Validity of Using Accreditation Phantom in Quality Control of Digital Tomosynthesis

AIM

This study was undertaken to compare the two image-quality phantoms commonly used in full-field digital mammography (FFDM) and digital breast tomosynthesis (DBT) imaging.

METHODS

Mammography units with two targets and three filters resulting in three possible target/filter combinations and two kVp values which are widely used (28 and 32) were used for the comparison. The automatic exposure control system was used in combination with the selected kVp. The CIRS 15 mammographic accreditation phantom (MAP) and CIRS 20 (BR3D) breast imaging phantom were used with the three target/filter combinations and two kVp values. A total of 24 images were acquired and evaluated. Image score was determined as the smallest sized object detectable. The data were analyzed by using Mann-Whitney test.

RESULTS

There were significant (p<0.001) differences between the detectability of fibers present in the two phantoms, but there were no differences in the detectability of specks.

CONCLUSION

The finding in FFDM and DBT showed there were significant differences between the two phantoms (p<0.02) in fibers and specks visibility. The CIRS 20 phantom provided greater visibility of smaller structures, while the MAP was more suitable for assessing image quality of both FFDM and DBT imaging systems.

Effect of exposure factors on image quality in screening mammography

INTRODUCTION

The aim of this research was to study the effect of exposure factors on image quality for digital screening mammography units in Kuwait which use Tungsten (W) targets with Rhodium (Rh) and Silver (Ag) as filters.

METHODS

Mammography Accreditation Phantom Model 015 was imaged using a Hologic Selenia Digital mammography unit with W targets and Rh and Ag filters. Four images, each at 26, 28, 30, and 32 kVp, were obtained using each target-filter combination (W/Rh and W/Ag). The images were evaluated by five senior technologists for the number of specks, fibers and masses visible on each image. Statistical analysis was carried out using non-parametric tests at p = 0.05 level.

RESULTS

There were significant changes in the visibility of fibers and specks between different kVp values with W/Rh (p < 0.001). However, with W/Ag combination, significant differences were observed in the fibers only (p < 0.001). Among the kVp values used, 28 kV emerged as the optimal value. Comparison of images obtained with the two filter materials, led to significant differences in the visibility of fibers and specks (p < 0.008). At 32 kVp, there were significant differences in the visibility of specks only (p < 0.008).

CONCLUSION

A W/Rh target-filter combination provides better image quality than that provided by W/Ag. In particular, 30 and 32 kVp X-ray beams produce higher quality images than the lower kV values.

Mammographic Phantoms Frequently Used to Determine Image Quality: A Comparative Study

Appropriate diagnosis depends on the image quality of the mammographic system. Phantoms are normally used, since they have physical properties similar to those of different human tissues, and are important tools for quality assurance of mammography equipment, evaluation of image quality, and accurate determination of patient dosage. The aim of this study was to evaluate various mammographic phantoms used to determine the image quality of digital mammographic equipment.

METHODS

Three phantoms were used: an American College of Radiology accreditation phantom, an MTM 100/R, and a tissue-equivalent phantom. Tungsten/silver target/filter material was used with four variable exposures (25, 28, 30, and 32 kVp). In total, there were 12 images. The images were evaluated by scoring the visibility of the structures, and a total score out of 100% was recorded. Statistical analysis was conducted using non-parametric tests.

RESULTS

There was no significant difference in the visibility of structures among the phantoms at different kVp. However, there were significant differences (p=0.04) in the visibility of the tumor masses when the kVp was varied. In addition, visibility rates differed significantly between the three phantoms (p≤0.05).

CONCLUSION

All the phantoms used in this study were suitable for evaluating digital mammography systems. However, the exposure setting for evaluation must be carefully considered. The tissue-equivalent phantom performed better in terms of the visibility rate to assess image quality in the digital mammography units.