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 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.

The non-linear elastic response of arteries implies that their mechanical properties depend strongly on blood pressure Thus, dynamic measurements of both the diameter and pressure curves over the whole cardiac cycle are necessary to characterise properly the elastic behaviour of an artery We propose a novel method of estimating these mechanical properties based on the analysis of the arterial diameter against pressure curves derived from ultrasonic and photoplethysmographic measurements An ultrasonic echo tracking device has been developed that allows continuous recording of the internal diameter of peripheral arteries It measures the diameter 300 times per second with a resolution of 25 microns This system is linked to a commercially available light-plethysmograph which continuously records the finger arterial pressure (025 kPa accuracy) Because of the finite pulse wave velocity, the separation between the diameter and the pressure measurement sites causes a hysteresis to appear in the recorded diameter-pressure curve Using a model based on haemodynamic considerations, the delay between the diameter variations and the finger arterial pressure is first eliminated As the pulse wave velocity depends on the pressure, the delay is determined for each pressure value The relationship between pressure and diameter is then described by a non-linear mathematical expression with three parameters, which best fits the recorded data The dynamic local behaviour of the vessel is fully characterised by these parameters Compliance, distensibility and pulse wave velocity can then be calculated at each pressure level Thus, the mechanical behaviour of peripheral human arteries can now be characterised non-invasively over the pressure range of the whole cardiac cycle The results obtained in vivo on human radial and brachial arteries show that a thorough analysis of the compliance-pressure curves and their modifications (curving, shift) is needed in order to compare two different vessels in a meaningful way

https://iopscience.iop.org/article/10.1088/0143-0815/12/1/003/pdf

Non-invasive estimate of the mechanical properties of peripheral arteries from ultrasonic and photoplethysmographic measurements.

In this study, age and sex differences in diameter and compliance of the common carotid artery (CCA) were evaluated in 119 healthy subjects with a phase-locked echo-tracking system. The diameter and pulsatile diameter changes were measured, and pressure strain elastic modulus (Ep) and stiffness (beta) were calculated and used as the inverse estimate of compliance. The carotid diameter increased more rapidly in males and was larger than in females from 25 years of age. The relative diameter change was equal in both sexes, and decreased from 12% to 14% in younger subjects to approximately 5% in elderly subjects. Compliance decreased almost linearly and in parallel in males and females up to 45 years of age. Between 45 and 60 years the decrease was more marked in females than in males, whereas it was by far more marked in males between 60 and 70 years of age.

Diameter and compliance in the human common carotid artery — variations with age and sex

A scanning system is described which is capable of making a two dimensional display of the blood flowing in arteries. It has been especially designed for display of the carotid bifurcation but can be adapted for other blood vessels. Normally it uses continuously generated energy and detects the Doppler shifted signals from the blood flowing in the arteries at peak velocity as the arterial pulse propagates through the segment of vessel being scanned. The system is directional so that flow in only a single direction with reference to the beam is displayed at any one time. The Doppler shifted signals reflected by the blood flowing at peak velocity are detected by filters with varying frequency ranges. Signals from each filter activated are color-coded. The color display is made from the filter activated by the highest Doppler frequency shifted signals. Thus the arteries are displayed by colors corresponding to the highest peak velocities in their segments. Stenotic areas where peak velocities will be greater than in non-stenosed regions will thus be displayed by colors differing from that used to represent normal peak velocities. These regions of increased peak velocities correlate reliably in 95% of cases with arterial stenoses occluding more than 74% of the arterial diameter. Occluded vessels which do not appear at their appropriate position on the image are also reliably displayed in 95% of cases. The display of normal carotid bifurcations by normal colors in the Doppler scan is also reliable in 93% of cases but the display of slightly increased velocities may result from haemodynamic causes as often as from localized small stenoses.

Color coded ultrasonic differential velocity arterial scanner (Echoflow)

Wells (Wells et al. , 1977) found that malignant tumors within the breast gave rise to a Doppler shifted signal with a systolic modulation while benign masses gave no such strong signal. On the basis of the observation it was suggested that Doppler scanning of the breast might provide a screening procedure for the identification of malignancies without the use of ionizing radiation. The breasts of nine women were scanned for the presence of Doppler signals with a systolic modulation. In all seven of the women who had a palpable mass in the breast, such Doppler signals were elicited despite the fact that two of the masses proved to be benign. The other two women had no palpable mass in their breasts. In the first case no Doppler signal was elicited from an area of radiological abnormality which proved to be malignant. In the second case an abnormal signal was elicited from the breast of a woman dying of metastatic carcinoma which probably did not originate in the breast. Spectral analysis of the signals elicited from a malignant breast lesion show that they have the high rates of flow during diastole characteristic of blood flowing into a vasculature of low resistance and that they are multi-directional. It would seem that more extensive investigation of this procedure should be made before it is adopted as a screening procedure for breast cancer.

Breast carcinoma detection by ultrasonic Doppler signals.

A digital technique is described for the tracking of variations in range of echoes reflected specularly from interfaces.

A digital technique for tracking moving interfaces

The vertebral arteries have always been difficult to examine with ultrasonic Doppler systems. While a number of different techniques have been proposed none would seem to be satisfactory and all suffer from difficulty in identifying, with certainty, the signals arising from the vertebral arteries. The exception to this restriction would appear to be the identification of retrograde vertebral artery flow in “steal” syndromes. The authors raise the question however, whether clinical bias may not play a significant part in such successful examinations since “steal” syndromes can be diagnosed by means other than Doppler recording and the results of such investigations are usually known to the operator before the Doppler examination is made. An example where such clinical bias was responsible for a false diagnosis of a “steal” syndrome is given. The authors describe a pulsed-Doppler technique using a single gate which they believed enabled the identification of the vertebral artery with greater certainty than previous techniques. Critical analysis of their results however, show that this technique is still not satisfactory and that recordings from other arteries are still being made under the impression that the signals are arising from the vertebral artery.

D.N. White

Papers

Color coded ultrasonic differential velocity arterial scanner (Echoflow)

Breast carcinoma detection by ultrasonic Doppler signals.

A digital technique for tracking moving interfaces

Non-invasive techniques for the recording of vertebral artery flow and their limitations.