Imaging in Peripheral Vascular Disease Flashcards
Objectives of vascular imaging
Localise and grade disease Identify the most significant lesions and separate stenoses from occlusions Evaluate the success of interventions
The Ankle/Brachial pressure index
Tibial divided by the brachial systolic pressure measured by Doppler Normally 1-1.4, as the pressure in legs is the same or slightly higher PVD causes a reduction in tibial pressure such that ABPI <1.0
Angiographic techniques for imaging vascular disease
Show the position and the severity by showing residual lumen diameter Use injected contrast CT, MRA and DSA
DSA is
Digital subtraction angiography A image is taken before the contrast is added and subtracted from the contrast image to reduce the masking effect of tissues around the vessels
Vascular ultrasound
Visualises flow in real time Quantitative measurements Shows flow direction
Advantages of duplex ultrasound
Cheap and non-invasive Combines B-mode imaging and colour flow mapping But is operator dependent
B-mode imaging
Visualises vessel walls Resolution is relatively poor Diameter measurements inaccurate
Colour flow mapping
Codes the image for movement direction and magnitude Allows for visualisation of the lumen Stenosis appears as turbulence and an acceleration through the narrowing
Spectral Doppler
Allows for the precise measurement of stenosis Uses a narrow Doppler beam to discretely measure blood velocity Displays a classic Doppler spectrum of arterial blood velocity
Peak systolic velocity (PSV)
The highest velocity within one cardiac cycle The highest point in the Doppler spectrum Normally between 90-140cm/s Values above this may indicate arterial stenosis
Doppler spectrum
Normally tri-phasic, becomes bi- and mono- phasic with increasing stenosis Allows for precise stenosis measurements because there is a fixed inverse relationship between vessel diameter and flow velocity
Arterial occlusion
No flow in occluded segment. Monophasic waveform proximal and distal to occlusion
Grading disease with spectral Doppler
Doppler Spectrum
Lower Limb angiography duplex investigation
performed with patient supine
includs aorto-iliacs, fermoro-popliteal and tibial arteries
30-60mins
Duplex ultrasound report
Accuracy of Duplex as percentage of DSA performance
Highest for femoro-popliteal segment and lowest for aorto-iliac (bowel gas) and tibial segments (vessel calcification)
Comparitive accuracy of Duplex, CTA and MRA
MRA is most sensitive
Duplex is most cost effective
