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      Ultra Low Dose CT Pulmonary Angiography with Iterative Reconstruction

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          Abstract

          Objective

          Evaluation of a new iterative reconstruction algorithm (IMR) for detection/rule-out of pulmonary embolism (PE) in ultra-low dose computed tomography pulmonary angiography (CTPA).

          Methods

          Lower dose CT data sets were simulated based on CTPA examinations of 16 patients with pulmonary embolism (PE) with dose levels (DL) of 50%, 25%, 12.5%, 6.3% or 3.1% of the original tube current setting. Original CT data sets and simulated low-dose data sets were reconstructed with three reconstruction algorithms: the standard reconstruction algorithm “filtered back projection” (FBP), the first generation iterative reconstruction algorithm iDose and the next generation iterative reconstruction algorithm “Iterative Model Reconstruction” (IMR). In total, 288 CTPA data sets (16 patients, 6 tube current levels, 3 different algorithms) were evaluated by two blinded radiologists regarding image quality, diagnostic confidence, detectability of PE and contrast-to-noise ratio (CNR).

          Results

          iDose and IMR showed better detectability of PE than FBP. With IMR, sensitivity for detection of PE was 100% down to a dose level of 12.5%. iDose and IMR showed superiority to FBP regarding all characteristics of subjective (diagnostic confidence in detection of PE, image quality, image noise, artefacts) and objective image quality. The minimum DL providing acceptable diagnostic performance was 12.5% (= 0.45 mSv) for IMR, 25% (= 0.89 mSv) for iDose and 100% (= 3.57 mSv) for FBP. CNR was significantly (p < 0.001) improved by IMR compared to FBP and iDose at all dose levels.

          Conclusion

          By using IMR for detection of PE, dose reduction for CTPA of up to 75% is possible while maintaining full diagnostic confidence. This would result in a mean effective dose of approximately 0.9 mSv for CTPA.

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          Most cited references23

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          Multidetector computed tomography for acute pulmonary embolism.

          The accuracy of multidetector computed tomographic angiography (CTA) for the diagnosis of acute pulmonary embolism has not been determined conclusively. The Prospective Investigation of Pulmonary Embolism Diagnosis II trial was a prospective, multicenter investigation of the accuracy of multidetector CTA alone and combined with venous-phase imaging (CTA-CTV) for the diagnosis of acute pulmonary embolism. We used a composite reference test to confirm or rule out the diagnosis of pulmonary embolism. Among 824 patients with a reference diagnosis and a completed CT study, CTA was inconclusive in 51 because of poor image quality. Excluding such inconclusive studies, the sensitivity of CTA was 83 percent and the specificity was 96 percent. Positive predictive values were 96 percent with a concordantly high or low probability on clinical assessment, 92 percent with an intermediate probability on clinical assessment, and nondiagnostic if clinical probability was discordant. CTA-CTV was inconclusive in 87 of 824 patients because the image quality of either CTA or CTV was poor. The sensitivity of CTA-CTV for pulmonary embolism was 90 percent, and specificity was 95 percent. CTA-CTV was also nondiagnostic with a discordant clinical probability. In patients with suspected pulmonary embolism, multidetector CTA-CTV has a higher diagnostic sensitivity than does CTA alone, with similar specificity. The predictive value of either CTA or CTA-CTV is high with a concordant clinical assessment, but additional testing is necessary when the clinical probability is inconsistent with the imaging results. Copyright 2006 Massachusetts Medical Society.
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            Low-tube-voltage, high-tube-current multidetector abdominal CT: improved image quality and decreased radiation dose with adaptive statistical iterative reconstruction algorithm--initial clinical experience.

            To investigate whether an adaptive statistical iterative reconstruction (ASIR) algorithm improves the image quality at low-tube-voltage (80-kVp), high-tube-current (675-mA) multidetector abdominal computed tomography (CT) during the late hepatic arterial phase. This prospective, single-center HIPAA-compliant study was institutional review board approved. Informed patient consent was obtained. Ten patients (six men, four women; mean age, 63 years; age range, 51-77 years) known or suspected to have hypervascular liver tumors underwent dual-energy 64-section multidetector CT. High- and low-tube-voltage CT images were acquired sequentially during the late hepatic arterial phase of contrast enhancement. Standard convolution FBP was used to reconstruct 140-kVp (protocol A) and 80-kVp (protocol B) image sets, and ASIR (protocol C) was used to reconstruct 80-kVp image sets. The mean image noise; contrast-to-noise ratio (CNR) relative to muscle for the aorta, liver, and pancreas; and effective dose with each protocol were assessed. A figure of merit (FOM) was computed to normalize the image noise and CNR for each protocol to effective dose. Repeated-measures analysis of variance with Bonferroni adjustment for multiple comparisons was used to compare differences in mean CNR, image noise, and corresponding FOM among the three protocols. The noise power spectra generated from a custom phantom with each protocol were also compared. When image noise was normalized to effective dose, protocol C, as compared with protocols A (P = .0002) and B (P = .0001), yielded an approximately twofold reduction in noise. When the CNR was normalized to effective dose, protocol C yielded significantly higher CNRs for the aorta, liver, and pancreas than did protocol A (P = .0001 for all comparisons) and a significantly higher CNR for the liver than did protocol B (P = .003). Mean effective doses were 17.5 mSv +/- 0.6 (standard error) with protocol A and 5.1 mSv +/- 0.3 with protocols B and C. Compared with protocols A and B, protocol C yielded a small but quantifiable noise reduction across the entire spectrum of spatial frequencies. Compared with standard FBP reconstruction, an ASIR algorithm improves image quality and has the potential to decrease radiation dose at low-tube-voltage, high-tube-current multidetector abdominal CT during the late hepatic arterial phase.
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              Abdominal CT with low tube voltage: preliminary observations about radiation dose, contrast enhancement, image quality, and noise.

              To prospectively investigate the effect of low tube voltage on radiation dose, contrast enhancement, image quality, and image noise at abdominal dynamic computed tomography (CT). The institutional review board approved this study. Prior informed consent was obtained from all patients. Forty patients (24 women, 16 men; mean age, 62 years) underwent initial abdominal CT at 120 kV with 100 mL of contrast material (protocol A). Then all patients were randomly assigned to one of two protocols (protocol B, CT at 90 kV with 100 mL contrast material; protocol C, CT at 90 kV with 80 mL contrast material). The CT numbers of their abdominal organs were assessed quantitatively and qualitatively. Statistical analysis was performed by using the two-tailed paired t test, Kruskal-Wallis test, and kappa test of interobserver agreement. The radiation dose was measured with a phantom that consisted of glass-rod dosimeters. Quantitative analysis revealed that protocols B and C yielded significantly better enhancement of the aorta, liver, pancreas, spleen, and kidney than did protocol A (P < .05). With qualitative analysis, the difference among the three protocols in regard to image quality was not significant. At 90 kV versus 120 kV, the radiation dose reduction in the center of the phantom was 56.8% (6.3 vs 14.6 mGy); in the periphery, it was 46.2% (13.6 vs 25.3 mGy). By decreasing the tube voltage, the amount of contrast material can be reduced without image quality degradation. In scans obtained with a low tube voltage, the radiation dose can be reduced as much as 56.8%, and higher contrast material enhancement can be achieved. RSNA, 2005
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                Author and article information

                Contributors
                Role: Editor
                Journal
                PLoS One
                PLoS ONE
                plos
                plosone
                PLoS ONE
                Public Library of Science (San Francisco, CA USA )
                1932-6203
                9 September 2016
                2016
                : 11
                : 9
                : e0162716
                Affiliations
                [1 ]Department of diagnostic and interventional Radiology, Technische Universität München, Munich, Germany
                [2 ]Philips GmbH, Innovative Technologies, Research Laboratories, Hamburg, Germany
                [3 ]Department of diagnostic and interventional Radiology, Universitätsklinikum Tübingen, Tübingen, Germany
                [4 ]Lehrstuhl für Biomedizinische Physik, Physik-Department & Institut für Medizintechnik, Technische Universität München, Garching, Germany
                Universidad Francisco de Vitoria, SPAIN
                Author notes

                Competing Interests: Thomas Köhler and Bernhard Brendel are employees of Philips GmbH, Innovative Technologies. The remaining authors have no financial disclosures and had complete, unrestricted access to the study data at all stages of the study. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

                • Conceptualization: AS PN DM AF.

                • Data curation: AS.

                • Formal analysis: AS DM PN.

                • Investigation: MR VR.

                • Methodology: AS PN DM.

                • Project administration: AS DM PN.

                • Resources: AS DM.

                • Software: AS TK BB.

                • Supervision: ER PN DM.

                • Validation: AS DM PN.

                • Visualization: AS.

                • Writing – original draft: AS.

                • Writing – review & editing: AS PN DM.

                Author information
                http://orcid.org/0000-0003-4394-862X
                Article
                PONE-D-16-13461
                10.1371/journal.pone.0162716
                5017721
                27611830
                9902c65f-9f34-4e35-9fae-1aa97c45926b
                © 2016 Sauter et al

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                History
                : 24 April 2016
                : 26 August 2016
                Page count
                Figures: 4, Tables: 0, Pages: 12
                Funding
                The authors received no specific funding for this work.
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