Creation of radiopaque thrombi for in vivo experiments.

PURPOSE: A number of percutaneous thrombectomy devices are undergoing investigation for treatment of patients with venous thromboembolism. Use of radiopaque thrombus to monitor thrombus delivery and assess thrombectomy has been previously reported. The purpose of this project was to quantitatively test the effect of mixing different ratios of blood and contrast material to facilitate maximum thrombus formation and radiopacity. MATERIALS AND METHODS: The following ratios of blood and contrast material were mixed: 2 mL blood to 8 mL contrast material (ratio = 0.25), 4 mL blood to 6 mL contrast material (ratio = 0.67), 6 mL blood to 4 mL contrast material (ratio = 1.5), and 8 mL blood to 2 mL contrast material (ratio = 4). Contrast material was added at day 0, 3, or 6. Each sample received one of two ionic contrast agents to opacify the clots. At day 14, thrombus mass and opacity were determined. RESULTS: Three combinations of blood and contrast material produced maximum thrombus and radiopacity. These were sodium iothalamate 30% with a ratio of 4 with contrast material added on day 0 and sodium iothalamate 60% with a ratio of 1.5 with contrast material added on day 3 or 6. CONCLUSIONS: When forming radiopaque thrombi, significant differences can result from the ratio of blood to contrast material used. Contrast material type can also affect radiopacity and mass formed. The use of optimal ratios of blood to contrast material should maximize device evaluation with minimal wasting of valuable resources such as test subjects, physician time, and equipment.

A comparison of wavelet and Joint Photographic Experts Group lossy compression methods applied to medical images.

This presentation focuses on the quantitative comparison of three lossy compression methods applied to a variety of 12-bit medical images. One Joint Photographic Exports Group (JPEG) and two wavelet algorithms were used on a population of 60 images. The medical images were obtained in Digital Imaging and Communications in Medicine (DICOM) file format and ranged in matrix size from 256 x 256 (magnetic resonance [MR]) to 2,560 x 2,048 (computed radiography [CR], digital radiography [DR], etc). The algorithms were applied to each image at multiple levels of compression such that comparable compressed file sizes were obtained at each level. Each compressed image was then decompressed and quantitative analysis was performed to compare each compressed-then-decompressed image with its corresponding original image. The statistical measures computed were sum of absolute differences, sum of squared differences, and peak signal-to-noise ratio (PSNR). Our results verify other research studies which show that wavelet compression yields better compression quality at constant compressed file sizes compared with JPEG. The DICOM standard does not yet include wavelet as a recognized lossy compression standard. For implementers and users to adopt wavelet technology as part of their image management and communication installations, there has to be significant differences in quality and compressibility compared with JPEG to justify expensive software licenses and the introduction of proprietary elements in the standard. Our study shows that different wavelet implementations vary in their capacity to differentiate themselves from the old, established lossy JPEG.

Assessment of resident knowledge: subjective assessment versus performance on the ACR in-training examination.

RATIONALE AND OBJECTIVES: The authors assessed the ability of faculty and residents to predict the ranked performance of residents on the American College of Radiology (ACR) In-Training Examination. MATERIALS AND METHODS: Radiology faculty at Penn State Geisinger Health System (PSGHS), the Medical College of Virginia (MCV), and the University of Virginia (UVA) and residents at PSGHS and MCV ranked the expected performances of residents taking the 1997 ACR In-Training Examination. Surveyed faculty and residents were blinded to the actual performances on the examination. Forty-nine residents took the examination (21 at PSGHS, 22 at MCV, six at UVA), and 37 faculty members (11 at PSGHS, 11 at MCV, 15 at UVA) participated in the study. Correlation analysis was performed to assess the agreement between the subjective and actual ranking of residents in each residency class. RESULTS: Faculty were moderately accurate in the overall ranking of resident performances (r = 0.34). High levels of concordance for ranking individual residents correlated with accuracy in only certain cases. Differences in agreement and accuracy of the respondents existed between PSGHS and MCV (P = .0001 and .0014, respectively). The concordance of respondents increased significantly from the 1st- to the 2nd-year class at MCV (P = .0002), whereas accuracy increased significantly between these classes for the PSGHS (P = .042). CONCLUSION: Faculty are only moderately successful in ranking resident performances on the ACR In-Training Examination, and a high level of agreement is not necessarily indicative of increased accuracy. The concordance and accuracy of subjective rankings differ among residency programs and classes.