Instructions for physician
1. Clinical range of use of PET scans
PET is a useful tool in specific clinical indications. PET is used mostly in staging of cancer diseases, detecting therapy response as well as in recurrence of cancer. Clinical applications are also in cardiology, endocrinology, neurology and paediatric neurology. The list of indications is continuously growing.
A referral by a physician is required for examinations and a financial obligation is needed in patients outside from the hospital district. It is important to include the imaging reports and images of the earlier studies as the PET finding is always compared with findings in anatomical imaging examinations.
In most cancer examinations 18-FDG (glucose derivative) is used as tracer. The whole human body can be scanned in less than a half an hour.
Due to limited availability of examinations PET scans are performed in selected patient groups. First, the patient has to have treatment options and, second, the examination has to yield such therapeutic information, which cannot be obtained with conventional methods. PET scan can be used to diagnose cancer in situations where it is difficult to take a biopsy. After the treatments a PET scan helps in discerning between scar tissue from the treatment and remaining cancer tissue. Response for medical treatment can also be assessed using PET.
2. How do I prepare a patient for a PET scan?
It is important that the patient is informed about the preparations e.g. fasting and medication before the scan. A general recommendation is that the patient should fast for 6 hours before the examination (water can be drunk) and that heavy physical exertion and alcohol intake should be avoided for 24 hours. Smoking should be avoided 2-4 hours before the examination.
The patient should reserve about two hours for a PET examination. The scanning in an FDG-PET does not begin until 50 minutes after the tracer has been injected. The scanning time is about ½ hour or less. The sugar balance of diabetetic patients should be good and the examination is performed in the fasting state. The scan is not performed if the patient’s blood sugar exceeds 10 mmol/l. Patients whose diabetes is treated with diet or tablets should fast normally for 6 hours before the examination (water can be drunk freely). If the patient uses insulin, he/she can eat and drink as normal before the examination.
(& scan area)
|Pause of medical therapy||Preceeding diet||Premedication||Other|
|18F-FDG (whole body)||Usually not (diabetes patients, see separate instruction!)||Fasting min. 6hrs, preferably overnight (water can be drunk)||As needed diazepam 5 – 15 mg p.o. (administered at the PET Centre). Furosemide 20 mg i.v. as needed (administered at the PET Centre)||Heavy physical exertion should be avoided 24hrs before the scan. Diabetes patients at a good sugar balance (the examination cannot be carried out if fP-Gluc > 10 mmol/l)|
|18F-FDG (heart)||Separately agreed upon||Fasting 10hrs, no alcohol or caffeine 24hrs||0 min: Acipimox 250mg p.o.
Acetylsalicylic acid 250mg p.o.
60 min: Acipimox 250mg p.o.
|18F-FDG (brain)||Usually not (diabetes patients, see separate instruction!)||Fasting min. 6hrs, preferably overnight (water can be drunk)|
|18F-DOPA (brain)||Levodopa: 12h
Dopamine agonists: 2 days. Selegiline: 2 days
|Low protein (30g/day) for 1 day. Fasting 6hrs (water can be drunk)||Karbidopa 100mg p.o. 60min before scan (administered at the PET Centre)|
|18F-DOPA (whole body)||Diazoxide and somatostatine analogues: 24hrs Cortisone: 2 days||Fasting 6hrs (water can be drunk)||Not usually|
|11C-flumazenil (brain)||Epilepsy medicines: no pause. Benzodiazepines: separately agreed upon||Normal (if scan conducted under anaesthesia, full fasting 4hrs)||Not usually|
|11C-methionine||No||Fasting 6hrs, no alcohol 24hrs (water can be drunk)||Not usually|
|11C-metomidate||Ketoconazole and metyrapone, and spironolactone: 2 weeks||Fasting 6hrs||Not usually|
|11C-acetate||Usually not||Fasting 6hrs. No alcohol, coffee, tea, cola beverages 12hrs||Not usually|
|18F-BPA||No||Fasting 6hrs, no alcohol 24hrs||Not usually|
4. PET scanning times during special situations
The staging of cancer should be performed before the therapies are begun, as the metabolic activity may change after cytotoxic drugs. Assessment on treatment response should be performed as follows: 4-6 wk after cytotoxic drug courses, 8-10 wk after radiotherapy has ended and 6 wk after performed operations.
5. Contraindications for PET scans
Pregnancy is an absolute contraindication for a PET scan. The examination can be performed in breastfeeding mothers.
6. Checklist for the most important matters when sending a patient for a PET
- Referral and financial obligation
- Include results for earlier anatomical imagings and reports to the PET Centre (CT, MRI)
- Include history of earlier diseases and given treatments (cytotoxic chemotherapies, radiotherapies, surgical procedures) and latest times of these treatments.
- Inform the patient about the examination
- Diabetes patients require special attention when sent for a PET scan