Technology

Transit Time Ultrasound

Accurate, Direct, Continuous “The Gold Standard” - PDF

Drost, C.J., "Vessel Diameter-Independent Volume Flow Measurements Using Ultrasound", Proceedings San Diego Biomedical Symposium, 17, p. 299-302, 1978. U.S. PATENT 4,227,407, 1980.

A Transonic perivascular flowprobe (Fig. 1) consists of a probe body which houses ultrasonic transducers and a fixed acoustic reflector. The transducers are positioned on one side of the vessel or tube under study and the reflector is positioned midway between the two transducers on the opposite side of the vessel. The flowmeter's electronic ultrasonic circuitry directs a flowprobe through an upstream and a downstream measurement cycle.

Schematic view of the perivascular Transonic ultrasonic volume flowsensor.

theory1

Fig. 1: Using wide beam illumination, two transducers pass ultrasonic signals back and forth, alternately intersecting the flowing liquid in upstream and downstream directions. The flowmeter derives an accurate measure of the "transit time" it took for the wave of ultrasound to travel from one transducer to the other. The difference between the upstream and downstream integrated transit times is a measure of volume flow rather than velocity.

Upstream Transit-Time Measurement Cycle
An electrical excitation causes the downstream transducer to emit a plane wave of ultrasound. This ultrasonic wave intersects the vessel or tubing under study in the upstream direction, then bounces off the "acoustic reflector," again intersects the vessel and is received by the upstream transducer where it is converted into electrical signals. From these signals, the flowmeter derives an accurate measure of the "transit time" it took for the wave of ultrasound to travel from one transducer to the other.

Downstream Transit-Time Measurement Cycle
The same transmit-receive sequence of the upstream cycle is repeated, but with the transmitting and receiving functions of the transducers reversed so that the liquid flow under study is bisected by an ultrasonic wave in the downstream direction. Again, the flowmeter derives and records from this transmit-receive sequence an accurate measure of transit time.

Just as the speed of a swimmer depends, in part, on water currents, the transit time of ultrasound passing through a vessel / conduit is affected by the motion of liquid flowing through that vessel. During the upstream cycle, the sound wave travels against flow and total transit time is increased by a flow-dependent amount. During the downstream cycle, the sound wave travels with flow and total transit time is decreased by the same flow-dependent amount. The Transonic flowmeter subtracts the downstream transit time from the upstream transit time utilizing wide-beam ultrasonic illumination. This difference of integrated transit times is a measure of volume flow.

Wide Bean Illumination

One ray of the ultrasonic beam undergoes a phase shift in transit time proportional to the average velocity of the liquid times the path length over which this velocity is encountered. With wide-beam ultrasonic illumination (Fig. 2), the receiving transducer sums (integrates) these velocity - chord products over the vessel's full width and yields volume flow: average velocity times the vessel's cross sectional area. Since the transit time is sampled at all points across the vessel diameter, volume flow measurement is independent of the flow velocity profile. Ultrasonic beams which cross the acoustic window without intersecting the vessel do not contribute to the volume flow integral. Volume flow is therefore sensed by perivascular probes even when the vessel is smaller than the acoustic window (Fig. 2).

theory2

Fig. 2: The vessel is placed within a beam that fully and evenly illuminates the entire blood vessel. The transit time of the wide beam then becomes a function of the volume flow intersecting the beam, independent of vessel dimensions.

theory3

Fig. 3: Angle insensitivity of the Transonic flowprobe: T = transducer

a) The ultrasonic beam intersects the vessel twice on its reflective pathway. During each intersection, the transit time of the beam is modified by a vector component of the flow. The full transit time of the ultrasonic beam senses the sum of these two vector components, that is, the flow itself.

b) With misalignment, one vector component of the flow becomes greater and the second vector component diminishes, with little consequence to their sum.

Validations of the Transit Time Technolgy

1V Gorewit, R.C., Bristol, D.G., Aromando, M., and Thomas, G.G., "Mammary Blood Flow of Cows Measured by Ultrasonic and Electromagnetic Flow Meter," Journal of Dairy Science, Vol. 67 sup., p. 159, 1984. (cow, ext pudic a., chronic, against EM)

2V Barnes, R.J., Comline, R.S., Dobson, A., Drost, C.J., "Further Analysis of the Timecourse of the Changes in Blood Flow in Response to Feeding in the Ruminoticulum of the Sheep," International Union of Physiologists Society Satellite Conference on "Comparative Aspects of the Physiology of Digestion in Ruminants," Physiology Dept., Veterinary College, Univ. of Sydney, Australia, 1983. (sheep, coeliac, chronic, against microsphere)

3V Barnes, R.J., Comline, R.S., Dobson, A., and Drost, C.J., "An Implantable Transit-Time Ultrasonic Blood Flow Meter," Journal of Physiology, Vol. 345, pp. 2-3P, 1983. (sheep, coeliac, uterine [pregnant sheep]chronic, against microsphere)

4V Drost, C.J., Thomas, G.G., Hillman, P.E., and Scott, N.R., "Ultrasonic Transit-Time Measurement of Bloodflow in the Chicken Leg," Proceedings of the 9th Annual NE Bioengineering Conference, Pergamon Press, Elmsford NY, pp. 387-390, 1981. (chicken, common dorsal metatarsal a., against beaker stop watch)

5V Drost, C.J., Thomas, G.G., and Sellers, A.F., "In Vivo Validation of the Transit-Time Ultrasonic Volume Flow Meter," Proceedings of the 7th Annual NE Bioengineering Conference, Troy NY: Center for Biomedical Engineering, pp. 220-223, 1979. (sheep, carotid, in vivo calibration, syringe with know volume, chronic,)

6V Hartman, J., Koerner, J., Lancaster, L., Gorczynski, R., "In Vivo Calibration of a Transit-Time Ultrasound System for Measuring Ascending Aorta Volume Flow," The Pharmacologist, Vol. 27, No. 3, p. 217, 1985. (dog, aorta, against EM, pump withdrawal, thermodilution)

8V Wilkening, R.B., Boyle, D.W., Meschia, G., "Measurement of Oxygen Consumption of the Pelvic Limb in Fetal Sheep," Presentation: American Pediatric Society 1987. (fetal sheep, pelvic limb, against microspheres)

9V Eisemann, J.H., Huntington, G.B., and Ferrell, C.L., Blood Flow to Hindquarters of Steers Measured by Transit Time Ultrasound and Indicator Dilution, Journal of Dairy Science, Vol. 70, p. 1385-1390, 1987. (steer, abdominal aorta, against indicator dilution (PAH))

11V Wilkening, R.B., Boyle, D.W., and Meschia, G., Measurement of Blood Flow and Oxygen Consumption in the Pelvic Limb of the Fetal Sheep, Proceed. Soc. Exper. Biol. Med., Vol. 187, pp. 498-505, 1988. (fetal sheep, pelvic limb, against microspheres)

12V Gorewit, R.C., Aromando, M.C., Bristol, D.G., Measuring Bovine Mammary Gland Blood Flow Using a Transit-Time Ultrasonic Flowprobe, Journal of Dairy Science, Vol. 72, No. 7, 1989. (cow, ext pudic a., chronic, against EM)

13V Randall, N.J., Beard, R.W., Sutherland, I.A., Figueroa, J.P., Drost, C.J., Nathanielsz, P.W., Validation of Thermal Techniques for Measurement of Pelvic Organ Blood Flows in the Nonpregnant Sheep: Comparison with Transit-Time Ultrasonic and Microsphere Measurements of Blood Flow, American Journal of Obstetrics and Gynecology, Vol. 158, No. 65, p. 1-8, 1988. (sheep,internal iliac a, against microspheres)

14V Neutze, S.A., Oddy, V.H., Gooden, J.M., Edwards, S.R., Nandra, K.S., "Calibration of An Ultrasonic Blood Flow Meter in the Sheep," Proceedings of the Nutrition Society of Australia, Vol. 14, p.146, 1989. (sheep, portal, in situ calibration, venous outflow)

15V Spencer, J., Moore, P., Hanson, M., "Studies of Reflex Control of Fetal Carotid and Femoral Blood Flow in Hypoxia," Proceedings of the Society for the Study of Fetal Physiology, Vol. 16, C6, 1989. (sheep, femoral, beaker stopwatch)

16V Vilardi, J., Powers, R.J. "Relationship of Temperature and Hematocrit to the Accuracy of Flow Measurement by Transit Time Ultrasound," ELSO Extracorporeal Life Support Organization, Vol. 1, p. 23, 1989. (ECMO, against roller pump)

17V ""Depner, T., Rizwan, S., Stasi, T., Pressure Effects on Roller Pump Blood Flow during Hemodialysis, ASAIO Trans. 1990 Jul-Sep; 36(3): M456. (extracorporeal, hemodialysis, roller pump)

18V Takata, M., Robotham, J.L., Effects of Inspiratory Diaphragmatic Descent on Inferior Vena Caval Venous Return, Journal of Applied Physiology, Vol. 69, pp. 1961-1972, 1990 . (dog, vena cava [thoracic, abdominal], acute EM)

19V Wong, D.H., Watson, T., Gordon, I.L., Wesley, R., Tremper, K.T., Zaccari, J., Stemmer, P. Comparison of Changes in Transit Time Ultrasound, Esophageal Doppler and Thermodilution Cardiac Output after Changes in Preload, Afterload, and Contractility in Pigs, Anesthesiology Analogs, Vol. 72, p. 584-588, 1991. (pig, cardiac output, ascending aorta, esophageal Doppler, thermodilution)

20V Lundell, A, Bergqvist, E., Mattson, E., Nilsson, B., Volume Blood Flow Measurements with a Transit Time Flowmeter: An In Vivo and In Vitro Variability and Validation Study, Clin Physiology 1993; 13: 547-557. (sheep, carotid, exsanguination, beaker stopwatch, in vitro, rotational pump)

21V Welch, W.J., Deng, X., Snellen, H., Wilcox C.S., "Validation of Miniature Ultrasonic Transit-Time Flow Probes for Meaurement of Renal Blood Flow in Rats, American Journal of Physiology, Vol. 268, No. 1, Pt. 2, p. F175-178, 1995. (rat, renal, carotid, calibrated syringe pump, microsphere, PAH clearance, ex vivo, rabbit femoral)

22V Rubertsson, S., Arvidsson, D., Wiklund, L., Haglund, U., "Comparison of Blood Flow Measurement in the Portal Vein and Pulmonary Artery Using Transit-Time Ultrasound Flowmetry and Thermodilution Techniques," Surgical Research Communications, Vol. 13, p. 309-316, 1993. (pig, pulmonary artery, thermal dilution)

23V Hartman, J., Olszanski, D.A., Hullinger, T.G., and Brunden, M.N., In Vivo Validation of a Transit-Time Ultrasonic Volume Flow Meter, Journal of Pharmacological and Toxicological Methods, Vol. 31, No. 3, p. 153-160, 1994. (dog, acute: exsangination , chronic: EM, pump withdrawal)

24V Shiraishi, H., Silverman, N.H., Rudolph, A.M., Accuracy of Right Ventricular Output Estimated by Doppler Echocardiography in the Sheep Fetus, American Journal of Obstetrics & Gynecology, Vol. 168, p. 947-953, 1993. (fetal sheep,cardiac output, microsphere, Doppler echocardiography, gold standard)

25V ' DAlmeida, M.S., Gaudin, C., Lebrec, D., Validation of 1- and 2- Transit Time Ultrasound Flow Probes on Mesenteric Artery and Aorta of Rats, Am. Journal of Physiology, Vol. 268, Vol. 3, Pt. 2, p. H1368-1372, 1995. (rat, sma, ab aorta)

26V Bednarik, J.A., May, C.N., Evaluation of a Transit-Time System for the Chronic Measurement of Blood FLow in Conscious Sheep, Journal of Applied Physiology, Vol. 78, No. 2, p. 524-530, 1995. (sheep, chronic, LAD, cranial

mesenteric, left renal, left external iliac, PA, )

27V Grant, D.A., Franzini, C., Wild, J., Walker, Continuous Measurement of Blood Flow in the Superior Sagittal Sinus of the Lamb, American Journal of Physiology, Vol. 269, p. R274-279, 1995. (newborn sheep, acute, sagittal sinus, venous outflow, gravimetric)

28V Akers, T., Bolen, G., Gomez, J., Hodgson-Smith, A., Merrill, J., Anderson, G., Huddleson, J., Moretz, T., Kirvan, K., Kirvan, D., Sutton, R.G., Riley, J.B., "In Vitro Comparison of ECC Blood Flow Measurement Techniques," Proceedings of the American Society of Extracorporeal Technology, p. 17-22, 1990. (extracorporeal comparison, EM, roller pump, doppler, ultrasonic transit time)

29V 'Dean, D.A., Cabreriza, S.E., Jia, C-X, DAlessandro, D.A., Sardo, M.J., Chalik, N., Soto, P.F., Dickstein, M.L., Spotnitz, H.M., Validation Study of a New Transit-Time Ultrasonic Flow Probe for Continuous Measurements on the Great Vessels, ASAIO J. 1996 Sep-Oct; 42(5): M671-6. (pig, ascending aorta, CO probe, right heart bypass model, calibrated roller pump)

30V Wen, C., Li, M., Whitworth, J.A., Validation of Transonic Small Animal Flowmeter for Measurement of Cardiac Output and Regional Blood Flow in the Rat, Journal of Cardiovascular Pharmacology, Vol. 27, No. 4, p. 482-486, 1996. (rat, ascending aorta 3SS, renal, mesenteric, hindlimb 1RB, pump)

31V 'DAlmeida, M.S., Cailman, S., Lebrec, D., Validation of transit-time ultrasound flow probes to directly measure portal blood flow in conscious rats, Am J Physiol. 1996 Dec; 271(6 Pt 2): H2701-9. (rat, sma, ab aorta, radioactive microspheres)

32V Sokol, G.M., Leichty, ER.A., Boyle, D.W. Comparison of Steady-State Diffusion and Transit Time Ultrasonic Measurements of Umbilical Blood Flow in the Chronic Fetal Sheep Preparation, American Journal of Obstetrics, Gynecology, Vol. 174, No.5, p. 1456-1460, 1996.(fetal sheep, umbilical, chronic, )

33V Xavier, F., Yu, M., McNeill, J.R. Validation of a Flow-Differential Technique for the Recording of Splenic Blood Volume Changes to Vasoactive Agents, Journal of Cardiovascular Pharmacology, Vol. 28 No. 5, p. 605-610, 1996. (cat, splenic, acute)

34V Onizuka, M., Flatebo, T., Nicolaysen, C., Lymph Flow Pattern in the Intact Thoracic Duct In Sheep, Journal of Physiology, Vol. 503, No. 1, p. 223-234, 1997. (sheep, thoracic duct, lymph)

35V Amaral, S.L., Michelini, L.C., Validation of Transit-Time Flowmetry for Chronic Measurements of Regional Blood Flow in Resting and Exercising Rats, Brazilian Journal of Medical and Biological Research, Vol. 30, p. 897-908, 1997. (rat, renal, iliac, chronic, 1RB, 2SB probe)

36V Evans, R.G., Stevenson, K.M., Malpas, S.C., Fitzgerald, S.M., Shweta, A., Tomoda, F., Anderson, W.P., Chronic Renal Blood Flow Measurement in Dogs by Transit Time Ultraound Flowmetry, Journal of Pharmacological Toxicological Methods, Vol. 38, No. 1, p. R33-39, 1997. (renal, dog, chronic)

37V Rabiee, AR, Lean, Il I.J., Gooden, J.M., Miller, B.G., Short-Term Studies of Ovarian Metabolism in the Ewe, Animal Reproductive Science, Vol. 47, No. 1-2, p. 43-58, 1997. (sheep, ovarian arterio-venous plexus)

38V Cales, P., Oberti, F., Veal, N., Fort, J., Kaasis, M., Moal, F., Aub, C., Vuillenin, E., Pilette, C., Rifflet, H., Trouv, R., Splenorenal Shunt Blood Flow by Transit-Time Ultrasound as an Index if Collateral Circulation in Portal Hypertensive Rats, Hepatology, Vol. 28, p. 1269-1274, 1998. (rat, sleno-renal shunt)

39V ""Remond, D., Ostigues, M.I., Isserty, A., Lefaivere, J., Technical Note: Measuring Portal Blood Flow in Sheep Using An Ultrasonic Transit Time Flow Probe, Journal of Animal Science, Vol. 76, No. 10, p. 2712-1216, 1998. (sheep, A-Probe, portal BF)

40V ""Beldi, G., Basshard, A., Hess, OM, Athaud, U., Walpoth, B.H., Transit Time Flow Measurement: Experimental Validation and Comparison of Three Different Systems, Ann Thorac Surg 2000; 70: 212-7. (1705AHM) (40V). (pump, in vitro comparison of Transonic, Cardiomed and Triton against roller pump)

41V ""Ullrich, R., Bloch, k.D., Ichinose, F., Steudel, W., Zapol, W.M., Hypoxic Pulmonary Blood Flow Redistribution and Arterial Oxygenation in Endotoxin-Challenged NOS2-Deficient Mice, Journal of Clinical Investigation, Vol. 104, No. 10, p. 1421-1429, 1999.(mouse, 1RB, pulmonary blood flow distribution compared with microspheres)

42V Royse, A.G., Royse, C.F., Groves, K.L., Bus, B., Yu, G., Blood Flow in Composite Arterial Grafts and Effect of Native Coronary Flow, Ann Thorac Surg 1999; 68: 1619-22. (1593AH). (clinical, IMA & radial artery comparison against timed collection)

43V Picker, O., Schindler, A., Scheeren, T.W., Accuracy and Reproducibility of Long-Term Implanted Transit-Time Ultrasound Flow Probes in Dogs, Intensive Care Medicine, Vol. 26, No. 5, p. 601-607, 2000. (dog, pulmonary a., probes implanted for range of 6-47 months)

44V Benkowski, R., Lynch, B., Morello, G., Morley, D., Noon, G.P., "Real Time Flow Measurement for a Continuous Flow VAD," ASAIO J 2001; 47920 133. (1786AH)

45V Canver, C.C., Cooler, S.D., Murray, E.L., Nichols, R.D., Heisey, D.M., Clinical Importance of Measuring Coronary Graft Flows in the Revascularized Heart. Ultrasonic or Electromagnetic? J. Cardiovasc Surg (Torino)1997; 38: 211-5. (1130AH)(human, coronary artery bypass grafts, acute) 1308AH

46V Veal, N., Oberti, F., Moal, F, Vuillemin, E., Fort, J., Kaassis, M., Pilette, C., Cales, P., "Spleno-renal shunt blood flow is an accurate index of collatera circulation in different models of portal hypertension and after pharmacological changes in rats," J Hepatol, Vol. 32, No. 3, p. 434-40, 2000. (2333A)

47V Janssen, B., Debets, J., Leenders, P., Smits, J., "Chronic Measurement of Cardiac Output in Conscious Mice," American Journal of Physiology, Vol. 282, p. R928-R935, 2002 .

48V Sanisoglu I, Guden M, Balci C, Sagbas E, Duran C, Akpinar B., "Comparison of intraoperative transit-time flow measurement with early postoperative magnetic resonance flow mapping in off-pump coronary artery surgery," Tex Heart Inst J. 2003; 30(1): 31-7. (2751AH)

49V Groom R, Tryzelaar J, Forest R, Niimi K, Cecere G, Donegan D, Katz S, Weldner P, Quinn R, Braxton J, Blank S, Kramer R, Morton J., Intra-operative quality assessment of coronary artery bypass grafts, Perfusion. 2001 Nov; 16(6): 511-8. (49V) 2754AH

50V Werchan, P.M., Schadt, J.C., Fanton, J.W., Laughlin, M.H., "Cerebral and spinal cord blood flow dynamics during high sustained +Gz," Aviat Space Environ Med, Vol. 65, No. 6, p. 501-9, 1994. 1719A

51V Canver, C.C., Dame, N., Ultrasonic Assessment of Internal Thoracic Artery Graft Flow in the Revascularized Heart, Ann Thorac Surg 1994; 58:135-8. (368AH) (51V). (368AH)

52V Huntington GB, Eisemann JH, Whitt JM , Portal blood flow in beef steers: comparison of techniques and relation to hepatic blood flow, cardiac output and oxygen uptake, J Anim Sci. 1990 Jun; 68(6): 1666-73. (183A)