Standard Uptake Values (SUV)
The information contained in PET and SPECT images is related to the physical concentration of tracer in tissue. If all images distortions are corrected by the reconstruction procedure, the value units are activity concentrations, for instance Bq/ml. The uptake in tissue is dependent on many factors. It is directly proportional to the injected activity, and inversely related to the mass within the tracer can distribute. To calculated a measure of tracer uptake which is better comparable among patients (therefore Standard Uptake Value) the measured activities are therefore divided by the injected dose and multiplied by the (mean) body mass. PMOD supports three variants of this calculation:
In addition to the patient weight (and size) the SUV calculation has to know the injected dose. For correcting the physical radioactive decay of all activities to the same time the program also requires information about radionuclide, the time of dose calibration, time of injection, the activity remaining in the syringe and when it was measured. Also required is the scan start time, because the PET measurements are decay-corrected to the scan start.
For correct SUV values it is important that all the entries are correctly filled in. PMOD tries to extract the information from the image header. However, dependent on the file format this information or part of it may be missing. Another factor is, whether the dose information has been entered by the technicians during the scan. If the information is incomplete, it has to be edited interactively in the dialog window before the SUV can be calculated.
SUV Value Inspection Window
The SUV (Standard Uptake Value) button
below the data inspector button is a shortcut for opening the data inspector with the SUV tab selected
The window can be extended with the >> button for adjustments.
The upper part of the SUV panel shows the information which is involved in the calculation of the SUV. It requires that the image units are kBq/cc, and that all information fields in the dialog are correctly filled in. Per default, the scan start time is read from the acquisition time field of DICOM. However, as situations have been met where this information was wrong whereas the series time was correct, the Scan Date and Time radio button allows switching to the Series or the Acquisition time. Note that using the Copy to Study Info button the corrected information can be saved for later use, and for saving it together with the data.
The lower part serves for showing the different SUVs of the current pixel. The displayed SUV value changes whenever the cursor is moved over the image.
The calculation of statistics in SUV units is directly supported on the original image by the VOI functionality, provided that all required information is available. Explicit SUV images can be calculated with the SUV Image Calculatio external tool.