This highlights the importance of
H MRS to
prove the presence of hepatic encephalopathy,
even when the blood analyses are normal.
Future studies include the investigation of the
metabolic profile in patients with hepatic
encephalopathy before and after treatment,
either medical or surgical. Another future project
would include the investigation of hepatic
encephalopathy in feline patients. It is suspected
that the pathophysiology in cats with hepatic
encephalopathy may be slightly different from
that found in dogs, since they respond in very
variable ways to medical and surgical treatments.
Shown in Fig. 3 is the typical short echo time
magnetic resonance spectra of a malignant
tumour (glioblastoma multiforme) in a nine-year-
old dog. The high peak of choline, extremely low
acetylaspartate and the high amount of lipids
correlate with a high degree of necrosis.
Neoplastic and inflammatory
Intracranial neoplasias and meningoencephalitis
are common diseases in dogs. Conventional
MRI allows characterising the morphology of the
lesion; however, it is not always possible to
distinguish between a neoplastic process and
an inflammatory one. This is crucial because the
treatment, as well as the prognosis, may be
H MRS in the brain of dogs with
neoplasia and inflammatory meningoencephalitis
in order to study the metabolic profile of these
diseases and to investigate if there were any
metabolites that could serve as indicators for
of the brain, including thalamus, parietal lobes, temporal lobes and
occipital lobes (Fig. 1), basal ganglia and cerebellum.
This study showed no differences between right and left hemispheres
and no differences between sexes. Statistically, significant metabolite
concentration in different regions of the brain was found. For instance,
the concentration of
acetylaspartate was highest in the parietal lobes
and lowest in the cerebellum, whilst the choline concentration was
highest in the basal ganglia and lowest in the occipital lobe. This study
provided reference values for clinical and research studies employing
H MRS technique. What follows are various clinical applications.
Brain metabolite abnormalities in dogs
Hepatic encephalopathy is a neurological condition associated with failure
of the liver to detoxify neurotoxins. The pathogenesis is complex, but it
appears that ammonia plays a central role in the damage of the brain.
Ammonia is produced primarily in the gastrointestinal tract. Typically, a
high amount of ammonia is extracted by the liver via the urea cycle. When
the liver function is not correct, the ammonia accumulates in the brain,
and, once there, the astrocytes are responsible for ammonia detoxification.
The ammonia gets metabolised and converted into glutamine. Too high
levels of glutamine in the brain produce brain oedema and the neurological
signs characteristic of hepatic encephalopathy.
H MRS was performed in the brain of six dogs with hepatic
encephalopathy (because of portosystemic shunts or chronic hepatitis),
and they were compared to 12 normal dogs. We found characteristic
differences between these groups: dogs with hepatic encephalopathy
showed high levels of glutamine and lower levels of myo-inositol (Fig. 2).
Furthermore, choline and
acetylaspartate concentration were slightly
lower in dogs with hepatic encephalopathy than in the control dogs.
In some dogs, the concentration of ammonia in blood was normal.
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M E D I C A L T E C H N O L O G Y & R E S E A R C H
Fig. 2 Single voxel
short echo time
spectroscopy on the
basal ganglia region of
a seven-year-old golden
retriever with chronic
liver disease and
Fig. 3 Typical short
echo time magnetic
resonance spectra of a
malignant tumour in a