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99mTc-HMPAO is a lipophyllic complex that accumulates in the brain proportional to regional perfusion. The SPECT images reflects regional cerebral uptake at the time of injection.
In Alzheimers, one classically sees bilateral decreased CBF in the temporal and parietal lobes. A correlation is seen between the severity of these defects and the severity of the patient's dementia.
Pick's disease is a rare frontal dementia characterised by bilateral, diffuse decreased frontal lobe perfusion.
Multi infarct dementia is characterised clinically by multiple cerebral infacts that occur sporadically and produce a step-wise deteriation in function. 99mTc-HMPAO findings, which support this diagnosis, include multiple, bilateral, and randomly distributed cortical perfusion defects that follow vascular territories. The basal ganglia may also be involved (spared in Alzheimer's).
To distinguish frontal lobe dementia patterns from parieto-temporal lobe disease.
The presence of sedating medications at the time of injection may alter the distribution of 99mTc-HMPAO. A list of the patient's medications will be required by Nuclear Medicine staff, who will advise which, if any, need to be withheld.
If problems with cooperation are envisaged, this should be noted on the referral. If anxiolytic or sedating medication is required (administered at least 15 minutes after the radiopharmaceutical injection), this must be prescribed by the referring doctor or GP and accompany the patient.
On arrival, an IV line is inserted. The patient is left lying comfortably in a dim, quiet room for about 20 minutes, after which 99mTc-HMPAO is injected.
SPECT/CT imaging takes place about 30-90 minutes later and takes about 30 minutes. The patient will need to keep their head perfectly still during this time.
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