[Derivation of Conversion Formula of Image Quality Figure (IQFinv) Values by Old and New Analysis Software for Mammographic Contrast-detail Phantom].

PURPOSE: This study deals with the conversion of the image quality figure (IQFinv) values with CDMAM Analyser ver. 1 (old analysis software) used to analyse the images of CDMAM 3.4 phantom into the IQFinv values with a new analysis software, that is, CDMAM Analyser (ver. 2 and ver. 2.3), which is a software improved to be closer to human visual evaluation. METHODS: The IQFinv values were calculated using four mammography units and three analysis software. The IQFinv values using the old and new software were compared. RESULTS: The IQFinv values had no difference according to mammography units and beam quality. The conversion formula of IQFinv from CDMAM Analyser ver. 1 to CDMAM Analyser ver. 2 was derived. Furthermore, the conversion formula of IQFinv from CDMAM Analyser ver. 1 to CDMAM Analysis ver. 2.3 was also derived. CONCLUSION: Using each conversion formula, the IQFinv values using the old software can be converted to those using the new software. There was a slight difference between the IQFinv values using the new software.

[Comparison between Variance and Edge Methods for Measuring Image Resolution Properties in Digital Mammography].

We studied the image resolution properties in digital mammography using the variance and edge response function methods. The associated measurements were made using a polymethylmethacrylate phantom of 0-40 mm thickness while maintaining the incident dose to the detector constant, as well as with and without using the phantom but by varying the level of exposure to the detector. The results obtained using the two methods were compared on the object plane of the mammography unit with compensation for the magnification and rejection of the scattered radiation. In this unit, the imaging process of resolution enhancement may be performed according to the phantom thickness, shape of test device, exposure level, and so on. The modulation transfer function values of the variance method were slightly higher than those of the edge method, approximately 6% at 2 cycles/mm and 8% at 4 cycles/mm without resolution enhancement processing. We concluded that the variance method is more suitable than the edge method for the constancy test or quality control because of its lower coefficient of variation.

[Comparison of Contrast to Noise Ratio and Signal Difference to Noise Ratio Based on QA and QC Guidelines in CR Mammography].

The measurement methods of contrast to noise ratio (CNR) and signal difference to noise ratio (SDNR) in digital mammography are different among several quality assurance (QA) guidelines, that is, the type of pixel value (PV), phantom shape, location of aluminum plate, and the size of region of interest (ROI) principally differ in data acquisition. We compared CNR (SDNR) obtained from three QA guidelines. They are the European Reference Organisation for Quality Assured Breast Screening and Diagnostic Services (EUREF), the International Electrotechnical Commission (IEC), and the International Atomic Energy Agency (IAEA). In EUREF and IEC, CNR was calculated using linearized pixel value (LPV). In IAEA, because the type of pixel value to use in SDNR was not specified, SDNR was calculated using PV and LPV, and CNR was calculated using LPV. Target/filter combinations are molybdenum/molybdenum (Mo/Mo) and molybdenum/rhodium (Mo/Rh). Applied various tube voltages are 25, 30, and 35 kV, and various phantom thicknesses are 20, 45, and 70 mm of polymethyl methacrylate (PMMA). The PV-SDNR of IAEA showed the largest value among the three methods, following LPV-CNR of IEC, LPV-CNR of EUREF at 20 mm PMMA thickness. In IAEA, SDNR changed by the kind of pixel value (PV or LPV). When CNR is calculated, every researcher should describe the type of guidelines, the kind of pixel value, and formula for calculation.

[Influence of Detector Radiation Damage on CR Mammography Quality Control].

Recently, radiation damage to the detector apparatus employed in computed radiography (CR) mammography has become problematic. The CR system and the imaging plate (IP) applied to quality control (QC) program were also used in clinical mammography in our hospital, and the IP to which radiation damage has occurred was used for approximately 5 years (approximately 13,000 exposures). We considered using previously acquired QC image data, which is stored in a server, to investigate the influence of radiation damage to an IP. The mammography unit employed in this study was a phase contrast mammography (PCM) Mermaid (KONICA MINOLTA) system. The QC image was made newly, and it was output in the film, and thereafter the optical density of the step-phantom image was measured. An input (digital value)-output (optical density) conversion curve was plotted using the obtained data. The digital values were then converted to optical density values using a reference optical density vs. digital value curve. When a high radiation dose was applied directly, radiation damage occurred at a position on the IP where no object was present. Daily QC for mammography is conducted using an American College of Radiology (ACR) accreditation phantom and acrylic disc, and an environmental background density measurement is performed as one of the management indexes. In this study, the radiation damage sustained by the acrylic disc was shown to differ from that of the background. Thus, it was revealed that QC results are influenced by radiation damage.

[Measurement of residual effect in the amorphous selenium flat panel detector system].

The purpose of this study was to evaluate the residual effect generated by the amorphous selenium flat panel detector system (a-Se FPD). A residual effect occurs as a result of the addition of delayed electrons by previous X-ray irradiation joining the signal and change in detector sensitivity caused by hole-electron recombination or trapped electrons in a-Se. To evaluate the effect of previous radiation exposure, we irradiated a-Se FPD that were half-shielded by a 3 mm thick lead plate. A residual effect was generated in irradiated areas, with the unirradiated areas serving as reference points. Next, we removed the lead plate and took a new image using uniform irradiation. The difference in pixel value between irradiated and nonirradiated areas was measured using a variety of time intervals between each exposure. Through a comparison of pixel values from images taken over various time intervals, we discovered our system needs 20 hours to return to a normal state and become capable of producing a residual-free image.

[Development of comprehensive image processing technique for differential diagnosis of liver disease by using multi-modality images-pixel-based cross-correlation method using a profile-].

Imaging techniques such as high magnetic field imaging and multidetector-row CT have been markedly improved recently. The final image-reading systems easily produce more than a thousand diagnostic images per patient. Therefore, we developed a comprehensive cross-correlation processing technique using multi-modality images, in order to decrease the considerable time and effort involved in the interpretation of a radiogram (multi-formatted display and/or stack display method, etc). In this scheme, the criteria of an attending radiologist for the differential diagnosis of liver cyst, hemangioma of liver, hepatocellular carcinoma, and metastatic liver cancer on magnetic resonance images with various sequences and CT images with and without contrast enhancement employ a cross-correlation coefficient. Using a one-dimensional cross-correlation method, comprehensive image processing could be also adapted for various artifacts (some depending on modality imaging, and some on patients), which may be encountered at the clinical scene. This comprehensive image-processing technique could assist radiologists in the differential diagnosis of liver diseases.

[Estimation of entrance skin dose from fluoroscopy for tracking fiducial markers during real-time tumor-tracking radiotherapy-simulation with a sine wave respiration model-].

The real-time tumor-tracking radiotherapy system includes two sets of fluoroscopes that detect the fiducial markers in or near the tumor constantly during radiotherapy. The treatment beam is irradiated to the tumor only when fiducial markers are located in the target position. Treatment time is extended in case of large respiratory tumor motion. A high-power fluoroscopic X-ray is required in the case of fiducial markers in parenchymal organs with heavy X-ray attenuation. It was a concern that radiodermatitis was caused by an increasing entrance skin dose from the fluoroscopic X-ray. In order to estimate the entrance skin dose from the fluoroscopic X-ray, we measured the entrance skin dose rate through the use of a method recommended by the Japanese Society of Radiological Technology. We applied sine wave simulation to resemble the respiratory motion of the tumor. In conclusion, we confirm that entrance skin dose from fluoroscopy during RTRT is lower than the threshold dose for radiodermatitis.

Evaluation of the spatial resolution of multiplanar reconstruction images.

We present a simple method for evaluating the spatial resolution of multi-slice computed tomography (MSCT) multiplanar reconstruction images (MPRs). We scanned a bead phantom to obtain the three-dimensional point spread function (PSF), and bead-centric MPRs were generated. The modulation transfer function (MTF) was calculated from the MPRs via a two-dimensional Fourier transform (2DFFT) of the PSF. The results showed that, when MPRs were reconstructed using axial images less than or equal to a nominal 1.0-mm slice-width with a standard kernel for the abdomen, the MTF in the longitudinal direction (z-direction) was superior to that in the in-plane (x-y plane) direction. It was also found that the arbitrary-angle MTFs of MPRs were between the MTFs of the in-plane and longitudinal directions. It was confirmed that this method can be used to evaluate MPR spatial resolution.

[Selection of parameters for multi-objective frequency processing in CR mammography: visual evaluation of mammographic phantom images].

The multi-objective frequency processing installed in the FCR5000R (Fuji Film Medical) is superior to the conventional processing used in the FCR9000 (Fuji Film Medical) in evaluating frequency processing. A suitable combination of parameters for multi-frequency-processing in computed radiography (CR) mammography was evaluated. The paired-comparison method using phantom images was performed for the visual evaluation. Results showed that the evaluation score of mass and fiber lesions depended on the multi-frequency balance type (MRB) parameter, and the low-frequency-cycle emphasizing parameter had the highest score. In contrast, the score of microcalcifications depended on the degree of multi-frequency enhancement (MRE). The most suitable parameters for the multi-frequency processing of every size and type of breast lesion were not obtained. However, MRB=A, MRT=p, and MRE=1.0 can be recommend for CR mammography.

[Measurement of effective dose of the assisting person in diagnostic X-ray examination].

We measured the effective dose received by the person assisting the patient at diagnostic X-ray examination. Measurement was done when a patient's chest, abdomen, lumbar vertebrae, hip joint, skull, cervical vertebrae, or knee joint was examined by radiography. A body phantom including human bones exposed to radiation was used in the role of the patient. Some exposure conditions for these measurements were the same as those used routinely in computed radiography. Effective dose was measured directly with an ionization survey meter. As a result, the effective dose of the person assisting with axial projection of the hip joint was 124 microSv, which was higher than that for other regions and projections. If the assisting person helped a patient without using any protective device, the effective dose would be low enough to ignore. However, because medical staff are frequently exposed to radiation, optimal protection is crucial to prevent unnecessary radiation.

[Significance of the visual evaluation method using the two-visit method (two-sample preference test suggested by Ferris)].

To increase the accuracy of the visual evaluation method, we studied the significance of the two-sample preference test using the two-visit method, as proposed by Ferris. Advantages of this method include not only its ability to estimate whether the image quality of the sample is statistically the same but also its ability to distinguish the difference between samples more clearly than when using the conventional two-sample preference test or paired-comparison method. However, a disadvantage is that this method involves two observations of the same sample. When using chest images, even if a difference between the samples is not recognizable by the conventional method, a significant difference can be elicited with this method. The data obtained by this method can be evaluated with the paired-comparison method, so some samples may be ranked as well. Therefore, we verified that the two-sample preference test, which Ferris formulated, is useful in visual evaluations.