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Brachytherapy to treat prostate cancer uses transrectal ultrasound to guide implantation of titanium-shelled radioactive seeds. Transperitoneal implantation allows errors in placement that cause suboptimal dosimetry. Conventional ultrasound cannot reliably image implanted seeds; therefore, seed misplacements cannot be corrected in the operating room. Previously, an algorithm based on singular spectrum analysis was shown to image palladium seeds better than B-mode ultrasound could. The algorithm is now applied to imaging an iodine seed in gel and in beef tissue as a function of seed angle relative to the incident ultrasound. Results indicate that both seed types are imaged reliably by the algorithm. [ABSTRACT FROM AUTHOR]

Transrectal-ultrasound-guided brachytherapy uses small titanium-shelled radioactive seeds to locally treat prostate cancer. During the implantation procedure, needles inserted transperitoneally cause gland movement resulting in seed misplacement and suboptimal dosimetry. In a previous study, an algorithm based on singular spectrum analysis (SSA) applied to envelope-detected ultrasound signals was proposed to determine seed locations [J. Mamou and E. J. Feleppa, J. Acoust. Soc. Am. 121, 1790–1801 (2007)]. Successful implementation of the SSA algorithm could allow correcting dosimetry errors during the implantation procedure. The algorithm demonstrated promise when the seed orientation was parallel to the needle and normal to the ultrasound beam. In this present study, the algorithm was tested when the seed orientation deviated up to 22° from normality. Experimental data from a seed in an ideal environment and in beef were collected with a single-element, spherically focused, 5 MHz transducer. Simulations were designed and evaluated with the algorithm. Finally, objective quantitative scoring metrics were developed to evaluate the algorithm performance and for comparison with B-mode images. The results quantitatively established that the SSA algorithm always outperformed B-mode images and that seeds could be detected accurately up to a deviation of approximately 10°. [ABSTRACT FROM AUTHOR]

Ultrasound-guided brachytherapy using titanium-shelled radioactive seeds is a popular, effective means of treating prostate cancer. Unfortunately, implantation using needles inserted transperitoneally causes gland movement and distortion, which often results in seed misplacement and dosimetry errors. If actual seed locations could be determined in the operating room, then corrections to dosimetry errors could be made immediately. However, seed specularity, shadowing, and tissue clutter make imaging seeds difficult using conventional ultrasound. Singular spectrum analysis (SSA) shows promise for reliably imaging radioactive seeds implanted in the prostate and enabling additional corrective implantations to be made in the operating room. SSA utilizes eigenvalues derived from the diagonalized correlation matrix of envelope-detected radio-frequency echo signals to yield a P value indicative of the likelihood of a seed-specific repetitive signal. We demonstrated the potential of SSA for seed detection and imaging and illustrated the trade-off considerations for optimization of SSA in clinical applications using simulations assessing performance as a function of different levels of noise and the presence of repetitive signals with various repetition periods; experiments in an ideal scattering environment; and experiments using seeds implanted in beef. [ABSTRACT FROM AUTHOR]

An analytic model is described for application in ultrasonic tissue characterization. The model is applicable to clinical broadband pulse echo systems. It treats spectra derived from received echo signals and relates them to physical tissue properties. The model can be applied to deterministic tissue structures (e.g., retinal detachments, larger blood vessels, and surface layers of the kidney) and to stochastic tissue structures (e.g., various tumors). The beam patterns included in the model are those generated by focused transducers typically used in high-resolution clinical ultrasound. Appropriate calibration procedures are also treated; these are needed for interpretation of absolute spectral parameters. The results obtained with the analytic model have been used to design a digital processing system and the associated techniques which are now being applied during examinations of the eye and abdominal organs. The results have proven useful in interpreting data from various types of tissues. To illustrate the application of these results, representative clinical data, obtained from the digital system, are presented for two types of tissue architectures. The first case is a detached retina representing a deterministic structure characterized by well-defined thickness and reflection coefficients. The second case is asteroid hyalosis and represents a stochastic entity in which the positions of small scattering particles are best described in statistical terms, and characterization is accomplished by means of normalized power spectra. [ABSTRACT FROM AUTHOR]

Presents an obituary for Frederic L. Lizzi, fellow of the Acoustical Society of America.

This study seeks to develop more-sensitive and -specific ultrasonic methods of imaging cancerous prostate tissue and thereby to improve means of guiding biopsies and planning, targeting, and monitoring treatment. Ultrasonic radio-frequency, echo-signal data, and clinical variables, e.g., PSA, voiding function, etc., during biopsy examinations were acquired. Spectra of the radio-frequency signals were computed in each biopsied region, and used to train neural networks; biopsy results served as the gold standard. A lookup table gave scores for cancer likelihood on a pixel-by-pixel basis from locally computed spectral-parameter and global clinical-parameter values. ROC curves used leave-one-patient- and leave-one-biopsy-out approaches to minimize classification bias. Resulting ROC-curve areas were 0.80±0.03 for neural-networks versus 0.66±0.03 for conventional classification. TTIs generated from data acquired pre-surgically showed tumors that were unrecognized in conventional images and during surgery. 3-D renderings of prostatectomy histology and TTIs showed encouraging correlations, which shows promise for improving the detection and management of prostate cancer, e.g., for biopsy guidance, planning dose-escalation and tissue-sparing options for radiation or cryotherapy, and assessing the effects of treatment. Combining MRS parameters with US spectral parameters appears capable of further improving prostate-cancer imaging. [Work supported by NIH.] [ABSTRACT FROM AUTHOR]

Ultrasonic tissue characterization based on spectrum analysis of radio-frequency (rf) echo signals is proving to be clinically useful in ophthalmology and abdominal studies. Parameters computed using spectrum analysis can be theoretically related to scattering properties of tissue such as scatterer size and impedance and therefore to histology. Such parameters can also be correlated empirically with clinical features, histopathology, treatment history, etc. They appear to be useful for clinical evaluation of disease, particularly detecting, diagnosing, staging, and monitoring cancer. Although parameters can be presented graphically or numerically, two-dimensional parameter images significantly facilitate the interpretation provided by tissue characterization. The portrayal of parameters in three dimensions further enhances the visualization of parameter distributions, and provides an even more powerful tool for tissue evaluation. In addition, three-dimensional (3-D) presentations of the surfaces of tissue structures permit assessment of spatial relationships and quantitative estimation of volume. These methods have been applied fruitfully in a number of medical applications, including evaluation of intraocular tumors, cancers of the liver, clots and thrombi, skin lesions, and prostate tissue. [This research has been supported by NIH Grants EY01212, EY01480, CA38400, and RR05853.] [ABSTRACT FROM AUTHOR]