A Method for Validating PET and SPECT Cameras for Quantitative Clinical Imaging Trials Using Novel Radionuclides

Our aim is to report methodology that has been developed to calibrate and verify PET and SPECT quantitative image accuracy and quality assurance for use with nonstandard radionuclides, especially with longer half-lives, in clinical imaging trials. Methods: Procedures have been developed for quantitative PET and SPECT image calibration for use in clinical trials. The protocol uses a 3-step approach: check quantitative accuracy with a previously calibrated radionuclide in a simple geometry, check the novel trial radionuclide in the same geometry, and check the novel radionuclide in a more challenging, complex geometry (the National Electrical Manufacturers Association [NEMA] NU-2 International Electrotechnical Commission [IEC] image-quality phantom). The radionuclides used in the trial as an example are ¹²⁴I (PET) and ¹³¹I (SPECT). In both cases, whole-body tomographic SPECT and PET imaging with accompanying low-dose CT are required. PET accuracy is based on calibrating the dose calibrator to produce quantitative images for radionuclides other than ¹⁸F, with all images reconstructed on each individual site's PET systems. For SPECT, an independent sensitivity measurement is made and then used to calibrate the SPECT images reconstructed at the core laboratory. After calibration, the final testing for both PET and SPECT uses the NEMA NU-2 IEC image-quality phantom to derive several metrics including quantitative accuracy based on an average SUV (SUV_avg). Results: Using the method described, 7 sites in Australia have been qualified for 10 PET/CT scanners using ¹²⁴I imaging and 8 SPECT/CT systems for ¹³¹I. One PET/CT system was found to give a result outside the specification of an SUV_avg of 1.0 ± 0.05. All SPECT/CT systems gave an SUV_avg accurate to within ±10% (SUV_mean, 1.0 ± 0.1) of the true value for reconstructed radioactivity concentration in Bq/cm³ Conclusion: A general methodology has been developed to calibrate and validate PET and SPECT systems for quantitative imaging in clinical trials. The preparation of the test objects and the procedures is relatively simple and can generally be implemented by the staff at the site of the imaging center with the equipment supplied by the clinical trials organization.