Radiation risk:
1
mammogram:
<0.4 cGy per view ≈ background radiation on flight LA→Auck =
less radiation
than CXR;
1
AXR ≈
radiation of 100 CXRs
1
abdo CT =
radiation of 800 CXRs
Trauma
CTs =
40.2mSv ≈1005 CXRs
Estimated
that
For
every 1000
CT abdo → 1 new CA over a lifetime... 1:1800 risk of fatal CA
CT
use assoc
with a 0.4% ↑ in all CAs in USA (NEJM
2007;
357:2277-84)
CT
Oral
contrast
requires ≈90mins to opacify the bowel
CT
in pregnancy
→ 1:200 risk of fetal CA (or 1:400 risk of fatal fetal CA)
But no risk in congenital malformations
Don't do it.
USS
Echofeatures
of
LN suggesting malignancy:
>1cm,
hypoechoic
/
loss of echogenic hilum
distinct
margins,
round
shape
MRI
Gadolinium
= iv contrast agent, used mainly for
vascular imaging
risks:
NSF= nephrogenic systemic fibrosis
Causes interstitial fibrosis affecting
kidneys & skin (→
dermopathy)
Occurs in people with renal impairment
MR breast: uses gadolinium
Useful in lactating breasts, high risk
‘screening’, DCIS extent,
lobular ca
PET
scanning
PET = positron emission
tomography
=
nuclear
medicine imaging which reflects functional processes in the body
Functional
imaging: abN
cellular metabolic activity tends to precede structural change
Basis
cancer
cells exhibit enhanced glycolysis
gl.
preferentially concentrated as tumours have ↑gl
uptake cf normal tissues (2o
to ↑ gl membrane transporters)
marker:
F-18-FDG (fluro-dexoy-D-gl) = radiolabelled
analogue of gl… (F-18-FDG phosphorylated by hexokinase cannot
diffuse out of
cell (ie trapped))… concentrated in malignant cell
positron
emission on decay: collides with electron → 2
photons… traveling at 180o to each other → PET scanner
detects
photons & determines position
influencing
factors:
tissue
oxygenation
gl
utilisation
regional
bl flow
local inflammatory reaction