Practical assessment of the display performance of radiology workstations

The performance of 14 primary clinical display monitor workstations in use in the Radiology Department of a large acute NHS Trust was assessed using the methods and guidelines described by the American Association of Physicists in Medicine Task Group 18. Tests undertaken included the measurement of ambient light, display uniformity, luminance ratio, luminance response, maximum luminance and spatial resolution. Four display monitors failed to meet at least one of the test's guideline tolerances. In addition a number of display monitors were found to be operating at settings that might reduce their useful life span. These devices were either replaced or recalibrated by the installers, or were subject to local adjustment to ensure applicable standards were met. Consequently the study suggests that quality assurance testing of display monitors used for image reporting is necessary and valuable to ensure that images are viewed at an appropriate standard.

A survey of MRI quality assurance programmes

There are currently no national guidelines on appropriate quality assurance (QA) test frequencies for MRI equipment in clinical use. From a random selection of 45 hospitals in England, who were contacted by phone, 35 hospitals agreed to participate in a survey of MRI QA and were sent a questionnaire requesting information on the range and frequency of QA tests, as well as the staff groups who conduct these tests. Twenty-four completed replies were received, representing a 68% response rate from the distributed questionnaires. Of these, 79% undertook some form of QA, typically conducted by the radiographic staff. Tests were most often undertaken on the head coil, but there was a considerable variation in the frequency and range of tests undertaken at different hospitals. For example, exactly half of the respondents conducted signal to noise ratio (SNR) tests on both head and body coils, but only 13% of centres extended this test to other coils. Results from this survey should inform radiology departments regarding practice at other hospitals and should assist in formulating the frequency and scope of appropriate MRI QA programmes.

Patient dose optimization in plain radiography based on standard exposure factors

A computational technique for assessing patient dose in plain radiography is described allowing a large number of examinations to be assessed and enabling dose optimization to be promoted. Entrance surface dose (ESD) was calculated for more than 1500 standard exposure settings in an initial dose assessment. Validation of the technique showed good agreement with thermoluminescent dosimetry and showed broad agreement between the standard exposures and the exposure settings used in practice. The dose assessment was repeated 18 months later using the same techniques for almost 2000 standard exposure settings. In both cases, calculated doses showed good compliance with national diagnostic reference levels where available. Suggested investigation levels were established and set at twice the mean dose for each of 47 examinations. Radiology departments were encouraged to review and optimize doses exceeding these levels. The computed mean ESD in the review study was less than the corresponding value in the initial study in 37 of the 47 examinations. The dose reduction was attributable partly to equipment replacement, but primarily to optimization of exposure settings. The technique employed here provides a valid and cost effective method of complying with statutory requirements for the assessment of representative patient dose and is useful in assisting the ongoing process of dose optimization.

Variations in radiation dose between the same model of multislice CT scanner at different hospitals

The variation in exposure factors and patient dose, between seven centres using identical multislice CT scanners, was investigated for six standard examinations. Dose values were compared with each other and the relevant diagnostic reference level (DRL) for each examination. The range in weighted CT dose index (CTDI(w)) values between the seven centres was small for abdominal scans and head scans. For other scans however, such as functional endoscopic sinonasal surgery (FESS) the variations in CTDI(w) were as high as a factor of seven between the lowest and the highest values. At one centre a program of dose optimization had been undertaken and this centre had CTDI(w) values ranging from 3% to 64% lower than the average value for the seven centres. This demonstrates that significant dose reduction can be achieved through close collaboration between medical physicists, radiologists and radiographers.