Management of malignant pleural effusion: challenges and solutions.

Malignant pleural effusion (MPE) is a sign of advanced cancer and is associated with significant symptom burden and mortality. To date, management has been palliative in nature with a focus on draining the pleural space, with therapies aimed at preventing recurrence or providing intermittent drainage through indwelling catheters. Given that patients with MPEs are heterogeneous with respect to their cancer type and response to systemic therapy, functional status, and pleural milieu, response to MPE therapy is also heterogeneous and difficult to predict. Furthermore, the impact of therapies on important patient outcomes has only recently been evaluated consistently in clinical trials and cohort studies. In this review, we examine patient outcomes that have been studied to date, address the question of which are most important for managing patients, and review the literature related to the expected value for money (cost-effectiveness) of indwelling pleural catheters relative to traditionally recommended approaches.

Clinical apparatus for the reduction of dose area product for patients undergoing x-ray catheterization.

PURPOSE: The authors describe a design for prepatient region of interest attenuators (ROIAs) to reduce dose area product (DAP) for clinical use. The authors describe a model to predict DAP values from x-ray technique parameters recorded during a clinical procedure for image sequences obtained in the presence or absence of ROIAs. The model was developed primarily to determine what the DAP to a patient undergoing cardiac catheterization with a ROIA would have been if no ROIA had been used allowing a determination of DAP reduction. METHODS: Copper ROIAs with thicknesses that vary gradually so as not to cause significant image artifacts were constructed. X-ray image sequences were acquired on a clinical catheterization system with and without ROIAs with varying x-ray technique parameters. DAP values were measured for all said exposures using an ionization chamber and compared to a model the authors developed. RESULTS: The model can predict DAP values within 3.5% on average with or without ROIAs when compared to ionization chamber measurements. CONCLUSIONS: The proposed experimental design is adequate for measuring DAP reductions on the order of 1.5-3.5 that are expected when introducing a ROIA during patient catheterization imaging.

The geometric calibration of cone-beam systems with arbitrary geometry.

A method is proposed to determine the cone-beam x-ray acquisition geometry of an imaging system using a phantom consisting of discrete x-ray opaque markers defining two parallel rings sharing a common axis. The phantom generates an image of two ellipses which are fitted to an ellipse model. A phantom-centric coordinate system is used to simplify the equations describing the ellipse coefficients such that a solution describing the acquisition geometry can be obtained via numerical optimization of only three of the nine unknown variables. We perform simulations to show how errors in the fit of the ellipse coefficients affect estimates of the acquisition geometries. These simulations show that for ellipse projections sampled with 1200 markers, 25 microm errors in marker positions and a source-detector distance (SDD) of 1.6 m, we can measure angles describing detector rotation with a mean error of <0.002 degrees and a standard deviation (SD) of <0.03 degrees. The SDD has a mean error of 0.004 mm and SD = 0.24 mm. The largest error is associated with the determination of the point on the detector closest to the x-ray source (mean error = 0.05 mm, SD = 0.85 mm). A prototype phantom was built and results from x-ray experiments are presented.

The physics of computed radiography: measurements of pulse height spectra of photostimulable phosphor screens using prompt luminescence.

Computed radiography (CR) is a digital technology that employs reusable photostimulable phosphor (PSP) imaging plates (IP) to acquire radiographic images. In CR, the x-ray attenuation pattern of the imaged object is temporarily stored as a latent charge image within the PSP. The latent image is optically readout as photostimulated luminescence (PSL) when the phosphor is subsequently stimulated using a scanning laser. The multiple stages necessary to create a CR image make it difficult to investigate either experimentally or theoretically. In order to examine the performance of the CR system at a fundamental level separate measurements of the processes involved are desirable. Here pulse height spectroscopy is used to study the prompt violet light emission or prompt luminescence (PL) from commercial PSP screens. Since the mechanism by which light escapes from the phosphor is identical for PL and PSL, observations and conclusions based on the pulse height spectra (PHS) of PL are relevant to the understanding of the behavior of the PSL light emission that outputs the radiographic image in CR. The PL PHS of screens of different thickness and optical properties were measured and compared with the PHS of conventional phosphors. A new method for calibration of the PHS in terms of the absolute number of optical photons per x-ray is introduced and compared to previously established methods.