Evaluation of Irreversible Compression Ratios for Medical Images Thin Slice CT and Update of Canadian Association of Radiologists (CAR) Guidelines

Abstract

In June 2008, the Canadian Association of Radiologists published its Standards for Irreversible Compression in Digital Diagnostic Imaging within Radiology (Canadian Association of Radiologists 2012). The study suggested that at low levels of compression there was no difference in diagnostic accuracy between uncompressed JPEG and JPEG 2000. There were two exceptions; CT neurological and CT body images resulted in lower rating of image quality (Koff et al., J Digit Imaging 22(6):569-78, 2009). The slice thicknesses used in the previous study were greater than 5 mm. However, other studies (Ringl et al., Radiology 240:869-87, 2006) suggest that thin CT slices might modify image tolerance to irreversible compression. Therefore, a new clinical evaluation using CT slices less than 3 mm was initiated. We examined CT images in four body regions (chest, body, musculoskeletal, and neurological). Twenty-five radiologists from across Canada participated. Each read a total of 70 CTs in his specialty; 10 at each of seven levels of compression (uncompressed, JPEG and JPEG 2000 at low, medium, and high compression (varying by region)). Each reader diagnosed the case, rated his confidence, and compared the compressed to the uncompressed image and rated the degree of degradation. Data were analyzed for sensitivity, specificity, accuracy, confidence, and degradation at three levels and two types of compression as well as the original image. There were no overall differences in sensitivity, specificity, accuracy, or confidence. JPEG images, at all levels of compression, were rated lower in terms of perceived difference (4.16/5 vs. 4.53/5 for JPEG 2000 and 4.68/5 for uncompressed). However, the rating of perceived difference was not significantly correlated with accuracy. Analysis of individual body regions did not reveal any systematic effects of compression in any region.

About a method for compressing x-ray computed microtomography data

“…An additional difficulty is represented by the lack of compression methods standardization making comparison and selection of the compression level nearly impossible [18]. In medical radiology, usually the reconstructed CT images are stored and compressed [21,22]. In the present literature, only one study proposed the lossy compression for raw/projection images in multi-slice medical CT [23].…”

Evaluating image quality measures to assess the impact of lossy data compression applied to climate simulation data

“…The authors in [BXH∗17] indicate that the SSIM threshold chosen was largely inspired by suggestions from the medical imaging field, where lossy compression is typically used to reduce unmanageable data volumes (e.g., [CP16, KR12, Wan11, KS06]). Indeed, the loss of critical information (a concern shared by climate scientists) is understandably a concern with procedures such as computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound imaging (e.g., [KBMG13, KMLH10, GKS∗12b]). However, an acceptable SSIM threshold varies by application, and the authors in [BXH∗ 17] acknowledge that further research is required to confidently select one for CESM images.…”

PACS for the Developing World

“…2) Given the larger file size for radiographic studies compared to the alphanumeric data produced by electronic medical records, DW-PACS should be able to perform image compression. There is well-established evidence that moderate levels of irreversible ('lossy') compression can be applied to all types of radiologic imaging without significant visual quality loss or image degradation (19,20). DW-PACS should therefore be capable of supporting both reversible ('lossless') and, more importantly, irreversible data compression.…”