Table 1.
Detailed DICOM tags with explanations
| Clinical data/DICOM field name | DICOM tag/units | QC check |
|---|---|---|
| Scanner make/manufacturer | (0008,0070) | Check this information against the accredited site scanner and compare to the baseline and prior scans. |
| Patient height/patient size | (0010,1020) (cm) | This tag has to be verified against the patient’s clinical dossier and across the longitudinal scans record. It is imperative for SUV measurements corrected for body surface area (SUVBSA) and lean body mass (SUVLBM) or glucose corrected (SUVg). |
| Patients weight | (0010,1030) (kg) | This tag has to be verified against the patient’s clinical dossier. It is common that, during the course of a therapy, subjects change weight. It is important that the IG mandate the use of a calibrated scale at the PET department and that each patient is weighed prior to each PET scan, and this information is correctly recorded in the PET scanner, as well as the clinical dossier. This parameter has a direct impact on the SUV, and a recent publication by Lasnon et al. [31] confirms imperative and obligatory monitoring and verification of the source data. |
| Scanner serial number/device serial number | (0018,1000) | Check this information against the accredited site scanner and compare to the baseline and prior scans. |
| Software versions | (0018,1020) | Check this information against the accredited site scanner and compare to the baseline and prior scans. |
| Scanner model/ manufacturer model name | (0008,1090) | Check this information against the accredited site scanner and compare to the baseline and prior scans. |
| Reconstruction diameter | (0018,1100) (mm) | Check this parameter to ensure that the reconstruction diameters of the PETAC and AC-CT series are equal. Smaller AC-CT reconstruction diameter could inflict truncation artifacts. |
| Time per bed/actual frame duration | (0018,1242) (ms) | This DICOM tag should be checked to ensure it is in compliance with the IG. Furthermore, for all subsequent scans within the same subject, the time per bed should be consistent with the baseline acquisition. This parameter is in direct relationship with the radiopharmaceutical dose a patient receives and the scanning protocol established by the vendor, but often in day-to-day clinical practice it might be acceptable to modify it; however, for patients taking part in a clinical study where SUV measurements will be performed, this parameter should remain constant. |
| The radiopharmaceutical injection time/radiopharmaceutical start time | (0018,1072) (h:min:s) | This information should be routinely recorded in the injection record dossier for the patient at the PET department, and this record is considered source data. The injection time is not the same as the assay time. Those two always differ, unless an automatic injection is used. The injection time is usually entered manually into the acquisition protocol of the scanner. Those two records should match explicitly and should refer to the actual injection time and not the dose assay time. This requires synchronization of all clocks at the PET department—the hot lab, the injection room, the control room, and the scanner itself. Any mismatch between the clocks should be rectified immediately and, if not possible, prior to scanning patients, it should be documented and reported to the sponsor. Based on the experience of the co-authors of these guidelines, up to 1 min difference between all clocks is acceptable and it would not have a major impact on SUV measurements for isotopes such as 18F. For some scanner makes and models, the dose is decay corrected automatically and the information is captured in the proprietary DICOM tags. |
| Collimator type | (0018,1181) | Ensure same collimator applied, which would affect image quality and quantification. |
| Acquisition mode (2D/3D) | (0018:9732) | This tag may or may not be present to check, but it is imperative that the mode of acquisition is consistent between baseline and all follow-up scans. While in low BMI patients, the mode of acquisition may not significantly affect the visual readout; it could affect the SUV. For patients with high/obese BMI, both visual and SUV readouts could be affected more severely. |
| Uptake time/N/A | N/A | UT is another parameter very well documented affecting SUVs. The UT should be checked in the DICOM tags by calculating the difference between the Radiopharmaceutical Injection Time, and the earliest scan start time [earliest acquisition time (0008.0032)-radiopharmaceutical start time (0018,1072)]. Furthermore, it should be checked for compliance with the IG for the baseline and all subsequent scans. Some post-processing software use the Series Start time tag. The authors of these guidelines suggest not to use the Series Start time as this tag could be erroneously changed during export of the data from a PACS or another stand-alone post-processing software. |
| Radiopharmaceutical dose/radionuclide total dose | (0018.1074) (h:min:s) | The net injected radiopharmaceutical dose recorded in the patient’s clinical dossier/PET department records should match the dose in the DICOM tag. It is usually entered manually into the scanner, and it should be reliable as a source data. It is acceptable within the nuclear medicine practice to use ± 10% variability from the prescribed dose and to base the dose on the patient weight. Thus, for all follow-up scans, in the absence of drastic weight change, the net injected dose should be within ± 10% of the baseline net injected dose. Greater variability could affect the available radiopharmaceutical in the body and influence the SUV comparability artificially. In the case a patient incurs weight change, which results in greater than 10% dose change compared to the baseline scan, this should be recorded and available during QC for verification. Dose assay time is not the same as dose injection time, and since those two always differ, the net injected dose should be decay corrected accordingly to account for the difference between the time of assay and the actual time of injection. To calculate manually the net injected dose, the residual activity in the syringe with any tubing (dose “N” at time “n”) is subtracted from the assayed dose (dose “A” at time “a”) and decayed accordingly to account for the difference in time between “a” and “n”. This is vital for radioisotopes with very short half-life. |
| Scanning position | N/A | Patient position should remain constant across all scans unless the position is changed due to the inability of the patient to comply. Often, during the course of treatment, subjects may experience significant weakness and inability to keep their arms up or lay supine. If patient’s position is changed at a follow-up scan compared to the baseline, there should be a reasonable explanation about this in the clinical dossier and provided to the sponsor. |
| Scan direction | N/A | The acquisition time (0008.0032) of the most superior and most inferior transaxial slice is used to determine the scan direction. The scan direction (caudal vs. cranial) should remain consistent with the baseline scan. While a single-bed-position or two-bed-position acquisition scan direction change would not influence greatly the SUV measurements, multiple-bed-position acquisition especially for high-grade tumors could show large changes in SUV measurements due to change in scan direction. By itself, this factor may not be significant enough to influence a patient’s management and change the patient’s classification from one category to another, but in combination with other factors, the SUVs could be influenced enough to bring artificial noise. |
| Reconstruction algorithm/reconstruction method | (0054,1103) | Usually, during the scanner qualification process, the acquisition and reconstruction parameters are established for each scanner to be used in a specific clinical study. In the frame of a specific clinical trial, when accreditation of scanners is mandated, it is specified what manufacturer availed parameters should be used for each patient taking part of the study. Those parameters may be different from one to another study. It is best that the longitudinal PET scans for all subjects in a given study are acquired and reconstructed with the same exact parameters and be cross-checked for all scans, including acquisition and reconstruction field of view (FOV), mode of acquisition (e.g., 2D vs. 3D), matrix size, slice thickness, reconstruction algorithm, and used corrections. |
| Corrections applied/corrected image | (0028,0051) | |
| Matrix size/rows & columns | (0028,0010) (0028,0011) | |
| Slice thickness | (0018,0050) |
N/A not applicable