Biological effects;
s omeof which may be hazardous;
may be caused by ultrasound through thermal;
mechanicaolr otherm echanismTs.h e mechanicaelf fect may includem icrostreaminsgt;
a blec avitationb y trapped bubbleso r transiencta vitationT. he ultrasounde xposure is specifiedb y the ultrasonicfi eldp arameterTsh. e dosei s definedb y the absorbedq uantityo f energyI.n diagnostic applicationss;
p ecificationo f the ultrasonice xposureis basedo n measuremenotfs the beama ndp ulses hapesin water;
t hes patialp eakt emporaal verag(eS PTA) valueo f intensityis generallyq uoted.T he AmericanI nstituteo f Ultrasoundin Medicine( 1977)h asi ssueda statemeñt-3 that SPTA intensitieos f< 100m W cm-z seemt o be safe. Most contemporaryin strumentsf or echocardiology operatew ith exposurebs elowthis level (see Table1 ). It should be realized, however, that despite the occasionapl ublicationo f resultsi ndicatingt hatadverse biologicale ffectsm ayoccur under certainc onditionso f low ultrasoniec xposuret,h ep resentlayc cepte'ds afele vel of 100m W cm-2 is somewhaatr bitrarilsye ts incei t is not a level abovew hich,with scientificp roof,d amageo ccurs and beloww hichall is safe.I n additionc, ertaina nomalies in the practicaul seo f the definedle veld o exist.T hesem ay excludeth euse of higherin tensitiews hichwould improve the signal-to-noisera tio. Anomalies occur when the attenuationin tissue is added. This is illustratedi n Figure2 . Over the courseo f severayl earst heA mericanIn stitute of Ultrasoundin Medicine issueds everasl tatementosn the safe use of diagnosticu ltrasound.T he first one appeareidn August1 976w, asr evisedin October1 978a, nd concernedt he famous 100 mW cm-2 intensity level mentioneda bove.The documentw as known as the Statemenotn Mammalianin vivo UltrasonicB iological Effects',[ seef,o r exampleR, eference1(p 520),R eferenc2e (pp 2-4) and Reference3 ].T he secondo newas issuedi n October 1982a nd revisedi n March 1983a nd October 1983. This was called 'AIUM Statemenot n Clinical Safety'i,n which the 100m W cm-2 level was replacedb y 'exposurea t intensitiest ypical of present diagnostic ultrasoundin struments'[,s eeR eference5 (p RI0)]. The mostr ecentp ublicationco ncernintgh es afeu seo f ultrasoundi n obstetricsis the result of a Consensus DevelopmentC onference,j ointly sponsored by the NationalI nstituteos f Healtha ndthe NationalC enterf or Devicesa nd RadiologicaHl ealthof the Food and Drug Administratio(nF DA), [seeR eference6 (pp R54-R58)]. Some of the conclusionsa re that the manufacturearsre recommendetdo report the output levels to the FDA accordingt o the requirementisn the AIUM/NEMA Safety Standar~d, and that for each examinationth e 'specific exposure informations hould be recorded. Furthermoree, chographysh ould be applied solely on medical indication and routine ultrasounds creening would not be indicateda t this time. Only the patient's benefit should be taken into account and the patient shouldb e informedo f the clinical indicationt,h especific benefita nd the potentiarl isk and alternativeif, any. It is a remarkablef act that, whereas in all the documentist is emphasizetdh at noc onfirmedb iological effectso n patientso f diagnosticu ltrasoundin struments' havee verb eenr eportedn, everthelesths e prudentu se,at leasti n obstetricsis, so stronglyr ecommended;
