DDUSIV
Digital Defocused Ultrasound Image Velocimetry

Joshua Adams

Digital Defocused Ultrasound Image Velocimetry (DDUSIV) is a technique which utilizes signal processing of out-of-focus data to locate and track particles just outside the focal plane of traditional ultrasound imaging.

Ultrasound imaging devices typically use an array (usually 1D) of transducers to send and receive pressure signals. Knowing the direction a signal was sent and the time it takes for echoes to be reflected back to the transducer elements, one can build a depth image based on the intensity of the echoes.

The limitation of ultrasound imaging is the relatively slow sampling rate. A signal is typically sent out in one direction at a time. If one is interested in imaging to a particular depth, one has to wait some amount of time for that signal to travel to that depth and back, which is governed by the speed of sound in the target. This wait time places an upper bound on the number of samples that may be performed per second. For 2D imaging, this allows for pixel resolutions of a few hundred pixels by a few hundred pixels at up to 100 frames per second, but is too slow to sample densely a 3D volume.

Our technique extracts positional information of reflectors outside the main focal plane by deconvolving the unique radiation pattern of the array from the response of the reflectors in the image. This may then guide a system to determine an offset distance and direction of the reflector from the focal plane, which yields extra positional information from standard imaging.

 

Cardiac DENSE Imaging

Abbas Moghaddam

DENSE MRI is a new phase contrast method that provides a 3D Lagrangian frame work for analysis of myocardial deformation. In contrast with MR Tagging, which is affected by tag fading and provides only the in-plane Lagrangian displacement, DENSE has a higher spatial and temporal resolution (almost 1 mm and 10 ms respectively) and is able to image the entire cardiac cycle.

DENSE MRI is a new phase contrast method that provides a 3D Lagrangian frame work for analysis of myocardial deformation. In contrast with MR Tagging, which is affected by tag fading and provides only the in-plane Lagrangian displacement, DENSE has a higher spatial and temporal resolution (almost 1 mm and 10 ms respectively) and is able to image the entire cardiac cycle. However, DENSE is time consuming and therefore the full potential of this novel method has not been revealed. Some of efforts we have done in this field are as below:

• combination of Short Axis (S.A) and Long Axis (L.A) images that provides a more comprehensive data from DENSE MRI in 20 to 40% shorter time. <SA_LA.jpg>
• demonstration of the sequential initiation of myocardial strain as well as heterogeneous contraction patterns across the ventricle wall based on a single slice long axis DENSE MRI of a beagle heart for the whole cardiac cycle. <Media:Example.ogg>
• measurement of mechanical deformations in the cardiac wall through parameters like torsion along the long axis, thickening and shortening indices, principal strain and total deformation values.
  Just to appreciate the potentials of the DENSE MRI look how the particle tracking covers the atrium as well as the ventricle: <Media:Example.ogg>