Imaging in vascular disease Flashcards
What is the main premise of ultrasound?
converts sound waves into pictures.
Sound waves inaudible to human ear but they they travel through the tissue from a small probe placed directly on gel on skin.
And collects echoes that bounce back,
.
What is doppler ultrasound used to look at?
blood flow and velocity within vessels.
Frequency transmitted back depends on which way the red blood cells are moving.
Difference between the transmitted and received frequencies is used to calculate the speed and direction of blood flow.
How does doppler ultrasound look graphically?
red indicates blood flow towards probe and blue indicated blood flow away from probe
mix of red and blue - turbulent blood flow
Advantages of ultrasound?
safe , low cost, quick ,good for imaging soft tissues and for dynamic , real time assessment of blood flow
What is ultrasound used for in vascular surgery?
percutaneous access- using a needle to puncture a blood vessel- ultrasound used to visualise the vessel and guide the needle safely into it
assess the diameter of blood vessels (abdominal aortic aneurysm surveillance, vein mapping and symptomatic carotid stenosis)
assess atherosclerosis- assess pattern and macroscopic appearance of it and degree of stenosis in vessels
assess dynamic blood flow-
diagnosis +/- treatment pseudoaneurysms ( injection of thrombin into the pseudoaneurysm)
surveillance for endovascular abdominal aortic aneurysm repairs:
endoleaks-bloods leaks back out into the aneurysm sac and significance of this is that of this is that it repressurises the aneurysm sac and returns the risk of rupture
Surveying bypass grafts , particularly vein grafts- helps us to identify developing stenosis, as a result of intimal hyperplasia
What are the limitations of ultrasound?
operator dependent and therefore has potentially variable results
anything that creates further impedance to the transmission and receipt of soundwaves such as dressing, bowel gas and excess adipose tissue will degrade the image quality and make accurate diagnosis more challenging
How does computed tomography work?
Combining multiple x ray images taken from different angles around the body to create a detailed cross sectional or slice of the inside of body
What is a CT angiogram?
a specific type of CT which uses dye (usually referred to as contrast) to highlight blood vessels
What phases does a CT angiogram show?
early and a late arterial phase
a portal venous phase
excretory phase
What does a Ct venogram show?
focussed on the venous phase to highlight the veins rather than the arteries
What colours are for what on CT Angiogram?
very dense tissues -white
air-appears black
Advantages of Ct angiograms?
widely availible
quick to perform
helpful to diagnose a range of vascular pathologies:
-diagnose a range of vascular pathologies
-pre-operative planning
-post operative surveillance
What can CTA be used to show?
demonstrate bleeding (such as in ruptured AAA or trauma)
acute occlusion ( emboli in acute limb ischaemia) , chronic disease (atherosclerosis) and other abnormalities of the vessel wall (such as aneurysms of the vessel wall)
Practical considerations of CTA?
cannula needs to be in vein as leaking of contrast outside of vein causes pain, swelling and localised skin reactions
contrast used is also excreted by kidneys so risk of contract induced nephropathy
Ct delivers ionising radiation so should be avoided in pregnancy
need to lie still for long period of tiime
What are diagnostic limitations of CTA?
any metalwork in body will create significant artefact-which can make interpretation difficult
over estimation of calcification
poor differentiation of disease in crural vessels
How do MRAs work?
use a magnetic field and radiofrequency pulses to manipulate the alignment of protons within body tissues
MRA advantages and limitations?
uses gadolinium-based contrast contrast to demonstrate the lumen of a vessel and therefore better than CT angio at showing disease in crural vessels
limitations:
not suitable for some patients with metalwork
not always readily available
patients can find very claustrophobic
not suitable for patients with poor renal function
How does Digital subtraction angiography work?
DSA requires a needle to be inserted into a blood vessel and deliver contrast directly into the lumen
What does DS capture pictures called runs with?
fluoroscopy imaging
What does fluoroscopy imaging do to pictures?
takes away particular features of the image such as bones
Where is DSA most commonly performed?
via femoral artery under local anaesthetic and can provide a complete arterial map of the leg
What is the main advantages of DSA?
facilitates diagnosis and treatment in the same setting.
If stenosis is identified, angioplasty (which uses balloon to stretch up the narrowing) can be performed - followed up by a stent if required to help improve long term patency.
What are the main disadvantages of DSA?
invasive
-pseudoaneurysm
-bleeding
-dissection
-distal embolisation
contrast
-nephropathy
-allergic recation
-extravasation
ionising radiation
-skin reactions
-theoretical risk of cancer
patient position
