Patient weight-based acquisition protocols to optimize18F-FDG PET/CT image quality

The choice of injected dose of 18F-FDG and acquisition time is important in obtaining consistently high-quality PET images. The aim of this study was to determine the optimal acquisition protocols based on patient weight for 3-dimensional lutetium oxyorthosilicate PET/CT. Methods: This study was a retrospective analysis of 76 patients ranging from 29 to 101 kg who were injected with 228-395.2 MBq of 18F-FDG for PET imaging. The study population was divided into 4 weightbased groups: less than 45 kg (group 1), 45-59 kg (group 2), 60-74 kg (group 3), and 75 kg or more (group 4). We measured the true coincidence rate, random coincidence rate, noise-equivalent counting rate (NECR), and random fraction and evaluated image quality by the coefficient of variance (COV) in the largest liver slices. Results: The true coincidence rate, random coincidence rate, and NECR significantly increased with increasing injected dose per kilogram (r 5 0.91, 0.83, and 0.90; all P < 0.01). NECR maximized at 10.11 MB/kg in underweight patients. The true coincidence rate differed significantly among the 4 groups, except for group 3 versus group 4 (P < 0.01). The ratio of the true coincidence rate for group 2 to groups 3 and 4 was 1.4 and 1.6, respectively. The average random fraction for all 4 groups was approximately 35%. The COV of the 4 groups differed for all pairs (P < 0.01). The COVs in overweight patients were larger than those in underweight patients, and image quality in overweight patients was poor. Conclusion: We modified acquisition protocols for 18F-FDG PET/CT according to the characteristics of a 3-dimensional lutetium orthosilicate PET scanner and PET image quality based on patient weight. The optimal acquisition time was approximately 1.4-1.6 times longer in overweight patients than in normal-weight patients. Estimation of optimal acquisition times using the true coincidence rate is more important than other variables in improving PET image quality. © 2011 by the Society of Nuclear Medicine, Inc.Thesis of Nagaki, Akio / 長木 昭男 博士学位論文(金沢大学 / 大学院医薬保健学総合研究科

CT tube current for attenuation map in a combined PET/CT system: obese patient simulated phantom study

Objective: The CT portion of PET/CT provides attenuation correction of the PET emission scan. This study was performed to evaluate how much the CT tube current can be lowered while still providing attenuation maps on PET images. Methods: Two body phantoms (outside diameters of 300 and 500 mm) were used to investigate, and PET/CT acquisitions were performed with an Aquiduo PCA-7000B (Toshiba Medical Systems, Otawara, Japan). The CT scan was performed with the following parameters (120 kVp; 0.5-s rotation; 10, 20, 40, 80, 160, 200, 320, 460 mA). After the CT scan, PET images for 18F-FDG (5.3 kBq/mL) were obtained for 4 min/bed position. The linear attenuation coefficients for 18F-FDG in 300- and 500-mm phantoms, pixel values and SD of CT images, radioactivity concentration values and hot- and cold-sphere contrast on PET images in the 500-mm phantom were evaluated. Results: In the 300-mm phantom, all eight tube currents gave average linear attenuation coefficients of approximately 0.095 cm -1. In contrast, the average linear attenuation coefficients of the 500-mm phantom at 10, 20, and 40 mA were significantly decreased (0.081, 0.087, and 0.092 cm -1, respectively; p < 0.05) as compared to 0.096 cm -1 of the other tube currents. Further, CT pixel values decreased 10 and 20 mA. Thus, the background radioactivity concentration values at 10 and 20 mA were substantially underestimated to be 57 and 80%, respectively (p < 0.05); the hot-sphere contrast values at 10 and 20 mA were 0.26 and 0.29; the cold-sphere contrast values at 10, 20, and 40 mA were -0.33, -0.16, and 0.08. Conclusions: Although the linear attenuation coefficients in the 300-mm phantom remained the same with varying CT tube currents, the 500-mm phantom yielded significant differences in the range 10-40 mA. Therefore, the CT tube currents for attenuation correction should be adjusted over 40 mA in obese patients. © 2012 The Japanese Society of Nuclear Medicine

Performance of myocardial perfusion imaging using multi-focus fan beam collimator with resolution recovery reconstruction in a comparison with conventional SPECT

Objective: IQSPECT is an advanced high-speed SPECT modality for performing myocardial perfusion imaging (MPI), which uses a multi-focus fan beam collimator with resolution recovery reconstruction. The aim of this study was to compare IQSPECT compared with conventional SPECT interms of performance based on standard clinical protocols. In addition, we examined the concordance between conventional and IQSPECT in patients with coronary artery disease (CAD). Methods: Fifty-three patients undergoing rest-gated MPI for the evaluation of known or suspected coronary artery disease were enrolled in this study. In each patient, conventional SPECT (99mTc-tetrofosmin, 9.6 min; 201Tl, 12.9 min) was performed, immediately followed by IQSPECT, using a short acquisition time (4.3 min for 99mTc-tetrofosmin and 6.2 min for 201Tl). A quantitative analysis was performed on an MPI polar map using a 20-segment model of the left ventricle. An automated analysis by gated SPECT was carried out to determine the left ventricular volume and function, including the end-diastolic volume, end-systolic volume and left ventricular ejection fraction (LVEF). The degree of concordance between conventional SPECT and IQ-SPECT images was evaluated according to linear regression and Bland-Altman analyses. Results: The segmental percent uptake exhibited a significant correlation between IQSPECT and conventional SPECT (

Differential impact of multi-focus fan beam collimation with L-mode and conventional systems on the accuracy of myocardial perfusion imaging: Quantitative evaluation using phantoms

Introduction: A novel IQ-SPECTTM method has become widely used in clinical studies. The present study compares the quality of myocardial perfusion images (MPI) acquired using the IQ-SPECTTM (IQ-mode),conventional (180° apart: C-mode) and L-mode (90° apart: L-mode) systems. We assessed spatial resolution, image reproducibility and quantifiability using various physical phantoms. Materials and Methods: SPECT images were acquired using a dual-headed gamma camera with C-mode, L-mode, and IQ-mode acquisition systems from line source, pai and cardiac phantoms containing solutions of 99mTc. The line source phantom was placed in the center of the orbit and at ± 4.0, ± 8.0, ± 12.0, ± 16.0 and ± 20.0 cm off center. We examined quantifiability using the pai phantom comprising six chambers containing 0.0, 0.016, 0.03, 0.045, 0.062, and 0.074 MBq/mLof 99m-Tc and cross-calibrating the SPECT counts. Image resolution and reproducibility were quantified as myocardial wall thickness (MWT) and %uptake using polar maps. Results: The full width at half maximum (FWHM) of the IQ-mode in the center was increased by 11% as compared with C-mode, and FWHM in the periphery was increased 41% compared with FWHM at the center. Calibrated SPECT counts were essentially the same when quantified using IQ-and C-modes. IQ-SPECT images of MWT were significantly improved (P<0.001) over L-mode, and C-mode SPECT imaging with IQ-mode became increasingly inhomogeneous, both visually and quantitatively (C-mode vs. L-mode, ns; C-mode vs. IQ-mode, P<0.05). Conclusion: Myocardial perfusion images acquired by IQ-SPECT were comparable to those acquired by conventional and L-mode SPECT, but with significantly improved resolution and quality. Our results suggest that IQ-SPECT is the optimal technology for myocardial perfusion SPECT imaging

Validation of optimal cut-off frequency using a Butterworth filter in single photon emission computed tomography reconstruction for the target organ: Spatial domain and frequency domain

In single photon emission computed tomography (SPECT) images, we evaluated cut-off frequency using two methods: spatial domain method (normalized mean square error: NMSE) and frequency domain method (radius direction distribution function in the power spectrum: Pr (n)) and we calculated the optimal cut-off frequency of the Butterworth filter according to the nuclide and collimator used, and the target organ. The optimized cut-off frequencies (Fc) were determined for nuclides of 99m-Tc, 123-I, 201-Tl, and LEHR and LEGP collimators, and compared. The Pr (n) was used to evaluate the SPECT images for frequency domain analysis, and the NMSE method was used for the assessment of images in spatial domain. In the brain phantom for both of these methods of analysis, the optimal Fc varies depending on the nuclide and collimator. Fc in use for 99m-Tc is 0.802 [cycles/cm] with LEHR and 0.656 [cycles/cm] with LEGP. However, those in use for 123-I are 0.656 [cycles/cm] with LEHR. In the myocardial phantom, the appropriate Fc are 0.516 [cycles/cm] with LEHR, and 0.469 [cycles/cm] with LEGP in use of 99m-Tc. We concluded that the cut-off frequency of the Butterworth filter should be changed in reconstructing SPECT images according to the collimator, nuclide and target organs.我々は，脳ファントム及び心臓ファントムで周波数空間と実空間の評価でSPECT 画像における使用核種，コリメータ及び標的臓器のButterworthフィルタの最適遮断周波数の算出を試みた。周波数空間での評価は動径強度分布関数（Pr（n））を用い，実空間での評価はNMSE法を用いた。脳ファントムでは核種として99m-Tcと123-Iを用い，心臓ファントムでは99m-Tc及び201-Tlを使用した。また，コリメータはLEHR及びLEGPを使用した。脳ファントムでは99m-Tcにおける最適遮断周波数は，LEHRで0.802 [cycles/cm], LEGPで0.656 [cycles/cm] と変化した。しかし123-IではLEHRで0.656 [cycles/cm]であった。心臓ファントムでは99m-TcでLEHRは0.516 [cycles/cm], LEGPで0.469 [cycles/cm]と変化した。また，同様に201-Tlでも異なった遮断周波数が算出された。この結果から，SPECT画像再構成時でのButterworthフィルタの遮断周波数は，使用核種，コリメータ，標的臓器により変化させなければならない。原著Original Article