Fluoroscopy
Ultrasound
CT, MRI
What’s the difference between plain imaging and cross-sectional imaging?
plain - xray
cross - CT scan
Why is it easier to pick out anatomy on C.T. scans rather than xrays
bc everything is superimposed from front to back whereas CT is a slice where you can see the anatomy in relationship of one part of the anatomy relative to another
How does the effect of increasing the spatial resolution of an x-ray differ to when done to an MRI?
xray - increased clarity
MRI - more pixelated, lower level of detail
What’s the difference between the level of detail that can be viewed on the MRI than on plain film?
MRI can identify individual muscle fibres, articular cartilage, and muscles in addition to bone, soft tissue and fat that can be seen by plain film.
Does MRI or plain film have a higher contrast resolution?
MRI
Does MRI or plain film have a higher spatial resolution?
plain film
What tissues can be identified by plain film / on an xray?
bone and soft tissue
within soft tissue might be able to pick up difference between fat, the subcutaneous fat, the muscle and other soft tissues deeper
What tissues can be identified by an MRI?
bone, articular cartilage, muscles very distinctly from the subcutaneous fat
within the muscles can see individual fibres
Why do MRIs have a higher level of detail than plain film?
bc it has many more shades of grey within the soft tissue
What are the most common and basic sequences of images that can be produced by an MRI?
the T1 and T2 weighted sequences
What is the difference between the T1 and T2 weighted sequences on MRI imaging?
T1 - fluid is black
T2 - fluid is white
How are contrast agents administered?
IV or enterally (oral / PR) before a scan
In what weighted sequence of MRI imaging do Paramagnetic contrast agents have their strongest effect and why?
in T1 weighted imaging bc they predominantly alter the T1 relaxation time in the tissues in which they have accumulated
How do contrast agents differ to the surrounding material on x-rays?
they are either more or less dense than surrounding materials
How do contrast agents differ to the surrounding material on MRI scans?
they are paramagnetic, so they have an impact on the MRI signal
What are examples of solid viscera?
the liver, kidneys, spleen
What are examples of hollow viscera?
the bladder and the bowel
Would ultrasound be a good imaging modality for looking at the bowel and why?
no because it is very good at looking at the solid organs, not the hollow organs
Where are intra-peritoneal organs located?
within the cavity of the peritoneum
Where is the retroperitoneum located?
behind the peritoneum
Where is the retroperitoneum located?
behind the peritoneum
Do the retro-peritoneal organs have no specific delineating anatomical structures?
no, they don’t
What is often used as a first line test for looking at the solid viscera?
ultrasound probes - liver, limbs
What imaging modalities are used for the bowels?
X-ray – a good first line test
CT & MRI are increasingly used (avoids endoscopy, uses cannulas instead)
On a plain film, what is a normal calibre of the bowels?
large - up to 5 cm
small - up to 3 cm
What is the criteria for a dilated bowel?
much more air and wider calibre of bowel
What causes a dilate bowel?
a blockage
What does free air near the bowel indicate?
that the bowel is ruptured or perforated
that the normal distribution of bowel gas has been disrupted
How are the large and small bowels differentiated between on the plain films?
large - is peripheral, frames the small bowel, might contain (liquid, hard) faeces, up to 5cm
small - up to 3cm, is more central within the abdomen, contains fluid and air, is constrained by encircling valvulae conniventes, which are more widely spaced in the ileum than they are in the jejunum
How do the mucosal folds differ on the bowels?
large - the haustral folds are interspaced with the plicae circulares which are just seen on the edges of the bowel
small - the valvulae conniventes lines across the entire width of the small bowel
Where are the plicae circulares located?
on the edges of the large bowels - they don’t cross the entire width of the bowel
What happens to plicae circulares or the valvulae conniventes if the bowel is distended?
they can be effaced or flattened out
How large is the caecum on plain film?
9cm
What are the plicae circulares otherwise known as?
circular folds
valves of Kerckring
plicae circulae
valvulae conniventes
How does a barium contrast cause a double contrast?
one contrast being the barium, the other contrast being the gas
the double contrast is where the barium is stuck to the wall of the stomach
How are double contrast barium enemas achieved?
both barium and then gas have been put with a tube in the back passage PR
the patient is rolled around to try and get the contrast to go up through the sigmoid, up the descending colon along the transverse and back down and then fill up with air
How do double contrast barium enemas work?
x-rays of the colon and rectum are taken using two forms of contrast to make the structures easier to see
a radiocontrast agent is put into the rectum (PR)
What structures are investigated for using a double contrast barium enema?
masses, polyps and lesions within the large bowel
Why are double contrast barium enemas diffficult to achieve in elderly patients?
bc they are moved around a lot to get the contast where it needs to flow through internally
What group of patients are most likely to need a double contrast barium enema?
elderly patients
What are double contrast barium enemas being replaced with?
CT colonographies
What does a CT colonography involve?
air is put into the large bowel
a C.T. scan is performed
How is a CT colonography carried out?
laxatives are used to clear out the large bowel
the patient arrives in the hospital and comes to C.T. scanner
a little tube is put in through which air and buscopan are used to relax the bowel
when the bowel is well inflated, the C.T. scan produces axial slices which might show abnormalities
What is the most common disease to affect the small bowel?
IBD
How can a rectal tumour affect the rectal fascia?
causes it to become irregular with some strands and some little nodules
How can MRIs be used when analysing rectal tumours?
can be used to stage the rectal tumour - to see exactly how far the tumour is extending into the surrounding tissues
whether that patient might be resectable for surgery / whether they need chemo radiotherapy / other treatents
