Info for doctor

Instructions for physician in charge of the patient
1. Clinical range of use of PET scans

2. How do I prepare a patient for a PET scan?

3. Instructions for preliminary preparations for PET examinations

4. PET scanning times during special situations

5. Contraindications for PET scans

6. Checklist for the most important matters when sending a patient for a PET scan

7. Useful PET links

1. Clinical range of use of PET scans

The PET Centre is the national supplier of diagnostic PET scans. In addition to scientific research, PET is a useful tool within select clinical areas. Of these PET is used mostly in assessment of treatment response in and staging of cancer diseases, as well as in recurrence detection. Currently there are two PET-CT devices applicable for fusion imaging at the PET Centre. The device further enhances the diagnostic accuracy. Apart for the aforementioned, clinical applications for the method can also be found within cardiology, endocrinology, neurology and paediatric neurology. You can download a summary of the clinical use of PET scans and the current prices from the following link (Indications). The list of areas of use becomes longer and changes along with medical proof of verification of the usefulness of the method. Approximately 1200 diagnostic scans are conducted annually at the Turku PET Centre; of these 70-80 % are connected to cancer diseases. As needed it is good to consult the personnel of the PET Centre (Contact information) beforehand, as regarding conducting a PET scan. A referral by a physician is required for examinations and a patient from outside the hospital district to which the Turku University Hospital belongs also has to have an obligation of payment. It is extremely important to either send in advance or with the patient current earlier imaging results (CT, MRI) and their statements, as the PET finding is always compared with findings in anatomical imaging examinations. The statement and images of a diagnostic PET scan are delivered to the referring physician either by mail or the statement can also be sent by fax in urgent cases. The statement is dictated in the data management program of the hospital. PET is applicable for visualization of practically all cancers. Cancer tissue uses considerably more sugar than normal tissue and the PET image shows this metabolic discrepancy. In cancer examinations generally 18-FDG glucose derivate is used as tracer substance. The whole human body can be scanned in half an hour and the quality of the images is excellent. The premises for a useful clinical tool in cancer diagnostics and follow-up of the treatment are therefore good.

Due to limited availability of examinations PET scans are only offered to carefully limited patient groups. Firstly, the patient has to still benefit from treatment and secondly, this examination has to yield such from a therapeutic aspect significant information, which cannot be achieved with traditional methods of examination. PET scans can be used in diagnosing cancer in such situations, where it is difficult to take a biopsy and the scan can be used to assess the local and regional spreading and to search for metastases lying further away. After the treatment a PET scan helps in discerning between scar tissue from the treatment and remaining cancer tissue. Response for medicinal treatment can also be assessed using PET. If, for instance, there is an indeterminate change of 5-30 mm in diametre in the lungs in place from where a biopsy could only be taken through opening the thorax, the malignity of the change can be determined using the PET method without an operation.

2. How do I prepare a patient for a PET scan?

When referring a patient to a PET scan it is essentially important for the success of the examination that the patient is informed of the preliminary preparations regarding fasting, medicinal breaks and possible premedication before the scan. In the table below are presented instructions for these preliminary preparations in connection with different tracer substances. As 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. When glucose derivate (FDG) is used as tracer substance a small amount of diazepam is often given to the patient before the scan in order to minimize muscular tension and physiological uptake in brown adipose tissue. Thus the patient should, if possible, arrive to the examination without car or alternatively with a driver. Normally the patient should reserve about two hours for a PET examination, as for instance the scanning in an FDG-PET does not begin until 50 minutes after the tracer substance has been injected. The scanning time is about  ½ hour. Patients with diabetes are a special group as regarding FDG examinations, as their sugar balance should be good and the examination requires fasting. There is no point in conducting the scan if the patient’s blood sugar exceeds 10 mmol/l, when the results of the imaging no longer are reliable, as there is a high occurrence of incorrect negative results. Patients whose diabetes is treated with diet or tablets fast normally 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.

3. Instructions for preliminary preparations for PET examinations
Tracer substance

(& scan area)

Medicine pause Preceding 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).As needed furosemide 20 mg i.v. (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
11C-choline No Fasting 6hrs
18F-BPA No Fasting 6hrs, no alcohol 24hrs Not usually

4. PET scanning times during special situations

One should strive to conduct staging of cancer patients before the therapies are begun, as the metabolic activity in found anatomical changes may be entirely extinguished already after only one course of cytotoxic drugs, for instance among patients with lymphoma. Assessment on treatment response should be drafted as follows if this is possible as regarding the overall care of the patient: 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 conducted on breastfeeding mothers.

6. Checklist for the most important matters when sending a patient for a PET

  • Referral and obligation of payment (contact information)
  • Send results for earlier anatomical imagings and statements in advance or with the patient to the PET Centre (CT, MRI)
  • In addition to earlier found diseases and the question at issue do record the history of given treatments (cytotoxic chemotherapies, radiotherapies, surgical procedures) and latest times of treatment.
  • Inform the patient of the examination (How do I prepare a patient for a PET scan?)
  • Diabetes patients require special attention when sent for a PET scan