Comparison of Power Doppler with Colour Duplex ... - Iua2012.org

Pankaj K Jha; Mohsen Chabok; Richard Parker & M Aslam
Imperial College, London, UK
&
Norfolk & Norwich University Hospital, Norwich, UK

• Lower limb arterial disease (PAD) is due to
Atherosclerosis producing stenosis /occlusion.
• Treatment requires accurate assessment of the anatomical
location and degree of disease in the arterial tree.
• Digital subtraction Angiography (DSA) is the gold
standard investigation but Colour flow Duplex imaging
(CDI) is usual first line modality.
• Power Doppler Ultrasound (PDUS) is based on
measurement of amplitudes of reflected doppler echoes
and is clinically used in Carotid imaging.

• Duplex Ultrasound has been claimed to be as good as
arteriography.
‣ Karacagil S, Lofburg AM, Granbo A, Lorelius LE, Bergqvist D. Value of duplex scanning in evaluation of crural and foot arteries in limbs
with severe lower limb ischemia – a prospective comparison with angiography. Eur J Vasc Endovasc Surg 1996; 12:300-3
‣ Sensier Y, Hartshorne T, Thrush A, Nydahl S, Bolia A, London NJM. A prospective comparison of lower limb duplex scanning and
arteriography. Euro J Vasc Endovasc Surg 1996; 11: 170-5
‣ Sensier Y, Fishwick G, Owen R, Pemberton M, Bell PRF, London NJM. A comparison between colour duplex ultrasonography and
arteriography for imaging infra popliteal arterial lesions. Eur J Vasc Endovasc Surg 1998; 15: 44-50
‣ Collins R, Burch J, Cranny G, Aguiar-Ibáñez R, Craig D, Wright K, Berry E, Gough M, Kleijnen J, Westwood M. Duplex ultrasonography,
magnetic resonance angiography, and computed tomography angiography for diagnosis and assessment of symptomatic, lower limb
peripheral arterial disease: systematic review. BMJ 2007;334:1257 doi:10.1136/bmj.39217.473275.55
‣ Wilson YG, George JK, Wilkins DC, Ashley S. Duplex assessment of runoff before femorocrural reconstruction. Br J Surg 1997; 84: 1360-3.
• Colour Duplex Ultrasound has limitations:
• Time consuming & operator dependent
• Difficulty in penetrating calcified walls
• Difficult to detect low post stenotic flow
• Aliasing also introduces errors in velocity measurements
Reduced sensitivity and specificity for crural arteries
‣ Allard L, Cloutier G, Durrand LG et al. Limitations of ultrasonic duplex scanning for diagnosing lower limb arterial stenosis in the
presence of adjacent segment disease. J Vasc Surg 1994; 19: 650-7.
‣ Polak JF. Carotid ultrasound. Radiol Clin N Am 2001; 39: 569–89.
‣ Horrow MM, Stassi J, Shurman A, Brody J, Kirby CL, Rosenberg HL. The limitations of carotid sonography: interpretive and technologyrelated
errors. AJR 2000;174:189–94.

• Power Doppler Ultrasound (PDUS) produces intravascular
colour images generated from measurement of amplitude of
the reflected doppler echoes.
– It is therefore independent of:
‣ Angle of insonation – No aliasing
‣ Velocity & Direction of blood flow
– It is dependent on:
‣ Density of blood cells in the lumen
• Increased sensitivity for displaying the continuity of vessels.
‣ Weskott H-P. Amplitude Doppler US: slow blood flow detection level tested with a flow phantom. Radiology 1997; 202: 125–30.
‣ Keberle M, Jenett M, Beissert M, Jahns R, Haerten R, Hahn D. Three dimensional power Doppler sonography in screening for carotid
artery disease. J Clin Ultrasound 2000;28:441–51.
‣ Rubin JM, Bude RO, Carson PL, Bree RL, Adler RS. Power Doppler US: a potentially useful alternative to mean frequency-based color
doppler US. Radiology. 1994;190:853-856.
‣ Jung EM, Clevert DA, Rupp N. B-flow and color-coded B-flow in sonographic diagnosis of filiform stenosis of the internal carotid
artery. Fortschr Rontgenstr 2003; 175: 1251–8.

• Use of Power Doppler in lower limb vascular
assessment is limited
‣ Guo Z, Fenster A. Three-dimensional power Doppler imaging: A phantom study to quantify vessel stenosis. Ultrasound Med Biol
1996; 22: 1059 –1069.
‣ Cloutier G , Qin Z, Garcia D, Soulez G, Olivia V, Durand LG. Assessment of Arterial stenosis in a flow model with power Doppler
angiography: Accuracy and Observations on blood echogenicity. Ultrasound in Med. & Biol., 2000; 26; 9: 1489–1501.
• Difficulties in using Power Doppler:
– Susceptible to motion artefact
– Cannot detect direction of flow
– Reduced Depth penetration
– Sometimes difficult to distinguish artery from vein
‣ Rubin JM, Adler RS. Power Doppler expands standard color capability. Diagn Imaging. December 1993:66-69.
‣ Hamper UM, DeJong MR, Caskey CI, Sheth S. Power Doppler imaging: clinical experience and correlation with color Doppler US
and other imaging modalities. Radiographics. 1997;17:499-513

• To prospectively compare the accuracy of Power
Doppler Ultrasound (PDUS) with Colour flow
Duplex Imaging (CDI) and Digital subtraction
Angiography (DSA) in the assessment of Popliteal
and Infra-Popliteal segments of the lower limb
arterial tree.

• Eligibility: patients referred for Fontaine class II – IV PVD
• Patients would undergo routine Colour flow assessment.
• Power Doppler would then be used to assess Popliteal
artery and beyond.
• If indicated patients would then be assessed by DSA
• Arteries divided in these segments for comparison:
• Above Knee Popliteal • Proximal Peroneal
• Below Knee Popliteal • Mid Peroneal
• Tibio-Peroneal Trunk • Lower Peroneal
• Proximal Posterior Tibial
• Proximal Anterior Tibial • Mid Posterior Tibial
• Mid Anterior Tibial • Distal Posterior Tibial
• Distal Anterior Tibial • Dorsalis Pedis

Scanning Protocol based on: Abigail Thrush & Timothy Hartshorne, “Peripheral
Vascular Ultrasound How, Why and When”. 2ed Elsevier Churchill Livingstone.
• Colour Flow Duplex Imaging:
• Sequential longitudinal and Cross sectional views
• Velocity measurements to give PSV ratio at stenosis (V s /V p )
• Length of stenosis / occlusion & overall continuity of segment
• Power Doppler Ultrasound:
• Sequential longitudinal and Cross sectional views
• Luminal diameter measurements (NASCET)
• Length of stenosis / occlusion & overall continuity of segment
• DSA:
• Reported by Consultant Radiologists of min 5 years standing
• Stenosis measurements according to angiographic protocols

• Statistics:
• Sample size calculation: A sample size of 38 pairs will have
90% power to detect a difference in proportions of 0.30 and
the method of analysis is a McNemar's test of equality of
paired proportions with a 5% significance level (two-sided).
• nQuery® version 4.0 software was used to calculate the sample size.
• McNemar’s test was the main test to compare the two
ultrasound measurements.
• All results were recorded on Microsoft Excel spread sheets and
statistical calculations were carried out using SPSS/PASW software
version 18: SPSS/PASW for Windows, Rel. 18.0.3. 2010. Chicago: SPSS
Inc

Demographics: 38 limbs from 20 patients
Characteristics
Results
Age Range (Mean ± Std Dev) 54 – 85 (70.1 ± 9.16) years
Males (%) 16 (80)
Resting ABPI (mean ± Std Dev) 0.66 ± 0.24
Rutherford Stage of Disease
Number of limbs (%)
Grade 0
Grade 1
Grade 2
Grade 3
Grade 4
Grade 5
2 (5.3%)
8 (21.1%)
1 (2.6%)
15 (39.5%)
11 (28.9%)
1 (2.6%)
Risk Factors (%)
Smoking 18 (90%)
Diabetes Mellitus 15 (75%)
Hypertension 20 (100%)
Hyperlipidaemia 18 (90%)
Ischaemic Heart Disease 14 (70%)
Renal Failure (CKD stage)
1
2
3
4
5
7 (35%)
8 (40%)
5 (25%)
0 (0%)
0 (0%)

Comparison of images from the 2 modalities:
BK Popliteal Artery
Mid Posterior Tibial Artery

CDUS y-axis
McNemar’s test p-value:
PDUS x-axis
AK P 0.004
AK P BK P TP
T
PAT MAT DAT DPA PPA MPA LP
A
PPT MPT DPT
BK P 0.0005
TPT 0.07
PAT 0.02
MAT 0.02
DAT 0.003
DPA 0.007
PPA 0.0005
MPA

• PDUS had increased sensitivity for distal vessel disease
• CDUS tended to over estimate stenosis in distal vessels
• Results agreed with published reports on flow
phantom studies and Carotid artery assessment
studies
• Potential errors and difficulties:
• Small study with selected patients
• Different operators measured the stenosis by the 3 modalities
• Heavy calcifications produced inferior images
• Colour blooming

• This study concludes that in patients with severe peripheral
vascular disease Power Doppler Ultrasound provides better
correlation with Digital Subtraction Angiogram findings of
stenosis or occlusions than a Colour Doppler Ultrasound in the
Popliteal and Infra-Popliteal arteries.
• Its use may be more suited to the difficult distal vessels if
accurate localisation of arterial stenosis is necessary.