Three-dimensional computerized display of physiologic models and data.
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Acetylcholine↗
Biomedical subjects
J F Greenleaf
Publications and source records attributed to J F Greenleaf.
Time delay estimation using wavelet transform for pulsed-wave ultrasound.
The windowed cross-correlation (WCC) technique has recently attracted attention in pulsed-wave (PW) ultrasound for measurement of tissue motion and blood flow velocity because of its performance advantages over the conventional Doppler method. The WCC measures tissue motion and blood flow velocity via estimation of time delays of backscattered signals in two consecutive echoes. In this paper, we propose a wavelet transform-based cross-correlation (WTCC) technique for the time delay estimation in PW ultrasound. The WTCC consists of three steps: (i) computing wavelet transforms (WTs) of received echoes, (ii) computing cross-correlations in the wavelet domain, and (iii) estimating the time delays by maximizing the estimated cross-correlations. Dyadic or continuous wavelets may be used in the proposed approach. The WTCC has a unique feature of using varying time-frequency windows in processing compared with the WCC which only uses a single fixed window. Our computer simulations show that, compared with the WCC, the WTCC provides a better estimation of time delays (lower failure rate and lower estimate error) and its performance is more consistent under various conditions, and more robust with window size. In the simulations, we also tested a specific continuous wavelet for the WTCC that was the emitted pulse itself and found the corresponding WTCC outperforms the WTCC with a regular dyadic wavelet.
Bias↗
Three-dimensional reconstruction of color Doppler jets in the human heart.
A computer algorithm has been developed for segmentation and three-dimensional (3D) reconstruction of Doppler color-flow images. The algorithm enables the user to select a range of velocities, represented by colors, for segmentation and subsequent 3D reconstruction. The reconstructed flows are assigned a color palette and merged with the volume-rendered gray-scale image to produce a 3D image containing both flow and anatomic information. The results demonstrate the application of the algorithm to regurgitant and shunt jets with complex spatial and velocity patterns. We conclude that 3D reconstruction of selected color spectra (e.g., velocities) of Doppler color flows and surrounding anatomy is feasible in the clinical setting.
Algorithms↗
Accuracy of three-dimensional volume measurement using biplane transesophageal echocardiographic probe: in vitro experiment.
Two phased-array scanning methods can be used for volumetric transesophageal echocardiographic imaging: (1) pull-back "breadloaf" reconstruction, and (2) rotation "fan-like" reconstruction. The purpose of this study was to (1) test accuracy and precision of pull-back versus rotational geometries for three-dimensional volume determination, and (2) test accuracy of the resulting surface/volume rendered images. The endoscope shaft was inserted into a tube with the handle connected to a stepper device. Seventeen balloons (61 to 471 ml) were put into a water bath consecutively. Two scans were performed: (1) pull-back: the probe was withdraw in 1 mm steps to obtain parallel "breadloaf" slices, and (2) rotational: the probe was rotated in increments of 1.8 degrees, 3.6 degrees, or 5.4 degrees to obtain "fan-like" slices. Each image was digitized for computer analysis. The data were interpolated into 128 x 128 x 128 voxels for three-dimensional reconstruction. Volume measurement was done using a stereometric random marking method. Volumes obtained from the reconstructed images were compared with the true volume (weight) by linear regression analysis. Excellent correlation between measured and actual volumes was obtained from rotation scans as follows: for 1.8 degrees steps (r = 0.9987, SEE = 6.5 ml), for 3.6 degrees steps (r = 0.9959, SEE = 11.5 ml), and for 5.4 degrees steps (r = 0.9943, SEE = 13.5 ml). The pull-back scans showed r = 0.9990, SEE = 5.8 ml. Three-dimensional surface/volume rendered images of the balloons indicate that 1.8 degrees rotation scans are almost as good as 1 mm pull-back scans. We conclude that volume measurements from rotation scans in vivo will not be hindered by scan geometry or software interpolation.
Animals↗
Ultrasound bioeffects and regulatory issues: an introduction for the echocardiographer.
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Animals↗
Proton MR chemical shift imaging using double and triple phase contrast acquisition methods.
Conventional chemical shift magnetic resonance (MR) imaging with the phase contrast technique has a number of limitations with respect to quantitative accuracy. The hypothesis of this study is that the accuracy of phase contrast chemical shift MR may be improved by increasing the number of basis images from two to three. Water and fat images were obtained from phantoms and volunteers with a 1.5 T MR system using double and triple acquisition phase contrast chemical shift methods. Longitudinal relaxation time and relative water and fat content were calculated from these basis images. The T1 relaxation times of the aqueous component of composite phantoms were determined more accurately using the triple acquisition method than with the double acquisition method. In vivo studies demonstrate that the triple acquisition method separated fat and water signals more accurately and showed less field inhomogeneity dependence than the modified double acquisition method. The new method also provided a map of static field magnetic inhomogeneity and tissue magnetic susceptibility. The triple acquisition phase contrast chemical shift imaging technique should improve the prospect for quantitative tissue characterization in clinical MR.
Adipose Tissue↗
Improvement in specificity of ultrasonography for diagnosis of breast tumors by means of artificial intelligence.
A set of ultrasonograms of lesions from 200 patients between the ages of 14 and 93 years who underwent mammography followed by ultrasonographic examination and excisional biopsy has been studied with computer vision techniques to improve the ultrasonographic specificity of the diagnosis. Selected features representing the texture of the lesion were calculated and then classified by an artificial neural network. This network was biased toward correctly classifying all the malignant cases at the expense of some misclassification of the benign cases. The network diagnosed the malignant cases with 100% sensitivity and 40% specificity (compared with 0% specificity for the radiologists diagnosing the same set of cases in the breast imaging setting), and tests performed with a leave-one-out technique indicate that the network will generalize well to new cases. This suggests that methods based on neural network classification of texture features show promise for potentially decreasing the number of unnecessary biopsies by a significant amount in patients with sonographically identifiable lesions.
Adolescent↗
Mayo Clinic and Medical School Biodynamics Research Unit.
The facilities that make up the Mayo Biodynamics Research Unit include the dynamic spatial reconstructor (DSR), which when fully operational will generate raw data at 200 million samples per second. Processing of these data will require a computer capable of several billion arithmetic operations per second.
Biomechanical Phenomena↗
Early recognition of heart transplant rejection by backscatter analysis from serial 2D ECHOs in a heterotopic transplant model.
The acute phase of heart transplant rejection was evaluated with two-dimensional echocardiographic (2D ECHO) image analysis in a modified Mann's cervical heterotopic transplant. Serial 2D ECHO images were obtained daily, and myocardial biopsies were obtained on the day of transplant, on day 3 after transplant, and after total rejection. Brightness of serial 2D myocardial ECHO images significantly increased to day 3 after transplant, indicating increased backscatter during hyperacute rejection. Histologically this was associated with myocardial edema. These results suggest a potential noninvasive means of recognizing acute cardiac rejection. Heart transplant rejection is characterized by myocardial edema during the early stages. Myocardial edema resulting from ischemia increases the backscatter of ultrasound, which is seen as increased brightness on 2D ECHOs. Hence we hypothesized that myocardial edema observed histologically during a hyperacute rejection process can be seen on serial 2D ECHOs of the transplanted heart. Serial 2D ECHOs were obtained in five goats that had undergone a modified Mann's cervical heterotopic transplant. Image parameters were kept constant throughout each experiment. After each experiment, 2D ECHOs of a soft-tissue phantom were also recorded with the same image parameters and were used for normalizing the myocardial brightness estimated from 2D ECHO images. Visually, brightness of 2D ECHO images of all transplanted myocardia increased to day 3 after transplantation; thereafter, the brightness decreased but was still greater than on the day of transplantation. The measured mean (+/- SD) relative integrated brightness increased from 0.60 +/- 0.38 on the day of transplantation to 1.05 +/- 0.43 (p less than 0.005) on day 3 after transplantation and decreased to 0.70 +/- 0.33 (p less than 0.05) on day 7 after transplantation.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗