Comparison of ultrasound quality assurance phantom measurements from matched and mixed scanner-transducer combinations.

Our goal in this work was to compare the results of common phantom tests made using matched and mixed ultrasound (US) scanner-transducer combinations. Sets of common US quality assurance (QA) measurements were made using matched US scanner-transducer combinations (i.e., transducers purchased for use with a particular scanner), as well as unmatched (mixed) combinations. Measurements of vertical and horizontal distance accuracy, and depth of penetration were performed using three common transducer types. Means, standard deviations, and differences between the mean mix and match measurements divided by the standard deviation (match-mix difference, or MMD), and two-sided, paired t-tests were computed for the groups of mixed and matched measurements. MMDs for vertical and horizontal distance accuracy test results were less than 0.87 in all cases, well below our threshold value of 2.0, which indicates that a significant difference exists. MMDs for the depth of penetration measurements were less than 1.50, again below the threshold value. These results suggest that all of the mixed and matched data sets were very similar. The more sensitive t-tests indicate statistically significant differences in only 2 of the 18 pairs of data sets. In conclusion, this study suggests that QA measurements generated by mixed or matched scanner-transducer combinations are very comparable. The ability to obtain QA phantom test data from mixed scanner-transducer combinations reduces the time required for US QA testing.

Artefacts found in computed radiography.

Artefacts on radiographic images are distracting and may compromise accurate diagnosis. Although most artefacts that occur in conventional radiography have become familiar, computed radiography (CR) systems produce artefacts that differ from those found in conventional radiography. We have encountered a variety of artefacts in CR images that were produced from four different models plate reader. These artefacts have been identified and traced to the imaging plate, plate reader, image processing software or laser printer or to operator error. Understanding the potential sources of CR artefacts will aid in identifying and resolving problems quickly and help prevent future occurrences.

Quantification of fluoroscopic imaging system contrast by using video waveform monitoring.

A noninvasive method was developed for quantifying the overall contrast of fluoroscopic imaging systems within the clinical setting by using a simple phantom and common video test equipment. In this method, an acrylic phantom with four holes filled with varying amounts of air and aluminum is placed on the entrance exposure side of a patient-equivalent acrylic phantom. The air- and aluminum-filled holes provide a stepped gray-scale pattern that is displayed on the examination room viewing monitor when the phantom is fluoroscopically imaged under automatic brightness control. A video waveform monitor or oscilloscope is then used to quantify those video signal voltage levels as a contrast index value, which is defined as the maximum range of the video signal voltage levels of the gray-scale steps. The method is repeatable and allows quantification of the contrast of the imaging system. It can also be used to optimize video parameters, provide comparative data for quality control monitoring, and characterize overall contrast differences between systems. Experience with this method suggests that there is excellent correlation between the clinical perception of image contrast and the contrast index, with contrast index changes of approximately 15% being seen clinically.

Real-time measurement of radiation exposure to patients during diagnostic coronary angiography and percutaneous interventional procedures.

OBJECTIVES: The aim of this study was to accurately assess the radiation exposure received by patients during cardiac catheterization in a large sample representative of the current state of practice in cardiac angiography. BACKGROUND: Radiation exposure to patients and laboratory staff has been recognized as a necessary hazard in coronary angiography. The effects on x-ray exposure of the increased complexity of coronary angiographic procedures and, in particular, the increasing use of coronary artery stenting, have not been adequately addressed in previous studies. METHODS: X-ray exposure measurements were performed on a consecutive series of 972 patients undergoing 992 diagnostic and interventional studies in the Mayo Clinic catheterization laboratory within an eight week period in late 1997. Data were acquired from 706 diagnostic procedures and 286 interventional procedures using a real-time exposure measurement system to continuously calculate and record the exposure rate and total exposure, reflecting all parameters relevant to the specific patient and procedure situation. RESULTS: The median exposure for all 992 procedures was 41.8 mC/kg (162.1 R); the corresponding values for diagnostic and interventional procedures were 34.9 and 95.6 mC/kg, respectively (135.3 vs. 370.5 R). There were significant differences in the fluoroscopy exposure time between diagnostic and interventional procedures: 4.7 min vs. 21.0 min. Heavier patients (>83 kg) received x-ray exposures at a significantly higher rate than did lighter patients (<83 kg) during both fluoroscopy and cine; 44.9 mC/kg/min (173.9 R/min) vs. 27.9 mC/kg/min (108.3 R/min) for cine exposure rate and 2.3 mC/kg/min (8.8 R/min) vs. 1.5 mC/kg/min (5.8 R/min) for fluoroscopy exposure rate. CONCLUSIONS: Changes in practice have led to higher values for patient x-ray radiation exposures during cardiac catheterization procedures. The real-time display and recording of x-ray exposure facilitates the reduction of exposure in the catheterization laboratory.

Quantitative evaluation of low-cost frame-grabber boards for personal computers.

Nine moderately priced frame-grabber boards for both Macintosh (Apple Computers, Cupertino, CA) and IBM-compatible computers were evaluated using a Society of Motion Pictures and Television Engineers (SMPTE) pattern and a video signal generator for dynamic range, gray-scale reproducibility, and spatial integrity of the captured image. The degradation of the video information ranged from minor to severe. Some boards are of reasonable quality for applications in diagnostic imaging and education. However, price and quality are not necessarily directly related.

Effects of ionizing radiation and magnetic fields on digital data stored on floppy disks.

PURPOSE: To evaluate the effect of x rays and magnetic fields on high-density, 3.5-inch floppy disks. MATERIALS AND METHODS: A 1-Mbyte worksheet file was stored on 20 recently purchased high-density floppy disks. Five disks were stored as controls. Five other disks were then exposed to 70-kVp and 6-MV x rays with exposures of 100-1,000 R (0.026-0.26 C.kg-1). Ten other disks were exposed to magnetic fields with a maximum strength of 1,000 G. Magnetic fields around an airport metal detector and x-ray unit were measured. Another set of 10 disks was passed through the metal detector 50 times and through the x-ray unit 12 times. RESULTS: Ionizing radiation had no effect on the data stored on the disks. Magnetic fields with a maximum strength of 500 G had no effect, but field strengths of 1,000 G completely erased the data. Neither the airport metal detector nor the x-ray unit had any effect on the data. CONCLUSION: Airport metal detectors and x-ray scanners have no effect on digital data stored on floppy disks.