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Reconstructing past changes in global sea level under different climate forcings provides vitalinformation about the evolution, dynamics, and sensitivity of Earth’s climate system, such astimescales of ice-mass loss in relation to radiative forcing and naturally precedented rates ofsea-level rise. Quantifying these processes requires well-resolved sea-level/ice-volumerecords with good age control and temporal continuity over different climate states.Global sea-level changes are well-constrained since the last glacial maximum byradiometrically-dated corals and paleoshoreline data, and fairly well-constrained over the lastglacial cycle. There are relatively few such records for time intervals before the last glacialcycle, however, and among these there are some significant deviations. Two of theserecords rely on the 'marginal basin’ method, which exploits the strong sensitivity ofseawater δ18O in the Mediterranean and Red Sea to sea-level changes in the relativelynarrow and shallow straits which connect the basins with the open ocean. Here, wepresent a new 'Med-Red sea-level stack’ spanning the last 500 ky, which improves onprevious Mediterranean and Red Sea sea-level reconstructions. It includes new andmore highly resolved component sea-level records, and new probabilistic analysesthat reduce uncertainties by accounting for stratigraphy in the component records. [ABSTRACT FROM AUTHOR]

Global ice volume (sea level) and deep‐sea temperature are key measures of Earth's climatic state. We synthesize evidence for multi‐centennial to millennial ice‐volume and deep‐sea temperature variations over the past 40 million years, which encompass the early glaciation of Antarctica at ∼34 million years ago (Ma), the end of the Middle Miocene Climate Optimum, and the descent into bipolar glaciation from ∼3.4 Ma. We compare different sea‐level and deep‐water temperature reconstructions to build a resource for validating long‐term numerical model‐based approaches. We present: (a) a new template synthesis of ice‐volume and deep‐sea temperature variations for the past 5.3 million years; (b) an extended template for the interval between 5.3 and 40 Ma; and (c) a discussion of uncertainties and limitations. We highlight key issues associated with glacial state changes in the geological record from 40 Ma to present that require attention in further research. These include offsets between calibration‐sensitive versus thermodynamically guided deep‐sea paleothermometry proxy measurements; a conundrum related to the magnitudes of sea‐level and deep‐sea temperature change at the Eocene‐Oligocene transition at 34 Ma; a discrepancy in deep‐sea temperature levels during the Middle Miocene; and a hitherto unquantified non‐linear reduction of glacial deep‐sea temperatures through the past 3.4 million years toward a near‐freezing deep‐sea temperature asymptote, while sea level stepped down in a more uniform manner. Uncertainties in proxy‐based reconstructions hinder further distinction of "reality" among reconstructions. It seems more promising to further narrow this using three‐dimensional ice‐sheet models with realistic ice‐climate‐ocean‐topography‐lithosphere coupling, as computational capacities improve. Plain Language Summary: Global ice volume (hence, sea level) and deep‐sea temperature are important measures of Earth's climatic state. To better understand Earth's climate cycles in response to its orbitally driven insolation cycles, we evaluate and synthesize evidence for ice‐volume (sea‐level) and deep‐sea temperature variations at multi‐centennial to millennial resolution throughout the last 40 million years. These last 40 million years encompass the major build‐up of Antarctic glaciation from about 34 million years ago, and development of extensive Northern Hemisphere ice sheets from about 3.4 million years ago. We present a new template synthesis of ice‐volume (sea‐level) and deep‐sea temperature for the past 5.3 million years, with extension through the interval between 5.3 and 40 Ma with wider uncertainties. We also highlight a number of remaining questions about major climate transitions, including the early glaciation history of Antarctica, the end of the so‐called Middle Miocene Climate Optimum from about ∼14.5 Ma, and the descent over the past several million years into conditions with extensive ice‐age maxima in both hemispheres. Key Points: New synthesis of sea level and deep‐sea temperature over 40 million years, at millennial resolution, across seven different methodsDiscrepancies between Eocene‐Oligocene and Middle Miocene sea‐level reconstructions are highlighted for focussed future researchPlio‐Pleistocene glacial deep‐sea temperature asymptoted to a freezing limit by ∼1.25–0.9 Ma; glacial sea‐level minima decreased ∼linearly [ABSTRACT FROM AUTHOR]

Objectives: To investigate the diagnostic accuracy of a modified three-material decomposition calcium subtraction (CS) algorithm for the detection of arterial stenosis in dual-energy CT angiography (DE-CTA) of the lower extremity runoff compared to standard image reconstruction, using digital subtraction angiography (DSA) as the reference standard.Methods: Eighty-eight patients (53 males; mean age, 65.9 ± 11 years) with suspected peripheral arterial disease (PAD) who had undergone a DE-CTA examination of the lower extremity runoff between May 2014 and May 2015 were included in this IRB-approved, HIPAA-compliant retrospective study. Standard linearly blended and CS images were reconstructed and vascular contrast-to-noise ratios (CNR) were calculated. Two independent observers assessed subjective image quality using a 5-point Likert scale. Diagnostic accuracy for ≥ 50% stenosis detection was analyzed in a subgroup of 45 patients who had undergone additional DSA. Diagnostic accuracy parameters were estimated with a random-effects logistic regression analysis and compared using generalized estimating equations.Results: CS datasets showed higher CNR (15.3 ± 7.3) compared to standard reconstructions (13.5 ± 6.5, p < 0.001). Both reconstructions showed comparable qualitative image quality scores (CS, 4.64; standard, 4.57; p = 0.220). Diagnostic accuracy (sensitivity, specificity, positive and negative predictive values) for CS reconstructions was 96.5% (97.5%, 95.6%, 90.9%, 98.1) and 93.1% (98.8%, 90.4%, 82.3%, 99.1%) for standard images.Conclusions: A modified three-material decomposition CS algorithm provides increased vascular CNR, equivalent qualitative image quality, and greater diagnostic accuracy for the detection of significant arterial stenosis of the lower extremity runoff on DE-CTA compared with standard image reconstruction.Key Points: • Calcified plaques may lead to overestimation of stenosis severity and false positive results, requiring additional invasive digital subtraction angiography (DSA). • A modified three-material decomposition algorithm for calcium subtraction provides greater diagnostic accuracy for the detection of significant arterial stenosis of the lower extremity runoff compared with standard image reconstruction. • The application of this algorithm in patients with heavily calcified vessels may be helpful to potentially reduce inconclusive CT angiography examinations and the need for subsequent invasive DSA. [ABSTRACT FROM AUTHOR]

Carbon releases into the climate system produce global warming and ocean acidification events that can be reversed eventually by carbon sequestration. However, the underlying controls on the timescales of carbon removal, and their dependence on the amplitude of the initial perturbation, are poorly understood. Here, we assess a series of late Paleocene-early Eocene (LPEE) carbon cycle perturbations (∼56-52 Ma) of different amplitudes to constrain carbon removal timescales. Carbon isotope excursions (CIEs) and sedimentation patterns for the largest event, the Paleocene-Eocene Thermal Maximum (PETM), allow identification of a light carbon injection that appeared ∼85 kyr after the PETM onset. This CIE may have been triggered by orbital forcing of long (∼400 kyr) and short (∼100 kyr) eccentricity maxima. The various LPEE light carbon injections were followed by exponential carbon removal trends with half-life (t 1 / 2) estimates of ∼6-26 kyr. These values are smaller than background estimates for the modern carbon cycle (t 1 / 2 > 100 kyr), which reveals accelerated light carbon sequestration. We find that one estimated t 1 / 2 period coincided temporally with ocean acidification recovery in different locations with contrasting paleo-water depths. This pattern indicates enhanced chemical weathering following LPEE CIEs; however, chemical weathering timescales are an order of magnitude longer than the observed t 1 / 2 estimates. This reveals that several carbon processes were optimized during LPEE CIE recovery. Similar t 1 / 2 estimates are obtained for light carbon injections of different sizes, which suggests that carbon removal was optimized to conditions induced by the initial perturbation. Temperature controls on oxygen solubility may have accelerated the oceanic biological pump in proportion to each LPEE carbon injection. This process may have caused accelerated carbon sequestration during LPEE CIE recovery and produced the short carbon removal timescales identified by t 1 / 2 estimates of LPEE carbon cycle perturbations. • Carbon removal was accelerated after late Paleocene-early Eocene carbon releases. • Accelerated carbon sequestration depended on the carbon injection magnitude. • Temperature increases may have optimized carbon sequestration. • The Paleocene-Eocene Thermal Maximum had two orbitally controlled carbon releases. [ABSTRACT FROM AUTHOR]

Paleocene-Eocene sedimentary archives record a series of global warming events called hyperthermals. These events occurred across a long-term increasing temperature trend and were associated with light carbon injections that produced carbon isotope excursions (CIEs). Early Eocene hyperthermals occurred close to both long (∼405 kyr) and short (∼100 kyr) eccentricity maxima. It has been proposed that under long-term global warming, orbital forcing of climate crossed a thermodynamic threshold that destabilized carbon reservoirs and produced Early Eocene hyperthermals. However, orbital control on triggering of the largest hyperthermal, the Paleocene-Eocene Thermal Maximum (PETM), remains unclear. Identification of the precise orbital phasing of the PETM has been hindered by extensive calcium carbonate (CaCO 3) dissolution, which introduces uncertainty into PETM age models. Here, we report orbital signatures in marine sediments from Contessa Road (Italy), a western Tethyan section with reduced PETM CaCO 3 dissolution compared to other deep ocean sites. Orbitally controlled lysocline depth adjustments and orbital phasing of the PETM CIE onset close to both long and short eccentricity maxima are documented here. Precession-based age models from the well-resolved PETM section of Ocean Drilling Program (ODP) Site 1262 (South Atlantic) confirm these results and reveal that the PETM CIE onset was partially triggered by an orbitally controlled mechanism. Climate processes associated with orbital forcing of both long and short eccentricity maxima played an important role in triggering the carbon cycle perturbations of all Paleocene-Eocene CIE events. • Orbital controls influenced Paleocene-Eocene Thermal Maximum triggering. • The Paleocene-Eocene Thermal Maximum appeared close to a long eccentricity maximum. • The Paleocene-Eocene Thermal Maximum appeared close to a short eccentricity maximum. • The Paleocene-Eocene Thermal Maximum contained multiple lysocline shoaling events. [ABSTRACT FROM AUTHOR]

Kawasaki disease (KD) is the leading cause of acquired coronary disease in children and may lead to subsequent myocardial ischemia and infarction. Because coronary computed tomographic angiography (CTA) is the most sensitive noninvasive test in patients with atherosclerosis, the aim of this study was to retrospectively evaluate coronary CTA performed in patients with KD for aneurysm, stenosis, and calcified and noncalcified coronary artery disease (CAD). Clinical histories and prior stress and imaging test results were reviewed. Thirty-two patients underwent coronary CTA for KD, and 385 coronary segments were evaluated. Twenty-three of 32 patients had ≥1 diseased coronary segment. There were 20 aneurysms, 7 lesions, and 75 segments (20%) with nonobstructive CAD (16% noncalcified, 2% calcified, and 2% mixed). All nonobstructive and obstructive CAD was in patients with histories of acute-phase coronary artery dilatation or aneurysm (echocardiographic z score 4 to 44), and were almost always associated with normal stress imaging test results on followup. No lesion or CAD was found in coronary computed tomographic angiographic studies performed in a control group referred for other indications (n = 32,422 segments evaluated). The median coronary computed tomographic angiographic dose-length product was 59 mGy cm (interquartile range 32 to 131), the median unadjusted radiation dose was 0.8 mSv (interquartile range 0.4 to 1.8), and the median age- and size-adjusted radiation dose was 1.3 mSv (interquartile range 0.7 to 2.3). In conclusion, high-risk patients with histories of KD had nonobstructive and obstructive CAD not visualized by other noninvasive imaging tests. In properly selected high-risk patients with KD, coronary CTA may identify a subset at increased risk for future coronary pathology who may benefit from medical therapy. [ABSTRACT FROM AUTHOR]

The island of Santorini in the Aegean Sea is one of the world's most violent active volcanoes. Santorini has produced numerous highly explosive eruptions over at least the past ∼360 kyrs that are documented by the island's unique proximal tephra record. However, the lack of precise eruption ages and comprehensive glass geochemical datasets for proximal tephras has long hindered the development of a detailed distal tephrostratigraphy for Santorini eruptions. In light of these requirements, this study develops a distal tephrostratigraphy for Santorini covering the past ∼360 kyrs, which represents a major step forward towards the establishment of a tephrostratigraphic framework for the Eastern Mediterranean region. We present new EPMA glass geochemical data of proximal tephra deposits from twelve Plinian and numerous Inter-Plinian Santorini eruptions and use this dataset to establish assignments of 28 distal marine tephras from three Aegean Sea cores (KL49, KL51 and LC21) to specific volcanic events. Based on interpolation of sapropel core chronologies we provide new eruption age estimates for correlated Santorini tephras, including dates for major Plinian eruptions, Upper Scoriae 1 (80.8 ± 2.9 ka), Vourvoulos (126.5 ± 2.9 ka), Middle Pumice (141.0 ± 2.6 ka), Cape Thera (156.9 ± 2.3 ka), Lower Pumice 2 (176.7 ± 0.6 ka), Lower Pumice 1 (185.7 ± 0.7 ka), and Cape Therma 3 (200.2 ± 0.9 ka), but also for 17 Inter-Plinian events. Older Plinian and Inter-Plinian activity between ∼310 ka and 370 ka, documented in the distal terrestrial setting of Tenaghi Philippon (NE Greece), is independently dated by palynostratigraphy and complements the distal Santorini tephrostratigraphic record. [ABSTRACT FROM AUTHOR]

Extreme global warming can produce hydroclimate changes that remain poorly understood for sub-tropical latitudes. Late Palaeocene-early Eocene (LPEE; ~58-52 Ma) proto-Mediterranean zones of the western Tethys offer opportunities to assess hydroclimate responses to massive carbon cycle perturbations. Here, we reconstruct LPEE hydroclimate conditions of these regions and find that carbon cycle perturbations exerted controls on orbitally forced hydroclimate variability. Long-term (~6 Myr) carbon cycle changes induced a gradual precipitation/moisture reduction, which was exacerbated by some short-lived (<200 kyr) carbon cycle perturbations that caused rapid warming and exceptionally dry conditions in western Tethyan continental areas. Hydroclimate recovery following the greatest short-lived global warming events took ~24-27 kyr. These observations support the notion that anthropogenically driven warming can cause widespread aridification with impacts that may last tens of thousands of years., (© 2024. The Author(s).)

Antarctic climate warming and atmospheric CO 2 rise during the last deglaciation may be attributed in part to sea ice reduction in the Southern Ocean. Yet, glacial-interglacial Antarctic sea ice dynamics and underlying mechanisms are poorly constrained, as robust sea ice proxy evidence is sparse. Here, we present a molecular biomarker-based sea ice record that resolves the spring/summer sea ice variability off East Antarctica during the past 40 thousand years (ka). Our results indicate that substantial sea ice reduction culminated rapidly and contemporaneously with upwelling of carbon-enriched waters in the Southern Ocean at the onset of the last deglaciation but began at least ~2 ka earlier probably driven by an increasing local integrated summer insolation. Our findings suggest that sea ice reduction and associated feedbacks facilitated stratification breakup and outgassing of CO 2 in the Southern Ocean and warming in Antarctica but may also have played a leading role in initializing these deglacial processes in the Southern Hemisphere.

The last interglacial (LIG; ~130 to ~118 thousand years ago, ka) was the last time global sea level rose well above the present level. Greenland Ice Sheet (GrIS) contributions were insufficient to explain the highstand, so that substantial Antarctic Ice Sheet (AIS) reduction is implied. However, the nature and drivers of GrIS and AIS reductions remain enigmatic, even though they may be critical for understanding future sea-level rise. Here we complement existing records with new data, and reveal that the LIG contained an AIS-derived highstand from ~129.5 to ~125 ka, a lowstand centred on 125-124 ka, and joint AIS + GrIS contributions from ~123.5 to ~118 ka. Moreover, a dual substructure within the first highstand suggests temporal variability in the AIS contributions. Implied rates of sea-level rise are high (up to several meters per century; m c -1 ), and lend credibility to high rates inferred by ice modelling under certain ice-shelf instability parameterisations.

Objectives: The aim of this study was to evaluate a prototype dual-energy computed tomography calcium subtraction algorithm and its impact on luminal visualization in patients with heavily calcified coronary arteries., Materials and Methods: Twenty-nine patients (62% male; mean age, 64 ± 7 years) who had undergone dual-energy coronary computed tomography angiography were retrospectively included in this institutional review board-approved, Health Insurance Portability and Accountability Act-compliant study. Linearly blended (M&#95;0.6) and calcium-subtracted images were reconstructed. Two independent observers assessed luminal visualization of the coronary arteries in a segment-based analysis, subjective image quality, and diagnostic confidence using 5-point Likert scales. Contrast-to-noise ratios for both data sets were calculated. Wilcoxon testing and Cohen's κ were used for statistical comparisons., Results: Calcium-subtracted image series showed improved lumen visualization of the coronary arteries (P = 0.008), with excellent interreader agreement (mean score, 3.3; κ = 0.82), compared with M&#95;0.6 series (mean score, 2.9; κ = 0.77). The calcium subtraction algorithm improved diagnostic confidence compared with the M&#95;0.6 reconstructions (mean scores, 4.0 and 3.1, respectively; all P ≤ 0.002). The image quality analysis showed no significant differences between calcium-subtracted and M&#95;0.6 data sets (subjectively: mean scores, 4.1 and 4.2, respectively, P = 0.442; objectively: mean contrast-to-noise ratio, 37.0 and 38.2, respectively, P = 0.733)., Conclusions: A prototype algorithm for calcium subtraction improves coronary lumen visualization and diagnostic confidence in patients with heavy coronary calcifications without differences in conventional subjective and objective measures of image quality.

Background: The use of cardiac computed tomography (CT) for quantification of ventricular function is limited by relatively high radiation dose., Objectives: The goal of this study was to describe the radiation exposure and image quality of 70 kVp functional cardiac CT in patients with congenital heart disease (CHD)., Methods: A retrospective review of 70 kVp ECG gated functional CT scans using tube current modulation was performed in CHD patients at a single institution. Quantitative and qualitative (assessed by myocardial segment, 1-4; 1 = optimal) image quality was determined. Per segment image quality was compared between thin (1.5 mm) and thick (8 mm) reconstructions and by patient age and size. Scan DLP was used to estimate radiation dose., Results: 72 scans were performed during the time of review (7/2013-6/2015). Median patient age was 19.5 years (8.0, 27.1) and BMI was 20.1 (16.6, 24.5) kg/m(2). Median functional scan DLP was 78.8 (45.5, 98) and unadjusted and adjusted procedural mSv were 1.10 (0.64, 1.37) and 1.13 (0.90, 1.37). Image quality of 1 was achieved in all myocardial segments in >75% of scans. Patients with a weight ≥75 kg were more likely to have a scan achieve optimal image when using thick reconstructions compared to thin (81.3% vs. 43.8%; p = 0.028)., Conclusions: Imaging of ventricular function with 70 kVp in CHD patients can be done with low radiation doses and provides diagnostic image quality, particularly for patients <75 kg. In larger patients, thicker slice reconstruction improved image quality., (Copyright © 2016 Society of Cardiovascular Computed Tomography. Published by Elsevier Inc. All rights reserved.)

Objective: The objective of our study was to show the feasibility of distinguishing between uric acid (UA) and non-UA renal stones using two consecutive spatially registered low- and high-energy scans acquired on a conventional CT system., Subjects and Methods: A total of 33 patients undergoing clinically indicated dual-source dual-energy CT examinations to differentiate UA from non-UA renal stones were enrolled in this study. Immediately after patients underwent clinically indicated dual-source dual-energy CT, two consecutive scans (one at 80 kV and one at 140 kV) were obtained on a conventional CT scanner over the region limited to the stones identified on the dual-source scans. After 3D deformable registration of the 80- and 140-kV images, UA and non-UA stones were identified using commercial software. The sensitivity, specificity, and accuracy of stone classification were calculated using the dual-source results as the reference standard., Results: A total of 469 stones were identified in the dual-source examinations (26 UA and 443 non-UA stones). The average in-plane stone diameter was 4.4 ± 2.5 (SD) mm (range, 2.0-18.9 mm). The overall sensitivity, specificity, and accuracy for identifying UA stones were 73.1%, 90.1%, and 89.1%, respectively. The sensitivity, specificity, and accuracy were 94.7%, 96.9%, and 96.8% for stones 3 mm or larger (n = 341 [19 UA and 322 non-UA])., Conclusion: Accurate differentiation of UA from non-UA renal stones is feasible using two consecutively acquired and spatially registered conventional CT scans.

Objective: The objective of our study was to evaluate the accuracy of subtraction color-map images created from contrast-enhanced CT (CECT) and unenhanced CT for the diagnosis of pancreatic necrosis in the early stage of acute pancreatitis., Materials and Methods: Forty-eight patients underwent unenhanced CT and CECT within 72 hours from the onset of acute pancreatitis. Subtraction color-map images were created from unenhanced CT and CECT using a 3D nonrigid registration method. Three radiologists reviewed two image sets: CECT alone and subtraction color-map images in conjunction with CECT. Readers evaluated each image set for the presence of pancreatic necrosis. The reference standard for pancreatic necrosis was CT or MRI 1 week or more after the onset of acute pancreatitis. The performance of each image set for the prediction of pancreatic necrosis was calculated and compared using the McNemar test., Results: Eleven of the 48 patients developed pancreatic necrosis. There were no technical failures creating the subtraction images. The sensitivity, specificity, and accuracy for predicting pancreatic necrosis with CECT were 64%, 97%, and 90%, respectively, for reader 1; 73%, 87%, and 83% for reader 2; and 73%, 87%, and 83% for reader 3. The sensitivity, specificity, and accuracy for predicting pancreatic necrosis with the subtraction color maps were 100%, 100%, and 100%, respectively, for reader 1; 100%, 95%, and 96% for reader 2; and 82%, 92%, and 90% for reader 3. Accuracy significantly improved with the addition of subtraction color maps compared with CECT alone for reader 1 (p = 0.03) and reader 2 (p = 0.02) but not for reader 3 (p = 0.37)., Conclusion: A subtraction color map is accurate in the diagnosis of pancreatic necrosis in the early stage of acute pancreatitis.

Objective: The objective of our study was to evaluate in phantoms the differences in CT image noise and artifact level between two types of commercial CT detectors: one with distributed electronics (conventional) and one with integrated electronics intended to decrease system electronic noise., Materials and Methods: Cylindric water phantoms of 20, 30, and 40 cm in diameter were scanned using two CT scanners, one equipped with integrated detector electronics and one with distributed detector electronics. All other scanning parameters were identical. Scans were acquired at four tube potentials and 10 tube currents. Semianthropomorphic phantoms were scanned to mimic the shoulder and abdominal regions. Images of two patients were also selected to show the clinical values of the integrated detector., Results: Reduction of image noise with the integrated detector depended on phantom size, tube potential, and tube current. Scans that had low detected signal had the greatest reductions in noise, up to 40% for a 30-cm phantom scanned using 80 kV. This noise reduction translated into up to 50% in dose reduction to achieve equivalent image noise. Streak artifacts through regions of high attenuation were reduced by up to 45% on scans obtained using the integrated detector. Patient images also showed superior image quality for the integrated detector., Conclusion: For the same applied radiation level, the use of integrated electronics in a CT detector showed a substantially reduced level of electronic noise, resulting in reductions in image noise and artifacts, compared with detectors having distributed electronics.

Objective: The purpose of this study is to assess the ability of a novel automatic tube potential selection tool to reduce radiation dose while maintaining diagnostic quality in CT angiography (CTA) and contrast-enhanced abdominopelvic CT., Materials and Methods: One hundred one CTA examinations and 90 contrastenhanced abdominopelvic examinations were performed using an automatic tube potential selection tool on a 128-MDCT scanner. Two vascular radiologists and two abdominal radiologists evaluated the image quality for sharpness, noise, artifact, and diagnostic confidence. In a subset of patients who had undergone prior studies (CTA, 28 patients; abdominopelvic CT, 25 patients), a side-by-side comparison was performed by a separate radiologist. Dose reduction and iodine contrast-to-noise ratio resulting from use of the tool were calculated., Results: For CTA, 80 or 100 kV was selected for 73% of the scans, with a mean dose reduction of 36% relative to the reference 120-kV protocol. For abdominopelvic CT examinations, 80 or 100 kV was used for 55% of the scans, with a mean dose reduction of 25%. Overall dose reduction relative to the reference 120-kV protocol was 25% and 13% for CTA and abdominopelvic CT scans, respectively. Over 98% of scans had acceptable sharpness, noise texture, artifact, and diagnostic confidence for both readers and diagnostic tasks; 94-100% of scans had acceptable noise. Iodine contrast-to-noise ratio was significantly higher than (p < 0.001) or similar to (p = 0.11) that of prior scans, and equivalent quality was achieved despite the dose reduction., Conclusion: Automatic tube potential selection provides an efficient and quantitativeway to guide the selection of the optimal tube potential for CTA and abdominopelvic CT examinations.

Objective: The purpose of this study was to determine whether the use of an automated CT kilovoltage (kV) selection tool (Auto kV) can result in lower radiation dose without sacrificing image quality in contrast-enhanced abdominopelvic CT., Materials and Methods: Tube potential, radiation dose, and iodine contrast-to-noise ratio (CNR) were retrospectively evaluated in 36 patients who underwent abdominopelvic CT with Auto kV, and compared with results from size-matched control patients using identical protocols. Two radiologists evaluated image quality (sharpness, noise, and diagnostic confidence) blinded to kV. Volume CT dose index (CTDI(vol)) was also compared with what each patient would have received from scanning at 120 kV., Results: Mean (SD) CTDI(vol) was 16.0 (4.4) mGy after Auto kV versus 19.5 (4.0) mGy using standard 120-kV prescription and was 19.3 (6.0) mGy in control subjects (yielding dose reductions of 18.0% and 17.2%, respectively; p < 0.001 for both). Thirty of 36 patients were scanned at 100 kV (median dose reduction, 25%). Auto kV images were rated as very sharp in 33 (92%) and 36 (100%) cases versus 36 (100%) and 35 (97%) of the control cases, with all cases scored as having optimal noise. Readers had full diagnostic confidence in 34 (94%) and 36 (100%) of Auto kV cases; one reader scored "probably confident" in two cases (6%). Iodine CNRs for the aorta, liver, and portal vein were similar between Auto kV cases and control cases (p > 0.50, all comparisons)., Conclusion: The use of an automated kV selection tool results in significant dose savings while maintaining diagnostic image quality and iodine CNR.

Objective: The purpose of this study was to evaluate in phantoms the dose reduction to anterior surfaces and image quality with organ-based tube-current modulation in head and thoracic CT., Materials and Methods: Organ-based tube-current modulation is designed to reduce radiation dose to superficial radiosensitive organs, such as the lens of the eye, thyroid, and breast, by decreasing the tube current when the tube passes closest to these organs. Dose and image quality were evaluated in phantoms for clinical head and thorax examination protocols with and without organ-based tube-current modulation. Surface dose reduction as a function of position was measured using a 32-cm CT dose index (CTDI) phantom, an anthropomorphic adult phantom, and ion chambers. Surface dose reduction as a function of patient size was investigated using three semianthropomorphic phantoms with posteroanterior dimensions of 14, 25, and 31 cm. Image noise (the SD of CT numbers in regions of interest) was evaluated for the anthropomorphic and the semianthropomorphic phantoms., Results: For equivalent scanner output (volume CTDI), the dose to the midline of the anterior surface was reduced by 27-50%, depending on the anatomic region (head or thorax) and phantom size, and the dose to the posterior surface was correspondingly increased. Image noise was not significantly different between scans with and without organ-based tube-current modulation (p = 0.85)., Conclusion: Organ-based tube-current modulation can reduce the dose to the anterior surface of patients without increasing image noise by commensurately increasing the dose to the posterior surface. This technique can reduce the dose to anterior radiosensitive organs for head and thoracic CT scans.