The influence of respiratory motion on the cumulative SUV-volume histogram and fractal analyses of intratumoral heterogeneity in PET/CT imaging

Early Monitoring Response to Therapy in Patients with Brain Lesions Using the Cumulative SUV Histogram

Gamma Knife treatment is an alternative to traditional brain surgery and whole-brain radiation therapy for treating cancers that are inaccessible via conventional treatments. To assess the effectiveness of Gamma Knife treatments, functional imaging can play a crucial role. The aim of this study is to evaluate new prognostic indices to perform an early assessment of treatment response to therapy using positron emission tomography imaging. The parameters currently used in nuclear medicine assessments can be affected by statistical fluctuation errors and/or cannot provide information on tumor extension and heterogeneity. To overcome these limitations, the Cumulative standardized uptake value (SUV) Histogram (CSH) and Area Under the Curve (AUC) indices were evaluated to obtain additional information on treatment response. For this purpose, the absolute level of [11C]-Methionine (MET) uptake was measured and its heterogeneity distribution within lesions was evaluated by calculating the CSH and AUC indices. CSH and AUC parameters show good agreement with patient outcomes after Gamma Knife treatments. Furthermore, no relevant correlations were found between CSH and AUC indices and those usually used in the nuclear medicine environment. CSH and AUC indices could be a useful tool for assessing patient responses to therapy.

The association between 18F-fluorodeoxyglucose PET intratumoral metabolic heterogeneity and pathological parameters in non-small cell lung cancer

OBJECTIVE

The aim of this study was to evaluate the association between intratumoral metabolic heterogeneity on F-fluorodeoxyglucose (F-FDG) PET imaging and the pathological type, differentiation and T stage of non-small cell lung cancer (NSCLC).

METHODS

Two hundred thirty-four consecutive patients who were performed pretreatment F-FDG PET/computed tomography and pathologically diagnosed as NSCLC were assessed retrospectively. Metabolic heterogeneity factor (MHF) derived from the volume-threshold function from 40 to 90% was calculated for primary lesions. The association between MHF and the pathological type, differentiation and T stage of NSCLC were analyzed, respectively.

RESULTS

The MHF values were statistically different among pathological types, differentiation and T stages (F = 17.611, 23.932 and 11.082, P all < 0.001). MHF showed a stepwise increase with the reduced degree of differentiation and increase of T stage. The trend analysis presented a strong positive relationship between MHF and T stage (P < 0.05), but a correlated inversely and strongly relationship was demonstrated between MHF and diffferentiation (P < 0.001). Moreover, multivariate ordinal logistic regression analysis showed that MHF was independently associated with tumor T stage and differentiation after adjusting for clinical factors.

CONCLUSION

MHF showed high association with pathological parameters, which can be used to accurately predict the biological behaviors of tumors from the molecular level thus to provide important biological information for tumor diagnosis and treatment.

Activity painting: PET images of freely defined activity distributions applying a novel phantom technique

The aim of this work was to develop a novel phantom that supports the construction of highly reproducible phantoms with arbitrary activity distributions for PET imaging. It could offer a methodology for answering questions related to texture measurements in PET imaging. The basic idea is to move a point source on a 3-D trajectory in the field of view, while continuously acquiring data. The reconstruction results in a 3-D activity concentration map according to the pathway of the point source. A 22Na calibration point source was attached to a high precision robotic arm system, where the 3-D movement was software controlled. 3-D activity distributions of a homogeneous cube, a sphere, a spherical shell and a heart shape were simulated. These distributions were used to measure uniformity and to characterize reproducibility. Two potential applications using the lesion simulation method are presented: evaluation in changes of textural properties related to the position in the PET field of view; scanner comparison based on visual and quantitative evaluation of texture features. A lesion with volume of 50x50x50 mm3 can be simulated during approximately 1 hour. The reproducibility of the movement was found to be >99%. The coefficients of variation of the voxels within a simulated homogeneous cube was 2.34%. Based on 5 consecutive and independent measurements of a 36 mm diameter hot sphere, the coefficient of variation of the mean activity concentration was 0.68%. We obtained up to 18% differences within the values of investigated textural indexes, when measuring a lesion in different radial positions of the PET field of view. In comparison of two different human PET scanners the percentage differences between heterogeneity parameters were in the range of 5-55%. After harmonizing the voxel sizes this range reduced to 2-16%. The general activity distributions provided by the two different vendor show high similarity visually. For the demonstration of the flexibility of this method, the same pattern was also simulated on a small animal PET scanner giving similar results, both quantitatively and visually. 3-D motion of a point source in the PET field of view is capable to create an irregular shaped activity distribution with high reproducibility.

Comparison of image quality between step-and-shoot and continuous bed motion techniques in whole-body 18F-fluorodeoxyglucose positron emission tomography with the same acquisition duration

OBJECTIVE

This study aimed to compare the qualities of whole-body positron emission tomography (PET) images acquired by the step-and-shoot (SS) and continuous bed motion (CBM) techniques with approximately the same acquisition duration, through phantom and clinical studies.

METHODS

A body phantom with 10-37 mm spheres was filled with ¹⁸F-fluorodeoxyglucose (FDG) solution at a sphere-to-background radioactivity ratio of 4:1 and acquired by both techniques. Reconstructed images were evaluated by visual assessment, percentages of contrast (%Q _H) and background variability (%N) in accordance with the Japanese guideline for oncology FDG-PET/computed tomography (CT). To evaluate the variability of the standardized uptake value (SUV), the coefficient of variation (CV) for both maximum SUV and peak SUV was examined. Both the SUV values were additionally compared with those of standard images acquired for 30 min, and their accuracy was evaluated by the %difference (%Diff). In the clinical study, whole-body ¹⁸F-FDG PET/CT images of 60 patients acquired by both techniques were compared for liver signal-to-noise ratio (SNRliver), CV at end planes, and both SUV values.

RESULTS

In the phantom study, the visual assessment and %Q _H values of the two techniques did not differ from each other. However, the %N values of the CBM technique were significantly higher than those of the SS technique. Additionally, the CV and %Diff for both SUV values in the CBM images tended to be slightly higher than those in SS images. In the clinical study, the SNRliver values of CBM images were significantly lower than those of SS images, although the CV at the end planes in CBM images was significantly lower than those in SS images. In the Bland-Altman analysis for both SUV values, the mean differences were close to 0, and most lesions exhibited SUVs within the limits of agreement.

CONCLUSIONS

The CBM technique exhibited slightly lesser uniformity in the center plane than the SS technique. Additionally, in the phantom study, the CV and %Diff of SUV values in CBM images tended to be slightly higher than those of SS images. However, since these differences were subtle, they might be negligible in clinical settings.