Optimization of tube potential-filter combinations for film-screen mammography: a contrast detail phantom study

This study evaluated how tube potential-filter combinations [with a molybdenum (Mo) anode and either an Mo or a rhodium (Rh) filter] influence image quality and radiation dose to breasts of different thicknesses in film-screen mammography using a new mammography phantom (CDMAM Phantom Type 3.4). A 28-kVp/Mo tube potential-filter combination is recommended for a breast (phantom) thickness of 40 mm or less, 28 kVp/Rh for a breast (phantom) thickness of 60 mm or less, and 30 kVp/Rh for a breast (phantom) thickness greater than 60 mm.     

Quality assurance breast phantoms for screen-film mammography: design and use.

Used properly, well-designed breast phantoms are a very useful part of the mammography QA program. However, they should be designed specifically for the purpose. The principles involved are discussed and illustrated by the design of the unit shown in figure 1. QA phantoms also must be applied appropriately. Procedures are described for checking the consistency of film density, evaluating image quality, and checking phototimer operation. The simple film density measurement test (table 2) also provides a useful check on the constancy of patient dose levels. However, errors may result when QA phantoms are used for dosimetry, primarily because their composition differs from that of the mixture BR12, which is usually taken as the standard for dosimetry measurement. Procedures are described for computing average glandular dose, as well as measuring the two required quantities: the beam HVL and the exposure in air required for proper film density.     

Mammography phototimer technique chart

A phototimer technique chart for mammography is presented along with the methodology used to design it. The chart is based on accurate measurement of breast thickness and helps overcome the inability of the phototimer to track as breast thickness varies. In clinical practice, the chart results in the consistent attainment of optimally exposed films and decreased number of retakes.     

The intensity of scattered radiation in mammography

The ratio of scattered-to-primary radiation has been measured for a range of x-ray tube voltages, field sizes and phantom thicknesses that typify clinical mammographic situations. The relative intensity of scattered radiation measured was essentially independent of kVp but increased as the phantom thickness and radiation field size increased. For the range of field sizes and phantom thicknesses that typify clinical situations the intensity of scattered radiation varied from about 40 to 85% of the primary beam intensity indicating that only from about 54 to 71% of the primary beam contrast is imaged in mammography.     

Development of a phantom to test fully automated breast density software – A work in progress

ObjectivesMammographic density (MD) is an independent risk factor for breast cancer and may have a future role for stratified screening. Automated software can estimate MD but the relationship between breast thickness reduction and MD is not fully understood. Our aim is to develop a deformable breast phantom to assess automated density software and the impact of breast thickness reduction on MD.MethodsSeveral different configurations of poly vinyl alcohol (PVAL) phantoms were created. Three methods were used to estimate their density. Raw image data of mammographic images were processed using Volpara to estimate volumetric breast density (VBD%); Hounsfield units (HU) were measured on CT images; and physical density (g/cm³) was calculated using a formula involving mass and volume. Phantom volume versus contact area and phantom volume versus phantom thickness was compared to values of real breasts.ResultsVolpara recognized all deformable phantoms as female breasts. However, reducing the phantom thickness caused a change in phantom density and the phantoms were not able to tolerate same level of compression and thickness reduction experienced by female breasts during mammography.ConclusionOur results are promising as all phantoms resulted in valid data for automated breast density measurement. Further work should be conducted on PVAL and other materials to produce deformable phantoms that mimic female breast structure and density with the ability of being compressed to the same level as female breasts.Advances in knowledgeWe are the first group to have produced deformable phantoms that are recognized as breasts by Volpara software.     

Basic study for the measurement of the bone mineral density of the calcaneus by using the radiographic contrast

We performed a fundamental study for the measurement of the bone mineral density (BMD) of the calcaneus by using the radiographic contrast (RC). The RC of the bone radiography is proportional to the product of the thickness of the bone H(b), the gradient of the image detector system and the difference of the linear attenuation coefficient between the bone and the soft tissue. Therefore, the radiographic contrast per unit bone thickness (RC/H(b)) can be used as a good measure of the BMD. Though the linearity of RC/H(b) is maintained for x-rays with the monochromatic energy spectrum, the energy spectrum of the x-rays employed in clinical examinations is continuous. The relationship between RC/H(b) value and BMD value was examined by two kinds of added filter (Al with 5 mm and 15 mm thickness) and two kinds of bone phantoms (the phantom with 1 cm and 4 cm thickness, which is made by a bone equivalent material). The experimental results obtained from the 1 cm bone phantom indicated an approximately linear relationship. However, the experimental results obtained from the 4 cm bone phantom indicated a non-linear relationship due to the beam hardening. Therefore, the estimation of the calcaneus BMD value in clinical practice is performed by using the relationship between RC/H(b) and BMD values obtained from experimental results for the bone phantom with 4 cm thickness.     

Dose and image-quality evaluation in synchrotron radiation mammography

Monochromatic X-ray beam produced by synchrotron radiation may be considered an ideal probe in some fields of diagnostic radiology. In this paper the potential of monochromatic synchrotron radiation X-ray beam in mammography is analyzed. The image quality of four different phantom radiographs, obtained using two different energies equal to 17 and 18 keV, respectively, and a mammographic film/screen system, is assessed. The doses have been determined for both energies by using thermoluminescent dosimeters and a 5-cm thick phantom having a composition of 50% water and 50% fat. The results have been compared with those obtained in the same manner using a mammographic unit equipped with a molybdenum anode, molybdenum filter tube and antiscanner grid. The radiographs obtained with synchrotron radiation show higher contrast and less blur than those obtained with a conventional mammographic system. The average breast doses, 1.55 and 0.80 mGy at 17 and 18 keV, respectively, are comparable with the dose (1.51 mGy) of the conventional technique. Correspondence to: M. Gambaccini     

计算机X射线摄影系统与屏-片系统能量响应的对照研究

目的探讨计算机X射线摄影(CR)影像像素值与曝光因子(kVp和mAs)、被照体厚度的关系，传统屏-片系统照片密度与曝光因子、被照体厚度的关系，并对两种能量响应的关系进行比较，为使用CR影像像素值和成像板(IP)平均入射照射量的测量值作为自动曝光控制系统的设定参数提供依据。方法厚度为10、15、20cm的丙烯树脂板分别在50～90、70～120、90～140kVp和密度档为-2时成像，对照屏-片系统与CR系统在不同管电压、相同被照体和密度档时的自动曝光响应。以上测试都使用滤线栅，用电离室测量IP的入射照射量。结果在获得满足临床诊断要求的情况下，CR所需曝光量大约是高速屏-片系统的2倍。CR系统的管电压像素值关系曲线与管电压照射量曲线相同。10cm被照体时，50～90kVp间的照片密度差值为1．21，像素差值为270；而20cm被照体时，90～130kVp间的密度差值为0．30，像素差值为100；15cm被照体时密度和像素差值居于两者之间，分别为0．62和160。结论Kodak CR900系统的感度值与中速屏-片系统的感度比较接近。均匀野影像的曝光指示器值EI和IP照射量测量值可以用来设定自动曝光控制系统的光电计时器。屏-片系统照片密度和CR影像像素值随kVp变化的规律以及两者的差异，对自动曝光控制系统的校准起参照作用。     

旋转DSA技术在肺栓塞诊疗中应用的研究

目的研究旋转DSA技术在肺栓塞(pulmonary embolism，PE)诊疗中的应用。方法建立小型猪肺栓塞模型13头，进行常规肺动脉造影并应用旋转DSA技术，对造影结果进行分析、评价和研究。结果将每头猪的肺分为相应的15条血管，共有195条血管。以病理阳性结果为标准，评价肺动脉造影及旋转。DSA技术诊断PE的价值。肺动脉造影及旋转。DSA共有47个血管阳性(24．1％)，敏感性为98％，特异性为99％，诊断准确性98％；有2个血管数字减影肺动脉造影阳性，病理阴性，假阳性率为1％；有1个血管数字减影肺动脉造影阴性，病理阳性，假阴性率为2％。结论旋转DSA技术有助于肺栓塞诊断，尤其对疑似病变有一定临床意义。     

Image quality and breast dose of 24 screen-film combinations for mammography

In this study the effect of different mammographic screen-film combinations on image quality and breast dose, and the correlation between the various image quality parameters, breast dose and the sensitometric parameters of a film were investigated. Three Agfa (MR5-II, HDR, HT), two Kodak (Min-R M, Min-R 2000), one Fuji (AD-M), one Konica (CM-H) and one Ferrania (HM plus) single emulsion mammographic films were combined with three intensifying screens (Agfa HDS, Kodak Min-R 2190 and Fuji AD-MA). The film characteristics were determined by sensitometry, while the image quality and the dose to the breast of the resulting 24 screen-film combinations were assessed using a mammography quality control phantom. For each combination, three images of the phantom were acquired with optical density within three different ranges. Two observers assessed the quality of the 72 phantom images obtained, while the breast dose was calculated from the exposure data required for each image. Large differences among screen-film combinations in terms of image quality and breast dose were identified however, that, could not be correlated with the film's sensitometric characteristics. All films presented the best resolution when combined with the HDS screen at the expense of speed, and the largest speed when combined with the AD-MA screen, without degradation of the overall image quality. However, an ideal screen-film combination presenting the best image quality with the least dose was not identified. It is also worth mentioning that the best performance for a film was not necessarily obtained when this was combined with the screen provided by the same manufacturer. The results of this study clearly demonstrate that comparison of films based on their sensitometric characteristics are of limited value for clinical practice, as their performance is strongly affected by the screens with which they are combined.     

The quality mammographic image. A review of its components

Seven major factors resulting in a quality or high contrast and high resolution mammographic image have been discussed. The following is a summary of their key features: 1) Dedicated mammographic equipment. --Molybdenum target material --Molybdenum filter, beryllium window --Low kVp usage, in range of 24 to 30 --Routine contact mammography performed at 25 kVp --Slightly lower kVp for coned compression --Slightly higher kVp for microfocus magnification 2) Film density --Phototimer with adjustable position --Calibration of phototimer to optimal optical density of approx. 1.4 over full kVp range 3) Breast Compression --General and focal (coned compression). --Essential to achieve proper contrast, resolution and breast immobility. --Foot controls preferable. 4) Focal Spot. --Size recommendation for contact work 0.3 mm. --Minimum power output of 100 mA at 25 kVp desirable to avoid movement blurring in contact grid work. --Size recommendation for magnification work 0.1 mm. 5) Grid. --Usage recommended as routine in all but magnification work. 6) Film-screen Combination. --High contrast--high speed film. --High resolution screen. --Specifically designed cassette for close film-screen contact and low radiation absorption. --Use of faster screens for magnification techniques. 7) Dedicated processing. --Increased developing time--40 to 45 seconds. --Increased developer temperature--35 to 38 degrees. --Adjusted replenishment rate and dryer temperature. All seven factors contributing to image contrast and resolution affect radiation dosage to the breast. The risk of increased dosage associated with the use of various techniques needs to be balanced against the risks of incorrect diagnosis associated with their non-use.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of image quality between 70 kVp and 80 kVp: application to paediatric cardiac CT

Purpose

To evaluate noise level and contrast-to-noise ratio (CNR) with various kVp-mAs pairs producing the same computed tomography dose index (CTDI) value. The 80 kVp and new 70-kVp settings were compared.

Materials and methods

The noise was measured in 10 ovoid water phantoms with different diameters from 10 cm to 28 cm. Contrast was obtained from CTs of iodine-filled tubes. Spiral acquisition protocols at 70 kVp and 80 kVp, with the same CTDI, were applied. In the clinical study, two matched groups, each of 21 paediatric patients, underwent 70-kVp or 80-kVp ECG-gated iodinated-enhanced sequential CT.

Results

Noise was significantly higher with 70 kVp than 80-kVp settings for all phantom sizes. Estimated CNR with phantoms was higher at 70 kVp than 80 kVp, and the difference decreased from 17 % to 3 % as phantom size increased. The mean CNR in paediatric patients was 15.2 at 70 kVp and 14.3 at 80 kVp (ns). The CNR difference was significantly larger in the small-child subgroup.

Conclusion

Noise level is slightly higher at the 70-kVp than the 80-kVp setting, but the CNR is higher, particularly for small children. Therefore, 70 kVp may be appropriate for contrast-enhanced CT examinations and 80 kVp for non-enhanced CT in small children.

Key Points

? 70-kVp settings provide a slightly higher noise level compared to 80-kVp settings. ? The CNR is higher with 70-kVp than with 80-kVp settings. ? Without contrast, 80-kVp settings may be preferable over 70-kVp settings.     

Patient investigation of average glandular dose and incident air kerma for digital mammography

Our aim in this study was to investigate the incident air kerma (IAK) and average glandular dose (AGD) for polymethylmethacrylate (PMMA) phantoms and patient breasts for each thickness by use of digital mammography units, and to determine the correlation between phantom and patient measurements. An additional aim was to calculate the numerical value of the diagnostic reference level (DRL) for digital mammography in Japan based on the AGD from patient measurements. Patient-based IAK and AGD values were calculated for 300 patients who underwent mammographic examinations at three institutions. On examination of a 40-mm PMMA phantom, the IAK and the AGD were 7.89 and 1.84 mGy, respectively. The mean patient breast thickness was 37.6 mm, and the mean IAK and the AGD calculated from actual patient data for breast thicknesses between 40 mm and 50 mm were 8.91 and 2.08 mGy, respectively. Approximately 20 % of the 300 patients had IAK >10 mGy. The distributions of patient-based IAK and AGD values were higher than the IAK and AGD values for the PMMA phantom. The patient dose with use of the PMMA phantom can be underestimated. The DRL was calculated from patient-based AGDs of the regular breast thickness as 2.0 mGy in Japan.     

A phantom-based evaluation of an exposure equalization technique in mammography

An anatomical filter based exposure equalization technique in mammography is evaluated quantitatively using a phantom. The evaluation is carried out by a comparative observer performance study, comparing the equalization technique with a conventional one based on visualization of low contrast, 6 mm circular details and high contrast, 0.5 mm and 0.25 mm small size details. These details are situated at the phantom edge, simulating the breast periphery. Visualization of these details is studied with respect to the parameters of tube voltage, optical density, detail location and phantom thickness. Phantom images are interpreted independently by three observers using a four-point grading scale. Use of the Wilcoxon signed ranks test for paired data shows statistically highly significant improvement (p < 0.0001) in the visualization of details for the equalization technique for all values of the parameters studied. The improvement is independent of tube voltage but dependent on optical density, detail location and phantom thickness. Optimal performance is obtained for detail location closer to the outer border of the simulated breast periphery and/or further away from the film, as well as for a greater phantom thickness simulating both thick and dense breast.     

Radiation doses received in the UK Breast Screening Programme in 1997 and 1998

The mean glandular doses (MGDs) to samples of women attending for mammographic screening are measured routinely at screening centres in the UK Breast Screening Programme (NHSBSP). This paper reviews the data collected during screening in the NHSBSP in 1997 and 1998 for 23,752 films, using 171 X-ray sets, for 8745 women. Average MGD was 2.03 mGy per oblique film and 1.65 mGy per craniocaudal film, similar to the MGDs found previously in the NHSBSP for the years 1994 and 1995. MGD was found to increase with compressed breast thickness where the tube potential was selected manually, so that the average dose for 10 cm thick breasts was 2.7 times the average for all breasts. For large breasts (> 70 mm) the use of X-ray sets such as the IGE DMR, which automatically select the beam quality for each breast, resulted in lower doses compared with sets using manual tube potential selection. MGD to the standard breast was found to vary from 0.7 to 2.2 mGy and to be correlated with the average MGD per mediolateral oblique film for the women screened on that system (R = 0.79). No correlation between age and MGD was found within the invited age range of 50-64 years.     

Tissue bulge during stereotactic core biopsy

In full field digital mammography (FFDM) the whole breast is subjected to compression with a perspex compression paddle in order to reduce breast thickness and improve image quality. Once a mammographic abnormality has been detected using FFDM and a decision to proceed with a stereotactic (X-ray) guided core biopsy has been made, a different compression paddle is utilised. This paddle has a central aperture in order to allow access to the lesion for biopsy.Clinical observations made during biopsy procedures have revealed that a bulge of tissue forms within the aperture. The magnitude of the bulge of tissue and BI-RAD breast density was recorded in 15 consecutive patients. Results showed an average of 18.7% (range 11.3–30%) increase in the breast thickness (over the bulge region) compared to the surrounding compressed breast.BI-RAD breast density category 3 had on average the lowest measured thickness and the greatest percentage of tissue bulge. Overall, results confirm that for all patients there was a measurable tissue bulge that varied from 6 mm to 10 mm, representing between 10.14% and 23.08% of additional tissue not measured by the machine. In clinical practice a perceivable difference in lesion visibility was subjectively indicated between the FFDM images and the stereotactic scout biopsy image.The suggested hypothesis from these observations is that there may be an association between the magnitude of the tissue bulge and the ability to accurately perceive certain lesions during stereotactic biopsy procedures. A phantom study is in progress to determine how lesion visibility varies with the amount of tissue bulge.     

Mammographic equipment, technique, and quality control

The most important improvements in mammographic technique were the introduction of single- or double-emulsion high-contrast film-screen combinations for mammography, the use of a specially designed low-kilovoltage Bucky grid to reduce scattered radiation, and the introduction of smaller focal spots to improve imaging geometry. Magnification techniques, especially the spot-film technique, yields clearer delineation of high-contrast microcalcifications. Dedicated mammographic equipment with specially designed x-ray tubes is necessary for modern high-quality mammography. However, in many modern mammographic units, the automatic exposure controller still fails to provide appropriate and constant optical film density over a wide range of tissue thickness and absorption. Extended-cycle processing of single-emulsion mammographic films can yield better image contrast and reduce exposure by up to 30%. Exposure times of less than 1 second are recommended to avoid the unnecessary higher doses caused by longer exposure times and reciprocity law failure. The wide dynamic range in mammography can be reduced by a beam equalization filter, and thus be better adapted to the decreased latitude of modern high-contrast mammographic screen-film systems. Mammographic film reading (detection of subtle microcalcifications) can be facilitated by modern computer evaluation of previously digitized mammograms. Standardization and assurance of image quality have been major challenges in the technical development of mammography. Different technical and anthropomorphic phantoms have been designed to measure and compare practical image quality. Detailed quality control measures have been developed. The benefit of a single or annual screening mammography, calculated in gained life expectancy, by far outweighs the relative risk for radiation-induced breast cancer.     

Development of an imaging-planning program for screen/film and computed radiography mammography for breasts with short chest wall to nipple distance

Objective

Imaging breasts with a short chest wall to nipple distance (CWND) using a traditional mammographic X-ray unit is a technical challenge for mammographers. The purpose of this study is the development of an imaging-planning program to assist in determination of imaging parameters of screen/film (SF) and computed radiography (CR) mammography for short CWND breasts.

Methods

A traditional mammographic X-ray unit (Mammomat 3000, Siemens, Munich, Germany) was employed. The imaging-planning program was developed by combining the compressed breast thickness correction, the equivalent polymethylmethacrylate thickness assessment for breasts and the tube loading (mAs) measurement. Both phantom exposures and a total of 597 exposures were used for examining the imaging-planning program.

Results

Results of the phantom study show that the tube loading rapidly decreased with the CWND when the automatic exposure control (AEC) detector was not fully covered by the phantom. For patient exposures with the AEC fully covered by breast tissue, the average fractional tube loadings, defined as the ratio of the predicted mAs using the imaging-planning program and mAs of the mammogram, were 1.10 and 1.07 for SF and CR mammograms, respectively. The predicted mAs values were comparable to the mAs values, as determined by the AEC.

Conclusion

By applying the imaging-planning program in clinical practice, the experiential dependence of the mammographer for determination of the imaging parameters for short CWND breasts is minimised.The automatic exposure control (AEC) system of a mammographic X-ray unit plays an important role in acquiring a mammogram with sufficient image quality and acceptable radiation dose to the patient. By implementing appropriate quality control procedures [1^,2] for a traditional mammographic X-ray unit, both screen/film (SF) and computed radiography (CR) mammograms can provide sufficient image quality for clinical diagnosis. At present, SF mammography still plays an important role in the screening and diagnosis of breast cancer in many countries. Many acceptable limits for digital mammography have been developed based on a series of assessments of SF mammographic units [2].For traditional mammographic X-ray units, the AEC system keeps the dose to the AEC detector constant over the whole range of breast thickness. However, for a breast with short chest wall to nipple distance (CWND), the AEC detector may not be entirely covered by the compressed breast, even if the AEC detector is moved to the nearest chest wall position. Under such circumstances, the AEC detector may receive some X-rays that are not attenuated by breast tissue, as shown in Figure 1. Consequently, the mammogram is underexposed because of the AEC prematurely terminating the exposure. In some instances, the SF mammogram of a short CWND breast is unacceptable for clinical diagnosis.Open in a separate windowFigure 1Illustration of the underexposure effect for a breast with short chest wall to nipple distance when imaging with a traditional mammographic X-ray unit. AEC, automatic exposure control.To acquire sufficient image quality in clinical practice, the exposure parameters of short CWND breasts are frequently determined by mammographers depending on their experience. Since compressed breast thicknesses (CBTs) and breast content varies with each patient, the determination of exposure parameters for short CWND breasts is a technical challenge for the mammographer. In our clinical practice, the image quality of these mammograms varied significantly depending on the exposure parameters selected. The repeat rate of SF mammograms at our institution for short CWND breasts is 11%, compared with 3% for all patients. This implies that mistakes in exposure settings may occur and may lead to either under- or overexposure, resulting in insufficient image quality and unnecessary patient radiation exposure.At present, very few attempts [3] have been made to develop an imaging technique for the short CWND breasts. The suitable exposure parameters of a short CWND breast may be acquired by the modification of imaging settings of a phantom exposure. The purpose of this study is the development of an imaging-planning program to assist in determination of imaging parameters of SF and CR mammography for short CWND breasts.     

Patient dose and risk in mammography

Patient dose in mammography is estimated by two different methods which are compared and which give good agreement. A mean tissue dose of about 1 mGy per film is found for a breast of 4.5 cm compressed thickness. Variables which affect dose are then considered quantitatively, including compressed breast thickness, tube potential, grids, magnification and beam collimation. The variables having the greatest effect are breast thickness and magnification. For example, an 8 cm breast receives about four times the mean tissue dose of a 3.5 cm breast. Similarly, using a magnification factor of about 2, dose is increased about four times in the primary beam, but the adverse consequences may be largely removed with conventional collimation to part of the breast only. Finally, the dose estimates are combined with existing data on breast cancer induction to predict the risk of carcinogenesis in a breast screening programme. For example, in a screening centre performing 15,000 examinations per year, only one induced cancer is predicted in about 7 years of screening under average UK conditions of age and breast thickness.     

Breast compression in mammography: how much is enough?

The amount of breast compression that is applied during mammography potentially influences image quality and the discomfort experienced. The aim of this study was to determine the relationship between applied compression force, breast thickness, reported discomfort and image quality. Participants were women attending routine breast screening by mammography at BreastScreen New South Wales Central and Eastern Sydney. During the mammographic procedure, an 'extra' craniocaudal (CC) film was taken at a reduced level of compression ranging from 10 to 30 Newtons. Breast thickness measurements were recorded for both the normal and the extra CC film. Details of discomfort experienced, cup size, menstrual status, existing breast pain and breast problems were also recorded. Radiologists were asked to compare the image quality of the normal and manipulated film. The results indicated that 24% of women did not experience a difference in thickness when the compression was reduced. This is an important new finding because the aim of breast compression is to reduce breast thickness. If breast thickness is not reduced when compression force is applied then discomfort is increased with no benefit in image quality. This has implications for mammographic practice when determining how much breast compression is sufficient. Radiologists found a decrease in contrast resolution within the fatty area of the breast between the normal and the extra CC film, confirming a decrease in image quality due to insufficient applied compression force.