Reproducibility of Leeds TOR(MAM) mammographic test object plates.

Image quality test objects are essential tools for quality assurance in any branch of radiology. A major problem in test object construction is to make all examples of the test object closely comparable so that results from different examples can be compared. In mammography, the TOR(MAM) test object is considered to be the most sensitive of those generally available in the UK. This paper reports a comparison of 19 examples of this test object design, using five film scorers. Small differences in mean score were found to be statistically significant in about half of the test object plates tested. However, none of the plates differed from the overall mean at the 95% confidence level. Mean differences of score between single plates did not exceed 8%.

Short communication: kilovoltage measurement with rhodium target and filters on mammography X-ray machines.

X-ray machines used for mammography have, until recently, almost exclusively employed molybdenum (Mo) as anode material and filtration. In the UK, the RMI model 232 kVp meter is used extensively for the measurement of kilovoltage on such equipment. This unit is provided with switchable internal calibration only for molybdenum and molybdenum, or tungsten and aluminium, as anode and filtration, respectively. However, rhodium (Rh) has recently been introduced for filtration with either a molybdenum or rhodium anode in mammography equipment but, as yet, calibration facilities are not available for rhodium spectra. In this work, appropriate corrections for readings obtained with the RMI 232 kVp meter are derived for use with rhodium as filtration material with either molybdenum or rhodium anode material. An intercomparison between measurements made with four RMI model 232 kVp meters and nine IGE DMR X-ray sets was undertaken. The reproducibility of the instruments was confirmed and measurements of tube potential made on each of the X-ray sets pooled. Measurements were made from a nominal 25-35 kVp using Mo/Mo, Mo/Rh and Rh/Rh target/filter combinations. Corrections for readings obtained with Mo/Rh and Rh/Rh were produced by comparison with readings obtained with Mo/Mo, assuming stability of tube potential between anodes. The results are compared with data recently produced by the manufacturer of the meter.

Entrance doses during lateral lumbar spine and antero-posterior abdomen examinations: generator waveform dependence.

In North Trent, UK, an entrance dose survey of lateral lumbar spine and antero-posterior (AP) abdomen examinations has been carried out in 17 radiology departments. The survey comprised 294 lateral lumbar spine and 322 AP abdomen entrance dose measurements. The mean entrance doses were found to be approximately half of the relevant national reference entrance dose levels of 30 mGy and 10 mGy, respectively. The effect of generator waveform on entrance dose was studied by separating the generators into two types: "pulsating potential" (PP) generators and "constant potential" (CP) generators for each examination. PP generators comprised 23% of the total number of examinations. The mean entrance dose and radiographic exposure factors from CP generators were found to be significantly lower than those from PP generators. The use of CP type generators, together with low attenuation components can significantly reduce patient entrance doses for these examinations.

Reduction of radiation doses in leg lengthening procedures by means of audit and computed tomography scanogram techniques.

Children with congenital bone dysplasias may benefit from leg lengthening procedures. Such procedures, by necessity, require frequent and regular imaging. It is necessary to minimize the total radiation dose to these patients, and particularly the dose to the gonads. In the present study the films of 13 patients who had completed leg lengthening procedures were reviewed. The number of films was assessed together with the use of appropriate gonad shielding. In a second part of the study, thermoluminescent dosemeter measurements of radiation doses to a phantom were made for both plain radiographs (with and without gonad protection) and computed tomography (CT) scanograms. The results show that audit plays an important role in assessing radiographic practice with respect to accurate placement of gonad protection and confirm that a significant dose reduction can be accomplished by careful use of this lead shielding. Dose reduction can also be achieved by using alternative radiographic techniques such as CT scanograms. Other techniques such as ultrasound or dual-energy X-ray absorptiometry are briefly discussed. These may play an important additional part in the reduction of total radiation dose to the patients.