<p>The purpose of this work was to: a) Determine whether the amount of colour in a power Doppler image is dependent on the angle between the examined vessel and the soundbeam and/or on the velocity of the flow within the vessel; b) Investigate if a dependency on flow velocity could be used for the detection of volume flow differences and c) Define clinical applications utilising the improved sensitivity to low flow of PD.</p><p>In the experimental studies (study I and II) a silicon tube in a water bath was insonated, the insonation angle and the volume flow changed and the resulting images stored, transferred to a personal computer and analysed with regard to the amount of colour present in the image.</p><p>In study III and IV the ability of power Doppler to depict low flow was used to produce a map of the perfusion in well perfused organs, lack of colour in all or part of an organ taken as a sign of decreased perfusion. 150 patients with a renal transplant (study III) and 15 patients with abdominal trauma (study IV) were examined; the detected areas of decreased perfusion were correlated to other imaging modalities, laboratory and clinical records in order to determine the underlying pathology.</p><p>In study V the power Doppler sensitivity was used to look for and describe small portosystemic shunts in 141 patients with liver cirrhoses and suspected portal hypertension.</p><p>The colour representation in a power Doppler image was found to be dependent both on the insonation angle and the flow velocity. Computer analysis of the images could detect differences in volume flow down to a change of 10 ml/min.</p><p>Of the 150 renal transplants, areas of decreased perfusion were found in 12, all of which could be given a plausible explanation (2 focal infections, 4 AV fistulae, 1 kinked segmental artery and 5 with problems related to an accessory artery).</p><p>Of the 20 organs (7 livers and 13 spleens) examined in the 15 trauma patients, 5 were found to have areas without colour, corresponding to localised haematomas. Using computed tomography as gold standard, ultrasound showed neither false positive nor false negative findings.</p><p>Of the 141 patients with cirrhosis, 40 had Doppler ultrasound findings of a shunt, consistent with a portal hypertension. 7 of these 40 shunts showed a typical “ball ” or “corkscrew ” pattern.</p><p>Conclusion: The colour in a power Doppler image is dependent not only on reflector concentration (as it should be in theory) but also on the insonation angle and the velocity of the flow. This can be used to detect relative changes in volume flow. Clinical applications of power Doppler include mapping of organ perfusion and the detection of small vessels. These applications are based on the high sensitivity of power Doppler.</p>

The purpose of this work was to: a) Determine whether the amount of colour in a power Doppler image is dependent on the angle between the examined vessel and the soundbeam and/or on the velocity of the flow within the vessel; b) Investigate if a dependency on flow velocity could be used for the detection of volume flow differences and c) Define clinical applications utilising the improved sensitivity to low flow of PD. In the experimental studies (study I and II) a silicon tube in a water bath was insonated, the insonation angle and the volume flow changed and the resulting images stored, transferred to a personal computer and analysed with regard to the amount of colour present in the image. In study III and IV the ability of power Doppler to depict low flow was used to produce a map of the perfusion in well perfused organs, lack of colour in all or part of an organ taken as a sign of decreased perfusion. 150 patients with a renal transplant (study III) and 15 patients with abdominal trauma (study IV) were examined; the detected areas of decreased perfusion were correlated to other imaging modalities, laboratory and clinical records in order to determine the underlying pathology. In study V the power Doppler sensitivity was used to look for and describe small portosystemic shunts in 141 patients with liver cirrhoses and suspected portal hypertension. The colour representation in a power Doppler image was found to be dependent both on the insonation angle and the flow velocity. Computer analysis of the images could detect differences in volume flow down to a change of 10 ml/min. Of the 150 renal transplants, areas of decreased perfusion were found in 12, all of which could be given a plausible explanation (2 focal infections, 4 AV fistulae, 1 kinked segmental artery and 5 with problems related to an accessory artery). Of the 20 organs (7 livers and 13 spleens) examined in the 15 trauma patients, 5 were found to have areas without colour, corresponding to localised haematomas. Using computed tomography as gold standard, ultrasound showed neither false positive nor false negative findings. Of the 141 patients with cirrhosis, 40 had Doppler ultrasound findings of a shunt, consistent with a portal hypertension. 7 of these 40 shunts showed a typical “ball ” or “corkscrew ” pattern. Conclusion: The colour in a power Doppler image is dependent not only on reflector concentration (as it should be in theory) but also on the insonation angle and the velocity of the flow. This can be used to detect relative changes in volume flow. Clinical applications of power Doppler include mapping of organ perfusion and the detection of small vessels. These applications are based on the high sensitivity of power Doppler.