- Email: [email protected]
Basic principles of haemodynamics
Abstracts
S6
in this pilot study. The vascular patterns recorded at PD and CD were compared with cytology and, when surgery was performed, with histology. Three PD signs were classified a posterior: A) a vascular perilesional halo (Ring Sun); B) peri- and intralesional vascular signal (Complex Ring Sing), subdivided into: B,) with moderate intralesional vascularisation, homogeneous structure and regular calibre and flow of vessels and B,) with high intralesional vascularisation, anarchical structure and winding calibre and flow of vessels; C) a vascular perilesional halo characterised by a peripheral large afferent vessel with winding calibre and flow (Delta Sign). All the tumoral lesions (diagnosed at histology) showed a pattern type B, but one that had a pattern type C (diagnosed as undifferentiated carcinoma) and one that had a type B,, (diagnosed as papillary carcinoma). All the other lesions with PD pattern type A and B, were hyperplasias. Nevertheless, were found hyperplasias with a pattern type B,: in these cases the study of flow indices was helpful in differentiating goitre from benign or malignant tumours. All the patients with tumoural lesion at cytology were surgically treated and 18 patients with cytological finding of hyperplasia as well. The remaining 77 patients were followed for 6-24 months at 6 month intervals. During this period, 6 of the 24 patients with B, pattern developed autonomously function thyroid nodules. Finally, in respect to CD, PD has a higher sensitivity (97.2% vs. 89.7%), specificity (82.5% vs. 51%), positive (59.3% vs. 34.3%) and negative predictive value (99% vs. 95%). In conclusion, PD seems to provide a better characterisation of hypoechoic thyroid nodules allowing a more accurate selection of the patients to subject to tine needle biopsy. Thursday 20th November Session Iv: Quantification and Calibration
?? 4.1
Basic Principles of Haemodynamics
L. Pourcelot. Unite hem
316, CHU Bretonneau 37044
Tours Cedtq France
Instantaneous blood flow velocity in arteries is determined by several parameters, among which the most significant are: (1) the value of instantaneous arterial blood pressure P, (2) the local velocity of pressure wave, (3) the arterial compliance C or elasticity, (4) the impedance of peripheral arterial network, (5) the
impedance matching between great arteries and distal organs, and (6) the instantaneous velocity distribution across the vessel of interest. The interpretation of Doppler velocity curves and Doppler spectra is relatively complex, because these curves traduce instantaneous changes in flow conditions into the vessels of interest. In order to make this interpretation more simple, it is possible to examine three different situations: 1 - The distal circulation corresponds to a low resistance system. In this case there is a continuous diastolic flow in all arteries supplying the corresponding organ. The flow is called resistive flow, and is typical of organs with high metabolic rate like brain, kidneys, liver, spleen, placenta. 2 - The distal circulation corresponds to a high resistance system. The continuous diastolic flow is no longer present. The flow is called compliant flow and its diastolic components depend on the distance from the left ventricle and the elasticity of supplying vessels. A typical compliant flow is observed in leg vessels supplying muscles. 3 - The local flow (at the level of the Doppler sample volume) is disturbed by a stenosis, so that flow distribution across the vessel is no longer parabolic. The frequency analysis of Doppler signals reveals a combination of low and high velocities in the vicinity of the stenosis. It is possible through that analysis of the flow components to determine non invasively the percentage of reduction in vessel area. It is possible to modelize the cardiovascular system and several models have been proposed. Among these models, two are of interest for routine applications: -the first is a global model, based, on the flow-pressure relationship: Q = AP/R + C. GP/St (1). This model is easy to apply for low resistance circulation areas. In order to make easier the use of the mathematical formula (l), a simplified graph of flow/pressure characteristics is used in practice. On this graph it is possible to explain most of the changes in flow velocity curves observed in physiological and pathological situations, like changes in pO2 and pCO2, intracranial hypertension, intracranial oedema, gravidic hypertension with low placental flow, etc.. . f-the second is a physical non linear model with distributed parameters associated with combined elements: elastic tapered segments, bifurcations and pathological segments. It allows to determine the time course of instantaneous flow velocity curves at different levels of the arterial tree. Changes in peripheral resistance, vascular elasticity, arterial and venous pressure, tissue pressure, etc. can be taken into account by the
Abstracts
model in order to calculate the new velocity curves or other flow parameters. As an example it is possible to determine the values of intracranial pressure, diastolic and systolic components of cerebral blood flow, resistive index in case of acute and chronic intracranial hypertension. One of the major interests of this model is its potential integration in an expert system for therapeutic decision, follow-up of disease and teaching. In conclusion, a good understanding of haemodynamics is essential, in parallel with clinical knowledge and practical training, for performing high quality examinations in patients.
4.2 0
Vector Doppler
P.R. Hoskins PR. Department of Medical Physics, Royal Infinary,
Edinburgh, UK
Conventional Doppler systems estimate only the velocity component in the direction of the Doppler beam. This leads to the dependence of Doppler frequency shift on the angle between the beam and the direction of motion. For calculation of true blood velocity the operator manually measures the angle between the beam and the vessel using the machine cursor in order that conversion can be performed from Doppler frequency shift to velocity. The review will describe vector Doppler systems which have been developed to date; those which combine Doppler ultrasound data from 2 and 3 independent beam directions to obtain measurements of 2 and 3 velocity components respectively. The author has developed a vector Doppler technique based on the use of a linear array in which velocity magnitude and beam-vector angle are automatically calculated, without the need for manual angle entry by the operator. The estimated velocity magnitude is essentially angle independent when the technique is applied to spectral Doppler or colour flow images. The flow model experiments showed that the true beam-vector angle was different from the manually measured angle by an amount varying from 5-25, indicating the large inaccuracy of the conventional angle-correction technique. In colour flow mode the angle itself may be displayed as a colour image; using this approach regions of recirculation can clearly be seen as areas in which the angle varies through 360. Prospects for commercial implementation of this technique will be discussed; there should be no reason why the technique cannot be developed with modification of conventional linear arrays.
s7
0
4.4
A Flow Model, Simulating Pathological Vessel System of a Malignant Musculoskeletal Tumour; Doppler Results
G. Bodner, M. Verius, R. Huttary, S. Giacomuzzi, A. Dessl. Department of Radiology, University of Innsbruck, Innsbruck, Austria
Purpose: To construct a phantom with pathological vessel architecture, based on typical pathological anatomical features (stenosis, a-v shunts, occlusion, self -loops) of high vascular malignant musculoskeletal tumours and correlate Doppler results. Materials and methods: A squeeze pump creates a constant pulsative flow of simulated blood (waterglyzerin with particles of cellulose) within silicone tubes. The pulsative flow (bi-triphase) can be obtained by using a proportional valve which converts the constant flow of the squeeze pump. Neovascular architecture was rebuilt with silicone tubes, such as trifurcation, a-v shunts, self loops and abrupt calibre changes of the silicone tubes, based on anarchic vessel - architecture of 5 malignant musculoskeletal tumours, examined in angiography and colour Doppler and power Doppler ultrasound. Results: Similar Doppler-spectral waves can be simulated in a flow model compared to Doppler ultrasound on high vascular soft tissue tumours, especially in AVshunts and on the abrupt calibre changes of the silicon tubes. Conclusion: To interpret different spectral waves of Doppler ultrasound signals in pathological vessel architecture of bone tumours.
?? 4.5
A New Phantom for Three-Dimensional Ultrasound Volume Measurement
D.C. Barratt, K.N. Humphries, K.E. Fredfeldt, R.M. Greenhalgh, A.H. Davies. Depatient of Surgery, Charing Cross Hospital, London, UK
Introduction: An important application for three-dimensional (3D) ultrasound imaging systems is the measurement of volume, yet the accuracy achievable from such systems is uncertain. A new 3D ultrasound volume phantom has been designed and constructed for the purpose of validating the accuracy of small volume measurement using 3D ultrasound systems. The phantom was used to test the accuracy of one such system.
S6
in this pilot study. The vascular patterns recorded at PD and CD were compared with cytology and, when surgery was performed, with histology. Three PD signs were classified a posterior: A) a vascular perilesional halo (Ring Sun); B) peri- and intralesional vascular signal (Complex Ring Sing), subdivided into: B,) with moderate intralesional vascularisation, homogeneous structure and regular calibre and flow of vessels and B,) with high intralesional vascularisation, anarchical structure and winding calibre and flow of vessels; C) a vascular perilesional halo characterised by a peripheral large afferent vessel with winding calibre and flow (Delta Sign). All the tumoral lesions (diagnosed at histology) showed a pattern type B, but one that had a pattern type C (diagnosed as undifferentiated carcinoma) and one that had a type B,, (diagnosed as papillary carcinoma). All the other lesions with PD pattern type A and B, were hyperplasias. Nevertheless, were found hyperplasias with a pattern type B,: in these cases the study of flow indices was helpful in differentiating goitre from benign or malignant tumours. All the patients with tumoural lesion at cytology were surgically treated and 18 patients with cytological finding of hyperplasia as well. The remaining 77 patients were followed for 6-24 months at 6 month intervals. During this period, 6 of the 24 patients with B, pattern developed autonomously function thyroid nodules. Finally, in respect to CD, PD has a higher sensitivity (97.2% vs. 89.7%), specificity (82.5% vs. 51%), positive (59.3% vs. 34.3%) and negative predictive value (99% vs. 95%). In conclusion, PD seems to provide a better characterisation of hypoechoic thyroid nodules allowing a more accurate selection of the patients to subject to tine needle biopsy. Thursday 20th November Session Iv: Quantification and Calibration
?? 4.1
Basic Principles of Haemodynamics
L. Pourcelot. Unite hem
316, CHU Bretonneau 37044
Tours Cedtq France
Instantaneous blood flow velocity in arteries is determined by several parameters, among which the most significant are: (1) the value of instantaneous arterial blood pressure P, (2) the local velocity of pressure wave, (3) the arterial compliance C or elasticity, (4) the impedance of peripheral arterial network, (5) the
impedance matching between great arteries and distal organs, and (6) the instantaneous velocity distribution across the vessel of interest. The interpretation of Doppler velocity curves and Doppler spectra is relatively complex, because these curves traduce instantaneous changes in flow conditions into the vessels of interest. In order to make this interpretation more simple, it is possible to examine three different situations: 1 - The distal circulation corresponds to a low resistance system. In this case there is a continuous diastolic flow in all arteries supplying the corresponding organ. The flow is called resistive flow, and is typical of organs with high metabolic rate like brain, kidneys, liver, spleen, placenta. 2 - The distal circulation corresponds to a high resistance system. The continuous diastolic flow is no longer present. The flow is called compliant flow and its diastolic components depend on the distance from the left ventricle and the elasticity of supplying vessels. A typical compliant flow is observed in leg vessels supplying muscles. 3 - The local flow (at the level of the Doppler sample volume) is disturbed by a stenosis, so that flow distribution across the vessel is no longer parabolic. The frequency analysis of Doppler signals reveals a combination of low and high velocities in the vicinity of the stenosis. It is possible through that analysis of the flow components to determine non invasively the percentage of reduction in vessel area. It is possible to modelize the cardiovascular system and several models have been proposed. Among these models, two are of interest for routine applications: -the first is a global model, based, on the flow-pressure relationship: Q = AP/R + C. GP/St (1). This model is easy to apply for low resistance circulation areas. In order to make easier the use of the mathematical formula (l), a simplified graph of flow/pressure characteristics is used in practice. On this graph it is possible to explain most of the changes in flow velocity curves observed in physiological and pathological situations, like changes in pO2 and pCO2, intracranial hypertension, intracranial oedema, gravidic hypertension with low placental flow, etc.. . f-the second is a physical non linear model with distributed parameters associated with combined elements: elastic tapered segments, bifurcations and pathological segments. It allows to determine the time course of instantaneous flow velocity curves at different levels of the arterial tree. Changes in peripheral resistance, vascular elasticity, arterial and venous pressure, tissue pressure, etc. can be taken into account by the
Abstracts
model in order to calculate the new velocity curves or other flow parameters. As an example it is possible to determine the values of intracranial pressure, diastolic and systolic components of cerebral blood flow, resistive index in case of acute and chronic intracranial hypertension. One of the major interests of this model is its potential integration in an expert system for therapeutic decision, follow-up of disease and teaching. In conclusion, a good understanding of haemodynamics is essential, in parallel with clinical knowledge and practical training, for performing high quality examinations in patients.
4.2 0
Vector Doppler
P.R. Hoskins PR. Department of Medical Physics, Royal Infinary,
Edinburgh, UK
Conventional Doppler systems estimate only the velocity component in the direction of the Doppler beam. This leads to the dependence of Doppler frequency shift on the angle between the beam and the direction of motion. For calculation of true blood velocity the operator manually measures the angle between the beam and the vessel using the machine cursor in order that conversion can be performed from Doppler frequency shift to velocity. The review will describe vector Doppler systems which have been developed to date; those which combine Doppler ultrasound data from 2 and 3 independent beam directions to obtain measurements of 2 and 3 velocity components respectively. The author has developed a vector Doppler technique based on the use of a linear array in which velocity magnitude and beam-vector angle are automatically calculated, without the need for manual angle entry by the operator. The estimated velocity magnitude is essentially angle independent when the technique is applied to spectral Doppler or colour flow images. The flow model experiments showed that the true beam-vector angle was different from the manually measured angle by an amount varying from 5-25, indicating the large inaccuracy of the conventional angle-correction technique. In colour flow mode the angle itself may be displayed as a colour image; using this approach regions of recirculation can clearly be seen as areas in which the angle varies through 360. Prospects for commercial implementation of this technique will be discussed; there should be no reason why the technique cannot be developed with modification of conventional linear arrays.
s7
0
4.4
A Flow Model, Simulating Pathological Vessel System of a Malignant Musculoskeletal Tumour; Doppler Results
G. Bodner, M. Verius, R. Huttary, S. Giacomuzzi, A. Dessl. Department of Radiology, University of Innsbruck, Innsbruck, Austria
Purpose: To construct a phantom with pathological vessel architecture, based on typical pathological anatomical features (stenosis, a-v shunts, occlusion, self -loops) of high vascular malignant musculoskeletal tumours and correlate Doppler results. Materials and methods: A squeeze pump creates a constant pulsative flow of simulated blood (waterglyzerin with particles of cellulose) within silicone tubes. The pulsative flow (bi-triphase) can be obtained by using a proportional valve which converts the constant flow of the squeeze pump. Neovascular architecture was rebuilt with silicone tubes, such as trifurcation, a-v shunts, self loops and abrupt calibre changes of the silicone tubes, based on anarchic vessel - architecture of 5 malignant musculoskeletal tumours, examined in angiography and colour Doppler and power Doppler ultrasound. Results: Similar Doppler-spectral waves can be simulated in a flow model compared to Doppler ultrasound on high vascular soft tissue tumours, especially in AVshunts and on the abrupt calibre changes of the silicon tubes. Conclusion: To interpret different spectral waves of Doppler ultrasound signals in pathological vessel architecture of bone tumours.
?? 4.5
A New Phantom for Three-Dimensional Ultrasound Volume Measurement
D.C. Barratt, K.N. Humphries, K.E. Fredfeldt, R.M. Greenhalgh, A.H. Davies. Depatient of Surgery, Charing Cross Hospital, London, UK
Introduction: An important application for three-dimensional (3D) ultrasound imaging systems is the measurement of volume, yet the accuracy achievable from such systems is uncertain. A new 3D ultrasound volume phantom has been designed and constructed for the purpose of validating the accuracy of small volume measurement using 3D ultrasound systems. The phantom was used to test the accuracy of one such system.