Tri- and bi-exponential diffusion analyses of the kidney: effect of respiratory-controlled acquisition on diffusion parameters.

This study examined whether respiratory-controlled acquisition influences diffusion parameters obtained with intravoxel incoherent motion (IVIM) analysis using tri-exponential and bi-exponential models. Ten healthy volunteers were examined on a 3.0 T MRI system to obtain coronal diffusion-weighted images of both kidneys. The participants were scanned twice using respiratory-triggering (RT) and free-breathing (FB) acquisition to assess the repeatability of the measurements. We determined mean signal intensities in the renal cortex at each b value. Then, perfusion-related diffusion coefficient (Dp), fast-free diffusion coefficient (Df), slow-restricted diffusion coefficient (Ds), and their corresponding fractions (Fp, Ff, and Fs, respectively) were calculated using tri-exponential function. Moreover, perfusion-related diffusion coefficient (D*), the fraction (F), and perfusion-independent diffusion coefficient (D) were calculated using bi-exponential function. Normalized root-mean-square errors for the tri- and bi-exponential analyses (nRMSEtri and nRMSEbi, respectively) were determined to assess the deviation of the fitted to measured data, i.e., the fitting accuracy. Additionally, repeatability coefficients (RCs) were calculated from Bland-Altman plots to evaluate the repeatability of each diffusion parameter. These values were compared between the RT and FB groups. Dp and D* in the RT group were significantly lower than those in the FB group (P < 0.05). In addition, the RT group showed significantly lower nRMSEtri and nRMSEbi values than those in the FB group (P < 0.05). Moreover, Dp, Ds, Fs, and D* at RT showed lower RC values than those at FB. Respiratory-controlled acquisition affects perfusion-related diffusion parameters of the kidney obtained using tri-exponential and bi-exponential analyses.

Extended Lifetime of Respiratory Droplets in a Turbulent Vapor Puff and Its Implications on Airborne Disease Transmission.

To quantify the fate of respiratory droplets under different ambient relative humidities, direct numerical simulations of a typical respiratory event are performed. We found that, because small droplets (with initial diameter of 10 µm) are swept by turbulent eddies in the expelled humid puff, their lifetime gets extended by a factor of more than 30 times as compared to what is suggested by the classical picture by Wells, for 50% relative humidity. With increasing ambient relative humidity the extension of the lifetimes of the small droplets further increases and goes up to around 150 times for 90% relative humidity, implying more than 2 m advection range of the respiratory droplets within 1 sec. Employing Lagrangian statistics, we demonstrate that the turbulent humid respiratory puff engulfs the small droplets, leading to many orders of magnitude increase in their lifetimes, implying that they can be transported much further during the respiratory events than the large ones. Our findings provide the starting points for larger parameter studies and may be instructive for developing strategies on optimizing ventilation and indoor humidity control. Such strategies are key in mitigating the COVID-19 pandemic in the present autumn and upcoming winter.

Reproducibility of diaphragm position assessed with a voluntary breath-holding device.

PURPOSE: To evaluate the reproducibility of diaphragm position in our new breath-holding radiotherapy for abdominal tumors using image-guided radiation therapy (IGRT) and a voluntary breath-holding device, Abches. MATERIALS AND METHODS: Patients treated with abdominal tumors using IGRT with Abches were enrolled. Twenty patients without dementia or severe lung disease were analyzed. Each fraction of all patients was set up with kV cone-beam CT with reference to the vertebral bodies. Before daily treatment, electronic portal imaging device (EPID) images of the diaphragm at breath-holding exhale phase were acquired. The difference in the diaphragm position relative to the vertebral body was analyzed by comparing EPID images and the digitally reconstructed radiograph of the planning CT. We evaluated the reproducibility of two axes: superior-inferior (S-I) and right-left (R-L) with the EPID measurements. RESULTS: The 443 irradiation data sets were analyzed. The interfractional reproducibility of the diaphragm relative to vertebral bodies was 1.7 ± 1.4 mm in the S-I and 1.4 ± 1.2 mm in the R-L direction. CONCLUSION: This technique has good interfractional reproducibility and visibility of the diaphragm during irradiation. Its use is feasible in the routine clinical setting and irradiation.

Ciliated hepatic foregut cyst. A report of one case and a review of the literature.

We encountered a patient with a ciliated hepatic foregut cyst (CHFC), which is an uncommon cystic lesion of the liver and hard to distinguish from malignant tumor in imaging features. Cases of CHFC are very rare, five cases were reported in the 19th century and 53 cases in the 20th century. The histogenesis of CHFC is still unclear, but most authors consider that it could arise from the embryonic foregut. A few cases of CHFC mimicking neoplasm were reported. When the diagnosis of CHFC was obtained by fine needle aspiration, close follow-up is necessary in order to find early malignant change.