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so what is a multi-phase abdominal CT CT
scanning can be performed at various
different intervals after contrast
administration CT scans that are
performed at different intervals have
different structures that are pacified
based on the pathology that's being
evaluated and it's used to characterize
the enhancement of mass lesions that are
within solid organs so this is an
example of a multi-phase abdominal CT it
involves a non-contrast image which you
can see on the left we then have an
early arterial phase image which is
performed at about 15 to 20 seconds
after injection a portal venous phase
which is performed about 35 to 40
seconds after injection and then a
delayed phase which is usually performed
at about 6 to 10 minutes after injection
although this can be delayed further
depending on what's being evaluated so
this is an example of a non-contrast
study if you take a look at this it's
actually very hard to differentiate
between adjacent solid organs so you can
see here the end of the liver and then
there's a soft tissue density here which
and it's hard to characterize exactly
what this is again you see here the
kidneys and you can see here a soft
tissue density which is probably
vascular but again it's very hard to
characterize what this is without
intravenous contrast on the arterial
phase you can actually see the aorta and
you can see the superior mesenteric
artery very well here we have a small
portion of the renal artery and here we
have contrast within the kidney which
helps you differentiate the cortex from
the medulla you can also now see the
difference between the margin of the
liver and the adjacent gallbladder this
exam is performed in the portal venous
phase
so most CT scans are performed in the
portal venous phase because it allows
for the best evaluation of the solid
organs so again you can see here the
liver and you can actually see finer
detail within the liver so you can see
the vessels within the liver a lot
better than you could on the other two
scans that we just looked at you can
also see the difference between the
margin of the liver and the adjacent
gallbladder and you can still see very
well the difference in
cortex of the kidney and the medulla you
now have contrast persistent within the
aorta into the superior mesenteric
artery it's a little bit less dense than
it was on the arterial phase but now you
see the venous system a little bit
better here so here's one renal vein and
then here's the other renal vein and you
can see the inferior vena cava as well
this image is an image of the delayed
phase and on this you can see that a
large amount of contrast is seen within
the renal excreting system so you can
see it within the proximal ureter and
you can see it within the renal pelvis
on both sides as well so the delayed
phase is often used to evaluate the
kidneys and the collecting system the
ureters and the urinary bladder as well
so let's take a look at this this is the
arterial phase what structures do you
see Oh pacified in the arterial phase
so we see the aorta and its branches
best Oh pacified you do have some
opacification of other structures as
well but the best visualized are the
aorta and its branches and how about the
portal venous phase what structures
would you see best identified in the
portal venous phase
so this actually shows us multiple
different structures it shows us the IVC
and its branches so the entire venous
system is well seen the portal vein and
its branches are well seen as well and
this is actually the best phase to
evaluate solid organ prank uma as well
and then here we have the delayed phase
and as we discussed the renal collecting
system the ureters and the urinary
bladder are best seen on the delayed
phase so what phases are most CT scans
performed in
so it's actually the portal Venus phase
as we discussed and this is because the
solid organs are best seen in the portal
Venus phase so we've gone over the
different techniques that can be used to
evaluate an abdominal CT scan and we've
gone over some of the pros and cons of
each one and when each one should be
used the three major factors are
intravenous contrast oral contrast and
different delays of time after the
administration of intravenous contrast
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