Counting fast or slow, aloud or silently? A comparison of adult stutterers and non-stutterers.

This study assesses factors influencing the capacity to maintain a steady rhythm during explicit counting activities. There are three counting paces (count every 800, 1200, or 1600 ms) and three experimental conditions (count silently, aloud and aloud in the presence of someone). The study also assesses the effect of a speech disorder, namely stuttering, on this counting ability by comparing the performance of a group of adult stutterers (n = 21) to that of a group of adult non-stutterers (n = 24). For temporal variability, in addition to replicating the fact that counting more slowly leads to lower performance, the results show that there are benefits to expect when participants count aloud instead of silently. There is no main effect of group, but the interaction between the experimental condition, the counting pace, and the group is significant. Adult non-stutterers are better than adult stutterers in the silent and long time-interval conditions (1600 ms). The significantly higher variability at 1600 ms indicates a loss of efficiency in the capacity to keep time constant when counting is slow, and it is in this condition that stutterers will gain the most benefits from counting aloud instead of silently.

Investigation of the Axial Gap Clearance in a Hydrodynamic-Passive Magnetically Levitated Rotary Blood Pump Using X-Ray Radiography.

The HeartWare HVAD is a radial rotary blood pump with a combination of passive magnetic and hydrodynamic bearings to levitate the impeller. The axial gap size between impeller and housing in this bearing and its sensitivity to speed, flow, and pressure difference is difficult to assess. Shear stresses are exceptionally high in this tiny gap making it important for blood damage and related adverse events. Therefore, the aim of this study was to measure the axial gap clearance in the HVAD at different operating conditions employing radiography. To quantify the gap size in the HVAD, the pump was positioned 30 mm in front of the X-ray source employing a microfocus X-ray tube with an acceleration voltage up to 300 kV. Beams were detected on a flat panel detector (Perkin Elmer XRD 1611-CP3). The pump was connected to a tubing circuit with a throttle to adjust flow (0, 5, 10 L/min) and a water glycerol mixture to set the desired viscosity (1, 4, 8 mPas). Rotational speed was varied between 1800 and 3600 rpm. In this study, for clinically relevant conditions at 5 L/min and 2700 rpm, the axial gap was 22 µm. The gap size increased with rotational speeds dependent on the viscosity (2.8, 6.9, and 9.4 µm/1000 rpm for 1, 4, and 8 mPas, respectively), but was independent from the volume flow and the pressure head at constant speeds. In summary, using X-ray radiographic imaging small gaps in a rotary blood pump during operation can be measured in a nondestructive contact-free way. The axial hydrodynamic bearing gap in the HVAD pump was determined to be in the range of about three times the diameter of a red blood cell. Its dependence on operating volume flow and generated pressure head across the pump is not pronounced.

Validating plastic scintillation detectors for photon dosimetry in the radiologic energy range.

PURPOSE: Photon dosimetry in the kilovolt (kV) energy range represents a major challenge for diagnostic and interventional radiology and superficial therapy. Plastic scintillation detectors (PSDs) are potentially good candidates for this task. This study proposes a simple way to obtain accurate correction factors to compensate for the response of PSDs to photon energies between 80 and 150 kVp. The performance of PSDs is also investigated to determine their potential usefulness in the diagnostic energy range. METHODS: A 1-mm-diameter, 10-mm-long PSD was irradiated by a Therapax SXT 150 unit using five different beam qualities made of tube potentials ranging from 80 to 150 kVp and filtration thickness ranging from 0.8 to 0.2 mmAl + 1.0 mmCu. The light emitted by the detector was collected using an 8-m-long optical fiber and a polychromatic photodiode, which converted the scintillation photons to an electrical current. The PSD response was compared with the reference free air dose rate measured with a calibrated Farmer NE2571 ionization chamber. PSD measurements were corrected using spectra-weighted corrections, accounting for mass energy-absorption coefficient differences between the sensitive volumes of the ionization chamber and the PSD, as suggested by large cavity theory (LCT). Beam spectra were obtained from x-ray simulation software and validated experimentally using a CdTe spectrometer. Correction factors were also obtained using Monte Carlo (MC) simulations. Percent depth dose (PDD) measurements were compensated for beam hardening using the LCT correction method. These PDD measurements were compared with uncorrected PSD data, PDD measurements obtained using Gafchromic films, Monte Carlo simulations, and previous data. RESULTS: For each beam quality used, the authors observed an increase of the energy response with effective energy when no correction was applied to the PSD response. Using the LCT correction, the PSD response was almost energy independent, with a residual 2.1% coefficient of variation (COV) over the 80-150-kVp energy range. Monte Carlo corrections reduced the COV to 1.4% over this energy range. All PDD measurements were in good agreement with one another except for the uncorrected PSD data, in which an over-response was observed with depth (13% at 10 cm with a 100 kVp beam), showing that beam hardening had a non-negligible effect on the PSD response. A correction based on LCT compensated very well for this effect, reducing the over-response to 3%. CONCLUSION: In the diagnostic energy range, PSDs show high-energy dependence, which can be corrected using spectra-weighted mass energy-absorption coefficients, showing no considerable sign of quenching between these energies. Correction factors obtained by Monte Carlo simulations confirm that the approximations made by LCT corrections are valid. Thus, PSDs could be useful for real-time dosimetry in radiology applications.

Reducing residual-motion artifacts in iterative 3D CBCT reconstruction in image-guided radiation therapy.

PURPOSE: Recent evaluations of a 3D iterative cone-beam computed tomography (iCBCT) reconstruction method available on Varian radiation treatment devices demonstrated that iCBCT provides superior image quality when compared to analytical Feldkamp-Davis-Kress (FDK) method. However, iCBCT employs statistical penalized likelihood (PL) that is known to be highly sensitive to inconsistencies due to physiological motion occurring during the acquisition. We propose a computationally inexpensive extension of iCBCT addressing this deficiency. METHODS: During the iterative process, the gradients of PL are modified to avoid the generation of motion-related artifacts. To assess the impact of this modification, we propose a motion simulation generating CBCT projections of a moving anatomy together with artifact-free images used as ground truth. Contrast-to-noise ratio and power spectra of difference images are computed to quantify the impact of the motion on reconstructed CBCT volumes as well as the effect of the proposed modification. RESULTS: Using both simulated and clinical data, it is shown that the motion of patient's abdominal wall during the acquisition results in artifacts that can be quantified as low-frequency components in volumes reconstructed with iCBCT. Further, a quantitative evaluation demonstrates that the proposed modification of PL reduces these low-frequency components. While preserving the advantages of PL, it effectively suppresses the propagation of motion-related artifacts into clinically important regions, thus increasing the motion resiliency of iCBCT. CONCLUSIONS: The proposed modified iterative reconstruction method significantly improves the quality of CBCT images of anatomies suffering from residual motion.

A new, exceptionally preserved juvenile specimen of Eusaurosphargis dalsassoi (Diapsida) and implications for Mesozoic marine diapsid phylogeny.

Recently it was suggested that the phylogenetic clustering of Mesozoic marine reptile lineages, such as thalattosaurs, the very successful fish-shaped ichthyosaurs and sauropterygians (including plesiosaurs), among others, in a so-called 'superclade' is an artefact linked to convergent evolution of morphological characters associated with a shared marine lifestyle. Accordingly, partial 'un-scoring' of the problematic phylogenetic characters was proposed. Here we report a new, exceptionally preserved and mostly articulated juvenile skeleton of the diapsid reptile, Eusaurosphargis dalsassoi, a species previously recovered within the marine reptile 'superclade', for which we now provide a revised diagnosis. Using micro-computed tomography, we show that besides having a deep skull with a short and broad rostrum, the most outstanding feature of the new specimen is extensive, complex body armour, mostly preserved in situ, along its vertebrae, ribs, and forelimbs, as well as a row of flat, keeled ventrolateral osteoderms associated with the gastralia. As a whole, the anatomical features support an essentially terrestrial lifestyle of the animal. A review of the proposed partial character 'un-scoring' using three published data matrices indicate that this approach is flawed and should be avoided, and that within the marine reptile 'superclade' E. dalsassoi potentially is the sister taxon of Sauropterygia.

Monte Carlo calculation of the dose perturbations in a dual-source HDR/PDR afterloader treatment unit.

PURPOSE: Currently, there are high dose rate afterloaders available that can drive two different radioactive sources simultaneously. The source-source and source-cable attenuations are not taken into account by current planning systems. The purpose of this work is to characterize these effects and their overall impact on clinically relevant metrics. METHODS AND MATERIALS: A (192)Ir ((169)Yb) Flexitron source is modeled within a Monte Carlo code, and its water dose distribution is evaluated. A second source (cable) is placed parallel at various distances to quantify the dose perturbations. The dual-source setup is then transposed to clinical prostate plans (n = 11). Each plan D90 is compared to the single-source D90. The worst-case scenario (two sources traveling in closely located positions) establishes the upper bounds of the deviations. Two setups are considered with sources constrained in catheter pairs or freely distributed. A metric proportional to the dwell times and R(-2) (where R is the intersource separation) helps determine the source position in each configuration. RESULTS: The dose profiles vs. R(-2) (3-20 mm) show a maximal dose reduction effect of 65% (25%) for (169)Yb ((192)Ir) at small distances. A shadow region with at least 10% dose difference extends up to 10 cm. A similar study with a steel drive cable shows similar behavior with a maximal decrease of 10% (3%) under irradiation of a (169)Yb ((192)Ir) source. The relative D90 difference with the single source setup is 2.3% on average, up to 3.7%. It is obtained by superimposing the contributions from catheter pairs in the dual-source loading. CONCLUSION: Overall deviations observed in D90 compared to a single source setup are not significant for all cases studied.

The collapsed cone algorithm for (192)Ir dosimetry using phantom-size adaptive multiple-scatter point kernels.

The aim of this work was to investigate how dose distributions calculated with the collapsed cone (CC) algorithm depend on the size of the water phantom used in deriving the point kernel for multiple scatter. A research version of the CC algorithm equipped with a set of selectable point kernels for multiple-scatter dose that had initially been derived in water phantoms of various dimensions was used. The new point kernels were generated using EGSnrc in spherical water phantoms of radii 5 cm, 7.5 cm, 10 cm, 15 cm, 20 cm, 30 cm and 50 cm. Dose distributions derived with CC in water phantoms of different dimensions and in a CT-based clinical breast geometry were compared to Monte Carlo (MC) simulations using the Geant4-based brachytherapy specific MC code Algebra. Agreement with MC within 1% was obtained when the dimensions of the phantom used to derive the multiple-scatter kernel were similar to those of the calculation phantom. Doses are overestimated at phantom edges when kernels are derived in larger phantoms and underestimated when derived in smaller phantoms (by around 2% to 7% depending on distance from source and phantom dimensions). CC agrees well with MC in the high dose region of a breast implant and is superior to TG43 in determining skin doses for all multiple-scatter point kernel sizes. Increased agreement between CC and MC is achieved when the point kernel is comparable to breast dimensions. The investigated approximation in multiple scatter dose depends on the choice of point kernel in relation to phantom size and yields a significant fraction of the total dose only at distances of several centimeters from a source/implant which correspond to volumes of low doses. The current implementation of the CC algorithm utilizes a point kernel derived in a comparatively large (radius 20 cm) water phantom. A fixed point kernel leads to predictable behaviour of the algorithm with the worst case being a source/implant located well within a patient/phantom for which low doses at phantom edges can be overestimated by 2-5 %. It would be possible to improve the situation by using a point kernel for multiple-scatter dose adapted to the patient/phantom dimensions at hand.

Calcifications in low-dose rate prostate seed brachytherapy treatment: post-planning dosimetry and predictive factors.

BACKGROUND AND PURPOSE: The brachytherapy dose algorithm of the American Association of Physicists in Medicine Task Group (TG) Report 43 overrides all tissue materials with water. In reality, dose discrepancies will occur around tissue calcifications. This study investigates these perturbations in low dose rate prostate brachytherapy dosimetry. MATERIALS AND METHODS: 43 cancer patients with prostatic calcifications are identified. Geant4 Monte Carlo (MC) simulations are made with materials assigned based on TG186 recommendations. Five dose calculation scenarios are presented: MC in water (MCW), MCW with calcifications, (MCCA), MCCA with seeds (MCCASEED) and full tissue definition and seeds with dose to medium in medium (FMC) and dose to water in medium (FMC-Dw,m). RESULTS: The mean FMC prostate D90 (V100) difference relative to TG43 is -6.4% (range [-1.8, -14.1]) (-2.6% [-0.3, -6.7]). For MCCA we obtained -3.9% [-1.0, -8.7] (-1.5% [-0.2, -4.1]). The mean urethra D10 difference is -4.5% [-1.3, -9.9] for FMC, -2.4% [-0.7, -5.1] with MCCA. FMC-Dw,m D90 has a -0.45% smaller dose difference than FMC on average. The calcification/prostate volume ratio is a good predictor of dose perturbation (R(2)=0.75). CONCLUSION: Based on these results, calcifications alter the dose coverage and may have severe dose perturbation that requires recalculation.

Quantifying the effect of seed orientation in postplanning dosimetry of low-dose-rate prostate brachytherapy.

PURPOSE: Radioactive seed orientations are usually ignored in clinical brachytherapy dosimetry for prostate implants. Associated with the anisotropic dose distribution of seeds, these orientations could cause dose differences between the planning configurations and the clinical postplanning dosimetry. This study will quantify the impact of seed orientation on the dosimetry. METHODS: 3D seed positions and θ and φ polar angles were obtained using five independent fluoroscopic images for 287 patients. Five dose calculation methods are compared: TG43-1D (1), TG43-2D parallel to implant axis (2) and with orientations (3), Monte Carlo (MC) simulations parallel (4), and MC simulations with orientations (5). GEANT4 v4.9.6 MC simulations were made in 1 mm(3) voxelized geometries based on the DICOM-RT information. Materials were assigned using thresholds based on the HU number, as recommended in TG186 reports. Seed voxels are overridden with prostatic materials and the layered mass geometry [Enger et al., Phys. Med. Biol. 57(19), 6269-6277 (2012)] allows subsequent placement of the source geometry. 500 million histories were used per patient. 3D dose and DVHs for each structure were calculated. RESULTS: The various seed orientations do not result in statistically significant differences on the dose metrics for the clinical target volume (CTV) or the urethra, based on the Student t-test p-value. Difference as low as -0.238% and 0.059% has been seen on the CTV D90, respectively, for the MC and the TG43. The difference between parallel and oriented calculations for the organs at risk (OARs) can differ by 2% on average. CONCLUSIONS: Based on the results from this study, seed orientations have no significant impact of CTV and urethra dose metrics but can affect OARs that are external to the CTV.