Background Cartilage loss is irreversible progress, so physicians have to catch the detection of joint space narrowing as early as possible. It is stated that physical disability in rheumatoid arthritis (RA) is associated with joint space narrowing rather than erosion , so early detection of progressive joint damage is the most important. But in DICOM which is the international standard for medical images, 1 pixel on radiographic images is 0.15mm, so the detection of the change which is lower than that is impossible.
Objectives To solve a limitation associated with the resolution, we used radiographic images reconstructed by super-resolution system by utilizing total variation filter combined a shock filter, which is a non-linear filter, to emphasize the edges in images . Theoretically image resolution becomes four times (Fig. 1). We measured the distance between joint space of metacarpophalangeal (MCP) joint and confirmed the validity of the new measurement procedure of the distance between joint space by using super resolution image.
Methods We prepared the super resolution-radiographic images processed by total variation filter and a shock filter and cropped the images of MCP joint. We measured the distance between joint space by three methods, 1) conventional measurement; distance between two points, 2) measurement by using normal vector from the top of joint surface of phalanx bone, 3) measurement using joint space area calculated by integration method (Fig. 2). Each method processed on MATLAB®. The 2), 3) methods were processed by curve fitting method which create parabolic curve by choosing some points of joint surface. We performed measurement five times by each method to confirm the accuracy by using super resolution image and standard DICOM image.
Results We measured Lt 3rd MCP joint with 49 y.o. female, rheumatoid arthritis patient by each measurement on super resolution image and standard DICOM image.
The measurement results are shown in Table 1. It was significantly different between super resolution and normal resolution by two points measurement with f-test. Although it was not significantly different on condition about resolution by the measurement using curve fitting methods with f-test, the value with super resolution image tended to be smaller than that with normal resolution.
Conclusions The accuracy of measuring the joint space distance of MCP joint was improved by using super-resolution image. Curve fitting method was also supposed to be useful about the evaluation of joint space narrowing. This result suggested that it is possible to detect the change less than 0.1mm beyond the limitation of DICOM image.
Ann Rheum Dis. 2011 May;70(5):733-739.
IEEE Global Conference on Consumer Electronics (GCCE2013) 2013;: 447-448.
Disclosure of Interest K. Funahashi: None declared, T. Kojima Grant/research support from: Takeda Pharma Corporation, Janssen Pharmaceutical, and Astellas Pharma Corporation., Speakers bureau: Mitsubishi Tanabe Pharma Corporation, Takeda Pharma Corporation, Eisai Pharma Corporation, Abbvie, Bristol-Myers Squibb, Pfizer, Chugai Pharma Corporation, Janssen Pharmaceutical, and Astellas Pharma Corporation, N. Takahashi Speakers bureau: Abbvie Japan Co. Ltd, Eisai Co. Ltd, UCB Japan Co. Ltd,Mitsubishi Tanabe Pharma Corporation, Takeda Pharmaceutical Company Ltd, Pfizer Co. Ltd, Chugai PharmaceuticalCo. Ltd, Janssen Pharmaceutical K.K., and Bristol-Myers Squibb Co. Ltd., T. Goto: None declared, M. Shimizu: None declared, N. Ishiguro Grant/research support from: Daiichi Sankyo, Takeda Pharmaceutical, Hisamitsu Pharmaceutical, Otsuka Pharmaceutical, Taisho Toyama Pharmaceutical, Kaken Pharmaceutical, Eisai, Janssen Pharmaceutical, Bristol-Myers Squibb, Abbott Japan, Chugai Pharmaceutical, Mitsubishi Tanabe Pharmaceutical, Astellas Pharma, and Pfizer Japan, Speakers bureau: Daiichi Sankyo, Takeda Pharmaceutical, Hisamitsu Pharmaceutical, Otsuka Pharmaceutical, Taisho Toyama Pharmaceutical, Kaken Pharmaceutical, Eisai, Janssen Pharmaceutical, Bristol-Myers Squibb, Abbott Japan, Chugai Pharmaceutical, Mitsubishi Tanabe Pharmaceutical, Astellas Pharma, and Pfizer Japan.