Eric Laffon

Measurement of cardiac ventricular volumes using multidetector row computed tomography: comparison of two- and three-dimensional methods

This study compared a three-dimensional volumetric threshold-based method to a two-dimensional Simpson’s rule based short-axis multiplanar method for measuring right (RV) and left ventricular (LV) volumes, stroke volumes, and ejection fraction using electrocardiography-gated multidetector computed tomography (MDCT) data sets. End-diastolic volume (EDV) and end-systolic volume (ESV) of RV and LV were measured independently and blindly by two observers from contrast-enhanced MDCT images using commercial software in 18 patients. For RV and LV the three-dimensionally calculated EDV and ESV values were smaller than those provided by two-dimensional short axis (10%, 5%, 15% and 26% differences respectively). Agreement between the two methods was found for LV (EDV/ESV: r=0.974/0.910, ICC=0.905/0.890) but not for RV (r=0.882/0.930, ICC=0.663/0.544). Measurement errors were significant only for EDV of LV using the two-dimensional method. Similar reproducibility was found for LV measurements, but the three-dimensional method provided greater reproducibility for RV measurements than the two-dimensional. The threshold value supported three-dimensional method provides reproducible cardiac ventricular volume measurements, comparable to those obtained using the short-axis Simpson based method.

Estimating the amount of FDG uptake in physiological tissues

INTRODUCTION It is known that for a fixed amount of injected tracer, the amount available for a tissue of interest will be less if other tissues show intense uptake. The aim of this study was to estimate the magnitude of 2-deoxy-2-[(18)F]fluoro-D-glucose (18FDG) uptake amount in physiological tissues that may show an intense uptake in current clinical practice. METHODS A formula was established providing an estimate of the percentage of injected 18FDG molecules (P; in %) that are irreversibly trapped in an 18FDG-positive tissue during a PET examination. RESULTS P ≅ 0.17*exp(-λt(acq))*TLG/W, where λ is the (18)F physical decay constant, t(acq) is the injection-acquisition time delay, TLG is total lesion glycolysis (g) and W is the patient weight (kg). The magnitude of P was calculated in two patients showing an intense uptake in brown fat, myocardium and bowels: 0.5, 3.5, and 4.2% respectively. CONCLUSIONS A formula is available to quickly estimate the amount of 18FDG uptake in tissues. We suggest that the accumulation of different physiological uptakes may actually affect SUV quantification in a tissue of interest.

Variability of Total Lesion Glycolysis by 18F-FDG–Positive Tissue Thresholding in Lung Cancer

The aim of this work was to assess the variability of total lesion glycolysis (TLG) measurements in lung cancer patients, obtained with fixed percentages of the maximum standardized uptake value (SUVmax) thresholds. Methods: Thirteen lesions (10 patients) were analyzed in 10 successive 2.5-min frames of an 18F-FDG PET dynamic acquisition obtained between 60 and 110 min after injection. 18F-FDG–positive lesion volume, associated average SUV (SUVmean), and TLG (volume × SUVmean) were assessed in each frame using thresholds of 40%, 50%, 60%, 70%, and 80%. For each threshold, the average relative SD of TLG, leading to relative measurement error and repeatability, was calculated over the lesion series. The dependence of TLG variability on volume and SUVmean variability was also assessed. Results: The average relative SD of TLG correlated strongly with threshold: 1.0866 × exp(0.0472 × threshold) (r = 0.999; P < 0.01). For the 40% threshold, average TLG over the series was 225.9 g (range, 41.7–1,086.3), relative measurement error and repeatability were 14.5%–20.4% (95% confidence interval), and no significant difference was found between TLG and volume variability. For the other thresholds, TLG variability was significantly lower or greater than volume or SUVmean variability, respectively. Conclusion: In current clinical practice, a formula allows quick estimation of TLG variability for any percentage of the SUVmax threshold: the higher the threshold the greater the TLG variability.

SUVpeak Performance in Lung Cancer: Comparison to Average SUV from the 40 Hottest Voxels

The performance of an average SUV over a 1-mL-volume sphere within an 18F-FDG–positive lesion resulting in the highest possible value (SUVpeakW) was compared with that of an average SUV computed from the 40 hottest voxels, irrespective of their location within the lesion (SUVmax-40). Methods: Dynamic PET performed in 20 lung cancer lesions yielded for each SUV metric its mean value, relative measurement error, and repeatability (MEr-R). Results: SUVpeakW mean value was significantly 9.66% lower than that of SUVmax-40 (P < 0.0001). SUVpeakW and SUVmax-40 MEr-R were significantly lower than the MEr-R of SUVmax (the hottest voxel): 9.35%–13.21% and 8.84%–12.49% versus 13.86%–19.59%, respectively, (95% confidence limit; P < 0.0001). Although being marginal, SUVpeakW MEr-R was not significantly greater than SUVmax-40 MEr-R (P = 0.086). Conclusion: SUVmax-40 is more likely to represent the most metabolically active portions of tumors than SUVpeakW, with close variability performance.

Le mésothéliome pleural : place de l’imagerie

Resume L’imagerie joue un role essentiel dans la prise en charge des patients porteurs d’un mesotheliome pleural. Cet article presente les roles respectifs de l’echographie, de la tomodensitometrie, de la resonance magnetique et de la tomographie a emission de positons dans le diagnostic, la stadification et l’evaluation post-therapeutique.

Transit‐time method to demonstrate whether or not an impedance matching occurs at the pulmonary junction

We read with great interest the article by Bradlow et al (1) in which the transit-time method was used to assess the pressure wave velocity (PWV) in the proximal right and left pulmonary arteries (RPA and LPA, respectively). Any attempt in this field is of value because it may actually open up potential applications, such as the screening of individuals at risk for pulmonary arterial hypertension (PAH) (1). However, there remain questions about fluid mechanics in general, and, in particular, about the comparison of the Bradlow et al results with those we previously obtained in the main pulmonary artery (MPA) in healthy volunteers (2). We strongly believe that the values for RPA and LPA PWV reported by Bradlow et al (1) cannot be directly compared with those we reported for MPA PWV (2). The reason is not related to the difference in assessment methods, but rather to fluid mechanics. Indeed, the MPA divides into the RPA and LPA, the PWV of which involves vessel impedance and cross-sectional area (CSA) (2,3). The Bradlow et al (1) analysis did not address the issue of a possible different impedance of MPA and RPA LPA that would generate a reflected PW back to the right ventricle. This point can be addressed if separate results on the three vessels PWV and CSA are provided. Indeed, it can theoretically be shown that impedance matching is obtained when: