Cyril Jaudet

The retrospective binning method improves the consistency of phase binning in respiratory-gated PET/CT

This study assesses the accuracy of prospective phase-gated PET/CT data binning and presents a retrospective data binning method that improves image quality and consistency. Respiratory signals from 17 patients who underwent 4D PET/CT were analysed to evaluate the reproducibility of temporal triggers used for the standard phase-based gating method. Breathing signals were reprocessed to implement retrospective PET data binning. The mean and standard deviation of time lags between automatic triggers provided by the Real-time Position Management (RPM, Varian) gating device and inhalation peaks derived from respiratory curves were computed for each patient. The total number of respiratory cycles available for 4D PET/CT according to the binning mode (prospective versus retrospective) was compared. The maximum standardized uptake value (SUV(max)), biological tumour volume (BTV) and tumour trajectory measures were determined from the PET/CT images of five patients. Compared to retrospective binning (RB), prospective gating approach led to (i) a significant loss in breathing cycles (15%) and (ii) the inconsistency of data binning due to temporal dispersion of triggers (average 396 ms). Consequently, tumour characterization could be impacted. In retrospective mode, SUV(max) was up to 27% higher, where no significant difference appeared in BTV. In addition, prospective mode gave an inconsistent spatial location of the tumour throughout the bins. Improved consistency with breathing patterns and greater motion amplitude of the tumour centroid were observed with retrospective mode. The detection of the tumour motion and trajectory was improved also for small temporal dispersion of triggers. This study shows that the binning mode could have a significant impact on 4D PET images. The consistency of triggers with breathing signals should be checked before clinical use of gated PET/CT images, and our RB method improves 4D PET/CT image quantification.

A new respiratory gating device to improve 4D PET/CT

PURPOSE Respiratory motion creates artifacts in positon emission tomography with computed tomography (PET/CT) images especially for lung tumors, and can alter diagnosis. To account for motion effects, respiratory gating techniques have been developed. However, the lack of measures strongly correlated with tumor motion limits their accuracy. The authors developed a real-time pneumotachograph device (SPI) allowing to sort PET and CT images depending on lung volumes. METHODS The performance of this innovative respiratory tracking system was characterized and compared to a standard system. Our experimental setup consisted in a movable platform and a thorax phantom with six fillable spheres simulating lung tumors. The accuracy of SPI to detect inhalation peaks was also determined on volunteers. A comparison with the real-time position management (RPM) device, that relies on abdominal height measurement, was then investigated. RESULTS Experiments showed a high accuracy of the measured signal compared to the input signal (R = 0.88 to 0.99), and of the detection of the inhalation peaks (error of 0.1 +/- 5.8 ms) necessary for prospective binning mode. Activity recovery coefficient was improved (until +39%) and the smearing effect was reduced (until 2.74 times lower) with SPI compared to ungated PET/CT acquisition. The spatial distribution of activity in spheres was similar for 4D PET gated with SPI and RPM. Significant improvement of the binning stability and matching between PET and CT were highlighted for irregular breathing patterns with SPI. CONCLUSIONS SPI is an innovative device that provides better binning performance than the current gating device on phantom experiments. Future works will focus on patients where the authors expect a significant improvement of specificity and sensitivity of PET/CT examinations.

Limits of radiomic-based entropy as a surrogate of tumor heterogeneity: ROI-area, acquisition protocol and tissue site exert substantial influence

Entropy is a promising quantitative imaging biomarker for characterizing cancer imaging phenotype. Entropy has been associated with tumor gene expression, tumor metabolism, tumor stage, patient prognosis, and treatment response. Our hypothesis states that tumor-specific biomarkers such as entropy should be correlated between synchronous metastases. Therefore, a significant proportion of the variance of entropy should be attributed to the malignant process. We analyzed 112 patients with matched/paired synchronous metastases (SM#1 and SM#2) prospectively enrolled in the MOSCATO-01 clinical trial. Imaging features were extracted from Regions Of Interest (ROI) delineated on CT-scan using TexRAD software. We showed that synchronous metastasis entropy was correlated across 5 Spatial Scale Filters: Spearman’s Rho ranged between 0.41 and 0.59 (P = 0.0001, Bonferroni correction). Multivariate linear analysis revealed that entropy in SM#1 is significantly associated with (i) primary tumor type; (ii) entropy in SM#2 (same malignant process); (iii) ROI area size; (iv) metastasis site; and (v) entropy in the psoas muscle (reference tissue). Entropy was a logarithmic function of ROI area in normal control tissues (aorta, psoas) and in mathematical models (P < 0.01). We concluded that entropy is a tumor-specific metric only if confounding factors are corrected.

Quality controls and delineation protocol of PET/CT gated acquisition in function of the movement amplitude, size of spheres and signal over background ratio

This study presents quality controls and segmentation tools for gated acquisition imaging of moving tumors. We study the effect of different amplitudes in a bin in function of sizes of spheres and signal to background ratios. Simple rules are then derived to establish which bins are appropriate to quantify tumor activity and to delineate volume. Finally the threshold technics for gated acquisition exams are discussed in function of the different parameters. Our experimental setup consisted of a movable platform, a thorax phantom with 6 fillable spheres and a real time position management device allowing to synchronize the PET/CT image with movement. The spheres were filled with F-Fluoro-2-deoxy-glucose and the activity in the tank was adjusted to obtain signal to background ratios from 3.5 to 20 (228 combinations of experimental parameters were studied). Maximal activity, optimal threshold and elongation of the sphere images between static and moving tumors were then compared with our own matlab program. Significant changes had appearing for movement superior to 7.5 mm in a bin leading to an activity decrease, an increase of the optimal threshold and an elongation in the movement direction. These effects were accentuated for low SBR and a sphere diameter inferior to 20 mm. The optimal threshold value was around 35% for large spheres and high SBR. This value increase when the sphere size and the SBR decrease. We then deduce from our measurements the relevant parameters for the delineation procedure. In conclusion, the effect of movement were successfully quantified in function of the sphere size, SBR and movement in a bin. Calibration threshold curves are now available in a clinical routine used for gated acquisitions.

Comparison of an alternative and existing binning methods to reduce the acquisition duration of 4D PET/CT.

PURPOSE Respiratory motion is a source of artifacts that reduce image quality in PET. Four dimensional (4D) PET/CT is one approach to overcome this problem. Existing techniques to limiting the effects of respiratory motions are based on prospective phase binning which requires a long acquisition duration (15-25 min). This time is uncomfortable for the patients and limits the clinical exploitation of 4D PET/CT. In this work, the authors evaluated an existing method and an alternative retrospective binning method to reduce the acquisition duration of 4D PET/CT. METHODS The authors studied an existing mixed-amplitude binning (MAB) method and an alternative binning method by mixed-phases (MPhB). Before implementing MPhB, they analyzed the regularity of the breathing patterns in patients. They studied the breathing signal drift and missing CT slices that could be challenging for implementing MAB. They compared the performance of MAB and MPhB with current binning methods to measure the maximum uptake, internal volume, and maximal range of tumor motion. RESULTS MPhB can be implemented depending on an optimal phase (in average, the exhalation peak phase -4.1% of the entire breathing cycle duration). Signal drift of patients was in average 35% relative to the breathing amplitude. Even after correcting this drift, MAB was feasible in 4D CT for only 64% of patients. No significant differences appeared between the different binning methods to measure the maximum uptake, internal volume, and maximal range of tumor motion. The authors also determined the inaccuracies of MAB and MPhB to measure the maximum amplitude of tumor motion with three bins (less than 3 mm for movement inferior to 12 mm, up to 6.4 mm for a 21 mm movement). CONCLUSIONS The authors proposed an alternative binning method by mixed-phase binning that halves the acquisition duration of 4D PET/CT. Mixed-amplitude binning was challenging because of signal drift and missing CT slices. They showed that more than three bins were necessary for a more accurate measurement of the maximum amplitude of the tumor motion. However, the current 4D-CT technology limits the increase of the number of bins in 4D PET/CT because of missing CT slices. One can reconstruct 4D PET images with more bins but without attenuation/scatter correction.

Dynamic Scintigraphy With SPECT-CT of Postoperative Salivary Leak.

This 65 year-old woman, 1 month postoperative after maxillary sinus carcinoma (pT4N0cM0) excision and reconstruction, presented with significant left facial clear fluid wound leakage. A salivary or cerebrospinal leakage was suspected. Fluid analysis, CT, and MRI were noncontributory. Dynamic salivary scintigraphy with SPECT-CT allowed for the detection and localization of the leakage from the left parotid gland. Radioactive dose rate of the wound bandage was 50 μSv/h compared with 0.05 μSv/h for background and confirmed the diagnosis. Left total parotidectomy resulted in resolution.