Lecture 23- Contrast Media & Radiology Flashcards
What is contrast media ?
A substance used to increase the contrast of structures or fluids within the body in medical imaging.
Which imaging techniques can contrast media be used ?
- CT scans
- X-rays
- ultrasounds
- MRI scans
- fluoroscopy ( most common one)
What would be considered a negative contrast ?
- black on film
- this would indicate Air or Co2 or water
What would be considered a positive contrast ?
- white on film
-
What are the advantages of using contrast media ?
- biologically inert
- cost effective
- safe when you use a low osmolality and viscosity
- heat and chemically stable
What is the half life of contrast media ?
30-60 minutes
How is contrast media excreted ?
95% of it is glomerular filtered in the kidney
-
What are the side effects of using contrast media ?
- reactions due to high osmolality
- endothelial damage
- vasodilation
- vascular pain
- thrombosis and thrombophlebitis
What are the two types of reactions patients can experience due to contrast media ?
1) idiosyncratic reactions ( occurs within 20 minutes) - this can be classified into either a)mild b)moderate c)severe
2) non-idiosyncratic reactions which is delayed (30mins-7 days)
Idiosyncratic reactions
- an unpredictable reaction which generally occurs within 20 minutes.
- they are unrelated to the dose of the contrast medium.
- the mechanism by which it is caused is ‘ anaphylactoid reaction’
Non-idiosyncratic reactions
These are dose related reactions and depend on the physiological properties of the contrast medium ( eg osmolality, concentration of injected substance, volume)
- often are delayed reactions ( 30 mins -7 days)
What to assess before you administer contrast media ?
1) whether the patient has had previous reactions to contrast media
2) whether they have renal disease
3) identifying any risk factors eg diabetes , dehydration , over age of 70, hypertension, sepsis .
What is a posterior - anterior x ray ?
The most common projection used to take a chest x ray.
- this is where the x ray beams hit the posterior part r the chest before the anterior part.
- the patient is asked to stand with their chest against the film.
- the image viewed is like looking at the patient face to face.
What is an anterior-posterior x ray ?
This is where x ray beams hit the front of the chest before they hit the back of the chest.
- patients back is placed on the film.
- the image produced is as if you are looking at the patient face to face.
POsterior - anterior projection image of the chest
Insert image
Anterior -posterior projection image
Insert image
CT/MRI scan image produced
It is as if you are looking through the patients feet upwards
Define nuclear medicine
- involves the administration of radio pharmaceuticals labelled with radioactive tracer into the patient.
- these substances have a specific affinity for body tissues.
- anatomical details is limited in these studies , nuclear medicine is useful in displaying physiological function.
- devices used : Gamma camera and the PET scanner which detects the radiation emitted by the tracer in the body.
What are the risks of nuclear medicine ?
Small doses of radiation which actually have little risk.
What are the benefits to nuclear medicine ?
- detect diseases in their earliest stages
- PET scans can tell whether a tumour is malignant or benign.
- prevents a patient from getting dangerously worse
When can nuclear medicine be used ?
- look at the excretory function of the kidneys , blood flow to the heart muscle , iodine concentrating ability of the thyroid
AP or PA would give a larger appearance of the heart ?
AP
