MRI
t r a c t i o n s
o f m u s c l e s a t t a c h e d t o
o t h e r
s o f t t i s s u e s . T h e s e m o v e m e n t s m a y b e
v o l u n t a r y o r r e f l e x .
T h e m o v e m e n t s o f t h e i n t e r n a l o r g -
a n s
a r e
i n v o l u n t a r y ;
t h e y
i n c l u d e
t h e
h e a r t b e a t
a n d
p e r i s t a l s i s
.
m o v e m e n t, lo s s o f
S e e
a k i n e s i a
.
m o x ib u s tio n
A f o r m
o f t r e a t m e n t ,
o f t e n u s e d w i t h
a c u p u n c t u r e
,
i n w h i c h a c o n e o f w o r m
-
w o o d
l e a v e s
( m o x a )
o r
c e r t a i n
o t h e r
p l a n t m a t e r i a l s i s b u r n e d j u s t a b o v e t h e
s k i n t o r e l i e v e i n t e r n a l p a i n .
m o x is y ly te
A
v a s o d i l a t o r d r u g
u s e d t o t r e a t
R a y n a u d ’s
d i s e a s e
.
S i d e e f f e c t s i n c l u d e n a u s e a , d i a r -
r h o e a , h o t f l u s h e s , h e a d a c h e , a n d d i z z i n e s s .
M RI
T h e
a b b r e v i a t i o n
f o r
m a g n e t i c
r e s o -
n a n c e
i m a g i n g .
M R I
i s
a
d i a g n o s t i c
t e c h n i q u e t h a t p r o d u c e s c r o s s - s e c t i o n a l
o r t h r e e - d i m e n s i o n a l i m a g e s o f o r g a n s
a n d o t h e r b o d y s t r u c t u r e s .
HOW IT IS DONE
T h e
p a t i e n t
l i e s
i n s i d e
a s c a n n e r
s u r -
r o u n d e d b y a l a r g e , p o w e r f u l m a g n e t . A
r e c e i v i n g m a g n e t i s p l a c e d a r o u n d t h e
p a r t o f t h e b o d y t o b e i n v e s t i g a t e d . I f
l a r g e a r e a s , s u c h a s t h e a b d o m e n , a r e t o
b e i m a g e d , t h e r e c e i v i n g m a g n e t i s f i t -
t e d
i n s i d e
t h e
s c a n n e r ;
f o r
a
s m a l l e r
a r e a , s u c h a s a j o i n t , a m a g n e t m a y b e
p l a c e d a r o u n d t h e p a r t t o b e s c a n n e d .
T h e s c a n n e r g e n e r a t e s a s t r o n g m a g -
n e t i c f i e l d , w h i c h c a u s e s t h e a t o m s i n
t h e
b o d y
t o
l i n e
u p
p a r a l l e l
t o
e a c h
o t h e r . S h o r t p u l s e s o f r a d i o w a v e s f r o m
a
r a d i o f r e q u e n c y
s o u r c e
b r i e f l y
k n o c k
t h e
a t o m s
o u t
o f
a l i g n m e n t .
A s
t h e
a t o m s
r e a l i g n
t h e y
e m i t
t i n y
s i g n a l s ,
w h i c h
a r e
d e t e c t e d
b y
t h e
r e c e i v i n g
m a g n e t . I n f o r m
a t i o n a b o u t t h e s e s i g n a l s
i s p a s s e d t o a c o m p u t e r , w h i c h b u i l d s
u p
a n
i m a g e
b a s e d
o n
t h e
s i g n a l s ’
s t r e n g t h a n d l o c a t i o n .
M R I i m a g e s c a n b e e n h a n c e d b y u s e
o f a
c o n t r a s t m e d i u m
t o h i g h l i g h t p a r t i c -
u l a r b o d y s t r u c t u r e s ,
s u c h a s t u m o u r s
a n d b l o o d v e s s e l s .
WHY IT IS DONE
I m a g e s f r o m M R I a r e s i m i l a r t o t h o s e
p r o d u c e d b y
C T s c a n n i n g
,
b u t t h e y g i v e
g r e a t e r
c o n t r a s t
b e t w e e n
n o r m a l
a n d
a b n o r m a l
t i s s u e s .
M R I
i s
u s e f u l
f o r
s t u d y i n g t h e b r a i n a n d s p i n a l c o r d , t h e
i n t e r n a l
s t r u c t u r e
o f t h e
e y e
a n d
e a r ,
t h e i n t e r n a l o r g a n s , a n d b l o o d f l o w .
MAGNETIC RESONANCE IMAGING (MRI)
A valuable diagnostic technique, MRI has been in use since the early 1980s. The
patient lies down and is surrounded by a massive electromagnet and is exposed to
short bursts of powerful magnetic fields and radio-waves. The bursts stimulate protons
(hydrogen nuclei) in the patient’s tissues to emit radio signals, which are detected and
analysed by computer to create an image of a “slice” of the patient’s body.
THE SCANNING PROCESS
An MRI scanner consists of a
powerful electromagnet, a radio-
wave emitter, and a radio-wave
detector. A plane of the body is
selected for imaging and the
electromagnet is turned on.
.
R a d i o - w a v e s o u r c e
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R a d i o - w a v e s t i m u l a t i o n
2
Next, the radio-wave source emits a
powerful pulse of radio-waves, which
knocks the protons out of alignment.
1
Normally, the protons (nuclei) of
the body’s hydrogen atoms point
randomly in different directions, but under
the influence ofthe scanner’s powerful
magnetic field they align themselves in
the same direction.
R a d io - w a v e
3
However, milliseconds later, the protons
realign themselves. As they do so, they
emit faint radio signals, which are picked up
by the scanner’s radio-wave detector.
M
517
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