A new blood Row imaging system is described that com- bines a conventional pulsed Doppler device and a newly developed au- tocorrelator. In the system blood flow within a given cross section of a live organ is displayed in real time. The direction of blood Row and its variance are expressed by means of a difference in color and its hue, respectively. Experiments were conducted with a mechanical and an electrical scanner using phantoms, and good agreement with the theory was obtained. Studies on clinical significance have also been carried out for normal and diseased hearts, and successful results have been found.

http://bme.elektro.dtu.dk/31545/documents/kasai_et_al_1985.pdf

Real-Time Two-Dimensional Blood Flow Imaging Using an Autocorrelation Technique

Doppler ultrasound has now developed to the point where the rate of flow of blood in a given vessel can be measured with appropriate instrumentation. The theoretical basis of Doppler flow measurement is reviewed in this paper, with particular emphasis on the potential and actual sources of error. Three distinct approaches are identified, and the strengths and weaknesses of each discussed. The separate errors involved in estimating the vessel cross-sectional area, the angle of approach, and the Doppler shift are analyzed, together with the question of the uniformity of scattering from the blood. In vivo and in vitro tests of the accuracy obtained using a number of Doppler flow measuring instruments are then reviewed. It is concluded that the Doppler methods are capable of good absolute accuracy when suitably designed equipment is used in appropriate situations, with systematic errors of 6% of less. There are, however, considerable random errors, attributable primarily to errors in measuring the cross-sectional area and the angle of approach. Repeating the measurement of flow several times and averaging the results can reduce these random errors to an acceptable level.

Measurement of blood flow by ultrasound: accuracy and sources of error.

A novel focused active microwave system is investigated for detecting tumors in the breast. In contrast to X-ray and ultrasound modalities, the method reviewed here exploits the breast-tissue physical properties unique to the microwave spectrum, namely, the translucent nature of normal breast tissues and the high dielectric contrast between malignant tumors and surrounding lesion-free normal breast tissues. The system uses a pulsed confocal technique and time-gating to enhance the detection of tumors while suppressing the effects of tissue heterogeneity and absorption. Using published data for the dielectric properties of normal breast tissues and malignant tumors, the authors have conducted a two-dimensional (2-D) finite-difference time-domain (FDTD) computational electromagnetics analysis of the system. The FDTD simulations showed that tumors as small as 2 mm in diameter could be robustly detected in the presence of the background clutter generated by the heterogeneity of the surrounding normal tissue. Lateral spatial resolution of the tumor location was found to be about 0.5 cm.

/pdf/correction-to-two-dimensional-fdtd-analysis-of-a-pulsed-1wtpeyr9tq.pdf

Correction to "Two-Dimensional FDTD Analysis Of A Pulsed Microwave Confocal System For Breast Cancer Detection: Fixed-Focus And Antenna-Array Sensors"

Doppler signal processing cannot only be employed to detect the local blood velocity as function of time, but also to assess transcutaneously the displacement of the arterial walls during the cardiac cycle (distension waveform) and, hence, the time-dependent changes in arterial diameter relative to its initial diameter at the start of a cardiac cycle. The distension waveform normalized with respect to the local pulse pressure provides useful information about the local elasticity of the arterial wall. The displacement of the arterial wall can be obtained by processing the RF-signals within a sample volume coinciding with the arterial wall. To evaluate this method a dedicated high-speed memory system has been developed storing the RF-signal, as obtained with a conventional echo-imager in M-mode, over a number of successive sweeps covering a selected depth range. The data are transferred line after line to a personal computer (PC) and processed on the fly, thereby relieving the memory requirements of the PC. It can be concluded that a RF-signal memory in combination with a PC provides a useful tool to extract detailed diameter waveforms from the RF-signals obtained. Although the system does not process the signals in real-time the process can be considered to be on-line since the results become available within one minute after the acquisition of the data is completed.

Assessment of the distensibility of superficial arteries.

A theoretical treatment of the scattering of ultrasound from blood is given, assuming that the blood behaves essentially as a continuum. The scattering then arises from fluctuations in the mass density and compressibility of the blood, which is caused by a fluctuation in the red cell concentration. An expression for the received signal in ultrasonic blood velocity measurements is given. The stochastic properties of the signal are discussed with reference to the information content about the velocity field of the blood. Since the signal is Gaussian, all available information is contained in the power spectrum, which is a blurred approximation to the velocity distribution in the region of observation.

A Theoretical Study of the Scattering of Ultrasound from Blood

The relationship between the instantaneous frequency and the mean frequency of ultrasonic Doppler signals in blood velocity measurements is discussed. The probability distribution density for the instantaneous frequency is calculated. The time interval histogram (TIH), which has been used to characterize the Doppler signal, is found to be an approximation of this probability density. The probability density will also describe the output of phase-lock loop analysis of the Doppler signal. The variance of mean frequency estimators is calculated, and the implication of this for practical estimators is discussed. The effect of hard limiting of the signal on the estimator performance is also discussed.

Instantaneous Frequency, Mean Frequency, and Variance of Mean Frequency Estimators for Ultrasonic Blood Velocity Doppler Signals

A theoretical treatment of the scattering of ultrasound from blood is given, assuming that the blood behaves essentially as a continuum The scattering then arises from fluctuations in the mass density and compressibility of the blood, which is caused by a fluctuation in the red cell concentration An expression for the received signal in ultrasonic blood velocity measurements is given The stochastic properties of the signal are discussed with reference to the information content about the velocity field of the blood Since the signal is Gaussian, all available information is contained in the power spectrum, which is a blurred approximation to the velocity distribution in the region of observation

/pdf/a-theoretical-study-of-the-scattering-of-ultrasound-from-4cbulu3fs0.pdf

A Theoretical-Study of the Scattering of Ultrasound from Blood

Methods for obtaining image-guided Doppler blood velocity measurements are briefly reviewed Preference is given to a time-sharing scheme in which the Doppler measurement is turned off during the data-acquisition period for a 2-D image frame (typically 20 ms) The signal dropout that occurs during the image-updating period is removed from the Doppler audio by inserting a synthetic signal segment The synthetic signal is generated by passing white noise through a discrete-time FIR (finite-impulse response) filter with filter coefficients that are a windowed version of the Doppler signal measured immediately prior to the imaging interrupt It is shown that the artificial signal has spectral properties (and thus audible sound) similar to those of the real Doppler signal segment on which it is based The time-sharing method is analyzed and evaluated experimentally, using dedicated hardware The proposed algorithm allows for the design of time-shared Doppler/imaging systems that carry out pulsed or continuous Doppler measurements with essentially real-time imaging guidance >

A time-shared ultrasound Doppler measurement and 2-D imaging system

A new Doppler frequency estimator operating in the discrete time domain is derived from an analysis of the Doppler signal statistics. It is shown that the estimator gives a nearly unbiased estimate of the mean frequency of the signal spectrum, regardless of the spectrum shape. The discrete time implementation gives the advantage that, under specified conditions, the range-velocity product of a pulsed Doppler velocity meter can be increased.

Bjorn A. J. Angelsen

Papers

A Theoretical Study of the Scattering of Ultrasound from Blood

Instantaneous Frequency, Mean Frequency, and Variance of Mean Frequency Estimators for Ultrasonic Blood Velocity Doppler Signals

A Theoretical-Study of the Scattering of Ultrasound from Blood

A time-shared ultrasound Doppler measurement and 2-D imaging system

Discrete Time Estimation of the Mean Doppler Frequency in Ultrasonic Blood Velocity Measurements