Method For Tissue Characterization Research Articles

Optical Monitoring and Diagnotics for Biomedical Applications. Optical Diagnostic Methodology for Laser Therapy Control: in the Case of Laser Angioplasty and Photorefractive Keratectomy.

Optical diagnostic methodologies for theraperutic control during laser therapy are discussed. Interventional therapy and endoscopic therapy are significantly important to reduce therapeutic invation to improve quality of life of patients. To reduce the risk of serious complication in particular tissue perforation, novel tissue characterization method should be developed. Meanwhile, automatic controlled surgical procedure should be established in precise laser ablation therapy such as photorefractive keratectomy. The real time monitoring laser ablation process/results are necessary to attain feedback control. I review these diagnostic methods during laser therapy in the case of laser angioplasty and photorefractive keratectomy.

Radiology at the Centennial and Beyond

Within months of the first report of the x-ray, Harvey Cushing, an intern at Massachusetts General Hospital and the future surgeon in chief at the Peter Bent Brigham Hospital, recognized the impact of Roentgen's discovery on medical practice. As Evens points out in this issue ofTHE JOURNAL, radiology developed rapidly as an important diagnostic and therapeutic modality. 2 A century later, radiology has become a mainstay of medical diagnosis and patient management. Today, advanced technologies such as magnetic resonance imaging (MRI), computed tomography, ultrasound, and radiotracer imaging are called on routinely to provide clinicians with information essential for efficient and effective treatment. The newest of these technologies, MRI, continues to be exploited for its vast potential. The development of high-speed MRI has led to quantitative methods for tissue characterization and for measuring tissue perfusion and blood flow. These methods promise not only to expand our diagnostic potential particularly in

Radial diffusion coefficient mapping.

The two-dimensional mapping of the effective diffusion coefficient of water in tissues may provide a useful method of tissue characterization to complement T1 and T2 relaxation time studies for diagnostic purposes. Current diffusion techniques rely on the application of large gradient strengths and long echo times to achieve the required sensitivity. This, in turn, limits the applicability of the technique to tissues having long T2s with rapid water diffusion. In addition, the inherent directionality of these methods results in only the partial encoding of diffusion information. A modified diffusion sequence is presented, radial diffusion mapping (RAD), which provides enhanced sensitivity diffusion maps by employing gradient sensitization in three orthogonal directions. Results in both phantoms and volunteers are presented, together with an investigation of the effects of T2 on the measurement accuracy. Using RAD, a two- to five-fold improvement in sensitivity was achieved, thus significantly enhancing the dynamic range of the method and allowing more accurate in vivo diffusion measurements to be carried out.

Analysis of the evolution of focal cerebral ischemia in the rat using the eigenimage filter.

The eigenimage filter was used to evaluate the results of a MRI study of cerebral ischemia in a rat model. This linear filter segments a desired feature in an image sequence from other features which may interfere with its observation. The animals were imaged temporally, after occlusion of the middle cerebral artery, to investigate the evolution of the ischemic process. The temporal evolution of ischemia was evaluated by analysis of the "eigenimages," calculated T2 and T1 map images, and images for the angles between signature vectors defined in the eigenimage technique. The eigenimages and angle map images demonstrated an improved visibility of the lesion at all time points, as compared to the original images and T2 and T1 map images. The eigenimages also demonstrated signal intensity changes within the area of ischemia. These changes are speculated to be related to variations in local cerebral blood flow resulting in varying degrees of tissue damage. The eigenimage intensities and the angles between signature vectors demonstrated time-related changes similar to the T2 and T1 values. Since the eigenimage filter and angle calculations are not dependent upon physical models (like T2 and T1), and the errors associated with these models, they may be preferable as methods for tissue characterization.

The use of narrowband ultrasound for characterization of tissue in a thin layer

Most tissue characterization methods use RF data originating from backscattering processes in the insonified tissue. Characterization of the tissue of a thin layer (e.g., an artery wall) poses problems because of the small amount of data available. To avoid problems that arise from the use of short (broadband) pulses the method proposed uses long and almost monochromatic pulses. The frequency dependence of the acoustic parameters can be assessed by using different central emission frequencies. A deconvolution algorithm is used to separate overlapping reflections from closely spaced tissue interfaces. Wiener inverse filtering together with correlation of deconvolved signals results in an accurate determination of the position of specular reflectors. The accuracy of the peak values detected in the envelope signal is not sufficient for quantitative determination of tissue parameters, but still much better than results from the analysis of short waveforms.

The envelope correlation spectrum algorithm as a method for ultrasonic tissue characterization: J.M.C. Gallet and J.P. Jones, Department of Radiological Sciences, University of California Irvine, Irvine, CA 92717

The envelope correlation spectrum algorithm as a method for ultrasonic tissue characterization: J.M.C. Gallet and J.P. Jones, Department of Radiological Sciences, University of California Irvine, Irvine, CA 92717

Echographic tissue characterization in diffuse parenchymal liver disease: Correlation of image structure with histology

Seventy livers were examined in vitro using a computerized ultrasound B-mode data acquisition and analysis system. For tissue characterization, statistical parameters from pattern recognition algorithms describing image brightness and image structure were used. Reference classification based on histopathology as well as on chemical/morphometrical analysis led to the diagnostic classes of normal, fatty liver, fibrosis/cirrhosis and fatty fibrosis/cirrhosis. Comparing the two reference methods for ultrasound tissue characterization, reclassification based on chemical/morphometrical analysis resulted in a significant increase in diagnostic accuracy. The strong correlations between statistical ultrasound image parameters and morphometrical features reflect the relevance of our statistical approach to ultrasound tissue characterization.

Echographic Tissue Characterization in Diffuse Parenchymal Liver Disease: Correlation of Image Structure with Histology

Seventy livers were examined in vitro using a computerized ultrasound B-mode data acquisition and analysis system. For tissue characterization, statistical parameters from pattern recognition algorithms describing image brightness and image structure were used. Reference classification based on histopathology as well as on chemical/morphometrical analysis led to the diagnostic classes of normal, fatty liver, fibrosis/cirrhosis and fatty fibrosis/cirrhosis. Comparing the two reference methods for ultrasound tissue characterization, reclassification based on chemical/morphometrical analysis resulted in a significant increase in diagnostic accuracy. The strong correlations between statistical ultrasound image parameters and morphometrical features reflect the relevance of our statistical approach to ultrasound tissue characterization.

Ultrasonic method and apparatus for tissue characterization and imaging nonlinear parameter

A method and apparatus for tissue characterization and imaging of nonlinear parameter data include an array of ultrasonic transducer elements to transmit ultrasonic pulses along a beam toward the tissue and to receive echoes of the ultrasonic pulses. The ultrasonic transducer elements are driven so that the ultrasonic pulses are transmitted at different power levels. The echoes of the ultrasonic pulses are analyzed at each of the different power levels to obtain the nonlinear parameter data along the beam. The beam is scanned in a two-dimensional plane of the tissue. The nonlinear parameter data is displayed according to the two-dimensional plane.

Ultrasonic method and apparatus for tissue characterization and imaging of nonlinear parameter

Ultrasonic method and apparatus for tissue characterization and imaging of nonlinear parameter

Ultrasonic Analysis for Ocular Tumor Characterization and Therapy Assessment

In ophthalmology, ultrasonic tissue characterization methods can distinguish among types of intraocular tumors, differentiate between subclasses of a given general type of tumor, provide parameters of use in treatment planning, and detect and grade changes in tissue during the course of therapy.

On the estimation of acoustic attenuation coefficient from peaks of echo envelope

A noticeable problem in estimating the acoustic attenuation coefficient (the slope of the attenuation versus frequency, a parameter denoted by β) of soft tissue using current frequency-domain methods is the large variance of the estimate. As a consequence, the reliability of the measurement of the value of β as a method of tissue characterization is reduced. This variance of the β estimate can be much decreased by using a newly developed time-domain method—the envelope peak (EP) method. When the value of β is estimated from the same rf samples of one A line based on the maximum-likelihood principle, theoretical analysis indicates that in comparison with the frequency methods, the EP method produces more independent data points for least-squares fitting, each data point having a smaller variance. The results of these two effects is a reduction of nearly 50 times in the variance of the β estimate under typical scan conditions. Preliminary results from phantom experiments and in vivo liver scan supported the above analysis.

Properties of acoustical speckle in the presence of phase aberration part I: First order statistics

The first order statistical properties of acoustical speckle patterns are studied as a function of several types of random and structured phase error. Such errors may arise from tissue velocity inhomogeneities or limitations in the acoustical imaging system. In this paper, we review the theory describing the statistical properties of speckle, describe a computer model which predicts the mean speckle brightness in the presence of phase aberrations, and report experiments in which we measure the effect of these aberrations on speckle brightness and variance. We find that the average speckle brightness is significantly reduced by even mild phase aberrations. The phase aberrations studied include focal point errors, random phase errors, and structured errors. Good agreement is found between experiment and computer simulation. We then discuss the implications of these results for imaging through aberrating media, tissue characterization and phase compensation methods.

Properties of acoustical speckle in the presence of phase aberration. Part I: First order statistics.

The first order statistical properties of acoustical speckle patterns are studied as a function of several types of random and structured phase error. Such errors may arise from tissue velocity inhomogeneities or limitations in the acoustical imaging system. In this paper, we review the theory describing the statistical properties of speckle, describe a computer model which predicts the mean speckle brightness in the presence of phase aberrations, and report experiments in which we measure the effect of these aberrations on speckle brightness and variance. We find that the average speckle brightness is significantly reduced by even mild phase aberrations. The phase aberrations studied include focal point errors, random phase errors, and structured errors. Good agreement is found between experiment and computer simulation. We then discuss the implications of these results for imaging through aberrating media, tissue characterization and phase compensation methods.

Proton NMR spectroscopy in canine myocardial infarction.

Proton NMR spectroscopy was used to study the relationship between proton relaxation times and other resonances in the proton spectra, such as lipids, creatine, and choline/carnitine in subacute (8-day-old) myocardial infarctions. Eight mongrel dogs received operative ligation of the left anterior descending coronary artery (four were permanently occluded, four were occluded for 1 h and reperfused) and were sacrificed 8 days later so that tissue samples could be prepared for NMR spectroscopy. The results of this study indicate that (for the core of infarcted tissue) the lipids do not contribute directly to the increased bulk relaxation times associated with myocardial infarction and that the lipid peaks (2.3, 1.2, 0.8 ppm) and creatine peak (3.0 ppm) are more specific to the kind of infarct than to the relaxation times. Therefore, analysis of the proton spectrum of myocardial tissue may serve as a method for tissue characterization.

Ultrasonic Tissue Characterization in Cardiology

The standard clinical applications of echocardiography involve display of the smooth surfaces of the heart, such as the endocardium, epicardium and valve leaflets. A relatively new area of endeavor in cardiac ultrasound is the attempt to evaluate myocardial tissue composition and/or structure based on the acoustic properties of the heart. The rationale for this area of study - termed ultrasound tissue characterization - is that ultrasound interacts (is absorbed or reflected) differently with abnormal myocardium than with normal myocardium. This rationale stems from the common clinical observation that certain abnormalities of the heart (calcification, amyloidosis, and others) affect the appearance of échocardiographie images. Several approaches to the evaluation of tissue composition with ultrasound include the display of acoustically abnormal tissue using gray scale or color encoding, the measurement of classical acoustic variables, and computer-based analysis of ultrasound signals and images. Promising results have been obtained through the use of ultrasound tissue characterization methods to identify acute ischemia, acute and chronic myocardial infarction, cardiomyopathies, myocardial contusion, and intracardiac masses. Although many technical problems remain to be solved, ultrasound tissue characterization may soon be added to the routine diagnostic armamentarium of the cardiologist.

Echocardiography in Coronary Artery Disease

1. Direct ultrasonic visualization of the coronary arteries.- 2. Regional and global left ventricular function analysis.- 3. Echocardiography during reversible ischemia in animal models.- 4. Echo-doppler cardiography during percutaneous transluminal coronary angioplasty.- 5. Exercise echocardiography.- 6. Dipyridamole-echocardiography test.- 7. Echocardiography in experimental myocardial infarction in animals.- 8. Myocardial perfusion imaging by contrast two-dimensional echocardiography.- 9. Echocardiography in the differential diagnosis of patients with chest pain.- 10. Acute myocardial infarction in man.- 11. Evaluation of the effect of thrombolytic therapy on left and right ventricular function by two-dimensional echocardiography and cineventriculography.- 12. The mechanical complications of acute myocardial infarction.- 13. Left ventricular aneurysm and infarct expansion.- 14. Left ventricular thrombus: diagnosis, anticoagulation, and systemic embolization.- 15. Doppler echocardiography in coronary artery disease.- 16. Epicardial echocardiography: assessment of myocardial effects of ischemia and revascularization.- 17. Transesophageal echocardiography during abdominal aortic surgery.- 18. Ultrasonic tissue characterization methods in the diagnosis of coronary artery disease.- 19. Direct epicardial visualization of the coronary arteries.

Tissue characterization by magnetic resonance imaging in hypertrophic cardiomyopathy

A method for providing tissue characterization of the myocardium has been sought for years. Magnetic resonance imaging (MRI) has demonstrated excellent soft tissue differentiation and has been proposed as a method for tissue characterization. This capability of MRI is suggested from previous studies that showed changes in signal intensity of ischemic compared with normal myocardium in experimental preparations. 1,2 Measurement of magnetic relaxation times, T1 and T2, in animal studies have verified a difference in these times between normal and ischemically damaged myocardium. 1–3 Recently, we encountered a patient with hypertrophic cardiomyopathy (HC) in whom MRI provided more accurate anatomic depiction of the condition than other imaging techniques. MRI also revealed differences in signal intensity at various sites in the left ventricular (LV) myocardium due to fibrosis and myocardial ischemia.

An improved stochastic approach to RF amplitude analysis in ultrasonic cardiac tissue characterization

We carried out a series of studies to improve the reproducibility of methods for ultrasonic myocardial tissue characterization using a stochastic approach to amplitude analysis of radiofrequency signals previously reported from our laboratory. Analysis of transducer scanner characteristics, data acquisition and processing, and data display from studies in tissue phantoms permit us to define some features of a parameter for expression of tissue character. The ratio of mean to standard deviation of the amplitude histogram from our system is explored as now implemented in our laboratory for reproducible measurements. The theoretical basis for understanding the utility of this method in defining tissue architecture and pathologic conditions requires further work.

An improved stochastic approach to rf amplitude analysis in ultrasonic cardiac tissue characterization.

We carried out a series of studies to improve the reproducibility of methods for ultrasonic myocardial tissue characterization using a stochastic approach to amplitude analysis of radiofrequency signals previously reported from our laboratory. Analysis of transducer scanner characteristics, data acquisition and processing, and data display from studies in tissue phantoms permit us to define some features of a parameter for expression of tissue character. The ratio of mean to standard deviation of the amplitude histogram from our system is explored as now implemented in our laboratory for reproducible measurements. The theoretical basis for understanding the utility of this method in defining tissue architecture and pathologic conditions requires further work.