Læknablaðið - 15.03.1984, Side 50

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LÆK.NABLADIÐ
scanning like CT is an effective method of
diagnosing and distinguishing between extra-
cerebral and intra-cerebral lesions (Fig. 7).
There are good grounds for believing that the
problem of the isodense subdural haematoma
which is encountered with CT scanning can
almost certainly be obviated with NMR (8). In
vascular malformation and giant aneurysms
(Fig. 8) flow dependent sequences allow their
diagnosis without the need for any contrast
media. Performed as the initial investigation
NMR removes the need for angiography
where the size of site of the angioma would
preclude operation and in other cases pro-
vides useful anatomical information comple-
menting the angiogram.
In the study of the brain stem, the upper
cervical cord and lesions impinging on the
midline ventricular system the sagittal plane is
extremely valuable. The assessment of conge-
nital and acquired abnormalities (Fig. 9) at or
adjacent to the cranial vertebral junction is
simplified by the use of NMR imaging and this
will probably allow the more invasive proce-
dures to be avoided (9).
The exquisite discrimination between grey
and white matter shown on T^ weighted
images (Fig. 10) has now been well document-
ed and their application to the study of the
normal time course of myelination in the
infant brain and to the diagnosis of demyelinat-
ing disorders has been reported by the Ham-
mersmith Group (10, 11).
Although images weighted by T2 (Fig. 11)
are relatively featureless they have been
shown to be a sensitive scan mode in the
detection of a wide variety of intra-cranial
pathologies (12).
As with CT orbital examinations display the
globes, optic nerve and extra-ocular muscles
contrasted against the retrobulbar fat. The
multiplanar facility of NMR is useful to
establish the precise relationship of tumours
to normal structures (13).
BODY SCANNING
Despite the inevitable degrading effects of
involuntary body movements such as respira-
tion and peristalsis satisfactory images of the
abdomen and pelvis can be obtained with a
scan time of between 2 and 4 minutes (14). The
principal solid organs can be identified and
several textural and density differences are
noted as between the liver and spleen. Depo-
sits of fat give a high signal and in the retro-
peritoneal space this allows the kidneys and
adrenal glands to be clearly outlined (Fig. 12).
The walls and lumen of the principal blood
vessels are readily identified on flow depen-
dent sequences and the spinal column and
paravertebral muscles are well shown. More
significantly the spinal cord can be displayed
without the use of intra-thecal contrast media
which is necessary in CT. Within the pelvis the
bladder can be clearly identified with its walls
being contrasted against surrounding extra-
peritoneal fat and urine within. In the male a
combined study of transverse and sagittal
sections allows the mutual relationships be-
tween the bladder, prostate, seminal vesicles
and rectum to be shown in detaii (Fig. 13). In
the female the uterus is seen as a homogen-
Fig. 8. Transverse scans in a patient with a giant
supra-sellar aneurysm. The contents of the aneu-
rysm give a zero signal with a) the modified SSFP
sequence and b) the unmodified SSFP sequence
indicating the presence of blood in motion.