Computerized scheme for evaluating mammographic phantom images.

PURPOSE: The authors developed a computer algorithm to automatically evaluate images of the American College of Radiology (ACR) mammography accreditation phantom. METHODS: The developed algorithm consist of the edge detection of wax insert, nonuniformity correction of background, and correction for magnification and also calculate the cross-correlation coefficient by image matching technique. The algorithm additionally evaluates target shape for fibers, target contrast for speck groups, and target circularity for masses. To obtain an ideal template image without noise and spatial resolution loss, the wax insert containing the embedded test pattern was extracted from the phantom and radiographed. Two template images and ten test phantom images were prepared for this study. The results of evaluation using the algorithm outputs were compared with the averaged results of observer studies by six skilled observers. RESULTS: In comparing the results from the algorithm outputs with the results of observers, the authors found that the computer outputs were well correlated with the evaluations by observers, and they indicate the quality of the phantom image. The correlation coefficients between results of observer studies and two outputs of computer algorithm, i.e., the cross-correlation coefficient by template matching and indices of target shape for fibers, were 0.89 (95% confidence interval, 0.82-0.93; hereinafter the same) and 0.85 (0.76-0.91). The correlation coefficients between observer's results and two outputs: the cross-correlation coefficient and indices of target contrast for speck groups, were 0.83 (0.79-0.86) and 0.85 (0.81-0.88) and between observer's results and two outputs: the cross-correlation coefficient and indices of target circularity for masses, were 0.90 (0.84-0.94) and 0.87 (0.77-0.92). CONCLUSIONS: Image evaluation using the ACR phantom is indispensable in quality control of a mammography system. The proposed algorithm is useful for quality control and image evaluation of mammography units.

Echo-planar imaging is superior to fast spin-echo diffusion-weighted imaging for cranioplasty using titanium mesh in brain magnetic resonance imaging: a phantom study.

This study aimed to compare the radiofrequency (RF) shielding effects of titanium mesh of echo-planar imaging (EPI) versus fast spin-echo (FSE) diffusion-weighted imaging (DWI) to establish a suitable sequence for patients who undergo cranioplasty and for whom titanium mesh was used in brain magnetic resonance imaging (MRI). A 1.5-T MRI scanner with clinical setting sequences was used. A phantom for the examination constructed using a sucrose solution in a plastic container was used to compare the signal attenuation (SA) ratio, area of RF shielding effect (Area), normalized absolute average deviation (NAAD), and apparent diffusion coefficient (ADC) between EPI and FSE-DWI. EPI provided significantly better SA ratio, Area, and NAAD (P < 0.01). When the number of slices increased, the RF shielding became more negative. There was no significant difference in the ADC. Regardless of the k-trajectory, EPI-DWI had a lower RF shielding effect than FSE-DWI in patients undergoing cranioplasty.

[A Proposal for the Optimal Material for Evaluating Diffusion-weighted Image by Using Solid Phantom].

Recently, diffusion-weighted imaging (DWI) has become essential for diagnosing acute cerebral infractions and detecting lesions via magnetic resonance imaging (MRI). Investigations using phantoms have been performed to evaluate the optimizing parameters before clinical practice. However, there have been no studies on extracting appropriate phantom materials. It is known that the apparent diffusion coefficient (ADC) changes with temperature. To extract optimal materials from polyethylene glycol, sucrose, and dextrin in previous studies, evaluations were performed using ADC with temperature change and signal-to-noise ratio (SNR) . Results of comparison with difference between true and measured values depend on the Stokes-Einstein formula for ADC change with temperature change; the highest value was obtained for polyethylene glycol. In the SNR measurement, when the temperature increased, the rate of change of ADC decreased. Polyethylene glycol showed the highest value. According to these results, it can be concluded that polyethylene glycol can be extracted when nearest to true value and when there is a high SNR, thus making polyethylene glycol the most suitable material for diffusion-weighted image phantoms.

Effects of k-space orders on the time-intensity curves in dynamic contrast-enhanced magnetic resonance imaging of the breast based on simulation study.

PURPOSE: This study aims to investigate the influence of time-intensity curves (TICs) on the shapes using a dynamic contrast-enhanced magnetic resonance imaging (MRI) study depending on the Cartesian and radial orders for benign and cancerous breast tumors. METHODS: Based on kinetic curve parameters, the signal intensities of six concentration gradients comprising two benign and four cancer models were used. The study aimed to construct a dynamic simulated image by creating a digital phantom image according to the following steps: (1) creating a simple numerical phantom, (2) setting the signal intensity in the contrast area, (3) creating the k-space in each time phase, (4) extracting data from k-space in each time phase, (5) filling in the k-space and adding data to the k-space assembly, and (6) creating a magnitude image. The TICs of Cartesian (centric and sequential) and radial (full-length [RFL] and half-length [RHL]) orders were created and sigmoid curve fitting was performed to compare these curves. Maximum slope (MS, s-1), width of the response (WOR, s), and primary signal response (PSR) were then calculated. Phase encode steps were set for 512 and 256. RESULTS: MS was significantly decreased by radial order in the cancer model. No change was observed in WOR in Cartesian order, whereas RFL and RHL orders increased in the cancer models. PSR increased remarkably in the radial orders of cancer models. The difference in the fill slope in radial orders was remarkable when the TIC was steeper compared with when it was gentle, especially RHL. In WOR, both radial RFL and RHL were well matched except for the one benign model, and the shape of radial TIC was similar to sequential order as compared to centric order in 256 steps. CONCLUSION: The effects of Cartesian and radial orders on the patterns of TICs in a dynamic contrast-enhanced MRI study of benign and cancerous breast tumors were revealed. Interestingly, the TIC gradient of radial orders became gentler, particularly in the breast cancer MRI.

Are the recorded data of flash glucose monitoring systems influenced by radiological examinations?

The FreeStyle Libre Pro® flash glucose monitoring system is easy to use in diabetes care. However, the influence of radiological examination on recorded data has not been reported. The sensor should be removed prior to examinations involving strong magnetic or electromagnetic radiation. In the present study, it was assumed that radiological examination was performed without removing the FreeStyle Libre Pro® sensor in certain unanticipated situations. We researched the integrity of data recorded by the FreeStyle Libre Pro® system following exposure to chest X-rays, computed tomography (CT), radiotherapy (RT), and magnetic resonance imaging (MRI). Fifty sensors were exposed to chest X-ray, CT, RT, and MRI (1.5-T and 3.0-T), and the recorded data were compared with those obtained before the tests. Ten sensors were included in each group. There were no unread data or errors when the sensors were read. No change was observed before and after the examination for all tests.

A mask method to assess the uniformity of fat suppression in phantom studies.

Fat suppression is a technique used to suppress the signals from adipose tissues, during clinical evaluation of the tissues near the fat-tissue boundary. However, in cases where the scan area has a complicated shape, the effect of fat suppression may demonstrate poor uniformity, resulting in diagnosis-related difficulties. To improve the uniformity of fat suppression, phantom studies are more suitable than volunteer studies. In this study, we evaluated the reliability of the region of interest (ROI) dependency using an unevenness phantom, to develop a method to assess the uniformity of fat suppression while using whole magnetic resonance imaging by masking the surrounding phantom. We modulated different ROI sizes, which were eroded from 100% to approximately 50%, and observed that the normalized absolute average deviation and error increased with decreased ROI. Using our method, more objective, concrete, and accurate data could be obtained by including the whole-body phantom (whole poor uniformity area).

[Physical and imaging properties of heavy metal filter combinations in chest radiography]

We have investigated the performance characteristic of the heavy metal filters with higher atomic numbers by comparing their patient exposures, tube loadings, radiographic contrasts, and noise Wiener spectra with those of a combination of copper and aluminum filter which has been used widely in chest radiography. Seven heavy metal filters were used for this study. As for a tungsten filter, two filters different in thickness were used. One is 0.05 mm thick, and the other 0.10 mm. The other metal filters were respectively combined with a tungsten filter with a thickness of 0.05 mm. Among the all filters investigated, tube loading of tungsten filter with 0.05 mm thick is minimum. Tungsten with 0.1 mm thick and tungsten with 0.05 mm+ barium show the larger advantages in patient exposure than those of the other filters. It was found that the magnitude of patient exposure varied slightly with the difference of image receptor used. The use of heavy metal filters showed the small advantages in the patient exposure reduction ( approximately 20%) compared with that of conventional copper filter. The use of heavy metal filters showed increasing tube loading ( approximately 5 times) compared with that of conventional copper filter. Noise Wiener spectra of heavy metal filters showed comparable with those of conventional copper filter. In conclusion, the use of heavy metal filter combinations offer no significant advantages over optimal conventional filters.