Gain setting in doppler haemodynamic monitors

Abstract

This invention relates to a method of automatically setting the gain of an echo signal in a Doppler ultrasound haemodynamic monitor. In essence the invention comprises monitoring the strength of velocity components measured by the apparatus, and identifying a group of such components occupying a particular band within the overall velocity spectrum. The signal gain is then adjusted so that the perceived with of the band falls within predetermined limits. The monitoring or assessment of the velocity components is preferably undertaken when the overall flow velocity is high e.g. during systole.

1 ) A method of automatically setting signal gain in a Doppler ultrasound haemodynamic monitor, said method including the steps of: 
 assessing the strength of components of the blood velocity spectrum to identify a group of velocity components above a predetermined level occupying a band within the velocity spectrum; and    adjusting the gain setting so that the perceived width of said band falls within predetermined limits.    
     
     
         2 ) A method as claimed in  claim 1  wherein said predetermined limits are derived from clinical testing.  
     
     
         3 ) A method as claimed in  claim 1  or  claim 2  including assessing the strength of components of the velocity spectrum whilst the overall velocity is high.  
     
     
         4 ) A method as claimed in  claim 3  wherein the assessment is made during systole.  
     
     
         5 ) A method as claimed in any one of the preceding claims further including applying a smoothing step to said band so as to avoid rapid changes in gain setting.  
     
     
         6 ) A method as claimed in  claim 5  wherein said smoothing step is achieved by applying a control variable to counts of said velocity components or bins above said predetermined level.  
     
     
         7 ) A method as claimed in  claim 6  wherein said control variable is applied to counts of said velocity components above said predetermined limit but below a further, higher, predetermined limit i.e. within a band.  
     
     
         8 ) A method as claimed in  claim 7  wherein a decrement or increment is applied to said control variable according to whether said counts of said velocity components above said predetermined limit are above or below said predetermined limits.  
     
     
         9 ) A method as claimed in  claim 8  wherein if the discrepancy or error between the count and the threshold is large, then a large correcting decrement or increment is applied to the control variable and if the discrepancy or error is small then a small correcting decrement or increment is applied.  
     
     
         10 ) A method of automatically setting signal gain in a Doppler ultrasound haemodynamic monitor, said method including the steps of: 
 establishing a base gain value; and    automatically adjusting the received signal gain in real time to bring the same within a band defined about said base gain value.    
     
     
         11 ) A method of detecting movement of a Doppler transducer in a Doppler ultrasound haemodynamic monitor, said method including: 
 setting the signal gain according to the method claimed in any one of  claims 1  to  10 ;    storing the width of the velocity band; and    monitoring the distribution of velocities to determine the onset of non-laminar flow and hence possible transducer movement.    
     
     
         12 ) A Doppler ultrasound haemodynamic monitor including an automatic gain setting facility constructed and arranged to operate according to the method claimed in any one of  claims 1  to  10 .