A MONTE-CARLO SIMULATION FRAMEWORK FOR JOINT OPTIMISATION OF IMAGE QUALITY AND PATIENT DOSE IN DIGITAL PAEDIATRIC RADIOGRAPHY.

In paediatric radiography, according to the as low as reasonably achievable (ALARA) principle, the imaging task should be performed with the lowest possible radiation dose. This paper describes a Monte-Carlo simulation framework for dose optimisation of imaging parameters in digital paediatric radiography. Patient models with high spatial resolution and organ segmentation enable the simultaneous evaluation of image quality and patient dose on the same simulated radiographic examination.

ITERATIVE SCATTER CORRECTION FOR GRID-LESS BEDSIDE CHEST RADIOGRAPHY: PERFORMANCE FOR A CHEST PHANTOM.

The aim of this work was to experimentally compare the contrast improvement factors (CIFs) of a newly developed software-based scatter correction to the CIFs achieved by an antiscatter grid. To this end, three aluminium discs were placed in the lung, the retrocardial and the abdominal areas of a thorax phantom, and digital radiographs of the phantom were acquired both with and without a stationary grid. The contrast generated by the discs was measured in both images, and the CIFs achieved by grid usage were determined for each disc.

Comparison of radiologist and CAD performance in the detection of CT-confirmed subtle pulmonary nodules on digital chest radiographs.

Objectives: Detection of subtle pulmonary nodules on digital radiography is a challenging task for radiologists. The aim of this study was to evaluate the performance of a newly approved computer aided detection (CAD) system.

Materials And Methods: The sensitivity of 3 radiologists and of a CAD system for the detection of pulmonary nodules from 5 to 15 mm in size on digital chest radiography of 117 patients was compared.

Digital chest radiography: an update on modern technology, dose containment and control of image quality.

The introduction of digital radiography not only has revolutionized communication between radiologists and clinicians, but also has improved image quality and allowed for further reduction of patient exposure. However, digital radiography also poses risks, such as unnoticed increases in patient dose and suboptimum image processing that may lead to suppression of diagnostic information. Advanced processing techniques, such as temporal subtraction, dual-energy subtraction and computer-aided detection (CAD) will play an increasing role in the future and are all targeted to decrease the influence of distracting anatomic background structures and to ease the detection of focal and subtle lesions.

Measurement of the modulation transfer function of digital X-ray detectors with an opaque edge-test device.

A variant of the edge method for the determination of the pre-sampled modulation transfer function (MTF) of digital X-ray imaging devices has been developed and accepted as the standard method in the novel DQE measurement standard IEC 62220-1. An opaque tungsten edge-test device accomplishes the ideal step-like profile of the incident X rays. The edge spread function is measured over a large region across the edge transition that enables an accurate MTF measurement including the 'low-frequency drop'.

Retrospective patient dose analysis of a digital radiography system in routine clinical use.

The log files generated in the flat-panel detector based digital radiography systems (Philips Digital Diagnost) at 11 different hospitals were used to acquire data regarding the dose-area product (DAP) and the entrance air kerma (EAK) for all X-ray examinations performed in routine clinical use. A retrospective statistical analysis of the data with respect to the dose levels was performed for several examination types. The resulting average dose levels were compared with the diagnostic reference levels (DRLs).

Status and prospects of digital detector technology for CR and DR.

Projection radiography is in the middle of the transition from conventional screen-film imaging to digital image acquisition modalities, mainly based on imaging plates (computed radiography, CR) and flat-panel detectors (direct radiography, DR). Cassette-based CR has been available for the past 20 y, and constitutes the major part of direct radiography installations in hospitals today. direct radiography systems based on large-area amorphous silicon active matrix arrays are commercially available for the last 5 y and exist basically in two different types: with scintillators or photoconductors as X-ray conversion material ('indirect' or 'direct' type).

Flat-panel-detector chest radiography: effect of tube voltage on image quality.

Purpose: To compare the visibility of anatomic structures in direct-detector chest radiographs acquired with different tube voltages at equal effective doses to the patient.

Materials And Methods: The study protocol was approved by the institutional internal review board, and written informed consent was obtained from all patients. Posteroanterior chest radiographs of 48 consecutively selected patients were obtained at 90, 121, and 150 kVp by using a flat-panel-detector unit that was based on cesium iodide technology and automated exposure control.

Determination of the modulation transfer function using the edge method: influence of scattered radiation.

The edge method for measuring the modulation transfer function (MTF) has recently gained popularity due to its simplicity and appropriateness particularly for digital imaging systems. Often edge test devices made of rather thin metal sheets are used, which are semitransparent to x rays and may generate scattered radiation. The effect of this scattered radiation on the determined MTF was investigated both theoretically (assuming an ideal detector) and experimentally using a CsI-based digital detector.

Determination of the detective quantum efficiency of a digital x-ray detector: comparison of three evaluations using a common image data set.

The detective quantum efficiency (DQE) of an x-ray digital imaging detector was determined independently by the three participants of this study, using the same data set consisting of edge and flat field images. The aim was to assess the possible variation in DQE originating from established, but slightly different, data processing methods used by different groups. For the case evaluated in this study differences in DQE of up to +/-15% compared to the mean were found.

Comparison of an automatic versus a semiautomatic mode for gray-scale adaptation for digital chest radiography.

Purpose: To compare image quality of digital chest radiographs using 2 modes of gradation adjustment.

Methods: We compared image quality and visualization of anatomic landmarks of 50 chest radiographs after digital processing using a semiautomatic mode with a fixed gamma of 2.6 and an automatic mode with individual gamma adaptation.

Skeletal applications for flat-panel versus storage-phosphor radiography: effect of exposure on detection of low-contrast details.

Purpose: To compare exposure requirements for similar detection performance with flat-panel detectors and the most recent generation of storage-phosphor plates in the simulated scatter of typical skeletal radiographic examinations.

Materials And Methods: A contrast-detail test object was covered with varying thicknesses of acrylic to simulate skeletal exposure conditions in the wrist, knee, and pelvis. Three series were obtained with increasing thicknesses of a simulated soft-tissue layer (5, 10, and 20 cm) and increasing tube voltage (50, 70, and 90 kVp).

Accuracy of a simple method for deriving the presampled modulation transfer function of a digital radiographic system from an edge image.

Several methods for accurately deriving the presampled modulation transfer function (MTF) of a pixelated detector from the image of a slightly slanted edge have been described in the literature. In this paper we report on a simple variant of the edge method that produces sufficiently accurate MTF values for frequencies up to the Nyquist frequency limit of the detector with little effort in edge alignment and computation. The oversampled ESF is constructed in a very simple manner by rearranging the pixel data of N consecutive lines corresponding to a lateral shift of the edge by one pixel.

Principles of image processing in digital chest radiography.

Image processing has a major impact on image quality and diagnostic performance of digital chest radiographs. Goals of processing are to reduce the dynamic range of the image data to capture the full range of attenuation differences between lungs and mediastinum, to improve the modulation transfer function to optimize spatial resolution, to enhance structural contrast, and to suppress image noise. Image processing comprises look-up table operations and spatial filtering.

Direct digital radiography versus storage phosphor radiography in the detection of wrist fractures.

Aim: To define the value of digital radiography with a clinical flat panel detector system for evaluation of wrist fractures in comparison with state of the art storage phosphor radiography.

Material And Methods: Hard copy images of 26 fractured wrist specimens were acquired with the same exposure dose on a state of the art storage phosphor radiography system and a clinical flat panel detector. Image features like cortical bone surface, trabecular bone, soft tissues and fracture delineation were independently analysed by 4 observers using a standardised protocol.