Sinogram-affirmed Iterative Reconstruction Research Articles

Assessment of organ dose and image quality in head and chest CT examinations: a phantom study

The purpose of this study is to assess dose for radiosensitive organs and image quality in head and chest computed tomography (CT) examinations. Our focus was in the brain, eye lens and lung organs using two protocols; one protocol with fixed mAs and filtered back projection (FBP) and another with tube current modulation (TCM) and sinogram affirmed iterative reconstruction (SAFIRE). Measurements were performed on a 128-slice CT scanner by placing thermoluminescent dosimeters (TLDs) in an anthropomorphic adult phantom. Results were compared to a CT-Expo software. Objective image quality was assessed in terms of signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). SPSS software was used for data analyses. Results showed that, using TCM, doses were reduced by 22.84%–25.06% for brain, by 21.82%–23.48% for eye lens and by 54%–53.22% for lung with TLD and CT-Expo respectively. The increased SNR and CNR values achieved for scans performed with TCM combined with iterative reconstruction techniques were 38.68%–58.81% and 38.91%–43.60% respectively. We conclude that, using TCM, a significant mean organ dose reduction is achieved for brain, eye lens and lung organs. Then, combined with iterative reconstruction, image quality was well maintained in terms of SNR and CNR. Thus it is highly recommended in clinical practice optimization in head and chest CT examinations.

Optimization of Scan and Reconstruction Parameters for Renal Artery CT Angiography with Iterative Reconstruction at Low kVp Compared with Filtered Back Projection at 120 kVp Acquisition

Background: As cross-sectional images expanded in clinical practice, the number of renal lesions discovered incidentally has been increasing. CT protocols for renal mass evaluation may include pre- and post-contrast phase. However, a major concern with respect to those multiphase techniques is often the radiation dose. One further critical issue is how to minimize the radiation dose while image quality is optimized in routine daily clinical practice. Objectives: To evaluate the image quality and radiation dose of renal artery CT angiography (CTA) with optimal sinogram affirmed iterative reconstruction (SAFIRE) strength level at 80 kVp for optimizing the scan and reconstruction parameters of renal artery CTA, in comparison to 120 kVp acquisition with filtered back projection (FBP). Patients and Methods: Sixty consecutive patients were classified into three groups prospectively in this study: 1) 80 kVp group (n = 30) with FBP and 2) 80 kVp group with SAFIRE (S4) and 3) 120 kV group (n = 30) with FBP. CT values and noise were measured, contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) of the renal artery CTA were calculated for quantitative assessment. Subjective image quality was evaluated by two experienced abdominal radiologists with a five-point scale in a blinded and randomized setting for qualitative assessment. Volume CT dose index (CTDIvol) and size-specific dose estimate (SSDE) were calculated and estimated for each subject presented in this study. Results: As for quantitative assessment, CNR, SNR and CT values of renal artery in 80kVp group with SAFIRE strength levels or FBP were higher than those of 120 kVp group with FBP (all Ps < 0.05), the mean noise gradually decreased in 80kVp group when increasing the SAFIRE strength levels (S1 - S5). As for qualitative assessment, the overall image quality, vessel sharpness, segmental renal artery displayed in maximum intensity projection (MIP) or multiplanar reformation (MPR), and diagnostic confidence of the two groups were all accepted by two radiologists (inter-observer agreement ranged from 0.600 to 0.940) (score ≥ 3). The overall image quality of 80 kVp with SAFIRE 4 was similar to that of 120 kVp group with FBP (P = 0.412), as well as segmental renal artery displayed in MIP and diagnostic confidence (P = 0.095 and P = 0.061, respectively). As for radiation dose reduction, 80kVp group could reduce 32.7% CTDIvol and 31.2% SSDE compared to the 120 kVp group. Conclusion: In patients with BMI lower than 28 kg/m2, renal artery CTA at 80 kVp with SAFIRE is feasible and can provide satisfactory images for clinical applications. This method also provides reduction in radiation dose. SAFIRE strength level 4 is recommended for reconstructing renal artery CTA.

High-pitch Dual-source Computed Tomography Coupled with Sinogram-affirmed Iterative Reconstruction: Image Quality and Radiation Dose in Children

High-pitch Dual-source Computed Tomography Coupled with Sinogram-affirmed Iterative Reconstruction: Image Quality and Radiation Dose in Children

The applying of a low tube voltage combined with low dose of iodixanol to renal artery CT imaging in elderly patients

Objective To explore the clinical application of 80 kVp tube voltage combined with low dose and low concentration contrast agent in CT imaging of renal artery (CTA) in elderly patients. Methods 160 elderly patients undergoing CT angiography of renal artery or abdominal aorta in our hospital from August 2016 to June 2017 were randomized to control group (routine-dose CT with 120 kVp at 120 mAs, contrast agent of 70 ml, n=40) and double low group (X-ray tube voltage at 80 kVp and contrast agent of 50 ml), which was re-divided to double low-150 mAs group, double low-180 mAs group, and double low-210 mAs group (n=40, each). The CT value of bilateral renal arteries, their branches, and abdominal aorta at the same height of renal artery, signal to noise ratio (SNR), contrast to noise ratio (CNR), the effective radiation dose, and the incidence of adverse reaction were measured after sinogram-affirmed iterative reconstruction (SAFIRE). And the image quality was evaluated and rated on a scale from 1 to 5 by two independent qualified radiologists. Results The vascular enhancement was significantly higher in the three double low groups than in the control group (all P 0.05), while statistical differences were found in SNR and CNR in the control group versus double low-150 mAs and double low-180 mAs groups (all P<0.05). As compared with the control group, effective radiation dose was decreased in the three double low groups by 63.3% (150 mAs), 56.2% (180 mAs), 48.8% (210 mAs), respectively. All image scores in four groups were over 3 points.Mild adverse effects were observed in four cases from the control group, and no adverse effect occurred in the other three groups. Conclusions 80 kVp tube voltage combined with low dose and low concentration contrast agent can appropriately increase tube current. Combined with SAFIRE, it can not only help maintain image quality, but also decrease the damage of organs by reducing the doses of radiation and contrast agent. Key words: Tomography, computed; Contrast media; Renal artery

Application of 80-kVp scan and rawdata-basediterative reconstructionfor reduced iodine load abdominal-pelvic CT in patients at risk of contrast-induced nephropathy referred for oncological assessment: effects on radiation dose, image quality and renal function.

To evaluate the image quality, radiation dose, and renal safety of contrast medium (CM)-reduced abdominal-pelvic CT combining 80-kVp and sinogram-affirmed iterative reconstruction (SAFIRE) in patients with renal dysfunction for oncological assessment. We included 45 patients with renal dysfunction (estimated glomerular filtration rate <45 ml perminper1.73 m2) who underwent reduced-CM abdominal-pelvic CT (360 mgIkg-1, 80-kVp, SAFIRE) for oncological assessment. Another 45 patients without renal dysfunction (estimated glomerular filtration rate>60 ml per lmin per1.73 m2) who underwent standard oncological abdominal-pelvic CT (600 mgIkg-1, 120-kVp, filtered-back projection) were included as controls. CT attenuation, image noise, and contrast-to-noise ratio (CNR) were compared. Two observers performed subjective image analysis on a 4-point scale. Size-specific dose estimate and renal function 1-3 months after CT were measured. The size-specific dose estimate and iodine load of 80-kVp protocol were32 and 41%,, respectively, lower than of 120-kVp protocol (p < 0.01). CT attenuation and contrast-to-noise ratio of parenchymal organs and vessels in 80-kVp images were significantly better than those of 120-kVp images (p < 0.05). There were no significant differences in quantitative or qualitative image noise or subjective overall quality (p > 0.05). No significant kidney injury associated with CM administration was observed. 80-kVp abdominal-pelvic CT with SAFIRE yields diagnostic image quality in oncology patients with renal dysfunction under substantially reduced iodine and radiation dose without renal safety concerns. Advances in knowledge: Using 80-kVp and SAFIRE allows for 40% iodine load and 32% radiation dose reduction for abdominal-pelvic CT without compromising image quality and renal function in oncology patients at risk of contrast-induced nephropathy.

Variations in MTF and NPS between CT scanners with two different IR algorithms and detectors

The use of iterative reconstruction (IR) in computed tomography (CT) has become a useful tool for improved image quality or for reduced dose in CT examinations. In this study, the image quality of the two different Siemens IR algorithms, sinogram affirmed iterative reconstruction (SAFIRE) and advanced modelled iterative reconstruction (ADMIRE), were evaluated and compared. Differences between the Stellar detector and the conventional detector and similarities between scanners with the same detector and IR algorithm were also examined. The objective image quality parameters modulation transfer function (MTF) and noise power spectrum (NPS) were measured on a Catphan 600 phantom (The Phantom Laboratory Incorporated, NY) for five different Siemens CT scanners. MTF was calculated from the circular edge of the sensitometry targets in Catphan to facilitate measurements at different contrasts and dose levels. The results showed that the image quality was improved by using ADMIRE compared to SAFIRE on the same CT scanner equipped with the Stellar detector for certain specific tasks. The MTF was higher for the three low contrast objects when the sharp reconstruction kernel was applied. The CT scanners equipped with the Stellar detector showed an improved image quality compared to the CT scanners equipped with the conventional detector. Larger differences in MTF and NPS were observed between the detectors than between SAFIRE and ADMIRE.

Value of 100 kVp scan with sinogram-affirmed iterative reconstruction algorithm on a single-source CT system during whole-body CT for radiation and contrast medium dose reduction: an intra-individual feasibility study

To perform an intra-individual investigation of the usefulness of a contrast medium (CM) and radiation dose-reduction protocol using single-source computed tomography (CT) combined with 100 kVp and sinogram-affirmed iterative reconstruction (SAFIRE) for whole-body CT (WBCT; chest-abdomen-pelvis CT) in oncology patients. Forty-three oncology patients who had undergone WBCT under both 120 and 100 kVp protocols at different time points (mean interscan intervals: 98 days) were included retrospectively. The CM doses for the 120 and 100 kVp protocols were 600 and 480 mg iodine/kg, respectively; 120 kVp images were reconstructed with filtered back-projection (FBP), whereas 100 kVp images were reconstructed with FBP (100 kVp-F) and the SAFIRE (100 kVp-S). The size-specific dose estimate (SSDE), iodine load and image quality of each protocol were compared. The SSDE and iodine load of 100 kVp protocol were 34% and 21%, respectively, lower than of 120 kVp protocol (SSDE: 10.6±1.1 versus 16.1±1.8 mGy; iodine load: 24.8±4versus 31.5±5.5 g iodine, p<0.01). Contrast enhancement, objective image noise, contrast-to-noise-ratio, and visual score of 100 kVp-S were similar to or better than of 120 kVp protocol. Compared with the 120 kVp protocol, the combined use of 100 kVp and SAFIRE in WBCT for oncology assessment with an SSCT facilitated substantial reduction in the CM and radiation dose while maintaining image quality.

Evaluating Low-kV Dual-source CT Angiography by High-pitch Spiral Acquisition and Iterative Reconstruction in Pediatric Congenital Heart Disease Patients.

We retrospectively evaluated the qualities of pediatric cardiovascular dual-source computed tomography (DSCT) images reconstructed by sinogram-affirmed iterative reconstruction (SAFIRE) and filtered back projection (FBP). We analyzed the cases of 287 congenital heart disease (CHD) patients < 5 years old, referred to our department in August 2013-March 2015. We divided them into two groups according to tube voltage (70 kVp, n=147; 80 kVp, n=140). All images were acquired by a CARE kV system and reconstructed by FBP and SAFIRE. The attenuation, noise, and signal-to-noise ratio (SNR) at each region of the heart and great vessels were measured. The volume CT dose index and dose-length product values were recorded. Compared to FBP, reconstruction by SAFIRE showed that the attenuation volume was significantly lower by 0.4% except for the ascending aorta (p<0.05), the noise value was lower by about 20% (p<0.05), and the SNR was higher by approx. 25% (p<0.05). The radiation dose in the 70 kVp group was significantly lower than that in the 80 kVp group. No significant differences in SNR were observed between the patient groups. DSCT image acquisition with SAFIRE using the CARE kV system results in low image noise and radiation dose in pediatric patients with CHD.

Image quality of CT angiography in young children with congenital heart disease: a comparison between the sinogram-affirmed iterative reconstruction (SAFIRE) and advanced modelled iterative reconstruction (ADMIRE) algorithms

To compare the image quality of computed tomography angiography (CTA) reconstructed by sinogram-affirmed iterative reconstruction (SAFIRE) with that of advanced modelled iterative reconstruction (ADMIRE) in children with congenital heart disease (CHD). Thirty-one children (8.23±13.92 months) with CHD who underwent CTA were enrolled. Images were reconstructed using SAFIRE (strength 5) and ADMIRE (strength 5). Objective image qualities (attenuation, noise) were measured in the great vessels and heart chambers. Two radiologists independently calculated the contrast-to-noise ratio (CNR) by measuring the intensity and noise of the myocardial walls. Subjective noise, diagnostic confidence, and sharpness at the level prior to the first branch of the main pulmonary artery were also graded by the two radiologists independently. The objective image noise of ADMIRE was significantly lower than that of SAFIRE in the right atrium, right ventricle, and myocardial wall (p<0.05); however, there were no significant differences observed in the attenuations among the four chambers and great vessels, except in the pulmonary arteries (p>0.05). The mean CNR values were 21.56±10.80 for ADMIRE and 18.21±6.98 for SAFIRE, which were significantly different (p<0.05). In addition, the diagnostic confidence of ADMIRE was significantly lower than that of SAFIRE (p<0.05), while the subjective image noise and sharpness of ADMIRE were not significantly different (p>0.05). CTA using ADMIRE was superior to SAFIRE when comparing the objective and subjective image quality in children with CHD.

Image quality, diagnostic accuracy, and potential for radiation dose reduction in thoracoabdominal CT, using Sinogram Affirmed Iterative Reconstruction (SAFIRE) technique in a longitudinal study.

ObjectiveTo step-wise evaluate image quality of sinogram-affirmed iterative reconstruction (SAFIRE) in reduced-dose (RD) thoracoabdominal computed tomography (CT) compared to full-dose (FD) and RD filtered back projection (FBP) in a longitudinal study.Materials and methods122 patients were included in this prospective study. 49 patients (14 men: mean age ± SD, 56±0.4 years; 35 women: 58±1.3 years) completed FD, RD1 (80%-dose) and RD2 (60%-dose) thoracoabdominal CT. Each CT dataset was reconstructed with FBP and SAFIRE. For quantitative image analysis image noise was measured in defined tissue regions. Qualitative image evaluation was performed according to the European Guidelines on Quality criteria for CT. Additionally artifacts, lesion conspicuity, and edge sharpness were assessed.ResultsCompared to FD-FBP noise in soft tissue increased by 12% in RD1-FBP and 27% in RD2-FBP reconstructions, whereas SAFIRE lead to a decrease of 28% (RD1) and 17% (RD2), respectively (all p <0.001). Visually sharp reproduction, lesion conspicuity, edge sharpness of pathologic findings, and overall image quality did not differ statistically significant between FD-FBP and RD-SAFIRE datasets. Image quality decreased in RD1- and RD2-FBP compared to FD-FBP, reaching statistically significance in RD2 datasets (p <0.001). In RD1- and RD2-FBP (p <0.001) streak artifacts were noted.ConclusionUsing SAFIRE the reference mAs in thoracoabdominal CT can be reduced by at least 30% in clinical routine without loss of image quality or diagnostic information.

The Acceptability of Iterative Reconstruction Algorithms in Head CT: An Assessment of Sinogram Affirmed Iterative Reconstruction (SAFIRE) vs. Filtered Back Projection (FBP) Using Phantoms

BackgroundComputed tomography (CT) is the primary imaging investigation for many neurologic conditions with a proportion of patients incurring cumulative doses. Iterative reconstruction (IR) allows dose optimization, but head CT presents unique image quality complexities and may lead to strong reader preferences. ObjectivesThis study evaluates the relationships between image quality metrics, image texture, and applied radiation dose within the context of IR head CT protocol optimization in the simulated patient setting. A secondary objective was to determine the influence of optimized protocols on diagnostic confidence using a custom phantom. Methods and SettingA three-phase phantom study was performed to characterize reconstruction methods at the local reference standard and a range of exposures. CT numbers and pixel noise were quantified supplemented by noise uniformity, noise power spectrum, contrast-to-noise ratio (CNR), high- and low-contrast resolution. Reviewers scored optimized protocol images based on established reporting criteria. ResultsIncreasing strengths of IR resulted in lower pixel noise, lower noise variance, and increased CNR. At the reference standard, the image noise was reduced by 1.5 standard deviation and CNR increased by 2.0. Image quality was maintained at ≤24% relative dose reduction. With the exception of image sharpness, there were no significant differences between grading for IR and filtered back projection reconstructions. ConclusionsIR has the potential to influence pixel noise, CNR, and noise variance (image texture); however, systematically optimized IR protocols can maintain the image quality of filtered back projection. This work has guided local application and acceptance of lower dose head CT protocols.

Application of Third-generation Dual-source CT for Ultra-high Resolution Temporal Bone Imaging Using Automated Tube Voltage Adaptation in Children with Hearing Impairment.

Objective To evaluate the radiation dose and image quality of the third-generation dual-source CT using automated tube voltage adaptation (CARE kV) in temporal bone scanning in pediatric patients with hearing impairment. Methods Totally 27 children with hearing impairment less than 18 years old were randomly divided into two groups:Group A (n=14),examined with CARE kV (reference with 100 kV and 214 mA)and sinogram-affirmed iterative reconstruction;and Group B (n=13),examined with CARE kV (reference with 100 kV and 171 mA)and advanced modeled iterative reconstruction. The scan range was from eyebrow to the end of the mastoid process. CT values and image noise were measured.The signal to noise ratio (SNR)was calculated. Subjective image quality was assessed by two radiologists and later in a consensus reading. Results There was no significant difference in CT value,image noise,and SNR between these two groups (all P>0.05). Also,the subjective scores of the 10 anatomical structures showed no significant difference (all P>0.05). The CT dose index volume and dose-length product were (11.62+1.92)mGy and (106.92+37.48)mGy·cm,respectively,in group B and (21.28+2.19)mGy (t=12.15,P<0.001)and (229.65+56.26)mGy·cm (t=6.62,P<0.001)in group A,decreased by 45% and 53%. Conclusion Compared with the second-generation dual-source CT,the third-generation dual-source CT for the scanning of temporal bone with CARE kV can ensure image quality and reduce radiation dose.

Effect of Radiation Dose Reduction and Reconstruction Algorithm on Image Noise, Contrast, Resolution, and Detectability of Subtle Hypoattenuating Liver Lesions at Multidetector CT: Filtered Back Projection versus a Commercial Model-based Iterative Reconstruction Algorithm.

Purpose To determine the effect of radiation dose and iterative reconstruction (IR) on noise, contrast, resolution, and observer-based detectability of subtle hypoattenuating liver lesions and to estimate the dose reduction potential of the IR algorithm in question. Materials and Methods This prospective, single-center, HIPAA-compliant study was approved by the institutional review board. A dual-source computed tomography (CT) system was used to reconstruct CT projection data from 21 patients into six radiation dose levels (12.5%, 25%, 37.5%, 50%, 75%, and 100%) on the basis of two CT acquisitions. A series of virtual liver lesions (five per patient, 105 total, lesion-to-liver prereconstruction contrast of -15 HU, 12-mm diameter) were inserted into the raw CT projection data and images were reconstructed with filtered back projection (FBP) (B31f kernel) and sinogram-affirmed IR (SAFIRE) (I31f-5 kernel). Image noise (pixel standard deviation), lesion contrast (after reconstruction), lesion boundary sharpness (average normalized gradient at lesion boundary), and contrast-to-noise ratio (CNR) were compared. Next, a two-alternative forced choice perception experiment was performed (16 readers [six radiologists, 10 medical physicists]). A linear mixed-effects statistical model was used to compare detection accuracy between FBP and SAFIRE and to estimate the radiation dose reduction potential of SAFIRE. Results Compared with FBP, SAFIRE reduced noise by a mean of 53% ± 5, lesion contrast by 12% ± 4, and lesion sharpness by 13% ± 10 but increased CNR by 89% ± 19. Detection accuracy was 2% higher on average with SAFIRE than with FBP (P = .03), which translated into an estimated radiation dose reduction potential (±95% confidence interval) of 16% ± 13. Conclusion SAFIRE increases detectability at a given radiation dose (approximately 2% increase in detection accuracy) and allows for imaging at reduced radiation dose (16% ± 13), while maintaining low-contrast detectability of subtle hypoattenuating focal liver lesions. This estimated dose reduction is somewhat smaller than that suggested by past studies. © RSNA, 2017 Online supplemental material is available for this article.

Noise Texture Deviation: A Measure for Quantifying Artifacts in Computed Tomography Images With Iterative Reconstructions.

The aims of this study were to introduce the measure noise texture deviation as quantitative parameter for evaluating iterative reconstruction (IR)-specific artifacts in computed tomography (CT) images and to test whether IR-specific artifacts, quantified through this measure, are reduced in advanced modeled IR (ADMIRE) as compared with sinogram-affirmed IR (SAFIRE) images of the liver ex vivo and in patients with hypodense liver lesions. In the ex vivo study part, an abdominal phantom was used. In the institutional review board-approved in vivo study part, 40 consecutive patients (mean age, 63 years) with hypodense liver lesions undergoing abdominal CT in the portal-venous phase were included. Images were reconstructed with filtered back projection, with the second-generation IR algorithm SAFIRE and with the third-generation IR algorithm ADMIRE. Noise power spectra and noise texture deviation were calculated in the phantom; image noise was measured in the phantom and in patients. Two blinded readers evaluated all image data regarding IR-specific artifacts (plastic-like, blotchy appearance); patient data were evaluated regarding conspicuity and confidence for detecting hypodense liver lesions. Image noise was significantly reduced at increasing IR levels (P < 0.001) with both algorithms, with no significant differences between corresponding strength levels of SAFIRE and ADMIRE (all, P > 0.05). Noise power spectra were similar at corresponding strength levels of SAFIRE and ADMIRE (all, P > 0.05). Noise texture deviation in ADMIRE was reduced compared with corresponding strength levels of SAFIRE (all, P < 0.001) and strongly correlated with subjective IR-specific artifacts (r = 0.88, P < 0.001). Iterative reconstruction-specific artifacts were significantly reduced in ADMIRE compared with that in SAFIRE images at strength levels 3 or greater, both ex vivo and in vivo (all, P < 0.001). There were no significant differences in the readers' ratings of lesion conspicuity and lesion confidence in detecting hypodense liver lesions between SAFIRE and ADMIRE (P > 0.05). Only lesion conspicuity was superior with SAFIRE and ADMIRE compared with filtered back projection (all, P < 0.001). Noise texture deviation is a quantitative measure reflecting IR-specific artifacts and is reduced in CT images with ADMIRE compared with SAFIRE.

Cerebral CT angiography with iterative reconstruction at 70 kVp and 30 mL iodinated contrast agent: Initial experience

ObjectivesTo evaluate the radiation dose and image quality of cerebral CT angiography (CTA) at 70kVp with 30mL iodinated contrast agent. MethodsOne hundred patients were prospectively classified into two groups: Group A (n=50), 120kVp cerebral CTA with 60mL iodinated contrast agent reconstructed by filtered back projection (FBP) and Group B (n=50), 70kVp with 30mL iodinated contrast agent reconstructed by sinogram-affirmed iterative reconstruction (SAFIRE). CT values, noise, signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the internal carotid artery (ICA) and middle cerebral artery (MCA) were measured. Subjective image quality was evaluated. Effective dose (ED) was calculated. ResultsThe mean CT values of the ICA and MCA of Group B were higher than those of Group A (all P<0.001). The mean noise of Group A was lower than that of Group B (P<0.001). SNRICA, SNRMCA and CNRICA, CNRMCA of Group A were higher than Group B (all P<0.001). There was no difference in vessel sharpness, noise, and overall quality between the two groups (all P>0.05). ED of Group B (0.2±0.0mSv) was lower than Group A (1.3±0.1 mSv) (p<0.001). ConclusionCerebral CTA with iterative reconstruction at 70kVp and 30mL iodinated contrast agent is feasible, allowing for substantial dose reduction compared with conventional cerebral CTA protocol.

Cerebral bone subtraction CT angiography using 80kVp and sinogram-affirmed iterative reconstruction: contrast medium and radiation dose reduction with improvement of image quality.

The purpose of this study was to evaluate the feasibility of a contrast medium (CM), radiation dose reduction protocol for cerebral bone-subtraction CT angiography (BSCTA) using 80-kVp and sinogram-affirmed iterative reconstruction (SAFIRE). Seventy-five patients who had undergone BSCTA under the 120- (n=37) or the 80-kVp protocol (n=38) were included. CM was 370mgI/kg for the 120-kVp and 296mgI/kg for the 80-kVp protocol; the 120- and the 80-kVp images were reconstructed with filtered back-projection (FBP) and SAFIRE, respectively. We compared effective dose (ED), CT attenuation, image noise, and contrast-to-noise ratio (CNR) of two protocols. We also scored arterial contrast, sharpness, depiction of small arteries, visibility near skull base/clip, and overall image quality on a four-point scale. ED was 62% lower at 80- than 120-kVp (0.59±0.06 vs 1.56±0.13mSv, p<0.01). CT attenuation of the internal carotid artery (ICA) and middle cerebral artery (MCA) was significantly higher on 80- than 120-kVp (ICA: 557.4±105.7 vs 370.0±59.3 Hounsfield units (HU), p<0.01; MCA: 551.9±107.9 vs 364.6±62.2 HU, p<0.01). The CNR was also significantly higher on 80- than 120-kVp (ICA: 46.2±10.2 vs 36.9±7.6, p<0.01; MCA: 45.7±10.0 vs 35.7±9.0, p<0.01). Visibility near skull base and clip was not significantly different (p=0.45). The other subjective scores were higher with the 80- than the 120-kVp protocol (p<0.05). The 80-kVp acquisition with SAFIRE yields better image quality for BSCTA and substantial reduction in the radiation and CM dose compared to the 120-kVp with FBP protocol.

Radiation dose reduction using 100-kVp and a sinogram-affirmed iterative reconstruction algorithm in adolescent head CT: Impact on grey-white matter contrast and image noise.

To retrospectively evaluate the image quality and radiation dose of 100-kVp scans with sinogram-affirmed iterative reconstruction (IR) for unenhanced head CT in adolescents. Sixty-nine patients aged 12-17 years underwent head CT under 120- (n = 34) or 100-kVp (n = 35) protocols. The 120-kVp images were reconstructed with filtered back-projection (FBP), 100-kVp images with FBP (100-kVp-F) and sinogram-affirmed IR (100-kVp-S). We compared the effective dose (ED), grey-white matter (GM-WM) contrast, image noise, and contrast-to-noise ratio (CNR) between protocols in supratentorial (ST) and posterior fossa (PS). We also assessed GM-WM contrast, image noise, sharpness, artifacts, and overall image quality on a four-point scale. ED was 46% lower with 100- than 120-kVp (p < 0.001). GM-WM contrast was higher, and image noise was lower, on 100-kVp-S than 120-kVp at ST (p < 0.001). CNR of 100-kVp-S was higher than of 120-kVp (p < 0.001). GM-WM contrast of 100-kVp-S was subjectively rated as better than of 120-kVp (p < 0.001). There were no significant differences in the other criteria between 100-kVp-S and 120-kVp (p = 0.072-0.966). The 100-kVp with sinogram-affirmed IR facilitated dramatic radiation reduction and better GM-WM contrast without increasing image noise in adolescent head CT. • 100-kVp head CT provides 46% radiation dose reduction compared with 120-kVp. • 100-kVp scanning improves subjective and objective GM-WM contrast. • Sinogram-affirmed IR decreases head CT image noise, especially in supratentorial region. • 100-kVp protocol with sinogram-affirmed IR is suited for adolescent head CT.

Dual-Source Single-Energy Multidetector CT Used to Obtain Multiple Radiation Exposure Levels within the Same Patient: Phantom Development and Clinical Validation.

Purpose To develop, in a phantom environment, a method to obtain multidetector computed tomographic (CT) data sets at multiple radiation exposure levels within the same patient and to validate its use for potential dose reduction by using different image reconstruction algorithms for the detection of liver metastases. Materials and Methods The American College of Radiology CT accreditation phantom was scanned by using a dual-source multidetector CT platform. By adjusting the radiation output of each tube, data sets at six radiation exposure levels (100%, 75%, 50%, 37.5%, 25%, and 12.5%) were reconstructed from two consecutive dual-source single-energy (DSSE) acquisitions, as well as a conventional single-source acquisition. A prospective, HIPAA-compliant, institutional review board-approved study was performed by using the same DSSE strategy in 19 patients who underwent multidetector CT of the liver for metastatic colorectal cancer. All images were reconstructed by using conventional weighted filtered back projection (FBP) and sinogram-affirmed iterative reconstruction with strength level of 3 (SAFIRE-3). Objective image quality metrics were compared in the phantom experiment by using multiple linear regression analysis. Generalized linear mixed-effects models were used to analyze image quality metrics and diagnostic performance for lesion detection by readers. Results The phantom experiment showed comparable image quality between DSSE and conventional single-source acquisition. In the patient study, the mean size-specific dose estimates for the six radiation exposure levels were 13.0, 9.8, 5.8, 4.4, 3.2, and 1.4 mGy. For each radiation exposure level, readers' perception of image quality and lesion conspicuity was consistently ranked superior with SAFIRE-3 when compared with FBP (P ≤ .05 for all comparisons). Reduction of up to 62.5% in radiation exposure by using SAFIRE-3 yielded similar reader rankings of image quality and lesion conspicuity when compared with routine-dose FBP. Conclusion A method was developed and validated to synthesize multidetector CT data sets at multiple radiation exposure levels within the same patient. This technique may provide a foundation for future clinical trials aimed at estimating potential radiation dose reduction by using iterative reconstructions. © RSNA, 2016 Online supplemental material is available for this article.

Indirect CT Venography at 80 kVp with Sinogram-Affirmed Iterative Reconstruction Compared to 120 kVp with Filtered Back Projection: Assessment of Image Quality and Radiation Dose.

ObjectiveTo evaluate the image quality and radiation dose of indirect computed tomographic venography (CTV) using 80 kVp with sinogram-affirmed iterative reconstruction (SAFIRE) and 120 kVp with filtered back projection (FBP).Materials and MethodsThis retrospective study was approved by our institution and informed consent was waived. Sixty-one consecutive patients (M: F = 27: 34, mean age 60 ± 16, mean BMI 23.6 ± 3.6 kg/m2) underwent pelvic and lower extremity CTVs [group A (n = 31, 120 kVp, reconstructed with FBP) vs. group B (n = 30, 80 kVp, reconstructed with SAFIRE)]. The vascular enhancement, image noise, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) were compared. Subjective image analysis for image quality and noise was performed by two radiologists. Radiation dose was compared between the two groups.ResultsCompared with group A, higher mean vascular enhancement was observed in the group B (group A vs. B, 118.8 ± 15.7 HU vs. 178.6 ± 39.6 HU, p < 0.001), as well as image noise (12.0 ± 3.8 HU vs. 17.9 ± 6.1 HU, p < 0.001) and CNR (5.1 ± 1.9 vs. 7.6 ± 3.0, p < 0.001). The SNRs were not significantly different in both groups (11.2 ± 4.8 vs. 10.8 ± 3.7, p = 0.617). There was no significant difference in subjective image quality between the two groups (all p > 0.05). The subjective image noise was higher in the group B (p = 0.036 in reader 1, p = 0.005 in reader 2). The inter-observer reliability for assessing subjective image quality was good (ICC 0.746~0.784, p < 0.001). The mean CT dose index volume (CTDIvol) and mean dose length product (DLP) were significantly lower in group B than group A [CTDIvol, 6.4 ± 1.3 vs. 2.2 ± 2.2 mGy (p < 0.001); DLP, 499.1 ± 116.0 vs. 133.1 ± 45.7 mGy × cm (p < 0.001)].ConclusionsCTV using 80 kVp combined with SAFIRE provides lower radiation dose and improved CNR compared to CTV using 120 kVp with FBP.

Reaching for better image quality and lower radiation dose in head and neck CT: advanced modeled and sinogram-affirmed iterative reconstruction in combination with tube voltage adaptation.

The aim of this study was to evaluate image quality and radiation dose in low-dose head and neck CT comparing two different commercially available iterative reconstruction algorithms: sinogram-affirmed iterative reconstruction (SAFIRE) and advanced modeled iterative reconstruction (ADMIRE) with fixed and automated tube voltage adaptation (TVA). CT examinations of 103 patients were analysed. 58 patients were examined on a single-source CT at fixed tube voltage of 120 kV and reconstructed with filtered back projection (FBP) and SAFIRE (Strength Level 3). 45 patients were examined in a single-source mode on a dual-source CT with automated TVA and reconstructed with FBP and ADMIRE (Strength Levels 2 and 3). Image noise was calculated in seven anatomical volumes of interest. Subjective evaluation of the CT images was performed using a four-grade scale. Mean CT numbers of FBP and the corresponding iterative reconstruction did not differ significantly (p = 0.74-0.99). Image noise was lower with both iterative reconstruction techniques than with FBP (SAFIRE 3: -22.3%; ADMIRE 2: -14.9%; ADMIRE 3: -24.2%; all p < 0.05); hence, the signal-to-noise ratio and the contrast-to-noise values were higher. Subjective image quality revealed a more favourable result for the iterative reconstruction. ADMIRE 3 in combination with automated TVA showed 14.4% (p < 0.05) less image noise with a 7.5% lower radiation dose than SAFIRE 3 with fixed tube voltage. Higher image quality at lower radiation dose can be achieved using ADMIRE in combination with automated TVA.