Optimized ultrasound imaging catheters for use in the vascular system.

Clinical experience with 6 and 9 Fr ultrasound imaging catheters (UICs) reveals that several transducer and catheter tip varieties are needed for optimum imaging of diseased intravascular sites. Our UIC design has combined established catheter design and very high frequency ultrasound imaging technology to create a versatile, user configured system for intravascular ultrasound imaging. Optimum use requires proper strategic selection of transducer and catheter sizes, frequencies of operation, and interventional accessories.

Wideband harmonic imaging: a novel contrast ultrasound imaging technique.

A novel ultrasonic imaging method, wideband harmonic imaging, for nonlinear imaging of microbubble contrast agents is evaluated. In wideband harmonic mode, two pulses of alternate phase are send out. The image is then processed from the sum of both pulses, resulting in an image of nonlinear scatterers such as microbubbles. A prototype ultrasound system, Siemens Elegra, was evaluated with in vitro investigations and animal trials, using conventional, harmonic and wideband harmonic settings with the galactose based ultrasound contrast agent Levovist. Wideband harmonic imaging offers superior sensitivity for ultrasound contrast agents compared to conventional imaging and harmonic imaging. At low transmit power settings (MI 0. 1-0.5) the nonlinear response is already sufficient to generate a image of the blood pool distribution of Levovist in the rabbit kidney including the microvasculature, with clear delineation of vessels and perfused parenchyma. At high transmit amplitudes, nonlinear tissue response reduced the apparent image contrast between contrast agent and tissue. The results suggest that wideband harmonic imaging is currently the most sensitive contrast imaging technique, maintaining highest spatial resolution. This may add to image quality and offer new clinical potential for the use of ultrasound contrast agents such as Levovist.

The use of a microcomputer in the evaluation of echocardiograms.

A low-cost microcomputer system is used to calculate cardiac parameters from echocardiographic (Echo) measurements and produce a chartable report. The system is simple, uses Basic language, and provides for data storage.

US extended-field-of-view imaging technology.

PURPOSE: To develop an ultrasound (US) extended-field-of-view scanning technique that combines the convenience of a real-time scanner with the spatial advantages of a static B-mode scanner and provides a panoramic image in real time without position sensors or cumbersome articulated arms. MATERIALS AND METHODS: An image-registration-based position-sensing technique was used to track probe motion and reconstruct a large composite image during real-time scanning. The probe motion (translation and rotation) was estimated by combining multiple local motion vectors. This computationally intensive process required a special programmable image processor. RESULTS: Large, resolution-preserved composite images up to 60 cm long were obtained. Measurement accuracy as determined with phantom experiments was better than 5%. The method could be applied to any probe or image format. CONCLUSION: In addition to providing a panoramic image to expand diagnostic capabilities, extended-field-of-view US provides a more easily interpretable image and is an effective cross-specialty communication tool.

B-mode enhancement at phase-inversion US with air-based microbubble contrast agent: initial experience in humans.

Pulse- or phase-inversion ultrasonography (US) sums the signals returned from two 180 degrees ultrasound pulses. Linear scattering from tissue results in a signal void while nonlinear signals from microbubbles stand out. The technique was applied with a US contrast agent in 39 human subjects. B-mode enhancement of vessels and organ parenchyma was seen in all cases. Enhancement occurred from flowing and stationary microbubbles. The flow-independent enhancement of normal and abnormal tissue represents a major advance in contrast material-enhanced US with many potential applications especially in tumor imaging.

Sequence and timing of ventricular wall motion in patients with bundle branch block. Assessment by radionuclide cineangiography.

We determined the sequence and timing of inward ventricular wall motion by least-square phase analysis of radionuclide cineangiograms in 10 patients with left bundle branch block (LBBB), five patients with right bundle branch block (RBBB) and 11 patients with normal conduction. All LBBB and RBBB patients had normal coronary arteries and no segmental wall motion abnormalities. The left ventricle (LV) was divided into eight segments and the right ventricle (RV) into three; sequence and timing were scored by three observers. In normal subjects, wall motion begins in either or both ventricles and ends in the LV or both ventricles. In patients with LBBB it begins in the RV and ends in the LV; in patients with RBBB is begins in the LV and ends in the RV or both ventricles. The intraventricular wall motion is also altered in the ventricle ipsilateral to a bundle branch block. In LBBB, the mean time of onset of LV wall motion is delayed 1.9 frames (38 msec), whereas RV wall motion is normal. In RBBB, the onset of RV wall motion is delayed 1.3 frames (26 msec), whereas LV wall motion is not delayed.

Noninvasive identification of initial site of abnormal ventricular activation by least-square phase analysis of radionuclide cineangiograms.

Least-square phase analysis (LSPA) of radionuclide cineangiograms demonstrates the sequence of onset of inward ventricular movement noninvasively. To validate the method and explore its ability to identify abnormal initial sites of ventricular activation, LSPA was applied to 14 patients with pacemakers (one with electrodes in two locations) (group 1) and three patients with recurrent ventricular tachycardia (VT) (group 2) who had undergone electrophysiologic endocardial mapping. The segment in which the site of initial ventricular activation was located was correctly identified in 13 of 15 paced studies and in two of three group 2 patients during VT. Pacing increased the duration of spread of onset of inward ventricular movement, and the duration of spread of onset correlated well with the duration of the QRS (r = 0.80). The sequence of onset of inward ventricular movement during VT was similar to the sequence of depolarization in all three group 2 patients. These preliminary results suggest that the sequence of onset of ventricular contraction as depicted by LSPA is a valid representation of the actual contraction sequence and that LSPA or radionuclide cineangiography correctly identifies abnormal sites of initial ventricular activation.

Coronary artery disease: detection by phase analysis of rest/exercise radionuclide angiocardiograms.

Thirty-six patients with chest pain but no myocardial infarction or conduction defects and 4 volunteers (3 normals and 1 with asymptomatic aortic insufficiency) underwent radionuclide angiocardiography. Phase analysis was performed and the standard deviation (SD) ("spread") and skewness ("asymmetry") of the left ventricular (LV) phase histogram determined at rest and during maximum exercise. The SD of the LV phase histogram was of no value; however, when -0.1 was taken as the upper limit of normal skewness at maximum exercise, skewness was equally as sensitive as conventional criteria for coronary artery disease (CAD) and also more specific. The authors conclude that LV histogram skewness during maximum exercise may be superior to conventional criteria for detection of CAD with rest/exercise radionuclide angiocardiograms.