Attenuation Correction Of Emission Data Research Articles

Image Quality Assessment for Low-Dose-CT in Hybrid SPECT/CT Imaging.

Low-dose-computed tomography (LD-CT) is used in nuclear medicine hybrid imaging (e.g., SPECT/CT) for attenuation correction of emission data and anatomical correlation of findings. However, there are currently no standards for image quality (e. g., detectability) comparable to those for diagnostic CT. Therefore, the aim of this explorative study was to evaluate retrospective LDCT data in terms of CT image quality and detectability of anatomical structures. Two readers blindly scored abdominal LD-CT images (n = 40 patients) in terms of detectability (n = 20 structures/patient), image quality, and readers' confidence in scoring the image quality for a clinically hybrid imaging protocol. Results were analysed by ANOVA to identify factors (e. g., anatomical structures) that influenced performance scores. The inter-rater agreement was evaluated by determining the chance-corrected Cohen's Kappa coefficient. Image noise was acceptable for anatomical correlation in 96.1 % of the readings with an almost perfect inter-rater agreement (KBP = 0.85). A detectability of at least 80 % was observed in 13/20 (KBP ≥ 0.7) and 90 % in 9/20 (KBP ≥ 0.85) of the structures analysed by both readers. The confidence of both readers in scoring image quality was at least sufficient in 98.8 % of the examined patients (KBP = 0.95). Although LD-CT protocols commonly used in hybrid imaging have a poor image quality not suitable for primary CT diagnostics, they enable detection of a variety of anatomical structures. LDCT can therefore also be referenced in the associated reports for anatomical correlation of findings from SPECT imaging.

CT and PET Image Registration: Application to Thorax Area

Accurate attenuation correction of emission data is mandatory for quantitative analysis of PET images. One of the main concerns in CT-based attenuation correction (CTAC) of PET data in multimodalit ...

Comparison of integrated whole-body [11C]choline PET/MR with PET/CT in patients with prostate cancer

To evaluate the performance of conventional [(11)C]choline PET/CT in comparison to that of simultaneous whole-body PET/MR. The study population comprised 32 patients with prostate cancer who underwent a single-injection dual-imaging protocol with PET/CT and subsequent PET/MR. PET/CT scans were performed applying standard clinical protocols (5 min after injection of 793 ± 69 MBq [(11)C]choline, 3 min per bed position, intravenous contrast agent). Subsequently (52 ± 15 min after injection) PET/MR was performed (4 min per bed position). PET images were reconstructed iteratively (OSEM 3D), scatter and attenuation correction of emission data and regional allocation of [(11)C]choline foci were performed using CT data for PET/CT and segmented Dixon MR, T1 and T2 sequences for PET/MR. Image quality of the respective PET scans and PET alignment with the respective morphological imaging modality were compared using a four point scale (0-3). Furthermore, number, location and conspicuity of the detected lesions were evaluated. SUVs for suspicious lesions, lung, liver, spleen, vertebral bone and muscle were compared. Overall 80 lesions were scored visually in 29 of the 32 patients. There was no significant difference between the two PET scans concerning number or conspicuity of the detected lesions (p not significant). PET/MR with T1 and T2 sequences performed better than PET/CT in anatomical allocation of lesions (2.87 ± 0.3 vs. 2.72 ± 0.5; p = 0.005). The quality of PET/CT images (2.97 ± 0.2) was better than that of the respective PET scan of the PET/MR (2.69 ± 0.5; p = 0.007). Overall the maximum and mean lesional SUVs exhibited high correlations between PET/CT and PET/MR (ρ = 0.87 and ρ = 0.86, respectively; both p < 0.001). Despite a substantially later imaging time-point, the performance of simultaneous PET/MR was comparable to that of PET/CT in detecting lesions with increased [(11)C]choline uptake in patients with prostate cancer. Anatomical allocation of lesions was better with simultaneous PET/MR than with PET/CT, especially in the bone and pelvis. These promising findings suggest that [(11)C]choline PET/MR might have a diagnostic benefit compared to PET/CT in patients with prostate cancer, and now needs to be further evaluated in prospective trials.

Comparative Assessment of Energy-Mapping Approaches in CT-Based Attenuation Correction for PET

Reliable quantification in positron emission tomography (PET) requires accurate attenuation correction of emission data, which in turn entails accurate determination of the attenuation map (µ-map) of the object under study. One of the main steps involved in CT-based attenuation correction (CTAC) is energy-mapping, or the conversion of linear attenuation coefficients (µ) calculated at the effective CT energy to those corresponding to 511 keV. The aim of this study is to compare different energy-mapping techniques including scaling, segmentation, the hybrid method, the bilinear calibration curve technique and the dual-energy approach to generate the µ-maps required for attenuation correction. In addition, our newly proposed method involving a quadratic polynomial calibration curve was also assessed. The µ-maps generated for both phantom and clinical studies were assessed qualitatively and quantitatively. A cylindrical polyethylene phantom containing different concentrations of K(2)HPO(4) in water was scanned and the µ-maps calculated from the corresponding CT images using the above-referenced energy-mapping methods. The CT images of five whole-body data sets acquired on a GE Discovery LS PET/CT scanner were employed to generate µ-maps using different energy-mapping approaches that were compared with the µ-maps generated at 511 keV using (68)Ge/(68)Ga rod sources. In another experiment, the evaluation was performed on PET images of a clinical study corrected for attenuation using µ-maps generated using the above described methods. The evaluation was performed for three different tissue types, namely, soft tissue, lung, and bone. All energy-mapping methods yielded almost similar results for soft tissues. The mean relative differences between scaling, segmentation, hybrid, bilinear, and quadratic polynomial calibration curve methods and the transmission scan serving as reference were 6.60%, 6.56%, 6.60%, 5.96%, and 7.36%, respectively. However, the scaling method produced the largest difference (16%) for bone tissues. For lung tissues, the segmentation method produced the largest difference (14.9%). The results for reconstructed PET images followed a similar trend. For soft tissues, all energy-mapping methods yield results in nearly the same range. However, in bone tissues, the scaling method resulted in considerable bias in the µ-maps and the reconstructed PET images. The segmentation method also produced noticeable bias especially in regions with variable densities such as the lung, since a single µ is assigned to the lungs. Apart from the aforementioned case, despite small differences in the generated µ-maps, the use of different energy-mapping methods does not affect, to a visible or measurable extent, the reconstructed PET images.

Réduction des effets de la respiration en imagerie TEP pulmonaire par une acquisition synchronisée à la respiration associée à une TDM en apnée

Respiratory motion causes a spread of lesion uptake over a larger area in Positron Emission Tomography (PET) images for moving structures. When CT images are used for attenuation correction of emission data, this motion may alter the quantization of PET images. We present the clinical results of a respiratory-gated PET processing “CT-based” method, which aims to improve PET-CT coregistration by using an additional breath-hold CT (BH-CT). The CT-based protocol consisted in a 10-min List Mode respiratory-gated PET acquisition, followed by an end-expiration BH-CT acquisition. During these two examinations, the respiratory signal was recorded continuously. Eleven pulmonary lesions were studied. Patients underwent both a standard clinical PET protocol (free breathing) and the CT-based protocol. The respective performances of the CT-based and clinical PET methods were evaluated by comparing the distances between the lesions’ centroids on PET and CT images. SUV MAX (Standardized Uptake Value) and volume variations were also investigated. The CT-based method showed a significant reduction ( p = 0.049) of centroid distances (mean relative change versus standard method: 49%). We also noted a higher SUV MAX (mean change: 39%). Lesion volumes were significantly lower ( p = 0.026) in CT-based PET volumes (mean change: 43%) compared with standard ones. The CT-based method improves PET-CT coregistration of pulmonary lesions. This protocol should lead to more accurate attenuation correction and thus improve SUV measurement.

Getting through without charging through

We investigated radiation exposure of patients undergoing whole-body ¹⁸F-FDG PET/CT examinations at 4 hospitals equipped with different tomographs. <b>Methods:</b> Patient doses were estimated by using established dose coefficients for ¹⁸F-FDG and from thermoluminescent measurements performed on an anthropomorphic whole-body phantom. <b>Results:</b> The most relevant difference between the protocols examined was the incorporation of CT as part of the combined PET/CT examination: Separate low-dose CT scans were acquired at 2 hospitals for attenuation correction of emission data in addition to a contrast-enhanced CT scan for diagnostic evaluation, whereas, at the other sites, contrast-enhanced CT scans were used for both purposes. Nevertheless, the effective dose per PET/CT examination was similar, about 25 mSv. <b>Conclusion:</b> The dosimetric concepts presented in this study provide a valuable tool for the optimization of whole-body ¹⁸F-FDG PET/CT protocols. Further reduction of patient exposure can be achieved by modifications to the existing hardware and software of PET/CT systems.

Impact of metallic dental implants on CT-based attenuation correction in a combined PET/CT scanner.

Our objective was to study the effect of metal-induced artifacts on the accuracy of the CT-based anatomic map as a prerequisite for attenuation correction of the positron emission tomography (PET) emission data. Twenty-seven oncology patients with dental metalwork were enrolled in the present study. Data acquisition was performed on a PET/CT in-line system (Discovery LS, GE Medical Systems, Milwaukee, Wis.). Attenuation correction of emission data was done twice, using an 80-mA CT scan (PET(CT80)) and a (68)Ge transmission scan (PET(68Ge)). Average count in kBq/cc was measured in regions with and without artifacts and compared for PET(CT80) and PET(68Ge). Data analysis of region of interests (ROIs) revealed that the ratio (ROIs PET(CT80)/ROIs PET(68Ge)) and the difference (ROIs PET(CT80) minus ROIs PET(68Ge)) had a higher mean of values in regions with artifacts than in regions without artifacts (1.2+/-0.17 vs 1.06+/-0.06 and 0.68+/-0.67 vs 0.15+/-0.17 kBq/cc, respectively). For most of the studied artifactual ROIs, the PET(CT80) values were higher than those of the PET(68Ge). Attenuation correction of PET emission data using an artifactual CT map yields false values in regions nearby artifacts caused by dental metalwork. This may falsely estimate PET quantitative studies and may disturb the visual interpretation of PET scan.