Biomedical subjects
D Linker
Publications and source records attributed to D Linker.
The angle of incidence of the ultrasonic beam: a critical factor for the image quality in intravascular ultrasonography.
The effects of the angle of incidence of the ultrasound beam on the image quality were studied in 21 pressurized arterial specimens examined with a 30 MHz intravascular ultrasonographic catheter. When the ultrasonographic catheter was in an eccentric position in the vessel lumen, the videodensity of the segments of the vessel wall with the least favorable angle of interrogation (a shift of 49 +/- 6 degrees from the tangent to the tissue surface) was 27% +/- 19% lower than the videodensity measured with the catheter in the center of the lumen. When the catheter was placed in a position that was not parallel to the long axis of the vessel, a further decrease was observed, especially in the vessel wall opposite the position of the catheter. An artificial dissection was induced in eight specimens. Dropouts that involved the dissection plane and the underlying structures were produced with positions of the echographic catheter inducing a narrow angle between ultrasound beam and dissection plane. These experimentally induced artifacts were compared with similar findings from the in vivo evaluation of peripheral and coronary arteries. The angle of incidence of the ultrasound beam is a major determinant of the image quality in intravascular ultrasonography. Angle-dependent artifacts occur with eccentric and noncoaxial positions of the ultrasonographic catheter and, in particular, with imaging of large intraluminal dissections. Awareness of this problem may prevent image misinterpretation and has relevance for future improvement of catheter technology and design.
Congenital diaphragmatic hernia: determination of the optimal time for operation by echocardiographic monitoring of the pulmonary arterial pressure.
Preoperative stabilization and delayed operation rather than emergency repair of congenital diaphragmatic hernia (CDH) may improve survival, but there are no clear criteria for how long operation should be delayed. Because increased pulmonary vascular resistance (PVR) may be an important risk factor, we used Doppler echocardiography to study patients with CDH presenting with respiratory distress immediately after birth. During the study period 10 patients were admitted, but 2 were moribund on admission and died shortly thereafter. In the remaining patients the pulmonary arterial pressure (PAP) and direction of ductal shunt were estimated by Doppler echocardiography. Initial PAPs were in the range of 45 to 90 mm Hg, with bidirectional or right-to-left shunt through the ductus arteriosus. Reduction of pressure to 25 to 55 mm Hg, or reversal of shunt to left-to-right, reflecting decreased PVR, occurred after ventilation for 3 to 20 days (mean, 8 days). Patients underwent operation after there was evidence of reduced PVR. None developed persistent fetal circulation, and all 8 patients survived. We conclude that postponing operation until PVR has decreased seems to improve survival in patients with CDH presenting within hours of birth.
Digital signal and image processing in echocardiography. The American Society of Echocardiography.
Digital signal and image processing techniques are acquiring an increasingly important role in the generation and analysis of cardiac images. This is particularly true of 2D echocardiography, in which image acquisition, manipulation, and storage within the echocardiograph, as well as quantitative analysis of echocardiographic data by means of "off-line" systems, depend upon digital techniques. The increasing role of computers in echocardiography makes it essential that echocardiographers and technologists understand the basic principles of digital techniques applied to echocardiographic instrumentation and data analysis. In this article, we have discussed digital techniques as applied to image generation (digital scan conversion, preprocessing, and postprocessing) as well as to the analysis of image data (computer-assisted border detection, 3D reconstruction, tissue characterization, and contrast echocardiography); a general introduction to off-line analysis systems was also given. Experience with other cardiac imaging methods indicates that digital techniques will likely play a dominant role in the future of echocardiographic imaging.
Kaposi's sarcoma of genitourinary tract.
Kaposi's sarcoma of the external genitalia is rare. Four cases with the initial lesion on the glans penis and 13 cases with secondary involvement of the external genitalia are presented. A high association between Kaposi's sarcoma and malignant lymphoma is noted. The natural history is one of multiple recurrences in the immediate vicinity of the primary site or at distant locations at varying time intervals. Wide margin electron beam irradiation is the recommended treatment. A variety of chemotherapeutic agents also have produced favorable responses; yet prognosis for cure is poor because of the generalized nature of the disease--the course of which is nevertheless often prolonged.