119 research outputs found
Image and Signal Processing in Intravascular Ultrasound
Intravascular ultrasound (rvUS) is a new imaging mOdality providing real-time, crosssectional,
high-resolution images of the arterial lumen and vessel wall. In contrast to
conventional x-ray angiography that only displays silhouette views of the vessel lumen,
IVUS imaging permits visualization of lesion morphology and accurate measurements
of arterial cross-sectional dimensions in patients. These unique capabilities have led to
many important clinical applications including quantitative assessment of the severity,
restenosis, progression of atherosclerosis, selection and guidance of catheterbased
therapeutic procedures and short- and long-term evaluation of the outcome of an
intravascular intervention.
Like the progress of other medial imaging modalities, the advent of IVUS techniques
has brought in new challenges in the field of signal and image processing. Quantitative
analysis of IVUS images requires the identification of arterial structures such as the
lumen and plaque within an image. Manual contour tracing is well known to be time
consuming and subjective. Development of an automated contour detection method
may improve the reproducibility of quantitative IVUS and avoid a tedious manual
procedure. Computerized three-dimensional (3D) reconstruction of an IVUS image
series may extend the tomographic data to a more powerful volumetric assessment of
the vessel segment. Obviously, this could not be achieved without the advance of 3D
image processing techniques. Furthermore, it is demonstrated that processing of the
original radio frequency (RF) echo signals provides an efficient means to improve the
IVUS image quality as well as a new approach to extract volumetric flow information.
The goals of the studies reported in this thesis are therefore directed toward
development of video image and RF signal processing techniques for image
enhancement, automated contour detection, 3D reconstruction and flow imaging.
In this chapter several IVUS scanning mechanisms and some background information
about ultrasonic imaging are briefly introduced. The principles of different video-based
contour detection approaches and examples of contour detection in echocardiograms
are discussed. Subsequently, applications of RF analysis in IVUS images are reviewed,
followed by the scope of this thesis in the final part
Temporal averaging for quantification of lumen dimensions in intravascular ultrasound images
Quantitative analysis of arterial dimensions from high frequency intravascular ultrasound images (30 MHz) may be hampered by strong blood scattering. Replacement of blood by saline is one method to provide a clear view of the arterial lumen; another method is that of temporal averaging of successive ultrasound images. The accuracy of this latter method was tested by comparing the lumen area measurements on the temporal-averaged image, with the data of the same cross-section obtained from the single-frame and saline-filled images. The mean lumen area measured on the temporal-averaged images was similar to that measured on the single-frame images (mean difference: â0.02 ± 1.16 mm2; p = ns). The mean lumen a
ECG-Gated Three-dimensional Intravascular Ultrasound
Background Automated systems for the quantitative analysis of three-dimensional (3D) sets of intravascular ultrasound (IVUS) images have been developed to reduce the time required to perform volumetric analyses; however, 3D image reconstruction by these nongated systems is frequently hampered by cyclic artifacts.
Methods and Results We used an ECG-gated 3D IVUS image acquisition workstation and a dedicated pullback device in atherosclerotic coronary segments of 30 patients to evaluate (1) the feasibility of this approach of image acquisition, (2) the reproducibility of an automated contour detection algorithm in measuring lumen, external elastic membrane, and plaque+media cross-sectional areas (CSAs) and volumes and the cross-sectional and volumetric plaque+media burden, and (3) the agreement between the automated area measurements and the results of manual tracing. The gated image acquisition took 3.9±1.5 minutes. The length of the segments analyzed was 9.6 to 40.0 mm, with 2.3±1.5 side branches per segment. The minimum lumen CSA measured 6.4±1.7 mm2, and the maximum and average CSA plaque+media burden measured 60.5±10.2% and 46.5±9.9%, respectively. The automated contour-detection required 34.3±7.3 minutes per segment. The differences between these measurements and manual tracing did not exceed 1.6% (SD<6.8%). Intraobserver and interobserver differences in area measurements (n=3421; r=.97 to.99) were <1.6% (SD<7.2%); intraobserver and interobserver differences in volumetric measurements (n=30; r=.99) were <0.4% (SD<3.2%).
Conclusions ECG-gated acquisition of 3D IVUS image sets is feasible and permits the application of automated contour detection to provide reproducible measurements of the lumen and atherosclerotic plaque CSA and volume in a relatively short analysis time
Intravascular ultrasound predictors of outcome after peripheral balloon angioplasty
Objective:This study investigates the potential role of intravascular ultrasound (IVUS) in the outcome in patients undergoing percutaneous transluminal angioplasty (PTA) of the superficial femoral artery.Materials:Angiographic and the qualitative and quantitative IVUS data obtained at the narrowest site derived from 39 patients before and after PTA were analysed.Results:Angiographically the diameter of the remaining stenosis seen after PTA was classified as < 50% in 31 patients (success); in eight patients a failure was encountered. Evaluating at 6 months the functional and anatomic results of the PTA in 31 patients, the intervention was a success in 14 patients (Group I) and a failure in 17 patients (Group II). The remaining eight patients defined as angiographic failure following PTA comprised Group III. Neither qualitative nor quantitative IVUS data obtained before PTA could predict outcome. Conversely, after PTA, the extent of dissection was significantly more severe in Groups II and III than in Group I. Similarly, significant differences were found between Groups I and II for mean free lumen area (13.2 vs. 9.7 mm2, respectively) and mean free lumen diameter (4.1 vs. 3.5 mm, respectively). Quantitative data obtained in Group II were similar to those in Group III.Conclusion:This preliminary study demonstrates that following PTA the extent of dissection, free lumen area and diameter seen with IVUS are predictive factors of patency. Future studies with more patients are mandatory to further highlight the sensitivity of these observations
Identification and characterization of microRNAs expressed in the African malaria vector Anopheles funestus life stages using high throughput sequencing
Background: Over the past several years, thousands of microRNAs (miRNAs) have been identified in the genomes of various insects through cloning and sequencing or even by computational prediction. However, the number of miRNAs identified in anopheline species is low and little is known about their role. The mosquito Anopheles funestus is one of the dominant malaria vectors in Africa, which infects and kills millions of people every year. Therefore, small RNA molecules isolated from the four life stages (eggs, larvae, pupae and unfed adult females) of An. funestus were sequenced using next generation sequencing technology. Results: High throughput sequencing of four replicates in combination with computational analysis identified 107 mature miRNA sequences expressed in the An. funestus mosquito. These include 20 novel miRNAs without sequence identity in any organism and eight miRNAs not previously reported in the Anopheles genus but are known in non-anopheles mosquitoes. Finally, the changes in the expression of miRNAs during the mosquito development were determined and the analysis showed that many miRNAs have stage-specific expression, and are co-transcribed and co-regulated during development. Conclusions: This study presents the first direct experimental evidence of miRNAs in An. funestus and the first profiling study of miRNA associated with the maturation in this mosquito. Overall, the results indicate that miRNAs play important roles during the growth and development. Silencing such molecules in a specific life stage could decrease the vector population and therefore interrupt malaria transmission.IS
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