Analysis of refill curve shape in ultrasound contrast agent studies.

Contrast destruction and replenishment by Flash Echo Imaging (FEI) (also referred to as interval or intermittent imaging) has been qualitatively and quantitatively used for tissue blood refill measurements. Many features and capabilities of contrast refill in tissue blood flow and perfusion remain to be elucidated. To aid the development and full reliable utilization of the technique in medical practice, in this paper we undertake physical and mathematical modeling to evaluate different measures derivable from FEI and to provide a basis for the further study of sensitivity and stability of such measures for the detection and measurement of various flow properties and abnormalities. A phantom was developed and used to conduct a dynamic contrast study. Refill curves were investigated as a means of calculating the mean transit time (MTT) and investigating other information that can be determined from their shape. Exponential and error function fits and the area above these curves were used to estimate MTT. The bubble disruption zone was visually measured and theoretically modeled. Computer simulated refill curves based on the flow phantom for different velocity ranges were then computed and compared to the experimental refill curves. The simulated refill curves closely matched the experimental curves in both shape and MTT. The simulated refill curves matched the shape of the experimental results for different velocity ranges. Another simulation examined how a real circulatory system might influence refill. Different refill curve shapes were obtained for different vascular models. Models including the large arteries and veins showed a much faster initial slope than models where the large vessels were not included. Likewise, simulated "shunting" displayed a different slope than models without "shunting" and specific portions of the refill curve that could maximally distinguish shunting. This computer simulation could lead to some experimental hypotheses about differences between normal and cancerous blood flow.

Doppler quantitative measures by region to discriminate prostate cancer.

This study was conducted to assess if sonographic discrimination between healthy and cancerous prostate tissue might be improved using regional analysis of ultrasound (US) Doppler measures. A total of 39 subjects underwent 3-D Doppler sonography before radical prostatectomy. Cancer locations were identified from hematoxylin and eosin (H&E)-stained slides. Three prostate data volumes consisting of a frequency shift and power-mode Doppler US and whole mount histology images were spatially registered for each prostate, then divided into entirely 1 mL-sized regions of cancerous or noncancerous tissue. Each prostate was visually divided into a peripheral and a periurethral region within which US Doppler measures were calculated. Receiver operating characteristic (ROC) and simulated biopsy analyses within each prostate were performed. Mean speed in colored pixels (V), and speed-weighted pixel density (SWD) are good discriminators for prostate cancer in the periurethral and the peripheral regions, respectively. Using SWD in a simulated biopsy yields increased cancer detection in the peripheral region.

Analysis of three-dimensional Doppler ultrasonographic quantitative measures for the discrimination of prostate cancer.

OBJECTIVE: The purpose of this study was to determine whether several quantitative ultrasonographic measures have potential to discriminate prostate cancer from normal prostate and to determine the best combination of these measures. The true spatial distributions of cancer within the prostates studied were obtained histologically after radical prostatectomy. The relationship between Doppler ultrasonography and microvessel count was also investigated. METHODS: Three-dimensional Doppler ultrasonographic data were acquired from 39 patients before radical prostatectomy. The removed prostate was sectioned, and whole-mount hematoxylineosin-stained slides were used to identify all regions of cancer within each prostate. These histologic and ultrasonographic data were spatially registered. Doppler ultrasonographic measures were calculated within uniformly sized three-dimensional regions that were either entirely cancerous or noncancerous, and receiver operating characteristic analysis was performed on the results. Microvessel counts were made within each contiguous cancerous region and correlated with ultrasonographic measures. RESULTS: Color pixel density was the best simple measure for discriminating prostate cancer (accuracy, 80%). The mean power mode value (normalized mean power in color pixels) was inversely related to cancer with an accuracy of 1--normalized mean power in color pixels = 65% (low mean power is more cancerous). When color pixel density was combined with the normalized mean power in color pixels, its accuracy improved slightly to 84%. The peak microvessel count had a negative correlation with color pixel density as well as with cancer stage. CONCLUSION: Doppler ultrasonography does provide discriminatory information for prostate cancer, with color pixel density being the most promising measure.

Speckle decorrelation flow measurement with B-mode US of contrast agent flow in a phantom and in rabbit kidney.

PURPOSE: To use speckle decorrelation in the presence of ultrasonographic (US) contrast agent as an alternative flow measurement technique to Doppler US. MATERIALS AND METHODS: In vivo and in vitro studies were performed. A tube with flowing saline solution containing contrast agent was positioned horizontally across a US image. The amount of decorrelation between a series of images was recorded. The flow profile across the tube was generated by averaging the decorrelation values and was compared with a Doppler frequency shift image. In addition, B-mode images of six rabbit kidneys were obtained during and after intravenous injection of contrast agent. Images were analyzed to compute the correlation between successive points in time. RESULTS: The velocity profiles across the tube were parabolic, with the fastest flow rates measured in the center of the tube. In the rabbit kidneys, measurements indicated the largest decorrelation rates occurred in the larger vessels. The cortical decorrelation rates were significantly slower than those for the hilar vessels (P < .05) and were relatively angle independent. CONCLUSIONS: Decorrelation flow measurements can be used to estimate flow in vitro and in vivo similar to measurements obtained with Doppler US but with less angle dependence. These measurements could lead to a US perfusion technique.

3-D color Doppler image quantification of breast masses.

In this article, new measures obtained from color Doppler images are introduced and a pilot study is described, in which these and previously published indices are evaluated for use in future work. Twenty women with breast masses observed on mammography and going to surgical biopsy were studied. Of the masses, 11 proved to be benign and 9 were malignant. Both 3-D mean frequency shift (f-CDI) and power mode Doppler (p-CDI) imaging were performed. To identify the mass and other regions of interest, vessels were displayed as rotatable 3-D color volumes, superimposed on selectable grey-scale/color flow slices. Doppler signals were recorded in each of 6 ellipsoidal regions of interest in and around the mass and 2 in normal tissues. Seven measures were computed in each region, three from power mode, two from mean frequency and two from combinations of both. Radiologists rated the grey-scale appearances of the masses on a scale of 1 to 5 (5=most suspicious) for each of 6 conventional grey-scale criteria. Of the individual vascularity measures in individual ROIs, the log speed-weighted pixel density and log power-weighted pixel density in the lesion internal periphery showed the greatest discrimination of malignancy, although neither was statistically significant nor as good as the peak variables described below. The mean visual grey-scale rating was the best discriminator overall, but two peak vascularity measures each made promising scatterplots in conjunction with the average visual grey-scale rating. These two vascularity measures were the log peak normalized power-weighted pixel density (peak NPD) and log of peak mean Doppler frequency times the peak NPD (vM x NPD(M)). Each of these two values was the maximum in any one of the five chosen ROIs closely associated with the mass. A possible rationale for the relative success of these peak values is the blood signal's normalization and the inhomogeneity of most breast cancers and the expectation that the highest velocities (shunting) and largest collections of blood are not necessarily in the same region in and around the tumor. Peak NPD of cancers varied with age, decreasing by a factor of 45 from 33 to 77 y.

The 3D and 2D color flow display of breast masses.

A prospective study was performed in 24 women with breast masses on mammography going on to surgical biopsy. 2D and 3D power mode and frequency shift color flow Doppler scanning and display were compared. Vessels were displayed as rotatable color volumes in 3D, superimposed on gray-scale slices. The latter were stepped sequentially through the imaged volume. Radiologists rated the masses in each display (3D, 2D and videotapes) on a scale of 1 to 5 (5 = most suspicious) for each of six conventional gray-scale and six new vascular criteria. Thirteen masses proved to be benign and 11 were malignant. 3D provided a stronger subjective appreciation of vascular morphology and allowed somewhat better ultrasound discrimination of malignant masses than did the 2D images or videotapes (specificities of 85%, 79% and 71%, respectively, at a sensitivity of 90%). Only in 3D did the vascularity measures display a trend towards significance in this small study.