**2. Methods and materials**

#### **2.1. Mammogram selection**

The study cohort included 40 cases surgically verified and pathologically proven breast can‐ cers (mean age, 51.2 years; age range, 29–83 years). Histologic analysis demonstrated invasive ductal carcinoma in 25 cases, ductal carcinoma *in situ* in 10, and special type in 5. The median size of the lesions revealed by pathologic examination was 18.3 mm (range 3–45 mm). In addition, 60 cases (mean age, 48.4 years; age range, 28–82 years) including 48 with normal breast findings and 12 with benign conditions (mastopathy in 6; cyst in 3; fibroadenoma in 2; papilloma in 1) were selected. Mention this in abstract as well. Finally, 100 cases (48 normal, 40 with cancer, and 12 with benign lesions) were examined. ACR BI‐RADS for density, a predetermined breast density distribution was followed when selecting the cases: 10 were for cases with extremely dense breasts, 55 with heterogeneously dense breasts, 30 with scattered fibroglandular tissue, and 5 with entirely fatty breasts.

#### **2.2. Image acquisition and display**

With new developments in technology, opportunities for the use of tablet PCs in hospitals for management or diagnosis have increased because of the great advantages they have in terms of portability and applications for teleradiology [1–4]. An increasing number of reports have compared the use of mobile device screens with liquid‐crystal displays (LCDs) for diagnosis, and the accuracy of the former is now considered to be almost equal to that of the latter, or at least acceptable, for MRI diagnosis of spinal injury, radiography and CT diagnosis of intracranial hemorrhage and orthopedic injury, and CT diagnosis of pulmo‐

The viewing of digital mammograms using a soft‐copy reading device has many advantages in terms of image display, better handling, postprocessing capability, computer‐assisted diag‐ nosis, archiving of image information, and image data transmission [9]. High‐grade (so‐called medical purpose) LCDs, such as the 5‐megapixel (MP) LCD, are recommended for soft‐copy

Recently, a high‐resolution 4K color display has also been developed and is commercially available. 4K resolution refers to a display device or content having a horizontal resolution in the order of 4000 pixels. Several examples of 4K resolution exist in the fields of digital televi‐ sion and digital cinematography. To our knowledge, however, there is no definite consensus as to whether a 4K high‐resolution display monitor would be acceptable for reading of mam‐ mograms. In terms of access, portability and cost effectiveness, it would be useful to clarify

The purpose of this study was to assess the observer performance of 4K tablet PCs with a high‐resolution calibrated grayscale display monitor for detection of breast cancers on digital

The study cohort included 40 cases surgically verified and pathologically proven breast can‐ cers (mean age, 51.2 years; age range, 29–83 years). Histologic analysis demonstrated invasive ductal carcinoma in 25 cases, ductal carcinoma *in situ* in 10, and special type in 5. The median size of the lesions revealed by pathologic examination was 18.3 mm (range 3–45 mm). In addition, 60 cases (mean age, 48.4 years; age range, 28–82 years) including 48 with normal breast findings and 12 with benign conditions (mastopathy in 6; cyst in 3; fibroadenoma in 2; papilloma in 1) were selected. Mention this in abstract as well. Finally, 100 cases (48 normal, 40 with cancer, and 12 with benign lesions) were examined. ACR BI‐RADS for density, a predetermined breast density distribution was followed when selecting the cases: 10 were for cases with extremely dense breasts, 55 with heterogeneously dense breasts, 30 with scattered

nary embolism [5–8].

126 New Perspectives in Breast Imaging

reading in digital mammography [10–12].

whether 4K images actually afford better diagnostic accuracy.

mammograms, in comparison with 5‐MP LCDs.

fibroglandular tissue, and 5 with entirely fatty breasts.

**2. Methods and materials**

**2.1. Mammogram selection**

Mammograms were acquired using a flat‐panel digital mammography system (Senographe DS LaVerite; GE Healthcare). The spatial resolution was 100 μm per pixel (pixel dimension: 1800 × 2304) and the contrast resolution was 14 bits.

The images were displayed on two types of display: (i) two monochrome 5‐MP LCDs (MFGD5621HD, 2048 × 2560 pixels, 21.3 inch; BARCO); and (ii) two commercially available 4K tablet PCs with high‐resolution color monitors (4K UT‐MA6, 2560 × 3840 pixels, 20.8 inch; Panasonic) (**Figures 1** and **2**).

The physical properties of the two types of monitors are shown in **Table 1**.

The displays run with the PACS software (We VIEW Z; HITACHI) and viewing software spe‐ cialized for MGs (Plissimo MG, Panasonic). The luminance of both monitors was calibrated as recommended by the suppliers and at the start of the reading test.

#### **2.3. Image interpretation**

Four board‐certified radiologists assessed the mammograms in a dark environment (<10 lux). Each of the observers independently assessed 200 images (100 patients × 2 sides; MLO and CC views). The observers were asked to rate the images on the level of confidence using the BI‐ RADS lexicon: 1, negative; 2, benign; 3, probably benign; 4, suspicious; and 5, highly suggestive of malignancy.

In addition, on another occasion, the observers assessed the image quality in terms of bright‐ ness, contrast, sharpness, and noise, side‐by‐side for the 5‐MP LCDs versus the 4K tablet PCs (5‐step Likert scale, −2 = 5‐MP definitely better and +2 = 4K definitely better).

**Figure 1.** 4k UT‐MA6 (TOUGHPAD) 20.8 inches; Panasonic.

**Figure 2.** Two sets of 4K tablet PCs with high‐resolution color monitors (4K UT‐MA6, 2560 × 3840 pixels, 20.8 inch; Panasonic).


**Table 1.** The physical properties of the 5‐MP LCDs and 4K display monitors used in comparison with observer performance.

#### **2.4. Data and statistical analysis**

The observers' detection performance was evaluated using receiver operating characteristic (ROC) curve analysis. The confidence level results were used to construct ROC curves. This allowed to obtain the sensitivity, specificity, positive predictive value (PPV), negative predic‐ tive value (NPV), and accuracy of each monitor. Image quality ratings were tabulated for each reader and summarized across all readers. The confidence interval (CI) for the proportion of 4K ratings as similar (0), slightly better (±1), or better (±2) was obtained, considering the side‐by‐side comparison to be a single test condition. In the statistical analysis, differences at *P* < 0.05 were considered to be statistically significant.
