516 Journal of Equine Veterinary Science December 2004 Veterinary Review SUMMARY Doppler ultrasound is an emerging technology that has the potential to increase the diagnostic, monitoring, and predictive capabilities of equine theriogenologists and researchers. The technology is based on Doppler- shift frequencies, wherein the ultrasound frequency of echoes from moving red cells is increased or decreased as the cells move toward or away from the transducer. In spectral mode, the blood flow in a specific vessel can be assessed by placing a sample-gate cursor on the image of the lumen of the vessel. In addition, an angle cursor can be used to represent the angle of intersection of the ultra- sound beams with the direction of blood flow (Doppler angle). The Doppler-shift frequency and the Doppler angle are used by the instrument for computing blood ve- locity. The focused results from placement of a sample gate in an artery are displayed by a spectrum that repre- sents the changing velocities over time in association with the pulses of cardiac cycles. Peak systolic, end dia- stolic, and time-averaged maximum velocities are com- puted and shown for a selected cardiac cycle. Doppler in- dices (resistance index, RI; pulsatility index, PI) are ratios that are computed from various points on the spec- trum. The indices are relatable to the hemodynamics of the tissue supplied by the artery. Increasing RI or PI val- ues indicate increasing resistance and decreasing perfu- sion of the distal tissues. In color-flow mode, Doppler- shift frequencies are obtained from areas delineated by the operator on the B-mode image and are transformed and expressed as color-coded spots representing areas of blood flow. Vascular perfusion of a structure can be quan- From Animal Health and Biomedical Sciences, University of Wiscon- sin, Madison, a and Eutheria Foundation, Cross Plains, Wisconsin. b Reprint requests: Dr O. J. Ginther, Animal Health and Biomedical Sciences, 1656 Linden Dr, University of Wisconsin, Madison, WI 53706. 0737-0806/$ - see front matter © 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jevs.2004.11.005 Doppler Ultrasound in Equine Reproduction: Principles, Techniques, and Potential O. J. Ginther, VMD, PhD, a and Matthew D. Utt, MS b titated by the number of colored pixels in an image or can be estimated subjectively by the extent of the colored spots. The Doppler technology has the potential for pro- viding information on the status and future success of a structure. However, realization of the expected potential will depend on future experience and research. Key words: Color doppler; Mares; Reproduction; Ultrasound INTRODUCTION Transrectal B-mode (gray scale) ultrasonography has revolutionized diagnosing and monitoring of biologic and pathologic reproductive events in horses, as well as in cat- tle, in both clinical and research areas. 1,2 B-mode is used not only to identify and measure structures, but also to as- sess physiologic status. Moreover, the transvaginal route is used for ultrasound-guided entry of specific anatomic tar- gets for recovering or sampling of fluids and tissues (eg, oocyte aspiration, luteal biopsy) and inserting substances (eg, embryos, semen, follicular factors, hormones). An emerging facet of ultrasound that has the potential to fur- ther enhance diagnostic and predictive capabilities for clin- ical veterinarians and the depth and breadth of hypothesis testing for animal and veterinary research scientists is Doppler imaging of blood flow. Doppler ultrasound thus adds blood-flow information to the B-mode image about anatomy and function. The Doppler technology has had an increasing impact in human medicine and science for more than 2 decades 3-7 but is in its infancy for theriogenology and animal research purposes (eg, cattle, 8,9 dogs, 10 mares, 11-14 stallions 15 ). Scanners may be equipped for both continuous-wave and pulsed-wave Doppler applications. In continuous- wave scanning, an element is activated continuously, and the returning echo is received by another element. In con- trast, in pulsed-wave scanning, a transducer element is activated with a short burst or pulse, and the returning echo is received by the same element. This report will consider only pulsed-wave scanning, using both the B- mode and Doppler approaches. The B-mode or gray scale