A server-based solution for misregistration correction in PET/CT using limited-coverage and data-driven gated CT

Misregistration between CT and PET images can compromise lesion localization and the accuracy of tracer uptake quantification. Although repeating a limited-coverage (LC) CT scan may resolve the issue, most PET/CT systems require extending the LC CT to cover one to two PET bed positions, substantially increasing the patient's CT dose and adding the complexity of matching the LC CT to the corresponding PET positions. Consequently, many clinics instead repeat an LC PET/CT scan, which is operationally simpler but adds several minutes of unnecessary PET acquisition and still results in a significant increase in CT dose. A more efficient solution is needed-one that minimizes CT doses without necessitating an additional PET scan.

We aimed to develop a misregistration correction server (MCS) to solve the problems of excessive CT dose and unnecessary PET scans associated with current limited coverage (LC) CT and LC PET/CT procedures.

A new MCS was developed to embed the CT of PET/CT with either an LC CT or data-driven gated (DDG) CT to enable PET attenuation correction. Both LC CT and DDG CT can be positioned across PET bed positions and does not need a repeat PET. The MCS currently supports misregistration correction of 9 scanners within our hospital network: 8 GE DMI and 1 Siemens Quadra. It can simultaneously process data from all 9 scanners and return the WB CT embedded with LC CT or DDG CT to each requesting scanner for misregistration correction. Over 2,033 patient studies have been corrected. The dose implications of the MCS will be assessed.

The processing time from data transfer to output was approximately 1 min for LC CT and 3 min for DDG CT. The MCS workflow has minimal operational impact and eliminates the need for repeat PET acquisitions. The LC/DDG CT scan ranges were 17.5 ± 4.7 cm on the GE DMI and 22.1 ± 5.6 cm on the Siemens Quadra, with corresponding doses of 7.52 ± 4.18 mGy and 5.63 ± 4.46 mGy. Registration improved in 2,004 of 2,013 DMI studies and 13 of 20 Quadra studies. The dose length product (DLP) values for LC/DDG CT (DMI: 133.9 ± 87.8 mGy-cm; Quadra: 108.3 ± 90.6 mGy-cm) were substantially lower than the WB CT values (DMI: 569.0 ± 305.0 mGy-cm; Quadra: 641.8 ± 321.5 mGy-cm), representing only 23.5% and 16.8% of the corresponding WB DLP.

A new MCS has been developed to correct misregistration in PET/CT scanners from GE and Siemens. It can generate DDG CT from the cine CT data to correct for PET or DDG PET, or enable repeat CT of any coverage, avoiding the need for repeat PET and thereby reducing both CT dose and PET scan time. The additional doses in DLP accounted for 23.5% of the WB DLP for the GE DMI scanner and 16.8% for the Siemens Vision Quadra scanner.