Point-diffraction interferometer wavefront sensor with birefringent crystal.

A key technique in direct imaging of extrasolar planets with ground-based telescopes is extreme adaptive optics. It requires a wavefront sensor capable of achieving high accuracy with a small number of photons. Imada et al. [Appl. Opt.54, 7870 (2015)APOPAI0003-693510.1364/AO.54.007870] proposed a type of wavefront sensor that employs a point-diffraction interferometer (PDI). This type of sensor has problems concerning a low photon-usage efficiency and manufacturing feasibility. In addition, they did not give sufficient study on the optimum pinhole size. Here, we propose a novel PDI, with which these problems are overcome, and study the optimum pinhole size for it. The sensor is incorporated with birefringent crystal as the key component to achieve high efficiency and is feasible to manufacture realistically. We run numerical simulations to optimize the pinhole size, where the photon noise is evaluated.

Impact of Abnormal Remote Stress Myocardial Blood Flow by Dynamic CT Perfusion on Clinical Outcomes.

The objective of this study was to investigate the incremental prognostic value for adverse events of myocardial blood flow (MBF) derived from stress computed tomography perfusion (CTP) at remote myocardium over cardiac risk factors and ischemia. We prospectively analyzed 242 patients who underwent dynamic CTP and CT angiography. Adverse events were defined as a composite of all-cause mortality, non-fatal myocardial infarction, unstable angina, heart failure requiring hospitalization, peripheral artery disease, and stroke. MBF value was calculated in each myocardial segment and ischemia was defined as mild decrease in MBF in two consecutive segments or moderate decrease in a single segment accompanied with a coronary stenosis ≥50%. The mean MBF of the non-ischemic segments was defined as remote MBF. We divided the patients into two groups by median MBF value of 1.15 ml/min/g. During a median follow-up of 18 months, 18 patients had adverse events. Annual event rate showed a significant difference between patients with low (≤1.15 ml/min/g) and high (>1.15 ml/min/g) MBF (6.1% vs 1.8%, p = 0.02). Univariate analysis showed that low MBF was a significant predictor of events (hazard ratio (HR): 3.4; 95% confidence interval (CI): 1.2 to 12.0; p = 0.02). This relationship maintained significant after adjusted for the presence of ischemia and cardiac risk factors (HR: 3.0; 95%CI: 1.1 to 11.1; p = 0.04). In conclusion, MBF value ≤1.15 ml/min/g derived from dynamic CTP in remote myocardium is significantly related with poor outcome and this relationship was independent of myocardial ischemia and cardiac risk factors.

Double region of interest timing bolus technique following endovascular aortic repair: Short-term prognosis analysis.

OBJECTIVES: To compare the incidence rate of reintervention in patients with and without complication findings at aortic computed tomography using double region of interest timing bolus (DRTB) method after endovascular stent placement of the aorta. METHODS: We included 40 patients who underwent computed tomography of the aorta using DRTB method after endovascular stent placement. DRTB method allows to scan the aorta with a short injection time of 9 s by synchronizing the scan speed to the aortic flow. Complication findings at computed tomography were defined as endoleak, rupture, occlusion, and infection. The primary endpoint was reintervention, which was defined as any of the following three events: conversion to open repair, graft revision, or secondary intervention. RESULTS: The mean contrast medium during computed tomography angiography was 38.6 ± 3.9 mL. Complication findings at computed tomography were present in 10 patients (25%): endoleak (n = 9) and infection (n = 1). During a median follow-up of 7 months (interquartile range, 4-11 months), two patients experienced reintervention. Kaplan-Meier curves by complication findings showed that event rate at 6 months was significantly higher in patients with complication findings than in patients without (20% vs 0%, p = 0.01). No patients without complication findings at computed tomography experienced reintervention. CONCLUSIONS: No complication findings at computed tomography after intervention of the aorta resulted in good prognosis in patients who underwent aortic computed tomography using DRTB method.

Aortic CT angiography using the double region of interest timing bolus technique: feasibility of 80 kVp scanning in lean patients.

To investigate the feasibility of aortic computed tomography angiography (CTA) performed at 80 kVp in lean patients using the double region of interest timing bolus (DRTB) technique compared to 100 kVp scanning. This study was approved by the institutional ethics committee, and all patients provided written informed consent. We prospectively included 165 patients from July 2018 to February 2019. We used an 80 kVp protocol when the maximal tube current did not exceed the limit using automatic exposure control; otherwise, 100 kVp was selected. The scan parameters for aortic CTA were determined from the test scan data. Enhancement at six points of the aortoiliac arteries and noise at the bifurcation level were measured. We compared the enhancement and signal to noise ratio (SNR) using Student's t-test. The tube voltage was 80 kVp in 87 patients (53%). The enhancement of the aortoiliac arteries was significantly higher (449.3 ± 77.8 vs 378.7 ± 53.1 HU, p < 0.0001) and the SNR was similar (42.4 ± 11.1 vs 40.0 ± 10.6, p = 0.17), and the amount of contrast medium was lower (33.0 ± 2.5 vs 41.8 ± 3.3 ml, p < 0.001) in the 80 kVp group compared to the 100 kVp group. Reducing the tube current to 80 kVp could decrease the amount of contrast medium used compared to the 100 kVp protocol, while maintaining image quality, for aortic CTA using the DRTB technique.

Double ROI Timing Bolus Technique to Perform Aortic CT Angiography With a 9-Second Contrast Injection Duration.

OBJECTIVE. The purpose of this study was to investigate the feasibility of a double ROI timing bolus technique for performing aortic CT angiography (CTA) with 40 mL of contrast medium over 9 seconds. SUBJECTS AND METHODS. A prospective study from February to July 2018 included 106 patients with clinical indications for evaluation of aortic aneurysm or dissection or suspected aortic disease. Forty-seven of these patients had undergone prior aortic CTA by the conventional method. The scanning speed for the double ROI timing bolus technique was calculated from the time-attenuation curves of the ascending and descending aorta by use of the timing bolus data to synchronize aortic flow. The conventional scan was obtained by injection of 1.7 mL of contrast medium per kilogram of body weight for 25 seconds. Enhancement of six points on the aortoiliac arteries and superior vena cava was measured. The t test was used to compare the values. RESULTS. Use of the double ROI timing bolus method significantly reduced the amount of contrast medium injected compared with the amount for the conventional method (40.0 mL vs 88.0 ± 9.4 mL, p < 0.001). Use of the method significantly increased aortoiliac enhancement (403.3 ± 76.0 HU vs 359.7 ± 61.5 HU, p < 0.001) and significantly decreased enhancement of the superior vena cava (118.9 ± 46.2 HU vs 239.2 ± 130.5 HU, p < 0.001) compared with the conventional method. In the group with prior CTA images available, the effective dose was significantly lower with the double ROI timing bolus than with the conventional method (8.3 ± 1.7 mSv vs 12.4 ± 3.2 mSv, p < 0.01). CONCLUSION. Use of the double ROI timing bolus method can dramatically reduce the amount of contrast medium used during aortic CTA while improving aortic enhancement and reducing radiation dose.

Feasibility of dynamic myocardial CT perfusion using single-source 64-row CT.

BACKGROUND: Dynamic myocardial computed tomography perfusion (CTP) is an emerging technique to diagnose significant coronary stenosis. However, this procedure has not been reported using single-source 64-row CT. OBJECTIVE: To investigate the radiation dose and the diagnostic performance of dynamic CTP to diagnose significant stenosis by catheter exam. METHODS: We prospectively included 165 patients who underwent CTP exam under adenosine stress using a single-source 64-row CT. MBF was calculated using the deconvolution technique. Quantitative perfusion ratio (QPR) was defined as the myocardial blood flow (MBF) of the myocardium with coronary stenosis divided by the MBF of the myocardium without significant stenosis or infarct. Of the 44 patients who underwent subsequent coronary angiography, we assessed the diagnostic performance to diagnose ≥50% stenosis by quantitative coronary analysis (QCA). RESULTS: The average effective dose of dynamic CTP and the entire scans were 2.5 ±â€¯0.7 and 7.3 ±â€¯1.8 mSv, respectively. The MBF of the myocardium without significant stenosis was 1.20 ±â€¯0.32 ml/min/g, which significantly decreased to 0.98 ±â€¯0.24 ml/min/g (p < 0.01) in the area with ≥50% stenosis by CT angiography. The QPR of the myocardium with QCA ≥50% stenosis was significantly lower than 1 (0.84 ±â€¯0.32, 95% confidence interval (CI), 0.77-0.90, p < 0.001). The accuracy to detect QCA ≥50% stenosis was 82% (95%CI, 74-88%) using CT angiography alone and significantly increased to 87% (95%CI, 80-92%, p < 0.05) including QPR. CONCLUSION: Dynamic myocardial CTP could be performed using 64-row CT with a low radiation dose and would improve the diagnostic performance to detect QCA ≥50% stenosis than CT angiography alone.

Data for comparison of computed tomography angiography and dynamic myocardial perfusion to detect significant stenosis by coronary angiography.

This article describes data related to a research article titled "Feasibility of dynamic myocardial CT perfusion using single-source 64-row CT", Tomizawa et al. (in press) [1]. Decrease in the myocardial blood flow could be calculated by performing stress dynamic computed tomography perfusion. This article compares the receiver operating characteristics curve of computed tomography angiography and dynamic myocardial perfusion to diagnose significant stenosis by invasive coronary angiography.

Longer diabetes duration reduces myocardial blood flow in remote myocardium assessed by dynamic myocardial CT perfusion.

AIMS: To investigate the relationship of type 2 diabetes duration and myocardial blood flow (MBF) assessed by myocardial CT perfusion. MATERIALS AND METHODS: We prospectively included 140 patients with type 2 diabetes who underwent dynamic myocardial CT perfusion exam. MBF of the remote myocardium was calculated using the deconvolution technique and the Voronoi method. The relationships of MBF and diabetic duration, diabetic complications, conventional risk factors, coronary calcium, and coronary stenosis were assessed by logistic regression analysis. RESULTS: A weak but significantly negative relationship was present between diabetes duration and MBF (R2 = 0.05, p < 0.01). The average MBF of patients with a duration of >8 years was 13% lower than that of the remaining patients (1.11 ±â€¯0.35 vs 1.28 ±â€¯0.27 ml min-1 g-1, p < 0.01). Duration of one year was associated with a 6% increased risk for low MBF (<1.18 ml min-1 g-1) (odds ratio 1.06, 95% confidence interval 1.01-1.12, p < 0.05). Calcium score was also a significant factor for low MBF (odds ratio 1.08 (per 100 Agatston units), 95% confidence interval 1.01-1.17, p < 0.05). CONCLUSION: Longer diabetes duration is associated with lower MBF independent of conventional cardiac risk factors or the presence of coronary stenosis.

Simplified Bernoulli formula to predict flow limiting stenosis at coronary computed tomography angiography.

OBJECTIVE: To compare the diagnostic performance of estimated energy loss (EEL) with diameter stenosis (DS) to estimate significant stenosis by fractional flow reserve (FFR). MATERIALS AND METHODS: One hundred twenty-five patients were included. EEL was calculated using DS, lesion length, minimal lumen area and left ventricular volume. FFR ≤ 0.80 was determined significant. RESULTS: EEL improved the accuracy from 63% (95% confidence interval (CI): 55-72%) to 83% (95% CI: 75-89%, p < 0.0001). EEL increased the area under the receiver operating characteristics curve from 0.63 to 0.85 (p < 0.0001). CONCLUSIONS: EEL improved the diagnostic performance to detect functionally significant stenosis than DS.

High-risk Plaque and Calcification Detected by Coronary CT Angiography to Predict Future Cardiovascular Events After Percutaneous Coronary Intervention.

RATIONALE AND OBJECTIVES: The purpose of this study was to investigate whether high-risk plaque (HRP) and calcium assessed by coronary computed tomography (CT) could predict future cardiovascular events after second-generation drug-eluting stent (DES) placement. MATERIALS AND METHODS: We analyzed 317 patients from December 2012 to April 2015 who underwent coronary CT followed by DES placement. HRP was defined as a plaque with positive remodeling and low attenuation or a plaque with a napkin-ring sign. Coronary calcium was assessed by Agatston score (AS). Patients were divided into three groups: low risk, HRP negative and AS <400; intermediate risk, HRP positive and AS ≥400; high risk, HRP positive and AS ≥400. The primary end point was a composite of all-cause mortality, myocardial infarction, fatal arrhythmia, or repeated revascularization. Kaplan-Meier analysis was used to estimate the distribution of time to events. RESULTS: A total of 74 events (23%) occurred during a median follow-up of 25.8 months. Patients with primary end points had HRP more frequently (70% vs 51%, P = 0.003) and were more calcified (AS, 471 [interquartile range, 143-1614] vs 289 [interquartile range, 63-787]; P = 0.01) than patients without primary end points. The frequency of primary end point increased significantly in the intermediate- and high-risk patients (P = 0.0011). Multivariate analysis showed that the hazard ratio of the intermediate- and high-risk groups was 1.91 (95% confidence interval, 1.04-3.77; P = 0.037) and 2.66 (95% confidence interval, 1.27-5.73; P = 0.009), respectively. CONCLUSION: Plaque and calcification analysis by coronary CT could predict future cardiovascular events after second-generation DES placement.

Synthesis of n-type Mg2Si/CNT Thermoelectric Nanofibers.

Magnesium silicide (Mg2Si)/carbon nanotube (CNT) thermoelectric nanofibers for use as a flexible thermoelectric material were successfully synthesized through the combined processes of the sol-gel method, magnesiothermic reduction, and liquid-solid phase reaction. In the resulting product, each CNT was coated with Mg2Si which was an approximately 60-nm-thick single crystal. The synthesized Mg2Si-coated CNTs exhibited n-type thermoelectric behavior confirming that n-type thermoelectric composite nanofibers were successfully obtained.

Accuracy of computed tomography angiography to identify thin-cap fibroatheroma detected by optical coherence tomography.

BACKGROUND: Thin-cap fibroatheroma (TCFA) is assumed to cause acute coronary syndromes. OBJECTIVE: To compare the accuracy of different models for diagnosing TCFA using parameters derived by CT, validated against optical coherence tomography (OCT). METHODS: One hundred twenty-nine plaques in 106 patients were analyzed using data acquired by 64-row CT with a reconstruction thickness of 0.67 mm and an increment of 0.33 mm. TCFA was defined by OCT as a plaque with lipid content in ≥2 quadrants and the thinnest part of the fibrous cap measuring ≤65 µm. The following parameters were obtained from CT: remodeling index (RI), proportion of low-attenuation (LA) volume (<60 HU), minimum CT number and napkin-ring sign (NRS). We compared three models to predict TCFA: Model 1, RI > 1.1, minimum CT number <30 HU and NRS; Model 2, RI > 1.1, minimum CT number <30 HU or NRS; Model 3, regression model using RI, proportion of LA volume and NRS. RESULTS: In OCT, 83 plaques fulfilled the criteria of TCFA. The area under the receiver operating characteristics curve significantly (p < 0.01) increased to 0.96 (95% confidence interval (CI), 0.92-1.0) in model 3 as compared to models 1 (0.74, 95% CI, 0.68-0.80) and 2 (0.72, 95% CI, 0.67-0.79). Diagnostic accuracy of model 3 (93%) was significantly higher than that of models 1 (67%, p < 0.001) and 2 (80%, p = 0.001). Sensitivity and specificity of model 3 was 94% and 91%, respectively. CONCLUSION: Diagnostic performance to identify TCFA by coronary CTA improves when RI and proportion of LA volume are used as continuous values rather than dichotomizing these parameters.

A clinical model to identify patients with high-risk plaque by coronary computed tomography angiography.

OBJECTIVES: Current clinical models predict the pre-test probability of obstructive coronary artery disease, but these models do not predict the presence of high-risk plaques. Thus the objective of this study was to propose a model to predict high-risk plaque assessed by coronary computed tomography (CT) angiography. METHODS: This study was a retrospective cross-sectional study. A clinical model was derived from 2392 patients and verified by 733 patients who underwent coronary CT suspected of coronary artery disease. High-risk plaque was defined as a plaque with positive remodeling (remodeling index>1.1), low attenuation (<30Hounsfield units) and napkin-ring sign. The risk score was calculated from the following 6 variables with a maximum of 24 points: age, sex, hemoglobin A1c, systolic blood pressure, high-density lipoprotein and smoking status. RESULTS: The proportion of patients with high-risk plaque was 11% and 17% in the derivation and validation cohort, respectively. The area under the receiver operation characteristic curve was 0.71 (95% confidence interval (CI): 0.68 to 0.74) in the derivation cohort and 0.75 (95% CI: 0.70 to 0.79) in the validation cohort. The frequency of high-risk plaques was 4% in the low-risk group (≤8 points) while it was 53% in the high-risk group (≥17 points) of the derivation cohort. CONCLUSIONS: We propose a scoring system to detect high-risk plaque assessed by coronary CT. Patients in the high-risk group have a high prevalence of high-risk plaque and might benefit from lipid lowering therapy.

Diagnostic Phase of Calcium Scoring Scan Applied as the Center of Acquisition Window of Coronary Computed Tomography Angiography Improves Image Quality in Minimal Acquisition Window Scan (Target CTA Mode) Using the Second Generation 320-Row CT.

OBJECTIVE: To compare the image quality of coronary computed tomography angiography (CCTA) acquired under two conditions: 75% fixed as the acquisition window center (Group 75%) and the diagnostic phase for calcium scoring scan as the center (CS; Group CS). METHODS: 320-row cardiac CT with a minimal acquisition window (scanned using "Target CTA" mode) was performed on 81 patients. In Group 75% (n = 40), CS was obtained and reconstructed at 75% and the center of the CCTA acquisition window was set at 75%. In Group CS (n = 41), CS was obtained at 75% and the diagnostic phase showing minimal artifacts was applied as the center of the CCTA acquisition window. Image quality was evaluated using a four-point scale (4-excellent) and the mean scores were compared between groups. RESULTS: The CCTA scan diagnostic phase occurred significantly earlier in CS (75.7 ± 3.2% vs. 73.6 ± 4.5% for Groups 75% and CS, resp., p = 0.013). The mean Group CS image quality score (3.58 ± 0.63) was also higher than that for Group 75% (3.19 ± 0.66, p < 0.0001). CONCLUSIONS: The image quality of CCTA in Target CTA mode was significantly better when the center of acquisition window is adjusted using CS.

Optimized heart rate for 320-row cardiac CT can be feasibly predicted from prescan parameters.

To evaluate the degree of heart rate (HR) changes at rest (HRrest), during breath hold (HRtest), and during cardiac CT examinations (HRscan) in a large group of patients , and to derive and asses the feasibility of a predictive formula for HRscan. HRrest, HRtest, and HRscan were retrospectively compared in a total of 563 consecutive patients who underwent 320-row cardiac CT. Multiple regression analysis was performed to derive predictive formulae for HRscan in the entire study population and, in each group of patients with decreased (Dec) or increased (Inc) HR during breath hold. The predictive formula was evaluated as accurate when less than 5 % of the actual HRscan exceeded the predicted HRscan by ±5 beats per minute (bpm). The average values of the HRtest (65.3 ± 12.0 bpm) and HRscan (63.7 ± 11.9 bpm) significantly decreased from those of the HRrest (68.4 ± 11.9 bpm) (p < 0.0001). The predictive formula (HRscan = 3.601 + 0.113HRrest + 0.8HRtest) was determined to be accurate only in Group Dec. The HRtest significantly decreased from the HRrest, and the HRscan significantly decreased from the HRtest. An accurate predictive formula for HRscan could be built only for Group Dec.

Real-time point-diffraction interferometer and its analytical formulation.

We propose a novel wavefront sensor and study its performance with an analytical formulation. The sensor has a polarizing point-diffraction beam splitter. Using transmitted and reflected beams, we can build a real-time point-diffraction interferometer with high precision and efficiency. Our analytical studies reveal that wavefront errors might be measured incorrectly and that less precise estimates of wavefronts appear as the pinhole radius Rpin is increased. An investigation of propagating uncertainties shows that the wavefront measurement can be calibrated by estimating the pinhole effects and the polarizing properties with a precision of a few percent. Based on these studies, Rpin should be smaller than half of the Airy disk for better performance.

Measurement of complex amplitude with a point-diffraction interferometer.

We propose a pupil-plane wavefront sensor to measure instantaneous phase and amplitude aberrations, developing the configuration of the point-diffraction interferometer proposed by Imada et al. [Appl. Opt. (2015), accepted]. The previous configuration allows us to instantaneously acquire four phase-shifted interferograms, from which cosine and sine functions of the relative phase difference between the test and reference beams can be derived. Here, because the wavefront phase can be reconstructed from only its sine function when the aberration of the input beam is smaller than half that of the sensing wavelength, we directly measure the intensities of the test and the reference beams instead of two of the four interferograms. Using this proposed configuration enables reconstruction of not only the wavefront phase but also its amplitude. The conceptual design of the proposed sensor is described, and its performance is evaluated compared with the original point-diffraction interferometer through numerical simulations.

The feasibility of halfcycle reconstruction in high heart rates in coronary CT angiography using 320-row CT.

Our aim was to investigate when halfcycle reconstruction (HCR) was feasible in patients who were predicted to have a heart rate over 65 bpm in coronary CT angiography (CTA) using 320-row CT. Seventy-four patients who underwent multiple heart beat scanning were included. The time to reach 230 HU at the ascending aorta during the bolus tracking scan was recorded (T230). HCR image and multicycle reconstruction (MCR) image were reconstructed for each patient. Image quality for each coronary segment was rated on a 3-point scale (3: good, 1: poor). For each patient, we determined that a single beat acquisition was feasible for diagnosis (HCR group) when the number of segments graded score 1 in the HCR image was the same or less than that in the MCR image. Otherwise, we included the patients in the MCR group. HCR group and MCR group included 38 and 36 patients, respectively. Regression analysis showed that body height >1.66 m (odds ratio (OR), 5.74; CI 1.59-25.6; p < 0.007), T230 >16 s (OR 3.11; CI 1.07-9.58; p = 0.04), and heart rate ≤72 bpm (OR 3.18; CI 1.11-9.49; p = 0.03) were related with the HCR group. When all three criteria were fulfilled, the calculated probability that MCR would improve image quality was only 7 %. When the heart rate is ≤72 bpm, single heart beat acquisition is feasible for patients with body height >1.66 m and T230 > 16 s in coronary CTA using 320-row CT.