GB2278443A

GB2278443A - A real-time hybrid ultrasonic display/imaging system for medical and industrialapplications

Info

Publication number: GB2278443A
Application number: GB9306534A
Authority: GB
Inventors: Godallawaththa Path Gunarathne
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-03-27
Filing date: 1993-03-27
Publication date: 1994-11-30
Anticipated expiration: 2013-03-27
Also published as: GB9306534D0; GB2278443B

Abstract

Conventional ultrasonic display/imaging devices used in medical and industrial applications can suffer from one or more of the problems, such as, (i) poor temporal resolution (ii) poor lateral resolution (iii) high operator dependence and problems of interpretation (iii) high cost, complexity end large size The invention addresses many of the above problems. In the very basic form, it could be used particularly for medical diagnostics as a low cost, real-time, one-dimensional special mode monitoring/display device for observations such as, heart and fetal movements. In a more general form, the system could present pictorial information in 2-Dimension (may be extended to 3-Dimension), capable of operating in real-time B-scan, sector scan and focused scan modes for medical and industrial applications. In contrast to existing methods, the new system is developed by integrating the desirable features of a range of different principles, such as, digitally controlled precision phased array scanning, wide band analog processing in multiple channels, acousto-optical image reconstruction with the possibility of dynamic compensation, on-line image enhancement using an adaptive insonification approach. <IMAGE>

Description

2. SYSTEM DESCRIPTION The new system is described in two separate sections to highlight their novel features and claims; (i) in the simplest form as in Fig (1) and (ii) the main system as in Fig. 2.

2.1 The SimDlest Form - Real-time, Acousto-oDtical spacial mode display.

2.1.1 Introduction A conventional, method of presenting moving targets by ultrasonic means is the well known A-scan display, where, the distance amplitude information is presented on a CRT either as a rf or a rectified version of the received echo signals. Various ecographic techniques derived from time amplitude information is in use, one example of this is the M-mode display used in medical diagnostics. However, the signals displayed or recorded can be very complex leading to difficulties of interpretation and also limiting the applicability in real-time monitoring.

The system described in here under 2.1 is an alternative approach to the presentation of echographic signals. In contrast to existing systems, the approach taken here as claimed is by using acousto-optical methods, by which movements are presented directly as spacial movements in real-time and amplitude information as brightness. In this way moving targets are easily observed and the degree of movements are clearly interpreted. The acousto-optical method used can be one of many techniques, such as, photo-elastic, schlieren, Bragg diffraction etc.

Fig.1 shows one possible basic arrangement of the simplest one dimensional spacial mode display, using schlieren visualization. The system comprises of transducer (A) used either in transmitter and receiver or transceiver mode for generating and reception of ultrasound, a signal conditioning unit and the display device. The system is operated in pulse-echo mode using short insonifying pulses.

2.1.2 Transmitter/receiver In the simplest form, the insonifying beam generated by means of the transmitter/receiver (1) may be a plane wave front using a wide aperture single transducer, but may be replaced by a fixed focus cylindrical or spherical type for better resolution or a variable focus type using a multi-element probe for greater flexibility. Depending on the nature of inspection, the received signals may have a mixture of static components due to static targets, specular reflections and dynamic components due to moving targets.

2.1.3 Sinnal conditioner Received signals are conditioned using the signal conditioner block (2), which in the very simplest form may be a wide band power amplifier boosting up the power of the received signals to a level adequate to match the sensitivity requirements of the acousto-optic display technique used. The display would then represent an A-scan type display of moving targets in one-dimensional spacial form in a background of static targets.

In a more refined form, the signal conditioning unit may contain other elements to enhance other specific properties of the final display, such as an analog signal substraction unit to filter out static signals, thus presenting only dynamic components.

2.1.4 Display system The adaptation of an acousto-optical display method has given the system following advantages.

Firstly, it allowed the display of dynamic targets to be represented directly in spacial form with great accuracy and secondly in real-time.

The conditioned signals are passed on to the display unit which comprises of a second transducer (3), which re-convert the electrical signals into corresponding acoustic signals. These signals which are now in acoustic form propagate into the transparent medium (4) which acts as an acoustic modulator, thus forming an acoustic replica of the incoming signals. In the simplest form, the second transducer could be a simple pianer transducer, but, better results may be achieved with a cylindrical or spherical transducer defining a focal region as in Fig. 1.

As the acoustic signals reach a desired position, e.g. the focal area, a short pulse of stroboscopic light is emitted by triggering a miniature LED stroboscope (5). The trigger signal is derived from the same source triggering the transmitter (1), but, with a delay imposed using the delay device (6) to take into account of the transit time of the acoustic signals. The standard schlieren, photoelastic or other optical arrangement allow the visualisation of the acoustic signals in the medium either with the naked eye or by using a small video camera (such as a CCD camera)/monitor system.

2.1.5 Assemblv The whole system may be kinematicaliy assembied in a small enclosed space, comparable to the size of a small portable oscilloscope.

2.2. THE MAIN SYSTEM 2.2.1 Introduction This invention relates to the development of a new real-time imaging system utilizing a plurality of principles as highlighted in the abstract to overcome some problems inherent in the conventional methods, thus, achieving an unusual combination of useful characteristics.

This system is capable of producing A-scan, B-scan, sector scan and focused scan in pseudo realtime, achieving very high temporal resolution compared to conventional methods. Furthermore, it is compact and portable and exhibit potential advantages in real-time medical, veterinary and industrial applications.

2.2.2 Background Earlier attempts to produce direct acousto-optical image reconstruction with field linearity and isochronicity has been reported by Hanstead (1972) as well as in UK patent No. 1,364,254 and also by other workers, Haymann(1977), Bar Cohen et.al (1978) etc. However, these were passive systems, in that they utilised only the energy contained within the echo signals to produce visualization and hence, the sensitivity was very low. Due to this reason and also due to lack of flexibility, none of these systems were adopted in practice.

A more recent development for NDT applications overcoming the problem of low sensitivity of the direct visualization methods was reported in the Ultrasonics International Conference Proceedings (1985), entitled a New ultrasonic Imaging system by Gunarathne and Szilard under a project sponsored by the United Kingdom Atomic Energy Authority, UK patent No.2,160,973. In this system, the problems of low sensitivity and flexibility associated with the Hanstead's direct visualization method was solved by introducing electronic amplification between a set of receiving and re-transmitting transducer arrays.

Despite the improvements made, this system also had many operational problems. The system could only produce images in the coaxial plane directly below the receiver aperture and had only a small field of view. Hence, the system was of limited use in many practical testing situations eg.

welds etc. Due to such practical problems, this system also did not enter into the industrial environment.

2.2.3 SPECIFIC FEATURES OF THE NEW HYBRID SYSTEM The specific features of this new development include a unique combination of the following 1. Ability to scan a test object within a required sector or focused along specified paths and sites using computer controlled phased array techniques.

2. Ability to achieve real-time image re-construction using a suitable acousto-optical technique incorporating field linearity and isochronicity.

3. Good resolution, sensitivity and the possibility of on-line image enhancement by adaptive insonification.

The first feature (1) gives the system the ability to examine a wide area of a given test object from any one probe position, thereby greatly alleviating the practical problems associated with coupling.

It also enables a way of applying dynamic compensation to bring about such features as field uniformity and off-axis compensation against geometrical distortions and isochronicity. This together with the real-time operation allows the user to steer and adjust the beam to achieve an optimal interactive examination of a given target site. With software control, it would also be possible to scan along specified paths within a test material, e.g. along a welded joint or allowed to perform sector scanning at high frame rates, thus extending the scope further into medical applications.

Fig 2 shows a basic block diagram of the system with a typical application in weld testing.

The hardware consists of four main components, namely, a phased array transceiver system (A,B) signal conditioning hardware connected to each transducer element forming a pluraiity of transmission channels (C), a re-transmitting transducer array (K), coupled to an acousto-optical visualization system (M,N), with associated electronics and dedicated digital control hardware and microcomputer interface.

2.2.4 Operation The system operation is as follows. Transceiver boards are actuated by computer (E) or by built-in dedicated hardware according to the trigger delay pattern required for a particular scan angle to steer or scan the test object (T). Ultrasonic wavefronts are therefore generated and transmitted into the medium according to the prescribed scan requirements entered in software. These wavefronts interact with the acoustic discontinuities within the test object medium giving rise to echoes which are received by the transducer array (A) and are passed on to the signal conditioning units (C) attached to each channel.

In the very simplest form the signal conditioning units would be a set of power amplifiers, but due to the requirement of off-axis imaging when the system is operating in the scan mode, software controlled dynamic compensation may be applied using additional hardware eg using analogue Charge Coupled Devices and variable gain control etc., built as part of the signal conditioners(C).

The conditioned signals are then re-converted into corresponding acoustic signals by means of the re-transmitting array (K), which forms part of the sonoptical focusing geometry of the acoustooptical system (M). A standard acousto-optical visualization technique such as the photo-elastic or schlieren method may be used. These acoustic signals propergate into the visualizing medium (N) of the acoustooptical system to produce an acoustic replica of the object field which is made visible by an ultra-short stroboscopic illumination synchronized with respect to the insonifying wavefornt but delayed by (G) to account for the transit time of the received echoes reaching their respective image points.

The sonoptical geometry is designed such that, when the scan angle is zero, (ie. on-axis) the received echo signals are brought into their respective image points at one instant of time irrespective of the axial distance of the defects within the test object, a property called 'isochronicity' and with constant object-to-image spacial relationship, a property called 'linearity'.

However, when the beam is at angles other than zero or near zero, as would be the case when steered or scanned, the linearity and isochronicity cannot be ensured without the need of some dynamic compensation for off-axis imaging. Hence the inclusion of dynamic compensation means (D) to the signal conditionning and pulse synchronization ciruits of the stroboscopic light source (F).

The extra degree of freedom introduced into this system by having a precision phased array scanner promotes practical applications, as is evident from Fig.2. In the transmission mode, insonifying energy is focused or directed into the target area. Under software control, a focal point, path or a site may be defined by the user or generated by an adaptive insonification technique under software control. Transmission energy may also be dynamically controlled to compensate for the lpsa of signal strength transmitted and received at oblique angles, thereby achieving field uniformity.

For the received echo signals, the system essentially behaves as an active acousto-optical imaging device operating in real-time, in a form analogous to the formation of an optical image. This is one of the fundamental advantages compared to conventional phased array imaging techniques as no further image reconstruction eg. by means of building up scan lines is required.

2.2.5 Further features It should be pointed out here, that according to one aspect of this invention, there are further distinct features when the system is operated in a scanning mode, compared to a conventional scanner. In a conventional scanning system, eg. a sector scanner, each frame is built up by successive scan lines, where as in this system for any angle a complete image is formed with just one pulse, while the pulse repetition rate could be as high as 1 kHz or more. Thus, the temporal resolution is extremely high at any given scan angle within its field of view at any instant of time.

Furthermore, in contrast to conventional methods, the whole effective aperture is utilized in each image frame giving superior lateral resolution without the need of any secondary processing.

Another feature is that as each scan angle represents a field rather than a line, the frame rate could also be very high compared to a conventional scanner, since, much coarser angular scanning steps could be implemented as it does not lead to direct image dilation, thus allowing a higher temporal resolution for the whole scan field, which is an attractive feature for medical applications.

Although, a very limited number of channels were used initially and the transducer element spacings were not meant for imaging body tissues, cardiac movements were observed and to the authors's knowledge, for the first time using any acousto-optical system.

2.2.6 The assemblv A prototype may be assembled incorporating all the units with a kinematically mounted acoustooptical visualization system within a space comparable to that occupied by a desk top computer.

Claims

3. CLAIMS

3.1 Claims under (2.1) - The simpiest stand-alone form of the new development 1. A system as described above under 2.1 is claimed for the purpose of displaying ultrasonic echo data in a form analogous to A-scan utilizing acousto-optical display methods to represent targets in spacial domain in real-time for potential applications in medical, veterinary and other industrial applications.

2. The simplest basic system claimed under 2.1 comprises of a transmitter/receiver means, signal amplification means and retransmission means using a single planar transducer coupled to a suitable acousto-optic modulator such as, photoelastic, schlieren or Brag diffraction cell etc. to form a corresponding real-time acoustic phase object, which is made visible by ultra-short stroboscopic illumination.

3. The basic system upgrade for higher performance claims under 2.1 include the use of one or more of the features such as focused or multi-element variable focus transceiver means, additional signal conditioning means to highlight useful features such as differentiating static targets from dynamic targets, focused cylindrical or spherical re-transmitter transducer means for high sensitivity and visual clarity of the spacial display.

4. The apparatus claims under 2.1 include an integrated assembly of all the essential units described above as a package, eg. miniature acousto-optical display arrangement comprising of a miniature LED stroboscope, CCD camera, small monitor of (approximately 5 "), signal conditioning unit with upgradable plugin boards, ultrasonic transceiver electronics with controls accessible to the user and standard peripheral interface devices.

3.2 CLAIMS - FOR THE MAIN SYSTEM - THE NEW HYBRID IMAGING SYSTEM 5. A system as described under the section 2.2, above is claimed for applications in medical, veterinary and Non-Destructive-Testing for the purpose of imaging or monitoring body tissues, flaws in structural assemblies and components etc., in seperate modes analogous to A-scan, B-scan, sector and focused scans in pseudo-real time.

6. The basic hybrid imaging system claims under section 2.2, comprises a linear phased array scanning transceiver means; signal conditioning means comprising of power amplifiers with or without dynamic compensation applied to each channel and to the stroboscopic synchronization system as described above to achieve optimal isochronicity and linearity; re transmission means using a second set of re-transmitting transducer array coupled to an acousto-optic focusing/imaging meadium, using a standard visualization means, such as, photo-elastic or schlieren technique.

7. The basic system upgrade for higher performance claims under section 2.2, include all compensation means including that described above for the purpose of regaining loss of linearity and isochronicity due to departures from on-axis imaging as would be the case for a scanned field. The basic system upgrade also include natural extension to imaging in 3 dimension by application of 2-dimensional arrays in place of linear arrays and with stereoscopic acousto-optical visualization.

8. The apparatus claims under section 2.2, include an integrated assembly of all the essential components described above including dedicated analog and digital hardware as appropriate with a miniature acousto-optical display arrangement with standard communication and peripheral interface devices for connection to external devices.

Amendments to the claims have been filed as follows 1. A system comprising a first transducer for converting acoustic signals into electrical signals; a transmitter for transmitting the electrical signals; a signal conditioner for conditioning the signal transmitted by the transmitter; a second transducer for reconverting the electrical signal into an acoustic signal; display means.

2. A system as claimed in claim 1 wherein the display means comprises an acoustic modulator and detecting means for detecting a signal propagating through the acoustic modulator.

3. A system according to claim 2 wherein the detecting means comprises stroboscopic means for producing to the display means ultra short stroboscopic illumination.

4. A system according to any one of the preceding claims wherein the signal conditioner comprises a wide band power amplifier.

5. A system according to claim 4 wherein the signal conditioner further comprises an analogue signal subtraction unit.

6. A system according to any one of the preceding claims wherein the first transducer comprises a wide aperture single transducer.

7. A system according to any one of claims 1 to 5 wherein the first transducer comprises a fixed focus cylindrical or spherical transducer.

8. A system according to any one of claims 1 to 5 wherein the first transducer comprises a variable focus multi element probe transducer.

9. A system according to any one of the preceding claims wherein the second transducer comprises a planar transducer.

10. A system according to any one of claims 1 to 8 wherein the second transducer comprises a cylindrical or spherical transducer.

11. A system according to any one of the preceding claims wherein the acoustic modulator comprises a transparent medium.

12. A system according to any one of the preceding claims comprising trigger means for triggering the transmitter at a predetermined time, and trigger means for triggering the stroboscopic means - 13. A system according to claim 12 wherein a single trigger is used to trigger both the transmitter and the stroboscopic means, and the system further comprises delay means for delaying activation of the stroboscopic means relative to the triggering of transmitter.

14. A system according to any one of the preceding claims wherein the transmitter comprises a phased array scanning means.

15. A system according to any one of the preceding claims further comprising compensation means for regaining loss of linearity and isochronicity during off axis imaging.

16. A system substantially as hereinbefore described with reference to the accompanying drawings.

Amendments to the claims have been filed as follows 1. A system for imaging a test medium the system comprising: a transducer adapted to direct an acoustic signal to the test medium, and to transmit a reflected acoustic signal received from the test medium to a receiver; a transmitter for transmitting the electrical signal; a signal conditioner for conditioning the signal transmitted by the transmitter; a second transducer for reconverting the electrical signal into an acoustic signal; display means.
2. A system according to claim 1 further comprising a transmitter for transmitting an electrical signal to the transducer from which an acoustic signal is produced.
3. A system as claimed in claim 2 wherein the display means comprises an acoustic modulator and detecting means for detecting a signal propagating through the acoustic modulator.
4. A system according to claim 3 wherein the detecting means comprises stroboscopic means for producing to the display means ultra short stroboscopic illumination.
5. A system according to any one of the preceding claims wherein the signal conditioner comprises a wide band power amplifier.
6. A system according to claim 5 wherein the signal conditioner further comprises an analogue signal subtraction unit.
7. A system according to any one of the preceding claims wherein the first transducer comprises a wide aperture single transducer.
8. A system according to any one of claims 1 to 6 wherein the first transducer comprises a fixed focus cylindrical or spherical transducer.
9. A system according to any one of claims 1 to 6 wherein the first transducer comprises a variable focus multi element probe transducer.
10. A system according to any one of the preceding claims wherein the second transducer comprises a planar transducer.
11. A system according to any one of claims 1 to 7 wherein the second transducer comprises a cylindrical or spherical transducer.
12. A system according to any one of the preceding claims wherein the acoustic modulator comprises a transparent medium.
13. A system according to any one of the preceding claims comprising trigger means for triggering the transmitter at a predetermined time, and trigger means for triggering the stroboscopic means.
14. A system according to claim 13 wherein a single trigger is used to trigger both the transmitter and the stroboscopic means, and the system further comprises delay means for delaying activation of the stroboscopic means relative to the triggering of transmitter.
15. A system according to any one of the preceding claims wherein the transmitter comprises a phased array scanning means.
16. A system according to any one of the preceding claims further comprising compensation means for regaining loss of linearity and isochronicity during off axis imaging.
17. A system substantially as hereinbefore described with reference to the accompanying drawings.