Higher Computed Tomography Number Research Articles

X-ray Computed Tomography (CT) to Scan the Structure and Characterize the Mud Cake Incorporated with Various Magnetic NPs Concentration: An Application to Evaluate the Wellbore Stability and Formation Damage

The X-ray computed tomography method has provided unrivalled data about the characterization and evolution of the internal/external structure of materials by analyzing CTN and non-destructive imaging approach. Applying this method on the appropriate drilling-fluid ingredients plays a significant role in generating proper mud cake quality to stabilize wellbore, and avoid formation damage and filtration loss by preventing drilling fluid invasion into the formation. In this study, smart-water drilling mud containing different concentrations of magnetite nanoparticles (MNPs) was used to assess the filtration loss properties and formation impairment. Conventional static filter press, non-destructive X-ray computed tomography (CT) scan images and high-resolution quantitative measurement of CT number method were used to estimate the filtrate volume and characterize the filter cake layers, hence evaluating the reservoir damage through hundreds of merged images. The CT scan data were combined with the HIPAX and Radiant viewer digital image processing. The variation in CT number of mud cake samples under different concentrations of MNPs and without MNPs concentration were analyzed, and hundreds of 3D images as a cross-sectional profile were used. This paper highlights the importance of MNPs property in terms of minimizing filtration volume and improving mud cake quality and thickness, and hence improving the wellbore stability. From the results, a notable reduction of filtrate drilling mud volume and mud cake thickness to 40.9% and 46.6%, respectively, were recorded for drilling fluids incorporated with 0.92 wt.% of MNPs. However, this study asserts that optimal MNPs should be implemented to guarantee the best filtration property. As confirmed from the results, increasing the MNPs concentration beyond the optimal value (up to 2 wt.%) increased the filtrate volume and mud cake thickness by 3.23 and 33.3%, respectively. CT scan profile images show two layers of mud cake produced from water-based drilling fluids possessing 0.92 wt.% MNPs. The latter concentration was found to be the optimal additive of MNPs as it caused a decrease in filtration volume, mud cake thickness, and pore spaces within the structure of the mud cake. Using the optimum MNPs, the CT number (CTN) shows a high CTN and density material, and uniform compacted thin mud cake structure (0.75 mm). The produced thin mud cake layer reveals the precipitation or exchange of elemental/mineral composition during fluid-solid interaction. These results confirm that MNPs could help in avoiding or reducing the formation damage, driving away drilling fluid from the formation, and improving borehole stability.

X‐ray computed tomography of deep‐sea clay as tools to detect rare earth elements and yttrium enrichment

AbstractPelagic clay that contains rare‐earth elements and yttrium (REY) at over 2000 ppm (termed “highly REY‐rich mud”) has been reported from a few areas in the western North Pacific Ocean through focused geochemical analyses. Those REY are carried by biogenic calcium phosphate, suggesting that the formation of highly REY‐rich mud involves enhanced biological productivity. However, detecting REY enrichment in sediment is time‐consuming, and the global significance of the formation of REY‐rich mud is still under debate. Here we perform x‐ray computed tomography (CT) analyses on cores recovered around Minamitorishima Island and demonstrate the positive correlation with highly REY‐rich mud and high CT numbers of the sediment. The variation of the CT number matches the wet bulk density. Further quantitative analyses using direct measurements of density and geochemistry suggest that a grain density increase and a porosity decrease due to the REY‐carrying biogenic apatite are essential to explain the high CT numbers in the REY‐enriched layer. While the chemical composition itself is of minor importance to elevate the CT numbers, our results suggest that x‐ray CT can be a proxy for highly REY‐rich mud.

High CT Attenuation Values Relative to the Brainstem Predict Fungal Hyphae Within the Sinus.

ObjectivesThere is currently no established objective diagnostic indicator for the differentiation of sinus fungal ball (SFB) from unilateral nonfungal chronic sinusitis (UCRS). This study evaluated whether computed tomography (CT) attenuation values relative to those of the brainstem (relative CT number) are useful for differentiating SFB from UCRS.Materials and MethodsConsecutive patients who were pathologically diagnosed with SFB or UCRS between 2013 and 2021 were retrospectively identified. The relative CT numbers of region of interest (ROIs) within the sinuses were compared between the two patient groups. Factors with predictive power for differentiating SFBs from UCRSs were identified by uni/multivariable logistic regression analyses.ResultsOne hundred and eighty-three patients with unilateral chronic sinusitis were finally analyzed (SFB, 86 cases; UCRS, 97 cases). Regardless of the presence or absence of calcified lesions, the relative CT numbers in SFB were significantly higher than those in UCRS. ROIs showing high relative CT numbers were those where fungal hyphae were present. In the uni/multivariable logistic regression analysis, age (p < 0.001), relative CT number (p < 0.001), and calcification (p = 0.002) had predictive value for distinguishing SFB from UCRS. Within those cases not showing calcification, age (p = 0.004) and relative CT number (p < 0.001) were predictive factors for differentiating SFB from UCRS. A relative CT number >1.5 was significantly associated with SFB (sensitivity, 70%; specificity, 91%), with a significantly larger area under the receiver operating characteristics curve than age.ConclusionsHigh relative CT numbers within the sinus are strongly associated with the presence of fungal hyphae, and measurement of relative CT number is a powerful adjunctive diagnostic method for distinguishing between SFB and UCRS.

The Value of On-Site Proton Audits

This study aimed to highlight the value and key findings of on-site proton audits. The authors performed 38 on-site measurement-based peer reviews of proton centers participating in National Cancer Institute-funded clinical trials. The reviews covered beam calibration, lateral and depth measurements, mechanical checks, treatment planning and clinical practice, and quality assurance (QA) practices. Program deficiencies were noted, and recommendations were made about ways institutions could improve their practices. Institutions received an average of 3 (range, 1-8) recommendations for practice improvements. The number of deficiencies did not decrease over time, highlighting the continued need for this type of peer review. The most common deficiencies were for Task Group-recommended QA compliance (97% of centers), computed tomography number (CTN) to relative linear stopping power conversion (59%), and QA procedures (53%). In addition, 32% of institutions assessed failed at least 1 lateral beam profile measurement (<90% of pixels passing 3% [global]/3 mm; 10% threshold), despite passing internal QA measurements. These failures occurred for several different plan configurations (large, small, shallow, and deep targets) and at different depths in the beam path (proximal to target, central, and distal). CTN to relative linear stopping power conversion curves showed deviations at low, mid, and high CTNs and highlighted areas of inconsistency between proton centers, with many centers falling outside of 2 sigma of the mean curve of their peers. All deficiencies from the peer review were discussed with the institutions, and many implemented dosimetric treatment planning and practice changes to improve the accuracy of their system and consistency with other institutions. This peer review program has been integral in confirming and promoting consistency and best practice across proton centers for clinical trials, minimizing deviations for outcomes data.

Investigation of imaging properties of novel contrast agents based on gold, silver and bismuth nanoparticles in spectral computed tomography using Monte Carlo simulation

Abstract In the present paper, some imaging properties of nanoparticles-based contrast agents including gold, bismuth, and silver were assessed and compared with conventional (iodinated) contrast agent in spectral computed tomography (CT). A spectral CT scanner with photon-counting detectors (PCD) and 6 energy bins was simulated using the Monte Carlo (MC) simulation method. The nanoparticles were designed with a diameter of 50 nm at concentrations of 2, 4, and 8 mg/ml. Water-filled cylindrical phantom was modeled with a diameter of 10 cm containing a hole with a diameter of 5 cm in its center, where was filled with contrast agents. The MC results were used to reconstruct images. Image reconstruction was accomplished with the filtered back-projection (FBP) method with hamming filter and linear interpolation method. CT number and contrast-to-noise ratio (CNR) of all studied contrast materials were calculated in spectral images. The simulations indicated that nanoparticle-based contrast agents have a higher CT number and CNR than the iodinated contrast agent at the same concentration and for all energy bins. In general, gold nanoparticles produced the highest CT number and CNR compared to silver and bismuth nanoparticles at the same concentration. However, at low energies (below 80 keV), silver nanoparticles performed similarly to gold nanoparticles and at high energies (120 keV), bismuth nanoparticles can be a good substitute for gold nanoparticles.

Verification of the Dose Reduction Effect via Diluted Injection in Dual-Energy Computed Tomography Using a Human Blood Flow Phantom.

Purpose We sought to examine the possibility of reducing the contrast medium dosage in dual-energy imaging using a saline-mixed injection with a virtual monochromatic energy method of dual-source computed tomography (CT). Methods An X-ray CT (SOMATOM Definition Flash: Siemens, Nurnberg, Germany) was employed. The mixing ratio of contrast medium and saline was gradually changed by 10%, followed by a mixed injection into a dynamic blood flow phantom (Nemoto Kyorindo, Japan) which is a hemodynamic simulation phantom to obtain time-enhancement curves (TECs). Exactly 64 TECs were prepared for each mixing ratio by changing the energy from 40 to 75 keV for monoenergetic imaging. The relationship between the image standard deviation (SD) and the energy of the virtual monochromatic image was determined. Combinations of the mixing ratio and energy (keV), which can maintain high CT numbers and low image SDs for 3D imaging, were tested, and the reduction rate of the contrast medium was calculated. Results The TECs for the mixed injection method changed linearly with the dilution rates. The mixing ratios were strongly correlated with the maximum CT number of the TEC (R2 = 0.98). Contrast CT numbers and image SDs increased by approximately 20% and 25%, respectively, as the energy decreased by 5 keV. The optimal conditions for reducing the contrast medium dose were a mixing ratio of 6:4 and 55 keV of energy. Conclusion The virtual monochromatic energy method reduced the contrast medium dosage by up to 40% for three-dimensional CT-angio (3DCTA) tests.

Experimental assessment on feasibility of computed tomography-based thermometry for radiofrequency ablation on tissue equivalent polyacrylamide phantom

Purpose: This study aimed to evaluate the effects of various computed tomography (CT) acquisition parameters and metal artifacts on CT number measurement for CT thermometry during CT-guided thermal ablation.Methods: The effects of tube voltage (100–140 kVp), tube current (20–250 mAs), pitch (0.6–1.5) and gantry rotation time (0.5, 1.0 s) as well as metal artifacts from a radiofrequency ablation (RFA) needle on CT number were evaluated using liver tissue equivalent polyacrylamide (PAA) phantom. The correlation between CT number and temperature from 37 to 80 °C was studied on PAA phantom using optimum CT acquisition parameters.Results: No statistical significant difference (p > 0.05) was found on CT numbers under the variation of different acquisition parameters for the same temperature setting. On the other hand, the RFA needle has induced metal artifacts on the CT images of up to 8 mm. The CT numbers decreased linearly when the phantom temperature increased from 37 to 80 °C. A linear regression analysis on the CT numbers and temperature suggested that the CT thermal sensitivity was –0.521 ± 0.061 HU/°C (R2 = 0.998).Conclusion: CT thermometry is feasible for temperature assessment during RFA with the current CT technology, which produced a high CT number reproducibility and stable measurement at different CT acquisition parameters. Despite being affected by metal artifacts, the CT-based thermometry could be further developed as a tissue temperature monitoring tool during CT-guided thermal ablation.

SU-E-T-599: The Variation of Hounsfield Unit and Relative Electron Density Determination as a Function of KVp and Its Effect On Dose Calculation Accuracy

Purpose: To investigate the differences in relative electron density for different energy (kVp) settings and the effect that these differences have on dose calculations. Methods: A Nuclear Associates 76-430 Mini CT QC Phantom with materials of known relative electron densities was imaged by one multi-slice (16) and one single-slice computed tomography (CT) scanner. The Hounsfield unit (HU) was recorded for each material with energies ranging from 80 to 140 kVp and a representative relative electron density (RED) curve was created. A 5 cm thick inhomogeneity was created in the treatment planning system (TPS) image at a depth of 5 cm. The inhomogeneity was assigned HU for various materials for each kVp calibration curve. The dose was then calculated with the analytical anisotropic algorithm (AAA) at points within and below the inhomogeneity and compared using the 80 kVp beam as a baseline. Results: The differences in RED values as a function of kVp showed the largest variations of 580 and 547 HU for the Aluminum and Bone materials; the smallest differences of 0.6 and 3.0 HU were observed for the air and lung inhomogeneities. The corresponding dose calculations for the different RED values assigned to the 5 cm thick slab revealedmore » the largest differences inside the aluminum and bone inhomogeneities of 2.2 to 6.4% and 4.3 to 7.0% respectively. The dose differences beyond these two inhomogeneities were between 0.4 to 1.6% for aluminum and 1.9 to 2.2 % for bone. For materials with lower HU the calculated dose differences were less than 1.0%. Conclusion: For high CT number materials the dose differences in the phantom calculation as high as 7.0% are significant. This result may indicate that implementing energy specific RED curves can increase dose calculation accuracy.« less

Correction of oral contrast artifacts in CT-based attenuation correction of PET images using an automated segmentation algorithm

Oral contrast is usually administered in most X-ray computed tomography (CT) examinations of the abdomen and the pelvis as it allows more accurate identification of the bowel and facilitates the interpretation of abdominal and pelvic CT studies. However, the misclassification of contrast medium with high-density bone in CT-based attenuation correction (CTAC) is known to generate artifacts in the attenuation map (mumap), thus resulting in overcorrection for attenuation of positron emission tomography (PET) images. In this study, we developed an automated algorithm for segmentation and classification of regions containing oral contrast medium to correct for artifacts in CT-attenuation-corrected PET images using the segmented contrast correction (SCC) algorithm. The proposed algorithm consists of two steps: first, high CT number object segmentation using combined region- and boundary-based segmentation and second, object classification to bone and contrast agent using a knowledge-based nonlinear fuzzy classifier. Thereafter, the CT numbers of pixels belonging to the region classified as contrast medium are substituted with their equivalent effective bone CT numbers using the SCC algorithm. The generated CT images are then down-sampled followed by Gaussian smoothing to match the resolution of PET images. A piecewise calibration curve was then used to convert CT pixel values to linear attenuation coefficients at 511 keV. The visual assessment of segmented regions performed by an experienced radiologist confirmed the accuracy of the segmentation and classification algorithms for delineation of contrast-enhanced regions in clinical CT images. The quantitative analysis of generated mumaps of 21 clinical CT colonoscopy datasets showed an overestimation ranging between 24.4% and 37.3% in the 3D-classified regions depending on their volume and the concentration of contrast medium. Two PET/CT studies known to be problematic demonstrated the applicability of the technique in clinical setting. More importantly, correction of oral contrast artifacts improved the readability and interpretation of the PET scan and showed substantial decrease of the SUV (104.3%) after correction. An automated segmentation algorithm for classification of irregular shapes of regions containing contrast medium was developed for wider applicability of the SCC algorithm for correction of oral contrast artifacts during the CTAC procedure. The algorithm is being refined and further validated in clinical setting.

Histogram analysis of computed tomography numbers of clinical T1 N0 M0 lung adenocarcinoma, with special reference to lymph node metastasis and tumor invasiveness

Purpose To predict lymph node metastasis and tumor invasiveness in lung adenocarcinoma from computed tomography findings, we examined computed tomography number histograms of clinical T1 N0 M0 lung adenocarcinomas. Patients and methods Histograms of pixel computed tomography numbers were made for 100 patients with clinical T1 N0 M0 lung adenocarcinoma. Pathological tumor stages were N0 in 80 patients, N1 in 7, N2 in 9, and T4 due to intrapulmonary metastasis in 4. Results The histogram showed 3 patterns: 1 peak at a low computed tomography number (n = 18), 1 peak at a high computed tomography number (n = 54), and 2 peaks at both low and high computed tomography numbers (n = 28). Histologically, adenocarcinoma with 1 peak at a low computed tomography number showed a large area of bronchioloalveolar carcinoma–like spread with little area of solid growing tumor or central fibrosis, whereas those with 1 peak at a high computed tomography number showed a large area of solid growing tumor or central fibrosis with little bronchioloalveolar carcinoma–like spread. Adenocarcinomas with 2 peaks had both types of areas. Lymph node or pulmonary metastases were seen in none (0%) of the adenocarcinomas with 1 peak at a low computed tomography number, in 1 (4%) with 2 peaks, and in 20 (37%) with 1 peak at a high computed tomography number. The former 2 types had metastases less frequently than those with 1 peak at a high computed tomography number ( P < .01). In the 79 patients with pathological T1 N0 M0, tumor involvement of the intratumoral vessels or pleura was seen in 1 of 18 (6%) adenocarcinomas with 1 peak at a low computed tomography number, which was significantly less frequent than the 18 of 34 (53%) with 1 peak at a high computed tomography number ( P < .001) and 10 of 27 (37%) with 2 peaks ( P < .05). Conclusion Clinical T1 N0 M0 adenocarcinomas with 1 peak at a low computed tomography number on histogram seldom had lymph node metastasis or tumor involvement of vessels or pleura. Limited surgical resection could be indicated for this type of adenocarcinoma, especially for elderly patients or patients with poor pulmonary function.

Computed tomographic distinction of submucosal lipoma and adenomatous polyp of the colon

Described here is a patient with 2 large pedunculated colonic tumors detected by barium enema radiography. By computed tomography (CT) 1 was found to be a submucosal lipoma characterized by oval shape, smooth demarcation, and homogeneous density with a CT number of -68 HU, whereas the other was an adenomatous polyp with slightly fuzzy outline and a much higher CT number. This case indicates that CT can be a definitive diagnostic modality for distinguishing between a colonic lipoma and other solid or cystic tumor of the colon.

Quantification of calcium in solitary pulmonary nodules using single- and dual-energy CT.

Separation of benign from malignant solitary pulmonary nodules by computed tomography (CT) is based on two assumptions: (a) those that are calcified are benign, and (b) high CT numbers reflect calcium deposits. The authors used dual-energy CT to quantify the minimum detectable calcium content in simulated nodules independent of absolute CT number and to separate high CT numbers due to calcium from those due to high-density organic material. A mineral concentration of 20 mg/cm/sup 3/ was detectable with this method. Dual-energy CT may be a more accurate method of detecting calcium in solitary pulmonary nodules than single-energy CT.

Corneal chrysiasis and clinical improvement with chrysotherapy in rheumatoid arthritis

The deposition of gold in the cornea-ocular chrysiasis-is a normal event during chrysotherapy. It may reflect tissue deposition of gold and be of value in predicting clinical improvement or toxic reactions. We studied 21 patients with rheumatoid arthritis on chrysotherapy but could find no relationship between the appearance of ocular chrysiasis, clinical improvement, and toxicity.

Detection and quantitation of myocardial infarction in vivo using transmission computed tomography.

In vivo studies were performed on 28 dogs to evaluate the usefulness of transmission computed tomography (CT) in the detection and quantitation of experimentally induced myocardial infarction. Intravenously administered contrast material was required to define the internal structure of the heart and to differentiate normal from infarcted tissue. Transmural infarcts with homogeneous central regions were visualized as areas of diminished contrast enhancement compared with the normal myocardium. All transmural infarcts of at least 24 hours' duration showed a surrounding border zone of patchy necrosis that was variable in size and had high CT numbers due to slow washout of the contrast material from this region. Infarct area determined from the images for individual slices correlated well (r = 0.976) with that calculated using pathology. The technique is very sensitive and can detect infarction within a papillary muscle. Nontransmural or patchy infarcts show up as areas of diffuse contrast enhancement without a central core of diminished enhancement. The distribution of the contrast material is similar to that of technetium-99m pyrophosphate in the border zone of the infarct in infusion studies, but in bolus studies it behaves more like thallium-201.