Fourier temporal interpolation improves electrocardiograph-gated myocardial perfusion SPECT.

UNLABELLED: The optimal temporal sampling rate in electrocardiograph-gated myocardial SPECT is questionable: low rates, typically 8 frames per cardiac beat (8fr/cb), favor image quality, whereas high rates, typically 16 frames per cardiac beat (16fr/cb), favor the accuracy of left ventricular (LV) functional parameters. We examined whether Fourier temporal interpolation (FTI) from 8fr/cb to 16fr/cb can combine the advantages of low and high rates. METHODS: In 34 patients imaged after stress injection of (99m)Tc-sestamibi, 4 sets of reconstructed gated slices were compared: a raw 16fr/cb acquisition (R16), a raw 8fr/cb acquisition (R8), a 16fr/cb set obtained by FTI of 8fr/cb projections (IP), and a 16fr/cb set obtained by FTI of 8fr/cb reconstructed slices (IS). LV ejection fraction (LVEF), end-diastolic volume (EDV), and end-systolic volume (ESV) obtained from the final LV volume curve were compared for the 4 datasets. Deviation of the whole LV volume curve was quantified for IP and IS with respect to R16. Image quality was evaluated by consensus reading of end-diastolic slices of the 4 sets. For R16, IP, and IS, cine display fluidity was quantified by a roughness index calculated from the LV volume curve. RESULTS: No differences in EDVs or ESVs were found among R16, IP, and IS, whereas R8 gave smaller EDVs and larger ESVs. LVEF was lower with R8, IP, and IS than with R16: -3.9%, -1.2%, and -1.3%, respectively. The LV volume curve was closer to R16 with IP than with IS. Image quality was better with IP and IS than with R8 and better with R8 than with R16. Cine display fluidity was better with IP than with R16 and better with R16 than with IS. CONCLUSION: FTI improved image quality not only over that provided by R16 but even over that provided by R8. The sole worsened LV functional parameter was LVEF, which was slightly underestimated with respect to that estimated by R16. Of the 2 FTI variants, IP was superior to IS for cine display fluidity and accuracy of the LV volume curve with respect to the data obtained with R16. Therefore, FTI to 16fr/cb performed before reconstruction on a pixel-by-pixel basis on 8fr/cb projections improves image quality and cine display fluidity over those of both R8 and R16 acquisitions at the sole cost of a 1% underestimation of LVEF.

Interobserver agreement of qualitative analysis and tumor delineation of 18F-fluoromisonidazole and 3'-deoxy-3'-18F-fluorothymidine PET images in lung cancer.

UNLABELLED: As the preparation phase of a multicenter clinical trial using (18)F-fluoro-2-deoxy-d-glucose ((18)F-FDG), (18)F-fluoromisonidazole ((18)F-FMISO), and 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) in non-small cell lung cancer (NSCLC) patients, we investigated whether 18 nuclear medicine centers would score tracer uptake intensity similarly and define hypoxic and proliferative volumes for 1 patient and we compared different segmentation methods. METHODS: Ten (18)F-FDG, ten (18)F-FMISO, and ten (18)F-FLT PET/CT examinations were performed before and during curative-intent radiotherapy in 5 patients with NSCLC. The gold standards for uptake intensity and volume delineation were defined by experts. The between-center agreement (18 nuclear medicine departments connected with a dedicated network, SFMN-net [French Society of Nuclear Medicine]) in the scoring of uptake intensity (5-level scale, then divided into 2 levels: 0, normal; 1, abnormal) was quantified by κ-coefficients (κ). The volumes defined by different physicians were compared by overlap and κ. The uptake areas were delineated with 22 different methods of segmentation, based on fixed or adaptive thresholds of standardized uptake value (SUV). RESULTS: For uptake intensity, the κ values between centers were, respectively, 0.59 for (18)F-FDG, 0.43 for (18)F-FMISO, and 0.44 for (18)F-FLT using the 5-level scale; the values were 0.81 for (18)F-FDG and 0.77 for both (18)F-FMISO and (18)F-FLT using the 2-level scale. The mean overlap and mean κ between observers were 0.13 and 0.19, respectively, for (18)F-FMISO and 0.2 and 0.3, respectively, for (18)F-FLT. The segmentation methods yielded significantly different volumes for (18)F-FMISO and (18)F-FLT (P < 0.001). In comparison with physicians, the best method found was 1.5 × maximum SUV (SUVmax) of the aorta for (18)F-FMISO and 1.3 × SUVmax of the muscle for (18)F-FLT. The methods using the SUV of 1.4 and the method using 1.5 × the SUVmax of the aorta could be used for (18)F-FMISO and (18)F-FLT. Moreover, for (18)F-FLT, 2 other methods (adaptive threshold based on 1.5 or 1.6 × muscle SUVmax) could be used. CONCLUSION: The reproducibility of the visual analyses of (18)F-FMISO and (18)F-FLT PET/CT images was demonstrated using a 2-level scale across 18 centers, but the interobserver agreement was low for the (18)F-FMISO and (18)F-FLT volume measurements. Our data support the use of a fixed threshold (1.4) or an adaptive threshold using the aorta background to delineate the volume of increased (18)F-FMISO or (18)F-FLT uptake. With respect to the low tumor-on-background ratio of these tracers, we suggest the use of a fixed threshold (1.4).