872 research outputs found

    Detailed Analysis of Scatter Contribution from Different Simulated Geometries of X-ray Detectors.

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    Scattering is one of the main issues left in planar mammography examinations, as it degrades the quality of the image and complicates the diagnostic process. Although widely used, anti-scatter grids have been found to be inefficient, increasing the dose delivered, the equipment price and not eliminating all the scattered radiation. Alternative scattering reduction methods, based on postprocessing algorithms using Monte Carlo (MC) simulations, are being developed to substitute anti-scatter grids. Idealized detectors are commonly used in the simulations for the purpose of simplification. In this study, the scatter distribution of three detector geometries is analyzed and compared: Case 1 makes use of idealized detector geometry, Case 2 uses a scintillator plate and Case 3 uses a more realistic detector simulation, based on the structure of an indirect mammography X-ray detector. This paper demonstrates that common configuration simplifications may introduce up to 14% of underestimation of the scatter in simulation results

    Predicted Impact of Barriers to Migration on the Serengeti Wildebeest Population

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    The Serengeti wildebeest migration is a rare and spectacular example of a once-common biological phenomenon. A proposed road project threatens to bisect the Serengeti ecosystem and its integrity. The precautionary principle dictates that we consider the possible consequences of a road completely disrupting the migration. We used an existing spatially-explicit simulation model of wildebeest movement and population dynamics to explore how placing a barrier to migration across the proposed route (thus creating two disjoint but mobile subpopulations) might affect the long-term size of the wildebeest population. Our simulation results suggest that a barrier to migration—even without causing habitat loss—could cause the wildebeest population to decline by about a third. The driver of this decline is the effect of habitat fragmentation (even without habitat loss) on the ability of wildebeest to effectively track temporal shifts in high-quality forage resources across the landscape. Given the important role of the wildebeest migration for a number of key ecological processes, these findings have potentially important ramifications for ecosystem biodiversity, structure, and function in the Serengeti

    Pediatric interventional radiography equipment: safety considerations

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    This paper discusses pediatric image quality and radiation dose considerations in state-of-the-art fluoroscopic imaging equipment. Although most fluoroscopes are capable of automatically providing good image quality on infants, toddlers, and small children, excessive radiation dose levels can result from design deficiencies of the imaging device or inappropriate configuration of the equipment’s capabilities when imaging small body parts. Important design features and setup choices at installation and during the clinical use of the imaging device can improve image quality and reduce radiation exposure levels in pediatric patients. Pediatric radiologists and cardiologists, with the help of medical physicists, need to understand the issues involved in creating good image quality at reasonable pediatric patient doses. The control of radiographic technique factors by the generator of the imaging device must provide a large dynamic range of mAs values per exposure pulse during both fluoroscopy and image recording as a function of patient girth, which is the thickness of the patient in the posterior–anterior projection at the umbilicus (less than 10 cm to greater than 30 cm). The range of pulse widths must be limited to less than 10 ms in children to properly freeze patient motion. Variable rate pulsed fluoroscopy can be leveraged to reduce radiation dose to the patient and improve image quality. Three focal spots with nominal sizes of 0.3 mm to 1 mm are necessary on the pediatric unit. A second, lateral imaging plane might be necessary because of the child’s limited tolerance of contrast medium. Spectral and spatial beam shaping can improve image quality while reducing the radiation dose. Finally, the level of entrance exposure to the image receptor of the fluoroscope as a function of operator choices, of added filter thickness, of selected pulse rate, of the selected field-of-view and of the patient girth all must be addressed at installation

    CT scanning for diagnosing blunt ureteral and ureteropelvic junction injuries

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    <p>Abstract</p> <p>Background</p> <p>Blunt ureteral and ureteropelvic (UPJ) injuries are extremely rare and very difficult to diagnose. Many of these injuries are missed by the initial trauma evaluation.</p> <p>Methods</p> <p>Trauma registry data was used to identify all blunt trauma patients with ureteral or UPJ injuries, from 1 April 2001 to 30 November 2006. Demographics, injury information and outcomes were determined. Chart review was then performed to record initial clinical and all CT findings.</p> <p>Results</p> <p>Eight patients had ureteral or UPJ injuries. Subtle findings such as perinephric stranding and hematomas, and low density retroperitoneal fluid were evident on all initial scans, and prompted delayed excretory scans in 7/8 cases. As a result, ureteral and UPJ injuries were diagnosed immediately for these seven patients. These findings were initially missed in the eighth patient because significant associated visceral findings mandated emergency laparotomy. All ureteral and UPJ injuries have completely healed except for the case with the delay in diagnosis.</p> <p>Conclusion</p> <p>Most blunt ureteral and UPJ injuries can be identified if delayed excretory CT scans are performed based on initial CT findings of perinephric stranding and hematomas, or the finding of low density retroperitoneal fluid.</p

    Is abdominal wall contraction important for normal voiding in the female rat?

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    BACKGROUND: Normal voiding behavior in urethane-anesthetized rats includes contraction of the abdominal wall striated muscle, similar to the visceromotor response (VMR) to noxious bladder distension. Normal rat voiding requires pulsatile release of urine from a pressurized bladder. The abdominal wall contraction accompanying urine flow may provide a necessary pressure increment for normal efficient pulsatile voiding. This study aimed to evaluate the occurrence and necessity of the voiding-associated abdominal wall activity in urethane-anesthetized female rats METHODS: A free-voiding model was designed to allow assessment of abdominal wall activity during voiding resulting from physiologic bladder filling, in the absence of bladder or urethral instrumentation. Physiologic diuresis was promoted by rapid intravascular hydration. Intercontraction interval (ICI), voided volumes and EMG activity of the rectus abdominis were quantified. The contribution of abdominal wall contraction to voiding was eliminated in a second group of rats by injecting botulinum-A (BTX, 5 U) into each rectus abdominis to induce local paralysis. Uroflow parameters were compared between intact free-voiding and BTX-prepared animals. RESULTS: Abdominal wall response is present in free voiding. BTX preparation eliminated the voiding-associated EMG activity. Average per-void volume decreased from 1.8 ml to 1.1 ml (p < 0.05), and reduced average flow from 0.17 ml/sec to 0.11 ml/sec (p < 0.05). Intercontraction interval (ICI) was not changed by BTX pretreatment. CONCLUSION: The voiding-associated abdominal wall response is a necessary component of normal voiding in urethane anesthetized female rats. As the proximal urethra may be the origin of the afferent signaling which results in the abdominal wall response, the importance of the bladder pressure increment due to this response may be in maintaining a normal duration intermittent pulsatile high frequency oscillatory (IPHFO)/flow phase and thus efficient voiding. We propose the term Voiding-associated Abdominal Response (VAR) for the physiologic voiding-associated EMG/abdominal wall response, to distinguish it from the visceromotor response (VMR) to noxious bladder distension

    Bilateral ureteropelvic disruption following blunt abdominal trauma: Case report

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    <p>Abstract</p> <p>Background</p> <p>Ureteral injury occurs in less than 1% of blunt abdominal trauma cases, partly because the ureters are relatively well protected in the retroperitoneum. Bilateral ureteral injury is extremely rare, with only 10 previously reported cases. Diagnosis may be delayed if ureteric injury is not suspected, and delay of 36 hours or longer has been observed in more than 50% of patients with ureteric injury following abdominal trauma, leading to increased morbidity.</p> <p>Case presentation</p> <p>A 29-year-old man was involved in a highway motor vehicle collision and was ejected from the front passenger seat even though wearing a seatbelt. He was in a preshock state at the scene of the accident. An intravenous line and left thoracic drain were inserted, and he was transported to our hospital by helicopter. Whole-body, contrast-enhanced computed tomography (CT) scan showed left diaphragmatic disruption, splenic injury, and a grade I injury to the left kidney with a retroperitoneal haematoma. He underwent emergency laparotomy. The left diaphragmatic and splenic injuries were repaired. Although a retroperitoneal haematoma was observed, his renal injury was treated conservatively because the haematoma was not expanding. In the intensive care unit, the patient's haemodynamic state was stable, but there was no urinary output for 9 hours after surgery. Anuresis prompted a review of the abdominal x-ray which had been performed after the contrast-enhanced CT. Leakage of contrast material from the ureteropelvic junctions was detected, and review of the repeat CT scan revealed contrast retention in the perirenal retroperitoneum bilaterally. He underwent cystoscopy and bilateral retrograde pyelography, which showed bilateral complete ureteral disruption, preventing placement of ureteral stents. Diagnostic laparotomy revealed complete disruption of the ureteropelvic junctions bilaterally. Double-J ureteral stents were placed bilaterally and ureteropelvic anastomoses were performed. The patient's postoperative progress was satisfactory and he was discharged on the 23<sup>rd </sup>day.</p> <p>Conclusion</p> <p>Diagnosis of ureteral injury was delayed, although delayed phase contrast-enhanced CT and abdominal x-rays performed after CT revealed the diagnosis early. Prompt detection and early repair prevented permanent renal damage and the necessity for nephrectomy.</p