F-DOPA brain PET for Parkinson's disease

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For most essential points to best prepare for the procedure, please download the patient information brochure (PDF).
For a more elaborate explanation of the procedure and related points, please continue to read ahead.

Brief introduction

Principle

Amino acids are the building blocks of proteins. Neurotransmitters are signalling molecules synthesized and released by neurons (nerve cells) that stimulate or inhibit other neurons and some other organs (e.g., muscles, sweat glands, etc.).

The human body can use an amino acid called L-3,4-dihydroxyphenylalanine (L-DOPA or 'levodopa') to synthesize 3 different neurotransmitters: 'dopamine', 'epinephrine' and 'norepinephrine'. These are all very important neurotransmitters, and their function depends on the site of their release.

¹⁸F-DOPA is the radiopharmaceutical (RP), which is taken up by the same cells that also take up L-DOPA. Most remarkably, it is taken up by cells of basal ganglia in the brain and certain tumour cells (described here).

Parkinsonian syndromes are conditions involving the brain that mainly result in muscle movement disorders. Common symptoms (also called 'parkinsonism') include bradykinesia (slowness of movements), rigidity, tremor, and postural instability. 'Idiopathic Parkinson's Disease' (IPD) is the most common cause of parkinsonism.

IPD is a progressive degenerative disorder wherein the neurons producing dopamine in brain structures called 'basal ganglia' gradually lose function, which results in progressively worsening parkinsonian symptoms. Symptoms can be reduced in early stages of the disease by increasing dopamine content of brain by increasing its production or reducing its breakdown. However, there are certain other conditions that do not directly affect dopamine production, but have symptoms somewhat similar to IPD. Distinguishing between 'true' Parkinson's disease (i.e., IPD) and other parkinsonian syndromes helps starting the correct treatment earlier.

F-DOPA is taken up by cells producing dopamine (e.g., the basal ganglia neurons). In IPD F-DOPA's uptake in the basal ganglia is reduced in absolute as well as relative terms, which in turn can be detected using F-DOPA PET-CT.

Indications (conditions in which advised)

Distinguishing IPD from other parkinsonian syndromes.

Considerations / steps before procedure

Prior appointment is a must as the RP spontaneously decays, and is not readily available at the diagnostic facility.
Patient must not be pregnant.
If breast feeding, please inform the staff for further directions.
Stop levodopa medication for 12 h.
4 hours’ fasting before scan.
Please let the staff know at the time of appointment if the patient is unable to lie still for ~20 min, has breathing difficulty, or might need special medical attention for the duration of visit.
Have at least 1/2 litre water within an hour before reporting for the scan. There is no need to hold urine.
Wear loose-fitting but warm clothes.
Do not bring expensive jewellery or accessories along with you for the scan.
Proof of doctor's request is necessary for starting the procedure.
The patient must be accompanied by a responsible carer.

What to expect as part of procedure?

Important steps

Patient registration and consent.
Handing over medical documents to the staff.
Taking carbidopa tablet.
Intravenous (IV) access is established (in form of cannula).
RP is injected through the cannula.
Waiting time of ~75 min (± 15 min) to allow sufficient time for RP to be taken up and eliminated by all organs. Pass urine just before the scan, and also before that (if needed).
Scan acquisition takes ~15 min on the scanner table.
Scan is briefly reviewed for adequacy and quality. Occasionally, a scan may be repeated or scanning of additional body parts may be considered. If everything is to staff’s satisfaction, then the patient may leave.

Discomfort / risks during procedure

Pain during IV cannula insertion.
There is risk of extravasation at the time of IV cannula insertion or RP injection. [Extravasation means that blood leaks through the walls of vein punctured by cannula’s needle].
RP does not cause any discomfort. It is injected in very minute quantity, so it does not alter function of any organ.

Time taken for the entire patient visit

Typical: 5 hours.
Be prepared for: 6.5 hours (can be further prolonged in case of unforeseen events like malfunctioning of scanner, delayed delivery of RP, etc.).

What to expect after procedure?

Precautions / special care

Maintain at least 1 metre-distance from pregnant ladies and children (below 10 years) for at least 5 hours after the scan.
Drink plenty of water throughout the day (3 to 4 litres).
Pass urine as frequently as possible.

Discomfort / risks

Both RP and X-rays expose the patient to ionizing radiation. However, radiation dose received as part of the entire procedure is not expected to cause any obvious harmful effect. Additionally, benefit from information received through the procedure greatly outweighs any theoretical risk associated with this radiation exposure.

Time taken for report generation

Typical (for self-paying patients): 12 hours.
Be prepared for: 36 hours (especially if some patient data or past scan data are missing).
Credit patients will receive their reports from the respective referring hospitals.

Additional reading

For additional information, please visit the following links.

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