Use of high-intensity focused ultrasound to control bleeding

We have shown recently that high-intensityfocused ultrasound (HIFU) can be used to achievehemostasis in two laboratory models of hemorrhage.First, we demonstrated that in rabbits we could stopboth profuse and minor oozing bleeds from liverincisions with HIFU application.1 Second, weshowed that in pigs we could stop moderate to pro-

fuse bleeding from major blood vessels that hadbeen surgically exposed and punctured.2 In the cur-rent study, we report on a further step in the devel-opment of acoustic hemostasis devices: mechanicalscanning HIFU for the hemostasis of large incisionsin blood vessels.

HIFU is a method of delivering large amounts ofenergy to a tissue of interest. The high energy levelis possible with the following method: (1) using alarge diameter ultrasound scan transducer, (2) excit-ing the transducer with high levels of electricalpower, and (3) focusing the ultrasound beam in asmall focal spot. In our experiments, we have used aconcave transducer, with a 3.5-cm aperture diame-ter, and excited with approximately 50 W of electricpower. We thus have achieved an energy level ofapproximately 3000 W/cm2 at the focal spot of theultrasound beam, which measures approximately 1mm in lateral cross section. Such intensity levels areabout 3 to 4 orders of magnitude larger than that ofthe diagnostic ultrasound scan (about 0.1 W/cm2).3The high intensity of the ultrasound beam can easi-ly lead to temperatures in excess of 100°C at the

Use of high-intensity focused ultrasoundto control bleedingShahram Vaezy, PhD, Roy Martin, PhD, Peter Kaczkowski, PhD, GeorgeKeilman, MS, Bryan Goldman, BA, Hadi Yaziji, MD, Steve Carter, MD,Michael Caps, MD, and Lawrence Crum, PhD, Seattle and Woodinville, Wash

Objective: High-intensity focused ultrasound (HIFU) has been shown to be effective incontrolling hemorrhage from punctures in blood vessels. The objective of the currentstudy was to investigate the capability of HIFU to stop bleeding after a more severe typeof vascular injury, namely longitudinal incisions of arteries and veins.Methods: The superficial femoral arteries, common femoral arteries, carotid arteries, andjugular veins of four anesthetized pigs were exposed surgically. A longitudinal incision,2 to 8 mm in length, was produced in the vessel. HIFU treatment was applied within 5seconds of the onset of the bleeding. The HIFU probe consisted of a high-power, 3.5-MHz, piezoelectric transducer with an ellipsoidal focal spot that was 1 mm in cross sec-tion and 9 mm in axial dimension. The entire incision area was scanned with the HIFUbeam at a rate of 15 to 25 times/second and a linear displacement of 5 to 10 mm. Atotal of 76 incisions and HIFU treatments were performed.Results: Control of bleeding (major hemosatsis) was achieved in all 76 treatments, withcomplete hemostasis achieved in 69 treatments (91%). The average treatment times ofmajor and complete hemostasis were 17 and 25 seconds, respectively. After the treat-ment, 74% of the vessels in which complete hemostasis was achieved were patent withdistal blood flow and 26% were occluded. The HIFU-treated vessels showed a consistentcoagulation of the adventitia surrounding the vessels, with a remarkably localized injuryto the vessel wall. Extensive fibrin deposition at the treatment site was observed.Conclusion: HIFU may provide a useful method of achieving hemostasis for arteries andveins in a variety of clinical applications. (J Vasc Surg 1999;29:533-42.)

533

From the Departments of Bioengineering (Drs Vaezy andMartin), Anesthesiology (Dr Martin and Mr Goldman),Radiology (Dr Carter), Surgery (Dr Caps), and Pathology (DrYaziji) and the Applied Physics Laboratory (Drs Kaczkowskiand Crum), University of Washington, and Sonic Concepts(Mr Keilman).

This work was supported by a grant from the Defense AdvancedResearch Programs Administration (DARPA) under its MURIprogram, no. N00014-96-0630, supervised by Dr Wallace A.Smith.

Reprint requests: Shahram Vaezy, PhD, Department ofBioengineering, University of Washington, Box 357962,Seattle, WA 98195.

Copyright © 1999 by the Society for Vascular Surgery andInternational Society for Cardiovascular Surgery, NorthAmerican Chapter.

0741-5214/99/$8.00 + 0 24/1/94371

focus after a few seconds of HIFU application.These high temperatures can result in coagulationnecrosis of tissue and the fusion of blood vesselwalls.2 HIFU may be useful in numerous applica-tions, including vascular surgery procedures such asvascular anastomoses, the treatment of iatrogenicvascular injuries, and the treatment of vascularinjuries resulting from blunt or penetrating trauma.

MATERIALS AND METHODSFour pigs (two male and two female; age range,

3 to 5 months; weight range, 30 to 100 kg) wereused for the experiments. The procedures were per-formed according to the guidelines of the UnitedStates National Institute of Health for the use of lab-oratory animals. The pigs underwent initial sedationin the animal housing facility with an intramuscularinjection of a mixture of acepromazine maleate andketamine hydrochloride at a dose of 1 mg/kg and22 mg/kg of body weight, respectively. After trans-port to the laboratory, the animals underwent anes-thesia with a ketamine hydrochloride/xylazinehydrochloride mixture, 8:1 ratio, at a dose of 3.5 to4 mL with dose to effect. The animals were intubat-ed and kept under anesthesia with halothane, withassisted positive pressure ventilation. The heart rateand the oxygen saturation level were monitoredthroughout the experiment.

The blood vessels of interest were exposed(Table I). A longitudinal incision, 2 to 8 mm inlength, was made with a no. 11 scalpel. Moderate toprofuse bleeding occurred with this transmuralinjury. The blood loss from the injury varied on the

basis of the incision length and the hemodynamiccondition of the animal. Bleeding rates as high as 40mL in 10 seconds were measured by collecting theblood in a beaker. HIFU treatment was appliedwithin 5 seconds of the incision by placing the tip ofthe cone (focal spot of the HIFU beam, describedbelow) on the bleeding site (Fig 1). The treatmentprotocol consisted of HIFU application for 2 to 10seconds, followed by a visual observation to assesswhether the bleeding had stopped. AdditionalHIFU treatments of a similar duration were appliedif the bleeding had not stopped. If 2 to 3 repeatedadditional treatments did not result in hemostasis,no more treatment was applied and the result wasrecorded as incomplete hemostasis. All treatmentswere performed with mechanical scanning of theHIFU probe. After the completion of the treatment,the patency of the vessel was determined by palpa-tion. Two time points—major and complete hemo-stasis—were recorded for each treatment. Majorhemostasis was defined as the reduction of the majorbleeding to a slow oozing (approximately 1mL/min), and complete hemostasis was defined as thecomplete arrest of bleeding. Statistical analysis of themajor and complete hemostasis times was performedwith t tests, assuming unequal variance of the popu-lations.

The HIFU transducer characteristics are describedelsewhere.2 Briefly, the transducer for the treatment(Sonic Concepts, Woodinville, Wash) was sphericallyconcave, with a focal length of 55 mm, an aperturediameter of 35 mm, and a resonant frequency of 3.5MHz. The half maximum beam width and length inthe focal region were 1 and 9 mm, respectively. Thedriving electronics were composed of an HP 33120Afunction generator (Hewlett Packard, Palo Alto,Calif) whose output was connected to an ENIAP400B power amplifier (ENI, Rochester, NY). Acustom-made electrical matching network was con-nected between the amplifier and the transducer. TheHIFU transducer was equipped with a conical hous-ing, which was made of clear plastic, with a height of

JOURNAL OF VASCULAR SURGERY534 Vaezy et al March 1999

Fig 1. Schematic drawing of high-intensity focused ultra-sound application to a bleeding vessel. Tip of conical hous-ing was placed on incision site, and mechanically-scannedhigh-intensity focused ultrasound was applied.

Table I. Blood vessels, lumen diameter, and wallthickness

Lumen Wall Blood vessel diameter (mm) thickness (mm)

Superficial femoral artery 2 ≤1Common femoral artery 3 to 5 1 to 2Carotid artery 4 to 6 1Jugular vein 8 to 10 <1

50 mm and a tip opening of 3.1 mm in diameter. Theconical housing was filled with degassed water forultrasonic coupling from the transducer to the tissue.The tip was covered with a polyurethane membrane.The cone geometry allowed the center of the focalspot of the transducer to be on the membrane.

The mechanical scanning of the HIFU probewas used to effectively enlarge the lateral cross sec-tion of the HIFU focal spot (approximately 1 mmwithout scanning). The scanning was done with anHP 3311A function generator (Hewlett Packard), aPA-138 power amplifier (LabWorks, Inc, CostaMesa, Calif), and an ET-126B electrodynamic shak-er (LabWorks, Inc). The frequency and amplitude ofthe scanning were 15 to 25 Hz and 5 to 10 mm,

respectively. Thus, the focus of the transducer wasspread over a linear dimension equal to the ampli-tude of the oscillations. The intensity at the focuswas in the range of 2500 to 3000 W/cm2 for alltreatments. Generally, lower intensities were used forthe treatment of moderate bleeding, and higherintensities were used for the profuse bleeding.

Heparin was administered in all the animals atapproximately half way through the experiment at adose of 5,000 or 10,000 units to ensure that the ani-mal was in an anticoagulated state. The blood clot-ting time was measured at several time points duringthe normal and anticoagulated states of the animals.The clotting time was assessed in both an open plas-tic dish and a closed glass tube. The clotting time of

JOURNAL OF VASCULAR SURGERYVolume 29, Number 3 Vaezy et al 535

Fig 2. Representative sequence of photographs obtained during incision and high-intensityfocused ultrasound scan treatment of superficial femoral artery. A, Scalpel blade just beforeproducing longitudinal cut. B, Bleeding jet from artery. C, High-intensity focused ultrasoundscan application with conical housing. Picture of conical housing is slightly blurry because ofits vibration during high-intensity focused ultrasound scan application. D, Artery after high-intensity focused ultrasound scan treatment and achievement of complete hemostasis. Incisionsite appears as a slit. Coagulated blood was observed in incision site. Each picture is approxi-mately 3 × 4 cm.

the heparinized blood was 2 to 10 times longer thanthat of the nonheparinized blood.

Control incisions were not performed because ofthe large amounts of blood loss that were observed.However, in other experiments, seven control punc-tures (four in femoral arteries and three in femoralveins) were allowed to bleed for 2 minutes freely andfor 2 minutes while the HIFU applicator cone washeld on the puncture.2 The punctures continued tobleed at the end of the 4 minutes, with a maximumreduction in the bleeding rate of approximately 50%to about 5 mL/min. This reduction did not meetthe definition of major hemostasis with a maximumbleeding rate of 1 mL/min.

All the animals were alive at the end of experiment

when they were killed with an overdose of the anes-thetic mixture, followed by a 2-mL KCl-saturatedsolution within 2 minutes. Representative tissue sam-ples were obtained from the HIFU-treated regionsand the normal regions of the blood vessels for histo-logic examination. The tissue samples were fixed informalin, embedded in paraffin, and stained withhematoxylin and eosin.

RESULTSFig 2 shows a representative sequence of pho-

tographs that were obtained during the incision andthe HIFU treatment of a superficial femoral artery.The scalpel blade is shown over the artery just beforethe incision was made (Fig 2A). A jet of blood


Fig 3. Four examples of high-intensity focused ultrasound-treated regions. A, Superficialfemoral artery. Vessel was patent after treatment. Incision site (arrowhead) appears as a faintslit. B, Superficial femoral artery. Vessel was occluded after treatment. C, Carotid artery. High-intensity focused ultrasound-treated region appears as slightly discolored, predominantly indark bands (arrows) that appear in direction of mechanical scanning of high-intensity focusedultrasound probe. Incision site (arrowhead) appears as a faint slit. D, Close-up view of high-intensity focused ultrasound-treated region on jugular vein. Meshwork of fibers is observed atthe treatment site. All scale bars are 2 cm.

squirted from the artery after the incision (Fig 2B).The application of HIFU, with the conical housing,started within 5 seconds of the incision (Fig 2C).The bleeding was completely arrested at the com-pletion of the HIFU treatment (Fig 2D). A total of76 incisions and HIFU treatments were performedin this study. The heart rates and the oxygen satura-tion levels of the animals were within normal rangethroughout the experiments.

Sixty-nine of the 76 treatments resulted in thecomplete cessation of bleeding (complete hemosta-sis), and seven treatments resulted in a significantreduction of bleeding (major hemostasis) withoutcomplete hemostasis (incomplete hemostasis). In allseven treatments with incomplete hemostasis, poortargeting of the HIFU was noted as a result of eithermassive bleeding and lack of visual cues for probepositioning (four cases) or inaccessibility of the inci-sion site in hard-to-reach regions (three cases). Thisled to conditions of overexposure of the vessel, atwhich point further treatment did not seem to reducethe bleeding. In this situation, it appeared that thevessel had become so necrosed that the vessel wallswould not fuse to close with further treatment.Therefore, no further treatment was applied, andclamping was used to achieve complete hemostasis.

Fig 3 shows four representative examples ofHIFU-treated vessels. Complete hemostasis wasachieved in all the vessels shown. Fig 3A shows asuperficial femoral artery with a slight discoloration ofthe vessel as a result of the HIFU treatment. Theartery was patent after the treatment. A patent vesselwas observed after 51 of the 69 treatments (74%) inwhich complete hemostasis was achieved. Fig 3Bshows a superficial femoral artery with severe discol-oration and deformation after the HIFU treatment.The treatment site was occluded after the treatment.An occluded site was observed after 18 of 69 treat-ments (26%). Fig 3C shows a carotid artery with theHIFU-treated region clearly seen on the adventitia.The adventitia was slightly discolored and hardened,predominantly in bands (Fig 3C) that appeared to bein the direction of the mechanical scanning of theHIFU probe. The artery was patent after the treat-ment. Fig 3D shows a close-up view of a jugular vein.A tight mesh of interlacing strands was observed atthe site of the HIFU treatment. The vessel was patentafter the treatment.

Occlusion of the vessel at the treatment site (18of 69 treatments; 26%) occurred in the superficialfemoral artery (17 cases) and in the carotid artery(one case). The occlusion appeared to be the resultof mechanical deformation of the vessel and not of

thrombosis of the blood. In the case of the superfi-cial femoral artery, the occlusions were within 5 cmaround the bend of the knee. In all cases, a signifi-cant spasm of the artery was observed before incis-ing the vessel, although considerable bleeding, inthe form of shooting jets, occurred as a result ofincision. The average major and complete hemosta-sis times for the treatments that resulted in theocclusion of the treatment sites were 22 and 34 sec-onds, respectively. These values, although slightlyhigher, were not significantly different from those ofthe treatments that resulted in patent vessels—15and 22 seconds, respectively. The P values of themajor and complete hemostasis times of patent ver-sus occluded vessels were .13 and .06, respectively.No relationship was found between either the inci-sion length or the HIFU intensity and the occur-rence of the occlusion.

Figs 4, 5, and 6 show the results of the histologicanalysis on three representative HIFU-treated bloodvessels in which complete hemostasis was achieved.Fig 4 shows a superficial femoral artery with an inci-sion (Fig 4A). A coagulated fibrin network wasobserved at the incision site, with red blood cellswithin the network (Fig 4B). Fig 5 shows anotherexample of a treated superficial femoral artery with anincision site (Fig 5A). Abundant serous fluid wasobserved in the coagulated fibrin network (Fig 5B).Fibrin was observed at the incision site and in the ves-sel lumen (Fig 5C). The internal elastic lamina on oneedge of the incision appeared to be in contact with themedia of the other edge of the incision. Although aprecise apposition of the incision edges was notachieved in this case (Fig 5B), the incision was sealedand complete hemostasis was achieved. Fig 6 shows acarotid artery with an incision (Fig 6A). Serous fluidwas focally observed at the incision site of the vessel,and within a well-developed fibrin network (Fig6A,B). The vessel wall on the opposite side of thelumen showed little or no evidence of HIFU-treat-ment (Fig 6C). Possible effects may include: (1) aslight denudation (Fig 6C), although no plateletaggregation or monocytic attachment (an expectedresponse to denudation) were observed at thedenudation site; or (2) the presence of edema fluid(Fig 6C), although these structures may be fatemboli. All vessels, examined by means of lightmicroscopy, exhibited focal swelling of the wall at theHIFU-treated site, without evidence of irreversibleinjury.

The mean times of major and complete hemostasisfor all vessels were 17 and 25 seconds, respectively.The range, mean, and standard deviation of the major


and complete hemostasis times for the blood vessels inwhich complete hemostasis was achieved are presentedin Table II. Complete hemostasis times, as short as 2seconds, were noted in the jugular vein. Fig 7 shows aplot of the mean and standard deviation of the majorand complete hemostasis times for all the HIFU-treat-ed vessels. The hemostasis times of the commonfemoral artery were the longest (28 and 46 seconds formajor and complete hemostasis, respectively), whereasthose of the jugular vein were the shortest (7 and 10seconds for major and complete hemostasis, respec-tively). Table III shows the results of t test compar-isons of all the vessels. A statistically significant differ-ence was observed for the time to control bleeding inthe small vessels as compared with the medium-sizedvessels (superficial femoral arteries compared withcommon femoral arteries; Table II). The hemostasistimes of the jugular vein were significantly shorter thanthe times of all the other vessels (Table II). A total of42 incisions and HIFU treatments were performedwhile the animals were heparinized. No statistically sig-nificant differences were found between the major andcomplete hemostasis times in normal and heparinizedconditions. The P values of the major and completehemostasis times of normal and heparinized condi-tions were .5 and .3, respectively.

DISCUSSIONWe have shown that the application of mechani-

cally scanned HIFU to blood vessel incisions, 2 to 8mm in length, results in rapid and effective hemo-stasis. The control of bleeding appears to be due to

a combination of tissue coagulation and fibrin depo-sition. Fibrin may have provided a substrate for sol-dering at the incision site, and the coagulated adven-titia appears to have sealed the breached wall, pro-viding extra support for the fibrin plug. The HIFUeffects on the blood vessel walls are thought to becaused by its thermal action.2-4 A temperature rise toapproximately 70°C has been measured at the focusof HIFU during the treatment of rabbit livers, withHIFU intensities that were similar to those used inthe current study.1 Similar temperatures have beenmeasured during successful vascular coagulation andwelding with electrocoagulation 5 and laser therapy.6At these temperatures, the alteration of the vesselwall components (collagen, elastin, and smoothmuscle) and substrate bonding (collagen-collagen,and collagen-elastin) is expected.7

In this study, while the use of mechanical-scan-ning HIFU for the hemostasis of vascular incisionswas shown, several interesting observations weremade. First, a statistically significant difference wasobserved for the time to control bleeding of thesmall vessels as compared with the time to controlbleeding of the medium-sized vessels. Although allthe tested arteries are of muscular type, the varyingcontent of collagen, elastin, and smooth muscle inthese vessels8 may result in varying effects of HIFUon the vessel. In fact, different temperature rangesare thought to produce different effects of vascularwelding.6 Second, a statistically-significant differ-ence was observed between the hemostasis times ofthe jugular vein and all the other vessels. The thinwall of the jugular vein seemed to be easily weldedwith a short application of HIFU. The extensiveinterlacing strands, observed on the jugular veinafter the HIFU treatment, and the low venous pres-sure may have important implications for the fasthemostasis times. Thirdly, 17 of the 18 occludedsites occurred within 5 cm of the bend of the kneein the superficial femoral artery while the vessel wasundergoing a spasm. The structural elasticity and thephysiologic state of a blood vessel may have signifi-cant implications for the optimal HIFU treatmentparameters. In fact, slightly higher hemostasis times,which bordered on statistical significance, were mea-sured for the treatments that resulted in the occlu-sion of the vessel, as compared with those thatresulted in a patent vessel. In general, a careful studyof the HIFU parameters, including the frequency,the intensity, the beam pattern, and the correspond-ing thermal action on vessel wall and its structuralcomponents, in varying physiologic conditions, mayprovide important information for the mechanism of


Fig 4. Histologic results of representative high-intensityfocused ultrasound-treated superficial femoral artery. A, Cross-sectional view with incision wound (arrow). B, Close-up view of incision site with fibrin network(arrow).

acoustic hemostasis of blood vessels. Finally, no dif-ficulty was experienced in stopping bleeding in ani-mals that had undergone treatment with heparin.The HIFU-induced hemostasis may be independentof normal thrombosis mechanisms.

The thermal effect of our 3.5-MHz HIFU isquite localized. The temperature is maximal at thefocus (cross section of 1 mm), with a steep declineof approximately 10°C/mm around the focalspot.1,9 This temperature profile can be even steep-er if a higher frequency HIFU or a shorter durationexcitation is used.10 Also, because of the shortHIFU excitation times, the tissue effects becomeessentially perfusion independent, providing amethod of thermal delivery without significant cool-ing between exposures. Such focal high tempera-tures offer a potential tool for the control of bleed-

ing in small places. In the current study, however,the mechanical scanning of HIFU was used toobtain an effective large thermal effect to control thebleeding of large incisions. This method may be use-ful for the rapid hemostasis of large lacerated surfaceareas of traumatized livers or spleens.

An important characteristic of HIFU is the radia-tion pressure, which results in a net bulk flow of liq-uid known as acoustic streaming.11 We found thiseffect to be useful in the control of bleeding. The jetof blood that squirted from the incision generally wasstopped as HIFU was applied, and the blood waspushed back into the vessel. We believe that acousticstreaming helped the hemostasis process by: (1) pro-ducing a more blood-free environment in which thevisualization of the incision site was easier, (2) allow-ing a better apposition of the incision edges because


Fig 5. Histologic results of representative high-intensity focused ultrasound-treated superficialfemoral artery. A, Cross-sectional view of vessel with incision wound (arrow). B, Close-up viewof outer layer of vessel wall. Abundant serous fluid (arrowhead) was observed in fibrin network.C, Fibrin was in incision slit (arrow) and in lumen of artery (black arrowhead).

Table II. Major and complete hemostasis times for high-intensity focused ultrasound treatment of surgi-cally exposed incised blood vessels

Approximate lumen Major hemostasis time Complete hemostasis time Blood vessel No. of trials diameter (mm) range (s; mean ± SD) range (s; mean ± SD)

Superficial femoral artery 40 2 3 to 75 3 to 85(16.2 ± 14.54) (24.8 ± 18.80)

Common femoral artery 7 3 to 5 15 to 40 29 to 65(28.3 ± 9.07) (46 ± 15.26)

Carotid artery 9 4 to 6 5 to 64 11 to 64(25.8 ± 17.03) (31.1 ± 14.94)

Jugular vein 13 8 to 10 2 to 20 2 to 30(6.7 ± 6.03) (10.3 ± 9.48)

SD, Standard deviation.

there was no exiting blood to hold the edges open,and (3) resulting in a more optimal deposition ofHIFU energy in the vessel wall because the bloodwas pushed away from the wound site before it could

carry away much heat. The acoustic streaming mech-anism may prove to be valuable in the treatment ofthose types of hemorrhage, such as bleeding ulcers,in which the blood flow causes difficulty in deposit-ing the coagulative energy.12

Two important studies are necessary for the fur-ther advancement of HIFU vascular hemostasis. First,the optimal HIFU parameters (frequency, intensity,and duration) must be determined for specific injuriesand blood vessels, particularly with the goal of keep-ing the vessel patent. The determination of burstingstrength and mechanical strength of the vessel afteracoustic hemostasis will be an integral part of thisstudy. Second, survival animal studies in which theHIFU treatment sites are monitored for a period afterthe treatment are essential in further evaluating theefficacy of acoustic hemostasis. Late effects will haveto be studied carefully to eliminate the possibility ofdeleterious effects, such as delayed arterial rupture as


Fig 6. Histologic results of representative high-intensity focused ultrasound-treated carotidartery. A, Cross-sectional view of vessel with incision wound (arrow). B, Close-up view of inci-sion. Serous fluid (arrowhead) and fibrin (arrow) were observed. C, Opposite side of lumen.Slight denudation (arrow) and edema fluid (arrowhead) may have occurred as a result of high-intensity focused ultrasound application.

Table III. Statistical analysis of major and com-plete hemostasis times

Common Carotid Jugular femoral artery artery vein

Superficial femoral artery .012 .147 .001.008 .295 .0007

Common femoral artery .711 .0003.70 .0003

Carotid artery .010.003

Results of the t test for different blood vessels. The P values forcomparison of the major (upper number) and complete (lowernumber) hemostasis times are presented.

a result of possible injury to the vessel wall during thetreatment. Such a study would include a careful his-tologic study of the vessels at the HIFU treatment siteand of the surrounding tissue. The above-mentionedstudies will have a significant effect on the clinical suc-cess of the acoustic hemostasis.

Acoustic hemostasis may provide a valuable toolfor the surgeon, in both trauma and elective situa-tions. The current blood vessel injury model, inwhich the injury is relatively minor and the bloodvessel wall is still intact, is akin to the situation afteran iatrogenic, catheter-related vascular injury. HIFUappears to be highly efficacious in this type of setting,and although it was applied to surgically exposed ves-sels in this experiment, HIFU has the capability forpercutaneous application as well. In fact, in the cur-rent study, we used HIFU without the use of amethod to control hemorrhage (eg, clamping) toallow the investigation of an extracorporeal applica-tion. In most surgical situations, clamping wouldperhaps provide a fast initial hemostatic mechanism,but HIFU provides the potential of complete hemo-stasis in the field and in surgical situations where easyaccess for clamping does not exist. The average treat-ment time for major and complete hemostasis of 17and 25 seconds in the current model represents a sig-nificant advantage over conventional suturing. Also,HIFU is capable of penetrating tissue to deliver itsenergy to a deep-seated region with millimeter preci-sion and without affecting the intervening tissue,while other hemostatic techniques, such as laser ther-apy and electrocautery, are surface techniques and

cannot penetrate tissue or blood. The transmission ofHIFU through pools of blood during trauma surgerymay prove to be an important capability of HIFU. AHIFU-based, acoustic hemostasis method, coupledwith an imaging method for localization, targeting,and treatment monitoring, may have extracorporeal,laparoscopic, and endoscopic applications.

We thank Frank Starr and Sherry Stemen for theirexpert work in animal experimentation and Starr Kaplanfor her artistic illustration in Fig 1.

REFERENCES

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2. Vaezy S, Martin R, Yaziji H, et al. Hemostasis of puncturedblood vessels using high intensity focused ultrasound.Ultrasound Med Biol 1998;24:903-10.

3. ter Haar G. Ultrasound focal beam surgery. Ultrasound MedBiol 1995;21:1089-100.

4. Hynynen K, Vykhodtseva NI, Chung AH, Sorrentino V,Colucci V, Jolesz FA. Thermal effects of focused ultrasoundon the brain: determination with MR imaging. Radiology1997;204:247-53.

5. Bergdahl B, Stenquist B. An automatic computerized bipolarcoagulator for dermatologic surgery. J Dermatol Oncol1993;19:225-7.

6. White RA, Kopchok G, Peng SK, et al. Laser vascular weld-ing—how does it work? Ann Vasc Surg 1987;1:461-4.

7. Bass LS, Treat MR. Laser tissue welding: a comprehensivereview of current and future clinical applications. Lasers SurgMed 1995;17:315-49.

8. Grant RA. Content and distribution of aortic collagen, elastinand carbohydrate in different species. J Atheroscler Res1967;7:463-72.


Fig 7. Histogram of major and complete hemostasis times of all high-intensity focused ultra-sound-treated vessels. Error bars represent standard deviations.

9. Hynynen K, Colucci V, Chung A, Jolesz F. Noninvasive arte-rial occlusion using MRI-guided focused ultrasound.Ultrasound Med Biol 1996;22:1071-7.

10. Hunt JW, Lalonde R, Ginsberg H, Urchuk S, Worthington A.Rapid heating: critical theoretical assessment of thermal gradi-ents found in hyperthermia treatments. Int J Hyperthermia1991;7:703-18.

11. Nyborg WL. Acoustic streaming. In: Mason, editor. Physical

acoustics: principles and methods. New York: AcademicPress; 1964. p. 265-331.

12. Silverstein FE, Protell RL, Gilbert DA, et al. Argon vs.neodymium YAG laser photocoagulation of experimentalcanine gastric ulcers. Gastroenterology 1979;77:491-6.

Submitted Jun 30, 1998; accepted Sep 8, 1998.


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Use of high-intensity focused ultrasound to control bleeding

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