ULTRASONOGRAPHY, DOPPLER
U
HOW ULTRASOUND SCANNING WORKS
Ultrasound waves are emitted by a
transducer, a device placed on the skin
over the area to be viewed. Gel is used
to ensure good contact between the
transducer and the skin. The transducer
contains a crystal that converts an
electric current into sound waves. The
waves have frequencies in the range of
1 to 15 million hertz. At these high
frequencies, they can be focused into
a fine parallel beam, which passes
Operator
through a “slice” ofthe body if the
transducer crystal is oscillated back and
forth. Some ofthe waves are reflected
at tissue boundaries, so a series of
echoes is returned. The transducer also
acts as a receiver, converting these
echoes into electrical signals, which
are processed and displayed on a
screen as two-dimensional images of
the scanned bodyslice. Bymoving the
transducer, different slices can be seen.
Using ultrasound
Ultrasound haswide applications in medicine
and is especially useful in obstetrics. It offers no
known riskto the baby. By movement ofthe
transducer across the outer wall ofthe abdomen,
views ofthe growing fetus are obtained from various
angles, so it is possible to screen for abnormalities.
Transducer
,
Ultrasound
wave beams
Electronic
hardware
Image
Parts of an ultrasound scanner
The transducer emits a beam of
high frequencywaves, which are
passed through a slice ofthe body;
the echoes are picked up by the
transducer and converted bythe
electronic hardware into an image
displayed on the monitor.
Monitor
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DISORDERS
A
b l o w
t o
t h e
o le c ra n o n
p r o c e s s
( t h e
r o u n d e d
p r o j e c t i o n
a t
t h e
t i p
o f t h e
e l b o w ) ,
o v e r
w h i c h
t h e
u l n a r
n e r v e
p a s s e s , c a u s e s a p i n s - a n d - n e e d l e s s e n s a -
t i o n a n d p a i n i n t h e f o r e a r m a n d f o u r t h
a n d f i f t h f i n g e r s . R e p e a t e d l e a n i n g o n t h e
e l b o w c a n h a v e a s i m i l a r e f f e c t .
P e r s i s t e n t n u m b n e s s a n d w e a k n e s s i n
a r e a s c o n t r o l l e d b y t h e u l n a r n e r v e m a y
b e
c a u s e d b y a n a b n o r m a l b o n y
o u t -
g r o w t h f r o m
t h e
h u m e ru s
( u p p e r - a r m
b o n e ) ,
w h i c h
m a y
b e
d u e
t o
o s t e o -
a rth rit is
o r t o a f r a c t u r e o f t h e h u m e r u s .
S u r g e r y i s n e e d e d t o r e l i e v e t h e p r e s s u r e
o n
t h e
n e r v e .
I f t h e
c o n d i t i o n
i s
l e f t
u n t r e a t e d ,
i t
m a y
c a u s e
p e r m a n e n t
d a m a g e t o t h e u l n a r n e r v e , w h i c h c a n
r e s u l t i n
c la w - h a n d
.
u ltra s o n o g ra p h y , D o p p le r
S e e
D o p p le r u lt ra s o n o g ra p h y .
u ltra s o u n d
S o u n d w i t h a f r e q u e n c y t h a t i s g r e a t e r
t h a n t h e h u m a n e a r ’s u p p e r l i m i t o f p e r -
c e p t i o n :
t h a t
i s ,
h i g h e r
t h a n
2 0 , 0 0 0
h e r t z ( c y c l e s p e r s e c o n d ) . U l t r a s o u n d i s
u s e d i n m e d i c i n e t o p r o d u c e i m a g e s o f
b o d y s t r u c t u r e s a n d t h u s a i d d i a g n o s i s
( s e e
u lt ra s o u n d s c a n n in g ),
o r i n t r e a t m e n t
t o a i d h e a l i n g o r t o d e s t r o y a b n o r m a l i -
t i e s s u c h a s k i d n e y s t o n e s ( s e e
u lt ra s o u n d
trea tm en t; lith o trip s y ).
U l t r a s o u n d t h a t i s
u s e d f o r t h e s e p u r p o s e s i s t y p i c a l l y i n
t h e r a n g e o f 1 - 1 5 m
i l l i o n h e r t z .
u ltra s o u n d s c a n n in g
A
d i a g n o s t i c
t e c h n i q u e
i n
w h i c h
v e r y
h i g h f r e q u e n c y s o u n d w a v e s a r e p a s s e d
i n t o t h e b o d y a n d t h e r e f l e c t e d e c h o e s
a n a l y s e d t o b u i l d a p i c t u r e o f t h e i n t e r -
n a l o r g a n s o r o f a f e t u s i n t h e u t e r u s .
U n l i k e m o s t o t h e r i m a g i n g t e c h n i q u e s ,
u l t r a s o u n d s c a n n i n g c a n p r o d u c e m o v -
i n g
i m a g e s . T h e
p r o c e d u r e
i s
p a i n l e s s
a n d i s c o n s i d e r e d s a f e .
WHY IT IS DONE
T h e
a b i l i t y
o f u l t r a s o u n d s c a n n i n g
t o
s h o w s o f t t i s s u e s m a k e s t h e p r o c e d u r e
u s e f u l f o r e x a m i n i n g f l u i d - f i l l e d o r s o f t
s t r u c t u r e s w i t h i n t h e b o d y . U l t r a s o u n d
w a v e s
c a n n o t ,
h o w e v e r ,
p a s s
t h r o u g h
b o n e o r g a s ; t h e r e f o r e , t h e y a r e o f l i m
-
i t e d u s e f o r v i e w i n g a n y a r e a s t h a t a r e
s u r r o u n d e d b y b o n e ( s u c h a s t h e b r a i n
i n a d u l t s )
o r t h o s e t h a t a r e f i l l e d w i t h
g a s ( s u c h a s t h e l u n g s o r t h e i n t e s t i n e s ) .
Obstetric and neonatal uses
O n e o f t h e
m o s t c o m m o n u s e s o f u l t r a s o u n d i s t o
v i e w t h e u t e r u s a n d f e t u s , a t a n y t i m e
d u r i n g
p re g n a n c y .
T h e a g e , s i z e , a n d g r o w t h r a t e o f t h e
f e t u s c a n b e d e t e r m
i n e d b y m
e a n s o f
u l t r a s o u n d . I f t h e
d a t e o f c o n c e p t i o n
i s k n o w n , t h e s c a n s h o w s w h e t h e r t h e
f e t u s
i s
o f t h e
e x p e c t e d
s i z e
f o r
i t s
a g e ;
c o n v e r s e l y ,
t h e
s i z e
o f t h e
f e t u s
c a n h e l p t o e s t a b l i s h t h e a c c u r a t e d a t e
o f c o n c e p t i o n a n d t h e r e f o r e h e l p d o c -
t o r s
a n d
m i d w i v e s
t o
p r e d i c t
t h e
e x p e c t e d d a t e o f d e l i v e r y .
U l t r a s o u n d s c a n s w i l l s h o w i f t h e r e i s
m
o r e t h a n o n e f e t u s ( s e e
p re g n a n c y , m u l-
t ip le ).
T h e y
a l s o
a i d
t h e
d e t e c t i o n
o f
c e r t a i n p r o b l e m s i n t h e f e t u s , s u c h a s
n e u ra l tu b e d e fe c ts
o r
c o n g e n i t a l
h e a r t
d i s e a s e ,
s o
t h a t a n a f f e c t e d i n f a n t
c a n
r e c e i v e
t r e a t m e n t
a s
s o o n
a s
p o s s i b l e
a f t e r b i r t h . I n a d d i t i o n , t h e s c a n s s h o w
t h e p o s i t i o n o f t h e p l a c e n t a
( t h e o r g a n
t h r o u g h w h i c h t h e f e t u s r e c e i v e s o x y -
768
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