Læknablaðið - 15.03.1984, Síða 57

LÆK.NABLAÐIÐ
115
UNIVERSITY HOSPITAL NOTTINGHftN NMR UNIT
increase the small diffenrences in attenuation
value between blood amd myocardium. Whilst
the heart walls are in motion during systole
little signal is generated but during diastole a
signal appears from which the image is
derived. The end diastolic dimensions of the
ventricular cavities and wall thickness can be
assessed. These measurements should have
wide applications in assessment of chamber
size in congenital and acquired heart disease.
Such images will also show alterations in the
configuration of the heart chambers as for
example in (L) ventricular aneurysm (Fig. 19).
By gating the data acquisition to a pulse wave
recording end-systolic images can be pro-
duced thus permitting an estimate of the ven-
tricular ejection fraction. Because the wall
thickness is also shown it should be possible to
distinguish the different patterns associated
with pressure and volume overload of the
ventricles. The greatest potential of the tech-
nique however is the possibility of combining
in one study an assessment of alteration in the
myocardium following ischaemia on the basis
of reduced perfusion and altered water con-
tent together with an estimate of the conse-
quent alterations in ventricular function.
An excellent display of normal gross anato-
mical features of the musculo-skeletal system
has been found in NMR scans of the limbs
(19). In primary bone neoplasms the soft tissue
extension and degree of marrow infiltration
by tumour can be clearly shown (20).
CONCLUDING REMARKS
One of the few shortcomings of NMR is its
inherent low sensitivity and unlike CT scan-
ning where the signal to noise per unit time
can in principle be increased by increasing the
x-ray beam intensity the NMR signal at a
given field strength cannot be so increased
because its size depends on the net concentra-
tion of atoms being imaged. The price which
we pay for both the great versatility of NMR
and its low sensitivity is in the relatively long
time which it takes to carry out an examina-
tion. To come to terms with this limitation
methods are being developed which allow
multiple slices to be acquired during a single
NMR exposure. The lack of fine bone detail
and the inability to show small areas of
calcification are further drawbacks to NMR
imaging. Work is currently in progress to
develop contrast media which, as have proved
Fig. 16. Transverse section through the pelvis of
a patient with lymphoma a) normal resolution;
b) high resolution scan. The tumour deposit lies
anterior to the vertebral body displacing the left
psoas laterally. The left iliac vessels are seen to be
encased by tumour.
Fig. 17. Sagittal scan m a patient with a recurrent
ovarian tumour indenting the anterior wall of the
bladder.