PurposeRecent developments in iterative image reconstruction enable absolute quantification of SPECT/CT studies by incorporating compensation for collimator-detector response, attenuation, and... Show morePurposeRecent developments in iterative image reconstruction enable absolute quantification of SPECT/CT studies by incorporating compensation for collimator-detector response, attenuation, and scatter as well as resolution recovery into the reconstruction process (Evolution; Q.Metrix package; GE Healthcare, Little Chalfont, UK). The aim of this experimental study is to assess its quantitative accuracy for potential clinical Tc-99m-sestamibi (MIBI)-related SPECT/CT application in neoadjuvant chemotherapy response studies in breast cancer.MethodsTwo phantoms were filled with MIBI and acquired on a SPECT/CT gamma camera (Discovery 670 Pro; GE Healthcare), that is, a water cylinder and a NEMA body phantom containing six spheres that were filled with an activity concentration reflecting clinical MIBI uptake. Subsequently, volumes-of-interest (VOI) of each sphere were drawn (semi)automatically on SPECT using various isocontour methods or manually on CT. Finally, prone MIBI SPECT/CT scans were acquired 5 and 90 min p.i. in a locally advanced breast cancer patient.ResultsActivity concentration in the four largest spheres converged after nine iterations of evolution. Depending on the count statistics, the accuracy of the reconstructed activity concentration varied between -4.7 and -0.16% (VOI covering the entire phantom) and from 6.9% to 10% (8.8 cm ? cylinder VOI placed in the center of the phantom). Recovery coefficients of SUVmax were 1.89 0.18, 1.76 +/- 0.17, 2.00 +/- 0.38, 1.89 +/- 0.35, and 0.90 +/- 0.26 for spheres with 37, 28, 22, 17, and 13 mm ?, respectively. Recovery coefficients of SUVmean were 1.07 +/- 0.06, 1.03 +/- 0.09, 1.17 +/- 0.21, 1.10 +/- 0.20, and 0.52 +/- 0.14 (42% isocontour); 1.10 +/- 0.07, 1.02 +/- 0.09, 1.13 +/- 0.19, 1.06 +/- 0.19, and 0.51 +/- 0.13 (36% isocontour with local background correction); and 0.96, 1.09, 1.03, 1.03, and 0.29 (CT). Patient study results were concordant with the phantom validation.ConclusionsAbsolute SPECT/CT quantification of breast studies using MIBI seems feasible (<17% deviation) when a 42% isocontour is used for delineation for tumors of at least 17 mm diameter. However, with tumor shrinkage, response evaluation should be handled with caution, especially when using SUVmax. Show less
