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Basic Principles in Radiology & Contrast media (Contrast media (X Rays…
Basic Principles in Radiology & Contrast media
Radiology: branch of medicine using radiation and other waves for the diagnosis & the treatment
Ionizing
radiation: X-rays, Natural radiation of Uranium, Alpha, beta, gamma
Non-ionizing
: MRI (Molecular imaging), Ultrasound (mechanical waves)
In radiodiagnosis, we use three of the
properties of X rays
:
-ability to
penetrate the tissues
,
-
photographic effect
,
-and
ability to cause certain substances to fluoresce
Radiation exposure: cosmic rays (the sun) , food chain (K, others) , geological sources (Rn) , man-made radiation (diagnostic, therapeutic, nuclear weapons testing, the shoe fluoroscope)
rad -
unit of absorbed radiation dose
. Equal to 100 ergs of energy deposited per gram of absorbing material. Equal to 1 cGy rem - unit of dose equivalence. Used to
compare relative effectiveness of different radiations
.
Rem =
Absorbed Dose
. Equal to 1 cSv ( 100 rem = 1 sv)
Gray - SI unit of
absorbed radiation dose
.
Sievert - SI
unit of dose equivalence
.
The single largest source of exposure to the population is radon.
RADIATION EFFECTS
The acute effects are considered to be those which happen in the immediate post irradiation period, i.e. from the time of radiation exposure up to six months to a year post exposure.
Acute effects are generally the result of large radiation exposure (greater than 200 rems, 2 Sv)
delivered to the whole body, or at least a major part of it, in a
very short time
.
The chronic effects of radiation result from
any but frequently relatively low exposure levels delivered over long periods
of time.
There are
three major categories of radiation effects
-
cancer
,
genetic
damage
and
birth
defects
.
Risk of radiation induced malignancy
Breast cancer: 50-200.
Thyroid cancer: 150.
Lung cancer: 50
Leukemia: 15-25
Skin cancer: in high doses
Nuclear magnetic resonance
also called magnetic resonance imaging, or MRI.
PET scanning
positron emission tomography, or PET scanning, which involves the emission of particles of antimatter by compounds injected into the body being scanned.
Contrast media
X Rays
Contrast Media: Negative ( air, CO2), Positive (contain iodine or barium)
Positive Contrast Media
Water suspension of Barium Sulphate ( studies of Dig.Tract)
Lipiodol Ultrafluid –
iodinated fatty acids
(hepatic chemio-embol., lymphography)
Water soluble Contrast Media
intravenous urography, angiography, i.v. contrast enhancement in CT
Kinetics ~ GFR when normal H-L 1,5-2h
Hematological
effects
Lungs
–
rise
in
pulm.art.pressure
, histamine release (vomiting, urticaria)
Heart
–
contractility
reduction, ventricular
fibrillation
~ osmolarity
Peripheral
vascular
: pain,
warmth
,
vasodilatation
Kidneys
:
proteinuria
,CMN (decreased GMR, DM and elder patiens)
Unpredictable reactions: allergic but usually
pseudoallergic
,
Reactions:
Mild (no treatment)
Moderate ( treatment, but not Int. Care )
Severe ( Int. Care necessary )
MRI
Paramagnetic Gadolinium (Gd compounds) -
increases
SI on T1W images
Superparamegnetic (
iron
oxide
compounds) –
decrease
SI in T2W images
„In the ideal situation ,
the contrast agent would accumulate within the liver or within the lesion , but not within both
”
Extracellular
contrast agents – initially distributed intravascularly, them moved interstitially and
eliminated by the kidneys
Hepatobiliary
contrast agents – in
part
moved from blood into
hepatobiliary
system, in
part eliminated by the kidneys
Reticuloendothelial
(
res
) contrast agents –
blood
–
res cells
–
macrophages
Ultrasound
Micro bubbles of air encapsulated in albumin, by galactose (Echovist – echocardiography) or galactose and fatty acids,
long term enhancement (Sonoview)
Liquid releases micro bubbles inside the blood (EchoGen)
ma6ar