Why and how is soft copy reading possible in clinical practice?
The properties of the human visual system (HVS) relevant to the diagnostic process are described after a brief introduction on the general problems and advantages of using soft copy for primary radiology interpretations. At various spatial and temporal frequencies the contrast sensitivity defines the spatial resolution of the eye-brain system and the sensitivity to flicker. The adaptation to the displayed radiological scene and the ambient illumination determine the dynamic range for the operation of the HVS. Although image display devices are determined mainly by state-of-the-art technology, analysis of the HVS may suggest technical characteristics for electronic displays that will help to optimize the display to the operation of the HVS. These include display size, spatial resolution, contrast resolution, luminance range, and noise, from which further consequences for the technical components of a monitor follow. It is emphasized that routine monitor quality control must be available in clinical practice. These image quality measures must be simple enough to be applied as part of the daily routine. These test instructions might also serve as elements of technical acceptance and constancy tests. (+info
A new filtering algorithm for medical magnetic resonance and computer tomography images.
Inner views of tubular structures based on computer tomography (CT) and magnetic resonance (MR) data sets may be created by virtual endoscopy. After a preliminary segmentation procedure for selecting the organ to be represented, the virtual endoscopy is a new postprocessing technique using surface or volume rendering of the data sets. In the case of surface rendering, the segmentation is based on a grey level thresholding technique. To avoid artifacts owing to the noise created in the imaging process, and to restore spurious resolution degradations, a robust Wiener filter was applied. This filter working in Fourier space approximates the noise spectrum by a simple function that is proportional to the square root of the signal amplitude. Thus, only points with tiny amplitudes consisting mostly of noise are suppressed. Further artifacts are avoided by the correct selection of the threshold range. Afterwards, the lumen and the inner walls of the tubular structures are well represented and allow one to distinguish between harmless fluctuations and medically significant structures. (+info
Image processing strategies in picture archiving and communication systems.
An image processing strategy is presented that assures very similar soft-copy presentation on diagnostic workstations of a picture archiving and communication system (PACS) over the lifetime of an image file and simultaneously provides efficient work-flow. The strategy is based on rigid partitioning of image processing into application- and display-device-specific processing. Application-specific processing is optimized for a reference display system. A description of this system is attached to the file header of the application-specifically processed image which is stored in the PACS. Every diagnostic display system automatically reproduces the image quality for which the application-specific processing was optimized by adjusting its properties by display-system-specific processing so that the system becomes effectively equal to the reference display system. (+info
In vivo targeting of acoustically reflective liposomes for intravascular and transvascular ultrasonic enhancement.
OBJECTIVES: The purpose of this study was to target acoustically reflective liposomes to atherosclerotic plaques in vivo for ultrasound image enhancement. BACKGROUND: We have previously demonstrated the development of acoustically reflective liposomes that can be conjugated for site-specific acoustic enhancement. This study evaluates the ability of liposomes coupled to antibodies specific for different components of atherosclerotic plaques and thrombi to target and enhance ultrasonic images in vivo. METHODS: Liposomes were prepared with phospholipids and cholesterol using a dehydration/ rehydration method. Antibodies were thiolated for liposome conjugation with N-succinimidyl 3-(2-pyridyldithio) propionate resulting in a thioether linkage between the protein and the phospholipid. Liposomes were conjugated to antifibrinogen or anti-intercellular adhesion molecule-1 (anti-ICAM-1). In a Yucatan miniswine model, atherosclerosis was developed by crush injury of one carotid and one femoral artery and ingestion of a hypercholesterolemic diet. After full plaque development the arteries were imaged (20-MHz intravascular ultrasound catheter and 7.5-MHz transvascular linear probe) after injection of saline, unconjugated liposomes and antibody conjugated liposomes. RESULTS: Conjugated liposomes retained their acoustically reflective properties and provided ultrasonic image enhancement of their targeted structures. Liposomes conjugated to antifibrinogen attached to thrombi and fibrous portions of the atheroma, whereas liposomes conjugated to anti-ICAM-1 attached to early atheroma. CONCLUSIONS: Our data demonstrate that this novel acoustic agent can provide varying targeting with different antibodies with retention of intravascular and transvascular acoustic properties. (+info
Signal-enhanced color Doppler sonography of deep venous thrombosis in the lower limbs and pelvis.
Detection of Doppler signal tends to be more difficult in peripheral veins owing to low flow velocity. This can be caused by nonoccluding thrombosis, post-thrombotic wall changes, or a deep anatomic location of pelvic veins. The last-mentioned frequently is accompanied by interference by bowel gas. In addition, inappropriate insonation angles adversely affect the outcome of color-coded Doppler interrogation. The purpose of the present study was to evaluate the effectiveness of signal-enhanced color Doppler sonography on peripheral veins in 31 patients clinically suspected of having deep vein thrombosis. As a result of diagnostic uncertainty, additional enhanced studies were performed on 43 venous segments. The enhancement led to a decrease in false-positive results (from four patients to one patient) and false-negative results (from four patients to two patients) compared to unenhanced studies. Evaluation of the deeply located pelvic veins profited the most through signal enhanced Doppler sonography. (+info
Lumen reduction measurements of the internal carotid artery before and after Levovist enhancement: reproducibility and agreement with angiography.
Our aim was to assess reproducibility of three different lumen reduction measuring methods--North American Symptomatic Carotid Endarterectomy Trial, European Carotid Surgery Trial, and common carotid--using power Doppler and color Doppler sonography before and after Levovist enhancement. We included 20 symptomatic patients with mild or severe carotid disease. North American Symptomatic Carotid Endarterectomy Trial, European Carotid Surgery Trial, and common carotid measurements on longitudinal views and European Carotid Surgery Trial measurements on transverse views were performed. Examinations were repeated and the results compared to assess reproducibility of measurements. Correlation with angiography was obtained by calculating Pearson correlation coefficients. Reproducibility was significantly better (P < 0.05) for European Carotid Surgery Trial and common carotid measurements (95% limits of agreement between -10% to 10% and -19% to 17%) as compared to North American Symptomatic Carotid Endarterectomy Trial measurements (95% limits of agreement between -11% to 21% and -21% to 23%). Variability of measurements after enhancement increased slightly (not significant) for both power and color Doppler sonography. Additionally, European Carotid Surgery Trial measurements, using nonenhanced power Doppler or color Doppler sonography, did not correlate significantly with angiography, whereas North American Symptomatic Carotid Endarterectomy Trial and common carotid measurements correlated well with angiography, particularly in power Doppler mode after enhancement (r = 0.88 and r = 0.82, respectively). We conclude that for lumen reduction measurements of the internal carotid artery with power and color Doppler sonography, the common carotid method is the only method that is reproducible and has good correlation with angiography, which slightly improves after Levovist enhancement. (+info
Statistical power of MRI monitored trials in multiple sclerosis: new data and comparison with previous results.
OBJECTIVES: To evaluate the durations of the follow up and the reference population sizes needed to achieve optimal and stable statistical powers for two period cross over and parallel group design clinical trials in multiple sclerosis, when using the numbers of new enhancing lesions and the numbers of active scans as end point variables. METHODS: The statistical power was calculated by means of computer simulations performed using MRI data obtained from 65 untreated relapsing-remitting or secondary progressive patients who were scanned monthly for 9 months. The statistical power was calculated for follow up durations of 2, 3, 6, and 9 months and for sample sizes of 40-100 patients for parallel group and of 20-80 patients for two period cross over design studies. The stability of the estimated powers was evaluated by applying the same procedure on random subsets of the original data. RESULTS: When using the number of new enhancing lesions as the end point, the statistical power increased for all the simulated treatment effects with the duration of the follow up until 3 months for the parallel group design and until 6 months for the two period cross over design. Using the number of active scans as the end point, the statistical power steadily increased until 6 months for the parallel group design and until 9 months for the two period cross over design. The power estimates in the present sample and the comparisons of these results with those obtained by previous studies with smaller patient cohorts suggest that statistical power is significantly overestimated when the size of the reference data set decreases for parallel group design studies or the duration of the follow up decreases for two period cross over studies. CONCLUSIONS: These results should be used to determine the duration of the follow up and the sample size needed when planning MRI monitored clinical trials in multiple sclerosis. (+info
Dodecafluoropentane ultrasonic contrast enhancement in carotid diagnosis: preliminary results.
To assess the efficacy in carotid diagnosis of an investigational dodecafluoropentane ultrasonic contrast enhancing agent, we compared B-mode, color flow, and duplex Doppler findings in 16 patients with common carotid artery bifurcation disease after dodecafluoropentane and saline injections. Dodecafluoropentane produced enhanced backscatter in all patients for 4 to 20 min (mean, 8.4+/-4.74 min) after intravenous injection. In six patients this enhancement improved the color flow and pulsed Doppler signal detection in areas of sonographic shadowing. The enhanced color flow information changed the diagnostic impression in one case. Dodecafluoropentane produced enhanced backscatter in the carotid artery in all patients, and for a mean duration longer than that reported for other agents. It has the potential to improve the efficacy of carotid ultrasonic evaluation. (+info