Multicentric characterization of organ-based tube current modulation in head computed tomography: A dosimetric and image quality study.

PURPOSE: To evaluate the efficiency of organ-based tube current modulation (OBTCM) in head Computed Tomography (CT) for different radiology departments and manufacturers. MATERIALS AND METHODS: Five CT scanners from four radiology departments were evaluated in this study. All scans were performed using a standard and a routine head protocol. A scintillating fiber optic detector was placed directly on the gantry to measure the tube exit kerma. Image quality was quantified on a 16-cm HEAD phantom by measuring the signal-to-noise ratio (SNR) and the standard deviation of the Hounsfield units (HU) of circular regions of interest placed in the phantom. The Noise Power Spectrum (NPS) was also studied. Measured values were compared on images with and without OBTCM. RESULTS: The reduction rates in tube exit kerma, on the anterior part, vary between 11 % and 74 % depending on the CT scanner and the protocol used. The tube exit kerma on the posterior part remains unchanged in GE and Canon CT scanners. On the contrary, the tube exit kerma to the posterior part increases by up to 39 % in Siemens CT scanner. Image noise and SNR increase by up to 10 % in the five CT scanners. Nonetheless, the differences in noise and SNR are statistically significant (p-value < 0.05).The analysis of the NPS indicates that the noise texture remains unchanged. CONCLUSION: OBTCM reduces the tube exit kerma to the anterior part of the gantry without reducing substantially image quality for head protocols.

Validation of a New Scintillating Fiber Dosimeter for Radiation Dose Quality Control in Computed Tomography.

(1) Background: The IVIscan is a commercially available scintillating fiber detector designed for quality assurance and in vivo dosimetry in computed tomography (CT). In this work, we investigated the performance of the IVIscan scintillator and associated method in a wide range of beam width from three CT manufacturers and compared it to a CT chamber designed for Computed Tomography Dose Index (CTDI) measurements. (2) Methods: We measured weighted CTDI (CTDIw) with each detector in accordance with the requirements of regulatory tests and international recommendations for the minimum, maximum and the most used beam width in clinic and investigated the accuracy of the IVIscan system based on the assessment of the CTDIw deviation from the CT chamber. We also investigated the IVIscan accuracy for the whole range of the CT scans kV. (3) Results: We found excellent agreement between the IVIscan scintillator and the CT chamber for the whole range of beam widths and kV, especially for wide beams used on recent technology of CT scans. (4) Conclusions: These findings highlight that the IVIscan scintillator is a relevant detector for CT radiation dose assessments, and the method associated with calculating the CTDIw saves a significant amount of time and effort when performing tests, especially with regard to new CT technologies.

COVID-19 and vaccination impact on radiology departments provided by Dose Archiving and Communication System.

OBJECTIVES: To study the impact of COVID-19 on chest CT practice during the different waves using Dose Archiving and Communication System (DACS). METHODS: Retrospective study including data from 86,136 chest CT acquisitions from 27 radiology centers (15 private; 12 public) between January 1, 2020, and October 13, 2021, using a centralized DACS. Daily chest CT activity and dosimetry information such as dose length product (DLP), computed tomography dose index (CTDI), and acquisition parameters were collected. Pandemic indicators (daily tests performed, incidence, and hospital admissions) and vaccination rates were collected from a governmental open-data platform. Descriptive statistics and correlation analysis were performed. RESULTS: For the first two waves, strong positive and significant correlations were found between all pandemic indicators and total chest CT activity, as high as R = 0.7984 between daily chest CT activity and hospital admissions during the second wave (p < 0.0001). We found differences between public hospitals and private imaging centers during the first wave, with private centers demonstrating a negative correlation between daily chest CT activity and hospital admissions (-0.2819, p = 0.0019). Throughout the third wave, simultaneously with the rise of vaccination rates, total chest CT activity decreased with significant negative correlations with pandemic indicators, such as R = -0.7939 between daily chest CTs and daily incidence (p < 0.0001). Finally, less than 5% of all analyzed chest CTs could be considered as low dose. CONCLUSIONS: During the first waves, COVID-19 had a strong impact on chest CT practice which was lost with the arrival of vaccination. Low-dose protocols remained marginal. KEY POINTS: • There was a significant correlation between the number of daily chest CTs and pandemic indicators throughout the first two waves. It was lost during the third wave due to vaccination arrival. • Differences were observed between public and private centers, especially during the first wave, less during the second, and were lost during the third. • During the first three waves of COVID-19 pandemic, few CT helical acquisitions could be considered as low dose with only 3.8% of the acquisitions according to CTDIvol and 4.3% according to DLP.

Accelerated sequences of 4D flow MRI using GRAPPA and compressed sensing: A comparison against conventional MRI and computational fluid dynamics.

PURPOSE: To evaluate hemodynamic markers obtained by accelerated GRAPPA (R = 2, 3, 4) and compressed sensing (R = 7.6) 4D flow MRI sequences under complex flow conditions. METHODS: The accelerated 4D flow MRI scans were performed on a pulsatile flow phantom, along with a nonaccelerated fully sampled k-space acquisition. Computational fluid dynamics simulations based on the experimentally measured flow fields were conducted for additional comparison. Voxel-wise comparisons (Bland-Altman analysis, L 2 $$ {L}_2 $$ -norm metric), as well as nonderived quantities (velocity profiles, flow rates, and peak velocities), were used to compare the velocity fields obtained from the different modalities. RESULTS: 4D flow acquisitions and computational fluid dynamics depicted similar hemodynamic patterns. Voxel-wise comparisons between the MRI scans highlighted larger discrepancies at the voxels located near the phantom's boundary walls. A trend for all MR scans to overestimate velocity profiles and peak velocities as compared to computational fluid dynamics was noticed in regions associated with high velocity or acceleration. However, good agreement for the flow rates was observed, and eddy-current correction appeared essential for consistency of the flow rates measurements with respect to the principle of mass conservation. CONCLUSION: GRAPPA (R = 2, 3) and highly accelerated compressed sensing showed good agreement with the fully sampled acquisition. Yet, all 4D flow MRI scans were hampered by artifacts inherent to the phase-contrast acquisition procedure. Computational fluid dynamics simulations are an interesting tool to assess these differences but are sensitive to modeling parameters.

Dinámica de contaminación de pasturas con huevos de nematodos gastrointestinales de bovinos en el Valle de Lerma, Salta / Dynamics of pasture contamination with bovine gastrointestinal nematode eggs in the Lerma Valley, Argentina

Resumen El Valle de Lerma (VDL) es una región ubicada en la parte central de la provincia de Salta, República Argentina, la cual da origen a la mayor parte de la producción láctea provincial. La nematodiasis gastrointestinal es uno de los problemas sanitarios de mayor impacto económico en los sistemas productivos de base pastoril. El objetivo de este trabajo fue caracterizar la variación estacional de la eliminación de huevos y géneros de nematodos al medio ambiente. Mensualmente se tomaron muestras de materia fecal en bovinos de recría para conteo de huevos por gramo (HPG) y coprocultivo para determinación de géneros en tres establecimientos ganaderos de la región. En todos ellos se observaron dos picos en los valores medios de HPG, que ocurrieron entre principios de verano y fines de otoño. Los géneros/especies más prevalentes fueron Cooperia pectinata, Haemonchus spp. y Cooperia punctata, seguidos por Oesophagostomum spp., Trichostrongylus spp. y Ostertagia spp. Estos resultados aportan nueva evidencia al conocimiento de la epidemiología de los nematodos gastrointestinales de los bovinos en la región del VDL.

Abstract The Lerma Valley (LV) is a region located in the central part of the province of Salta, Argentine Republic. The largest dairy production in the province originates in this region. Gastrointestinal nematodiasis is one of the health problems with the greatest economic impact in pastoral-based production systems. The objective of the present work was to characterize the seasonal variation of the elimination of eggs and genera of nematodes to the environment. Fecal matter samples were taken from rearing cattle to count eggs per gram (Epg) and culture for gender determination monthly in three farms in the region. In these, it was possible to observe that the Epg values ​​showed two peaks, which occurred between the beginning of summer and the end of autumn. Regarding the genera/species, the most prevalent were Cooperia pectinata, Haemonchus sp. and Cooperia punctata, followed by Oesophagostomum spp., Trichostrongylus spp. and Ostertagia spp. These results contribute with new evidence to the knowledge of the epidemiology of gastrointestinal nematodes of cattle in the LV region.

Numerical simulation of time-resolved 3D phase-contrast magnetic resonance imaging.

A numerical approach is presented to efficiently simulate time-resolved 3D phase-contrast Magnetic resonance Imaging (or 4D Flow MRI) acquisitions under realistic flow conditions. The Navier-Stokes and Bloch equations are simultaneously solved with an Eulerian-Lagrangian formalism. A semi-analytic solution for the Bloch equations as well as a periodic particle seeding strategy are developed to reduce the computational cost. The velocity reconstruction pipeline is first validated by considering a Poiseuille flow configuration. The 4D Flow MRI simulation procedure is then applied to the flow within an in vitro flow phantom typical of the cardiovascular system. The simulated MR velocity images compare favorably to both the flow computed by solving the Navier-Stokes equations and experimental 4D Flow MRI measurements. A practical application is finally presented in which the MRI simulation framework is used to identify the origins of the MRI measurement errors.

Impact of Thoracic Endografting on the Hemodynamics of the Native Aorta: Pre- and Postoperative Assessments of Wall Shear Stress and Vorticity Using Computational Fluid Dynamics.

PURPOSE: To quantify the hemodynamic consequences of thoracic endovascular aortic repair (TEVAR) by comparing the preoperative and postoperative wall shear stress (WSS) and vorticity profiles on computational fluid dynamics (CFD) simulations. MATERIALS AND METHODS: The pre- and postoperative computed tomography (CT) scans from 20 consecutive patients (median age 69 years, range 20-87) treated for different thoracic aortic pathologies (11 aneurysms, 5 false aneurysms, 3 penetrating ulcers, and 1 traumatic aortic rupture) were segmented to construct patient-specific CFD models using a meshless code. The simulations were run over the cardiac cycle, and the WSS and vorticity values measured at the proximal and distal landing zones were compared. RESULTS: The CFD runs provided 4-dimensional simulations of blood flow in all patients. WSS and vorticity profiles at the proximal landing zone (located in zones 0-3 in 15 patients) varied in 18 and 20 of the cases, respectively; WSS was increased in 11 cases and the vorticity in 9. Pre- and postoperative WSS median values were 4.19 and 4.90 Pa, respectively. Vorticity median values were 40.38 and 39.17 Hz, respectively. CONCLUSION: TEVAR induces functional alterations in the native thoracic aorta, though the prognostic significance of these changes is still unknown. CFD appears to be a valuable tool to explore aortic hemodynamics, and its application in a larger series would help define a predictive role for these hemodynamic assessments.

Combining Volumetric and Wall Shear Stress Analysis from CT to Assess Risk of Abdominal Aortic Aneurysm Progression.

Background Despite known limitations, the decision to operate on abdominal aortic aneurysm (AAA) is primarily on the basis of measurement of maximal aneurysm diameter. Purpose To identify volumetric and computational fluid dynamics parameters to predict AAAs that are likely to progress in size. Materials and Methods This study, part of a multicenter prospective registry (NCT01599533), included 126 patients with AAA. Patients were sorted into stable (≤10-mL increase in aneurysm volume) and progression (>10-mL increase in aneurysm volume) groups. Initial AAA characteristics of the derivation cohort were analyzed (maximal diameter and surface, thrombus and lumen volumes, maximal wall pressure, and wall shear stress [WSS]) to identify relevant parameters for a logistic regression model. Model and maximal diameter diagnostic performances were assessed in both cohorts and for AAAs smaller than 50 mm by using area under the receiver operating characteristic curve (AUC). Results Eighty-one patients were included (mean age, 73 years ± 7 years [standard deviation]; 78 men). The derivation and validation cohorts included, respectively, 50 and 31 participants. In the derivation cohort, there was higher mean lumen volume and lower mean WSS in the progression group compared with the stable group (60 mL ± 14 vs 46 mL ± 18 [P = .005] and 66% ± 6 vs 53% ± 9 [P = .02], respectively). Mean lumen volume and mean WSS at baseline were correlated to total volume growth (r = 0.47 [P = .002] and -0.42 [P = .006], respectively). In the derivation cohort, a regression model including lumen volume and WSS to predict aneurysm enlargement was superior to maximal diameter alone (AUC, 0.78 vs 0.52, respectively; P = .003); although no difference was found in the validation cohort (AUC, 0.79 vs 0.71, respectively; P = .51). For AAAs smaller than 50 mm, a regression model that included both baseline WSS and lumen volume performed better than maximal diameter (AUC, 0.79 vs 0.53, respectively; P = .01). Conclusion Combined analysis of lumen volume and wall shear stress was associated with enlargement of abdominal aortic aneurysms at 1 year, particularly in aneurysms smaller than 50 mm in diameter. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Mitsouras and Leach in this issue.

Reconciling PC-MRI and CFD: An in-vitro study.

Several well-resolved 4D Flow MRI acquisitions of an idealized rigid flow phantom featuring an aneurysm, a curved channel as well as a bifurcation were performed under pulsatile regime. The resulting hemodynamics were processed to remove MRI artifacts. Subsequently, they were compared with CFD predictions computed on the same flow domain, using an in-house high-order low dissipative flow solver. Results show that reaching a good agreement is not straightforward but requires proper treatments of both techniques. Several sources of discrepancies are highlighted and their impact on the final correlation evaluated. While a very poor correlation (r2 = 0.63) is found in the entire domain between raw MRI and CFD data, correlation as high as r2 = 0.97 is found when artifacts are removed by post-processing the MR data and down sampling the CFD results to match the MRI spatial and temporal resolutions. This work demonstrates that, in a well-controlled environment, both PC-MRI and CFD might bring reliable and correlated flow quantities when a proper methodology to reduce the errors is followed.

Low-dose biplanar radiography can be used in children and adolescents to accurately assess femoral and tibial torsion and greatly reduce irradiation.

PURPOSE: To evaluate in children the agreement between femoral and tibial torsion measurements obtained with low-dose biplanar radiography (LDBR) and CT, and to study dose reduction ratio between these two techniques both in vitro and in vivo. MATERIALS AND METHODS: Thirty children with lower limb torsion abnormalities were included in a prospective study. Biplanar radiographs and CTs were performed for measurements of lower limb torsion on each patient. Values were compared using Bland-Altman plots. Interreader and intrareader agreements were evaluated by intraclass correlation coefficients. Comparative dosimetric study was performed using an ionization chamber in a tissue-equivalent phantom, and with thermoluminescent dosimeters in 5 patients. RESULTS: Average differences between CT and LDBR measurements were -0.1° ±1.1 for femoral torsion and -0.7° ±1.4 for tibial torsion. Interreader agreement for LDBR measurements was very good for both femoral torsion (FT) (0.81) and tibial torsion (TT) (0.87). Intrareader agreement was excellent for FT (0.97) and TT (0.89). The ratio between CT scan dose and LDBR dose was 22 in vitro (absorbed dose) and 32 in vivo (skin dose). CONCLUSION: Lower limb torsion measurements obtained with LDBR are comparable to CT measurements in children and adolescents, with a considerably reduced radiation dose. KEY POINTS: • LDBR and CT lower-limb torsion measurements are comparable in children and adolescents. • LDBR considerably reduced radiation dose necessary for lower-limb torsion measurements. • LDBR can be used for evaluation of lower limb-torsion in orthopaediatric patients.

Impact of endografting on the thoracic aortic anatomy: comparative analysis of the aortic geometry before and after the endograft implantation.

PURPOSE: Although the widespread acceptance of thoracic endovascular aortic repair (TEVAR) as a first-line treatment option for a multitude of thoracic aortic diseases, little is known about the consequences of the device implantation on the native aortic anatomy. We propose a comparative analysis of the pre- and postoperative geometry on a clinical series of patients and discuss the potential clinical implications METHODS: CT pre- and postoperative acquisitions of 30 consecutive patients treated by TEVAR for different pathologies (20 thoracic aortic aneurysms, 6 false aneurysms, 3 penetrating ulcers, 1 traumatic rupture) were used to model the vascular geometry. Pre- and postoperative geometries were compared for each patient by pairing and matching the 3D models. An implantation site was identified, and focal differences were detected and described. RESULTS: Segmentation of the data sets was successfully performed for all 30 subjects. Geometry differences between the pre- and postoperative meshes were depicted in 23 patients (76 %). Modifications at the upper implantation site were detected in 14 patients (47 %), and among them, the implantation site involved the arch (Z0-3) in 11 (78 %). CONCLUSION: Modeling the vascular geometry on the basis of imaging data offers an effective tool to perform patient-specific analysis of the vascular geometry before and after the treatment. Future studies will evaluate the consequences of these changes on the aortic function.

Haemodynamic imaging of thoracic stent-grafts by computational fluid dynamics (CFD): presentation of a patient-specific method combining magnetic resonance imaging and numerical simulations.

OBJECTIVES: In the last decade, there was been increasing interest in finding imaging techniques able to provide a functional vascular imaging of the thoracic aorta. The purpose of this paper is to present an imaging method combining magnetic resonance imaging (MRI) and computational fluid dynamics (CFD) to obtain a patient-specific haemodynamic analysis of patients treated by thoracic endovascular aortic repair (TEVAR). METHODS: MRI was used to obtain boundary conditions. MR angiography (MRA) was followed by cardiac-gated cine sequences which covered the whole thoracic aorta. Phase contrast imaging provided the inlet and outlet profiles. A CFD mesh generator was used to model the arterial morphology, and wall movements were imposed according to the cine imaging. CFD runs were processed using the finite volume (FV) method assuming blood as a homogeneous Newtonian fluid. RESULTS: Twenty patients (14 men; mean age 62.2 years) with different aortic lesions were evaluated. Four-dimensional mapping of velocity and wall shear stress were obtained, depicting different patterns of flow (laminar, turbulent, stenosis-like) and local alterations of parietal stress in-stent and along the native aorta. CONCLUSIONS: A computational method using a combined approach with MRI appears feasible and seems promising to provide detailed functional analysis of thoracic aorta after stent-graft implantation. KEY POINTS : • Functional vascular imaging of the thoracic aorta offers new diagnostic opportunities • CFD can model vascular haemodynamics for clinical aortic problems • Combining CFD with MRI offers patient specific method of aortic analysis • Haemodynamic analysis of stent-grafts could improve clinical management and follow-up.

The role of stent-grafts in the management of aortic trauma.

Stent graft has resulted in major advances in the treatment of trauma patients with blunt traumatic aortic injury (TAI) and has become the preferred method of treatment at many trauma centers. In this review, we provide an overview of the place of stent grafts for the management of this disease. As a whole, TEVAR repair of TAIs offers a survival advantage and reduction in major morbidity, including paraplegia, compared with open surgery. However, endovascular procedures in trauma require a sophisticated multidisciplinary and experienced team approach. More research and development of TAI-specific endograft devices is needed and large, multicenter studies will help to clarify the role of TEVAR compared with open repair of TAI.

[Percutaneous fixation of unstable pelvic ring disruption under CT guidance]. / Osteosíntesis percutánea bajo control de tomografía computarizada de la disrupción posterior del anillo pélvico.

CT-guided percutaneous osteosynthesis of posterior disruption of an unstable pelvic ring is an alternative to the fluoroscopically guided procedure or to open reduction and internal fixation (ORIF), which is the technique of choice for unstable pelvic fracture with disruption of the sacroiliac joint or fracture of the sacral wing. However, ORIF has a high rate of morbidity and mortality, and the CT-guided procedure involves less blood loss and has a lower rate of infectious and postoperative complications. CT guidance of the percutaneous technique also has significant advantages over fluoroscopic guidance. The critical point is the placement of the guidewire inside the sacral body through the external surface of the iliac wing and of the fracture line or sacroiliac diastasis. We describe and illustrate the procedure through three cases, two sacroiliac articular disruptions and a fracture of the sacral wing.

Osteosíntesis percutánea bajo control de tomografía computarizada de la disrupción posterior del anillo pélvico / Percutaneous fixation of unstable pelvic ring disruption under CT guidance

La osteosíntesis percutánea de la disrupción posterior inestable del anillo pélvico controlada con tomografía computarizada (TC) es una alternativa al procedimiento guiado por fluoroscopia y a la técnica de reducción abierta y fijación interna (RAFI); esta última es la técnica de elección en esta patología. La técnica consiste en la colocación de la aguja de guía bajo control de TC en el interior del cuerpo sacro a través de la superficie externa de la pala ilíaca y de la línea de fractura o diástasis sacroilíaca. El procedimiento TC-guiado presenta menor tasa de complicaciones postoperatorias, infecciosas y pérdida hemática que la RAFI, que tiene una alta morbilidad y mortalidad. Comunicamos 3 casos, 2 disrrupciones articulares sacroilíacas y 1 fractura de ala sacra, tratados bajo control de TC (AU)

CT-guided percutaneous osteosynthesis of posterior disruption of an unstable pelvic ring is an alternative to the fluoroscopically guided procedure or to open reduction and internal fixation (ORIF), which is the technique of choice for unstable pelvic fracture with disruption of the sacroiliac joint or fracture of the sacral wing. However, ORIF has a high rate of morbidity and mortality, and the CT-guided procedure involves less blood loss and has a lower rate of infectious and postoperative complications. CT guidance of the percutaneous technique also has significant advantages over fluoroscopic guidance. The critical point is the placement of the guidewire inside the sacral body through the external surface of the iliac wing and of the fracture line or sacroiliac diastasis. We describe and illustrate the procedure through three cases, two sacroiliac articular disruptions and a fracture of the sacral wing (AU)

Implementation and evaluation of a national external quality control program for cervical cytology in Mexico.

OBJECTIVE: To evaluate cytology laboratories and the performance of cytotechnologists for establishing efficient external quality control for Mexico's National Program for the Prevention and Control of Cervical Cancer. MATERIAL AND METHODS: During January and February 1998, an onsite evaluation of all cytology laboratories of the Ministry of Health found that only 70% of the microscopes were in adequate working conditions, reagents were out of date, and working conditions were sub-optimal. A program for external quality control based on proficiency testing was established for cytotechnologists. Fifty slide sets with 20 Papanicolaou slides and 10 photographic slides were prepared. The sets were given to the cytotechnologists for evaluation and again one year later by courier. RESULTS: Twenty-one percent of microscopes were repaired and 9% replaced; reagents were distributed and laboratory facilities improved. Only 16% of cytotechnologists passed the initial proficiency test. Cytotechnologists received a refresher training course: one year later 67% of them passed the proficiency test. To ascertain that each slide was correctly diagnosed, 41 sets were rescreened by expert cytopathologists or cytologists and their diagnoses compared to the original ones. Thirty-seven sets had 86% to 96% concordance. CONCLUSIONS: This new system for external quality control of cervical cytology allowed the opportune and reliable evaluation of the performance of cytotechnologists.

Implementation and evaluation of a national external quality control program for cervical cytology in Mexico

OBJECTIVE: To evaluate cytology laboratories and the performance of cytotechnologists for establishing efficient external quality control for Mexico's National Program for the Prevention and Control of Cervical Cancer. MATERIAL AND METHODS: During January and February 1998, an onsite evaluation of all cytology laboratories of the Ministry of Health found that only 70 of the microscopes were in adequate working conditions, reagents were out of date, and working conditions were sub-optimal. A program for external quality control based on proficiency testing was established for cytotechnologists. Fifty slide sets with 20 Papanicolaou slides and 10 photographic slides were prepared. The sets were given to the cytotechnologists for evaluation and again one year later by courier. RESULTS: Twenty-one percent of microscopes were repaired and 9 replaced; reagents were distributed and laboratory facilities improved. Only 16 of cytotechnologists passed the initial proficiency test. Cytotechnologists received a refresher training course: one year later 67 of them passed the proficiency test. To ascertain that each slide was correctly diagnosed, 41 sets were rescreened by expert cytopathologists or cytologists and their diagnoses compared to the original ones. Thirty-seven sets had 86 to 96 concordance. CONCLUSIONS: This new system for external quality control of cervical cytology allowed the opportune and reliable evaluation of the performance of cytotechnologists.