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At least 505 records · Page 28

Pain in percutaneous liver core-needle biopsy: a randomized trial comparing the intercostal and subcostal approaches

Purpose: Effective pain control during and after percutaneous core needle liver biopsy is important with regard to ethical considerations and patient comfort. In this randomized double-blind study, we compared post-biopsy pain in the patients undergoing liver core-needle biopsy using either subcostal or intercostal approaches. Methods: All patients referred for ultrasound-guided CNLB between July 2017 and January 2018 to our interventional radiology department were randomized into two groups. Biopsy was performed through intercostal approach in the first group and through subcostal approach in the second group. The intensity of pain 0, 2, and 4 h after the procedure was compared in two groups using a 100-mm visual analogue scale. All biopsies were performed without procedural IV sedation. If patients’ discomfort demanded administration of IV analgesics during or after the procedure, then the patients were excluded from the study. Results: In patients without routine procedural IV sedation, there was no significant difference in the pain level between the intercostal and subcostal groups immediately after the procedure (p = 0.055), but we found a significant difference in the pain level between the two groups 2 (7.5 mm, p = 0.001) and 4 (2 mm, p = 0.001) h after the procedure. Conclusion: The minimum amount of change in the VAS score that is considered clinically important is 13 mm on a 100-mm scale. Pain differences at 2 and 4 h in the two groups in this study were statistically but not clinically significant. Therefore, the authors suggest the use of subcostal route for ultrasound-guided liver biopsy whenever possible, but the results do not warrant the routine use of post-procedure analgesics in whom biopsy is performed via intercostal route.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Computed tomographic perfusion with 160-mm coverage: comparative analysis of hepatocellular carcinoma treated by two transarterial chemoembolization courses relative to magnetic resonance imaging findings

Purpose: The aim of this study was to assess hepatocellular carcinoma (HCC) response with CT perfusion parameters before and after two transarterial chemo embolization (TACE) courses compared with MRI, and to search for predictive factors of response. Methods: 37 lesions (19 patients) were included between October 2015 and September 2017, based on the Barcelona Clinic Liver Cancer guidelines. CT perfusion with 160-mm coverage and MRI were performed before and after the first TACE course, and after the second TACE course. Quantitative perfusion parameters were compared to the response assessed with MRI using mRECIST criteria, defining response groups: complete response (CR), partial response (PR), no response (NR), response (including CR and PR), no complete response (NCR, including PR and NR). Results: Pre-TACE blood flow (BF) and hepatic arterial blood flow (HABF) were significantly higher in lesions with post-TACE 1 CR than in those with NCR (BF: 118.8 vs. 76.3 mL/100 g/min, p = 0.0231; HABF: 76 vs. 44.2 mL/100 g/min, p = 0.0112). Pre-TACE time to peak (TTP) and mean transit time (MTT) were significantly lower in lesions with post-TACE 2 response than in those with NR (TTP: 31.5 vs. 46.1 s, p = 0.0313; MTT: 15.8 vs. 22.8 s, p = 0.0204). Post-TACE 1 and post-TACE 2 perfusion parameters did not exhibit any statistically significant differences relative to MRI response. Conclusion: Our study did not find, after a first TACE course, perfusion parameters associated with a response to a second TACE course. However, baseline perfusion parameters analysis could lead to better therapeutic management of HCC by targeting lesions likely to respond well to TACE courses.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Characterization of renal stone composition by using fast kilovoltage switching dual-energy computed tomography compared to laboratory stone analysis: a pilot study

Purpose: To prospectively examine the diagnostic performance of fast kilovoltage switching dual-energy computed tomography (DECT) in characterization of in vivo renal stone composition compared with postoperative stone analysis. Methods: Consecutive consenting patients scheduled for endoscopic kidney stone surgery in a tertiary referral hospital from June 2015 to January 2016 were enrolled. Patients were preoperatively scanned with single-source, fast kilovoltage switching DECT. Stone compositions were determined regarding the effective atomic number measurements. Results of the stone compositions from DECT were compared to postoperative infrared spectroscopy stone analysis as the standard reference. Results: For the 39 patients enrolled in the study, DECT was able to detect uric acid stone with sensitivity of 88.9% and specificity of 100%. There was 100% positive predictive value, 96.8% negative predictive value, and 97.4% accuracy. For non-contrast CT scan, sensitivity was 88.9%, specificity was 96.7%, positive predictive value was 88.9%, negative predictive value was 96.7%, and accuracy was 94.8%. Of the 39 samples examined, 21 (54%) were single composition, whereas 18 (46%) were combined. Single composition stones were correctly characterized by DECT in 100% (8/8) for uric acid. Whereas the result of uric acid stone containing stone discrimination in mixed composition was not so good with Z{sub eff} alone, iodine imaging can compensated this fault. Conclusions: DECT provides excellent accuracy in characterizing uric acid stone compositions. With the addition of iodine image, all of uric acid-containing stones can be determined by the DECT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Validation of SE-EPI-based T2 mapping for characterization of prostate cancer: a new method compared with the traditional CPMG method

Purpose: We aim to compare the results of spin echo–echo planar imaging (SE-EPI)-based T2 mapping with those of the conventional Carr–Purcell–Meiboom–Gill (CPMG) method and to investigate the potential validity of SE-EPI-T2 mapping for the characterization of prostate cancer (PCa). Methods: Our retrospective study included 42 PCa patients and 42 noncancer patients who underwent 3.0T MRI with b values ranging from 0 to 2000 s/mm{sup 2} and echo times (TEs) ranging from 32 to 100 ms before biopsies. Bland–Altman analysis was used to compare the agreement between the two methods. The correlations between CPMG-T2 values and SE-EPI-T2 values at different b values were determined by Spearman’s rho analysis or Pearson analysis. The Mann–Whitney U test and two-sample t tests were used to analyze the differences between the cancerous and noncancerous groups. Results: Substantial agreement regarding the measurements was observed between the two methods. The average correlation between the CPMG-T2 values and SE-EPI-T2 values was moderate and positive, and the best correlations were found at b = 200 s/mm{sup 2} in the noncancer group (r = 0.557, P = 0.000) and at b = 100 s/mm{sup 2} in the cancer group (r = 0.537, P = 0.000). In addition, statistically significant differences were found between the noncancer and cancer groups in T2 values and ADC values (diff TEs) (P = 0.000). Conclusions: Substantial agreement in the measurements was found between the SE-EPI method and CPMG method. SE-EPI-based T2 mapping has potential clinical value for the prostate and can be considered an alternative to the traditional CPMG-T2 mapping method.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Intraluminal Radioactive Stent Compared with Covered Stent Alone for the Treatment of Malignant Esophageal Stricture

Objective: This study was designed to compare the clinical effectiveness of intraluminal radioactive stent loaded with iodine-125 seeds implantation versus covered stent alone insertion in patients with malignant esophageal stricture. Methods: We studied two groups of patients with malignant esophageal stricture. Group A comprised 28 patients (19 men and 9 women) who underwent intraluminal radioactive stent loaded with iodine-125 seeds implantation and were followed prospectively. Group B comprised 30 patients (18 men and 12 women) who had previously received covered stent alone insertion; these patients were evaluated retrospectively. There was no crossover between the two groups during follow-up. Informed consent was obtained from each patient, and our institutional review board approved the study. The dysphagia score, overall survival rates, complication rates, and reintervention rates were compared in the two groups. Results: There were no significant differences between the two groups in terms of baseline characteristics. Stent placement was technically successful and well tolerated in all patients. The dysphagia score was improved in both groups after stent placement. The median survival was significantly longer in group A than in group B: 11 versus 4.9 months, respectively (P < 0.001). The complications of chest pain, esophageal reflux, and stent migration was more frequent in group B, but this difference did not reach statistical significance. There was no statistical difference in reintervention between two groups. Conclusions: Intraluminal radioactive stent loaded with iodine-125 seeds implantation was a feasible and practical management in treating malignant esophageal stricture and was superior to covered stent alone insertion, as measured by survival.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Microwave Ablation Compared with Radiofrequency Ablation for Breast Tissue in an Ex Vivo Bovine Udder Model

Purpose: To compare the effectiveness of microwave (MW) ablation with radiofrequency (RF) ablation for treating breast tissue in a nonperfused ex vivo model of healthy bovine udder tissue. Materials and Methods: MW ablations were performed at power outputs of 25W, 35W, and 45W using a 915-MHz frequency generator and a 2-cm active tip antenna. RF ablations were performed with a bipolar RF system with 2- and 3-cm active tip electrodes. Tissue temperatures were continuously monitored during ablation. Results: The mean short-axis diameters of the coagulation zones were 1.34 {+-} 0.14, 1.45 {+-} 0.13, and 1.74 {+-} 0.11 cm for MW ablation at outputs of 25W, 35W, and 45W. For RF ablation, the corresponding values were 1.16 {+-} 0.09 and 1.26 {+-} 0.14 cm with electrodes having 2- and 3-cm active tips, respectively. The mean coagulation volumes were 2.27 {+-} 0.65, 2.85 {+-} 0.72, and 4.45 {+-} 0.47 cm{sup 3} for MW ablation at outputs of 25W, 35W, and 45W and 1.18 {+-} 0.30 and 2.29 {+-} 0.55 cm{sup 3} got RF ablation with 2- and 3-cm electrodes, respectively. MW ablations at 35W and 45W achieved significantly longer short-axis diameters than RF ablations (P < 0.05). The highest tissue temperature was achieved with MW ablation at 45W (P < 0.05). On histological examination, the extent of the ablation zone in MW ablations was less affected by tissue heterogeneity than that in RF ablations. Conclusion: MW ablation appears to be advantageous with respect to the volume of ablation and the shape of the margin of necrosis compared with RF ablation in an ex vivo bovine udder.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Portal Vein Embolization before Right Hepatectomy: Improved Results Using n-Butyl-Cyanoacrylate Compared to Microparticles Plus Coils

Background: There is currently no consensus in the literature on which embolic agent induces the greatest degree of liver hypertrophy after portal vein embolization (PVE). Only experimental results in a pig model have demonstrated an advantage of n-butyl-cyanoacrylate (NBCA) over 3 other embolic materials (hydrophilic gel, small and large polyvinyl alcohol particles) for PVE. Therefore, the aim of this human study was to retrospectively compare the results of PVE using NBCA with those using spherical microparticles plus coils. Methods: A total of 34 patients underwent PVE using either NBCA (n = 20), or spherical microparticles plus coils (n = 14). PVE was decided according to preoperative volumetry on the basis of contrast-enhanced CT. Groups were compared for age, sex, volume of the left lobe before PVE and future remnant liver ratio (FRL) (volume of the left lobe/total liver volume - tumor volume). The primary end point was the increase in left lobe volume 1 month after PVE. Secondary end points were procedure complications and biological tolerance. Results: Both groups were similar in terms of age, sex ratio, left lobe volume, and FRL before PVE. NBCA induced a greater increase in volume after PVE than did microparticles plus coils (respectively, +74 {+-} 69 % and +23 {+-} 14 %, p < 0.05). The amount of contrast medium used for the procedure was significantly larger when microparticles and coils rather than NBCA were used (respectively, 264 {+-} 43 ml and 162 {+-} 34 ml, p < 0.01). The rate of PVE complications as well as the biological tolerance was similar in both groups. Conclusion: NBCA seems more effective than spherical microparticles plus coils to induce left-lobe hypertrophy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Comparing Effective Doses During Image-Guided Core Needle Biopsies with Computed Tomography Versus C-Arm Cone Beam CT Using Adult and Pediatric Phantoms

PurposeTo compare the effective doses of needle biopsies based on dose measurements and simulations using adult and pediatric phantoms, between cone beam c-arm CT (CBCT) and CT.MethodEffective doses were calculated and compared based on measurements and Monte Carlo simulations of CT- and CBCT-guided biopsy procedures of the lungs, liver, and kidney using pediatric and adult phantoms.ResultsThe effective doses for pediatric and adult phantoms, using our standard protocols for upper, middle and lower lungs, liver, and kidney biopsies, were significantly lower under CBCT guidance than CT. The average effective dose for a 5-year old for these five biopsies was 0.36 ± 0.05 mSv with the standard CBCT exposure protocols and 2.13 ± 0.26 mSv with CT. The adult average effective dose for the five biopsies was 1.63 ± 0.22 mSv with the standard CBCT protocols and 8.22 ± 1.02 mSv using CT. The CT effective dose was higher than CBCT protocols for child and adult phantoms by 803 and 590 % for upper lung, 639 and 525 % for mid-lung, and 461 and 251 % for lower lung, respectively. Similarly, the effective dose was higher by 691 and 762 % for liver and 513 and 608 % for kidney biopsies.ConclusionsBased on measurements and simulations with pediatric and adult phantoms, radiation effective doses during image-guided needle biopsies of the lung, liver, and kidney are significantly lower with CBCT than with CT.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

Survival Analysis of Advanced HCC Treated with Radioembolization: Comparing Impact of Clinical Performance Status Versus Vascular Invasion/Metastases

PurposeIn this study, we aim to compare the effects of prognostic indicators on survival analysis for Barcelona Clinic Liver Cancer (BCLC) C patients undergoing yttrium-90 radioembolization (Y-90).MethodsA prospectively acquired database (2003–2017) for BCLC C hepatocellular carcinoma (HCC) patients that underwent radioembolization with Y-90 was searched. The criteria for BCLC C status (Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 1 or 2, metastases, and/or portal vein thrombosis (PVT)) were recorded. Kaplan–Meier survival analyses were performed from the date of the first radioembolization with Y-90, censored to curative treatment, to determine median overall survival (OS). Cox regression hazards model was used for multivariate analyses. Significance was set at P < 0.05.Results547 BCLC C patients treated with radioembolization with Y-90 had a median OS of 10.7 months (range: 9.5–12.9). 43% (233 of 547) patients classified as BCLC C solely by their ECOG PS had a median OS of 19.4 months (14.7–23.7); 57% (314 of 547) patients with PVT/metastases had a median OS of 7.7 months (6.7–8.7). On multivariate analysis, ECOG PS was not found to be a statistically significant prognostic indicator of OS in BCLC C whereas metastases and PVT exhibited hazards ratios (95%CI) of 0.51 (0.38–0.69) and 0.49 (0.38–0.63), respectively (P < 0.0001).ConclusionPatients classified as BCLC C due to ECOG PS 1 demonstrated longer survival when compared to those presenting with PVT, metastases and/or ECOG PS 2. Hence, ECOG PS 1, as an isolated variable, may not be a true indicator of advanced disease.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

No Increased Mortality After TIPS Compared with Serial Large Volume Paracenteses in Patients with Higher Model for End-Stage Liver Disease Score and Refractory Ascites

Purpose: To compare survival after transjugular intrahepatic portosystemic shunt (TIPS) creation versus serial large volume paracenteses (LVP) in patients with refractory ascites and higher Model for End-Stage Liver Disease (MELD) scores. Materials and Methods: In this retrospective study, from 1/1/2013 to 10/1/2018, 478 patients (294 male; mean age 58, range 23–89) underwent serial LVP (n = 386) or TIPS (n = 92) for ascites. Propensity-matched cohorts were constructed based on age, MELD, Charlson comorbidity index, varices, and hepatic encephalopathy. Survival was analyzed using a Cox proportional hazards model in which MELD score and TIPS were treated as time-dependent covariates. An interaction term was used to assess the impact of TIPS versus serial LVP on survival as a function of increasing MELD. Results: In the overall patient sample, higher MELD score predicted worse survival after either serial LVP or TIPS [hazard ratio (HR) = 1.13; p < 0.001], but there was no significant interaction between TIPS and higher MELD score conferring worse survival (HR = 1.01; p = 0.55). In 92 propensity-matched serial LVP and 92 TIPS patients, higher MELD score predicted worse survival after either serial LVP or TIPS (HR = 1.19; p < 0.001), but there was no significant survival interaction between TIPS and higher MELD (HR = 0.97; p = 0.22). In 30 propensity-matched serial LVP patients and 30 TIPS patients with baseline MELD greater than 18, TIPS did not predict worse survival (HR = 0.97; p = 0.94). Conclusion: Higher MELD predicts poorer survival after either serial LVP or TIPS, but TIPS creation is not associated with worse survival compared to serial LVP in patients with higher MELD scores Level of Evidence: Level 4, case series.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

A comparative analysis of the impacts of climate change and irrigation on land surface and subsurface hydrology in the North China Plain

The Community Land Model 4.0 (CLM4) was used to investigate and compare the effects of climate change and irrigation on terrestrial water cycle. Three climate change scenarios and one irrigation scenario (IRRIG) were simulated in the North China Plain (NCP), which is one of the most vulnerable regions to climate change and human perturbations in China. The climate change scenarios consist of (1) HOT (i.e. temperature increase by 2oC); (2) HOTWET (same with HOT but with an increase of precipitation by 15%); (3) HOTDRY (same with HOT but with a decrease of precipitation by 15%). In the IRRIG scenario, the irrigation scheme was calibrated to simulate irrigation amounts that match the actual irrigation amounts and irrigation was divided between surface water and groundwater withdrawals based on census data. Our results show that the impacts of climate change were more widespread while those of irrigation were concentrated only over the agricultural regions. Specifically, the mean water table depth was simulated to decline persistently by over 1 m annually due to groundwater exploitation during the period of 1980-2000, while much smaller effects were induced by climate change. Although irrigation has comparable effects on surface fluxes and surface soil moisture as climate change, it has much greater effects on water table depth and groundwater storage. Moreover, irrigation has much larger effects on the top layer soil moisture whereas increase in precipitation associated with climate change exerts more influence on lower layer soil moisture. This study emphasizes the need to accurately account for irrigation impacts in adapting to climate change.

climate change↗

Comparing Transformation Pathways Across Major Economies

This paper aims at providing an overview of the transformation pathways for the seven largest greenhouse-gas (GHG) emitting regions and countries in the world, in line with their contributions to limiting global average temperature increase to well below 2oC as compared to pre-industrial levels. We introduce the methodology for developing these pathways by initially discussing the iterative process by which global integrated assessment models (IAMs) initiated discussions by suggesting boundary conditions in the form of carbon budgets for different regions and countries. The carbon budgets subsequently agreed upon were then used in eleven different regional and national energy-economy models and IAMs for deriving low-carbon pathways in line with a well-below-2oC world. We present a comparative assessment of the resulting regional and national pathways, and of the challenges and opportunities associated with them.

Schaeffer, Roberto↗

Characterizing Turbulence at a Forest Edge: Comparing Sub-Filter Scale Turbulence Models in Simulations of Flow over a Canopy

In wildfires, atmospheric turbulence plays a major role in the transfer of turbulent kinetic energy. Understanding how turbulence feeds back into a dynamical system is important, down to the varying small scales of fuel structures (i.e. pine needles, grass). Large eddy simulations (LES) are a common way of numerically representing turbulence. The Smagorinsky model (1963) serves as one of the most studied sub-grid scale representations in LES. In this investigation, the Smagorinsky model was implemented in HIGRAD/FIRETEC, LANL’s coupled fire-atmosphere model. This study was motivated by the need to quantitatively investigate the vorticity budget equation in HIGRAD/FIRETEC. The Smagorinsky turbulent kinetic energy (TKE) was compared to FIRETEC’s 1.5-order TKE eddy-viscosity subgrid-scale model, known as the Linn turbulence model. This was done in simulations of flow over flat terrain with a homogeneous, cuboidal canopy in the center of the domain. Examinations of the modeled vertical TKE profile and turbulent statistics at the leading edge, and throughout the canopy, show that the Smagorinsky model provides comparable results to that of the original closure model posed in FIRETEC.

58 GEOSCIENCES↗

Eye-Safe KGd(WO{sub 4}){sub 2} Raman Lasers: Comparative Study of Pumping of Nd:KGd(WO{sub 4}){sub 2} Lasers With {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 13/2} Working Transitions{sup **}

This is a comparative study of eye-safe extracavity KGd(WO{sub 4}){sub 2} (KGW) Raman lasers that convert multimode emission from pulsed Nd:KGW lasers operating on the {sup 4}F{sub 3/2} → {sup 4}I{sub 11/2} and {sup 4}F{sub 3/2} → {sup 4}I{sub 13/2} transitions into the third Stokes component at λ = 1500 nm and the first Stokes component at λ = 1507 or 1538 nm. For equal sizes of the Raman and laser sections of a Raman laser emitting the third Stokes component, the pulse energy is higher (~14.2 mJ) and the divergence of the Stokes beam is lower (~9.4 mrad) for a lower energy of the Nd:KGW laser (~6.7 J). For pump pulse energies of 29–34 mJ, all the Raman lasers have essentially the same optical lasing efficiency of up to 36%. In terms of the electrical energy delivered to the flashlamp, however, the overall efficiency of the Raman laser for the third Stokes component is a factor of ~1.7 higher. The duration of the Raman pulses is comparable to that of the pump pulses and is ~20 ns for the first Stokes components. The pulse in the third Stokes component is shorter by a factor of 2.5–3. Given the different pump levels and the differences in the thermallyinduced optical distortions of the Nd:KGW laser components, the energy density distribution for beams of the first Stokes components is elliptical, while that of the third Stokes components is almost circular. The possibility of simultaneous lasing at wavelengths of 1507 and 1538 nm with parallel and mutually orthogonal polarizations of the Stokes waves is demonstrated.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Life Cycle Analysis of Extruded Films Based on Poly(lactic acid)/Cellulose Nanocrystal/Limonene: A Comparative Study with ATBC Plasticized PLA/OMMT Systems

Life cycle analysis (LCA) of limonene plasticized poly(lactic acid) (PLA) films containing cellulose nanocrystals (CNC) extracted, by acid hydrolysis, from Phormium tenax leaf fibres, was assessed and compared with the results of acetyl tributyl citrate (ATBC) plasticized PLA films, having equivalent mechanical properties, containing organo-modified montmorillonite (OMMT). Eco-Indicator 99 tool has been adopted as the main method for life cycle assessment. Results indicated that, despite CNC are biobased fillers obtained by natural sources, the related chemical extraction leads to a large environmental footprint and a relatively relevant energy expense. LCA characterization of these films demonstrated that the environmental impact of PLA/limonene film reinforced with 1% in weight of CNC (PLA/CNC/limonene) is comparable to the environmental impact of polylactic acid films reinforced with OMMT and plasticized with a petroleum based plasticizer (ATBC) (PLA/OMTT/ATBC). A “cradle to gate” approach has been considered for both the film typologies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Ultrafast all-optical digital comparator using quantum-dot semiconductor optical amplifiers

In this investigation, three types of 160 Gb/s all-optical digital comparators using quantum-dot semiconductor optical amplifiers (QD-SOAs) are constructed. These configurations have different combination patterns of logic gates and QD-SOAs. Based on numerical simulations, we investigate and evaluate the performance of the devices in terms of the number of logic gates and QD-SOAs, and the value of the extinction ratio (ER). In addition, we demonstrate the effect of amplified spontaneous emission (ASE) noise on the ER and Q-factor. The results show that two of the three configurations are superior to the other configuration in terms of circuit complexity, value of ER, and sensitivity to injection current. Moreover, these two configurations achieve ER values over 10 dB and Q-factor over 9, even when intense ASE noise is considered. The proposed configurations have several advantages such as high quality, easy configuration, insensitivity to injection current, and strong noise robustness, which are favorable for practical applications. This investigation also facilitates the specification of the pros and cons of each configuration, and the determination of the appropriate comparator according to the desired requirements.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Power distribution and BER in indoor VLC with PPM based modulation schemes: a comparative study

Visible light communication (VLC) uses an intensity-modulation and direct-detection scheme to transmit data. The light source utilized in VLC structures is constantly switched on and off rapidly, resulting in flickering. Furthermore, most of illumination systems exclude dimming support to permit customers to dim the light source to the desired stage. Therefore, the modulation scheme for information transmission in VLC should consist of flicker mitigation and dimming manage abilities. Double inverse pulse position modulation (DIPPM), sub-carrier pulse position modulation (SC-L-PPM), and M-ary variable pulse position modulation (M-VPPM) are recommended for minimizing the flicker issues and supporting an excessive degree of dimming for VLC systems. In this paper, a comparison is introduced between DIPPM, SC-L-PPM, and M-VPPM according to error performance and bit rate. In addition, a simulation is carried out to measure the optical power distribution for a LED lamp in an indoor room topology for each modulation technique. The obtained results indicated that SC-L-PPM is the best choice regarding the bit error rate (BER) and optical power distribution compared to the other two schemes. A 10{sup −6} BER is achieved with a very low power requirement at L = 8, while a remarkable power distribution of 1.5–6.5 dBm is observed from 3 × 5 × 5 m{sup 3} room corners to the center, respectively. According to the bit rate, it is noticed that, M-VPPM is the most efficient one compared to the two other schemes. It achieves 2.3 × 10{sup 7} bps at a signal to noise ratio (SNR) of 22 dB and M = 8.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

Comparative Analysis of Imaging and Measurements of Micrometer-Scale Fracture Aperture Fields Within a Heterogeneous Rock Using PET and X-ray CT

Knowledge of the spatial distribution of fracture apertures is essential for reliable characterization of flow and transport processes in fractured systems and for better understanding of physicochemical matrix–fracture interactions. Here, we propose and test two image-based methods, thereby extending the current experimental capabilities to characterize aperture size distribution in structurally heterogeneous geologic porous media noninvasively. The first approach utilizes an inversion method based on the dataset acquired from positron emission tomography (PET) and the second approach considers an extension of the classic missing attenuation technique that relies on clinical X-ray computed tomography (X-ray CT). Independent sets of imaging experiments are conducted on a fractured basalt core with heterogeneous matrix properties and aperture distributions to compare the two methodologies. A repeat of each experiment is conducted to verify the proposed workflows. The performance of these two imaging techniques is systematically evaluated through the analysis of signal-to-noise ratio, minimum fracture size detectability, and measurement errors. While both approaches provide a reliable estimation of fracture aperture distributions, PET yields a signal-to-noise ratio that is substantially higher than the corresponding X-ray CT measurements. Furthermore, uncertainties of the aperture values for PET are considerably lower ($\bar {\sigma}_{\text {d}} = 15\%$) compared to those obtained from X-ray CT ($\bar {\sigma}_{\text {d}} = 29\%$), allowing for the detection of minimum aperture sizes of 20 $\mu$m with 70% confidence level. Finally, these approaches provide key experimental tools for better understanding dynamic hydromechanical fracture properties in geologic systems.

58 GEOSCIENCES↗