Janet M. Busey

Model-Based Iterative Reconstruction Versus Adaptive Statistical Iterative Reconstruction and Filtered Back Projection in Liver 64-MDCT: Focal Lesion Detection, Lesion Conspicuity, and Image Noise

OBJECTIVE The purpose of this study is to compare three CT image reconstruction algorithms for liver lesion detection and appearance, subjective lesion conspicuity, and measured noise. MATERIALS AND METHODS Thirty-six patients with known liver lesions were scanned with a routine clinical three-phase CT protocol using a weight-based noise index of 30 or 36. Image data from each phase were reconstructed with filtered back projection (FBP), adaptive statistical iterative reconstruction (ASIR), and model-based iterative reconstruction (MBIR). Randomized images were presented to two independent blinded reviewers to detect and categorize the appearance of lesions and to score lesion conspicuity. Lesion size, lesion density (in Hounsfield units), adjacent liver density (in Hounsfield units), and image noise were measured. Two different unblinded truth readers established the number, appearance, and location of lesions. RESULTS Fifty-one focal lesions were detected by truth readers. For blinded reviewers compared with truth readers, there was no difference for lesion detection among the reconstruction algorithms. Lesion appearance was statistically the same among the three reconstructions. Although one reviewer scored lesions as being more conspicuous with MBIR, the other scored them the same. There was significantly less background noise in air with MBIR (mean [± SD], 2.1 ± 1.4 HU) than with ASIR (8.9 ± 1.9 HU; p < 0.001) or FBP (10.6 ± 2.6 HU; p < 0.001). Mean lesion contrast-to-noise ratio was statistically significantly higher for MBIR (34.4 ± 29.1) than for ASIR (6.5 ± 4.9; p < 0.001) or FBP (6.3 ± 6.0; p < 0.001). CONCLUSION In routine-dose clinical CT of the liver, MBIR resulted in comparable lesion detection, lesion characterization, and subjective lesion conspicuity, but significantly lower background noise and higher contrast-to-noise ratio compared with ASIR or FBP. This finding suggests that further investigation of the use of MBIR to enable dose reduction in liver CT is warranted.

Dual-Energy Liver CT: Effect of Monochromatic Imaging on Lesion Detection, Conspicuity, and Contrast-to-Noise Ratio of Hypervascular Lesions on Late Arterial Phase

OBJECTIVE The purpose of this study was to evaluate the effect of use of dual-energy CT monochromatic imaging in the late hepatic arterial phase on hyperenhancing focal lesion detection and lesion conspicuity. SUBJECTS AND METHODS This prospective study included 72 patients imaged with a single-source dual-energy CT scanner. Late arterial phase imaging was performed with dual energies of 140 and 80 kVp, and the portal venous and delayed phases were performed with a single energy of 120 kVp. Two deidentified image sets were created: set A consisted of 77-keV images only, and set B consisted of 40-, 50-, 70-, and 77-keV images and iodine-based contrast material decomposition images. Two independent reviewers identified hypervascular lesions and subjectively scored lesion conspicuity. Contrast-to-noise ratios were calculated, and radiation dose (volume CT dose index) was recorded. RESULTS The 128 lesions identified had a mean size of 1.7 ± 1.4 cm. There was no difference in lesion detection between the two reviewers or the two image sets. The contrast-to-noise ratio at 50 keV was 72% greater than that at 77 keV (p < 0.0001). Subjective conspicuity was statistically greatest at 50 keV (p < 0.0001). There was no statistical difference in mean volume CT dose index between the dual-energy (12.8 mGy) and the two single-energy (14.4 and 14.2 mGy) phases. CONCLUSION Viewing dual-energy CT images may result in the greatest subjective lesion conspicuity and measured contrast-to-noise ratio at 50 keV with equal detection of hyperenhancing liver lesions compared with viewing 77-keV images alone. In addition, the radiation doses of dual-energy CT may be similar to those of single-energy CT.

Standard and Reduced Radiation Dose Liver CT Images: Adaptive Statistical Iterative Reconstruction versus Model-based Iterative Reconstruction—Comparison of Findings and Image Quality

PURPOSE To investigate whether reduced radiation dose liver computed tomography (CT) images reconstructed with model-based iterative reconstruction ( MBIR model-based iterative reconstruction ) might compromise depiction of clinically relevant findings or might have decreased image quality when compared with clinical standard radiation dose CT images reconstructed with adaptive statistical iterative reconstruction ( ASIR adaptive statistical iterative reconstruction ). MATERIALS AND METHODS With institutional review board approval, informed consent, and HIPAA compliance, 50 patients (39 men, 11 women) were prospectively included who underwent liver CT. After a portal venous pass with ASIR adaptive statistical iterative reconstruction images, a 60% reduced radiation dose pass was added with MBIR model-based iterative reconstruction images. One reviewer scored ASIR adaptive statistical iterative reconstruction image quality and marked findings. Two additional independent reviewers noted whether marked findings were present on MBIR model-based iterative reconstruction images and assigned scores for relative conspicuity, spatial resolution, image noise, and image quality. Liver and aorta Hounsfield units and image noise were measured. Volume CT dose index and size-specific dose estimate ( SSDE size-specific dose estimate ) were recorded. Qualitative reviewer scores were summarized. Formal statistical inference for signal-to-noise ratio ( SNR signal-to-noise ratio ), contrast-to-noise ratio ( CNR contrast-to-noise ratio ), volume CT dose index, and SSDE size-specific dose estimate was made (paired t tests), with Bonferroni adjustment. RESULTS Two independent reviewers identified all 136 ASIR adaptive statistical iterative reconstruction image findings (n = 272) on MBIR model-based iterative reconstruction images, scoring them as equal or better for conspicuity, spatial resolution, and image noise in 94.1% (256 of 272), 96.7% (263 of 272), and 99.3% (270 of 272), respectively. In 50 image sets, two reviewers (n = 100) scored overall image quality as sufficient or good with MBIR model-based iterative reconstruction in 99% (99 of 100). Liver SNR signal-to-noise ratio was significantly greater for MBIR model-based iterative reconstruction (10.8 ± 2.5 [standard deviation] vs 7.7 ± 1.4, P < .001); there was no difference for CNR contrast-to-noise ratio (2.5 ± 1.4 vs 2.4 ± 1.4, P = .45). For ASIR adaptive statistical iterative reconstruction and MBIR model-based iterative reconstruction , respectively, volume CT dose index was 15.2 mGy ± 7.6 versus 6.2 mGy ± 3.6; SSDE size-specific dose estimate was 16.4 mGy ± 6.6 versus 6.7 mGy ± 3.1 (P < .001). CONCLUSION Liver CT images reconstructed with MBIR model-based iterative reconstruction may allow up to 59% radiation dose reduction compared with the dose with ASIR adaptive statistical iterative reconstruction , without compromising depiction of findings or image quality.

Prospectively ECG gated CT pulmonary angiography versus helical ungated CT pulmonary angiography: impact on cardiac related motion artifacts and patient radiation dose.

OBJECTIVE To compare prospectively ECG gated CT pulmonary angiography (CTPA) with routine helical ungated CTPA for cardiac related motion artifacts and patient radiation dose. SUBJECTS AND METHODS Twenty patients with signs and symptoms suspicious for pulmonary embolism and who had a heart rate below 85 were scanned with prospectively ECG gated CTPA. These gated exams were matched for several clinical parameters to exams from twenty similar clinical patients scanned with routine ungated helical CTPA. Three blinded independent reviewers subjectively evaluated all exams for overall pulmonary artery enhancement and for several cardiac motion related artifacts, including vessel blurring, intravascular shading, and double line. Reviewers also measured pulmonary artery intravascular density and image noise. Patient radiation dose for each technique was compared. Fourteen clinical prospectively ECG gated CTPA exams from a second institution were evaluated for the same parameters. RESULTS Prospectively ECG gated CTPA resulted in significantly decreased motion-related image artifact scores in lung segments adjacent to the heart compared to ungated CTPA. Measured image noise was not significantly different between the two types of CTPA exams. Effective dose was 28% less for prospectively ECG gated CTPA (4.9 mSv versus 6.8 mSv, p=0.02). Similar results were found in the prospectively ECG gated exams from the second institution. CONCLUSION Compared to routine helical ungated CTPA, prospectively ECG gated CTPA may result in less cardiac related motion artifact in lung segments adjacent to the heart and significantly less patient radiation dose.

Diagnostic Performance of Resting CT Myocardial Perfusion in Patients With Possible Acute Coronary Syndrome

OBJECTIVE Coronary CT angiography has high sensitivity, but modest specificity, to detect acute coronary syndrome. We studied whether adding resting CT myocardial perfusion imaging improved the detection of acute coronary syndrome. SUBJECTS AND METHODS Patients with low-to-intermediate cardiac risk presenting with possible acute coronary syndrome received both the standard of care evaluation and a research thoracic 64-MDCT examination. Patients with an obstructive (> 50%) stenosis or a nonevaluable coronary segment on CT were diagnosed with possible acute coronary syndrome. CT perfusion was determined by applying gray and color Hounsfield unit maps to resting CT angiography images. Adjudicated patient diagnoses were based on the standard of care and 3-month follow-up. Patient-level diagnostic performance for acute coronary syndrome was calculated for coronary CT, CT perfusion, and combined techniques. RESULTS A total of 105 patients were enrolled. Of the nine (9%) patients with acute coronary syndrome, all had obstructive CT stenoses but only three had abnormal CT perfusion. CT perfusion was normal in all other patients. To detect acute coronary syndrome, CT angiography had 100% sensitivity, 89% specificity, and a positive predictive value of 45%. For CT perfusion, specificity and positive predictive value were each 100%, and sensitivity was 33%. Combined cardiac CT and CT perfusion had similar specificity but a higher positive predictive value (100%) than did CT angiography. CONCLUSION Resting CT perfusion using CT angiographic images may have high specificity and may improve CT positive predictive value for acute coronary syndrome without added radiation and contrast. However, normal resting CT perfusion cannot exclude acute coronary syndrome.

Dual-energy CT Aortography with 50% Reduced Iodine Dose Versus Single-energy CT Aortography with Standard Iodine Dose.

RATIONALE AND OBJECTIVES Because many patients with aortic pathology also have compromised renal function, we wished to investigate dual-energy computed tomography (DECT) aortography with 50% reduced iodine dose compared to single-energy computed tomography (SECT) aortography with standard iodine dose. MATERIALS AND METHODS Fifty patients had DECT aortography with 50% reduced iodine dose. Thirty-four of these patients had prior SECT aortography with standard iodine dose. DECT images were reconstructed at both 50 and 77 keV and were compared to SECT 120 kVp images. Reviewers measured aortic attenuation, image noise, and scored vascular enhancement. Signal-to-noise ratios (SNR) and contrast-to-noise ratios (CNR) were calculated. Volume CT dose index was recorded. RESULTS Mean iodine dose was 47 g for SECT and 24 g for DECT. Aortic attenuation was highest at reduced iodine dose DECT 50 keV (570 ± 105 Hounsfield units [HU]) compared to 77 keV (239 ± 40 HU) or to standard iodine dose SECT 120 kVp (356 ± 69 HU) (P < 0.05). Image noise was greatest at 50 keV compared to 77 keV and 120 kVp (P < 0.05) but was similar between 77 keV and 120 kVp (P > 0.05). SNR and CNR were the same at 50 keV and 120 kVp (P > 0.05). Mean vascular enhancement scores were all above 3.0 (good, typical enhancement). Volume CT dose index was 11.7 mGy for DECT and 11.8 mGy for SECT (P = 0.37). CONCLUSIONS DECT aortography with 50% reduced iodine reconstructed at 50 keV resulted in significantly greater aortic attenuation, good subjective vascular enhancement, and comparable SNR and CNR compared to standard iodine dose SECT. DECT image noise at 77 keV was similar to SECT at 120 kVp.

Economic Outcome of Cardiac CT-Based Evaluation and Standard of Care for Suspected Acute Coronary Syndrome In the Emergency Department: A Decision Analytic Model

RATIONALE AND OBJECTIVES Cardiac computed tomography (CCT) in the emergency department may be cost saving for suspected acute coronary syndrome (ACS), but economic outcome data are limited. The objective of this study was to compare the cost of CCT-based evaluation versus standard of care (SOC) using the results of a clinical trial. MATERIALS AND METHODS We developed a decision analytic cost-minimization model to compare CCT-based and SOC evaluation costs to obtain a correct diagnosis. Model inputs, including Medicare-adjusted patient costs, were primarily obtained from a cohort study of 102 patients at low to intermediate risk for ACS who underwent an emergency department SOC clinical evaluation and a 64-channel CCT. SOC costs included stress testing in 77% of patients. Data from published literature completed the model inputs and expanded data ranges for sensitivity analyses. RESULTS Modeled mean patient costs for CCT-based evaluation were

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750 (24%) lower than the SOC (

The use of model-based iterative reconstruction to decrease ED radiation exposure

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Wide-detector axial CT versus 4 cm detector helical CT for transcatheter aortic valve replacement: iodine dose, radiation, and image quality

3134, respectively). Sensitivity analyses indicated that CCT was less expensive over a wide range of estimates and was only more expensive with a CCT specificity below 67% or if more than 44% of very low risk patients had CCT. Probabilistic sensitivity analysis suggested that CCT-based evaluation had a 98.9% probability of being less expensive compared to SOC. CONCLUSION Using a decision analytic model, CCT-based evaluation resulted in overall lower cost than the SOC for possible ACS patients over a wide range of cost and outcome assumptions, including computed tomography-related complications and downstream costs.