Ultrasound pulsatility imaging

A method is provided for observing three-dimensional pulsatile activity in a volume of a subject's tissue, which includes activating an ultrasonic probes array (25) subset portion (20) having a curvature including focussing the ultrasound energy of probes (25) constituting a selected contiguous portion of the subarray in a selected portion of a selected slice of tissue (21) along a line, converting the reflected ultrasound energy to output signals and providing output data corresponding to the pulsatile activity, varying the focus of ultrasound energy along the line and repeating the converting and processing steps to thereby select additional lines within the selected slice, selecting additional subsets of the ultrasound array of probes so as to select additional slices within the volume, and performing tomographic analysis of the output data corresponding to pulsatile activity in the plurality of selected portions of tissue, so as to obtain a three dimensional image of pulsatile activity in the preselected volume of tissue.

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What is claimed is:

1. A method for observing three-dimensional pulsatile activity in a preselected volume of tissue in a subject, the volume of tissue having a length, width, and depth, saidmethod including the steps of: placing an array of ultrasound probes in association with the surface of the subject; selecting a generally linear subset of the array arranged in association with a selected slice of the preselected volume of tissue, saidlinear subset forming a subarray of said array of probes, wherein the selected slice has a length and a width, and at least a predetermined depth; activating and focusing at least a selected contiguous portion of the selected subset of the array ofprobes, the selected contiguous portion of the selected subset of the array having a predetermined curvature, so that each probe is operative: to emit ultrasound waves in a preselected frequency waveband and at a preselected range of output intensities,to receive reflected ultrasound energy from the tissue in the preselected frequency waveband, and to convert the received reflected ultrasound energy into output signals corresponding thereto; and including focusing the ultrasound energy of the probesconstituting the selected contiguous portion of the subarray of probes in a selected portion of the selected slice of tissue along a selected line, wherein the selected line is contained within the selected slice and intersects the linear subset ofprobes; receiving, via the probes constituting the selected contiguous portion of the subarray of probes, the reflected ultrasound energy from the tissue and converting it into output signals corresponding to the reflected ultrasound energy; processingthe output signals from the probes constituting the selected contiguous portion of the subarray of probes so as to determine pulsatile activity in the selected portion of the selected tissue slice; providing output data corresponding to the pulsatileactivity in the selected portion of the selected tissue slice; varying the focus of the ultrasound energy along the line within the volume slice and repeating said step of receiving and converting and said steps of processing and of providing for eachof a sequence of selected portions of the selected tissue slice along the full extent of the selected line therewithin; selecting a sequence of contiguous portions of the selected subset of the array and repeating for each of the selected sequence saidstep of activating and focusing, said step of receiving and converting, and said step of processing, further repeating for each selected portion of tissue said step of providing output data, and further repeating for each of the selected sequence saidstep of varying the focus; thereby to select additional lines within the selected slice and to determine pulsatile activity and to provide output data corresponding thereto along a multiplicity of selected lines along the full extent of the selectedslice; selecting a sequence of subsets of the array of ultrasound probes and repeating thereon said step of selecting a sequence of contiguous portions of the selected subset of the array, thereby to select additional slices within the preselectedvolume, so as to determine pulsatile activity and to provide output data corresponding thereto along a multiplicity of slices of tissue within the preselected volume along the full extent thereof; and performing tomographic analysis of the output datacorresponding to pulsatile activity in the plurality of selected portions of tissue, so as to obtain a three dimensional image of pulsatile activity in the preselected volume of tissue.

2. A method according to claim 1 wherein the multiplicity of slices is a multiplicity of substantially parallel first slices, and said method further includes the steps of: selecting additional linear subsets of the array of ultrasonic probesarranged in association with a second tissue slice having a non-parallel alignment with respect to the first tissue slices; repeating said step of selecting a sequence of subsets of the array arranged in association with additional tissue slicesparallel to the second tissue slice; and performing tomographic analysis of the output data corresponding to pulsatile activity in the plurality of selected portions of tissue, so as to obtain a directional three dimensional image of pulsatile activityin the preselected volume of tissue.

3. A method according to claim 2 wherein said method further includes the steps, prior to said step of performing tomographic analysis, of: selecting further linear subsets of the array of ultrasonic probes arranged in association withsubsequent tissue slices having a non-parallel alignment with respect to both first and second tissue slices; and repeating said step of selecting a sequence of subsets of the array arranged in association with additional tissue slices parallel to thesecond tissue slice.

4. A method according to claim 1 wherein said step of processing the output signals includes the subsets of: converting the output signals into a summed output signal associated with the selected portion of the selected tissue slice; measuringvariation in the summed output signal as a function of time; and observing selected features of pulsatile activity in the time variation of the summed output signal associated with the selected portion of the selected tissue slice.

5. A method according to claim 4 wherein said substep of observing selected features of pulsatile activity includes the substep of applying gating circuitry to the time variation of the summed output signal associated with the selected portionof the selected tissue slice.

6. A method according to claim 4 wherein said substep of observing selected features of pulsatile activity includes the substeps of: performing spectral analysis of the summed output signal associated with the selected portion of the selectedtissue slice to produce a frequency spectrum associated therewith; selecting a reference pulsatile signal associated with the heart rate of the subject; performing spectral analysis of the reference pulsatile signal associated with the heart rate ofthe subject to produce a frequency spectrum associated therewith; and comparing the frequency spectrum of the summed output signal associated with the selected portion of the selected tissue slice with the frequency spectrum of the reference pulsatilesignal associated with the heart rate of the subject.

7. A method according to claim 6 wherein the reference pulsatile signal associated with the heart rate of the subject is an electrocardiogram signal.

8. A method according to claim 1 wherein said step of activating and focusing includes the substep of changing the curvature of the selected contiguous portion of the linear subarray of ultrasound probes, so as to focus the ultrasound energyvariably within the selected tissue slice and to observe pulsatile activity therein.

9. A method according to claim 1 wherein said step of activating and focusing includes the substep of adjusting the timing of the activation of at least a selected contiguous portion of the subarray of ultrasound probes, so as to focus theultrasound energy variably within the selected tissue slice and to observe pulsatile activity therein.

10. A method according to claim 1 wherein said step of activating and focusing includes the substep of varying the selected frequency waveband of the ultrasound waves emitted and received by the ultrasound probes.

11. A method according to claim 1 wherein the frequency waveband of the ultrasound waves emitted and received by the ultrasound probes is selected so as not to be substantially attenuated by bone tissue.

12. A method according to claim 1 wherein the frequency waveband of the ultrasound waves emitted and received by the ultrasound probes has a bandwidth of substantially 0.4 MHz in the frequency range 0.4-30.0 MHz and wherein the output intensityis in the range 100-300 mW/cm.sup.2.

13. A method according to claim 1 wherein the selected portion of the selected slice of tissue has a volume in the range 0.1 to 1.0 mm.sup.3.