- Email: [email protected]
Diagnostic applications of Doppler ultrasound
ULTRASONICS
~
INDUSTRY
~
Conference Paper
Diagnostic applications of Doppler ultrasound F. D. F i e l d e r and R. F. Baker*
The Doppler p r i n c i p l e u s i n g low i n t e n s i t y u l t r a s o u n d is a p plied to m e d i c a l d i a g n o s i s . In d i a g n o s i s of p r e g n a n c y a f r e quency of 2 - 2 . 5 M H z is c h o s e n . T h e U l t r a s o n i c Blood Flow D e t e c t o r h a s t r e m e n d o u s p o t e n t i a l f o r t h e d i a g n o s i s of pregnancy.
A field of r e s e a r c h which i s a r o u s i n g c o n s i d e r a b l e i n t e r e s t in m a n y a r e a s of m e d i c a l d i a g n o s i s is t h e a p p l i c a t i o n of t h e Doppler p r i n c i p l e u s i n g v e r y low i n t e n s i t y u l t r a s o u n d . E v e n at t h i s e a r l y s t a g e , the field i s so b r o a d t h a t it will only be p o s s i b l e to b r i e f l y d e s c r i b e s o m e of the m a n y a s p e c t s of t h i s work. B a s i c a l l y , t h e D o p p l e r e f f e c t in t h i s a p p l i c a t i o n i s t h a t when s o u n d w a v e s a r e r e f l e c t e d f r o m a m o v i n g object t h e y a r e s h i f t e d s l i g h t l y in f r e q u e n c y , t h e shift being p r o p o r t i o n a l to the speed of the object. In the living body t h e r e a r e n u m e r o u s f u n c t i o n a l m o v e m e n t s which r e f l e c t u l t r a s o u n d ; blood flowing t h r o u g h a r t e r i e s , the a c t i o n s of t h e h e a r t , i n t e s t i n a l m o v e m e n t s and p a s s a g e of u r i n e and g a s t r i c j u i c e s . The e q u i p m e n t r e q u i r e d to p e r f o r m the b a s i c f u n c t i o n of p r o d u c i n g an audible sound f r o m t h e s e m o v e m e n t s i s f a i r l y s i m p l e and c a n t h e r e f o r e be p r o d u c e d at a r e l a t i v e l y low cost. F i g 1 s h o w s a block d i a g r a m of a t y p i c a l i n s t r u m e n t . The u l t r a s o n i c s i g n a l is g e n e r a t e d by an o s c i l l a t o r at the r e q u i r e d f r e q u e n c y and c o n n e c t e d to one p i e z o - e l e c t r i c c r y s t a l in the t r a n s d u c e r a s s e m b l y . T h i s v i b r a t e s at the s a m e f r e q u e n c y and e m i t s high f r e q u e n c y sound into the body. T h e sound is r e f l e c t e d by i n t e r n a l o r g a n s b a c k to a s e c o n d c r y s t a l which c o n v e r t s it to e l e c t r i c a l e n e r g y which i s fed into a v e r y low n o i s e tuned a m p l i f i e r . A f t e r r e c t i f i c a t i o n it i s f u r t h e r a m p l i fied, f i l t e r e d and c o n n e c t e d to a l o u d s p e a k e r or h e a d p h o n e s . If no m o v e m e n t is p r e s e n t at the sight of t h e r e f l e c t i o n only a s l i g h t h i s s is h e a r d . If, h o w e v e r , t h e r e i s m o v e m e n t the f r e q u e n c y of t h e r e f l e c t e d sound a l t e r s s l i g h t l y and b e a t s with the t r a n s m i t t e d s i g n a l , the d i f f e r e n c e b e t w e e n the two c r e a t i n g an audible sound. A u s e f u l f e a t u r e is t h a t i s is p o s s i b l e , with c a r e f u l d e s i g n , t o c o n t r o l the o v e r a l l b e a m - w i d t h of t h e t r a n s d u c e r which g r e a t ly a s s i s t s the d e t e c t i o n of m i n u t e a r e a s of m o v e m e n t and d e t e r m i n i n g the location of t h e s e . The a c o u s t i c i n t e n s i t y of the u l t r a s o u n d m u s t be kept to t h e lowest u s a b l e level to r e d u c e any p o s s i b l e r i s k of s i d e e f f e c t s to the m i n i m u m . In t h i s c o n n e c t i o n , t h e r e is no e v i d e n c e f r o m the m a n y t h o u s a n d s of p r e g n a n t p a t i e n t s e x a m i n e d with t h i s type of i n s t r u m e n t to i n d i c a t e that any h a z a r d s e x i s t . In the v a r i o u s a p p l i c a t i o n s i n v e s t i g a t e d so f a r it h a s not b e e n found n e c e s s a r y to u s e an i n t e n s i t y g r e a t e r t h a n about 1 2 m W / c m 2 and in s o m e c a s e s only a few m i l l i w a t t s . T h i s is v a s t l y d i f f e r e n t to the m a n y w a t t s e m p l o y e d in s o m e t h e r a p e u t i c a p p l i c a t i o n s of u l t r a s o u n d . S e l e c t i o n of f r e q u e n c y is a n o t h e r i m p o r t a n t f a c t o r . Some of the m o v e m e n t s a r e f a i r l y slow s p e e d and if the f r e q u e n c y of the u l t r a s o u n d i s too low, t h e s h i f t is not g r e a t enough to c r e a t e an a u d i b l e b e a t . On the o t h e r hand, the a t t e n u a t i o n due to a b s o r p t i o n in t i s s u e i n c r e a s e s in a l m o s t d i r e c t p r o p o r t i o n to f r e q u e n c y . At h i g h e r f r e q u e n c i e s it would t h e r e f o r e be n e c e s s a r y to i n c r e a s e the a c o u s t i c i n t e n s i t y in o r d e r to obtain deep p e n e t r a t i o n . A s a t i s f a c t o r y c o m p r o m i s e is * Sonicaid Ltd, Hook Lane, N y e t i m b e r , B o g n o r R e g i s , S u s s e x , England 36
ULTRASONICS J a n u a r y 1969
~ _ ~ ~
-IH H amplifier
and filter
amplifier
Recorderc : l Loud l~] speaker HF generotor F i g 1 Block D i a g r a m of t y p i c a l i n s t r u m e n t
b e t w e e n 2MHz and 2 . 5 M H z and the m a j o r i t y of m o v e m e n t s can be h e a r d at t h i s f r e q u e n c y . B e f o r e going into v a r i o u s a p p l i c a t i o n s i n v e s t i g a t e d to date, it i s n e c e s s a r y to outline the d i f f i c u l t i e s e n c o u n t e r e d with the u s e of u l t r a s o u n d in the body. E v e r y individual s u b s t a n c e , w h e t h e r liquid or solid, h a s a d i f f e r e n t a c o u s t i c i m p e d a n c e which i s the p r o d u c t of the d e n s i t y and v e l o c i t y of sound in the m e d i u m . U l t r a s o u n d i s r e f l e c t e d at a n y i n t e r f a c e w h e r e a d i f f e r e n c e in i m p e d a n c e o c c u r s . The g r e a t e r the d i f f e r e n c e , the g r e a t e r i s the r e f l e c t i o n and c o n s e q u e n t l y l e s s s i g n a l c o n t i n u e s into the n e x t m e d i u m . In the body, a n i m a l o r h u m a n , t h e r e a r e s e v e r a l l a y e r s of v a r y i n g t i s s u e b e t w e e n t h e o u t e r s u r f a c e and any i n t e r n a l o r g a n . A v a s t d i f f e r e n c e o c c u r s b e tween a i r a n d body t i s s u e and t h i s i m p o s e s l i m i t a t i o n s on the u s e at the p r e s e n t t i m e . L u n g s , s t o m a c h and i n t e s t i n e a l l contain a i r or g a s and p r a c t i c a l l y the total s i g n a l i s p r e v e n t e d f r o m p a s s i n g t h r o u g h t h e s e c a v i t i e s . S c a t t e r i n g and a b s o r p tion a l s o r e d u c e the s i g n a l and t h i s a g a i n v a r i e s with the v a r i e t y of t i s s u e s e n c o u n t e r e d . T h e a t t e n u a t i o n due to a b s o r p tion at 2 . 4 M H z i s a p p r o x i m a t e l y 0 . 2 d B / c m f o r blood, 3 d B / c m for m u s c l e and r i s i n g to a r o u n d 1 0 d B / c m f o r s o m e bone s t r u c t u r e s . T h e r e f l e c t i o n and a t t e n u a t i o n o c c u r s with both the e m i t t e d and r e t u r n s i g n a l s , c o n s e q u e n t l y we r e c e i v e only a m i n u t e f r a c t i o n of the t r a n s m i t t e d sound. M o s t l i q u i d s , howe v e r , a r e e x c e l l e n t t r a n s m i s s i o ~ m e d i a and e x h i b i t v e r y little a t t e n u a t i o n , the f i g u r e for w a t e r being a s low a s 0. 0 1 4 d B / c m . By f a r the l a r g e s t i n i t i a l a p p l i c a t i o n f o r D o p p l e r i n s t r u m e n t s i s in o b s t e t r i c s which i s l a r g e l y b e c a u s e of the e a s e with which one can e m i t and r e c e i v e u l t r a s o u n d in a p r e g n a n t u t e r u s . In a p r e g n a n c y of 10-12 w e e k s p o r t i o n s of i n t e s t i n e c a n lie b e t w e e n the a b d o m i n a l wall and the u t e r u s and in m a n y c a s e s i m p e d e the t r a n s m i s s i o n of u l t r a s o u n d . H o w e v e r , lying a l m o s t in f r o n t of the u t e r u s i s the b l a d d e r and if t h i s is filled with u r i n e we h a v e an e x c e l l e n t t r a n s m i s s i o n tank t h r o u g h which the u l t r a s o u n d i s b e a m e d . V a r i o u s r e f l e c t i o n s
tJLTIEKa~DN~_~ ~ o c c u r at the s t a t i o n a r y i n t e r f a c e s but m o v e m e n t s of the foetal h e a r t and blood flow can be c l e a r l y d e t e c t e d . Fig 2 shows a p r e g n a n c y n e a r i n g full t e r m . It can be s e e n that, a p a r t f r o m p a t i e n t s with s e v e r e o b e s i t y , t h e r e i s only a f a i r l y thin l a y e r of v a r i o u s t i s s u e s b e t w e e n the o u t e r s u r f a c e and the u t e r u s . The u t e r i n e cavity is c o m p l e t e l y filled with liquor which c o n s i s t s of 98.8% w a t e r , the b a l a n c e c o n s i s t i n g of p r o t e i n , sodium c h l o r i d e and o t h e r s o l i d s , and at full t e r m t h e r e i s a p p r o x i m a t e l y 2 pints which e n t i r e l y s u r r o u n d s the foetus. With this c l e a r path for the u l t r a s o u n d we can d e t e c t the blood flow in the u m b i l i c a l cord, p l a c e n t a and m a j o r foetal v e s s e l s a s well a s the foetal h e a r t and m a t e r n a l a r t e r i e s and all of t h e s e a r e c l e a r l y identified. Due to the d i r e c t i o n a l p r o p e r t i e s of the t r a n s d u c e r the r e l a t i v e location of t h e s e o r g a n s can be d e t e r m i n e d .
INEXJBTP/Y
Conference Paper
E x t e r n a l palpation, i n t e r n a l palpation via l a p a r o t o m y , vaginal s m e a r , foetal e l e c t r o c a r d i o g r a m , r a d i o g r a p h y , blood sampling, all of which have r e q u i r e d a skilled o p e r a t o r and a technique of which the o r d i n a r y s h e e p f a r m e r would p e r h a p s be incapable, quite a p a r t f r o m the t i m e b e f o r e r e s u l t s w e r e obtained and c o s t s involved with t h e s e m e t h o d s . However, the a p p l i c a tion of the Doppler p r i n c i p l e u s i n g u l t r a s o u n d o f f e r s a method which the s h e e p b r e e d e r without any t e c h n i c a l knowledge could u s e p e r s o n a l l y to d e t e r m i n e p r e g n a n c y . In fact, what method could be m o r e p o s i t i v e and r e a s s u r i n g than to h e a r the actual foetal h e a r t beating ?
A second application for Doppler u l t r a s o u n d i s in the p e r i p h e r a l c i r c u l a t i o n of the body and a lot of valuable i n v e s t i g a tions a r e being c a r r i e d out in s e v e r a l p l a c e s . It is p o s s i b l e to follow the c o u r s e of an a r t e r y and such a b n o r m a l i t i e s a s cons t r i c t i o n s , a n e u r i s m s and e m b o l i s m s can be detected. In this connection, a study of the r e n a l a r t e r y is in hand in an a t t e m p t to d e t e r m i n e e a r l y s i g n s of t i s s u e r e j e c t i o n following kidney t r a n s p l a n t s . If a s u c c e s s f u l method i s developed, this could open up an e n t i r e l y new field. F u t u r e u s e s for this type of i n s t r u m e n t a r e m o s t encouraging. In c a r d i o l o g i c a l work it will be p o s s i b l e to m o n i t o r the blood flow in the m a j o r v e s s e l s a s well a s the m o v e m e n t s in the h e a r t . T h i s will r e d u c e the n e c e s s i t y of i n s e r t i n g p r o b e s into the v e s s e l s t o g e t h e r with the a s s o c i a t e d d i s c o m f o r t to the patient. The m o n i t o r i n g of c e r e b r a l blood flow following t h r o m b o s i s and h a e m o r r h a g e could give a c l e a r e r indication of the p a t i e n t ' s condition; the p a s s a g e of g a s t r i c j u i c e s and u r i n e will be a valuable study; the u s e of i n t r a - v a g i n a l t r a n s d u c e r s i s showing p r o m i s e in gynaecological work. New p o s s i b i l i t i e s a r e continually a r i s i n g and the i n d u s t r i a l field is virtually unexplored. T h e r e a r e obviously l i m i t a t i o n s at the p r e s e n t time. A i r in the lungs t e n d s to r e s t r i c t the u s e of t h i s a r e a , but this might well be o v e r c o m e . The advantages o v e r o t h e r m e t h o d s , howe v e r , a r e c o n s i d e r a b l e . The e s s e n t i a l equipment is low in c o s t and s i m p l e to o p e r a t e . It i s c o m p a c t and p o r t a b l e and the s a m e b a s i c unit can be u s e d for s e v e r a l applications with suitable t r a n s d u c e r s . Most i m p o r t a n t , p e r h a p s , i s that it c a u s e s no d i s c o m f o r t w h a t s o e v e r to the patient and in many c a s e s can even be u s e d without d i s t u r b a n c e f r o m sleep.
\ !
f !
t
]
!
i Fig 2 Section showing full t e r m pregnancy
V E T E R I N A R Y APPLICATION In animal b r e e d i n g , r e c e n t t r i a l s have shown that the u s e of a s m a l l , p o r t a b l e b a t t e r y o p e r a t e d U l t r a s o n i c Blood Flow Det e c t o r has t r e m e n d o u s potential for the d i a g n o s i s of p r e g nancy and a s this c o v e r s a wide field it is p r o p o s e d to m e n tion its application and r e s u l t s on sheep, although a c o n s i d e r able amount of work has been done on pigs and o t h e r a n i m a l s . F o r many g e n e r a t i o n s , s h e e p f a r m e r s with t r a d i t i o n a l knowledge, skill and e x p e r i e n c e have b r e d fine s h e e p and in turn p r o d u c e d good mutton and wool for our food and clothing. How then can s c i e n c e help t h e m ? In p a r t i c u l a r how can u l t r a s o n i c s help the s h e e p b r e e d e r ? With the many p r o b l e m s that e x i s t in m o d e r n s h e e p f a r m i n g s u c h a s the high c o s t of feeding stuffs, the m o r t a l i t y r a t e at lambing t i m e and the actual e c o n o m i c s of b r e e d i n g , the two i m p o r t a n t f a c t o r s which c o n c e r n the s h e e p f a r m e r and in which u l t r a s o u n d can help a r e the following:1 D i a g n o s i s of p r e g n a n c y in e w e s a s e a r l y a s p o s s i b l e so that e w e s found to be b a r r e n could e i t h e r be r e - m a t e d or fed n o r m a l l y on r e l a t i v e l y cheap r a t i o n s until the next mating season. 2 A c c u r a t e d i a g n o s i s of l i t t e r s i z e s , so that during the l a s t 6-8 w e e k s of p r e g n a n c y e w e s with twins, t r i p l e t s o r m o r e can be fed a c c o r d i n g l y , a s it i s g e n e r a l l y a c c e p t e d that good n u t r i tion at t h i s vital stage of g e s t a t i o n should r e s u l t in i n c r e a s e d l a m b b i r t h weights and a l s o r e d u c e lamb d e a t h s . Over the y e a r s t h e r e have been s e v e r a l m e t h o d s u s e d in many d i f f e r e n t c o u n t r i e s for d i a g n o s i s of p r e g n a n c y in e w e s :
During t r i a l s that have been conducted on s h e e p , the ewe was placed in the s h e a r i n g p o s i t i o n and the r e g i o n to be e x a m i n e d was the a r e a below the u m b i l i c u s . Olive oil o r s i m i l a r m e dium was applied on the abdomen in o r d e r to exclude a i r between the skin and t r a n s d u c e r . In e a r l y p r e g n a n c i e s foetal sounds w e r e d e t e c t e d when the t r a n s d u c e r w a s placed in f r o n t of the udder to e i t h e r side of the m i d i i n e , a s shown in Fig 3. F o e t a l h e a r t sounds r e c e i v e d w e r e of a " c l i p - c l o p " n a t u r e and the r a t e v a r i e d s o m e w h e r e between 140-200 b e a t s p e r minute. To avoid any confusion between the m a t e r n a l and foetal r a t e the t r a n s d u c e r was placed o v e r the e w e ' s own h e a r t , which when n o r m a l is 75-80 b e a t s p e r minute, and the d i f f e r e n c e in r a t e s i s then i m m e d i a t e l y a p p a r e n t . The p e r i o d of g e s t a t i o n for a ewe i s between 143-147 d a y s and during the initial t r i a l s an i n e x p e r i e n c e d o p e r a t o r d e t e c t e d foetal life a s e a r l y a s 52 days on s o m e e w e s and s u r p r i s i n g l y a c h i e v e d 100% a c c u r a c y in diagnosing p r e g n a n c y in 23 s h e e p at 80 d a y s and o v e r . This i n d i c a t e s that an u n t r a i n e d o p e r a t o r could e a s i l y use an u l t r a sonic i n s t r u m e n t and p e r h a p s a f t e r p r a c t i c e and t r a i n i n g could develop his own t e c h n i q u e s and p o s s i b l y achieve even g r e a t e r s u c c e s s in d i a g n o s i s . The length of t i m e n e c e s s a r y to d i a g n o s e p r e g n a n c y using u l t r a s o u n d is e x t r e m e l y i n t e r e s t ing, a s it took under 2 m i n u t e s to d e t e c t p r e g n a n c y and about 4 m i n u t e s to d e t e r m i n e n o n - p r e g n a n c y . The d i a g n o s i s of l i t t e r s i z e by u l t r a s o u n d was not so s u c c e s s ful and h a s v a r i e d b e t w e e n 50% and 75°/° a c c u r a c y , caused by the inability of the o p e r a t o r to p h y s i c a l l y count the v e r y r a p i d foetal h e a r t b e a t s and to d e t e r m i n e how many by the s l i g h t d i f f e r e n c e in r a t e s . However, it wilt be a p p r e c i a t e d that the ULTRASONICS J a n u a r y 1969
37
ULTRASCINICS
FOIR I N D U S T R Y
'I19B8 Conference Paper
e r r o r s o c c u r r i n g a r e not the fault of the i n s t r u m e n t , but that of the o p e r a t o r and that the inclusion of an instant r a t e m e t e r h e r e should solve this p r o b l e m and provide a much m o r e r e liable and a c c u r a t e guide to l i t t e r s i z e . The future in this field i s exciting, p a r t i c u l a r l y with the dev e l o p m e n t of a n c i l l a r y equipment for the U l t r a s o n i c Blood Flow D e t e c t o r such a s the R a t e m e t e r , C h a r t R e c o r d e r and p a r t i c u l a r l y the I n t e r n a l P r o b e - F i g s 4 and 5, with which it is felt that it might be p o s s i b l e to d i a g n o s e p r e g n a n c y much e a r l i e r , by d e t e c t i n g the flow of blood through the u t e r i n e a r t e r y into a g r a v i d or n o n - g r a v i d u t e r u s . A s s c i e n c e i s able to help the s h e e p b r e e d e r , it is p o s s i b l e that s c i e n c e may r e c e i v e a bonus with a feedback of i n f o r m a tion to the m e d i c a l field.
Fig 4 Internal t r a n s d u c e r for detection of u t e r i n e a r t e r y
Fig 3 N o r m a l t r a n s d u c e r position for diagnosing pregnancy in the ewe
38
ULTRASONICS J a n u a r y 1969
Fig 5 I n s t r u m e n t p r o d u c e d s p e c i f i c a l l y for v e t e r i n a r y applications
~
INDUSTRY
~
Conference Paper
Diagnostic applications of Doppler ultrasound F. D. F i e l d e r and R. F. Baker*
The Doppler p r i n c i p l e u s i n g low i n t e n s i t y u l t r a s o u n d is a p plied to m e d i c a l d i a g n o s i s . In d i a g n o s i s of p r e g n a n c y a f r e quency of 2 - 2 . 5 M H z is c h o s e n . T h e U l t r a s o n i c Blood Flow D e t e c t o r h a s t r e m e n d o u s p o t e n t i a l f o r t h e d i a g n o s i s of pregnancy.
A field of r e s e a r c h which i s a r o u s i n g c o n s i d e r a b l e i n t e r e s t in m a n y a r e a s of m e d i c a l d i a g n o s i s is t h e a p p l i c a t i o n of t h e Doppler p r i n c i p l e u s i n g v e r y low i n t e n s i t y u l t r a s o u n d . E v e n at t h i s e a r l y s t a g e , the field i s so b r o a d t h a t it will only be p o s s i b l e to b r i e f l y d e s c r i b e s o m e of the m a n y a s p e c t s of t h i s work. B a s i c a l l y , t h e D o p p l e r e f f e c t in t h i s a p p l i c a t i o n i s t h a t when s o u n d w a v e s a r e r e f l e c t e d f r o m a m o v i n g object t h e y a r e s h i f t e d s l i g h t l y in f r e q u e n c y , t h e shift being p r o p o r t i o n a l to the speed of the object. In the living body t h e r e a r e n u m e r o u s f u n c t i o n a l m o v e m e n t s which r e f l e c t u l t r a s o u n d ; blood flowing t h r o u g h a r t e r i e s , the a c t i o n s of t h e h e a r t , i n t e s t i n a l m o v e m e n t s and p a s s a g e of u r i n e and g a s t r i c j u i c e s . The e q u i p m e n t r e q u i r e d to p e r f o r m the b a s i c f u n c t i o n of p r o d u c i n g an audible sound f r o m t h e s e m o v e m e n t s i s f a i r l y s i m p l e and c a n t h e r e f o r e be p r o d u c e d at a r e l a t i v e l y low cost. F i g 1 s h o w s a block d i a g r a m of a t y p i c a l i n s t r u m e n t . The u l t r a s o n i c s i g n a l is g e n e r a t e d by an o s c i l l a t o r at the r e q u i r e d f r e q u e n c y and c o n n e c t e d to one p i e z o - e l e c t r i c c r y s t a l in the t r a n s d u c e r a s s e m b l y . T h i s v i b r a t e s at the s a m e f r e q u e n c y and e m i t s high f r e q u e n c y sound into the body. T h e sound is r e f l e c t e d by i n t e r n a l o r g a n s b a c k to a s e c o n d c r y s t a l which c o n v e r t s it to e l e c t r i c a l e n e r g y which i s fed into a v e r y low n o i s e tuned a m p l i f i e r . A f t e r r e c t i f i c a t i o n it i s f u r t h e r a m p l i fied, f i l t e r e d and c o n n e c t e d to a l o u d s p e a k e r or h e a d p h o n e s . If no m o v e m e n t is p r e s e n t at the sight of t h e r e f l e c t i o n only a s l i g h t h i s s is h e a r d . If, h o w e v e r , t h e r e i s m o v e m e n t the f r e q u e n c y of t h e r e f l e c t e d sound a l t e r s s l i g h t l y and b e a t s with the t r a n s m i t t e d s i g n a l , the d i f f e r e n c e b e t w e e n the two c r e a t i n g an audible sound. A u s e f u l f e a t u r e is t h a t i s is p o s s i b l e , with c a r e f u l d e s i g n , t o c o n t r o l the o v e r a l l b e a m - w i d t h of t h e t r a n s d u c e r which g r e a t ly a s s i s t s the d e t e c t i o n of m i n u t e a r e a s of m o v e m e n t and d e t e r m i n i n g the location of t h e s e . The a c o u s t i c i n t e n s i t y of the u l t r a s o u n d m u s t be kept to t h e lowest u s a b l e level to r e d u c e any p o s s i b l e r i s k of s i d e e f f e c t s to the m i n i m u m . In t h i s c o n n e c t i o n , t h e r e is no e v i d e n c e f r o m the m a n y t h o u s a n d s of p r e g n a n t p a t i e n t s e x a m i n e d with t h i s type of i n s t r u m e n t to i n d i c a t e that any h a z a r d s e x i s t . In the v a r i o u s a p p l i c a t i o n s i n v e s t i g a t e d so f a r it h a s not b e e n found n e c e s s a r y to u s e an i n t e n s i t y g r e a t e r t h a n about 1 2 m W / c m 2 and in s o m e c a s e s only a few m i l l i w a t t s . T h i s is v a s t l y d i f f e r e n t to the m a n y w a t t s e m p l o y e d in s o m e t h e r a p e u t i c a p p l i c a t i o n s of u l t r a s o u n d . S e l e c t i o n of f r e q u e n c y is a n o t h e r i m p o r t a n t f a c t o r . Some of the m o v e m e n t s a r e f a i r l y slow s p e e d and if the f r e q u e n c y of the u l t r a s o u n d i s too low, t h e s h i f t is not g r e a t enough to c r e a t e an a u d i b l e b e a t . On the o t h e r hand, the a t t e n u a t i o n due to a b s o r p t i o n in t i s s u e i n c r e a s e s in a l m o s t d i r e c t p r o p o r t i o n to f r e q u e n c y . At h i g h e r f r e q u e n c i e s it would t h e r e f o r e be n e c e s s a r y to i n c r e a s e the a c o u s t i c i n t e n s i t y in o r d e r to obtain deep p e n e t r a t i o n . A s a t i s f a c t o r y c o m p r o m i s e is * Sonicaid Ltd, Hook Lane, N y e t i m b e r , B o g n o r R e g i s , S u s s e x , England 36
ULTRASONICS J a n u a r y 1969
~ _ ~ ~
-IH H amplifier
and filter
amplifier
Recorderc : l Loud l~] speaker HF generotor F i g 1 Block D i a g r a m of t y p i c a l i n s t r u m e n t
b e t w e e n 2MHz and 2 . 5 M H z and the m a j o r i t y of m o v e m e n t s can be h e a r d at t h i s f r e q u e n c y . B e f o r e going into v a r i o u s a p p l i c a t i o n s i n v e s t i g a t e d to date, it i s n e c e s s a r y to outline the d i f f i c u l t i e s e n c o u n t e r e d with the u s e of u l t r a s o u n d in the body. E v e r y individual s u b s t a n c e , w h e t h e r liquid or solid, h a s a d i f f e r e n t a c o u s t i c i m p e d a n c e which i s the p r o d u c t of the d e n s i t y and v e l o c i t y of sound in the m e d i u m . U l t r a s o u n d i s r e f l e c t e d at a n y i n t e r f a c e w h e r e a d i f f e r e n c e in i m p e d a n c e o c c u r s . The g r e a t e r the d i f f e r e n c e , the g r e a t e r i s the r e f l e c t i o n and c o n s e q u e n t l y l e s s s i g n a l c o n t i n u e s into the n e x t m e d i u m . In the body, a n i m a l o r h u m a n , t h e r e a r e s e v e r a l l a y e r s of v a r y i n g t i s s u e b e t w e e n t h e o u t e r s u r f a c e and any i n t e r n a l o r g a n . A v a s t d i f f e r e n c e o c c u r s b e tween a i r a n d body t i s s u e and t h i s i m p o s e s l i m i t a t i o n s on the u s e at the p r e s e n t t i m e . L u n g s , s t o m a c h and i n t e s t i n e a l l contain a i r or g a s and p r a c t i c a l l y the total s i g n a l i s p r e v e n t e d f r o m p a s s i n g t h r o u g h t h e s e c a v i t i e s . S c a t t e r i n g and a b s o r p tion a l s o r e d u c e the s i g n a l and t h i s a g a i n v a r i e s with the v a r i e t y of t i s s u e s e n c o u n t e r e d . T h e a t t e n u a t i o n due to a b s o r p tion at 2 . 4 M H z i s a p p r o x i m a t e l y 0 . 2 d B / c m f o r blood, 3 d B / c m for m u s c l e and r i s i n g to a r o u n d 1 0 d B / c m f o r s o m e bone s t r u c t u r e s . T h e r e f l e c t i o n and a t t e n u a t i o n o c c u r s with both the e m i t t e d and r e t u r n s i g n a l s , c o n s e q u e n t l y we r e c e i v e only a m i n u t e f r a c t i o n of the t r a n s m i t t e d sound. M o s t l i q u i d s , howe v e r , a r e e x c e l l e n t t r a n s m i s s i o ~ m e d i a and e x h i b i t v e r y little a t t e n u a t i o n , the f i g u r e for w a t e r being a s low a s 0. 0 1 4 d B / c m . By f a r the l a r g e s t i n i t i a l a p p l i c a t i o n f o r D o p p l e r i n s t r u m e n t s i s in o b s t e t r i c s which i s l a r g e l y b e c a u s e of the e a s e with which one can e m i t and r e c e i v e u l t r a s o u n d in a p r e g n a n t u t e r u s . In a p r e g n a n c y of 10-12 w e e k s p o r t i o n s of i n t e s t i n e c a n lie b e t w e e n the a b d o m i n a l wall and the u t e r u s and in m a n y c a s e s i m p e d e the t r a n s m i s s i o n of u l t r a s o u n d . H o w e v e r , lying a l m o s t in f r o n t of the u t e r u s i s the b l a d d e r and if t h i s is filled with u r i n e we h a v e an e x c e l l e n t t r a n s m i s s i o n tank t h r o u g h which the u l t r a s o u n d i s b e a m e d . V a r i o u s r e f l e c t i o n s
tJLTIEKa~DN~_~ ~ o c c u r at the s t a t i o n a r y i n t e r f a c e s but m o v e m e n t s of the foetal h e a r t and blood flow can be c l e a r l y d e t e c t e d . Fig 2 shows a p r e g n a n c y n e a r i n g full t e r m . It can be s e e n that, a p a r t f r o m p a t i e n t s with s e v e r e o b e s i t y , t h e r e i s only a f a i r l y thin l a y e r of v a r i o u s t i s s u e s b e t w e e n the o u t e r s u r f a c e and the u t e r u s . The u t e r i n e cavity is c o m p l e t e l y filled with liquor which c o n s i s t s of 98.8% w a t e r , the b a l a n c e c o n s i s t i n g of p r o t e i n , sodium c h l o r i d e and o t h e r s o l i d s , and at full t e r m t h e r e i s a p p r o x i m a t e l y 2 pints which e n t i r e l y s u r r o u n d s the foetus. With this c l e a r path for the u l t r a s o u n d we can d e t e c t the blood flow in the u m b i l i c a l cord, p l a c e n t a and m a j o r foetal v e s s e l s a s well a s the foetal h e a r t and m a t e r n a l a r t e r i e s and all of t h e s e a r e c l e a r l y identified. Due to the d i r e c t i o n a l p r o p e r t i e s of the t r a n s d u c e r the r e l a t i v e location of t h e s e o r g a n s can be d e t e r m i n e d .
INEXJBTP/Y
Conference Paper
E x t e r n a l palpation, i n t e r n a l palpation via l a p a r o t o m y , vaginal s m e a r , foetal e l e c t r o c a r d i o g r a m , r a d i o g r a p h y , blood sampling, all of which have r e q u i r e d a skilled o p e r a t o r and a technique of which the o r d i n a r y s h e e p f a r m e r would p e r h a p s be incapable, quite a p a r t f r o m the t i m e b e f o r e r e s u l t s w e r e obtained and c o s t s involved with t h e s e m e t h o d s . However, the a p p l i c a tion of the Doppler p r i n c i p l e u s i n g u l t r a s o u n d o f f e r s a method which the s h e e p b r e e d e r without any t e c h n i c a l knowledge could u s e p e r s o n a l l y to d e t e r m i n e p r e g n a n c y . In fact, what method could be m o r e p o s i t i v e and r e a s s u r i n g than to h e a r the actual foetal h e a r t beating ?
A second application for Doppler u l t r a s o u n d i s in the p e r i p h e r a l c i r c u l a t i o n of the body and a lot of valuable i n v e s t i g a tions a r e being c a r r i e d out in s e v e r a l p l a c e s . It is p o s s i b l e to follow the c o u r s e of an a r t e r y and such a b n o r m a l i t i e s a s cons t r i c t i o n s , a n e u r i s m s and e m b o l i s m s can be detected. In this connection, a study of the r e n a l a r t e r y is in hand in an a t t e m p t to d e t e r m i n e e a r l y s i g n s of t i s s u e r e j e c t i o n following kidney t r a n s p l a n t s . If a s u c c e s s f u l method i s developed, this could open up an e n t i r e l y new field. F u t u r e u s e s for this type of i n s t r u m e n t a r e m o s t encouraging. In c a r d i o l o g i c a l work it will be p o s s i b l e to m o n i t o r the blood flow in the m a j o r v e s s e l s a s well a s the m o v e m e n t s in the h e a r t . T h i s will r e d u c e the n e c e s s i t y of i n s e r t i n g p r o b e s into the v e s s e l s t o g e t h e r with the a s s o c i a t e d d i s c o m f o r t to the patient. The m o n i t o r i n g of c e r e b r a l blood flow following t h r o m b o s i s and h a e m o r r h a g e could give a c l e a r e r indication of the p a t i e n t ' s condition; the p a s s a g e of g a s t r i c j u i c e s and u r i n e will be a valuable study; the u s e of i n t r a - v a g i n a l t r a n s d u c e r s i s showing p r o m i s e in gynaecological work. New p o s s i b i l i t i e s a r e continually a r i s i n g and the i n d u s t r i a l field is virtually unexplored. T h e r e a r e obviously l i m i t a t i o n s at the p r e s e n t time. A i r in the lungs t e n d s to r e s t r i c t the u s e of t h i s a r e a , but this might well be o v e r c o m e . The advantages o v e r o t h e r m e t h o d s , howe v e r , a r e c o n s i d e r a b l e . The e s s e n t i a l equipment is low in c o s t and s i m p l e to o p e r a t e . It i s c o m p a c t and p o r t a b l e and the s a m e b a s i c unit can be u s e d for s e v e r a l applications with suitable t r a n s d u c e r s . Most i m p o r t a n t , p e r h a p s , i s that it c a u s e s no d i s c o m f o r t w h a t s o e v e r to the patient and in many c a s e s can even be u s e d without d i s t u r b a n c e f r o m sleep.
\ !
f !
t
]
!
i Fig 2 Section showing full t e r m pregnancy
V E T E R I N A R Y APPLICATION In animal b r e e d i n g , r e c e n t t r i a l s have shown that the u s e of a s m a l l , p o r t a b l e b a t t e r y o p e r a t e d U l t r a s o n i c Blood Flow Det e c t o r has t r e m e n d o u s potential for the d i a g n o s i s of p r e g nancy and a s this c o v e r s a wide field it is p r o p o s e d to m e n tion its application and r e s u l t s on sheep, although a c o n s i d e r able amount of work has been done on pigs and o t h e r a n i m a l s . F o r many g e n e r a t i o n s , s h e e p f a r m e r s with t r a d i t i o n a l knowledge, skill and e x p e r i e n c e have b r e d fine s h e e p and in turn p r o d u c e d good mutton and wool for our food and clothing. How then can s c i e n c e help t h e m ? In p a r t i c u l a r how can u l t r a s o n i c s help the s h e e p b r e e d e r ? With the many p r o b l e m s that e x i s t in m o d e r n s h e e p f a r m i n g s u c h a s the high c o s t of feeding stuffs, the m o r t a l i t y r a t e at lambing t i m e and the actual e c o n o m i c s of b r e e d i n g , the two i m p o r t a n t f a c t o r s which c o n c e r n the s h e e p f a r m e r and in which u l t r a s o u n d can help a r e the following:1 D i a g n o s i s of p r e g n a n c y in e w e s a s e a r l y a s p o s s i b l e so that e w e s found to be b a r r e n could e i t h e r be r e - m a t e d or fed n o r m a l l y on r e l a t i v e l y cheap r a t i o n s until the next mating season. 2 A c c u r a t e d i a g n o s i s of l i t t e r s i z e s , so that during the l a s t 6-8 w e e k s of p r e g n a n c y e w e s with twins, t r i p l e t s o r m o r e can be fed a c c o r d i n g l y , a s it i s g e n e r a l l y a c c e p t e d that good n u t r i tion at t h i s vital stage of g e s t a t i o n should r e s u l t in i n c r e a s e d l a m b b i r t h weights and a l s o r e d u c e lamb d e a t h s . Over the y e a r s t h e r e have been s e v e r a l m e t h o d s u s e d in many d i f f e r e n t c o u n t r i e s for d i a g n o s i s of p r e g n a n c y in e w e s :
During t r i a l s that have been conducted on s h e e p , the ewe was placed in the s h e a r i n g p o s i t i o n and the r e g i o n to be e x a m i n e d was the a r e a below the u m b i l i c u s . Olive oil o r s i m i l a r m e dium was applied on the abdomen in o r d e r to exclude a i r between the skin and t r a n s d u c e r . In e a r l y p r e g n a n c i e s foetal sounds w e r e d e t e c t e d when the t r a n s d u c e r w a s placed in f r o n t of the udder to e i t h e r side of the m i d i i n e , a s shown in Fig 3. F o e t a l h e a r t sounds r e c e i v e d w e r e of a " c l i p - c l o p " n a t u r e and the r a t e v a r i e d s o m e w h e r e between 140-200 b e a t s p e r minute. To avoid any confusion between the m a t e r n a l and foetal r a t e the t r a n s d u c e r was placed o v e r the e w e ' s own h e a r t , which when n o r m a l is 75-80 b e a t s p e r minute, and the d i f f e r e n c e in r a t e s i s then i m m e d i a t e l y a p p a r e n t . The p e r i o d of g e s t a t i o n for a ewe i s between 143-147 d a y s and during the initial t r i a l s an i n e x p e r i e n c e d o p e r a t o r d e t e c t e d foetal life a s e a r l y a s 52 days on s o m e e w e s and s u r p r i s i n g l y a c h i e v e d 100% a c c u r a c y in diagnosing p r e g n a n c y in 23 s h e e p at 80 d a y s and o v e r . This i n d i c a t e s that an u n t r a i n e d o p e r a t o r could e a s i l y use an u l t r a sonic i n s t r u m e n t and p e r h a p s a f t e r p r a c t i c e and t r a i n i n g could develop his own t e c h n i q u e s and p o s s i b l y achieve even g r e a t e r s u c c e s s in d i a g n o s i s . The length of t i m e n e c e s s a r y to d i a g n o s e p r e g n a n c y using u l t r a s o u n d is e x t r e m e l y i n t e r e s t ing, a s it took under 2 m i n u t e s to d e t e c t p r e g n a n c y and about 4 m i n u t e s to d e t e r m i n e n o n - p r e g n a n c y . The d i a g n o s i s of l i t t e r s i z e by u l t r a s o u n d was not so s u c c e s s ful and h a s v a r i e d b e t w e e n 50% and 75°/° a c c u r a c y , caused by the inability of the o p e r a t o r to p h y s i c a l l y count the v e r y r a p i d foetal h e a r t b e a t s and to d e t e r m i n e how many by the s l i g h t d i f f e r e n c e in r a t e s . However, it wilt be a p p r e c i a t e d that the ULTRASONICS J a n u a r y 1969
37
ULTRASCINICS
FOIR I N D U S T R Y
'I19B8 Conference Paper
e r r o r s o c c u r r i n g a r e not the fault of the i n s t r u m e n t , but that of the o p e r a t o r and that the inclusion of an instant r a t e m e t e r h e r e should solve this p r o b l e m and provide a much m o r e r e liable and a c c u r a t e guide to l i t t e r s i z e . The future in this field i s exciting, p a r t i c u l a r l y with the dev e l o p m e n t of a n c i l l a r y equipment for the U l t r a s o n i c Blood Flow D e t e c t o r such a s the R a t e m e t e r , C h a r t R e c o r d e r and p a r t i c u l a r l y the I n t e r n a l P r o b e - F i g s 4 and 5, with which it is felt that it might be p o s s i b l e to d i a g n o s e p r e g n a n c y much e a r l i e r , by d e t e c t i n g the flow of blood through the u t e r i n e a r t e r y into a g r a v i d or n o n - g r a v i d u t e r u s . A s s c i e n c e i s able to help the s h e e p b r e e d e r , it is p o s s i b l e that s c i e n c e may r e c e i v e a bonus with a feedback of i n f o r m a tion to the m e d i c a l field.
Fig 4 Internal t r a n s d u c e r for detection of u t e r i n e a r t e r y
Fig 3 N o r m a l t r a n s d u c e r position for diagnosing pregnancy in the ewe
38
ULTRASONICS J a n u a r y 1969
Fig 5 I n s t r u m e n t p r o d u c e d s p e c i f i c a l l y for v e t e r i n a r y applications