Radiology Notes

 

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