Limitations of ultrasonic duplex scanning for diagnosing lower limb arterial stenoses in the presence of adjacent segment disease

Diagnosis of arterial disease of the lower extremities with duplex ultrasonography

The development of duplex scanning carries the prospect of an entire non-invasive work-up of patients with peripheral arterial occlusive disease. To obtain the best available estimates of its diagnostic accuracy, a meta-analysis of 71 studies evaluating duplex scanning was performed. Independent methodological judgement left 16 studies for data extraction. Pooled estimates (95 per cent confidence interval of sensitivity and specificity for detection of a stenosis greater than or equal to 50 per cent or occlusion in the aortoiliac tract were 86 (80-91) per cent and 97 (95-99) per cent respectively. The results for the femoropopliteal tract compared well with this, with a sensitivity of 80 (74-85) per cent and a specificity of 96 (94-98) per cent. The accuracy of detection of a stenosis greater than or equal to 50 per cent or an occlusion in the infragenicular arteries was lower with a sensitivity and specificity of 83 (59-96) per cent and 84 (69-93) per cent respectively. Duplex scanning is an accurate tool for assessment of atherosclerotic lesions in the aortoiliac and femoropopliteal tract and can replace routine preinterventional angiography in a substantial number of patients.

A prospective comparison of lower limb colour-coded Duplex scanning with arteriography

OBJECTIVE

To compare the diagnostic value of colour Duplex scanning with arteriography for the detection of arterial disease of the aortoiliac arteries, femoropopliteal arteries and the origins of the tibial vessels.

DESIGN

Prospective, semi-blind study.

SETTING

Vascular laboratory and radiology department, University Hospital.

METHODS

A total of 1658 arterial segments in 148 limbs were studied both by colour Duplex scanning and digital subtraction arteriography. Individual arterial segments were classified on the basis of peak systolic velocity ratios < 2.0, > or = 2.0 or an absent Doppler signal, as 0-49%, 50-99% diameter reduced, or occluded. The same arterial segments were similarly classified on the basis of arteriography and the two modalities were compared using a Kappa (k) analysis.

RESULTS

The overall agreement between arteriography and colour-coded Duplex was kappa = 0.74 (95% CI, 0.70-0.78), this indicates substantial agreement. Kappa values (95% CI) from the aortoiliac, femoropopliteal and the origins of the infrapopliteal arteries were kappa = 0.59 (0.49-0.73; moderate agreement), kappa = 0.80 (0.76-0.84; substantial agreement) and kappa = 0.48 (0.35-0.61; moderate agreement) respectively.

CONCLUSIONS

We conclude that there is substantial agreement between colour-coded Duplex and arteriography of the lower limbs, and that the ability of colour-coded Duplex to plan and guide lower limb vascular interventions requires investigation.

Three-dimensional power Doppler imaging: a phantom study to quantify vessel stenosis

This study investigated whether three-dimensional (3D) power Doppler imaging can be used to quantify arterial stenosis and its potential as an alternative to x-ray angiography. Three-dimensional power Doppler images of in vitro stenotic vessels were generated under different hemodynamic conditions with a 3D power Doppler imaging system. This system includes: a Macintosh Quadra 840AV computer used to perform 3D imaging acquisition, reconstruction and display; a computer-controlled motor-driven translation assembly used to move the transducer; and an ATL Ultramark 9 HDI ultrasound system. Three vascular- and tissue-mimicking phantoms containing three wall-less stenotic vessels with area reduction of 80%, 50% and 30% were imaged with different flow rates under both steady and pulsatile flow conditions and with different Doppler angles under steady flow condition. With the use of the blood mimic, experimental results demonstrated that power Doppler imaging is nearly independent on flow velocity and Doppler angle. It was also demonstrated that 3D power Doppler imaging can produce nonpulsatile angiographic-like 3D images of the flow field. The stenotic vessels were quantified with an overall accuracy of 8.3% of the vessel area and an overall precision of 7% of the vessel area under the conditions described in this paper. It is believed that 3D power Doppler imaging can be used to quantify arterial stenosis, and in some applications it could be an alternative to x-ray angiography.

Directional atherectomy versus balloon angioplasty in segmental femoropopliteal artery disease: two-year follow-up with color-flow duplex scanning

PURPOSE

Directional atherectomy is an endovascular interventional technique for excision and removal of obstructive arterial lesions. To evaluate whether atherectomy would provide better results than conventional balloon angioplasty (BA) in symptomatic femoropopliteal disease, a prospective randomized study comparing the early and late outcomes of these techniques was conducted. The rate of restenosis or occlusion was assessed by use of color-flow duplex scanning during the follow-up period.

METHODS

Seventy-three patients were randomized between atherectomy (38 patients) and BA (35 patients). All patients had segmental lesions of the femoropopliteal arteries amenable to either technique. The median follow-up duration was 13 months (range 1 to 39). Follow-up comprised regular clinical and hemodynamic assessment and color-flow duplex examinations. Restenosis was defined on the basis of a peak systolic velocity ratio of 2.5 or greater, and occlusion of the treated segment was diagnosed if flow signals were absent, that is, loss of patency.

RESULTS

Residual stenoses (> or = 30% diameter reduction) resulted in five patients (13%) undergoing atherectomy and three patients (9%) undergoing BA. At 1 month clinical and hemodynamic improvement by Society for Vascular Surgery/International Society for Cardiovascular Surgery criteria for lower limb ischemia was observed in 34 patients (89%) treated with atherectomy and in 34 (97%) treated with BA. By life-table analysis the cumulative rate of clinical and hemodynamic success at 2 years was 52% in patients treated with atherectomy and 87% in patients treated with BA (p = 0.06). The patency rate at 2 years of treated segments was 34% in the atherectomy group and 56% in patients treated with BA (p = 0.07). In patients with lesions greater than 2 cm, the 1-year patency rate of AT was significantly lower than BA (p = 0.03).

CONCLUSIONS

Atherectomy does not result in an improved clinical and hemodynamic outcome. Furthermore atherectomy of segmental atherosclerotic femoropopliteal disease does not result in a better patency rate than BA, and, in lesions with greater length than 2 cm, the atherectomy results are significantly worse.

Doppler velocity ratio measurements evaluated in a phantom model of multiple arterial disease

The objective of this study was to evaluate in vitro the accuracy of the Doppler velocity ratio (VR) (intrastenotic velocity/prestenotic or poststenotic velocity) under different geometric conditions simulating the presence of multiple stenoses. A steady flow loop model was used to test the influence of the presence of a concentric obstruction of 84% area reduction positioned at a distance of 10, 20 and 30 tube diameters, either proximal or distal to the stenosis under study. The stenosis under evaluation was either concentric or eccentric and had a percentage of area reduction ranging from 20% to 91%. An ultrasound color Doppler system was used to perform both pulsed-wave (PW) Doppler and color-flow velocity measurements. VRs were computed by dividing the maximum velocity of the jet by the velocity at 6 and 10 diameters both proximal and distal to the stenosis under study. A strong correlation was obtained between VR computed using color flow and PW Doppler velocities (r = 0.99). Results indicated that using the prestenotic velocity as a reference velocity generally provided a more sensitive VR index to grade arterial stenosis than using the poststenotic velocity. From a curve fit model, the measured percentages of stenosis were calculated from the VR data and compared to the true percentages. The correlation coefficient, r, was 0.95. When the proximal and distal stenoses were at 10 diameters of the stenosis investigated, r was 0.91, while it increased to 0.98 when the distance was 20 diameters or more. Although VR is theoretically not influenced by hemodynamic factors, we demonstrated that, in practice, the presence of multiple stenoses reduced its sensitivity. Volumetric flow measurements are suggested to obviate this limitation.

Classification of lower limb arterial stenoses from Doppler blood flow signal analysis with time-frequency representation and pattern recognition techniques

A pattern recognition system was used to classify Doppler blood flow signals for the determination of lower limb arterial stenoses. The diagnostic features were extracted from time-frequency representations of Doppler signals. Three techniques were tested to estimate time-frequency representations: the short-time Fourier transform, the autoregressive (AR) modeling, and the Bessel distribution. A boundary tracking algorithm was proposed to extract the frequency contour of the Doppler time-frequency representations. Based on the characteristics of the Doppler frequency contour, shape descriptors from an autoregressive analysis were proposed as diagnostic features. Simple algorithms were proposed to normalize these autoregressive shape descriptors. Amplitude distribution of the Doppler time-frequency representation was also found useful for stenosis classification. A total of 379 arterial segments from the aorta to the popliteal artery were classified by the pattern recognition system into three categories of diameter reduction (0-19%, 20-49%, and 50-99%). The short-time Fourier transform provided an overall accuracy of 80% (kappa = 0.38); AR modeling, 81% (kappa = 0.42); and the Bessel distribution, 82% (kappa = 0.43). All these results are better than those based on visual interpretation (accuracy = 76%, kappa = 0.29) performed by a trained technologist. The AR modeling and the Bessel distribution improved the performance of the pattern recognition system in comparison with the short-time Fourier transform. It is likely that with further improvement, the pattern recognition approach will be a useful clinical tool to quantify stenoses and to follow the disease progression with more reliability and less bias than visual interpretation as done currently in clinical practice.