Exploration of Optimal Reconstruction Parameters for 18F-FDG Total-body PET/CT with Ultra-low Activity Injection
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Abstract PURPOSE To explorer the optimal reconstruction parameters in oncologic 18 F-FDG total-body PET/CT studies with ultra-low activity injection. METHODS A total of 204 reconstructed PET images of 34 patients with a total of 58 lesions were analyzed by two experienced nuclear medicine physicians. Images were reconstructed with ordered subset expectation maximization (OSEM) algorithm (2 and 3 iterations) including time-of-flight (TOF) and point spread function (PSF) corrections and regularization ordered subset expectation maximization (ROSEM) (b-values of 0.3, 0.4, 0.5, and 0.6). General image quality was assessed using the five-point method including overall image quality, image clarity, noise, and lesion conspicuity. Image noise, signal-to-noise ratio, lesion size, SUVmax, SUVpeak and T/N were quantitatively analyzed by the third reader who did not participate in subjective image assessment. RESULTS In objective image quality indicators, noise decreased and a continuous increase of SNR with incremental β-values (0.3,0.4, 0.5 and 0.6) compared with OSEM3. In subjective image quality, OSEM2, ROSEM0.5 and ROSEM0.6 scored higher (all P<0.001) in overall image quality, image contrast and noise. The scores of ROSEM reconstructions were all higher in lesion conspicuity compared with OSEM3 (all P<0.001). In lesion detectability, SUVmax, SUVpeak and T/N increase with β value of ROSEM increase. Compared with OSEM3, there was a negative correlation between lesion size and the percentage increase of SUVpeak in OSEM2 and ROSEM reconstructions (all P<0.01). CONCLUSION In clinical practice, we recommended OSEM reconstruction with 3 iterations with a relatively short reconstruction time and we recommend ROSEM algorithm with b of 0.5 when reconstruction time is not considered.Keywords:
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Background The number of computed tomography (CT) examinations is increasing and leading to an increase in total patient exposure. It is therefore important to optimize CT scan imaging conditions in order to reduce the radiation dose. The introduction of iterative reconstruction methods has enabled an improvement in image quality and a reduction in radiation dose. Purpose To investigate how image quality depends on reconstruction method and to discuss patient dose reduction resulting from the use of hybrid and model-based iterative reconstruction. Material and Methods An image quality phantom (Catphan® 600) and an anthropomorphic torso phantom were examined on a Philips Brilliance iCT. The image quality was evaluated in terms of CT numbers, noise, noise power spectra (NPS), contrast-to-noise ratio (CNR), low-contrast resolution, and spatial resolution for different scan parameters and dose levels. The images were reconstructed using filtered back projection (FBP) and different settings of hybrid (iDose 4 ) and model-based (IMR) iterative reconstruction methods. Results iDose 4 decreased the noise by 15–45% compared with FBP depending on the level of iDose 4 . The IMR reduced the noise even further, by 60–75% compared to FBP. The results are independent of dose. The NPS showed changes in the noise distribution for different reconstruction methods. The low-contrast resolution and CNR were improved with iDose 4 , and the improvement was even greater with IMR. Conclusion There is great potential to reduce noise and thereby improve image quality by using hybrid or, in particular, model-based iterative reconstruction methods, or to lower radiation dose and maintain image quality.
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Abstract Introduction Cadaveric studies provide a means of safely assessing new technologies and optimizing scanning prior to clinical validation. Reducing radiation exposure in a clinical setting can entail incremental dose reductions to avoid missing important clinical findings. The use of cadavers allows assessment of the impact of more substantial dose reductions on image quality. Our aim was to identify a suitable low‐dose abdominopelvic CT protocol for subsequent clinical validation. Methods Five human cadavers were scanned at one conventional dose and three low‐dose settings. All scans were reconstructed using three different reconstruction algorithms: filtered back projection ( FBP ), hybrid iterative reconstruction (60% FBP and 40% adaptive statistical iterative reconstruction ( ASIR 40)), and model‐based iterative reconstruction ( MBIR ). Two readers rated the image quality both quantitatively and qualitatively. Results Model‐based iterative reconstruction images had significantly better objective image noise and higher qualitative scores compared with both FBP and ASIR 40 images at all dose levels. The greatest absolute noise reduction, between MBIR and FBP , of 34.3 HU (equating to a 68% reduction) was at the lowest dose level. MBIR reduced image noise and improved image quality even in CT images acquired with a mean radiation dose reduction of 62% compared with conventional dose studies reconstructed with ASIR 40, with lower levels of objective image noise, superior diagnostic acceptability and contrast resolution, and comparable subjective image noise and streak artefact scores. Conclusion This cadaveric study demonstrates that MBIR reduces image noise and improves image quality in abdominopelvic CT images acquired with dose reductions of up to 62%.
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Recent advances in computed tomographic (CT) scanning technique such as automated tube current modulation (ATCM), optimized x-ray tube voltage, and better use of iterative image reconstruction have allowed maintenance of good CT image quality with reduced radiation dose. ATCM varies the tube current during scanning to account for differences in patient attenuation, ensuring a more homogeneous image quality, although selection of the appropriate image quality parameter is essential for achieving optimal dose reduction. Reducing the x-ray tube voltage is best suited for evaluating iodinated structures, since the effective energy of the x-ray beam will be closer to the k-edge of iodine, resulting in a higher attenuation for the iodine. The optimal kilovoltage for a CT study should be chosen on the basis of imaging task and patient habitus. The aim of iterative image reconstruction is to identify factors that contribute to noise on CT images with use of statistical models of noise (statistical iterative reconstruction) and selective removal of noise to improve image quality. The degree of noise suppression achieved with statistical iterative reconstruction can be customized to minimize the effect of altered image quality on CT images. Unlike with statistical iterative reconstruction, model-based iterative reconstruction algorithms model both the statistical noise and the physical acquisition process, allowing CT to be performed with further reduction in radiation dose without an increase in image noise or loss of spatial resolution. Understanding these recently developed scanning techniques is essential for optimization of imaging protocols designed to achieve the desired image quality with a reduced dose. © RSNA, 2014
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Objective: To investigate the impact of iterative reconstruction method(iDose4) on the CT image quality and dose reduction by using phantom studies. Methods: A Catphan phantom was scanned by a 256-slice CT(Philips Brilliance iCT) with varied mAs from 20 to 200, the axial images were reconstructed by filtered back projection(FBP) and iDose4with a level of 1 to 6. Image quality was assessed with following aspect: CT value accuracy and consistency, image noise and signal-noise-ratio(SNR), low density resolution. Meanwhile the volume CT dose index CTDIvol and Dose length product DLP were recorded for dose evaluation. Results: The axial image CT values has a high degree of consistency(P0.05) for both iDose4and FBP reconstruction method. The image noise can be reduced in different degree with different iDose4level 1~6 reconstruction(9.46%~43.30%). When tube current reduced to 40%~50%(80~100 mAs), iDose4level 6 got image without significant difference regarding to the image noise compared to 200 mAs FBP image(P0.05); under the conditions of 50%~60% initial tube current(100~120 mAs), low density resolution could remain unchanged. Conclusion: iDose4can significantly reduce image noise and improve image quality, under the condition of 40% ~50% scanning dose can get satisfactory image quality. Thus iterative reconstruction has larger space to lower the scanning dose.
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Iterative reconstruction techniques for reducing radiation dose and improving image quality in CT have proved to work differently for different patient sizes, dose levels, and anatomical areas.This study aims to compare image quality in CT of the lungs between four high-end CT scanners using the recommended reconstruction techniques at different dose levels and patient sizes.A lung phantom and an image quality phantom were scanned with four high-end scanners at fixed dose levels. Images were reconstructed with and without iterative reconstruction. Contrast-to-noise ratio, modulation transfer function, and peak frequency of the noise power spectrum were measured.IMR1 Sharp+ and VEO improved contrast-to-noise ratio to a larger extent than the other iterative techniques, while maintaining spatial resolution. IMR1 Sharp+ also maintained noise texture.IMR1 Sharp+ was the only reconstruction technique in this study which increased CNR to a large extent, while maintaining all other image quality parameters measured in this study.
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The clinical utility of a latest generation iterative reconstruction algorithm (adaptive statistical iterative reconstruction [ASiR-V]) has yet to be elucidated for coronary computed tomography angiography (CCTA). This study evaluates the impact of ASiR-V on signal, noise and image quality in CCTA.Sixty-five patients underwent clinically indicated CCTA on a 256-slice CT scanner using an ultralow-dose protocol. Data sets from each patient were reconstructed at 6 different levels of ASiR-V. Signal intensity was measured by placing a region of interest in the aortic root, LMA, and RCA. Similarly, noise was measured in the aortic root. Image quality was visually assessed by 2 readers.Median radiation dose was 0.49 mSv. Image noise decreased with increasing levels of ASiR-V resulting in a significant increase in signal-to-noise ratio in the RCA and LMA (P < 0.001). Correspondingly, image quality significantly increased with higher levels of ASiR-V (P < 0.001).ASiR-V yields substantial noise reduction and improved image quality enabling introduction of ultralow-dose CCTA.
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To evaluate the performance of sinogram-affirmed iterative (SAFIRE) reconstruction on image quality of low-dose lung computed tomographic (CT) screening compared with filtered back projection (FBP).Three hundred four patients for annual low-dose lung CT screening were examined by a dual-source CT system at 120 kilovolt (peak) with reference tube current of 40 mA·s. Six image serials were reconstructed, including one data set of FBP and 5 data sets of SAFIRE with different reconstruction strengths from 1 to 5. Image noise was recorded; and subjective scores of image noise, images artifacts, and the overall image quality were also assessed by 2 radiologists.The mean ± SD weight for all patients was 66.3 ± 12.8 kg, and the body mass index was 23.4 ± 3.2. The mean ± SD dose-length product was 95.2 ± 30.6 mGy cm, and the mean ± SD effective dose was 1.6 ± 0.5 mSv. The observation agreements for image noise grade, artifact grade, and the overall image quality were 0.785, 0.595 and 0.512, respectively. Among the overall 6 data sets, both the measured mean objective image noise and the subjective image noise of FBP was the highest, and the image noise decreased with the increasing of SAFIRE reconstruction strength. The data sets of S3 obtained the best image quality scores.Sinogram-affirmed iterative reconstruction can significantly improve image quality of low-dose lung CT screening compared with FBP, and SAFIRE with reconstruction strength 3 was a pertinent choice for low-dose lung CT.
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