Stardard Operating Procedures (SOPs) for the acquisition and reconstruction of brain PET with 18F-FDG. e
These SOPs are –of course- mainly derived from the Guidelines of the European Association of Nuclear Medicine (EANM) published in 2009 (Varrone A et al. Eur J Nucl Med Mol Imaging. 2009 Dec;36(12):2103-10).
Patient preparation
Patients should fast for at least 4 h to allow optimal cerebral FDG uptake not influenced by increased serum glucose levels. Blood glucose levels should be checked prior to FDG administration (recommended glycaemia <160 mg/dl). Diabetics patients should ideally be injected in a euglycaemic situation during adequate therapeutic management.
-Voiding: before the scanning procedure is started, patients should void the bladder for maximum comfort during the study. The patient should be advised to void again after the scanning session to minimize radiation exposure.
-FDG administration: patients should be positioned comfortably in a quiet, dimly lit room several minutes before FDG administration and during the uptake phase of FDG (at least 20 min). They should be instructed not to speak, read or be otherwise active. Theoretically patients should be kept with either eyes open or closed but each center should fix its standard and always use the same. A retrospective study of the DLB consortium is ongoing to assess the impact on the analysis in SPM in DLB patients kept either eyes closed or open during FDG uptake time. It is desirable to have the cannula for intravenous administration in place 10 min before FDG administration.
-Sedation: In uncooperative patients (e.g. due to their cognitive/ behavioural state), it may be worthwhile to apply conscious sedation (e.g. using a short-acting benzodiazepine, such as intravenous midazolam). The sedative medication should be given at least 20 min after tracer injection, preferably starting only a few minutes before data acquisition
Recomended activity
– 300–600 MBq (typically 370 MBq) in 2-D mode
– 125–250 MBq (typically 150 MBq) in 3-D mode (RECOMMENDED)
Patients Positioning.
To prevent movement artefacts, the patient should be informed to avoid voluntary movement the head, and the patient’ s head can be fixed in place.
Equipment and Transmission Scan.
–If attenuation correction is based on transmi ssion images, better results are general ly achieved when the images are acquired before FDG injection if clinically feasible. Acquisition counts collected may vary between P E T system and post-processing procedures used.
-For PET/CT systems, the CT scan can be used for attenuation correction . The scanning parameters may vary according to the type of CT scanner. Usually the tube voltage is set at around 140 kV. The CT scan can be performed afterinjection of FDG. When performing PET/CT of the brain it is recommended to check for movements between the CT and the PET sessions, which might produce artef acts in the attenu ation correction
Acquisition Parameters (emission scan)
The acquisition should not start earlier than 30 min after injection (it is recommended that a standardized acquisition protocol with a fixed time for starting the acquisition is used in order to render the data from different patients or repeated scans comparable) and not later than 60 min after injection.
-If data are acquired in 3-D mode, appropriate scatter correction is mandatory
-the duration of emission image acquisition should be related to the minimum required number of detected events .Typically data are acquir ed over 15–30 min aiming to collect 50–200 million detected events.
-Dynamic List-Mode acquisition can be also performed (i.e. 4 frames of 5 minute) especially in case of high risk of motion artifacts.
Reconstruction Parameters
Images are reconstructed in the form of transaxial images of at least 128×128 pixels; a usual pixel size is 2–4 mm. Depending on the resolution of the PET system, a final image resolution of 4–6 mm FWHM typically yields images of adequate resolution and noise. Commonly used filters are Hanning or SheppLogan which should be finely tuned depending on application, injected activity, camera and acquisition type. and even physician’s preference. Iterative reconstruction methods, such as ordered-subset expectation maximization (OSEM), are recommended. Such methods may improve target-to-background ratio and are used in many recent PET and PET/CT systems. When available, time-of-flight information can be used during reconstruction.
Once the reconstructed data are available they should be exported from the work-station as Dicom files and sent to the collecting center in Genoa at the web site address: https://nextmr01.ge.infn.it/edlb_php/index.php