Reconstruction of three-dimensional tomographic patient models for radiation dose modulation in CT from two scout views using deep learning.

BACKGROUND: A tomographic patient model is essential for radiation dose modulation in x-ray computed tomography (CT). Currently, two-view scout images (also known as topograms) are used to estimate patient models with relatively uniform attenuation coefficients. These patient models do not account for the detailed anatomical variations of human subjects, and thus, may limit the accuracy of intraview or organ-specific dose modulations in emerging CT technologies. PURPOSE: The purpose of this work was to show that 3D tomographic patient models can be generated from two-view scout images using deep learning strategies, and the reconstructed 3D patient models indeed enable accurate prescriptions of fluence-field modulated or organ-specific dose delivery in the subsequent CT scans. METHODS: CT images and the corresponding two-view scout images were retrospectively collected from 4214 individual CT exams. The collected data were curated for the training of a deep neural network architecture termed ScoutCT-NET to generate 3D tomographic attenuation models from two-view scout images. The trained network was validated using a cohort of 55 136 images from 212 individual patients. To evaluate the accuracy of the reconstructed 3D patient models, radiation delivery plans were generated using ScoutCT-NET 3D patient models and compared with plans prescribed based on true CT images (gold standard) for both fluence-field-modulated CT and organ-specific CT. Radiation dose distributions were estimated using Monte Carlo simulations and were quantitatively evaluated using the Gamma analysis method. Modulated dose profiles were compared against state-of-the-art tube current modulation schemes. Impacts of ScoutCT-NET patient model-based dose modulation schemes on universal-purpose CT acquisitions and organ-specific acquisitions were also compared in terms of overall image appearance, noise magnitude, and noise uniformity. RESULTS: The results demonstrate that (1) The end-to-end trained ScoutCT-NET can be used to generate 3D patient attenuation models and demonstrate empirical generalizability. (2) The 3D patient models can be used to accurately estimate the spatial distribution of radiation dose delivered by standard helical CTs prior to the actual CT acquisition; compared to the gold-standard dose distribution, 95.0% of the voxels in the ScoutCT-NET based dose maps have acceptable gamma values for 5 mm distance-to-agreement and 10% dose difference. (3) The 3D patient models also enabled accurate prescription of fluence-field modulated CT to generate a more uniform noise distribution across the patient body compared to tube current-modulated CT. (4) ScoutCT-NET 3D patient models enabled accurate prescription of organ-specific CT to boost image quality for a given body region-of-interest under a given radiation dose constraint. CONCLUSION: 3D tomographic attenuation models generated by ScoutCT-NET from two-view scout images can be used to prescribe fluence-field-modulated or organ-specific CT scans with high accuracy for the overall objective of radiation dose reduction or image quality improvement for a given imaging task.

Consistency of Renal Stone Volume Measurements Across CT Scanner Model and Reconstruction Algorithm Configurations.

OBJECTIVE: The objective of this prospective study is to evaluate the consistency of renal stone volume estimation using dual-energy CT across scanner model and reconstruction algorithm configurations. SUBJECTS AND METHODS: Patients underwent scanning with routine kidney stone composition protocols on both second- and third-generation dual-source CT scanners. Images were reconstructed using filtered back projection and iterative reconstruction (IR). In addition, a modified IR kernel on the third-generation CT scanner was evaluated. Individual kidney stone volumes were determined and compared. RESULTS: No significant difference was noted in measured volumes between filtered back-projection data, IR data from the second-generation scanner, and the modified IR kernel data (p > 0.05). The third-generation commercially available IR kernel yielded lower volumes than did the other configurations (p < 0.0001). CONCLUSION: With the use of a modified kernel for the third-generation scanner, patients being monitored for changes in kidney stone volume can undergo scanning performed with second- or third-generation dual-energy CT scanners, and the images obtained can be reconstructed with either filtered back projection or IR without the introduction of bias into kidney stone volume measurements.

Utilizing bi-spectral index (BIS) for the monitoring of sedated adult ICU patients: a systematic review.

BACKGROUND: The ideal level of sedation in the ICU is an ongoing source of scrutiny. At higher levels of sedation, the current scoring systems are not ideal. BIS may be able to improve both. We evaluated literature on effectiveness of BIS monitoring in sedated mechanically ventilated (MV) ICU patients compared to clinical sedation scores (CSS). METHODS: For this systematic review, full text articles were searched in OVID, MEDLINE, EMBASE, and Cochrane databases from 1986 - 2014. Additional studies were identified searching bibliographies/abstracts from national/international Critical Care Medicine conferences and references from searched articles retrieved. Search terms were: 'Clinical sedation scale, Bi-spectral Index, Mechanical ventilation, Intensive care Unit'. Included were prospective, randomized and non-randomized studies comparing BIS monitoring with any CSS in MV adult (>18 yr old) ICU patients. Studies were graded for quality of evidence based on bias as established by the GRADE guidelines. Additional sources of bias were examined. RESULTS: There were five studies which met inclusion criteria. All five studies were either unclear or high risk for blinding of participants and blinding of outcome assessment. All papers had at least one source of additional high risk, or unclear/unstated. CONCLUSIONS: BIS monitoring in the mechanically ventilated ICU patient may decrease sedative drug dose, recall, and time to wake-up. The studies suggesting this are severely limited methodologically. BIS, when compared to subjective CSSs, is not, at this time, clearly indicated. An appropriately powered randomized, controlled study is needed to determine if this monitoring modality is of use on the ICU.

Quantitative Prediction of Stone Fragility From Routine Dual Energy CT: Ex vivo proof of Feasibility.

RATIONALE AND OBJECTIVES: Previous studies have demonstrated a qualitative relationship between stone fragility and internal stone morphology. The goal of this study was to quantify morphologic features from dual-energy computed tomography (CT) images and assess their relationship to stone fragility. MATERIALS AND METHODS: Thirty-three calcified urinary stones were scanned with micro-CT. Next, they were placed within torso-shaped water phantoms and scanned with the dual-energy CT stone composition protocol in routine use at our institution. Mixed low- and high-energy images were used to measure volume, surface roughness, and 12 metrics describing internal morphology for each stone. The ratios of low- to high-energy CT numbers were also measured. Subsequent to imaging, stone fragility was measured by disintegrating each stone in a controlled ex vivo experiment using an ultrasonic lithotripter and recording the time to comminution. A multivariable linear regression model was developed to predict time to comminution. RESULTS: The average stone volume was 300 mm3 (range: 134-674 mm3). The average comminution time measured ex vivo was 32 seconds (range: 7-115 seconds). Stone volume, dual-energy CT number ratio, and surface roughness were found to have the best combined predictive ability to estimate comminution time (adjusted R2 = 0.58). The predictive ability of mixed dual-energy CT images, without use of the dual-energy CT number ratio, to estimate comminution time was slightly inferior, with an adjusted R2 of 0.54. CONCLUSIONS: Dual-energy CT number ratios, volume, and morphologic metrics may provide a method for predicting stone fragility, as measured by time to comminution from ultrasonic lithotripsy.

Two-color-absorption sensor for time-resolved measurements of gasoline concentration and temperature.

A midinfrared absorption sensor for crank-angle-resolved in-cylinder measurements of gasoline concentration and gas temperature for spark-ignition internal-combustion engines is reported, and design considerations and validation testing in the controlled environments of a heated cell and shock-heated gases are discussed. Mid-IR laser light was tuned to transitions in the strong absorption bands associated with C-H stretching vibration near 3.4 microm, and time-resolved fuel vapor concentration and gas temperature were determined simultaneously from the absorption at two different wavelengths. These two infrared laser wavelengths were simultaneously produced by difference-frequency generation, which combines a near-IR signal laser with two near-IR pump lasers in a periodically poled lithium niobate crystal. Injection current modulation of the pump lasers produced intensity modulation of the mid-IR, which allowed the transmitted signals from the two laser wavelengths to be detected on a single detector and separated by frequency demultiplexing. Injection current modulation produced a wavelength modulation synchronous with the intensity modulation for each of the laser wavelengths, and accurate measurement of the gasoline absorption signal required the effects of wavelength modulation to be considered. Validation experiments were conducted for a single-component hydrocarbon fuel (2,2,4-trimethyl-pentane, commonly known as iso-octane) and a gasoline blend in a heated static cell (300 < or = T < or = 600 K) and behind planar shock waves (600 < T < 1100 K) in a shock tube. With a bandwidth of 10 kHz, the measured fuel concentrations agreed within 5% RMS and the measured temperature agreed within 3% RMS to the known values. The 10 kHz bandwidth is sufficient to resolve 1 crank-angle degree at 1600 RPM.