SUV Value Inspection and Statistics

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:

1. SUV Body mass [g/ml]: Directly uses the patient weight entered in the demographic patient information. This is the mostly used SUV.
2. SUV Lean Body Mass [g/ml]: First calculates a mean body mass from the patient weight, the height and the gender, which is used in the actual SUV calculation.
3. SUV Body Surface Area [cm²/ml]: In this case the uptake is normalized to the body surface area, which is calculated from the weight, the height and the gender.

Additionally, the Injected dose per cc [%ID/ml] is available for normalizing the uptake to the injected dose and then multiply with 100.

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 acquisition start time, because the PET measurements are decay-corrected to the acquisition start.

If all information has been entered by the technicians during the acquisitions, it is directly extracted from the DICOM header. Otherwise, the information has to be completed in a dialog window before the SUV can be calculated.

SUV Value Inspection

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 upper part serves for showing the SUVs of the current pixel. The SUV changes when the cursor is moved over the image. Note that the three different types of SUV and the image normalization value respect to the injected dose are displayed simultaneously.

The lower part 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 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 time.

Note that using the Copy to Study Info button the information can be saved for later use, and for saving together with the data.

SUV Statistics

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 Calculate SUV Image external tool.