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Accurate recording of Doppler ultrasound signals
S48
Abstracts
blinded to the results of the pre-operative magnetic resonance imaging (MRI). The results of the pre-operative TAUS and MRI in each case were then compared to the findings at laparotomy in order to assess the accuracy of TAUS at hepatic segmental localization. In 16 cases (80%) the MRI and TAUS accurately segmentally localized the hepatic lesions present. Both imaging modalities were incorrect compared with the findings at laparotomy in two cases (10%) and each were unsuccessful in two cases (10%). The findings of this study are that MRI and TAUS are equally accurate at segmental localization of hepatic pathology. Application of noise tolerant pseudo inverse filtering to perfect ultrasound reflections Young W.F.; McLaughlin S.; Spencer T. Department of Electrical Engineering, The Uni6ersity of Edinburgh, The King’s Buildings, Edinburgh EH9 3JL, UK Noise tolerant pseudo inverse filtering is proposed as a technique for reducing noise in ultrasound images. Conventional inverse filtering suffers from high noise sensitivity which is removed in our proposed pseudo inverse filter; making the filter robust and appropriate for use with ultrasound images. The proposed technique offers substantial improvements in lateral resolution for image features. Results are presented applying the proposed filters to ultrasound images of (near) perfect plane reflectors. Accurate recording of Doppler ultrasound signals Warner M.H.; Fairhead A.C. Department of Bio-Medical Physics and Bio-Engineering, Uni6ersity of Aberdeen, UK Accurate recording of Doppler signals is necessary for offline processing, signal replay or data storage. The ideal signals to record are the two quadrature channels, which are in the audio range. These signals are formed by the demodulation process, which separates Doppler shifts from the carrier frequency. Recording is difficult as phase and amplitude mismatch between channels leads to spurious frequencies being generated. Phase error must be B 9 2% and amplitude error B 9 2%. Conventional audio tape and DAT systems do not meet these specifications. Another option is to digitise the data and record directly to disk. Most acquisition systems are expensive, bulky and overly complex. Commercial soundcards are proposed as an alternative. Two stereo soundcards (ESS and NM) were tested. Generated sine waves were digitised at 44.1 kHz and 16 bits to test the cards’ performance over the audio range. Both cards performed well, with flat frequency response and low mismatch errors. A CW Doppler unit was used to test the system as a whole, as there are often small mismatches on the quadrature outputs. The NM system performed within the limits but the ESS system would need corrections prior to playback. The data is digital and easily accessible and these could be implemented in software. Our work needs high sampling rates and resolutions, producing huge amounts of data and potential storage space problems. Optical disk or CD storage is not an option for all users. Could smaller values be used without affecting signal quality?
Further tests using different recording conditions, and also aortic Doppler signals, suggest that this is so. The NM system is used to record signals from patients to enable us to do further off-line processing, such as improved maximum frequency detection and cardiac output calculation. This recording method has proved ideal as it is inexpensive, simple and can be used at bedside. It may also provide a means of making a permanent record of Doppler waveforms, that can be replayed through the instrument. On the measurement of the velocity of ultrasound in trabecular bone Strelitzki R.; Evans J.A. Centre for Bone and Body Composition Research, Uni6ersity of Leeds, Leeds General Infirmary, UK The use of ultrasound in the characterisation of trabecular bone for the detection of osteoporosis continues to increase. Commercial equipment uses short broadband pulses and reports velocity in the os calcis, where a marker is used as a time reference in order to compare transit times with and without the sample. Such measurements implicitly assume that the pulse shape is unchanged during its passage through the medium. However, considerable distortion of the shape can be caused both by frequency dependence of attenuation and velocity (dispersion). We have investigated velocity measurements applying phase spectral analysis and a cross correlation technique to calculate the phase and mean pulse velocity in a series of fixed human os calces. The group velocity was also calculated using the slope of the phase velocity as a function of frequency and found to be in the range 1500 – 1520 m s − 1. Negative dispersion was found in all the os calces. Consequently, the group velocity at any frequency was found to be as much as 3% less than the phase velocity at that frequency. When the cross correlation technique was applied, the velocity values obtained were slightly (up to 0.5%) greater than the phase velocity values at 750 KHz for the most bones. This has also been shown using a computer simulation. The ultrasound features of transient neonatal renal medullary hyperechogenicity Howlett D.C.; Greenwood K.L.; Jarosz J.M.; MacDonald L.M.; Saunders A.J.S. Department of Radiology, Guy’s Hospital, 2nd Floor Guy’s Tower, Guy’s and St. Thomas’ Trust, St. Thomas’ Street, London SE1 9RT, UK Purpose: Transient renal medullary hyperechogenicity (RMH) may be observed in healthy neonates in the first days of life. Hyperechoic medullary pyramids can arise in older infants, due to nephrocalcinosis, in a number of conditions including renal tubular acidosis, oxalosis and frusemide/ steroid therapy. A prospective ultrasound (US) study was performed to assess the incidence and transient nature of RMH in the newborn and to illustrate the US characteristics of this phenomenon. Materials and Methods: A total of 85 neonates (64 term, 21 preterm) were examined with US. The US examinations were carried out using Acuson 128XP/5 – 7.5 MHz transducers. The
Abstracts
blinded to the results of the pre-operative magnetic resonance imaging (MRI). The results of the pre-operative TAUS and MRI in each case were then compared to the findings at laparotomy in order to assess the accuracy of TAUS at hepatic segmental localization. In 16 cases (80%) the MRI and TAUS accurately segmentally localized the hepatic lesions present. Both imaging modalities were incorrect compared with the findings at laparotomy in two cases (10%) and each were unsuccessful in two cases (10%). The findings of this study are that MRI and TAUS are equally accurate at segmental localization of hepatic pathology. Application of noise tolerant pseudo inverse filtering to perfect ultrasound reflections Young W.F.; McLaughlin S.; Spencer T. Department of Electrical Engineering, The Uni6ersity of Edinburgh, The King’s Buildings, Edinburgh EH9 3JL, UK Noise tolerant pseudo inverse filtering is proposed as a technique for reducing noise in ultrasound images. Conventional inverse filtering suffers from high noise sensitivity which is removed in our proposed pseudo inverse filter; making the filter robust and appropriate for use with ultrasound images. The proposed technique offers substantial improvements in lateral resolution for image features. Results are presented applying the proposed filters to ultrasound images of (near) perfect plane reflectors. Accurate recording of Doppler ultrasound signals Warner M.H.; Fairhead A.C. Department of Bio-Medical Physics and Bio-Engineering, Uni6ersity of Aberdeen, UK Accurate recording of Doppler signals is necessary for offline processing, signal replay or data storage. The ideal signals to record are the two quadrature channels, which are in the audio range. These signals are formed by the demodulation process, which separates Doppler shifts from the carrier frequency. Recording is difficult as phase and amplitude mismatch between channels leads to spurious frequencies being generated. Phase error must be B 9 2% and amplitude error B 9 2%. Conventional audio tape and DAT systems do not meet these specifications. Another option is to digitise the data and record directly to disk. Most acquisition systems are expensive, bulky and overly complex. Commercial soundcards are proposed as an alternative. Two stereo soundcards (ESS and NM) were tested. Generated sine waves were digitised at 44.1 kHz and 16 bits to test the cards’ performance over the audio range. Both cards performed well, with flat frequency response and low mismatch errors. A CW Doppler unit was used to test the system as a whole, as there are often small mismatches on the quadrature outputs. The NM system performed within the limits but the ESS system would need corrections prior to playback. The data is digital and easily accessible and these could be implemented in software. Our work needs high sampling rates and resolutions, producing huge amounts of data and potential storage space problems. Optical disk or CD storage is not an option for all users. Could smaller values be used without affecting signal quality?
Further tests using different recording conditions, and also aortic Doppler signals, suggest that this is so. The NM system is used to record signals from patients to enable us to do further off-line processing, such as improved maximum frequency detection and cardiac output calculation. This recording method has proved ideal as it is inexpensive, simple and can be used at bedside. It may also provide a means of making a permanent record of Doppler waveforms, that can be replayed through the instrument. On the measurement of the velocity of ultrasound in trabecular bone Strelitzki R.; Evans J.A. Centre for Bone and Body Composition Research, Uni6ersity of Leeds, Leeds General Infirmary, UK The use of ultrasound in the characterisation of trabecular bone for the detection of osteoporosis continues to increase. Commercial equipment uses short broadband pulses and reports velocity in the os calcis, where a marker is used as a time reference in order to compare transit times with and without the sample. Such measurements implicitly assume that the pulse shape is unchanged during its passage through the medium. However, considerable distortion of the shape can be caused both by frequency dependence of attenuation and velocity (dispersion). We have investigated velocity measurements applying phase spectral analysis and a cross correlation technique to calculate the phase and mean pulse velocity in a series of fixed human os calces. The group velocity was also calculated using the slope of the phase velocity as a function of frequency and found to be in the range 1500 – 1520 m s − 1. Negative dispersion was found in all the os calces. Consequently, the group velocity at any frequency was found to be as much as 3% less than the phase velocity at that frequency. When the cross correlation technique was applied, the velocity values obtained were slightly (up to 0.5%) greater than the phase velocity values at 750 KHz for the most bones. This has also been shown using a computer simulation. The ultrasound features of transient neonatal renal medullary hyperechogenicity Howlett D.C.; Greenwood K.L.; Jarosz J.M.; MacDonald L.M.; Saunders A.J.S. Department of Radiology, Guy’s Hospital, 2nd Floor Guy’s Tower, Guy’s and St. Thomas’ Trust, St. Thomas’ Street, London SE1 9RT, UK Purpose: Transient renal medullary hyperechogenicity (RMH) may be observed in healthy neonates in the first days of life. Hyperechoic medullary pyramids can arise in older infants, due to nephrocalcinosis, in a number of conditions including renal tubular acidosis, oxalosis and frusemide/ steroid therapy. A prospective ultrasound (US) study was performed to assess the incidence and transient nature of RMH in the newborn and to illustrate the US characteristics of this phenomenon. Materials and Methods: A total of 85 neonates (64 term, 21 preterm) were examined with US. The US examinations were carried out using Acuson 128XP/5 – 7.5 MHz transducers. The