Ultrawund in Med. & Biol., Vol. 21, No. X. pp. 1059 - IOh9. I996 Copyright Cm 1996 World Fedrrstion for Ultrawund in MedIck & Biology Printed in the USA. All right\ reserved 03OI-5629/Yh $7I s.00 + .oo ELSEVIER PII: SO301-5629(96)00125-l *Original Contribution THREE-DIMENSIONAL POWER DOPPLER IMAGING: A PHANTOM STUDY TO QUANTIFY VESSEL STENOSIS ZHENYU Guo and AARON FENSTER Imaging Research Laboratories, The John P. Robarts Research Institute, London, Ontario, Canada; Department of Medical Biophysics, University of Western Ontario, London, Ontario, Canada Abstract-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 transla- tion 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 SO%, 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. Copyright 0 1996 World Federation for Ultrasound in Medicine & Biology Key Words: Power Doppler imaging, Three-dimensional imaging, Vessel stenosis. INTRODUCTION In colour Doppler imaging, the mean Doppler fre- quency shift of the local blood flow is encoded in colour and superimposed over the two-dimensional ( 2D) B-mode image (Mitchell 1990). Colour Doppler imaging therefore provides the spatial distribution of flow velocities in relation to the associated anatomic structure. thus depicting the flow field. Unfortunately, the appearance of the flow field in colour Doppler imaging is highly dependent on the instrument settings selected by the examiner (Baumgartner et al. 1991; Guo et al. 1995 ) . In the diagnosis of arterial stenosis, colour Doppler imaging is therefore used mainly for qualitative analysis of blood flow and for displaying the flow field to guide the Doppler sample volume placement for Doppler spectral analysis. In this irz vitro> Address correspondence to: Aaron Fenster, Imaging Research Laboratories, The John P. Robarts Research Institute, P.O. Box 5015, 100 Perth Drive, London. Ontario N6A 5K8. Canada. E-mail: afenster @irus.rri.uwo.ca study, we demonstrate the potential use of a new mo- dality of ultrasound imaging, three-dimensional (3D) power Doppler imaging, to depict directly the lumen geometry for stenosisquantification. Maim limitations CJ~’ &our Doppler imaging Some important limitations of mean frequency- basedcolour Doppler imaging have been described by Rubin and Adler ( 1993). One obvious limitation is re- lated to the way that colour Doppler imaging maps the electronic noise as background colour. Because the Doppler frequency shift is dependent on the rate of change of the phase angle, noise with its random phase angle appears asflow with random velocity and direction, which therefore presents as random colour. The random colour noise is of the same magnitude as the true colour from blood flow. Often the flow signal is overwhelmed if the instrument settingsare not properly selected, mak- ing the visualisation of the flow field difficult. Other limitations of colour Doppler imaging include Doppler 1059