Pascal Bailly

Background/Objectives: Determining whether 3,4-dihydroxy-6-[¹⁸F]fluoro-L-phenylalanine positron emission tomography/computed tomography ([¹⁸F]F-DOPA PET/CT) data indicate brain metastasis progression (MP) or brain radionecrosis (RN) is challenging. The aim of this study was to present a method usable in the clinical setting without dedicated software that relies on less than five minutes of SiPM PET/CT data collected immediately after [¹⁸F]F-DOPA injection. Methods: We prospectively enrolled 15 patients with 19 lesions. Each acquisition was conducted in list mode (LM) for 25 min using a four-ring SiPM PET/CT system. We reconstructed three volumes from the LM file: acquisition duration of 120 s (V120), 270 s (V270), and 10 min for the standard clinical volume (Vclin). We measured each lesion’s maximum voxel activity (LS_max) and the corresponding mean activity with its standard deviation (CL_mean, CL_sd). We then calculated the LS_max/CL_mean ratio and the coefficient of variation (COV), defined as 100 × (CL_sd/CL_mean). Results: Lesions were classified as RN (n = 7) and MP (n = 12). For all volumes, LS_max/CL_mean differed significantly. The COV parameter exhibited significant differences in all comparisons except for V120 vs. V270. The best diagnostic performances were observed for V120 and V270, with an accuracy of 94.7%. The AUC values were 97.6% in both cases. Conclusions: A simple, static [¹⁸F]F-DOPA PET/CT acquisition, starting 1.5 min after injection and lasting less than five minutes, permitted reaching excellent diagnostic performance (100% sensitivity, 91.7% specificity, and 97.6% AUC) in discriminating between RN and MP.

It is difficult to distinguish between the brain metastasis progression (BMP) and brain radionecrosis (BRN) on the basis of 18F-3,4-dihydroxyphenylalanine positron emission tomography/computed-tomography (18F-FDOPA PET/CT) data. The advent of silicon photomultiplier (SiPM) PET technology makes it possible to study dynamic volumes and potentially improve diagnostic accuracy. We developed a method for processing 18F-FDOPA PET/CT in the differential diagnosis between BMP and BRN. The method involves a short (3-second) sampling time during a 4-minute acquisition on a SiPM-PET/CT machine. We prospectively included 15 patients and 19 metastases. All acquisitions were performed in list mode acquisition for 25 min on a four-ring SiPM PET/CT system. We calculated the ratios between the maximum activity in the lesion’s voxel and the mean activity in the contralateral region (VOImax/CLmean) or the mean activity in the white matter (VOImax/WMmean). Seven lesions were classified as BMP and twelve were classified as BRN. Statistically significant intergroup differences in the VOImax/CLmean and VOImax/WMmean activity ratios were observed for both the clinical volume and the early acquisition. The best performing quantitative variable was the VOImax/CLmean ratio on early acquisition, with a diagnostic accuracy of 94.7%, a sensitivity of 100%, and a specificity of 91.7%. The 18F-FDOPA PET/CT data acquired a few minutes after the bolus injection confirms its value in differentiating between BMP and BRN, compared to the much longer classic clinical protocol.

Chronic obstructive pulmonary disease (COPD) is characterized by low vital capacity and tidal volume, which translate into smaller respiratory motions. We sought to demonstrate the limited respiratory motion in COPD by comparing respiratory-gated and free-breathing positron emission tomography (PET) images of lung nodules (“CT-based” and “Ungated” images) in patients with and without COPD. We studied 74 lung lesions (37 malignant) in 60 patients (23 patients with COPD; 37 without). An Ungated PET examination was followed by a CT-based acquisition. Maximum standard uptake value (SUV_max) for each lesion on PET images was measured. On CT images, we checked for the presence of emphysema and pleural adhesions or indentations associated with the nodules. Lastly, we used univariate and then multivariate analyses to determine the lung function parameters possibly affecting respiratory motion in patients with and without COPD. The mean “CT-based” vs. “Ungated” difference in SUV_max was 0.3 and 0.6 for patients with and without COPD, respectively. Statistical analysis revealed that lesion site, hyperinflation and pleural indentation were independently associated with a difference in SUVmax. PET lung lesion images in patients with COPD are barely influenced by respiratory motion. Thoracic hyperinflation in patients with COPD was found to be independently associated with an effect of respiratory motion on PET images. Moreover, pleural indentation limits the respiratory motion of lung nodules, regardless of the presence or absence of COPD.

In whole‐body positron emission tomography (PET) imaging, the detection of small uptake foci (i.e., around two or three times the tomograph's spatial resolution) is a critical issue. Indeed, spatial ...

Background: Respiratory motion causes uptake in positron emission tomography (PET) images of chest and abdominal structures to be blurred and reduced in intensity. Purpose: To compare two respiratory-gated PET binning methods (based on frequency and amplitude analyses of the respiratory signal) and to propose a “BH-based” method based on an additional breath-hold computed tomography (CT) acquisition. Material and Methods: Respiratory-gated PET consists in list-mode (LM) acquisition with simultaneous respiratory signal recording. A phantom study featured rectilinear movement of a 0.5-ml sphere filled with ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) solution, placed in a radioactive background (sphere-to-background contrast 6:1). Two patients were also examined. Three figures of merit were calculated: the target-to-background ratio profile (TBRP) in the axial direction through the uptake (i.e., the sphere or lesion), full-width-at-half-maximum (FWHM) values, and maximized standard uptake values (SUV_max). Results: In the phantom study, the peak TBRP was 0.9 for non-gated volume, 1.83 for BH-based volume, and varied between 1.13 and 1.73 for Freq-based volumes and between 1.34 and 1.66 for Amp-based volumes. A reference volume (REF-static) was also acquired for the phantom (in a static, “expiratory” state), with a peak TBRP at 1.88. TBRPs were computed for patient data, with higher peak values for all gated volumes than for non-gated volumes. Conclusion: Respiratory-gated PET acquisition reduces the blurring effect and increases image contrast. However, Freq-based and Amp-based volumes are still influenced by inappropriate attenuation correction and misregistration of mobile lesions on CT images. The proposed BH-based method both reduces motion artifacts and improves PET-CT registration.