Periodic Quality Control Research Articles

A importância do controle de qualidade em serviços de hemodinâmica e cardiologia intervencionista

OBJETIVO: Avaliar o desempenho de um equipamento de raios X utilizado em radiologia intervencionista e a qualidade de imagem produzida, aplicando alguns testes de controle de qualidade. MATERIAIS E MÉTODOS: O equipamento de raios X testado foi da marca Philips (Integris H3000), do serviço de hemodinâmica de um hospital do Rio de Janeiro. Foram utilizados objetos de teste de Leeds para avaliar a qualidade da imagem, e um sistema Radcal 9015 para medições dosimétricas. RESULTADOS: Nos modos high e normal, os valores medidos das taxas de kerma no ar foram diferentes dos esperados. Em alguns casos, os valores das taxas medidas não foram afetados pelo uso de diferentes modos de magnificação. A avaliação da qualidade da imagem apresentou resultados diferentes dos valores recomendados pelas normas. Isto pode levar à obtenção de imagens de menor qualidade e ao aumento da exposição à radiação de pacientes e profissionais. CONCLUSÃO: Os resultados mostraram a importância da aplicação periódica de testes de controle de qualidade, que permitem monitorar o desempenho do equipamento e estimar a exposição dos pacientes e trabalhadores. Os resultados obtidos sugerem a necessidade de uma revisão no sistema de aquisição de imagens do equipamento.

A series of surveys on assay for anti‐A/B antibody by Japanese ABO‐incompatible Transplantation Committee

The measurement of anti-blood groups A and B antibody (Ab) titers is considered to be important in ABO-incompatible transplantation. However, no standard method for quantitative determination has yet been established in Japan. Inter-examiner variability was likely because Ab titer was determined mainly by visual observation. In order to assess inter-institutional variation in the measurement of anti-A/B Ab titer, a series of surveys was conducted by the Japanese ABO-incompatible Transplantation Committee. In 2003, the first national survey was conducted. Serum samples from six healthy volunteers with blood groups A (n = 2), B (n = 2) and O (n = 2) were sent to 29 institutions and anti-A/B Ab titer was measured by their customary methods. Isohemagglutinin assay in serial-doubling dilutions of serum using a test tube was widely used in all institutions. Inter-institutional difference between maximum and minimum value reached as much as 32-fold in immunoglobulin M (IgM) and 256-fold in IgG. As detailed protocol for assay seemed to be different between institutions, we attempted to standardize the protocol based on the result of a questionnaire survey. In 2004, a second survey was conducted in the same manner as the previous one, except participation involved 38 institutions and the measurement was performed in a uniform way using a provisional standard protocol. Analysis of the survey revealed that intra-institutional variation was reduced to below eightfold, except that several institutions showed a large difference from the mean titer and required some guidance. A periodical quality control survey is considered necessary to improve the accuracy of measurement. Anti-A/B Ab titer would provide useful information towards the prediction of rejection and the indication of treatments such as (double filtration) plasmapheresis, splenectomy, anti-CD20 monoclonal antibody and intravenous immunoglobulin. Standardization of the assay for anti-A/B Ab titer is essential for the fulfillment of a precise multicenter study, which will elucidate the significance of the measurement of anti-A/B Ab titer.

Dynamic wedges – dosimetry and quality control

Summary Background Modern medical accelerators are usually equipped with a dynamic wedge option. It is a form of dose-rate modulation which makes use of the dynamic movement pairs of collimator jaws. Dynamic wedges may replace physical wedges but their use requires more complex dosimetry and quality control procedures. Film dosimetry has been proposed as a quality control tool in dynamic dose distribution. We present examples of extensive systematic calculation errors which were detected during complex dosimetry quality control procedures in two treatment planning systems. Aim The aim, in presenting QA procedures and examples of systematic errors which were detected and corrected, is to focus attention on the QA of dynamic accessories used in TPS before they are used in the clinical practice. This is an important issue which may have been frequently overlooked as the configuration of dynamic wedges in many treatment planning systems requires no dose measurement data. Measurements of verifications are often, overlooked. Materials/Methods Dynamic wedge dose distributions were generated by Clinac 2300 C/D accelerators (Varian) for beam energies of 6 and 15 MV. Measurements were performed with LA48 linear array of ionization chambers (PTW), and with dosimetric films X-Omat V and EDR-2 (Kodak). The dosimetric characteristics of the film were examined for a wide range of dose values and beam parameters. The results of the measurements were compared with dose distribution calculations produced by the treatment planning systems Helax and CadPlan/Eclipse. Results The initial results showed considerable differences between measurements and calculations. Larger differences were observed for larger wedge angles and lower energies. On the basis of these results, TPS manufacturers were able to tune their calculation algorithms which effectively reduced the observed differences from a level of −5.5% and −8% (for 15 and 6 MV respectively) for 60° wedges to a level of ±2% for the Helax system. Conclusions A comprehensive quality control procedure for a broad range of dynamic wedge parameters, on a Clinac 2300C/D, made it possible to achieve an improved agreement between measured and calculated results in radiotherapy. Such measurement procedures should be included in the recommendations for periodic quality control tests of accelerators.

TH-A-I-609-01: Design and Performance Characteristics of Digital Radiographic Receptors

Digital radiographic receptors have been available in medical imaging for the last two decades, but are just now becoming commonplace in the clinical environment in conjunction with the deployment and implementation of electronic image acquisition, display and archiving in radiology and the medical enterprise. Therefore, a need exists to identify the design and performance characteristics of these detectors to determine an appropriate system for a specific or general clinical task, and to keep abreast of the technological changes and innovations that are constantly occurring. Devices include Computed Radiography (CR) using photostimulable phosphor detectors, Charge-Coupled-Device (CCD) and Complementary Metal-Oxide Semiconductor (CMOS) cameras optically coupled to a phosphor scintillator, slot-scan CCD technology with linear or rectangular arrays, and thin-film-transistor (TFT) two-dimensional arrays coupled to phosphor converters and photodiodes or semiconductor detectors. Because digital devices produce images that are inherently signal to noise ratio limited (rather than contrast limited as is the case with analog film), each is designed to provide high spatial resolution simultaneous to delivering high detective quantum efficiency, and at the same time attempting to achieve low radiation dose. Some digital systems do this better than others. Quantitative analysis yields performance metrics including modulation transfer function (MTF), noise power spectrum (NPS), and detective quantum efficiency (DQE). Detector system applicability to a given imaging task, system cost, portability, image handling and practicality are issues that must be considered prior to purchase and implementation. This presentation gives the attendee an overview of these issues. Educational Objectives: 1. To understand the variety of digital detector technologies for medical radiography and mammography 2. To provide an overview of each detector from a physics/quantitative perspective 3. To compare the detectors in terms of image quality and radiation dose 4. To review some issues regarding acceptance testing and periodic quality control 5. To summarize the pros and cons with respect to user function, system integration, and costs

On Improving Navigation Accuracy of GPS/INS Systems

Direct georeferencing, also referred to as direct platform orientation (DPO), is defined as direct measurement of the imaging sensor external orientation parameters (EOP), using positioning and orientation sensors, such as the Global Positioning System (GPS) and Inertial Navigation System (INS) or Inertial Measurement Unit (IMU). Imaging sensors, most frequently supported by the DPO technique, are digital cameras, lidar systems, multi-spectral or hyper-spectral scanners, or interferometric synthetic aperture radar (INSAR). While for scanning sensors the use of DPO is compulsory, frame digital cameras can also directly benefit from this modern technique of sensor orientation. With direct sensor orientation, the requirement for ground control, tie-point matching and aerotriangulation (AT) is significantly reduced, or even entirely eliminated, resulting in shorter times of data acquisition and processing, and streamlined and highly automated data workflow and quality control. Most of the time, the requirement for ground control points is limited to periodic system calibrations and quality control check. Direct georeferencing is considered a fundamental technology of conventional mobile mapping systems (MMS). Despite significant progress in GSP/INS-based direct georeferencing technology in the last decade, there is still room for improvement in terms of better accuracy and better tolerance to GPS outages. This paper is focused on three error modeling and compensation techniques that could potentially improve GPS/INS system's performance on both land-based and airborne platforms: (1) extended gravity compensation, (2) IMU signal de-noising, and (3) stochastic modeling of IMU errors.

Mensuration and Cleaning of the Jets in Andersen Cascade Impactors

Fifty-three Andersen Cascade Impactors (404 stages) have been investigated using an automated visual stage mensuration technique. A cleaning method was suggested for stages with jets smaller than nominal diameters. The impact of nonapproved jet diameters on result parameters from particle size analysis was evaluated theoretically. The jet diameters were measured using the Andersen Visual Inspection Device. A stepwise cleaning procedure was performed to recover the jets of noncompliant stages, and after each step a new stage mensuration was performed. The result of this extensive investigation, including measurements of each jet, is compared to other studies, to tolerance limits applied at AstraZeneca Lund and also to limits used by the manufacturer. Sixteen of the investigated stages were outside applied tolerance limits due to too small average diameters. Insertion of a go gauge into every jet of the stages was the only technique of those tested that increased the jet diameters toward nominal dimensions. Moreover, the relative standard deviation of the jet diameters decreased considerably after use of go gauges. Stage mensuration is a valuable technique for detection of improper jet dimensions of the Andersen Cascade Impactor, and use of go gauges is an effective cleaning method especially for jets with small diameters. However, use of stop/go gauges as a periodical quality control test on a small number of randomly selected jets was a poorly discriminating test, as both compliant and noncompliant stages would most probably pass such a test.

Étude de la faisabilité du scorage automatique de fantômes mammographiques par traitement d’image

Nowadays, X-ray mammography is one of the most effective methods for early and reliable breast cancer detection and diagnosis. Periodic quality control in mammographic facilities is necessary to provide high quality mammograms. This evaluation is done by visual observation of mammographic phantom films. To prepare Full Field Digital Mammography advent and to get rid of this subjective quality control, digital image and signal processing techniques may be used in order to make this control easier and more objective. This paper presents an automatic method for scoring mammographic phantoms using digital image processing. Phantom films were first digitized and images containing microcalcifications, masses and fibers were extracted. Theses noisy and low contrasted images were preprocessed using an adaptive contrast enhancement method and then segmented in order to extract objects embedded in phantom images. Nine digitized phantom films were studied and results show that a more objective quality control evaluation of mammographic facilities can be done using digital image processing techniques on phantom images.

Essential issues of laboratory investigation for patients with haemophilia and bleeding disorders.

Apart from history-taking and physical examination, laboratory investigation is one of the essential issues for the definite diagnosis of haemophilia and bleeding disorders. The limited resources of medical personnel, equipment and reagents should be shared among several departments in the hospital, especially for serving patients with common genetic diseases such as thalassemia and haemoglobinopathies. Medical personnel require appropriate training to expand their skills in laboratory techniques. Laboratory procedures can be created, modified and simplified using locally produced and shared equipment. Molecular genetic studies can also be set up at different levels of hospital service using simple, rapid and low-cost methods. Finally, a system of periodic external quality control will guarantee the accuracy of laboratory results.

A correction method for diamond detector signal dependence with proton energy.

Small dosimeters as solid state detectors can be useful for the dosimetric characterization and periodic quality control of radiotherapy proton beams. The calibration of solid state detectors for proton beams is not a solved problem especially for ophthalmologic proton beams, where these detectors present a LET-dependent signal. In this work a PTW diamond detector has been selected because of its good signal reproducibility (0.3%) and stable response with accumulated dose. A method that takes into account the LET dependence of the diamond detector signal, at 62 MeV proton beam, is here proposed. In particular an empirical correction factor, kDD(Eo) (Rres), has been determined as a function of the residual range quality index, to correct the diamond detector signal for a proton beam of incident effective energy E0= 62 MeV. A dedicated software allows us to use the diamond detector as an on-line reference dosimeter, where an ionization chamber may be difficult to use, or for periodic quality control procedures. The article also reports a comparison between the signal dependence on proton energy of silicon, diamond, and radiochromic film detectors.

The saturation loss for plane parallel ionization chambers at high doseper pulse values

The use of plane parallel ionization chambers with electron beams with highdose per pulse entails dose uncertainties due to the overestimation of the ionrecombination factor, k, up to 20% if conventional dosimetric protocols areused. In this work MD-55-2 radiochromic films have been used as referencedosimeters to obtain dose to water per pulse DGAFw values for threeNovac7 (Hitesys) electron beams of E0 = 5.8 MeV. However, the beamcalibration by MD-55-2 films is time consuming and the use of plane parallelchambers is fundamental for a periodic quality control procedure. Three planeparallel chambers have been used and the general formula for the kdetermination has been tested using the calibration doses, DGAFw. Inparticular, consistent ion recombination factors ksat(V0) (with theion chamber polarized at V0), that follow the Boag theory, have beenestimated at different dose per pulse values for the three plane parallelionization chambers. This means that at present any ion chamber needs aspecific ksat(V0) determination by using a reference dosimeter forwhich the response is independent of the dose rate. An accurate determinationof ksat(V0), using a reference quality beam, can be used todetermine the dose to water per pulse for electron beams of different qualityand geometrical configuration.

Rapid Non-Destructive Raw Material Identification in the Cosmetic Industry with Near-Infrared Spectroscopy

Since January 1997 manufacturers of cosmetics products have to follow GMP guidelines. The manufacturer is required to supply extensive product information, comprehensive and exact production guidelines, analytical controls and detailed raw material data. As a result it is strongly recommended to each manufacturer of cosmetic products to install a quality control department. Regulations already accepted and applied in the Pharmaceutical Industry are expected to become more and more important for the cosmetic industry as well. In order to meet legal requirements the cosmetic industry will be forced to instigate a periodical quality control. To accommodate this protocol each container must be checked to see if the content corresponds to the description on the packaging material. A fast and reliable technology is necessary to fulfil these demands! Near-Infrared (NIR) technology plays an increasingly important role in manufacturing as industry strives to improve quality and process efficiency while reducing costs. By controlling the identity of every raw material container, rather than just a small number of samples, a significantly processing benefit will be assured.

Training in colposcopy: experience with a videocolposcopy test.

The authors evaluate the results of a videocolposcopy test (330 total cases, 12 cases of histologically confirmed CIN2 or more severe lesions) taken by 9 accredited and 17 unaccredited colposcopists during 1995. Seven of 9 accredited and 4 of 13 unaccredited colposcopists reached the requested standard (sensitivity > 90%, biopsy rate < 60%). Performance was definitely better when the test was not blind to the cytologic report (4 of 13 reached the requested standard) with respect to blind reading (none of 17). The study confirmed that colposcopy at unaccredited practices is poorly accurate. Colposcopic assessment of patients with abnormal smears should be centralized in accredited practices, which should undergo periodic quality control to guarantee screening efficacy. Tape-recorded videocolposcopy tests are a good, simple, practical and inexpensive method for interobserver quality control of colposcopic performance.

Analysis of the causes of false negative cytology reports on breast cancer fine needle aspirates

Forty-six (2.9%) false negative reports were recorded among adequate fine needle aspirates from 1609 consecutive histologically proven carcinomas, observed from 1991 to 1993. False negatives were more frequent among younger women (< 40 years = 7.1; 40-49 years = 4.0; 50-59 years = 3.6; 60-69 years = 1.7; > 69 years = 1.5%), lobular invasive subtypes (5.4%), and smaller tumours (pT1a = 4.2; pT1b = 7.6; pT1c = 1.9; pT2 = 2.1; pT3-4 = 1.5%). The latter findings is probably ascribable to better differentiation and less precise sampling of small non-palpable tumours. No significant association was found between the false negative rate and the sampler's or reader's skill and experience. The former finding may be ascribed to the wide use of sonography guided aspiration, even for palpable masses, and the latter to the fact that readers were highly experienced and undergo periodic quality control of individual performance. False negatives were reclassified at reviews as true false negatives, reading errors or inadequates in 27, 11, and eight cases, respectively. The observed findings suggest that in most cases cytological faults were due to the absence of cytological atypia in cells sampled from well differentiated tumours, rather than to misinterpretation or sampling from adjacent normal tissues.

Development and testing of SAR-visualizing phantoms for quality control in RF hyperthermia.

A new prototype of an elliptical standard phantom with fat-equivalent walls and a lamp matrix for SAR (specific absorption rate) visualization has been developed. This paper outlines the manufacture of solid components based upon either polyester resin or epoxy resin, as well as the adjustment of their electrical conditions (epsilon r, sigma) by admixtures of carbon and/or aluminium powder. Visualizing sensors (LED = light-emitting diodes, miniature lamps) are evaluated with respect to their transformation of electric field strength into light. Standard SAR patterns of the hyperthermia system BSD-2000 have been semiquantitatively assessed by the visualizing technique (power stepping method) and quantitatively by E field sensor scans. Extracted iso-SAR distributions are in good agreement with E field sensor scans performed with a lamp sensor coupled to a fibre or using a dipole probe with high resistive leads. The requirement for periodic quality control of SAR patterns of RF (radio frequency) hyperthermia systems is demonstrated. Comparisons between techniques are given, specifically with respect to the LED phantom of Schneider and van Dijk.

Cluster of Enterobacter cloacae pseudobacteremias associated with use of an agar slant blood culturing system.

From 1 February through 12 October 1990, 27 blood cultures processed at Shiprock Hospital were positive for Enterobacter cloacae; only 3 had been reported in the preceding 12 months. Twenty (74%) of the cultures were obtained from patients without clinical evidence of gram-negative septicemia. The increase in E. cloacae-positive blood cultures was temporally associated with the introduction of a new blood culturing system. To evaluate potential risk factors for an E. cloacae-positive blood culture (case-culture), we conducted a case-control study. Case-cultures were compared with 81 randomly selected cultures that were processed during the epidemic period and that were not positive for E. cloacae (controls). Because several factors suggested the possibility of pseudoinfection, we limited our analysis to the 20 blood cultures that appeared to be contaminants. Blood samples received in the laboratory during the midnight shift (5 of 20 [25%] versus 5 of 81 [6%]; odds ratio, 5.1; 95% confidence intervals, 1.01 to 24.6; P = 0.02) or present in the incubator with other E. cloacae-positive samples (17 of 20 [85%] versus 29 of 81 [36%]; odds ratio, 10.2, 95% confidence interval, 2.6 to 57.3; P < 0.001) were at increased risk for contamination. During mock experiments of the procedures for processing blood samples for culture, several breaks in aseptic technique and leakage from the blood culturing system were observed. Cultures of samples obtained from several environmental sites in the laboratory and the hand washings of two laboratory technicians grew E. cloacae. Plasmid and restriction enzyme analyses of E. cloacae isolates recovered from the patients' blood cultures, the two technicians' hand washings, and environmental sites in the laboratory indicated that all had identical plasmid profiles. Our findings suggest that the breaks in aseptic technique and the environmental contamination that occurred in association with the use of the new blood culturing system resulted in contamination of the blood cultures. This outbreak highlights the importance of routine environmental cleaning, periodic quality control assessments, and adherence to aseptic practices in clinical laboratories, particularly when new methods or equipment are introduced and/or new personnel are hired.

Measurement quality assurance.

The quality of a radiation protection program can be no better than the quality of the measurements made to support it. In many cases, that quality is unknown and is merely implied on the basis of a calibration of a measuring instrument. If that calibration is inappropriate or is performed improperly, the measurement result will be inaccurate and misleading. Assurance of measurement quality can be achieved if appropriate procedures are followed, including periodic quality control actions that demonstrate adequate performance. Several national measurement quality assurance (MQA) programs are operational or under development in specific areas. They employ secondary standards laboratories that provide a high-quality link between the National Bureau of Standards and measurements made at the field use level. The procedures followed by these secondary laboratories to achieve MQA will be described, as well as plans for similar future programs. A growing general national interest in quality assurance, combined with strong specific motivations for MQA in the area of ionizing radiation, will provide continued demand for appropriate national programs. Such programs must, however, employ procedures that are cost effective and must be developed with participation by all affected parties.

A degradation model for metallized polyester capacitors

Till now it was usual to think that the physical degradation of the end-spray contacts of metallized polyester capacitors, accelerated by exposure to high temperature, only implied an increase of the equivalent series resistance. This paper reports that together with this resistance increase, a contribution due to a parasitic capacitance must be taken into account to describe this degradation mechanism correctly. A degradation model is presented that enables fairly good fitting of experimental measurements of capacitance, dissipation factor and impedance vs. frequency of capacitors submitted to long-term tests, that exhibit an electrical behaviour deviating from the one described by the usual equivalent series circuit. The paper illustrates a technological analysis method that enables the consistence of the proposed model to be confirmed and that can currently be used to make quick estimations of the reliability performance of components by different manufacturers and to carry out periodic quality control. It was also seen that, in well manufactured capacitors, the described degradation mechanism is rather slow, with respect to the high temperature exposure time, so that the reliability level of these components is not affected.

Application de la technique d'immunodiffusion radiale à la détermination du titre d'un immunserum spécifique

The authors determine the titre of two monospecific immunosera by the radial immunodiffusion method. Because of the precision and rapidity of this technique, it is most suitable for: — periodic quality control of an immunoserum — the quantitative estimation of specific immunoglobulins adsorbed to the supporting medium in affinity chromatography.