Leg Arterial normal
Normal laminar arterial flow
Normal laminar flow: In the peripheral arteries of the limbs, flow will be triphasic with a ‘clear spectral window’ consistant with no turbulence. The spectral window is the area under the trace.
Stenotic arterial flow
Elevated peak systolic velocity at the stenosis with pansystolic spectral broadening.
Following the stenosis the turbulent flow may swirl in both directions.
NB: If the stenosis is short, there can be a return to triphasic flow dependant on the ingoing flow and quality of the vessels. Presence of triphasic flow does not exclude proximal stenosis in a symptomatic patient.
Arterial occlusion schematic
Monophasic flow: Will be present approach an occlusion (or near occlusion). The degree of loss of phasicity will be dependant on the quality of collateral circulation bridging the pathology.
Distal post-stenoic normal laminar arterial flow
Biphasic & Diminished Flow
SCAN PROTOCOL
Role of Ultrasound
- To date, there have been many criteria proposed for grading the degree of arterial narrowing from the duplex scan. Criteria which have been devised for the carotid duplex scan cannot be used for the peripheral arteries.
- Our clinics follow criteria proposed by Cossman et al 1989. The ratio of pre-stenosis : stenosis is most commonly used.
Your Laboratory should also select criteria that best suits your workplace.
Limitations
Heavily calcified vessels and large patient habitus reduce detail and may limit ability to obtain a good doppler trace accurately angle corrected.
Patient Preparation
- Some institutions fast their patient’s to aid visualisation of the aorta and iliac arteries.
- Our experience suggests fasting does not improve scan quality.
Equipment setup
A curvi-linear 3-6 MHz probe to examine the abdominal aorta and iliac arteries.
A linear 5-7 MHz probe for examining from the groin down.
Common Pathology
- Stenoses
- Occlusions
- Aneurysms
- Stents
- Grafts
SCANNING TECHNIQUE
Aorta and Iliac Arteries
- Patient supine on the bed.
- Using a curvilinear 3-5MHz transducer. Assess the aorta in longitudinal and transverse checking for aneurysms, plaque or associated abnormalities.
- Measure the maximum aortic diameter and peak systolic velocity.
- Locate the iliac arteries. Examine in B mode and colour doppler with peak systolic velocities taken at the LCIA origin, LIIA origin and the mid distal LEIA. Also measure and image any sites demonstrating aliasing on colour doppler.
- You will need firm gradually applied pressure to displace bowel gas. This may be uncomfortable on the patient. Ask for them to relax rather than tense their abdomen. Once a window is obtained, maintain the pressure until you have interrogated the area.
The Thigh arteries
- Change to linear probe (5-7MHz), patient still supine.
- Locate the common femoral vessels in the groin in the transverse plane.
- Assess the vessels in B-mode for plaque.
- In longitudinal, use colour doppler to confirm patency whilst checking for aliasing which may indicate stenoses.
- Take peak systolic measurements using spectral doppler at the Common femoral artery and Profunda femoris artery. Also the Superficial femoral artery at the origin, proximally, mid and distally.
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| Scan plane for the femoral artery as it passes through the adductor canal |
- The SFA dives into the adductor canal.
It can be difficult to assess in some patients due to large patient habitus or densely calcified vessels. If so, change from a linear probe to a curvilinear probe.
You should get good visualisation and a good doppler angle thanks to the natural course of the vessel.
Behind the knee
- If possible, roll the patient onto their ipsilateral side with the contralateral leg forward over the top.
- Locate the popliteal artery at the knee crease in transverse and follow proximally up between the hamstrings, and distally until you see the bifurcation (anterior tibial and tibio-peroneal trunk).
- Rotate into longitudinal and examine in b-mode, colour and spectral doppler.
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| TPT: Approach from the medial aspect. If the patient is unable to externally rotate their leg, roll them onto the ipsilateral side with the other leg forwards. This facilitates easy access from the proximal popliteal artery to the distal PTA and peroneal | Again, if having difficulty visualising the anatomy, change to a curvilinear probe as for the adductor canal. |
The Lower Leg
Posterior Tibial and Peroneal arteries
- Patient still positioned as above.
- Locate the posterior tibial and peroneal arteries by placing the toe of the probe on the distal tibia and scanning transverse.
- Examine with colour and spectral doppler, predominantly to confirm patency.
- If the velocity is less than 15cm/sec, this indicates diminished flow.
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| Scan plane to locate the distal PTA. | The distal peroneal artery. |
Anterior tibial artery
- Patient supine
- Locate the anterior tibial vessels by placing the probe transversely over the antero-lateral distal leg supeior to the ankle.
- Rotate into longitudinal and examine with colour/spectral doppler, predominantly to confirm patency.
- If the velocity is less than 15cm/sec, this indicates diminished flow.
- Follow distally to the dorsalis pedis artery over the proximal foot.
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| Scan plane to locate the distal ATA. | The Distal Anterior Tibial Artery: The distal ATA is visible directly over the antero-lateral aspect of the distal tibia. Follow this down over the Talus where it becomes the Dorsalis Pedis artery. |
Basic Hardcopy Imaging
A leg artery series should include a minimum imaging of the following;
- Aorta – long, trans with diameter and peak systolic velocity measurements
- Common and external iliac arteries.
- Superficial femoral artery
- Origin
- Proximal
- Mid
- Distal
- Popliteal artery
- Proximal
- Mid
- Distal
- Tibio-peroneal trunk
- Posterior tibial artery-distal
- Peroneal artery-distal
- Anterior tibial artery-distal
- Dorsalis pedis
Document the normal anatomy. The peak velocities. Any stenosis or occlusion lengths, including measurements from the groin crease, patella or malleolus.