Vasundhara Bajpai - Academia.edu (original) (raw)

Uploads

Papers by Vasundhara Bajpai

Research paper thumbnail of Definition of Compression Ratio: Difference Between Two Commercial JPEG2000 Program Libraries

Telemedicine and e-Health, 2008

The objective was to demonstrate the difference in the definition of compression ratio between tw... more The objective was to demonstrate the difference in the definition of compression ratio between two popular commercial JPEG 2000 program libraries. An institutional review board approved this study and waived informed consent. Using each of two JPEG 2000 libraries (libraries A and B), 20 abdomen computed tomography images with 12-bit depth (from scanner 1) and 20 images with 16-bit depth (from scanner 2) were compressed to three different nominal compression ratios: 10:1, 15:1, and 20:1. Achieved compression ratios (the original image file size to the compressed size) were compared with the nominal compression ratios using one-sample t-test tests. At each nominal compression level, the achieved compression ratios for scanner 1 images compressed using library A were approximately 1.33-fold greater than the nominal compression ratio (p < 0.0001), while the achieved compression ratios for the remaining three scanner-library combinations (scanner 1-library B, scanner 2-library A, and scanner 2-library B) were approximately the same as the nominal compression ratio (p-value range, 0.22-0.93). The definition of compression ratio is different between commercial JPEG 2000 program libraries. The definition should be standardized to facilitate the adoption and communication of an acceptable compression level.

Research paper thumbnail of Introduction to Grayscale Calibration and Related Aspects of Medical Imaging Grade Liquid Crystal Displays

Journal of Digital Imaging, 2008

Consistent presentation of digital radiographic images at all locations within a medical center c... more Consistent presentation of digital radiographic images at all locations within a medical center can help ensure a high level of patient care. Currently, liquid crystal displays (LCDs) are the electronic display technology of choice for viewing medical images. As the inherent luminance (and thereby perceived contrast) properties of different LCDs can vary substantially, calibration of the luminance response of these displays is required to ensure that observer perception of an image is consistent on all displays. The digital imaging and communication in medicine (DICOM) grayscale standard display function (GSDF) defines the luminance response of a display such that an observer's perception of image contrast is consistent throughout the pixel value range of a displayed image. The main purpose of this work is to review the theoretical and practical aspects of calibration of LCDs to the GSDF. Included herein is a review of LCD technology, principles of calibration, and other practical aspects related to calibration and observer perception of images presented on LCDs. Both grayscale and color displays are considered, and the influence of ambient light on calibration and perception is discussed.

Research paper thumbnail of Appendiceal Diverticulitis

Journal of Computer Assisted Tomography, 2007

To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography ... more To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography (n = 20) and clinical findings in 23 patients with appendiceal diverticulitis were retrospectively reviewed and compared with those in 23 patients with usual acute appendicitis. Computed tomography visualized the inflamed diverticula (up to 4 per patient) mostly as small (median, 7.5 mm) round cystic outpouchings at the distal appendix with contrast enhancement at the cyst wall in 16 (80%) patients with appendiceal diverticulitis. In 50% of appendiceal diverticulitis patients, computed tomographic diagnosis of accompanying appendicitis was false positive. Appendicolith was rarely observed in the appendiceal diverticulitis group (5% vs 48%, P = 0.002). No significant difference was observed in the clinical findings except for the patient age (median, 45 vs 31 years; P = 0.001). Most appendiceal diverticulitis can be differentiated from usual acute appendicitis at computed tomography by visualization of the inflamed diverticulum.

Research paper thumbnail of Regional variance of visually lossless threshold in compressed chest CT images: Lung versus mediastinum and chest wall

European Journal of Radiology, 2009

Objective: To estimate the visually lossless threshold (VLT) for the Joint Photographic Experts G... more Objective: To estimate the visually lossless threshold (VLT) for the Joint Photographic Experts Group (JPEG) 2000 compression of chest CT images and to demonstrate the variance of the VLT between the lung and mediastinum/chest wall. Subjects and methods: Eighty images were compressed reversibly (as negative control) and irreversibly to 5:1, 10:1, 15:1 and 20:1. Five radiologists determined if the compressed images were distinguishable from their originals in the lung and mediastinum/chest wall. Exact tests for paired proportions were used to compare the readers' responses between the reversible and irreversible compressions and between the lung and mediastinum/chest wall. Results: At reversible, 5:1, 10:1, 15:1, and 20:1 compressions, 0%, 0%, 3-49% (p < .004, for three readers), 69-99% (p < .001, for all readers), and 100% of the 80 image pairs were distinguishable in the lung, respectively; and 0%, 0%, 74-100% (p < .001, for all readers), 100%, and 100% were distinguishable in the mediastinum/chest wall, respectively. The image pairs were less frequently distinguishable in the lung than in the mediastinum/chest wall at 10:1 (p < .001, for all readers) and 15:1 (p < .001, for two readers). In 321 image comparisons, the image pairs were indistinguishable in the lung but distinguishable in the mediastinum/chest wall, whereas there was no instance of the opposite. Conclusion: For JPEG2000 compression of chest CT images, the VLT is between 5:1 and 10:1. The lung is more tolerant to the compression than the mediastinum/chest wall.

Research paper thumbnail of Differences in Compression Artifacts on Thin- and Thick-Section Lung CT Images

American Journal of Roentgenology, 2008

The purpose of our study was to show the difference of Joint Photographic Experts Group (JPEG) 20... more The purpose of our study was to show the difference of Joint Photographic Experts Group (JPEG) 2000 compression artifacts in the lung between thin- and thick-section CT images. Thirty-five thin-section (1 mm) and 35 corresponding thick-section (5 mm) images were compressed to reversible and irreversible 4:1, 6:1, 8:1, 10:1, and 15:1. In each compressed image, pixels outside the lung were replaced with those from the original image. By comparing the compressed and original images, three radiologists independently rated the compression artifacts using grades of 0 (none, the two images were indistinguishable), 1 (image differences were barely perceptible), 2 (image differences were subtle), or 3 (image differences were significant). At each compression level, thin and thick sections were compared for peak signal-to-noise ratio (PSNR) using paired t tests and for the readers&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; responses using Wilcoxon&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s signed rank tests and exact tests for paired proportions. Thin sections had smaller PSNR (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001). Thin sections had higher grades of artifacts than thick sections, showing significant differences at compression levels of 10:1 (mean score, 0.8 vs 0.4, 0.9 vs 0.1, 0.3 vs 0.0; p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.009 for the three readers) and 15:1 (1.9 vs 1.0, 1.9 vs 1.1, 1.5 vs 0.6; p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001). The percentages of distinguishable pairs (grades 1-3) were greater for thin sections than for thick sections, showing a statistically significant difference at 10:1 for two readers (31% vs 3% and 74% vs 37%; p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.006). The lung shows more compression artifacts on thin sections than on thick sections. Section thickness should be taken into consideration when adjusting the compression level for lung CT images.

Research paper thumbnail of Prediction of Perceptible Artifacts in JPEG 2000–Compressed Chest CT Images Using Mathematical and Perceptual Quality Metrics

American Journal of Roentgenology, 2008

To test a perceptual quality metric (high-dynamic range visual difference predictor, HDR-VDP) in ... more To test a perceptual quality metric (high-dynamic range visual difference predictor, HDR-VDP) in predicting perceptible artifacts in Joint Photographic Experts Group 2000 compressed thin-and thick-section abdomen computed tomography images.

Research paper thumbnail of Appendiceal Diverticulitis

Journal of Computer Assisted Tomography, 2007

To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography ... more To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography (n = 20) and clinical findings in 23 patients with appendiceal diverticulitis were retrospectively reviewed and compared with those in 23 patients with usual acute appendicitis. Computed tomography visualized the inflamed diverticula (up to 4 per patient) mostly as small (median, 7.5 mm) round cystic outpouchings at the distal appendix with contrast enhancement at the cyst wall in 16 (80%) patients with appendiceal diverticulitis. In 50% of appendiceal diverticulitis patients, computed tomographic diagnosis of accompanying appendicitis was false positive. Appendicolith was rarely observed in the appendiceal diverticulitis group (5% vs 48%, P = 0.002). No significant difference was observed in the clinical findings except for the patient age (median, 45 vs 31 years; P = 0.001). Most appendiceal diverticulitis can be differentiated from usual acute appendicitis at computed tomography by visualization of the inflamed diverticulum.

Research paper thumbnail of Definition of Compression Ratio: Difference Between Two Commercial JPEG2000 Program Libraries

Telemedicine and e-Health, 2008

The objective was to demonstrate the difference in the definition of compression ratio between tw... more The objective was to demonstrate the difference in the definition of compression ratio between two popular commercial JPEG 2000 program libraries. An institutional review board approved this study and waived informed consent. Using each of two JPEG 2000 libraries (libraries A and B), 20 abdomen computed tomography images with 12-bit depth (from scanner 1) and 20 images with 16-bit depth (from scanner 2) were compressed to three different nominal compression ratios: 10:1, 15:1, and 20:1. Achieved compression ratios (the original image file size to the compressed size) were compared with the nominal compression ratios using one-sample t-test tests. At each nominal compression level, the achieved compression ratios for scanner 1 images compressed using library A were approximately 1.33-fold greater than the nominal compression ratio (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001), while the achieved compression ratios for the remaining three scanner-library combinations (scanner 1-library B, scanner 2-library A, and scanner 2-library B) were approximately the same as the nominal compression ratio (p-value range, 0.22-0.93). The definition of compression ratio is different between commercial JPEG 2000 program libraries. The definition should be standardized to facilitate the adoption and communication of an acceptable compression level.

Research paper thumbnail of Introduction to Grayscale Calibration and Related Aspects of Medical Imaging Grade Liquid Crystal Displays

Journal of Digital Imaging, 2008

Consistent presentation of digital radiographic images at all locations within a medical center c... more Consistent presentation of digital radiographic images at all locations within a medical center can help ensure a high level of patient care. Currently, liquid crystal displays (LCDs) are the electronic display technology of choice for viewing medical images. As the inherent luminance (and thereby perceived contrast) properties of different LCDs can vary substantially, calibration of the luminance response of these displays is required to ensure that observer perception of an image is consistent on all displays. The digital imaging and communication in medicine (DICOM) grayscale standard display function (GSDF) defines the luminance response of a display such that an observer's perception of image contrast is consistent throughout the pixel value range of a displayed image. The main purpose of this work is to review the theoretical and practical aspects of calibration of LCDs to the GSDF. Included herein is a review of LCD technology, principles of calibration, and other practical aspects related to calibration and observer perception of images presented on LCDs. Both grayscale and color displays are considered, and the influence of ambient light on calibration and perception is discussed.

Research paper thumbnail of Appendiceal Diverticulitis

Journal of Computer Assisted Tomography, 2007

To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography ... more To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography (n = 20) and clinical findings in 23 patients with appendiceal diverticulitis were retrospectively reviewed and compared with those in 23 patients with usual acute appendicitis. Computed tomography visualized the inflamed diverticula (up to 4 per patient) mostly as small (median, 7.5 mm) round cystic outpouchings at the distal appendix with contrast enhancement at the cyst wall in 16 (80%) patients with appendiceal diverticulitis. In 50% of appendiceal diverticulitis patients, computed tomographic diagnosis of accompanying appendicitis was false positive. Appendicolith was rarely observed in the appendiceal diverticulitis group (5% vs 48%, P = 0.002). No significant difference was observed in the clinical findings except for the patient age (median, 45 vs 31 years; P = 0.001). Most appendiceal diverticulitis can be differentiated from usual acute appendicitis at computed tomography by visualization of the inflamed diverticulum.

Research paper thumbnail of Regional variance of visually lossless threshold in compressed chest CT images: Lung versus mediastinum and chest wall

European Journal of Radiology, 2009

Objective: To estimate the visually lossless threshold (VLT) for the Joint Photographic Experts G... more Objective: To estimate the visually lossless threshold (VLT) for the Joint Photographic Experts Group (JPEG) 2000 compression of chest CT images and to demonstrate the variance of the VLT between the lung and mediastinum/chest wall. Subjects and methods: Eighty images were compressed reversibly (as negative control) and irreversibly to 5:1, 10:1, 15:1 and 20:1. Five radiologists determined if the compressed images were distinguishable from their originals in the lung and mediastinum/chest wall. Exact tests for paired proportions were used to compare the readers' responses between the reversible and irreversible compressions and between the lung and mediastinum/chest wall. Results: At reversible, 5:1, 10:1, 15:1, and 20:1 compressions, 0%, 0%, 3-49% (p < .004, for three readers), 69-99% (p < .001, for all readers), and 100% of the 80 image pairs were distinguishable in the lung, respectively; and 0%, 0%, 74-100% (p < .001, for all readers), 100%, and 100% were distinguishable in the mediastinum/chest wall, respectively. The image pairs were less frequently distinguishable in the lung than in the mediastinum/chest wall at 10:1 (p < .001, for all readers) and 15:1 (p < .001, for two readers). In 321 image comparisons, the image pairs were indistinguishable in the lung but distinguishable in the mediastinum/chest wall, whereas there was no instance of the opposite. Conclusion: For JPEG2000 compression of chest CT images, the VLT is between 5:1 and 10:1. The lung is more tolerant to the compression than the mediastinum/chest wall.

Research paper thumbnail of Differences in Compression Artifacts on Thin- and Thick-Section Lung CT Images

American Journal of Roentgenology, 2008

The purpose of our study was to show the difference of Joint Photographic Experts Group (JPEG) 20... more The purpose of our study was to show the difference of Joint Photographic Experts Group (JPEG) 2000 compression artifacts in the lung between thin- and thick-section CT images. Thirty-five thin-section (1 mm) and 35 corresponding thick-section (5 mm) images were compressed to reversible and irreversible 4:1, 6:1, 8:1, 10:1, and 15:1. In each compressed image, pixels outside the lung were replaced with those from the original image. By comparing the compressed and original images, three radiologists independently rated the compression artifacts using grades of 0 (none, the two images were indistinguishable), 1 (image differences were barely perceptible), 2 (image differences were subtle), or 3 (image differences were significant). At each compression level, thin and thick sections were compared for peak signal-to-noise ratio (PSNR) using paired t tests and for the readers&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; responses using Wilcoxon&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s signed rank tests and exact tests for paired proportions. Thin sections had smaller PSNR (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001). Thin sections had higher grades of artifacts than thick sections, showing significant differences at compression levels of 10:1 (mean score, 0.8 vs 0.4, 0.9 vs 0.1, 0.3 vs 0.0; p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.009 for the three readers) and 15:1 (1.9 vs 1.0, 1.9 vs 1.1, 1.5 vs 0.6; p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001). The percentages of distinguishable pairs (grades 1-3) were greater for thin sections than for thick sections, showing a statistically significant difference at 10:1 for two readers (31% vs 3% and 74% vs 37%; p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.006). The lung shows more compression artifacts on thin sections than on thick sections. Section thickness should be taken into consideration when adjusting the compression level for lung CT images.

Research paper thumbnail of Prediction of Perceptible Artifacts in JPEG 2000–Compressed Chest CT Images Using Mathematical and Perceptual Quality Metrics

American Journal of Roentgenology, 2008

To test a perceptual quality metric (high-dynamic range visual difference predictor, HDR-VDP) in ... more To test a perceptual quality metric (high-dynamic range visual difference predictor, HDR-VDP) in predicting perceptible artifacts in Joint Photographic Experts Group 2000 compressed thin-and thick-section abdomen computed tomography images.

Research paper thumbnail of Appendiceal Diverticulitis

Journal of Computer Assisted Tomography, 2007

To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography ... more To describe the computed tomographic findings of appendiceal diverticulitis. Computed tomography (n = 20) and clinical findings in 23 patients with appendiceal diverticulitis were retrospectively reviewed and compared with those in 23 patients with usual acute appendicitis. Computed tomography visualized the inflamed diverticula (up to 4 per patient) mostly as small (median, 7.5 mm) round cystic outpouchings at the distal appendix with contrast enhancement at the cyst wall in 16 (80%) patients with appendiceal diverticulitis. In 50% of appendiceal diverticulitis patients, computed tomographic diagnosis of accompanying appendicitis was false positive. Appendicolith was rarely observed in the appendiceal diverticulitis group (5% vs 48%, P = 0.002). No significant difference was observed in the clinical findings except for the patient age (median, 45 vs 31 years; P = 0.001). Most appendiceal diverticulitis can be differentiated from usual acute appendicitis at computed tomography by visualization of the inflamed diverticulum.