Accuracy of iodine quantification using dual-energy computed tomography with focus on low concentrations.

BACKGROUND: Iodine quantification using dual-energy computed tomography (DECT) is helpful in characterizing, and follow-up after treatment of tumors. Some malignant masses, for instance papillary renal cell carcinomas (p-RCC), are hard to differentiate from benign lesions because of very low contrast enhancement. In these cases, iodine concentrations might be very low, and it is therefore important that iodine quantification is reliable even at low concentrations if this technique is used. PURPOSE: To examine the accuracy of iodine quantification and to determine whether it is also accurate for low iodine concentrations. MATERIAL AND METHODS: Twenty-six syringes with different iodine concentrations (0-30 mg I/mL) were scanned in a phantom model using a DECT scanner with two different kilovoltage and image reconstruction settings. Iodine concentrations were measured and compared to known concentration. Absolute and relative errors were calculated. RESULTS: For concentrations of 1 mg I/mL or higher, there was an excellent correlation between true and measured iodine concentrations for all settings (R = 0.999-1.000; P < 0.001). For concentrations <1.0 mg I/mL, the relative error was greater. Absolute and relative errors were smaller using tube voltages of 80/Sn140 kV than 100/Sn140 kV (P < 0.01). Reconstructions using a 3.0-mm slice thickness had less variance between repeated acquisitions versus 0.6 mm (P < 0.001). CONCLUSION: Iodine quantification using DECT was in general very accurate, but for concentrations < 1.0 mg I/mL the technique was less reliable. Using a tube voltage with larger spectral separation was more accurate and the result was more reproducible using thicker image reconstructions.

A quantitative analysis of extension and distribution of lung injury in COVID-19: a prospective study based on chest computed tomography.

BACKGROUND: Typical features differentiate COVID-19-associated lung injury from acute respiratory distress syndrome. The clinical role of chest computed tomography (CT) in describing the progression of COVID-19-associated lung injury remains to be clarified. We investigated in COVID-19 patients the regional distribution of lung injury and the influence of clinical and laboratory features on its progression. METHODS: This was a prospective study. For each CT, twenty images, evenly spaced along the cranio-caudal axis, were selected. For regional analysis, each CT image was divided into three concentric subpleural regions of interest and four quadrants. Hyper-, normally, hypo- and non-inflated lung compartments were defined. Nonparametric tests were used for hypothesis testing (α = 0.05). Spearman correlation test was used to detect correlations between lung compartments and clinical features. RESULTS: Twenty-three out of 111 recruited patients were eligible for further analysis. Five hundred-sixty CT images were analyzed. Lung injury, composed by hypo- and non-inflated areas, was significantly more represented in subpleural than in core lung regions. A secondary, centripetal spread of lung injury was associated with exposure to mechanical ventilation (p < 0.04), longer spontaneous breathing (more than 14 days, p < 0.05) and non-protective tidal volume (p < 0.04). Positive fluid balance (p < 0.01), high plasma D-dimers (p < 0.01) and ferritin (p < 0.04) were associated with increased lung injury. CONCLUSIONS: In a cohort of COVID-19 patients with severe respiratory failure, a predominant subpleural distribution of lung injury is observed. Prolonged spontaneous breathing and high tidal volumes, both causes of patient self-induced lung injury, are associated to an extensive involvement of more central regions. Positive fluid balance, inflammation and thrombosis are associated with lung injury. Trial registration Study registered a priori the 20th of March, 2020. Clinical Trials ID NCT04316884.

Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse.

Rationale: Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL.Objectives: To assess whether external expiratory resistances 1) affect expiratory diaphragmatic contraction during spontaneous breathing, 2) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and 3) reduce tidal atelectasis, preventing hyperinflation.Methods: Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined.Measurements and Main Results: Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), 1) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, 2) expiratory flow was reduced and the expiratory time constants became more homogeneous, and 3) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation.Conclusions: The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.

The Diaphragm Acts as a Brake during Expiration to Prevent Lung Collapse.

RATIONALE: The diaphragm is the major inspiratory muscle and is assumed to relax during expiration. However, electrical postinspiratory activity has been observed. Whether there is an expiratory diaphragmatic contraction that preserves lung patency has yet to be explored. OBJECTIVES: We hypothesized the occurrence of an expiratory diaphragmatic contraction directed at stabilizing peripheral airways and preventing or reducing cyclic expiratory lung collapse. METHODS: Mild acute respiratory distress syndrome was induced in 10 anesthetized, spontaneously breathing pigs. Lung volume was decreased by lowering end-expiratory airway pressure in a stepwise manner. We recorded the diaphragmatic electric activity during expiration, dynamic computed tomographic scans, and respiratory mechanics. In five pigs, the same protocol was repeated during mechanical ventilation after muscle paralysis. MEASUREMENTS AND MAIN RESULTS: Diaphragmatic electric activity during expiration increased by decreasing end-expiratory lung volume during spontaneous breathing. This enhanced the diaphragm muscle force, to a greater extent with lower lung volume, indicating a diaphragmatic electromechanical coupling during spontaneous expiration. In turn, the resulting diaphragmatic contraction delayed and reduced the expiratory collapse and increased lung aeration compared with mechanical ventilation with muscle paralysis and absence of diaphragmatic activity. CONCLUSIONS: The diaphragm is an important regulator of expiration. Its expiratory activity seems to preserve lung volume and to protect against lung collapse. The loss of diaphragmatic expiratory contraction during mechanical ventilation and muscle paralysis may be a contributing factor to unsuccessful respiratory support.

Body mass index is associated with pulmonary gas and blood distribution mismatch in COVID-19 acute respiratory failure. A physiological study.

Background: The effects of obesity on pulmonary gas and blood distribution in patients with acute respiratory failure remain unknown. Dual-energy computed tomography (DECT) is a X-ray-based method used to study regional distribution of gas and blood within the lung. We hypothesized that 1) regional gas/blood mismatch can be quantified by DECT; 2) obesity influences the global and regional distribution of pulmonary gas and blood; 3) regardless of ventilation modality (invasive vs. non-invasive ventilation), patients' body mass index (BMI) has an impact on pulmonary gas/blood mismatch. Methods: This single-centre prospective observational study enrolled 118 hypoxic COVID-19 patients (92 male) in need of respiratory support and intensive care who underwent DECT. The cohort was divided into three groups according to BMI: 1. BMI<25 kg/m2 (non-obese), 2. BMI = 25-40 kg/m2 (overweight to obese), and 3. BMI>40 kg/m2 (morbidly obese). Gravitational analysis of Hounsfield unit distribution of gas and blood was derived from DECT and used to calculate regional gas/blood mismatch. A sensitivity analysis was performed to investigate the influence of the chosen ventilatory modality and BMI on gas/blood mismatch and adjust for other possible confounders (i.e., age and sex). Results: 1) Regional pulmonary distribution of gas and blood and their mismatch were quantified using DECT imaging. 2) The BMI>40 kg/m2 group had less hyperinflation in the non-dependent regions and more lung collapse in the dependent regions compared to the other BMI groups. In morbidly obese patients, gas and blood were more evenly distributed; therefore, the mismatch was lower than in other patients (30% vs. 36%, p < 0.05). 3) An increase in BMI of 5 kg/m2 was associated with a decrease in mismatch of 3.3% (CI: 3.67% to -2.93%, p < 0.05). Neither the ventilatory modality nor age and sex affected the gas/blood mismatch (p > 0.05). Conclusion: 1) In a hypoxic COVID-19 population needing intensive care, pulmonary gas/blood mismatch can be quantified at a global and regional level using DECT. 2) Obesity influences the global and regional distribution of gas and blood within the lung, and BMI>40 kg/m2 improves pulmonary gas/blood mismatch. 3) This is true regardless of the ventilatory mode and other possible confounders, i.e., age and sex. Trial Registration: Clinicaltrials.gov, identifier NCT04316884, NCT04474249.

Measurement of transplanted pancreatic volume using computed tomography: reliability by intra- and inter-observer variability.

BACKGROUND: Unlike other solid organ transplants, pancreas allografts can undergo a substantial decrease in baseline volume after transplantation. This phenomenon has not been well characterized, as there are insufficient data on reliable and reproducible volume assessments. We hypothesized that characterization of pancreatic volume by means of computed tomography (CT) could be a useful method for clinical follow-up in pancreas transplant patients. PURPOSE: To evaluate the feasibility and reliability of pancreatic volume assessment using CT scan in transplanted patients. MATERIAL AND METHODS: CT examinations were performed on 21 consecutive patients undergoing pancreas transplantation. Volume measurements were carried out by two observers tracing the pancreatic contours in all slices. The observers performed the measurements twice for each patient. Differences in volume measurement were used to evaluate intra- and inter-observer variability. RESULTS: The intra-observer variability for the pancreatic volume measurements of Observers 1 and 2 was found to be in almost perfect agreement, with an intraclass correlation coefficient (ICC) of 0.90 (0.77-0.96) and 0.99 (0.98-1.0), respectively. Regarding inter-observer validity, the ICCs for the first and second measurements were 0.90 (range, 0.77-0.96) and 0.95 (range, 0.85-0.98), respectively. CONCLUSION: CT volumetry is a reliable and reproducible method for measurement of transplanted pancreatic volume.

Predictive value of secondary signs of obstruction in follow-up computed tomography of ureteral stones: a study with dynamic computed tomography.

OBJECTIVES: This study aimed to determine the ratio of obstruction and predictive values of secondary signs in follow-up computed tomography (CT) of ureterolithiasis patients; to correlate stone characteristics with obstruction; to compare enhancement of obstructed and non-obstructed kidneys; and to compare radiation dose of the dynamic CT protocol to an excretory-phase protocol. MATERIALS AND METHODS: This retrospective study assessed 49 follow-up CT scans of patients with remaining ureterolithiasis after a renal colic episode. Obstruction was measured as time taken to excretion of contrast medium in dynamic CT. Degree of secondary signs of obstruction was evaluated from the unenhanced CT. Data were collected on patients' gender and age, stone size and location, time from renal colic to follow-up, attenuation of the renal cortex and radiation dose. RESULTS: Obstruction was present in 28% (n = 14) at follow-up. Predictive values (sensitivity, specificity, positive predictive value, negative predictive value) were calculated for hydronephrosis (1.0, 0.63, 0.52, 1.0), hydroureter (1.0, 0.4, 0.4, 1.0), perirenal stranding (0.21, 0.94, 0.6, 0.75), Gerota's fascia (0.21, 0.97, 0.75, 0.76) and renal swelling (0.21, 0.97, 0.75, 0.76). Obstruction was not correlated with stone characteristics. Enhancement was lower in obstructed kidneys (p < 0.01). Radiation dose was reduced by 43% (1.8 mSv). CONCLUSIONS: Obstruction was found in 28% of patients. Secondary signs were scarce and of indeterminate value to the diagnosis of obstruction. The absence of hydronephrosis and hydroureter contradicted obstruction. Stone characteristics were not correlated with obstruction. Enhancement of the renal cortex was lower in obstructed kidneys. The dynamic protocol reduced the radiation dose.

Reabsorption atelectasis in a porcine model of ARDS: regional and temporal effects of airway closure, oxygen, and distending pressure.

Little is known about the small airways dysfunction in acute respiratory distress syndrome (ARDS). By computed tomography (CT) imaging in a porcine experimental model of early ARDS, we aimed at studying the location and magnitude of peripheral airway closure and alveolar collapse under high and low distending pressures and high and low inspiratory oxygen fraction (FIO2). Six piglets were mechanically ventilated under anesthesia and muscle relaxation. Four animals underwent saline-washout lung injury, and two served as healthy controls. Beyond the site of assumed airway closure, gas was expected to be trapped in the injured lungs, promoting alveolar collapse. This was tested by ventilation with an FIO2 of 0.25 and 1 in sequence during low and high distending pressures. In the most dependent regions, the gas/tissue ratio of end-expiratory CT, after previous ventilation with FIO2 0.25 low-driving pressure, was significantly higher than after ventilation with FIO2 1; with high-driving pressure, this difference disappeared. Also, significant reduction in poorly aerated tissue and a correlated increase in nonaerated tissue in end-expiratory CT with FIO2 1 low-driving pressure were seen. When high-driving pressure was applied or after previous ventilation with FIO2 0.25 and low-driving pressure, this pattern disappeared. The findings suggest that low distending pressures produce widespread dependent airway closure and with high FIO2, subsequent absorption atelectasis. Low FIO2 prevented alveolar collapse during the study period because of slow absorption of gas behind closed airways.